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7Local Loads
Procedure 7-1 Stresses in Circular Rings 437
Procedure 7-2 Design of Partial Ring Stiffeners 446
Procedure 7-3 Attachment Parameters 448
Procedure 7-4 Stresses in Cylindrical Shells fromExternal Local Loads 449
Procedure 7-5 Stresses in Spherical Shellsfrom External Local Loads 465References 472
435
Stresses caused by external local loads are a majorconcern to designers of pressure vessels The techniques foranalyzing local stresses and the methods of handling theseloadings to keep these stresses within prescribed limits hasbeen the focus of much research Various theories andtechniques have been proposed and investigated byexperimental testing to verify the accuracy of the solutions
Clearly the most significant findings and solutions arethose developed by Professor P P Bijlaard of CornellUniversity in the 1950s These investigations were spon-sored by the Pressure Vessel Research Committee of theWelding Research Council His findings have formed thebasis of Welding Research Council Bulletin 107 aninternationally accepted method for analyzing stresses dueto local loads in cylindrical and spherical shells The ldquoBij-laard Curvesrdquo illustrated in several sections of this chapterprovide a convenient and accurate method of analysis
Other methods are also available for analyzing stressesdue to local loads and several have been included hereinIt should be noted that the methods utilized in WRCBulletin 107 have not been included here in theirentirety The technique has been simplified for ease ofapplication For more rigorous applications the reader isreferred to this excellent source
Since this book applies to thin-walled vessels only thedetail included in WRC Bulletin 107 is not warrantedNo distinction has been made between the inside andoutside surfaces of the vessel at local attachments Forvessels in the thick-wall category these criteria would beinadequate
Other methods that are used for analyzing local loadsare as follows The designer should be familiar with thesemethods and when they should be applied
1 Roark Technical Note 8062 Ring analysis as outlined in Procedure 7-13 Beam on elastic foundation methods where the
elastic foundation is the vessel shell4 Bijlaard analysis as outlined in Procedures 7-4
and 7-55 WRC Bulletin 1076 Finite element analysis
These methods provide results with a varying degree ofaccuracy Obviously some are considered ldquoball parkrdquotechniques while others are extremely accurate The use ofone method over another will be determined by howcritical the loading is and how critical the vessel isObviously it would be uneconomical and impractical toapply finite element analysis on platform support clips It
would however be considered prudent to do so on thevessel lug supports of a high-pressure reactor Finiteelement analysis is beyond the scope of this book
Another basis for determining what method to usedepends on whether the local load is ldquoisolatedrdquo from otherlocal loads and what ldquofixrdquo will be applied for overstressedconditions For many loadings in one plane the ring-typeanalysis has certain advantages This technique takes intoaccount the additive overlapping effects of each load onthe other It also has the ability to superimpose differenttypes of loading on the same ring section It also providesan ideal solution for design of a circumferential ringstiffener to take these loads
If reinforcing pads are used to beef up the shell locallythen the Bijlaard and WRC 107 techniques provide idealsolutions These methods do not take into account closelyspaced loads and their influence on one another Itassumes the local loading is isolated This technique alsoprovides a fast and accurate method of distinguishingbetween membrane and bending stresses for combiningwith other principal stresses
For local loads where a partial ring stiffener is to beused to reduce local stresses the beam on elastic foun-dation method provides an ideal method for sizing thepartial rings or stiffener plates The stresses in the shellmust then be analyzed by another local load procedureShell stresses can be checked by the beam-on-elastic-foundation method for continuous radial loads about theentire circumference of a vessel shell or ring
Procedure 7-3 has been included as a technique forconverting various shapes of attachments to those whichcan more readily be utilized in these design proceduresBoth the shape of an attachment and whether it is of solidor hollow cross section will have a distinct effect on thedistribution of stresses location of maximum stresses andstress concentrations
There are various methods for reducing stresses atlocal loadings As shown in the foregoing paragraphsthese will have some bearing on how the loads areanalyzed or how stiffening rings or reinforcing plates aresized The following methods apply to reducing shellstresses locally
1 Increase the size of the attachment2 Increase the number of attachments3 Change the shape of the attachment to further
distribute stresses4 Add reinforcing pads Reinforcing pads should not be
thinner than 075 times nor thicker than 15 times the
436 Pressure Vessel Design Manual
thickness of the shell to which they are attached Theyshould not exceed 15 times the length of the attach-ment and should be continuously welded Shellstresses must be investigated at the edge of theattachment to the pad as well as at the edge of the pad
5 Increase shell thickness locally or as an entire shellcourse
6 Add partial ring stiffeners7 Add full ring stiffeners
The local stresses as outlined herein do not apply to localstresses due to any condition of internal restraint such asthermal or discontinuity stresses Local stresses as definedby this section are due to external mechanical loads Themechanical loading may be the external loads caused bythe thermal growth of the attached piping but this is nota thermal stress For an outline of external local loads seeldquoCategories of Loadingsrdquo in Chapter 1
Procedure 7-1 Stresses in Circular Rings [1ndash6]
Notation
Rm frac14 mean radius of shell inR1 frac14 distance to centroid of ring-shell inM frac14 internal moment in shell in-lbMc frac14 external circumferential moment in-lbMh frac14 external longitudinal moment (at clip or
attachment only) in-lbML frac14 general longitudinal moment on vessel
in-lbFT frac14 tangential load lb
F1F2 frac14 loads on attachment lbfafb frac14 equivalent radial load on 1-in length of
Enter applicable material chart in ASME Code Section II
B frac14 psi
For values of A falling to left of material line
B frac14 AE1
2
Table 7-1Moments and forces in shell M or T
Due to Internal Moment M TensionCompression Force T
Circumferential moment Mc M frac14 P(KmMc) T frac14
PethCmMcTHORNRm
Tangential force FT M frac14 P(KTFT)Rm T frac14 P
(CTFT)
Radial load Pr M frac14 P(KrFr)Rm T frac14 P
(CrFr)
Substitute R1 for Rm if a ring is used Values of Km KT Kr Cm CT and Cr are from Tables 7-4 7-5 and 7-6
fa
fa =
fa =
fb =
fb =
f1 = fa
f1 = fa + fb
f1 = fb
f1 =
fa + fb fb
d
d
f1
f1
Mh Mh
e
d
e
Mh = aF2 + bF1
F1 = F cos θ
F2 = F sin θ
Case 1 Case 2 Case 3 Case 4
Continuous rings
ea
b
θ
e
e e
e = 078 e = 078 e = 078
t F
F1F1
F2
F1
F1
6Mh
6Mh Mh
d + e
d + e
(d + e)(d + 2e)
(d + e)(d + 2e)
Rm
Rm t Rm t Rm t
d d
Figure 7-2 Determination of radial load f1 for various shell loadings
438 Pressure Vessel Design Manual
Procedure
External localized loads (radial moment or tangential)produce internal bending moments tension andcompression in ring sections The magnitude of thesemoments and forces can be determined by this procedurewhich consists essentially of the following steps
1 Find moment or tension coefficients based onangular distances between applied loads at eachload from Tables 7ndash4 7-5 and 7-6
2 Superimpose the effects of various loadings byadding the product of coefficients times loads aboutany given point
Notes
1 Sign convention It is mandatory that sign conven-tion be strictly followed to determine both themagnitude of the internal forces and tension orcompression at any pointa Coefficients in Tables 7-4 7-5 and 7-6 are for
Circumferential sf sffrac14 S2 thornS3 thornS4 sffrac14 ethTHORNS3 S6 S4
Local Loads 439
on the ring under consideration and loads Signsshown are for q measured in the clockwisedirection only
b Signs of coefficients in Tables 7-4 7-5 and 7-6 arefor outward radial loads and clockwise tangentialforces andmoments For loads andmoments in theopposite direction either the sign of the load or thesign of the coefficient must be reversed
2 In Figure 7ndash4 the coefficients have already beencombined for the loadings shown The loads must be
of equal magnitude and equally spaced Signs ofcoefficients Kr and Cr are given for loads in thedirection shown Either the sign of the load or thesign of the coefficient may be reversed for loads inthe opposite direction
3 The maximum moment normally occurs at the pointof the largest load however for unevenly spaced ormixed loadings moments or tension should beinvestigated at each load ie five loads require fiveanalyses
Figure 7-3 Sample ring section with various loadings
Figure 7-4 Values of coefficients Kr and Cr for various loadings
444 Pressure Vessel Design Manual
048044
040036032028024
020016012008004
0-004-008-012
-016
-020-024-028-032
-038-040-044-048
0 90 180 270 360Angledegrees
Valu
es o
f coe
ffici
ents
θ
K r
KT
Km
Figure 7-5 Graph of internal moment coefficients Km Kr and KT
048044
040036032028024
020016012008004
0
-004-008-012
-016
-020-024-028-032
-038-040-044
048
0 90 180 270 360Angle degrees
CT
Cm
Cr
Valu
es o
f coe
ffici
ents
θ
-
Figure 7-6 Graph of circumferential tensioncompression coefficients Cm Cr and CT
Local Loads 445
4 This procedure uses strain-energy concepts5 The following is assumed
a Rings are of uniform cross sectionb Material is elastic but is not stressed beyond
elastic limitc Deformation is caused mainly by bendingd All loads are in the same plane
e The ring is not restrained and is supported alongits circumference by a number of equidistantsimple supports (therefore conservative for useon cylinders)
f The ring is of such large radius in comparisonwith its radial thickness that the deflection theoryfor straight beams is applicable
Procedure 7-2 Design of Partial Ring Stiffeners [7]
Notation
ML frac14 longitudinal moment in-lbM frac14 internal bending moment shell in-lbFb frac14 allowable bending stress psifb frac14 bending stress psi
f or fn frac14 concentrated loads on stiffener due to radial ormoment load on clip lb
Fx frac14 function or moment coefficient(see Table 7-7) frac14 ebx (cos bx ndash sin bx)
Ev frac14 modulus of elasticity of vessel shell at designtemperature psi
Es frac14 modulus of elasticity of stiffener at designtemperature psi
e frac14 log base 271I frac14 moment of inertia of stiffener in4
Z frac14 section modulus of stiffener in3
K frac14 ldquospring constantrdquo or ldquofoundation modulusrdquolbin3
x frac14 distance between loads inb frac14 damping factor dimensionlessPr frac14 radial load lb
Formulas
1 Single load Determine concentrated load on eachstiffener depending on whether there is a radial loador moment loading single or double stiffener
f frac14bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume stiffener size and calculate Z and IProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener M
M frac14 f4b
bull Calculate bending stress fb
fb frac14 MZ
If bending stress exceeds allowable (Fb frac14 06Fy)increase size of stiffener and recalculate I Z b Mand fb
Table 7-7Values Of Function Fx
bx Fx bx Fx
0 10 055 01903
005 09025 06 01431
01 08100 065 00997
015 07224 07 00599
02 06398 075 00237
025 05619 08 (e)00093
03 04888 085 (e)00390
035 04203 09 (e)00657
04 03564 095 (e)00896045 02968 10 (e)01108
05 02415
Notes (Cont)
446 Pressure Vessel Design Manual
2 Multiple loads (see Figure 7-8) Determine concen-trated loads on stiffener(s) Loads must be of equalmagnitude
f frac14 fl frac14 f2 frac14 frac14 fn
bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume a stiffener size and calculate I and ZProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener
Step 1 Determine bx for each load (bx is in radians)Step 2 Determine Fx for each load from Table 7-7 or
calculate as follows
Fx frac14 ebx cos bx sin bx
Step 3 Calculate bending moment M
M frac14 f4b
XFx
bull Calculate bending stress fb
fb frac14 MZ
Notes
1 This procedure is based on the beam-on-elastic-foundation theory The elastic foundation is thevessel shell and the beam is the partial ring stiffenerThe stiffener must be designed to be stiff enough totransmit the load(s) uniformly over its full length
Figure 7-7 Dimensions forces and loadings for partial ring stiffeners
bx0frac14 0 F1 frac14 1
bx1frac14 __ F2 frac14 __
bx2frac14 __ F3 frac14 __
bxnfrac14 __ Fn frac14 __PFxfrac14 __
Local Loads 447
The flexibility of the vessel shell is taken intoaccount The length of the vessel must be at least 49ffiffiffiffiffiRt
pto qualify for the infinitely long beam theory
2 The case of multiple loads uses the principle ofsuperposition That is the effect of each load may bedetermined independent of the other loads and thetotal effect may be determined by adding the indi-vidual effects
3 This procedure determines the bending stress in thestiffener only The stresses in the vessel shell shouldbe checked by an appropriate local load procedureThese local stresses are secondary bending stressesand should be combined with primary membraneand bending stresses
Procedure 7-3 Attachment Parameters
This procedure is for use in converting the area ofattachments into shapes that can readily be applied in designprocedures Irregular attachments (not round square orrectangular) can be converted into a rectangle which has
bull The same moment of inertiabull The same ratio of length to width of the originalattachment
In addition a rectangular load area may be reduced to anldquoequivalentrdquo square area
Bijlaard recommends for non-rectangular attachmentsthe loaded rectangle can be assumed to be that which hasthe same moment of inertia with respect to the moment axisas the plan of the actual attachment Further it should beassumed that the dimensions of the rectangle in the longi-tudinal and circumferential directions have the same ratioas the two dimensions of the attachment in these directions
Dodge comments on this method in WRC Bulletin 198ldquoAlthough the lsquoequivalent moment of inertia procedurersquo issimple and direct it was not derived by any mathematicalor logical reasoning which would allow the designer torationalize the accuracy of the resultsrdquo
Dodge goes on to recommend an alternative procedurebased on the principle of superposition This methodwould divide irregular attachments into a composite ofone or more rectangular sub-areas
Neither method is entirely satisfactory and each ignoresthe effect of local stiffness provided by the attachmentrsquosshape An empirical method should take into consider-ation the ldquoarea of influencerdquo of the attachment whichwould account for the attenuation length or decay lengthof the stress in question
Studies by Roark would indicate short zones of influ-ence in the longitudinal direction (quick decay) anda much broader area of influence in the circumferentialdirection (slow decay larger attenuation) This would alsoseem to account for the attachment and shell acting asa unit which they of course do
Since no hard and fast rules have yet been determinedit would seem reasonable to apply the factors as outlinedin this procedure for general applications Very large orcritical loads should however be examined in depth
Notes
1 b frac14 tc thorn 2tw thorn 2ts where tw frac14 fillet weld size andts frac14 thickness of shell
2 Clips must be closer thanffiffiffiffiffiRt
pif running
circumferentially or closer than 6 in if runninglongitudinally to be considered as a singleattachment
xn
x2
x1
f2 f3f1 fn
Figure 7-8 Dimensions and loading diagram for beam onelastic foundation analysis
Rectangle to circlero = 0875 C1 C2
23 C 41 C234
C 1C 223
2C2
2C1
ro
C = 0875ro
Circle to square
C
ro
For radial load C = 07
Rectangle to square
2C1
2C2
C
C =
C 2C 123C =
For circumferential moment
For longitudinal moment
Figure 7-9 Attachment parameters for solid attachments
448 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
Stresses caused by external local loads are a majorconcern to designers of pressure vessels The techniques foranalyzing local stresses and the methods of handling theseloadings to keep these stresses within prescribed limits hasbeen the focus of much research Various theories andtechniques have been proposed and investigated byexperimental testing to verify the accuracy of the solutions
Clearly the most significant findings and solutions arethose developed by Professor P P Bijlaard of CornellUniversity in the 1950s These investigations were spon-sored by the Pressure Vessel Research Committee of theWelding Research Council His findings have formed thebasis of Welding Research Council Bulletin 107 aninternationally accepted method for analyzing stresses dueto local loads in cylindrical and spherical shells The ldquoBij-laard Curvesrdquo illustrated in several sections of this chapterprovide a convenient and accurate method of analysis
Other methods are also available for analyzing stressesdue to local loads and several have been included hereinIt should be noted that the methods utilized in WRCBulletin 107 have not been included here in theirentirety The technique has been simplified for ease ofapplication For more rigorous applications the reader isreferred to this excellent source
Since this book applies to thin-walled vessels only thedetail included in WRC Bulletin 107 is not warrantedNo distinction has been made between the inside andoutside surfaces of the vessel at local attachments Forvessels in the thick-wall category these criteria would beinadequate
Other methods that are used for analyzing local loadsare as follows The designer should be familiar with thesemethods and when they should be applied
1 Roark Technical Note 8062 Ring analysis as outlined in Procedure 7-13 Beam on elastic foundation methods where the
elastic foundation is the vessel shell4 Bijlaard analysis as outlined in Procedures 7-4
and 7-55 WRC Bulletin 1076 Finite element analysis
These methods provide results with a varying degree ofaccuracy Obviously some are considered ldquoball parkrdquotechniques while others are extremely accurate The use ofone method over another will be determined by howcritical the loading is and how critical the vessel isObviously it would be uneconomical and impractical toapply finite element analysis on platform support clips It
would however be considered prudent to do so on thevessel lug supports of a high-pressure reactor Finiteelement analysis is beyond the scope of this book
Another basis for determining what method to usedepends on whether the local load is ldquoisolatedrdquo from otherlocal loads and what ldquofixrdquo will be applied for overstressedconditions For many loadings in one plane the ring-typeanalysis has certain advantages This technique takes intoaccount the additive overlapping effects of each load onthe other It also has the ability to superimpose differenttypes of loading on the same ring section It also providesan ideal solution for design of a circumferential ringstiffener to take these loads
If reinforcing pads are used to beef up the shell locallythen the Bijlaard and WRC 107 techniques provide idealsolutions These methods do not take into account closelyspaced loads and their influence on one another Itassumes the local loading is isolated This technique alsoprovides a fast and accurate method of distinguishingbetween membrane and bending stresses for combiningwith other principal stresses
For local loads where a partial ring stiffener is to beused to reduce local stresses the beam on elastic foun-dation method provides an ideal method for sizing thepartial rings or stiffener plates The stresses in the shellmust then be analyzed by another local load procedureShell stresses can be checked by the beam-on-elastic-foundation method for continuous radial loads about theentire circumference of a vessel shell or ring
Procedure 7-3 has been included as a technique forconverting various shapes of attachments to those whichcan more readily be utilized in these design proceduresBoth the shape of an attachment and whether it is of solidor hollow cross section will have a distinct effect on thedistribution of stresses location of maximum stresses andstress concentrations
There are various methods for reducing stresses atlocal loadings As shown in the foregoing paragraphsthese will have some bearing on how the loads areanalyzed or how stiffening rings or reinforcing plates aresized The following methods apply to reducing shellstresses locally
1 Increase the size of the attachment2 Increase the number of attachments3 Change the shape of the attachment to further
distribute stresses4 Add reinforcing pads Reinforcing pads should not be
thinner than 075 times nor thicker than 15 times the
436 Pressure Vessel Design Manual
thickness of the shell to which they are attached Theyshould not exceed 15 times the length of the attach-ment and should be continuously welded Shellstresses must be investigated at the edge of theattachment to the pad as well as at the edge of the pad
5 Increase shell thickness locally or as an entire shellcourse
6 Add partial ring stiffeners7 Add full ring stiffeners
The local stresses as outlined herein do not apply to localstresses due to any condition of internal restraint such asthermal or discontinuity stresses Local stresses as definedby this section are due to external mechanical loads Themechanical loading may be the external loads caused bythe thermal growth of the attached piping but this is nota thermal stress For an outline of external local loads seeldquoCategories of Loadingsrdquo in Chapter 1
Procedure 7-1 Stresses in Circular Rings [1ndash6]
Notation
Rm frac14 mean radius of shell inR1 frac14 distance to centroid of ring-shell inM frac14 internal moment in shell in-lbMc frac14 external circumferential moment in-lbMh frac14 external longitudinal moment (at clip or
attachment only) in-lbML frac14 general longitudinal moment on vessel
in-lbFT frac14 tangential load lb
F1F2 frac14 loads on attachment lbfafb frac14 equivalent radial load on 1-in length of
Enter applicable material chart in ASME Code Section II
B frac14 psi
For values of A falling to left of material line
B frac14 AE1
2
Table 7-1Moments and forces in shell M or T
Due to Internal Moment M TensionCompression Force T
Circumferential moment Mc M frac14 P(KmMc) T frac14
PethCmMcTHORNRm
Tangential force FT M frac14 P(KTFT)Rm T frac14 P
(CTFT)
Radial load Pr M frac14 P(KrFr)Rm T frac14 P
(CrFr)
Substitute R1 for Rm if a ring is used Values of Km KT Kr Cm CT and Cr are from Tables 7-4 7-5 and 7-6
fa
fa =
fa =
fb =
fb =
f1 = fa
f1 = fa + fb
f1 = fb
f1 =
fa + fb fb
d
d
f1
f1
Mh Mh
e
d
e
Mh = aF2 + bF1
F1 = F cos θ
F2 = F sin θ
Case 1 Case 2 Case 3 Case 4
Continuous rings
ea
b
θ
e
e e
e = 078 e = 078 e = 078
t F
F1F1
F2
F1
F1
6Mh
6Mh Mh
d + e
d + e
(d + e)(d + 2e)
(d + e)(d + 2e)
Rm
Rm t Rm t Rm t
d d
Figure 7-2 Determination of radial load f1 for various shell loadings
438 Pressure Vessel Design Manual
Procedure
External localized loads (radial moment or tangential)produce internal bending moments tension andcompression in ring sections The magnitude of thesemoments and forces can be determined by this procedurewhich consists essentially of the following steps
1 Find moment or tension coefficients based onangular distances between applied loads at eachload from Tables 7ndash4 7-5 and 7-6
2 Superimpose the effects of various loadings byadding the product of coefficients times loads aboutany given point
Notes
1 Sign convention It is mandatory that sign conven-tion be strictly followed to determine both themagnitude of the internal forces and tension orcompression at any pointa Coefficients in Tables 7-4 7-5 and 7-6 are for
Circumferential sf sffrac14 S2 thornS3 thornS4 sffrac14 ethTHORNS3 S6 S4
Local Loads 439
on the ring under consideration and loads Signsshown are for q measured in the clockwisedirection only
b Signs of coefficients in Tables 7-4 7-5 and 7-6 arefor outward radial loads and clockwise tangentialforces andmoments For loads andmoments in theopposite direction either the sign of the load or thesign of the coefficient must be reversed
2 In Figure 7ndash4 the coefficients have already beencombined for the loadings shown The loads must be
of equal magnitude and equally spaced Signs ofcoefficients Kr and Cr are given for loads in thedirection shown Either the sign of the load or thesign of the coefficient may be reversed for loads inthe opposite direction
3 The maximum moment normally occurs at the pointof the largest load however for unevenly spaced ormixed loadings moments or tension should beinvestigated at each load ie five loads require fiveanalyses
Figure 7-3 Sample ring section with various loadings
Figure 7-4 Values of coefficients Kr and Cr for various loadings
444 Pressure Vessel Design Manual
048044
040036032028024
020016012008004
0-004-008-012
-016
-020-024-028-032
-038-040-044-048
0 90 180 270 360Angledegrees
Valu
es o
f coe
ffici
ents
θ
K r
KT
Km
Figure 7-5 Graph of internal moment coefficients Km Kr and KT
048044
040036032028024
020016012008004
0
-004-008-012
-016
-020-024-028-032
-038-040-044
048
0 90 180 270 360Angle degrees
CT
Cm
Cr
Valu
es o
f coe
ffici
ents
θ
-
Figure 7-6 Graph of circumferential tensioncompression coefficients Cm Cr and CT
Local Loads 445
4 This procedure uses strain-energy concepts5 The following is assumed
a Rings are of uniform cross sectionb Material is elastic but is not stressed beyond
elastic limitc Deformation is caused mainly by bendingd All loads are in the same plane
e The ring is not restrained and is supported alongits circumference by a number of equidistantsimple supports (therefore conservative for useon cylinders)
f The ring is of such large radius in comparisonwith its radial thickness that the deflection theoryfor straight beams is applicable
Procedure 7-2 Design of Partial Ring Stiffeners [7]
Notation
ML frac14 longitudinal moment in-lbM frac14 internal bending moment shell in-lbFb frac14 allowable bending stress psifb frac14 bending stress psi
f or fn frac14 concentrated loads on stiffener due to radial ormoment load on clip lb
Fx frac14 function or moment coefficient(see Table 7-7) frac14 ebx (cos bx ndash sin bx)
Ev frac14 modulus of elasticity of vessel shell at designtemperature psi
Es frac14 modulus of elasticity of stiffener at designtemperature psi
e frac14 log base 271I frac14 moment of inertia of stiffener in4
Z frac14 section modulus of stiffener in3
K frac14 ldquospring constantrdquo or ldquofoundation modulusrdquolbin3
x frac14 distance between loads inb frac14 damping factor dimensionlessPr frac14 radial load lb
Formulas
1 Single load Determine concentrated load on eachstiffener depending on whether there is a radial loador moment loading single or double stiffener
f frac14bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume stiffener size and calculate Z and IProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener M
M frac14 f4b
bull Calculate bending stress fb
fb frac14 MZ
If bending stress exceeds allowable (Fb frac14 06Fy)increase size of stiffener and recalculate I Z b Mand fb
Table 7-7Values Of Function Fx
bx Fx bx Fx
0 10 055 01903
005 09025 06 01431
01 08100 065 00997
015 07224 07 00599
02 06398 075 00237
025 05619 08 (e)00093
03 04888 085 (e)00390
035 04203 09 (e)00657
04 03564 095 (e)00896045 02968 10 (e)01108
05 02415
Notes (Cont)
446 Pressure Vessel Design Manual
2 Multiple loads (see Figure 7-8) Determine concen-trated loads on stiffener(s) Loads must be of equalmagnitude
f frac14 fl frac14 f2 frac14 frac14 fn
bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume a stiffener size and calculate I and ZProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener
Step 1 Determine bx for each load (bx is in radians)Step 2 Determine Fx for each load from Table 7-7 or
calculate as follows
Fx frac14 ebx cos bx sin bx
Step 3 Calculate bending moment M
M frac14 f4b
XFx
bull Calculate bending stress fb
fb frac14 MZ
Notes
1 This procedure is based on the beam-on-elastic-foundation theory The elastic foundation is thevessel shell and the beam is the partial ring stiffenerThe stiffener must be designed to be stiff enough totransmit the load(s) uniformly over its full length
Figure 7-7 Dimensions forces and loadings for partial ring stiffeners
bx0frac14 0 F1 frac14 1
bx1frac14 __ F2 frac14 __
bx2frac14 __ F3 frac14 __
bxnfrac14 __ Fn frac14 __PFxfrac14 __
Local Loads 447
The flexibility of the vessel shell is taken intoaccount The length of the vessel must be at least 49ffiffiffiffiffiRt
pto qualify for the infinitely long beam theory
2 The case of multiple loads uses the principle ofsuperposition That is the effect of each load may bedetermined independent of the other loads and thetotal effect may be determined by adding the indi-vidual effects
3 This procedure determines the bending stress in thestiffener only The stresses in the vessel shell shouldbe checked by an appropriate local load procedureThese local stresses are secondary bending stressesand should be combined with primary membraneand bending stresses
Procedure 7-3 Attachment Parameters
This procedure is for use in converting the area ofattachments into shapes that can readily be applied in designprocedures Irregular attachments (not round square orrectangular) can be converted into a rectangle which has
bull The same moment of inertiabull The same ratio of length to width of the originalattachment
In addition a rectangular load area may be reduced to anldquoequivalentrdquo square area
Bijlaard recommends for non-rectangular attachmentsthe loaded rectangle can be assumed to be that which hasthe same moment of inertia with respect to the moment axisas the plan of the actual attachment Further it should beassumed that the dimensions of the rectangle in the longi-tudinal and circumferential directions have the same ratioas the two dimensions of the attachment in these directions
Dodge comments on this method in WRC Bulletin 198ldquoAlthough the lsquoequivalent moment of inertia procedurersquo issimple and direct it was not derived by any mathematicalor logical reasoning which would allow the designer torationalize the accuracy of the resultsrdquo
Dodge goes on to recommend an alternative procedurebased on the principle of superposition This methodwould divide irregular attachments into a composite ofone or more rectangular sub-areas
Neither method is entirely satisfactory and each ignoresthe effect of local stiffness provided by the attachmentrsquosshape An empirical method should take into consider-ation the ldquoarea of influencerdquo of the attachment whichwould account for the attenuation length or decay lengthof the stress in question
Studies by Roark would indicate short zones of influ-ence in the longitudinal direction (quick decay) anda much broader area of influence in the circumferentialdirection (slow decay larger attenuation) This would alsoseem to account for the attachment and shell acting asa unit which they of course do
Since no hard and fast rules have yet been determinedit would seem reasonable to apply the factors as outlinedin this procedure for general applications Very large orcritical loads should however be examined in depth
Notes
1 b frac14 tc thorn 2tw thorn 2ts where tw frac14 fillet weld size andts frac14 thickness of shell
2 Clips must be closer thanffiffiffiffiffiRt
pif running
circumferentially or closer than 6 in if runninglongitudinally to be considered as a singleattachment
xn
x2
x1
f2 f3f1 fn
Figure 7-8 Dimensions and loading diagram for beam onelastic foundation analysis
Rectangle to circlero = 0875 C1 C2
23 C 41 C234
C 1C 223
2C2
2C1
ro
C = 0875ro
Circle to square
C
ro
For radial load C = 07
Rectangle to square
2C1
2C2
C
C =
C 2C 123C =
For circumferential moment
For longitudinal moment
Figure 7-9 Attachment parameters for solid attachments
448 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
thickness of the shell to which they are attached Theyshould not exceed 15 times the length of the attach-ment and should be continuously welded Shellstresses must be investigated at the edge of theattachment to the pad as well as at the edge of the pad
5 Increase shell thickness locally or as an entire shellcourse
6 Add partial ring stiffeners7 Add full ring stiffeners
The local stresses as outlined herein do not apply to localstresses due to any condition of internal restraint such asthermal or discontinuity stresses Local stresses as definedby this section are due to external mechanical loads Themechanical loading may be the external loads caused bythe thermal growth of the attached piping but this is nota thermal stress For an outline of external local loads seeldquoCategories of Loadingsrdquo in Chapter 1
Procedure 7-1 Stresses in Circular Rings [1ndash6]
Notation
Rm frac14 mean radius of shell inR1 frac14 distance to centroid of ring-shell inM frac14 internal moment in shell in-lbMc frac14 external circumferential moment in-lbMh frac14 external longitudinal moment (at clip or
attachment only) in-lbML frac14 general longitudinal moment on vessel
in-lbFT frac14 tangential load lb
F1F2 frac14 loads on attachment lbfafb frac14 equivalent radial load on 1-in length of
Enter applicable material chart in ASME Code Section II
B frac14 psi
For values of A falling to left of material line
B frac14 AE1
2
Table 7-1Moments and forces in shell M or T
Due to Internal Moment M TensionCompression Force T
Circumferential moment Mc M frac14 P(KmMc) T frac14
PethCmMcTHORNRm
Tangential force FT M frac14 P(KTFT)Rm T frac14 P
(CTFT)
Radial load Pr M frac14 P(KrFr)Rm T frac14 P
(CrFr)
Substitute R1 for Rm if a ring is used Values of Km KT Kr Cm CT and Cr are from Tables 7-4 7-5 and 7-6
fa
fa =
fa =
fb =
fb =
f1 = fa
f1 = fa + fb
f1 = fb
f1 =
fa + fb fb
d
d
f1
f1
Mh Mh
e
d
e
Mh = aF2 + bF1
F1 = F cos θ
F2 = F sin θ
Case 1 Case 2 Case 3 Case 4
Continuous rings
ea
b
θ
e
e e
e = 078 e = 078 e = 078
t F
F1F1
F2
F1
F1
6Mh
6Mh Mh
d + e
d + e
(d + e)(d + 2e)
(d + e)(d + 2e)
Rm
Rm t Rm t Rm t
d d
Figure 7-2 Determination of radial load f1 for various shell loadings
438 Pressure Vessel Design Manual
Procedure
External localized loads (radial moment or tangential)produce internal bending moments tension andcompression in ring sections The magnitude of thesemoments and forces can be determined by this procedurewhich consists essentially of the following steps
1 Find moment or tension coefficients based onangular distances between applied loads at eachload from Tables 7ndash4 7-5 and 7-6
2 Superimpose the effects of various loadings byadding the product of coefficients times loads aboutany given point
Notes
1 Sign convention It is mandatory that sign conven-tion be strictly followed to determine both themagnitude of the internal forces and tension orcompression at any pointa Coefficients in Tables 7-4 7-5 and 7-6 are for
Circumferential sf sffrac14 S2 thornS3 thornS4 sffrac14 ethTHORNS3 S6 S4
Local Loads 439
on the ring under consideration and loads Signsshown are for q measured in the clockwisedirection only
b Signs of coefficients in Tables 7-4 7-5 and 7-6 arefor outward radial loads and clockwise tangentialforces andmoments For loads andmoments in theopposite direction either the sign of the load or thesign of the coefficient must be reversed
2 In Figure 7ndash4 the coefficients have already beencombined for the loadings shown The loads must be
of equal magnitude and equally spaced Signs ofcoefficients Kr and Cr are given for loads in thedirection shown Either the sign of the load or thesign of the coefficient may be reversed for loads inthe opposite direction
3 The maximum moment normally occurs at the pointof the largest load however for unevenly spaced ormixed loadings moments or tension should beinvestigated at each load ie five loads require fiveanalyses
Figure 7-3 Sample ring section with various loadings
Figure 7-4 Values of coefficients Kr and Cr for various loadings
444 Pressure Vessel Design Manual
048044
040036032028024
020016012008004
0-004-008-012
-016
-020-024-028-032
-038-040-044-048
0 90 180 270 360Angledegrees
Valu
es o
f coe
ffici
ents
θ
K r
KT
Km
Figure 7-5 Graph of internal moment coefficients Km Kr and KT
048044
040036032028024
020016012008004
0
-004-008-012
-016
-020-024-028-032
-038-040-044
048
0 90 180 270 360Angle degrees
CT
Cm
Cr
Valu
es o
f coe
ffici
ents
θ
-
Figure 7-6 Graph of circumferential tensioncompression coefficients Cm Cr and CT
Local Loads 445
4 This procedure uses strain-energy concepts5 The following is assumed
a Rings are of uniform cross sectionb Material is elastic but is not stressed beyond
elastic limitc Deformation is caused mainly by bendingd All loads are in the same plane
e The ring is not restrained and is supported alongits circumference by a number of equidistantsimple supports (therefore conservative for useon cylinders)
f The ring is of such large radius in comparisonwith its radial thickness that the deflection theoryfor straight beams is applicable
Procedure 7-2 Design of Partial Ring Stiffeners [7]
Notation
ML frac14 longitudinal moment in-lbM frac14 internal bending moment shell in-lbFb frac14 allowable bending stress psifb frac14 bending stress psi
f or fn frac14 concentrated loads on stiffener due to radial ormoment load on clip lb
Fx frac14 function or moment coefficient(see Table 7-7) frac14 ebx (cos bx ndash sin bx)
Ev frac14 modulus of elasticity of vessel shell at designtemperature psi
Es frac14 modulus of elasticity of stiffener at designtemperature psi
e frac14 log base 271I frac14 moment of inertia of stiffener in4
Z frac14 section modulus of stiffener in3
K frac14 ldquospring constantrdquo or ldquofoundation modulusrdquolbin3
x frac14 distance between loads inb frac14 damping factor dimensionlessPr frac14 radial load lb
Formulas
1 Single load Determine concentrated load on eachstiffener depending on whether there is a radial loador moment loading single or double stiffener
f frac14bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume stiffener size and calculate Z and IProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener M
M frac14 f4b
bull Calculate bending stress fb
fb frac14 MZ
If bending stress exceeds allowable (Fb frac14 06Fy)increase size of stiffener and recalculate I Z b Mand fb
Table 7-7Values Of Function Fx
bx Fx bx Fx
0 10 055 01903
005 09025 06 01431
01 08100 065 00997
015 07224 07 00599
02 06398 075 00237
025 05619 08 (e)00093
03 04888 085 (e)00390
035 04203 09 (e)00657
04 03564 095 (e)00896045 02968 10 (e)01108
05 02415
Notes (Cont)
446 Pressure Vessel Design Manual
2 Multiple loads (see Figure 7-8) Determine concen-trated loads on stiffener(s) Loads must be of equalmagnitude
f frac14 fl frac14 f2 frac14 frac14 fn
bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume a stiffener size and calculate I and ZProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener
Step 1 Determine bx for each load (bx is in radians)Step 2 Determine Fx for each load from Table 7-7 or
calculate as follows
Fx frac14 ebx cos bx sin bx
Step 3 Calculate bending moment M
M frac14 f4b
XFx
bull Calculate bending stress fb
fb frac14 MZ
Notes
1 This procedure is based on the beam-on-elastic-foundation theory The elastic foundation is thevessel shell and the beam is the partial ring stiffenerThe stiffener must be designed to be stiff enough totransmit the load(s) uniformly over its full length
Figure 7-7 Dimensions forces and loadings for partial ring stiffeners
bx0frac14 0 F1 frac14 1
bx1frac14 __ F2 frac14 __
bx2frac14 __ F3 frac14 __
bxnfrac14 __ Fn frac14 __PFxfrac14 __
Local Loads 447
The flexibility of the vessel shell is taken intoaccount The length of the vessel must be at least 49ffiffiffiffiffiRt
pto qualify for the infinitely long beam theory
2 The case of multiple loads uses the principle ofsuperposition That is the effect of each load may bedetermined independent of the other loads and thetotal effect may be determined by adding the indi-vidual effects
3 This procedure determines the bending stress in thestiffener only The stresses in the vessel shell shouldbe checked by an appropriate local load procedureThese local stresses are secondary bending stressesand should be combined with primary membraneand bending stresses
Procedure 7-3 Attachment Parameters
This procedure is for use in converting the area ofattachments into shapes that can readily be applied in designprocedures Irregular attachments (not round square orrectangular) can be converted into a rectangle which has
bull The same moment of inertiabull The same ratio of length to width of the originalattachment
In addition a rectangular load area may be reduced to anldquoequivalentrdquo square area
Bijlaard recommends for non-rectangular attachmentsthe loaded rectangle can be assumed to be that which hasthe same moment of inertia with respect to the moment axisas the plan of the actual attachment Further it should beassumed that the dimensions of the rectangle in the longi-tudinal and circumferential directions have the same ratioas the two dimensions of the attachment in these directions
Dodge comments on this method in WRC Bulletin 198ldquoAlthough the lsquoequivalent moment of inertia procedurersquo issimple and direct it was not derived by any mathematicalor logical reasoning which would allow the designer torationalize the accuracy of the resultsrdquo
Dodge goes on to recommend an alternative procedurebased on the principle of superposition This methodwould divide irregular attachments into a composite ofone or more rectangular sub-areas
Neither method is entirely satisfactory and each ignoresthe effect of local stiffness provided by the attachmentrsquosshape An empirical method should take into consider-ation the ldquoarea of influencerdquo of the attachment whichwould account for the attenuation length or decay lengthof the stress in question
Studies by Roark would indicate short zones of influ-ence in the longitudinal direction (quick decay) anda much broader area of influence in the circumferentialdirection (slow decay larger attenuation) This would alsoseem to account for the attachment and shell acting asa unit which they of course do
Since no hard and fast rules have yet been determinedit would seem reasonable to apply the factors as outlinedin this procedure for general applications Very large orcritical loads should however be examined in depth
Notes
1 b frac14 tc thorn 2tw thorn 2ts where tw frac14 fillet weld size andts frac14 thickness of shell
2 Clips must be closer thanffiffiffiffiffiRt
pif running
circumferentially or closer than 6 in if runninglongitudinally to be considered as a singleattachment
xn
x2
x1
f2 f3f1 fn
Figure 7-8 Dimensions and loading diagram for beam onelastic foundation analysis
Rectangle to circlero = 0875 C1 C2
23 C 41 C234
C 1C 223
2C2
2C1
ro
C = 0875ro
Circle to square
C
ro
For radial load C = 07
Rectangle to square
2C1
2C2
C
C =
C 2C 123C =
For circumferential moment
For longitudinal moment
Figure 7-9 Attachment parameters for solid attachments
448 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
Enter applicable material chart in ASME Code Section II
B frac14 psi
For values of A falling to left of material line
B frac14 AE1
2
Table 7-1Moments and forces in shell M or T
Due to Internal Moment M TensionCompression Force T
Circumferential moment Mc M frac14 P(KmMc) T frac14
PethCmMcTHORNRm
Tangential force FT M frac14 P(KTFT)Rm T frac14 P
(CTFT)
Radial load Pr M frac14 P(KrFr)Rm T frac14 P
(CrFr)
Substitute R1 for Rm if a ring is used Values of Km KT Kr Cm CT and Cr are from Tables 7-4 7-5 and 7-6
fa
fa =
fa =
fb =
fb =
f1 = fa
f1 = fa + fb
f1 = fb
f1 =
fa + fb fb
d
d
f1
f1
Mh Mh
e
d
e
Mh = aF2 + bF1
F1 = F cos θ
F2 = F sin θ
Case 1 Case 2 Case 3 Case 4
Continuous rings
ea
b
θ
e
e e
e = 078 e = 078 e = 078
t F
F1F1
F2
F1
F1
6Mh
6Mh Mh
d + e
d + e
(d + e)(d + 2e)
(d + e)(d + 2e)
Rm
Rm t Rm t Rm t
d d
Figure 7-2 Determination of radial load f1 for various shell loadings
438 Pressure Vessel Design Manual
Procedure
External localized loads (radial moment or tangential)produce internal bending moments tension andcompression in ring sections The magnitude of thesemoments and forces can be determined by this procedurewhich consists essentially of the following steps
1 Find moment or tension coefficients based onangular distances between applied loads at eachload from Tables 7ndash4 7-5 and 7-6
2 Superimpose the effects of various loadings byadding the product of coefficients times loads aboutany given point
Notes
1 Sign convention It is mandatory that sign conven-tion be strictly followed to determine both themagnitude of the internal forces and tension orcompression at any pointa Coefficients in Tables 7-4 7-5 and 7-6 are for
Circumferential sf sffrac14 S2 thornS3 thornS4 sffrac14 ethTHORNS3 S6 S4
Local Loads 439
on the ring under consideration and loads Signsshown are for q measured in the clockwisedirection only
b Signs of coefficients in Tables 7-4 7-5 and 7-6 arefor outward radial loads and clockwise tangentialforces andmoments For loads andmoments in theopposite direction either the sign of the load or thesign of the coefficient must be reversed
2 In Figure 7ndash4 the coefficients have already beencombined for the loadings shown The loads must be
of equal magnitude and equally spaced Signs ofcoefficients Kr and Cr are given for loads in thedirection shown Either the sign of the load or thesign of the coefficient may be reversed for loads inthe opposite direction
3 The maximum moment normally occurs at the pointof the largest load however for unevenly spaced ormixed loadings moments or tension should beinvestigated at each load ie five loads require fiveanalyses
Figure 7-3 Sample ring section with various loadings
Figure 7-4 Values of coefficients Kr and Cr for various loadings
444 Pressure Vessel Design Manual
048044
040036032028024
020016012008004
0-004-008-012
-016
-020-024-028-032
-038-040-044-048
0 90 180 270 360Angledegrees
Valu
es o
f coe
ffici
ents
θ
K r
KT
Km
Figure 7-5 Graph of internal moment coefficients Km Kr and KT
048044
040036032028024
020016012008004
0
-004-008-012
-016
-020-024-028-032
-038-040-044
048
0 90 180 270 360Angle degrees
CT
Cm
Cr
Valu
es o
f coe
ffici
ents
θ
-
Figure 7-6 Graph of circumferential tensioncompression coefficients Cm Cr and CT
Local Loads 445
4 This procedure uses strain-energy concepts5 The following is assumed
a Rings are of uniform cross sectionb Material is elastic but is not stressed beyond
elastic limitc Deformation is caused mainly by bendingd All loads are in the same plane
e The ring is not restrained and is supported alongits circumference by a number of equidistantsimple supports (therefore conservative for useon cylinders)
f The ring is of such large radius in comparisonwith its radial thickness that the deflection theoryfor straight beams is applicable
Procedure 7-2 Design of Partial Ring Stiffeners [7]
Notation
ML frac14 longitudinal moment in-lbM frac14 internal bending moment shell in-lbFb frac14 allowable bending stress psifb frac14 bending stress psi
f or fn frac14 concentrated loads on stiffener due to radial ormoment load on clip lb
Fx frac14 function or moment coefficient(see Table 7-7) frac14 ebx (cos bx ndash sin bx)
Ev frac14 modulus of elasticity of vessel shell at designtemperature psi
Es frac14 modulus of elasticity of stiffener at designtemperature psi
e frac14 log base 271I frac14 moment of inertia of stiffener in4
Z frac14 section modulus of stiffener in3
K frac14 ldquospring constantrdquo or ldquofoundation modulusrdquolbin3
x frac14 distance between loads inb frac14 damping factor dimensionlessPr frac14 radial load lb
Formulas
1 Single load Determine concentrated load on eachstiffener depending on whether there is a radial loador moment loading single or double stiffener
f frac14bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume stiffener size and calculate Z and IProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener M
M frac14 f4b
bull Calculate bending stress fb
fb frac14 MZ
If bending stress exceeds allowable (Fb frac14 06Fy)increase size of stiffener and recalculate I Z b Mand fb
Table 7-7Values Of Function Fx
bx Fx bx Fx
0 10 055 01903
005 09025 06 01431
01 08100 065 00997
015 07224 07 00599
02 06398 075 00237
025 05619 08 (e)00093
03 04888 085 (e)00390
035 04203 09 (e)00657
04 03564 095 (e)00896045 02968 10 (e)01108
05 02415
Notes (Cont)
446 Pressure Vessel Design Manual
2 Multiple loads (see Figure 7-8) Determine concen-trated loads on stiffener(s) Loads must be of equalmagnitude
f frac14 fl frac14 f2 frac14 frac14 fn
bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume a stiffener size and calculate I and ZProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener
Step 1 Determine bx for each load (bx is in radians)Step 2 Determine Fx for each load from Table 7-7 or
calculate as follows
Fx frac14 ebx cos bx sin bx
Step 3 Calculate bending moment M
M frac14 f4b
XFx
bull Calculate bending stress fb
fb frac14 MZ
Notes
1 This procedure is based on the beam-on-elastic-foundation theory The elastic foundation is thevessel shell and the beam is the partial ring stiffenerThe stiffener must be designed to be stiff enough totransmit the load(s) uniformly over its full length
Figure 7-7 Dimensions forces and loadings for partial ring stiffeners
bx0frac14 0 F1 frac14 1
bx1frac14 __ F2 frac14 __
bx2frac14 __ F3 frac14 __
bxnfrac14 __ Fn frac14 __PFxfrac14 __
Local Loads 447
The flexibility of the vessel shell is taken intoaccount The length of the vessel must be at least 49ffiffiffiffiffiRt
pto qualify for the infinitely long beam theory
2 The case of multiple loads uses the principle ofsuperposition That is the effect of each load may bedetermined independent of the other loads and thetotal effect may be determined by adding the indi-vidual effects
3 This procedure determines the bending stress in thestiffener only The stresses in the vessel shell shouldbe checked by an appropriate local load procedureThese local stresses are secondary bending stressesand should be combined with primary membraneand bending stresses
Procedure 7-3 Attachment Parameters
This procedure is for use in converting the area ofattachments into shapes that can readily be applied in designprocedures Irregular attachments (not round square orrectangular) can be converted into a rectangle which has
bull The same moment of inertiabull The same ratio of length to width of the originalattachment
In addition a rectangular load area may be reduced to anldquoequivalentrdquo square area
Bijlaard recommends for non-rectangular attachmentsthe loaded rectangle can be assumed to be that which hasthe same moment of inertia with respect to the moment axisas the plan of the actual attachment Further it should beassumed that the dimensions of the rectangle in the longi-tudinal and circumferential directions have the same ratioas the two dimensions of the attachment in these directions
Dodge comments on this method in WRC Bulletin 198ldquoAlthough the lsquoequivalent moment of inertia procedurersquo issimple and direct it was not derived by any mathematicalor logical reasoning which would allow the designer torationalize the accuracy of the resultsrdquo
Dodge goes on to recommend an alternative procedurebased on the principle of superposition This methodwould divide irregular attachments into a composite ofone or more rectangular sub-areas
Neither method is entirely satisfactory and each ignoresthe effect of local stiffness provided by the attachmentrsquosshape An empirical method should take into consider-ation the ldquoarea of influencerdquo of the attachment whichwould account for the attenuation length or decay lengthof the stress in question
Studies by Roark would indicate short zones of influ-ence in the longitudinal direction (quick decay) anda much broader area of influence in the circumferentialdirection (slow decay larger attenuation) This would alsoseem to account for the attachment and shell acting asa unit which they of course do
Since no hard and fast rules have yet been determinedit would seem reasonable to apply the factors as outlinedin this procedure for general applications Very large orcritical loads should however be examined in depth
Notes
1 b frac14 tc thorn 2tw thorn 2ts where tw frac14 fillet weld size andts frac14 thickness of shell
2 Clips must be closer thanffiffiffiffiffiRt
pif running
circumferentially or closer than 6 in if runninglongitudinally to be considered as a singleattachment
xn
x2
x1
f2 f3f1 fn
Figure 7-8 Dimensions and loading diagram for beam onelastic foundation analysis
Rectangle to circlero = 0875 C1 C2
23 C 41 C234
C 1C 223
2C2
2C1
ro
C = 0875ro
Circle to square
C
ro
For radial load C = 07
Rectangle to square
2C1
2C2
C
C =
C 2C 123C =
For circumferential moment
For longitudinal moment
Figure 7-9 Attachment parameters for solid attachments
448 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
Procedure
External localized loads (radial moment or tangential)produce internal bending moments tension andcompression in ring sections The magnitude of thesemoments and forces can be determined by this procedurewhich consists essentially of the following steps
1 Find moment or tension coefficients based onangular distances between applied loads at eachload from Tables 7ndash4 7-5 and 7-6
2 Superimpose the effects of various loadings byadding the product of coefficients times loads aboutany given point
Notes
1 Sign convention It is mandatory that sign conven-tion be strictly followed to determine both themagnitude of the internal forces and tension orcompression at any pointa Coefficients in Tables 7-4 7-5 and 7-6 are for
Circumferential sf sffrac14 S2 thornS3 thornS4 sffrac14 ethTHORNS3 S6 S4
Local Loads 439
on the ring under consideration and loads Signsshown are for q measured in the clockwisedirection only
b Signs of coefficients in Tables 7-4 7-5 and 7-6 arefor outward radial loads and clockwise tangentialforces andmoments For loads andmoments in theopposite direction either the sign of the load or thesign of the coefficient must be reversed
2 In Figure 7ndash4 the coefficients have already beencombined for the loadings shown The loads must be
of equal magnitude and equally spaced Signs ofcoefficients Kr and Cr are given for loads in thedirection shown Either the sign of the load or thesign of the coefficient may be reversed for loads inthe opposite direction
3 The maximum moment normally occurs at the pointof the largest load however for unevenly spaced ormixed loadings moments or tension should beinvestigated at each load ie five loads require fiveanalyses
Figure 7-3 Sample ring section with various loadings
Figure 7-4 Values of coefficients Kr and Cr for various loadings
444 Pressure Vessel Design Manual
048044
040036032028024
020016012008004
0-004-008-012
-016
-020-024-028-032
-038-040-044-048
0 90 180 270 360Angledegrees
Valu
es o
f coe
ffici
ents
θ
K r
KT
Km
Figure 7-5 Graph of internal moment coefficients Km Kr and KT
048044
040036032028024
020016012008004
0
-004-008-012
-016
-020-024-028-032
-038-040-044
048
0 90 180 270 360Angle degrees
CT
Cm
Cr
Valu
es o
f coe
ffici
ents
θ
-
Figure 7-6 Graph of circumferential tensioncompression coefficients Cm Cr and CT
Local Loads 445
4 This procedure uses strain-energy concepts5 The following is assumed
a Rings are of uniform cross sectionb Material is elastic but is not stressed beyond
elastic limitc Deformation is caused mainly by bendingd All loads are in the same plane
e The ring is not restrained and is supported alongits circumference by a number of equidistantsimple supports (therefore conservative for useon cylinders)
f The ring is of such large radius in comparisonwith its radial thickness that the deflection theoryfor straight beams is applicable
Procedure 7-2 Design of Partial Ring Stiffeners [7]
Notation
ML frac14 longitudinal moment in-lbM frac14 internal bending moment shell in-lbFb frac14 allowable bending stress psifb frac14 bending stress psi
f or fn frac14 concentrated loads on stiffener due to radial ormoment load on clip lb
Fx frac14 function or moment coefficient(see Table 7-7) frac14 ebx (cos bx ndash sin bx)
Ev frac14 modulus of elasticity of vessel shell at designtemperature psi
Es frac14 modulus of elasticity of stiffener at designtemperature psi
e frac14 log base 271I frac14 moment of inertia of stiffener in4
Z frac14 section modulus of stiffener in3
K frac14 ldquospring constantrdquo or ldquofoundation modulusrdquolbin3
x frac14 distance between loads inb frac14 damping factor dimensionlessPr frac14 radial load lb
Formulas
1 Single load Determine concentrated load on eachstiffener depending on whether there is a radial loador moment loading single or double stiffener
f frac14bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume stiffener size and calculate Z and IProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener M
M frac14 f4b
bull Calculate bending stress fb
fb frac14 MZ
If bending stress exceeds allowable (Fb frac14 06Fy)increase size of stiffener and recalculate I Z b Mand fb
Table 7-7Values Of Function Fx
bx Fx bx Fx
0 10 055 01903
005 09025 06 01431
01 08100 065 00997
015 07224 07 00599
02 06398 075 00237
025 05619 08 (e)00093
03 04888 085 (e)00390
035 04203 09 (e)00657
04 03564 095 (e)00896045 02968 10 (e)01108
05 02415
Notes (Cont)
446 Pressure Vessel Design Manual
2 Multiple loads (see Figure 7-8) Determine concen-trated loads on stiffener(s) Loads must be of equalmagnitude
f frac14 fl frac14 f2 frac14 frac14 fn
bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume a stiffener size and calculate I and ZProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener
Step 1 Determine bx for each load (bx is in radians)Step 2 Determine Fx for each load from Table 7-7 or
calculate as follows
Fx frac14 ebx cos bx sin bx
Step 3 Calculate bending moment M
M frac14 f4b
XFx
bull Calculate bending stress fb
fb frac14 MZ
Notes
1 This procedure is based on the beam-on-elastic-foundation theory The elastic foundation is thevessel shell and the beam is the partial ring stiffenerThe stiffener must be designed to be stiff enough totransmit the load(s) uniformly over its full length
Figure 7-7 Dimensions forces and loadings for partial ring stiffeners
bx0frac14 0 F1 frac14 1
bx1frac14 __ F2 frac14 __
bx2frac14 __ F3 frac14 __
bxnfrac14 __ Fn frac14 __PFxfrac14 __
Local Loads 447
The flexibility of the vessel shell is taken intoaccount The length of the vessel must be at least 49ffiffiffiffiffiRt
pto qualify for the infinitely long beam theory
2 The case of multiple loads uses the principle ofsuperposition That is the effect of each load may bedetermined independent of the other loads and thetotal effect may be determined by adding the indi-vidual effects
3 This procedure determines the bending stress in thestiffener only The stresses in the vessel shell shouldbe checked by an appropriate local load procedureThese local stresses are secondary bending stressesand should be combined with primary membraneand bending stresses
Procedure 7-3 Attachment Parameters
This procedure is for use in converting the area ofattachments into shapes that can readily be applied in designprocedures Irregular attachments (not round square orrectangular) can be converted into a rectangle which has
bull The same moment of inertiabull The same ratio of length to width of the originalattachment
In addition a rectangular load area may be reduced to anldquoequivalentrdquo square area
Bijlaard recommends for non-rectangular attachmentsthe loaded rectangle can be assumed to be that which hasthe same moment of inertia with respect to the moment axisas the plan of the actual attachment Further it should beassumed that the dimensions of the rectangle in the longi-tudinal and circumferential directions have the same ratioas the two dimensions of the attachment in these directions
Dodge comments on this method in WRC Bulletin 198ldquoAlthough the lsquoequivalent moment of inertia procedurersquo issimple and direct it was not derived by any mathematicalor logical reasoning which would allow the designer torationalize the accuracy of the resultsrdquo
Dodge goes on to recommend an alternative procedurebased on the principle of superposition This methodwould divide irregular attachments into a composite ofone or more rectangular sub-areas
Neither method is entirely satisfactory and each ignoresthe effect of local stiffness provided by the attachmentrsquosshape An empirical method should take into consider-ation the ldquoarea of influencerdquo of the attachment whichwould account for the attenuation length or decay lengthof the stress in question
Studies by Roark would indicate short zones of influ-ence in the longitudinal direction (quick decay) anda much broader area of influence in the circumferentialdirection (slow decay larger attenuation) This would alsoseem to account for the attachment and shell acting asa unit which they of course do
Since no hard and fast rules have yet been determinedit would seem reasonable to apply the factors as outlinedin this procedure for general applications Very large orcritical loads should however be examined in depth
Notes
1 b frac14 tc thorn 2tw thorn 2ts where tw frac14 fillet weld size andts frac14 thickness of shell
2 Clips must be closer thanffiffiffiffiffiRt
pif running
circumferentially or closer than 6 in if runninglongitudinally to be considered as a singleattachment
xn
x2
x1
f2 f3f1 fn
Figure 7-8 Dimensions and loading diagram for beam onelastic foundation analysis
Rectangle to circlero = 0875 C1 C2
23 C 41 C234
C 1C 223
2C2
2C1
ro
C = 0875ro
Circle to square
C
ro
For radial load C = 07
Rectangle to square
2C1
2C2
C
C =
C 2C 123C =
For circumferential moment
For longitudinal moment
Figure 7-9 Attachment parameters for solid attachments
448 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
on the ring under consideration and loads Signsshown are for q measured in the clockwisedirection only
b Signs of coefficients in Tables 7-4 7-5 and 7-6 arefor outward radial loads and clockwise tangentialforces andmoments For loads andmoments in theopposite direction either the sign of the load or thesign of the coefficient must be reversed
2 In Figure 7ndash4 the coefficients have already beencombined for the loadings shown The loads must be
of equal magnitude and equally spaced Signs ofcoefficients Kr and Cr are given for loads in thedirection shown Either the sign of the load or thesign of the coefficient may be reversed for loads inthe opposite direction
3 The maximum moment normally occurs at the pointof the largest load however for unevenly spaced ormixed loadings moments or tension should beinvestigated at each load ie five loads require fiveanalyses
Figure 7-3 Sample ring section with various loadings
Figure 7-4 Values of coefficients Kr and Cr for various loadings
444 Pressure Vessel Design Manual
048044
040036032028024
020016012008004
0-004-008-012
-016
-020-024-028-032
-038-040-044-048
0 90 180 270 360Angledegrees
Valu
es o
f coe
ffici
ents
θ
K r
KT
Km
Figure 7-5 Graph of internal moment coefficients Km Kr and KT
048044
040036032028024
020016012008004
0
-004-008-012
-016
-020-024-028-032
-038-040-044
048
0 90 180 270 360Angle degrees
CT
Cm
Cr
Valu
es o
f coe
ffici
ents
θ
-
Figure 7-6 Graph of circumferential tensioncompression coefficients Cm Cr and CT
Local Loads 445
4 This procedure uses strain-energy concepts5 The following is assumed
a Rings are of uniform cross sectionb Material is elastic but is not stressed beyond
elastic limitc Deformation is caused mainly by bendingd All loads are in the same plane
e The ring is not restrained and is supported alongits circumference by a number of equidistantsimple supports (therefore conservative for useon cylinders)
f The ring is of such large radius in comparisonwith its radial thickness that the deflection theoryfor straight beams is applicable
Procedure 7-2 Design of Partial Ring Stiffeners [7]
Notation
ML frac14 longitudinal moment in-lbM frac14 internal bending moment shell in-lbFb frac14 allowable bending stress psifb frac14 bending stress psi
f or fn frac14 concentrated loads on stiffener due to radial ormoment load on clip lb
Fx frac14 function or moment coefficient(see Table 7-7) frac14 ebx (cos bx ndash sin bx)
Ev frac14 modulus of elasticity of vessel shell at designtemperature psi
Es frac14 modulus of elasticity of stiffener at designtemperature psi
e frac14 log base 271I frac14 moment of inertia of stiffener in4
Z frac14 section modulus of stiffener in3
K frac14 ldquospring constantrdquo or ldquofoundation modulusrdquolbin3
x frac14 distance between loads inb frac14 damping factor dimensionlessPr frac14 radial load lb
Formulas
1 Single load Determine concentrated load on eachstiffener depending on whether there is a radial loador moment loading single or double stiffener
f frac14bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume stiffener size and calculate Z and IProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener M
M frac14 f4b
bull Calculate bending stress fb
fb frac14 MZ
If bending stress exceeds allowable (Fb frac14 06Fy)increase size of stiffener and recalculate I Z b Mand fb
Table 7-7Values Of Function Fx
bx Fx bx Fx
0 10 055 01903
005 09025 06 01431
01 08100 065 00997
015 07224 07 00599
02 06398 075 00237
025 05619 08 (e)00093
03 04888 085 (e)00390
035 04203 09 (e)00657
04 03564 095 (e)00896045 02968 10 (e)01108
05 02415
Notes (Cont)
446 Pressure Vessel Design Manual
2 Multiple loads (see Figure 7-8) Determine concen-trated loads on stiffener(s) Loads must be of equalmagnitude
f frac14 fl frac14 f2 frac14 frac14 fn
bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume a stiffener size and calculate I and ZProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener
Step 1 Determine bx for each load (bx is in radians)Step 2 Determine Fx for each load from Table 7-7 or
calculate as follows
Fx frac14 ebx cos bx sin bx
Step 3 Calculate bending moment M
M frac14 f4b
XFx
bull Calculate bending stress fb
fb frac14 MZ
Notes
1 This procedure is based on the beam-on-elastic-foundation theory The elastic foundation is thevessel shell and the beam is the partial ring stiffenerThe stiffener must be designed to be stiff enough totransmit the load(s) uniformly over its full length
Figure 7-7 Dimensions forces and loadings for partial ring stiffeners
bx0frac14 0 F1 frac14 1
bx1frac14 __ F2 frac14 __
bx2frac14 __ F3 frac14 __
bxnfrac14 __ Fn frac14 __PFxfrac14 __
Local Loads 447
The flexibility of the vessel shell is taken intoaccount The length of the vessel must be at least 49ffiffiffiffiffiRt
pto qualify for the infinitely long beam theory
2 The case of multiple loads uses the principle ofsuperposition That is the effect of each load may bedetermined independent of the other loads and thetotal effect may be determined by adding the indi-vidual effects
3 This procedure determines the bending stress in thestiffener only The stresses in the vessel shell shouldbe checked by an appropriate local load procedureThese local stresses are secondary bending stressesand should be combined with primary membraneand bending stresses
Procedure 7-3 Attachment Parameters
This procedure is for use in converting the area ofattachments into shapes that can readily be applied in designprocedures Irregular attachments (not round square orrectangular) can be converted into a rectangle which has
bull The same moment of inertiabull The same ratio of length to width of the originalattachment
In addition a rectangular load area may be reduced to anldquoequivalentrdquo square area
Bijlaard recommends for non-rectangular attachmentsthe loaded rectangle can be assumed to be that which hasthe same moment of inertia with respect to the moment axisas the plan of the actual attachment Further it should beassumed that the dimensions of the rectangle in the longi-tudinal and circumferential directions have the same ratioas the two dimensions of the attachment in these directions
Dodge comments on this method in WRC Bulletin 198ldquoAlthough the lsquoequivalent moment of inertia procedurersquo issimple and direct it was not derived by any mathematicalor logical reasoning which would allow the designer torationalize the accuracy of the resultsrdquo
Dodge goes on to recommend an alternative procedurebased on the principle of superposition This methodwould divide irregular attachments into a composite ofone or more rectangular sub-areas
Neither method is entirely satisfactory and each ignoresthe effect of local stiffness provided by the attachmentrsquosshape An empirical method should take into consider-ation the ldquoarea of influencerdquo of the attachment whichwould account for the attenuation length or decay lengthof the stress in question
Studies by Roark would indicate short zones of influ-ence in the longitudinal direction (quick decay) anda much broader area of influence in the circumferentialdirection (slow decay larger attenuation) This would alsoseem to account for the attachment and shell acting asa unit which they of course do
Since no hard and fast rules have yet been determinedit would seem reasonable to apply the factors as outlinedin this procedure for general applications Very large orcritical loads should however be examined in depth
Notes
1 b frac14 tc thorn 2tw thorn 2ts where tw frac14 fillet weld size andts frac14 thickness of shell
2 Clips must be closer thanffiffiffiffiffiRt
pif running
circumferentially or closer than 6 in if runninglongitudinally to be considered as a singleattachment
xn
x2
x1
f2 f3f1 fn
Figure 7-8 Dimensions and loading diagram for beam onelastic foundation analysis
Rectangle to circlero = 0875 C1 C2
23 C 41 C234
C 1C 223
2C2
2C1
ro
C = 0875ro
Circle to square
C
ro
For radial load C = 07
Rectangle to square
2C1
2C2
C
C =
C 2C 123C =
For circumferential moment
For longitudinal moment
Figure 7-9 Attachment parameters for solid attachments
448 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
Figure 7-4 Values of coefficients Kr and Cr for various loadings
444 Pressure Vessel Design Manual
048044
040036032028024
020016012008004
0-004-008-012
-016
-020-024-028-032
-038-040-044-048
0 90 180 270 360Angledegrees
Valu
es o
f coe
ffici
ents
θ
K r
KT
Km
Figure 7-5 Graph of internal moment coefficients Km Kr and KT
048044
040036032028024
020016012008004
0
-004-008-012
-016
-020-024-028-032
-038-040-044
048
0 90 180 270 360Angle degrees
CT
Cm
Cr
Valu
es o
f coe
ffici
ents
θ
-
Figure 7-6 Graph of circumferential tensioncompression coefficients Cm Cr and CT
Local Loads 445
4 This procedure uses strain-energy concepts5 The following is assumed
a Rings are of uniform cross sectionb Material is elastic but is not stressed beyond
elastic limitc Deformation is caused mainly by bendingd All loads are in the same plane
e The ring is not restrained and is supported alongits circumference by a number of equidistantsimple supports (therefore conservative for useon cylinders)
f The ring is of such large radius in comparisonwith its radial thickness that the deflection theoryfor straight beams is applicable
Procedure 7-2 Design of Partial Ring Stiffeners [7]
Notation
ML frac14 longitudinal moment in-lbM frac14 internal bending moment shell in-lbFb frac14 allowable bending stress psifb frac14 bending stress psi
f or fn frac14 concentrated loads on stiffener due to radial ormoment load on clip lb
Fx frac14 function or moment coefficient(see Table 7-7) frac14 ebx (cos bx ndash sin bx)
Ev frac14 modulus of elasticity of vessel shell at designtemperature psi
Es frac14 modulus of elasticity of stiffener at designtemperature psi
e frac14 log base 271I frac14 moment of inertia of stiffener in4
Z frac14 section modulus of stiffener in3
K frac14 ldquospring constantrdquo or ldquofoundation modulusrdquolbin3
x frac14 distance between loads inb frac14 damping factor dimensionlessPr frac14 radial load lb
Formulas
1 Single load Determine concentrated load on eachstiffener depending on whether there is a radial loador moment loading single or double stiffener
f frac14bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume stiffener size and calculate Z and IProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener M
M frac14 f4b
bull Calculate bending stress fb
fb frac14 MZ
If bending stress exceeds allowable (Fb frac14 06Fy)increase size of stiffener and recalculate I Z b Mand fb
Table 7-7Values Of Function Fx
bx Fx bx Fx
0 10 055 01903
005 09025 06 01431
01 08100 065 00997
015 07224 07 00599
02 06398 075 00237
025 05619 08 (e)00093
03 04888 085 (e)00390
035 04203 09 (e)00657
04 03564 095 (e)00896045 02968 10 (e)01108
05 02415
Notes (Cont)
446 Pressure Vessel Design Manual
2 Multiple loads (see Figure 7-8) Determine concen-trated loads on stiffener(s) Loads must be of equalmagnitude
f frac14 fl frac14 f2 frac14 frac14 fn
bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume a stiffener size and calculate I and ZProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener
Step 1 Determine bx for each load (bx is in radians)Step 2 Determine Fx for each load from Table 7-7 or
calculate as follows
Fx frac14 ebx cos bx sin bx
Step 3 Calculate bending moment M
M frac14 f4b
XFx
bull Calculate bending stress fb
fb frac14 MZ
Notes
1 This procedure is based on the beam-on-elastic-foundation theory The elastic foundation is thevessel shell and the beam is the partial ring stiffenerThe stiffener must be designed to be stiff enough totransmit the load(s) uniformly over its full length
Figure 7-7 Dimensions forces and loadings for partial ring stiffeners
bx0frac14 0 F1 frac14 1
bx1frac14 __ F2 frac14 __
bx2frac14 __ F3 frac14 __
bxnfrac14 __ Fn frac14 __PFxfrac14 __
Local Loads 447
The flexibility of the vessel shell is taken intoaccount The length of the vessel must be at least 49ffiffiffiffiffiRt
pto qualify for the infinitely long beam theory
2 The case of multiple loads uses the principle ofsuperposition That is the effect of each load may bedetermined independent of the other loads and thetotal effect may be determined by adding the indi-vidual effects
3 This procedure determines the bending stress in thestiffener only The stresses in the vessel shell shouldbe checked by an appropriate local load procedureThese local stresses are secondary bending stressesand should be combined with primary membraneand bending stresses
Procedure 7-3 Attachment Parameters
This procedure is for use in converting the area ofattachments into shapes that can readily be applied in designprocedures Irregular attachments (not round square orrectangular) can be converted into a rectangle which has
bull The same moment of inertiabull The same ratio of length to width of the originalattachment
In addition a rectangular load area may be reduced to anldquoequivalentrdquo square area
Bijlaard recommends for non-rectangular attachmentsthe loaded rectangle can be assumed to be that which hasthe same moment of inertia with respect to the moment axisas the plan of the actual attachment Further it should beassumed that the dimensions of the rectangle in the longi-tudinal and circumferential directions have the same ratioas the two dimensions of the attachment in these directions
Dodge comments on this method in WRC Bulletin 198ldquoAlthough the lsquoequivalent moment of inertia procedurersquo issimple and direct it was not derived by any mathematicalor logical reasoning which would allow the designer torationalize the accuracy of the resultsrdquo
Dodge goes on to recommend an alternative procedurebased on the principle of superposition This methodwould divide irregular attachments into a composite ofone or more rectangular sub-areas
Neither method is entirely satisfactory and each ignoresthe effect of local stiffness provided by the attachmentrsquosshape An empirical method should take into consider-ation the ldquoarea of influencerdquo of the attachment whichwould account for the attenuation length or decay lengthof the stress in question
Studies by Roark would indicate short zones of influ-ence in the longitudinal direction (quick decay) anda much broader area of influence in the circumferentialdirection (slow decay larger attenuation) This would alsoseem to account for the attachment and shell acting asa unit which they of course do
Since no hard and fast rules have yet been determinedit would seem reasonable to apply the factors as outlinedin this procedure for general applications Very large orcritical loads should however be examined in depth
Notes
1 b frac14 tc thorn 2tw thorn 2ts where tw frac14 fillet weld size andts frac14 thickness of shell
2 Clips must be closer thanffiffiffiffiffiRt
pif running
circumferentially or closer than 6 in if runninglongitudinally to be considered as a singleattachment
xn
x2
x1
f2 f3f1 fn
Figure 7-8 Dimensions and loading diagram for beam onelastic foundation analysis
Rectangle to circlero = 0875 C1 C2
23 C 41 C234
C 1C 223
2C2
2C1
ro
C = 0875ro
Circle to square
C
ro
For radial load C = 07
Rectangle to square
2C1
2C2
C
C =
C 2C 123C =
For circumferential moment
For longitudinal moment
Figure 7-9 Attachment parameters for solid attachments
448 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
Table 7-5Values of coefficient Kr due to outward radial load Pr
Figure 7-4 Values of coefficients Kr and Cr for various loadings
444 Pressure Vessel Design Manual
048044
040036032028024
020016012008004
0-004-008-012
-016
-020-024-028-032
-038-040-044-048
0 90 180 270 360Angledegrees
Valu
es o
f coe
ffici
ents
θ
K r
KT
Km
Figure 7-5 Graph of internal moment coefficients Km Kr and KT
048044
040036032028024
020016012008004
0
-004-008-012
-016
-020-024-028-032
-038-040-044
048
0 90 180 270 360Angle degrees
CT
Cm
Cr
Valu
es o
f coe
ffici
ents
θ
-
Figure 7-6 Graph of circumferential tensioncompression coefficients Cm Cr and CT
Local Loads 445
4 This procedure uses strain-energy concepts5 The following is assumed
a Rings are of uniform cross sectionb Material is elastic but is not stressed beyond
elastic limitc Deformation is caused mainly by bendingd All loads are in the same plane
e The ring is not restrained and is supported alongits circumference by a number of equidistantsimple supports (therefore conservative for useon cylinders)
f The ring is of such large radius in comparisonwith its radial thickness that the deflection theoryfor straight beams is applicable
Procedure 7-2 Design of Partial Ring Stiffeners [7]
Notation
ML frac14 longitudinal moment in-lbM frac14 internal bending moment shell in-lbFb frac14 allowable bending stress psifb frac14 bending stress psi
f or fn frac14 concentrated loads on stiffener due to radial ormoment load on clip lb
Fx frac14 function or moment coefficient(see Table 7-7) frac14 ebx (cos bx ndash sin bx)
Ev frac14 modulus of elasticity of vessel shell at designtemperature psi
Es frac14 modulus of elasticity of stiffener at designtemperature psi
e frac14 log base 271I frac14 moment of inertia of stiffener in4
Z frac14 section modulus of stiffener in3
K frac14 ldquospring constantrdquo or ldquofoundation modulusrdquolbin3
x frac14 distance between loads inb frac14 damping factor dimensionlessPr frac14 radial load lb
Formulas
1 Single load Determine concentrated load on eachstiffener depending on whether there is a radial loador moment loading single or double stiffener
f frac14bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume stiffener size and calculate Z and IProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener M
M frac14 f4b
bull Calculate bending stress fb
fb frac14 MZ
If bending stress exceeds allowable (Fb frac14 06Fy)increase size of stiffener and recalculate I Z b Mand fb
Table 7-7Values Of Function Fx
bx Fx bx Fx
0 10 055 01903
005 09025 06 01431
01 08100 065 00997
015 07224 07 00599
02 06398 075 00237
025 05619 08 (e)00093
03 04888 085 (e)00390
035 04203 09 (e)00657
04 03564 095 (e)00896045 02968 10 (e)01108
05 02415
Notes (Cont)
446 Pressure Vessel Design Manual
2 Multiple loads (see Figure 7-8) Determine concen-trated loads on stiffener(s) Loads must be of equalmagnitude
f frac14 fl frac14 f2 frac14 frac14 fn
bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume a stiffener size and calculate I and ZProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener
Step 1 Determine bx for each load (bx is in radians)Step 2 Determine Fx for each load from Table 7-7 or
calculate as follows
Fx frac14 ebx cos bx sin bx
Step 3 Calculate bending moment M
M frac14 f4b
XFx
bull Calculate bending stress fb
fb frac14 MZ
Notes
1 This procedure is based on the beam-on-elastic-foundation theory The elastic foundation is thevessel shell and the beam is the partial ring stiffenerThe stiffener must be designed to be stiff enough totransmit the load(s) uniformly over its full length
Figure 7-7 Dimensions forces and loadings for partial ring stiffeners
bx0frac14 0 F1 frac14 1
bx1frac14 __ F2 frac14 __
bx2frac14 __ F3 frac14 __
bxnfrac14 __ Fn frac14 __PFxfrac14 __
Local Loads 447
The flexibility of the vessel shell is taken intoaccount The length of the vessel must be at least 49ffiffiffiffiffiRt
pto qualify for the infinitely long beam theory
2 The case of multiple loads uses the principle ofsuperposition That is the effect of each load may bedetermined independent of the other loads and thetotal effect may be determined by adding the indi-vidual effects
3 This procedure determines the bending stress in thestiffener only The stresses in the vessel shell shouldbe checked by an appropriate local load procedureThese local stresses are secondary bending stressesand should be combined with primary membraneand bending stresses
Procedure 7-3 Attachment Parameters
This procedure is for use in converting the area ofattachments into shapes that can readily be applied in designprocedures Irregular attachments (not round square orrectangular) can be converted into a rectangle which has
bull The same moment of inertiabull The same ratio of length to width of the originalattachment
In addition a rectangular load area may be reduced to anldquoequivalentrdquo square area
Bijlaard recommends for non-rectangular attachmentsthe loaded rectangle can be assumed to be that which hasthe same moment of inertia with respect to the moment axisas the plan of the actual attachment Further it should beassumed that the dimensions of the rectangle in the longi-tudinal and circumferential directions have the same ratioas the two dimensions of the attachment in these directions
Dodge comments on this method in WRC Bulletin 198ldquoAlthough the lsquoequivalent moment of inertia procedurersquo issimple and direct it was not derived by any mathematicalor logical reasoning which would allow the designer torationalize the accuracy of the resultsrdquo
Dodge goes on to recommend an alternative procedurebased on the principle of superposition This methodwould divide irregular attachments into a composite ofone or more rectangular sub-areas
Neither method is entirely satisfactory and each ignoresthe effect of local stiffness provided by the attachmentrsquosshape An empirical method should take into consider-ation the ldquoarea of influencerdquo of the attachment whichwould account for the attenuation length or decay lengthof the stress in question
Studies by Roark would indicate short zones of influ-ence in the longitudinal direction (quick decay) anda much broader area of influence in the circumferentialdirection (slow decay larger attenuation) This would alsoseem to account for the attachment and shell acting asa unit which they of course do
Since no hard and fast rules have yet been determinedit would seem reasonable to apply the factors as outlinedin this procedure for general applications Very large orcritical loads should however be examined in depth
Notes
1 b frac14 tc thorn 2tw thorn 2ts where tw frac14 fillet weld size andts frac14 thickness of shell
2 Clips must be closer thanffiffiffiffiffiRt
pif running
circumferentially or closer than 6 in if runninglongitudinally to be considered as a singleattachment
xn
x2
x1
f2 f3f1 fn
Figure 7-8 Dimensions and loading diagram for beam onelastic foundation analysis
Rectangle to circlero = 0875 C1 C2
23 C 41 C234
C 1C 223
2C2
2C1
ro
C = 0875ro
Circle to square
C
ro
For radial load C = 07
Rectangle to square
2C1
2C2
C
C =
C 2C 123C =
For circumferential moment
For longitudinal moment
Figure 7-9 Attachment parameters for solid attachments
448 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
Table 7-6Values of coefficient Cr due to radial load Pr
Figure 7-4 Values of coefficients Kr and Cr for various loadings
444 Pressure Vessel Design Manual
048044
040036032028024
020016012008004
0-004-008-012
-016
-020-024-028-032
-038-040-044-048
0 90 180 270 360Angledegrees
Valu
es o
f coe
ffici
ents
θ
K r
KT
Km
Figure 7-5 Graph of internal moment coefficients Km Kr and KT
048044
040036032028024
020016012008004
0
-004-008-012
-016
-020-024-028-032
-038-040-044
048
0 90 180 270 360Angle degrees
CT
Cm
Cr
Valu
es o
f coe
ffici
ents
θ
-
Figure 7-6 Graph of circumferential tensioncompression coefficients Cm Cr and CT
Local Loads 445
4 This procedure uses strain-energy concepts5 The following is assumed
a Rings are of uniform cross sectionb Material is elastic but is not stressed beyond
elastic limitc Deformation is caused mainly by bendingd All loads are in the same plane
e The ring is not restrained and is supported alongits circumference by a number of equidistantsimple supports (therefore conservative for useon cylinders)
f The ring is of such large radius in comparisonwith its radial thickness that the deflection theoryfor straight beams is applicable
Procedure 7-2 Design of Partial Ring Stiffeners [7]
Notation
ML frac14 longitudinal moment in-lbM frac14 internal bending moment shell in-lbFb frac14 allowable bending stress psifb frac14 bending stress psi
f or fn frac14 concentrated loads on stiffener due to radial ormoment load on clip lb
Fx frac14 function or moment coefficient(see Table 7-7) frac14 ebx (cos bx ndash sin bx)
Ev frac14 modulus of elasticity of vessel shell at designtemperature psi
Es frac14 modulus of elasticity of stiffener at designtemperature psi
e frac14 log base 271I frac14 moment of inertia of stiffener in4
Z frac14 section modulus of stiffener in3
K frac14 ldquospring constantrdquo or ldquofoundation modulusrdquolbin3
x frac14 distance between loads inb frac14 damping factor dimensionlessPr frac14 radial load lb
Formulas
1 Single load Determine concentrated load on eachstiffener depending on whether there is a radial loador moment loading single or double stiffener
f frac14bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume stiffener size and calculate Z and IProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener M
M frac14 f4b
bull Calculate bending stress fb
fb frac14 MZ
If bending stress exceeds allowable (Fb frac14 06Fy)increase size of stiffener and recalculate I Z b Mand fb
Table 7-7Values Of Function Fx
bx Fx bx Fx
0 10 055 01903
005 09025 06 01431
01 08100 065 00997
015 07224 07 00599
02 06398 075 00237
025 05619 08 (e)00093
03 04888 085 (e)00390
035 04203 09 (e)00657
04 03564 095 (e)00896045 02968 10 (e)01108
05 02415
Notes (Cont)
446 Pressure Vessel Design Manual
2 Multiple loads (see Figure 7-8) Determine concen-trated loads on stiffener(s) Loads must be of equalmagnitude
f frac14 fl frac14 f2 frac14 frac14 fn
bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume a stiffener size and calculate I and ZProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener
Step 1 Determine bx for each load (bx is in radians)Step 2 Determine Fx for each load from Table 7-7 or
calculate as follows
Fx frac14 ebx cos bx sin bx
Step 3 Calculate bending moment M
M frac14 f4b
XFx
bull Calculate bending stress fb
fb frac14 MZ
Notes
1 This procedure is based on the beam-on-elastic-foundation theory The elastic foundation is thevessel shell and the beam is the partial ring stiffenerThe stiffener must be designed to be stiff enough totransmit the load(s) uniformly over its full length
Figure 7-7 Dimensions forces and loadings for partial ring stiffeners
bx0frac14 0 F1 frac14 1
bx1frac14 __ F2 frac14 __
bx2frac14 __ F3 frac14 __
bxnfrac14 __ Fn frac14 __PFxfrac14 __
Local Loads 447
The flexibility of the vessel shell is taken intoaccount The length of the vessel must be at least 49ffiffiffiffiffiRt
pto qualify for the infinitely long beam theory
2 The case of multiple loads uses the principle ofsuperposition That is the effect of each load may bedetermined independent of the other loads and thetotal effect may be determined by adding the indi-vidual effects
3 This procedure determines the bending stress in thestiffener only The stresses in the vessel shell shouldbe checked by an appropriate local load procedureThese local stresses are secondary bending stressesand should be combined with primary membraneand bending stresses
Procedure 7-3 Attachment Parameters
This procedure is for use in converting the area ofattachments into shapes that can readily be applied in designprocedures Irregular attachments (not round square orrectangular) can be converted into a rectangle which has
bull The same moment of inertiabull The same ratio of length to width of the originalattachment
In addition a rectangular load area may be reduced to anldquoequivalentrdquo square area
Bijlaard recommends for non-rectangular attachmentsthe loaded rectangle can be assumed to be that which hasthe same moment of inertia with respect to the moment axisas the plan of the actual attachment Further it should beassumed that the dimensions of the rectangle in the longi-tudinal and circumferential directions have the same ratioas the two dimensions of the attachment in these directions
Dodge comments on this method in WRC Bulletin 198ldquoAlthough the lsquoequivalent moment of inertia procedurersquo issimple and direct it was not derived by any mathematicalor logical reasoning which would allow the designer torationalize the accuracy of the resultsrdquo
Dodge goes on to recommend an alternative procedurebased on the principle of superposition This methodwould divide irregular attachments into a composite ofone or more rectangular sub-areas
Neither method is entirely satisfactory and each ignoresthe effect of local stiffness provided by the attachmentrsquosshape An empirical method should take into consider-ation the ldquoarea of influencerdquo of the attachment whichwould account for the attenuation length or decay lengthof the stress in question
Studies by Roark would indicate short zones of influ-ence in the longitudinal direction (quick decay) anda much broader area of influence in the circumferentialdirection (slow decay larger attenuation) This would alsoseem to account for the attachment and shell acting asa unit which they of course do
Since no hard and fast rules have yet been determinedit would seem reasonable to apply the factors as outlinedin this procedure for general applications Very large orcritical loads should however be examined in depth
Notes
1 b frac14 tc thorn 2tw thorn 2ts where tw frac14 fillet weld size andts frac14 thickness of shell
2 Clips must be closer thanffiffiffiffiffiRt
pif running
circumferentially or closer than 6 in if runninglongitudinally to be considered as a singleattachment
xn
x2
x1
f2 f3f1 fn
Figure 7-8 Dimensions and loading diagram for beam onelastic foundation analysis
Rectangle to circlero = 0875 C1 C2
23 C 41 C234
C 1C 223
2C2
2C1
ro
C = 0875ro
Circle to square
C
ro
For radial load C = 07
Rectangle to square
2C1
2C2
C
C =
C 2C 123C =
For circumferential moment
For longitudinal moment
Figure 7-9 Attachment parameters for solid attachments
448 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
Figure 7-4 Values of coefficients Kr and Cr for various loadings
444 Pressure Vessel Design Manual
048044
040036032028024
020016012008004
0-004-008-012
-016
-020-024-028-032
-038-040-044-048
0 90 180 270 360Angledegrees
Valu
es o
f coe
ffici
ents
θ
K r
KT
Km
Figure 7-5 Graph of internal moment coefficients Km Kr and KT
048044
040036032028024
020016012008004
0
-004-008-012
-016
-020-024-028-032
-038-040-044
048
0 90 180 270 360Angle degrees
CT
Cm
Cr
Valu
es o
f coe
ffici
ents
θ
-
Figure 7-6 Graph of circumferential tensioncompression coefficients Cm Cr and CT
Local Loads 445
4 This procedure uses strain-energy concepts5 The following is assumed
a Rings are of uniform cross sectionb Material is elastic but is not stressed beyond
elastic limitc Deformation is caused mainly by bendingd All loads are in the same plane
e The ring is not restrained and is supported alongits circumference by a number of equidistantsimple supports (therefore conservative for useon cylinders)
f The ring is of such large radius in comparisonwith its radial thickness that the deflection theoryfor straight beams is applicable
Procedure 7-2 Design of Partial Ring Stiffeners [7]
Notation
ML frac14 longitudinal moment in-lbM frac14 internal bending moment shell in-lbFb frac14 allowable bending stress psifb frac14 bending stress psi
f or fn frac14 concentrated loads on stiffener due to radial ormoment load on clip lb
Fx frac14 function or moment coefficient(see Table 7-7) frac14 ebx (cos bx ndash sin bx)
Ev frac14 modulus of elasticity of vessel shell at designtemperature psi
Es frac14 modulus of elasticity of stiffener at designtemperature psi
e frac14 log base 271I frac14 moment of inertia of stiffener in4
Z frac14 section modulus of stiffener in3
K frac14 ldquospring constantrdquo or ldquofoundation modulusrdquolbin3
x frac14 distance between loads inb frac14 damping factor dimensionlessPr frac14 radial load lb
Formulas
1 Single load Determine concentrated load on eachstiffener depending on whether there is a radial loador moment loading single or double stiffener
f frac14bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume stiffener size and calculate Z and IProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener M
M frac14 f4b
bull Calculate bending stress fb
fb frac14 MZ
If bending stress exceeds allowable (Fb frac14 06Fy)increase size of stiffener and recalculate I Z b Mand fb
Table 7-7Values Of Function Fx
bx Fx bx Fx
0 10 055 01903
005 09025 06 01431
01 08100 065 00997
015 07224 07 00599
02 06398 075 00237
025 05619 08 (e)00093
03 04888 085 (e)00390
035 04203 09 (e)00657
04 03564 095 (e)00896045 02968 10 (e)01108
05 02415
Notes (Cont)
446 Pressure Vessel Design Manual
2 Multiple loads (see Figure 7-8) Determine concen-trated loads on stiffener(s) Loads must be of equalmagnitude
f frac14 fl frac14 f2 frac14 frac14 fn
bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume a stiffener size and calculate I and ZProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener
Step 1 Determine bx for each load (bx is in radians)Step 2 Determine Fx for each load from Table 7-7 or
calculate as follows
Fx frac14 ebx cos bx sin bx
Step 3 Calculate bending moment M
M frac14 f4b
XFx
bull Calculate bending stress fb
fb frac14 MZ
Notes
1 This procedure is based on the beam-on-elastic-foundation theory The elastic foundation is thevessel shell and the beam is the partial ring stiffenerThe stiffener must be designed to be stiff enough totransmit the load(s) uniformly over its full length
Figure 7-7 Dimensions forces and loadings for partial ring stiffeners
bx0frac14 0 F1 frac14 1
bx1frac14 __ F2 frac14 __
bx2frac14 __ F3 frac14 __
bxnfrac14 __ Fn frac14 __PFxfrac14 __
Local Loads 447
The flexibility of the vessel shell is taken intoaccount The length of the vessel must be at least 49ffiffiffiffiffiRt
pto qualify for the infinitely long beam theory
2 The case of multiple loads uses the principle ofsuperposition That is the effect of each load may bedetermined independent of the other loads and thetotal effect may be determined by adding the indi-vidual effects
3 This procedure determines the bending stress in thestiffener only The stresses in the vessel shell shouldbe checked by an appropriate local load procedureThese local stresses are secondary bending stressesand should be combined with primary membraneand bending stresses
Procedure 7-3 Attachment Parameters
This procedure is for use in converting the area ofattachments into shapes that can readily be applied in designprocedures Irregular attachments (not round square orrectangular) can be converted into a rectangle which has
bull The same moment of inertiabull The same ratio of length to width of the originalattachment
In addition a rectangular load area may be reduced to anldquoequivalentrdquo square area
Bijlaard recommends for non-rectangular attachmentsthe loaded rectangle can be assumed to be that which hasthe same moment of inertia with respect to the moment axisas the plan of the actual attachment Further it should beassumed that the dimensions of the rectangle in the longi-tudinal and circumferential directions have the same ratioas the two dimensions of the attachment in these directions
Dodge comments on this method in WRC Bulletin 198ldquoAlthough the lsquoequivalent moment of inertia procedurersquo issimple and direct it was not derived by any mathematicalor logical reasoning which would allow the designer torationalize the accuracy of the resultsrdquo
Dodge goes on to recommend an alternative procedurebased on the principle of superposition This methodwould divide irregular attachments into a composite ofone or more rectangular sub-areas
Neither method is entirely satisfactory and each ignoresthe effect of local stiffness provided by the attachmentrsquosshape An empirical method should take into consider-ation the ldquoarea of influencerdquo of the attachment whichwould account for the attenuation length or decay lengthof the stress in question
Studies by Roark would indicate short zones of influ-ence in the longitudinal direction (quick decay) anda much broader area of influence in the circumferentialdirection (slow decay larger attenuation) This would alsoseem to account for the attachment and shell acting asa unit which they of course do
Since no hard and fast rules have yet been determinedit would seem reasonable to apply the factors as outlinedin this procedure for general applications Very large orcritical loads should however be examined in depth
Notes
1 b frac14 tc thorn 2tw thorn 2ts where tw frac14 fillet weld size andts frac14 thickness of shell
2 Clips must be closer thanffiffiffiffiffiRt
pif running
circumferentially or closer than 6 in if runninglongitudinally to be considered as a singleattachment
xn
x2
x1
f2 f3f1 fn
Figure 7-8 Dimensions and loading diagram for beam onelastic foundation analysis
Rectangle to circlero = 0875 C1 C2
23 C 41 C234
C 1C 223
2C2
2C1
ro
C = 0875ro
Circle to square
C
ro
For radial load C = 07
Rectangle to square
2C1
2C2
C
C =
C 2C 123C =
For circumferential moment
For longitudinal moment
Figure 7-9 Attachment parameters for solid attachments
448 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
048044
040036032028024
020016012008004
0-004-008-012
-016
-020-024-028-032
-038-040-044-048
0 90 180 270 360Angledegrees
Valu
es o
f coe
ffici
ents
θ
K r
KT
Km
Figure 7-5 Graph of internal moment coefficients Km Kr and KT
048044
040036032028024
020016012008004
0
-004-008-012
-016
-020-024-028-032
-038-040-044
048
0 90 180 270 360Angle degrees
CT
Cm
Cr
Valu
es o
f coe
ffici
ents
θ
-
Figure 7-6 Graph of circumferential tensioncompression coefficients Cm Cr and CT
Local Loads 445
4 This procedure uses strain-energy concepts5 The following is assumed
a Rings are of uniform cross sectionb Material is elastic but is not stressed beyond
elastic limitc Deformation is caused mainly by bendingd All loads are in the same plane
e The ring is not restrained and is supported alongits circumference by a number of equidistantsimple supports (therefore conservative for useon cylinders)
f The ring is of such large radius in comparisonwith its radial thickness that the deflection theoryfor straight beams is applicable
Procedure 7-2 Design of Partial Ring Stiffeners [7]
Notation
ML frac14 longitudinal moment in-lbM frac14 internal bending moment shell in-lbFb frac14 allowable bending stress psifb frac14 bending stress psi
f or fn frac14 concentrated loads on stiffener due to radial ormoment load on clip lb
Fx frac14 function or moment coefficient(see Table 7-7) frac14 ebx (cos bx ndash sin bx)
Ev frac14 modulus of elasticity of vessel shell at designtemperature psi
Es frac14 modulus of elasticity of stiffener at designtemperature psi
e frac14 log base 271I frac14 moment of inertia of stiffener in4
Z frac14 section modulus of stiffener in3
K frac14 ldquospring constantrdquo or ldquofoundation modulusrdquolbin3
x frac14 distance between loads inb frac14 damping factor dimensionlessPr frac14 radial load lb
Formulas
1 Single load Determine concentrated load on eachstiffener depending on whether there is a radial loador moment loading single or double stiffener
f frac14bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume stiffener size and calculate Z and IProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener M
M frac14 f4b
bull Calculate bending stress fb
fb frac14 MZ
If bending stress exceeds allowable (Fb frac14 06Fy)increase size of stiffener and recalculate I Z b Mand fb
Table 7-7Values Of Function Fx
bx Fx bx Fx
0 10 055 01903
005 09025 06 01431
01 08100 065 00997
015 07224 07 00599
02 06398 075 00237
025 05619 08 (e)00093
03 04888 085 (e)00390
035 04203 09 (e)00657
04 03564 095 (e)00896045 02968 10 (e)01108
05 02415
Notes (Cont)
446 Pressure Vessel Design Manual
2 Multiple loads (see Figure 7-8) Determine concen-trated loads on stiffener(s) Loads must be of equalmagnitude
f frac14 fl frac14 f2 frac14 frac14 fn
bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume a stiffener size and calculate I and ZProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener
Step 1 Determine bx for each load (bx is in radians)Step 2 Determine Fx for each load from Table 7-7 or
calculate as follows
Fx frac14 ebx cos bx sin bx
Step 3 Calculate bending moment M
M frac14 f4b
XFx
bull Calculate bending stress fb
fb frac14 MZ
Notes
1 This procedure is based on the beam-on-elastic-foundation theory The elastic foundation is thevessel shell and the beam is the partial ring stiffenerThe stiffener must be designed to be stiff enough totransmit the load(s) uniformly over its full length
Figure 7-7 Dimensions forces and loadings for partial ring stiffeners
bx0frac14 0 F1 frac14 1
bx1frac14 __ F2 frac14 __
bx2frac14 __ F3 frac14 __
bxnfrac14 __ Fn frac14 __PFxfrac14 __
Local Loads 447
The flexibility of the vessel shell is taken intoaccount The length of the vessel must be at least 49ffiffiffiffiffiRt
pto qualify for the infinitely long beam theory
2 The case of multiple loads uses the principle ofsuperposition That is the effect of each load may bedetermined independent of the other loads and thetotal effect may be determined by adding the indi-vidual effects
3 This procedure determines the bending stress in thestiffener only The stresses in the vessel shell shouldbe checked by an appropriate local load procedureThese local stresses are secondary bending stressesand should be combined with primary membraneand bending stresses
Procedure 7-3 Attachment Parameters
This procedure is for use in converting the area ofattachments into shapes that can readily be applied in designprocedures Irregular attachments (not round square orrectangular) can be converted into a rectangle which has
bull The same moment of inertiabull The same ratio of length to width of the originalattachment
In addition a rectangular load area may be reduced to anldquoequivalentrdquo square area
Bijlaard recommends for non-rectangular attachmentsthe loaded rectangle can be assumed to be that which hasthe same moment of inertia with respect to the moment axisas the plan of the actual attachment Further it should beassumed that the dimensions of the rectangle in the longi-tudinal and circumferential directions have the same ratioas the two dimensions of the attachment in these directions
Dodge comments on this method in WRC Bulletin 198ldquoAlthough the lsquoequivalent moment of inertia procedurersquo issimple and direct it was not derived by any mathematicalor logical reasoning which would allow the designer torationalize the accuracy of the resultsrdquo
Dodge goes on to recommend an alternative procedurebased on the principle of superposition This methodwould divide irregular attachments into a composite ofone or more rectangular sub-areas
Neither method is entirely satisfactory and each ignoresthe effect of local stiffness provided by the attachmentrsquosshape An empirical method should take into consider-ation the ldquoarea of influencerdquo of the attachment whichwould account for the attenuation length or decay lengthof the stress in question
Studies by Roark would indicate short zones of influ-ence in the longitudinal direction (quick decay) anda much broader area of influence in the circumferentialdirection (slow decay larger attenuation) This would alsoseem to account for the attachment and shell acting asa unit which they of course do
Since no hard and fast rules have yet been determinedit would seem reasonable to apply the factors as outlinedin this procedure for general applications Very large orcritical loads should however be examined in depth
Notes
1 b frac14 tc thorn 2tw thorn 2ts where tw frac14 fillet weld size andts frac14 thickness of shell
2 Clips must be closer thanffiffiffiffiffiRt
pif running
circumferentially or closer than 6 in if runninglongitudinally to be considered as a singleattachment
xn
x2
x1
f2 f3f1 fn
Figure 7-8 Dimensions and loading diagram for beam onelastic foundation analysis
Rectangle to circlero = 0875 C1 C2
23 C 41 C234
C 1C 223
2C2
2C1
ro
C = 0875ro
Circle to square
C
ro
For radial load C = 07
Rectangle to square
2C1
2C2
C
C =
C 2C 123C =
For circumferential moment
For longitudinal moment
Figure 7-9 Attachment parameters for solid attachments
448 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
4 This procedure uses strain-energy concepts5 The following is assumed
a Rings are of uniform cross sectionb Material is elastic but is not stressed beyond
elastic limitc Deformation is caused mainly by bendingd All loads are in the same plane
e The ring is not restrained and is supported alongits circumference by a number of equidistantsimple supports (therefore conservative for useon cylinders)
f The ring is of such large radius in comparisonwith its radial thickness that the deflection theoryfor straight beams is applicable
Procedure 7-2 Design of Partial Ring Stiffeners [7]
Notation
ML frac14 longitudinal moment in-lbM frac14 internal bending moment shell in-lbFb frac14 allowable bending stress psifb frac14 bending stress psi
f or fn frac14 concentrated loads on stiffener due to radial ormoment load on clip lb
Fx frac14 function or moment coefficient(see Table 7-7) frac14 ebx (cos bx ndash sin bx)
Ev frac14 modulus of elasticity of vessel shell at designtemperature psi
Es frac14 modulus of elasticity of stiffener at designtemperature psi
e frac14 log base 271I frac14 moment of inertia of stiffener in4
Z frac14 section modulus of stiffener in3
K frac14 ldquospring constantrdquo or ldquofoundation modulusrdquolbin3
x frac14 distance between loads inb frac14 damping factor dimensionlessPr frac14 radial load lb
Formulas
1 Single load Determine concentrated load on eachstiffener depending on whether there is a radial loador moment loading single or double stiffener
f frac14bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume stiffener size and calculate Z and IProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener M
M frac14 f4b
bull Calculate bending stress fb
fb frac14 MZ
If bending stress exceeds allowable (Fb frac14 06Fy)increase size of stiffener and recalculate I Z b Mand fb
Table 7-7Values Of Function Fx
bx Fx bx Fx
0 10 055 01903
005 09025 06 01431
01 08100 065 00997
015 07224 07 00599
02 06398 075 00237
025 05619 08 (e)00093
03 04888 085 (e)00390
035 04203 09 (e)00657
04 03564 095 (e)00896045 02968 10 (e)01108
05 02415
Notes (Cont)
446 Pressure Vessel Design Manual
2 Multiple loads (see Figure 7-8) Determine concen-trated loads on stiffener(s) Loads must be of equalmagnitude
f frac14 fl frac14 f2 frac14 frac14 fn
bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume a stiffener size and calculate I and ZProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener
Step 1 Determine bx for each load (bx is in radians)Step 2 Determine Fx for each load from Table 7-7 or
calculate as follows
Fx frac14 ebx cos bx sin bx
Step 3 Calculate bending moment M
M frac14 f4b
XFx
bull Calculate bending stress fb
fb frac14 MZ
Notes
1 This procedure is based on the beam-on-elastic-foundation theory The elastic foundation is thevessel shell and the beam is the partial ring stiffenerThe stiffener must be designed to be stiff enough totransmit the load(s) uniformly over its full length
Figure 7-7 Dimensions forces and loadings for partial ring stiffeners
bx0frac14 0 F1 frac14 1
bx1frac14 __ F2 frac14 __
bx2frac14 __ F3 frac14 __
bxnfrac14 __ Fn frac14 __PFxfrac14 __
Local Loads 447
The flexibility of the vessel shell is taken intoaccount The length of the vessel must be at least 49ffiffiffiffiffiRt
pto qualify for the infinitely long beam theory
2 The case of multiple loads uses the principle ofsuperposition That is the effect of each load may bedetermined independent of the other loads and thetotal effect may be determined by adding the indi-vidual effects
3 This procedure determines the bending stress in thestiffener only The stresses in the vessel shell shouldbe checked by an appropriate local load procedureThese local stresses are secondary bending stressesand should be combined with primary membraneand bending stresses
Procedure 7-3 Attachment Parameters
This procedure is for use in converting the area ofattachments into shapes that can readily be applied in designprocedures Irregular attachments (not round square orrectangular) can be converted into a rectangle which has
bull The same moment of inertiabull The same ratio of length to width of the originalattachment
In addition a rectangular load area may be reduced to anldquoequivalentrdquo square area
Bijlaard recommends for non-rectangular attachmentsthe loaded rectangle can be assumed to be that which hasthe same moment of inertia with respect to the moment axisas the plan of the actual attachment Further it should beassumed that the dimensions of the rectangle in the longi-tudinal and circumferential directions have the same ratioas the two dimensions of the attachment in these directions
Dodge comments on this method in WRC Bulletin 198ldquoAlthough the lsquoequivalent moment of inertia procedurersquo issimple and direct it was not derived by any mathematicalor logical reasoning which would allow the designer torationalize the accuracy of the resultsrdquo
Dodge goes on to recommend an alternative procedurebased on the principle of superposition This methodwould divide irregular attachments into a composite ofone or more rectangular sub-areas
Neither method is entirely satisfactory and each ignoresthe effect of local stiffness provided by the attachmentrsquosshape An empirical method should take into consider-ation the ldquoarea of influencerdquo of the attachment whichwould account for the attenuation length or decay lengthof the stress in question
Studies by Roark would indicate short zones of influ-ence in the longitudinal direction (quick decay) anda much broader area of influence in the circumferentialdirection (slow decay larger attenuation) This would alsoseem to account for the attachment and shell acting asa unit which they of course do
Since no hard and fast rules have yet been determinedit would seem reasonable to apply the factors as outlinedin this procedure for general applications Very large orcritical loads should however be examined in depth
Notes
1 b frac14 tc thorn 2tw thorn 2ts where tw frac14 fillet weld size andts frac14 thickness of shell
2 Clips must be closer thanffiffiffiffiffiRt
pif running
circumferentially or closer than 6 in if runninglongitudinally to be considered as a singleattachment
xn
x2
x1
f2 f3f1 fn
Figure 7-8 Dimensions and loading diagram for beam onelastic foundation analysis
Rectangle to circlero = 0875 C1 C2
23 C 41 C234
C 1C 223
2C2
2C1
ro
C = 0875ro
Circle to square
C
ro
For radial load C = 07
Rectangle to square
2C1
2C2
C
C =
C 2C 123C =
For circumferential moment
For longitudinal moment
Figure 7-9 Attachment parameters for solid attachments
448 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
2 Multiple loads (see Figure 7-8) Determine concen-trated loads on stiffener(s) Loads must be of equalmagnitude
f frac14 fl frac14 f2 frac14 frac14 fn
bull Calculate foundation modulus K
K frac14 Evt
R2
bull Assume a stiffener size and calculate I and ZProposed size _____
I frac14 bh3
12
Z frac14 bh2
6
bull Calculate damping factor b based on proposedstiffener size
b frac14ffiffiffiffiffiffiffiffiffiK
4EsI4
r
bull Calculate internal bending moment in stiffener
Step 1 Determine bx for each load (bx is in radians)Step 2 Determine Fx for each load from Table 7-7 or
calculate as follows
Fx frac14 ebx cos bx sin bx
Step 3 Calculate bending moment M
M frac14 f4b
XFx
bull Calculate bending stress fb
fb frac14 MZ
Notes
1 This procedure is based on the beam-on-elastic-foundation theory The elastic foundation is thevessel shell and the beam is the partial ring stiffenerThe stiffener must be designed to be stiff enough totransmit the load(s) uniformly over its full length
Figure 7-7 Dimensions forces and loadings for partial ring stiffeners
bx0frac14 0 F1 frac14 1
bx1frac14 __ F2 frac14 __
bx2frac14 __ F3 frac14 __
bxnfrac14 __ Fn frac14 __PFxfrac14 __
Local Loads 447
The flexibility of the vessel shell is taken intoaccount The length of the vessel must be at least 49ffiffiffiffiffiRt
pto qualify for the infinitely long beam theory
2 The case of multiple loads uses the principle ofsuperposition That is the effect of each load may bedetermined independent of the other loads and thetotal effect may be determined by adding the indi-vidual effects
3 This procedure determines the bending stress in thestiffener only The stresses in the vessel shell shouldbe checked by an appropriate local load procedureThese local stresses are secondary bending stressesand should be combined with primary membraneand bending stresses
Procedure 7-3 Attachment Parameters
This procedure is for use in converting the area ofattachments into shapes that can readily be applied in designprocedures Irregular attachments (not round square orrectangular) can be converted into a rectangle which has
bull The same moment of inertiabull The same ratio of length to width of the originalattachment
In addition a rectangular load area may be reduced to anldquoequivalentrdquo square area
Bijlaard recommends for non-rectangular attachmentsthe loaded rectangle can be assumed to be that which hasthe same moment of inertia with respect to the moment axisas the plan of the actual attachment Further it should beassumed that the dimensions of the rectangle in the longi-tudinal and circumferential directions have the same ratioas the two dimensions of the attachment in these directions
Dodge comments on this method in WRC Bulletin 198ldquoAlthough the lsquoequivalent moment of inertia procedurersquo issimple and direct it was not derived by any mathematicalor logical reasoning which would allow the designer torationalize the accuracy of the resultsrdquo
Dodge goes on to recommend an alternative procedurebased on the principle of superposition This methodwould divide irregular attachments into a composite ofone or more rectangular sub-areas
Neither method is entirely satisfactory and each ignoresthe effect of local stiffness provided by the attachmentrsquosshape An empirical method should take into consider-ation the ldquoarea of influencerdquo of the attachment whichwould account for the attenuation length or decay lengthof the stress in question
Studies by Roark would indicate short zones of influ-ence in the longitudinal direction (quick decay) anda much broader area of influence in the circumferentialdirection (slow decay larger attenuation) This would alsoseem to account for the attachment and shell acting asa unit which they of course do
Since no hard and fast rules have yet been determinedit would seem reasonable to apply the factors as outlinedin this procedure for general applications Very large orcritical loads should however be examined in depth
Notes
1 b frac14 tc thorn 2tw thorn 2ts where tw frac14 fillet weld size andts frac14 thickness of shell
2 Clips must be closer thanffiffiffiffiffiRt
pif running
circumferentially or closer than 6 in if runninglongitudinally to be considered as a singleattachment
xn
x2
x1
f2 f3f1 fn
Figure 7-8 Dimensions and loading diagram for beam onelastic foundation analysis
Rectangle to circlero = 0875 C1 C2
23 C 41 C234
C 1C 223
2C2
2C1
ro
C = 0875ro
Circle to square
C
ro
For radial load C = 07
Rectangle to square
2C1
2C2
C
C =
C 2C 123C =
For circumferential moment
For longitudinal moment
Figure 7-9 Attachment parameters for solid attachments
448 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
The flexibility of the vessel shell is taken intoaccount The length of the vessel must be at least 49ffiffiffiffiffiRt
pto qualify for the infinitely long beam theory
2 The case of multiple loads uses the principle ofsuperposition That is the effect of each load may bedetermined independent of the other loads and thetotal effect may be determined by adding the indi-vidual effects
3 This procedure determines the bending stress in thestiffener only The stresses in the vessel shell shouldbe checked by an appropriate local load procedureThese local stresses are secondary bending stressesand should be combined with primary membraneand bending stresses
Procedure 7-3 Attachment Parameters
This procedure is for use in converting the area ofattachments into shapes that can readily be applied in designprocedures Irregular attachments (not round square orrectangular) can be converted into a rectangle which has
bull The same moment of inertiabull The same ratio of length to width of the originalattachment
In addition a rectangular load area may be reduced to anldquoequivalentrdquo square area
Bijlaard recommends for non-rectangular attachmentsthe loaded rectangle can be assumed to be that which hasthe same moment of inertia with respect to the moment axisas the plan of the actual attachment Further it should beassumed that the dimensions of the rectangle in the longi-tudinal and circumferential directions have the same ratioas the two dimensions of the attachment in these directions
Dodge comments on this method in WRC Bulletin 198ldquoAlthough the lsquoequivalent moment of inertia procedurersquo issimple and direct it was not derived by any mathematicalor logical reasoning which would allow the designer torationalize the accuracy of the resultsrdquo
Dodge goes on to recommend an alternative procedurebased on the principle of superposition This methodwould divide irregular attachments into a composite ofone or more rectangular sub-areas
Neither method is entirely satisfactory and each ignoresthe effect of local stiffness provided by the attachmentrsquosshape An empirical method should take into consider-ation the ldquoarea of influencerdquo of the attachment whichwould account for the attenuation length or decay lengthof the stress in question
Studies by Roark would indicate short zones of influ-ence in the longitudinal direction (quick decay) anda much broader area of influence in the circumferentialdirection (slow decay larger attenuation) This would alsoseem to account for the attachment and shell acting asa unit which they of course do
Since no hard and fast rules have yet been determinedit would seem reasonable to apply the factors as outlinedin this procedure for general applications Very large orcritical loads should however be examined in depth
Notes
1 b frac14 tc thorn 2tw thorn 2ts where tw frac14 fillet weld size andts frac14 thickness of shell
2 Clips must be closer thanffiffiffiffiffiRt
pif running
circumferentially or closer than 6 in if runninglongitudinally to be considered as a singleattachment
xn
x2
x1
f2 f3f1 fn
Figure 7-8 Dimensions and loading diagram for beam onelastic foundation analysis
Rectangle to circlero = 0875 C1 C2
23 C 41 C234
C 1C 223
2C2
2C1
ro
C = 0875ro
Circle to square
C
ro
For radial load C = 07
Rectangle to square
2C1
2C2
C
C =
C 2C 123C =
For circumferential moment
For longitudinal moment
Figure 7-9 Attachment parameters for solid attachments
448 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
Procedure 7-4 Stresses in Cylindrical Shells from External Local Loads [791011]
ML frac14 external longitudinal moment in-lbMc frac14 external circumferential moment in-lbMT frac14 external torsional moment in-lbMx frac14 internal circumferential moment
in-lbin
Mf frac14 internal longitudinal momentin-lbin
VL frac14 longitudinal shear force lbVc frac14 circumferential shear force lbRm frac14 mean radius of shell inro frac14 outside radius of circular attachment
inr frac14 corner radius of attachment in
KnKb frac14 stress concentration factors
See Note 1 See Note 2
hty
pica
l tc
bb b b
C1 05b
04h
03b
04h
025b
04h
03b
04hC2
C1 04b
05h
05b
05h
03b
05h
02b
04hC2
bbbb
hty
pica
l
Figure 7-10 Attachment parameters for nonsolid attachments
C
t
Pr
NMM
N
R m
Mc
N
MM
NN
MM
N
ML
Radial loadndashmembrane stress is compressive forinward radial load and tensile for outward load
Circumferential moment Longitudinal moment
Figure 7-11 Loadings and forces at local attachments in cylindrical shells
Local Loads 449
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
90deg
180deg
270deg
0deg
0deg
90deg
180deg
0deg90deg
180deg
270deg
270deg
φσ
σx
Figure 7-12 Stress indices of local attachments
2CSQ
2C2
2C1
rc
Figure 7-13 Load areas of local attachments Forcircular attachments use C frac14 0875ro
Figure 7-14 Dimensions for clips and attachments
Figure 7-15 Stress concentration factors (Reprinted by permission of the Welding Research Council)
450 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
KcKLK1K2 frac14 coefficients to determine b for rectan-gular attachments
Nx frac14 membrane force in shell longitudinallbin
Nf frac14 membrane force in shell circumferen-tial lbin
sT frac14 torsional shear stress psiss frac14 direct shear stress psisx frac14 longitudinal normal stress psisf frac14 circumferential normal stress psiC frac14 one-half width of square attachment in
CcCL frac14 multiplication factors for rectangularattachments
C1 frac14 one-half circumferential width ofa rectangular attachment in
C2 frac14 one-half longitudinal length of a rect-angular attachment in
h frac14 thickness of attachment indn frac14 outside diameter of circular attachment
inte frac14 equivalent thickness of shell and re-
inforcing intp frac14 thickness of reinforcing pad int frac14 shell thickness in
gbb1b2 frac14 ratios based on vessel and attachmentgeometry
Local Loads 451
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
Geometric Parameters
g frac14 Rm
t
b frac14 CRm
or for circular attachments
0875roRm
For rectangular attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
Procedure
To calculate stresses due to radial load Pr longitudinalmoment ML and circumferential moment Mc on a cylin-drical vessel follow the following steps
b values for radial load longitudinal moment andcircumferential moment vary based on ratios ofb1b2 Follow procedures that follow these steps tofind b values
Step 2 Using g and b values from Step 1 enter appli-cable graphs Figures 7-21 through 7-26 to
dimensionless membrane forces and bending momentsin shell
Step 3 Enter values obtained from Figures 7-21 through7-26 into Table 7-11 and compute stresses
Step 4 Enter stresses computed in Table 7-11 for variousload conditions in Table 7-12 Combine stresses inaccordance with sign convention of Table 7-12
Computing b Values for Rectangular Attachments
b1 frac14 C1
Rm
b2 frac14 C2
Rm
b1
b2
b Values for Radial LoadFrom Table 7-8 select values of K1 and K2 and compute
four b values as follows
Ifb1
b2 1 then b
frac141 1
3
b1
b2 1
eth1 K1THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
Loadarea
2C2
2C1
Figure 7-16 Dimensions of load areas
Table 7-8b Values of radial loads
K1 K2 b
Nf 091 148
Nx 168 12
Mf 176 088
Mx 12 125
Reprinted by permission of the Welding Research Council
452 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
Ifb1
b2lt 1 then b
frac141 4
3
1 b1
b2
eth1 K2THORN
ffiffiffiffiffiffiffiffiffiffib1b2
p
b Values for Longitudinal MomentFrom Table 7-9 select values of CL and KL and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mf b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
For Mx b frac14 KL
ffiffiffiffiffiffiffiffiffiffib1b
22
3
q
CL KL b
Nf
Nx
Mf
Mx
Table 7-9Coefficients for longitudinal moment ML
b1b2 g CL for Nf CL for Nx KL for Mf KL for Mx
15 075 043 180 124
50 077 033 165 116
025 100 080 024 159 111
200 085 010 158 111
300 090 007 156 111
15 090 076 108 104
50 093 073 107 103
05 100 097 068 106 102
200 099 064 105 102
300 110 060 105 102
15 089 100 101 108
50 089 096 100 107
1 100 089 092 098 105
200 089 099 095 101
300 095 105 092 096
15 087 130 094 112
50 084 123 092 110
2 100 081 115 089 107
200 080 133 084 099
300 080 150 079 091
15 068 120 090 124
50 061 113 086 119
4 100 051 103 081 112
200 050 118 073 098
300 050 133 064 083
Reprinted by permission of the Welding Research Council
251 2 3 5 6 7 8 9 10 11 12 13 14 15 164
1 2 3 5 6 7 8 9 10 11 12 13 14 15 164
5
75
10
15
β 1β 2
20
25
3
35
40
200300100
100
50
50
200300
300200 100 50 15
15
50100
200
300
15
15
CL for NX
CL for Nφ
Figure 7-17 Graph of coefficients CL for values Nf amp NX
from Table 7-9
25
6 7 8 9 10 11 12 13 14 15 16 17
5
75
10
15
β 1β 2
20
25
3
35
40
KL for MX
KL for MX
KL for Mφ
KL for Mφ
300
300
300
200
100
50
15
200
100
100200300
100200
50
50 50
15 15
15
Figure 7-18 Graph of coefficients KL for values Mf amp MX
from Table 7-9
Local Loads 453
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council
454 Pressure Vessel Design Manual
b Values for Circumferential MomentFrom Table 7-10 select values of Cc and Kc and
compute values of b as follows
For Nx and Nf b frac14ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mf b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
For Mx b frac14 Kc
ffiffiffiffiffiffiffiffiffiffib21b2
3
q
Cc Kc b
Nf
Nx
Mf
Mx
5375
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for MX
CC for NX
β1β
2
300
300
300
200
200
200
100
100
50
50
50
15
1515
100
Figure 7-20 Graph of coefficients Kc amp CC for valuesNX amp MX from Table 7-10
5
375
25
125
625
75
875
1
1125
125
1375
1625
175
1875
15
5
10 15 20 25 30 35 40
KC for Mφ
CC for Nφ
β1β
2
300
200
100
50
15
15 50
100
200
300
Figure 7-19 Graph of coefficients Kc amp CC for valuesNf amp Mf from Table 7-10
Table 7-10Coefficients for circumferential moment Mc
b1b2 g Cc for Nf Cc for Nx Kc for Mf KC for Mx
15 031 049 131 184
50 021 046 124 162
100 015 044 116 145
025 200 012 045 109 131
300 009 046 102 117
15 064 075 109 136
50 057 075 108 131
05 100 051 076 104 126
200 045 076 102 120
300 039 077 099 113
15 117 108 115 117
50 109 103 112 114
1 100 097 094 107 110
200 091 091 104 106
300 085 089 099 102
15 170 130 120 097
50 159 123 116 096
2 100 143 112 110 095
200 137 106 105 093
300 130 100 100 090
15 175 131 147 108
50 164 111 143 107
4 100 149 081 138 106
200 142 078 133 102
300 136 074 127 098
Reprinted by permission of the Welding Research Council