-
Section 7 - Boilers and Thermal Oil Systems 7-1
H [m 2 ] N 86018000
S e c t i o n 7
Boilers and Thermal Oil Systems
I. Boilers
A. General
1. Scope
1.1 For the purpose of these Rules, the term"boiler" includes
all closed vessels and piping systemsused for:
a) generating steam at pressure aboveatmospheric (steam
generators) or
b) raising the temperature of water above theboiling point
corresponding to atmosphericpressure (hot water generators).
The term "steam generator" also includes anyequipment directly
connected to the aforementionedvessels or piping systems in which
the steam is super-heated or cooled, the circulating line and the
casingsof circulating pumps serving forced-circulationboilers.
1.2 Steam and hot water generators as defined in1.1 are subject
to the Rules set out in B. to F., or, ifappropriate, in G.
Exhaust gas economizers are subject to the specialrequirements
set out in H. In respect of materials,manufacture and design, the
requirements specified inB., C. and D. apply as appropriate.
1.3 Hot water generators with a permissibledischarge temperature
of not more than 120 C and allsystems incorporating steam or hot
water generatorswhich are heated solely by steam or hot liquids are
notsubject to these Rules, but come under Section 8.2. Other
Rules
2.1 As regards their construction and installation,steam boiler
plants are also required to comply withthe applicable statutory
requirements and regulationsof the ship's country of
registration.
3. Documents for approval
Drawings of all boiler parts subject to pressure, suchas drums,
headers, tubes, manholes and inspectioncovers etc., are to be
submitted to the Society intriplicate.
These drawings must contain all the data necessary for
strength calculations and design assessment, such asworking
pressures, superheated steam temperatures,materials to be used and
full details of welds includingfiller materials.
Details and drawings are also to be submittedcovering the valves
and fittings and their arrangementtogether with a description of
the boiler plantspecifying the arrangement of the boiler
withreference to the ship's longitudinal axis, the essentialboiler
data and equipment items, e.g. steamconditions, heating surfaces,
allowable steam output,feed, firing system, safety valves,
controllers andlimiters.
4. Definitions
4.1 Steam boiler walls are the walls of the steamand water
spaces located between the boiler isolatingdevices. The bodies of
these isolating devices formpart of the boiler walls.
4.2 The maximum allowable working pressure(PB, design pressure)
is the approved steam pressurein bar (gauge pressure) in the
saturated steam spaceprior to entry into the superheater. In
continuous flowboilers, the maximum allowable working pressure
isthe pressure at the superheater outlet or, in the case
ofcontinuous flow boilers without a superheater, thesteam pressure
at the steam generator outlet.
4.3 The heating surface is that part of the boilerwalls through
which heat is supplied to the system,
a) the area in m2 measured on the side exposedto fire or exhaust
gas, or
b) in the case of electrical heating, theequivalent heating
surface:
Where N is the electric power in kW.
4.4 The allowable steam output is the maximumquantity of steam
(in metric tons/hour or kg/hour)which can be produced continuously
by the steamgenerator operating under the design
steamconditions.
5 Lowest water level - highest flue -dropping time
-
7-2 Section 7 - Boilers and Thermal Oil System
5.1 The highest flue is the highest point on theside of the
heating surface which is in contact with thewater and which is
exposed to flame radiation orheated by gases which temperature
exceeds 4000C atmaximum continuous power. The highest flue onwater
tube boilers with an upper steam drum is the topedge of the highest
gravity tubes.
5.2 The requirements relating the highest flue donot apply
to
Water tube boiler risers up to 102 mm outerdiameter
Once-through forced flow boilers
Superheaters
Flues and exhaust gas heated parts in whichthe temperature of
the heating gases does notexceed 4000C at maximum continuous
power
5.3 The lowest water level must lie at least 150mm above the
highest flue also when the ship heels 40to either side. Heated
surfaces with a set highest fluemust remain wetted even when the
ship is at the staticheeling angles laid down in Section 1, Table
1.1. Theheight of the water level is critical to the response ofthe
water level limiters.
5.4 The heat accumulated in furnaces and otherheated boiler
parts may not lead to any unduelowering of the water level due to
subsequentevaporation when the firing system is swiched off.The
lowest water level is to be set so that the droppingtime does not
exceed 5 minutes.
5.5 The "dropping time" is the time taken by thewater level,
under conditions of interrupted feed andallowable steam output, to
drop from the lowestworking level to the level of the highest point
of thegas or flame path, i.e.:
t VD v
t [min] dropping timeV [m3] volume of water in steam
generator
between the lowest working leveland the highest point of the gas
orflame path.
D [kg/min] allowable steam outputv' [m3/kg] specific volume of
the water at
saturation temperature
5.6 The lowest specified water level is to beindicated
permanently on the boiler shell by means ofa water level pointer.
Reference plates are to beattached additionally beside or behind
the water levelgauges pointing at the lowest water level.
6. Manual operation
6.1 The facility is to be provided for manualoperation. At least
the water level limiters mustremain active even in manual
operation.
6.2 Manual operation demands constant anddirect supervision of
the system.
6.3 For detailed requirements in respect ofmanual operation of
the firing system see Section 9.
7. Power of steam propulsion plants
On ships propelled by steam, the plant is to bedesigned that,
should one main boiler fail, sufficientpropulsive capacity will
remain to maintain adequatemanoeuvrability and to supply the
auxiliarymachinery.
B. Materials
1. General requirements
With respect to their workability during manufactureand their
characteristics in subsequent operation,materials used for the
manufacture of steam boilersmust satisfy the technical
requirements, particularlythose relating to high-temperature
strength and, whereappropriate, weldability.
2. Approved materials
The requirements specified in 1. are recognized ashaving been
complied with if the materials shown inTable 7.1 are used.
Materials not specified in the Society's Rules forMaterials may
be used provided that proof is suppliedof their suitability and
mechanical properties.
3. Material testing
3.1 The materials of boiler parts subject topressure, including
exhaust gas economizer tubes,must be tested by the Society in
accordance with theRules for Materials (cf. Table 7.1). Material
testing bythe Society may be waived in the case of:
a) Small boiler parts made of unalloyed steels,such as stay
bolts, stays of 100 mmdiameter, reinforcing plates, handhole
andmanhole covers, forged flanges and branchpipes up to DN 150 or
recognized standardand
b) Smoke tubes (tubes subject to externalpressure).
-
Section 7 - Boilers and Thermal Oil Systems 7-3
Table 7.1 Approved materials
Material and product form Limits of application
Material grades in accordancewith the Rules for
Classification
and Construction, Volume V,Rules for Material
Steel plates and steel strip - Plates and strip of
high-temperaturesteel, Section 3, H
Steel pipes - Seamless and welded pipes offerritic steels,
Section 4, B and C
Forging and formed parts :
a) drum, headers and similar hollow components with out
longitudinal seam
b) covers, flanges, branch pipes, end plates
-
Forging for boilers,vessels and pipeline
Section 5, E
Nuts and bolts
- Fasteners, Section 6,CHigh-temperature bolts to
DIN 17 240
300 C 40 bar M30
DIN 267Parts 3 and 4
or other equivalent standards
Steel castings
Cast steel for boilers, pressurevessels and pipelines.
300 CAlso GS 38 and GS 45 to DIN 1681
and GS 16 Mn5 and GS 20 Mn5 to DIN 17 182
Nodular cast iron 300 C 40 bar
DN 175 for valvesand fittings
Nodular cast ironSection 7, B
Lamellar (grey) cast iron :a) Boiler parts (only for unheated
surfaces and not for heaters in ther- mal oil systems)b) Valves and
fittings (except valves subject to dynamic stresses)
c) exhaust gas economiser
200 C 10 bar
200 mm diameter
200 C 10 bar DN 175
52 barsmoke gas temperature
600 Cwater outlet temperature
245 C
Grey cast ironSection 7, C
100 barsmoke gas temperature
700 Cwater outlet temperature
260 C
Grey cast iron of at least GG-25grade to Section 7, C
Valves and fittings of castcopper alloy
225 C 25 bar
Cast copper alloysSection 10, B
For the parts mentioned in a) and b), the properties of
thematerials are to be attested by Type B works test
certificates in accordance with EN 10204.1B orother equivalent
standards.
-
7-4 Section 7 - Boilers and Thermal Oil System
3.2 Special agreements may be made regarding thetesting of
unalloyed steels to recognized standards.
3.3 The materials of valves and fittings must betested by the
Society in accordance with the datasspecified in Table 7.2.
3.4 Parts not subject to material testing, such asexternal
supports, lifting brackets, pedestals etc. must bemade of materials
suitable for the intended purpose andin accordance with accepted
engineering practice.
C. Principles Applicable to Manufacture
1. Manufacturing processes applied to boilermaterials
Materials are to be checked for defects during themanufacturing
process. Care is to be taken to ensure thatdifferent materials
cannot be confused. During the courseof manufacture care is
likewise required to ensure thatmarks and inspection stamps on the
materials remainintact or are transferred in the prescribed
manner.
Boiler parts whose structure has been adversely affectedby hot
or cold forming are to be subjected to heattreatment in accordance
with the Rules for Materials,Volume V, Section 8, A.
Table 7.2 Testing of materials for valves andfittings
Type ofmaterials 1)
Servicetemperature
[C]
Testing requiredfor: PB in [bar]
DN in [mm]Steel, cast steel > 300 DN > 32
Steel, cast steel,nodular cast iron 300
PB x DN > 2500 2)or
DN > 250Copper alloys 225 PB x DN > 1500 2)1) No test is
required for grey cast iron.2) Testing may be required with if DN
is 32 mm.
2. Welding
The execution of welds, the approval of welding shopsand the
qualification testing of welders are to be inaccordance with Rules
for Welding, Volume VI,Section 3.
3. Riveting
Where, in special cases, boiler parts have to be riveted tobe
observed
4. Tube expansion
Tube holes must be carefully drilled and deburred. Sharpedges
are to be chamfered. Tube holes should be as closeas possible to
the radial direction, particularly in the case
of small wall thicknesses.
Tube ends to be expanded are to be cleaned andchecked for size
and possible defects. Wherenecessary, tube ends are to be annealed
beforebeing expanded.
5. Stays, stay tubes and stay bolts
5.1 Stays, stay tubes and stay bolts are to bearranged that they
are not subjected to undue bend-ing or shear forces.
Stress concentrations at changes in cross-section,in screw
threads and at welds are to be minimizedby suitable component
geometry.
5.2 Stays and stay bolts are to be welded byfull penetration
preferably. Any vibrational stressesare to be considered for long
stays.
5.3 Stays are to be drilled at both ends in sucha way that the
holes extend at least 25 mm into thewater or steam space. Where the
ends have beenupset, the continuous shank must be drilled to
adistance of at least 25 mm.
5.4 Wherever possible, the angle made by gus-set stays and the
longitudinal axis of the boilershall not exceed 30. Stress
concentrations at thewelds of gusset stays are to be minimized
bysuitable component geometry. Welds are to beexecuted as
full-strength welds. In firetube boilers,gusset stays are to be
located at least 200 mm fromthe firetube.
5.5 Where flat surfaces exposed to flames arestiffened by stay
bolts, the distance betweencenters of the stay bolts shall not
generally exceed200 mm.
6. Stiffeners, straps and lifting eyes
6.1 Where flat end surfaces are stiffened byprofile sections or
ribs, the latter shall transmittheir load directly (i.e. without
welded-on straps) tothe boiler shell.
6.2 Doubling plates may not be fitted atpressure parts subject
to flame radiation.Where necessary to protect the walls of the
boiler,strengthening plates are to be fitted below supportsand
lifting brackets.
7. Welding of flat unrimmed ends to boilershells
Flat unrimmed ends (disc ends) on largewaterspace boilers are
only permitted assocket-welded ends with a shell projection of 15
mm. The end/shell wall thickness ratio sB/sMshall not be greater
than 1,8. The end is to bewelded to the shell with a full-strength
weld.
-
Section 7 - Boilers and Thermal Oil Systems 7-5
8. Stand pipes and flanges
Stand pipes and flanges are to be of rugged design andproperly
welded to the shell. The wall thickness ofbranch pipes must be
sufficiently large safely towithstand additional external loads.
The wall thickness ofwelded-in pipe connections shall be
appropriate to thewall thickness of the part into which they are
welded.
Welding-neck flanges must be made of forged materialwith
favourable grain orientation.
9. Cleaning and inspection openings, cutouts andcovers
9.1 Steam boilers are to be provided with openingsthrough which
the space inside can be cleaned andinspected. Boiler vessels with
an inside diameter of morethan 1200 mm and those measuring over 800
mm indiameter and 2000 mm in length are to be provided withmeans of
access. Parts inside drums must not obstructinner inspection or
must be capable of being removed.
9.2 Inspection and access openings are required tohave the
following minimum dimensions:
Manholes 300 x 400 mm or 400 mm diameter,where the annular
height is > 150 mmthe opening measure shall be 320 x420 mm.
Headholes 220 x 320 mm or 320 mm diameter
Handholes 87 x 103 mm
Sight holes are required to have a diameter of atleast 50 mm;
they should, however, beprovided only when the design of
theequipment makes a handholeimpracticable.
9.3 The edges of manholes and other openings, e.g.for domes, are
to be effectively strengthened if the platehas been unacceptably
weakened by the cutouts. Theedges of openings closed with covers
are to be reinforcedby flanging or by welding on edge-stiffeners if
it is likelythat the tightening of the crossbars etc. would
otherwisecause undue distortion of the edge of the opening.
9.4 Cover plates, manhole stiffeners and crossbarsmust be made
of ductile material (not grey or malleablecast iron). Grey cast
iron (at least GG-20) may be usedfor handhole cover crossbars of
headers and sectionalheaders, provided that the crossbars arc not
located in theheating gas flow. Unless metal packings are used,
coverplates must be provided on the external side with a rim
orspigot to prevent the packing from being forced out. Thegap
between this rim or spigot and the edge of theopening is to be
uniform round the periphery and may notexceed 2 mm for boilers with
a working pressure of lessthan 32 bar, or 1 mm where the pressure
is 32 bar orover. The height of the rim or spigot must be at least
5mm greater than the thickness of the packing.
9.5 Only continuous rings may be used as packing.
The materials used must be suitable for the givenoperating
conditions.
10. Boiler drums, shell sections, headers andfiretubes, See the
Rules for Welding Volume VI,B.
D. Design Calculation
1. Design principles
1.1 Range of applicability of designformulae
1.1.1 The following strength calculations repre-sent the minimum
requirements for normaloperating conditions with mainly static
loading.Separate allowance must be made for additionalforces and
moments of significant magnitude.Proper treatment and adequate
monitoring of thefeedwater are assumed to be carried out.
1.1.2 The wall thicknesses arrived at by applyingthe formulae
are the minima required. Theundersize tolerances permitted by the
Rules forMaterials are to be added to the calculated values.
The greater local undersize tolerances for tubesneed not be
considered.
1.2 Design pressure pc1.2.1 In general, the design pressure is
equal tothe maximum allowable working pressure. Addi-tional
allowance is to be made for static pressuresof more than 0,5
bar.
1.2.2 In designing continuous-flow boilers, thepressure to be
applied is the maximum workingpressure anticipated in each of the
individual mainboiler sections at maximum continuous load and atthe
response threshold of the safety equipment.
1.2.3 The design pressure applicable to thesuperheated steam
lines from the boiler is themaximum working pressure which adequate
safetydevices prevent from being exceeded.
!
" #
-
7-6 Section 7 - Boilers and Thermal Oil System
1.3 Design temperature t
Strength calculations are based on the temperature at thecenter
of the wall thickness of the component in question.The design
temperature is made up of the referencetemperature and a
temperature allowance in accordancewith Table 7.3. The minimum
value is to be taken as250 C.
Table 7.3 Design temperatures
Referencetemperature
Allowance to be added
Unheatedparts
Heated parts, heatedmainly by
contact radiation
Saturationtemperatureat m.a.w.p
0 C 25 C 50 C
Superheatedsteamtemperature
15 C 1) 35 C 50 C
1) The temperature allowance may be reduced to 7 Cprovided that
special measures are taken to ensure thatthe design temperature
cannot be exceeded
1.4 Allowable stress
The design of structural components is to be based on
theallowable stress perm[N/mm2]. In each case, the minimumvalue
produced by the following relations is applicable :
1.4.1 Rolled and forged steels
For design temperatures up to 350 C
where Rm, 20 = guaranteed minimum tensileR
m,20
2,7strength [N/mm2] at roomtemperature
where ReH,t = guaran teed yie ld poin t or$ %
minimum 0,2 % proof stress atdesign temperature t.
For design temperature over 350 C
where Rm100000,t= mean 100000 hour creepR
m,100000,t
1,5strength at designtemperature t
1.4.2 Cast materials
a) Cast steel : ; ; Rm,203,2
ReH,t
2,0R
m,100000,t
2,0
b) Nodular cast ; Rm,204,8
ReH,t
3,0
iron :
c) Grey cast Rm,2011
iron :
1.4.3 Special arrangements may be agreed forhigh-ductility
austenitic steels.
1.4.4 In the case of cylinder shells with cutoutsand in contact
with water, a nominal stress of 170N/mm shall not be exceeded in
view of the pro-tective magnetite layer.
1.4.5 Mechanical characteristics are to be takenfrom the Rules
for Materials or from the standardsspecified therein.
1.5 Allowance for corrosion and wear
The allowance for corrosion and wear is to bec = 1 mm. For plate
thicknesses of 30 mm and overand for stainless materials, this
allowance may bedispensed with.
1.6 Special cases
Where boiler parts cannot be designed inaccordance with the
following Rules or on generalengineering principles, the dimensions
in eachindividual case must be determined by tests, e.g. bystrain
measurements
2. Cylindrical shells under internalpressure
2.1 Scope
The following design Rules apply to drums,shell rings and
headers up to a diameter ratio Da/Diof 1,7. Diameter ratios of up
to Da/Di 2 may bepermitted provided that the wall thickness is 80
mm.
2.2 Symbols
pc [bar] design pressures [mm] wall thicknessDi [mm] inside
diameterDa [mm] outside diameterc [mm] allowance for corrosion and
weard [mm] diameter of opening or cutout
hole diameter for expandedtubes and for expanded and seal-welded
tubes (see Fig. 7.1 a and7.1 b)inside tube diameter forwelded-in
pipe nipples andsockets (Fig. 7.1 c)
t,tl,tu [mm] pitch of tube holes (measured atcenter of wall
thickness for cir-
-
Section 7 - Boilers and Thermal Oil Systems 7-7
Fig. 7.1
Fig. 7.2
cumferential seams)v [ - ] weakening factor
for welds :the qualitative ratio of the weldedjoints to the
plate (weld quality rating)for holes drilled in the plate :the
ratio of the weakened to theunweakened plate section
perm [N/mm2] allowable stress (see 1.4)sA [mm] necessary wall
thickness at edge of
opening or cutout
sS [mm] wall thickness of branch pipeb [mm] supporting length of
parent componentls [mm] supporting length of branch pipel [mm]
width of ligament between two branch
pipes
l's [mm] internal projection of branch pipeAp [mm2] area under
pressureA [mm] supporting cross-sectional area
2.3 Design calculations
2.3.1 The necessary wall thickness s is given by theexpression
:
(1)s Da pc20 perm v pc
c
2.3.2 In the case of heated drums and headers with amax.
allowable working pressure of more than 25 bar,special attention is
to be given to thermal stresses.
For heated drums not located in the first pass (gastemperature
up to 1000 C max.), special certification inrespect of thermal
stresses may be waived subject to thefollowing provision:
Wall thickness up to 30 mm and adequate cooling of thewalls by
virtue of close tube arrangement. Thedescription "close tube
arrangement" is applicable if theligament perpendicular to the
direction of gas flow andparallel to the direction of gas flow does
not exceed 50mm and 100 mm respectively.
2.3.3 Weakening factor v
The weakening factor v is shown in Table 7.4.
Table 7.4 Weakening factor v
Construction Weakening factor vSeamless shellrings and drums
1,0
Shell rings anddrums withlongitudinalweld
weld quality rating see Rulesfor Welding
Rows of holes1)
1) The value of v for rows of holes may not be madegreater than
1,0 in the calculation. For staggeredpitches, see Appendix, Fig.
7.27.Refer also to Figures 7.1a-7.1c under paragraph 2.2
2.3.4 Weakening effects due to cutouts or indi-vidual branch
pipes are to be taken into account byarea compensation in
accordance with theexpression:
(2)Pc10
ApA
12
perm
The area under pressure Ap and the supportingcross-sectional
area A are defined in Fig. 7.2.
The values of the supporting lengths may notexceed:
for the parentcomponent b (Di sA c) ( sA c)for the branch pipe
ls 1,25 (d sS c) ( sS c)
-
7-8 Section 7 - Boilers and Thermal Oil System
Fig. 7.3
Where a branch projects into the interior, the valueintroduced
into the calculation as having a supportingfunction may not exceed
l's 0,5 lsCutouts exert a mutual effect if the ligament
l 2 (Di sA c) ( sA c)The area compensation is then as shown in
Fig. 7.3.
Where materials with different mechanical strengths areused for
the parent component and the branch orreinforcing plate, this fact
is to be taken into account inthe calculation. However, the
allowable stress in thereinforcement may not be greater than that
for the parentmaterial in the calculation.
Disc-shaped reinforcements should not be thicker thanthe actual
parent component thickness, and this thicknessis the maximum which
may be allowed for in thecalculation.
Disc-shaped reinforcements are to be fitted on theoutside.
The wall thickness of the branch pipe should not be morethan
twice the required wall thickness at the edge of thecutout.
In the case of tubular reinforcements, the following
wallthickness ratio is applicable :
sS c
sA c 2
2.4 Minimum allowable wall thickness
For welded and seamless shell rings the minimumallowable wall
thickness is 5 mm. For non-ferrous metals,stainless steels and
cylinder diameters up to 200 mm,smaller wall thicknesses may be
permitted. The wallthickness of drums into which tubes are expanded
is to besuch as to provide a cylindrical expansion length of
atleast 16 mm.
3. Cylindrical shells and tubes with an outsidediameter of more
than 200 mm subject toexternal pressure
3.1 Scope
The following Rules apply to the design of smoothand corrugated
cylindrical shells and tubes with anoutside diameter of more than
200 mm which aresubjected to external pressure. Firetubes are
tubesexposed to fire.
3.2 Symbols
pc [bar] design pressures [mm] wall thicknessd [mm] mean
diameter of smooth tubeda [mm] outside diameter of smooth tubedi
[mm] minimum inside diameter of
corrugated firetube
l [mm] length of tube or distancebetween two effective
stiffeners
h [mm] height of stiffening ringb [mm] thickness of stiffening
ringu [%] percentage out-of-roundness of
tube
a [mm] greatest deviation fromcylindrical shape (see Fig.
7.5)
perm [N/mm] allowable stressEt [N/mm] modulus of elasticity at
design
temperature
SK [-] safety factor against elasticbuckling
v [-] transverse elongation factor (0,3for steel)
c allowance for corrosion andwear
3.3 Design calculations
3.3.1 Cylindrical shells and smooth firetubes
Calculation of resistance to plastic deformation:
(3)Pc 10 perm
2(sc)d
1 0,1 dl
1 0,03 dsc
u
15 dl
Calculation of resistance to elastic buckling:
pc 20 EtSk
sc
da
(n 21) 1 nZ
2 2
sc
da
3
3 (12 )
-
Section 7 - Boilers and Thermal Oil Systems 7-9
Fig. 7.4
(4) n 21 2 n 211 n
Z
2
where : Z d
a
2 land n 2
n > Z
n (integer) is to be chosen as to reduce pc to its minimumvalue.
n represents the number of buckled folds occurringround the
periphery in the event of failure. n can beestimated by applying
the following approximationformula:
n 1,63 4 d
a
l
2
da
s c
3.3.2 In the case of corrugated tubes of Fox andMorrison types,
the necessary wall thickness s is given bythe expression:
(5)s pc20
diperm
1 mm
3.4 Allowable stress
Contrary to 1.4, the values for the allowable stress offiretubes
used in the calculations are to be as follows:
- Plain firetubes, horizontalR
e,H,t
2,5
Plain firetubes, verticalR
e,H,t
2,0
Corrugated tubesR
e,H,t
2,8 Tubes heated by
Re,H,t
2,0exhaust gases
3.5 Design temperature
Contrary to 1.3, the design temperature to be used forfiretubes
is shown in Table 7.5.
3.6 Stiffening
Apart from the firetube and firebox end-plates, the typesof
structure shown in Figure 7.4 can also be regarded asproviding
effective stiffening.
3.7 Safety factor SkA safety factor Sk of 3,0 is to be used in
the calculation ofresistance to elastic buckling. This value is
applicablewhere the out-of-roundness is 1,5 % or less. Where
theout-of-roundness is more than 1,5 % and up to 2 %, the
safety factor Sk to be applied is 4,0.
3.8 Modulus of elasticity
Table 7.6 shows the modulus of elasticity for steelin relation
to the design temperature.
Table 7.5 Design temperatures for shellsand tubes under
externalpressure
For tubes exposed to fire(firetubes) :
but at least 250 oC
plain tubest = saturation
temperature + 4 . s + 30 oC
corrugatedtubes
t = saturationtemperature + 3 . s + 30 oC
For tubes heated by exhaust gases
t = saturation tem-perature + 2 . s+ 15 oC
Table 7.6 Values for the modulus of elasticity
Designtemperature
[oC]
Et 1)[N/mm2]
20250300400500600
206000186400181500171700161900152100
1) Intermediate values should be interpolated
3.9 Allowance for corrosion and wear
An allowance of 1 mm for corrosion and wear is tobe added to the
wall thickness s. In the case ofcorrugated tubes, s is the wall
thickness of thefinished tube.
3.10 Minimum allowable wall thicknessand maximum wall
thickness
The wall thickness of smooth firetubes shall be atleast 7 mm,
that of corrugated firetubes at least 10mm. For small boilers,
non-ferrous metals andstainless steels, smaller wall thicknesses
are
-
7-10 Section 7 - Boilers and Thermal Oil System
u 4 a
d 100
& '& '& '& '
allowable. The maximum wall thickness may not exceed20 mm. Tubes
which are heated by flue gases < 1000 oCmay have a maximum wall
thickness of up to 30 mm.
3.11 Maximum unstiffened length
For firetubes, the length l between two stiffeners may notexceed
6 d. The greatest unsupported length shall notexceed 6 m or, in the
first pass from the front end-plate,5 m. Stiffenings of the type
shown in Figure 4 are to beavoided in the name zone, i. e. up to
approximately 2 dbehind the lining.
The plain portion of corrugated firetubes need not beseparately
calculated provided that its stressed length,measured from the
middle of the end-plate attachment tothe beginning of the first
corrugation, does not exceed250 mm.
3.12 Out-of-roundness
The out-of-roundness [%]
u 2 (d
max d
min)d
max d
min 100
of new smooth tubes is to be given the value u = 1,5 % inthe
design formula.
In the case of used firetubes, the out-of-roundness is tobe
determined by measurements of the diametersaccording to Fig.
7.5.
3.13 Firetube spacing
The clear distance between the firetube and boiler shellat the
closest point shall be at least 100 mm. The distancebetween any two
firetubes shall be at least 120 mm.
4. Dished end-plates under internal andexternal pressure
4.1 Scope
4.1.1 The following Rules apply to the design ofunstayed dished
end-plates under internal or external
pressure (see Fig. 7.6). The following requirementsare to be
complied with:
The radius R of the dished end may not exceed theoutside
end-plate diameter Da, and the knuckleradius r may not be less than
0,1 Da.
The height H may not be less than 0,18 Da.
The height of the cylindrical portion, with theexception of
hemispherical end-plates, shall be3,5 s, s being taken as the
thickness of theunpierced plate even if the end-plate is
providedwith a manhole. The height of the cylindricalportion need
not, however, exceed the followingvalues in Table 7.7.
Table 7.7 Height h of cylindrical portion
Wall thickness s[mm]
h[mm]
up to 50over 50 up to 80
over 80 up to 100over 100 up to 120
over 120
1501201007550
4.1.2 These Rules also apply to weldedend-plates. Due account is
to be taken of thequality rating of the weld (cf. 4.5 ).
4.2 Symbols
pc [bar] design pressures [mm] wall thickness of end-plateDa
[mm] outside diameter of end-plateH [mm] height of end-plate
curvatureR [mm] inside radius of dished endh [mm] height of
cylindrical portiond [mm] diameter of opening measured
along a line passing through thecenters of the end-plate and
theopening. In the case of openingsconcentric with the end-plate,
themaximum opening diameter.
perm[N/mm2] allowable stress (cf. 1.4) [-] coefficient of stress
in flange
-
Section 7 - Boilers and Thermal Oil Systems 7-11
Fig. 7.6
o [-] coefficient of stress in sphericalsection
v [-] weakening factorc [mm] allowance for corrosion and wearEt
[N/mm2] modulus of elasticity at design
temperature
sA [mm] necessary wall thickness at edge ofopening
Ss [mm] wall thickness of branch pipeb [mm] supporting length of
parent
component
l [mm] width of ligament between two branchpipes
ls [mm] supporting length of branch pipe
l's [mm] internal projection of branch pipeAp [mm] area subject
to pressureA [mm] supporting cross-sectional areaSk [-] safety
factor against elastic bucklingS'k [-] safety factor against
elastic buckling
at test pressure
4.3 Design calculation for internal pressure
4.3.1 The necessary wall thickness is given by
theexpression:
(6)s Da pc 40 perm v
c
The finished wall thickness of the cylindrical portion
must be at least equal to the required wall thickness ofa
cylindrical shell without weakening.
4.3.2 Design coefficients and oThe design coefficients are shown
in Fig. 7.7 inrelation to the ratio H / Da and parameters
and s / Da. ( ) *
For dished ends of the usual shapes, the height H canbe
determined as follows :
Shallow dished end (R = Da)H 0,1935 Da + 0,55 s
Deep dished end, ellipsoidal shape (R = 0,8 Da)H 0,255 Da + 0,36
s
The values of for unpierced end-plates also apply todished ends
with openings whose edges are locatedinside the spherical section
and whose maximumopening diameter is d 4 s, or whose edges
areadequately reinforced. The width of the ligamentbetween two
adjacent, non-reinforced openings mustbe al least equal to the sum
of the opening radiimeasured along the line connecting the centers
of theopenings. Where the width of the ligament is less thanthat
defined above, the wall thickness is to bedimensioned as though no
ligament were present, orthe edges of the openings are to be
adequately rein-forced.
-
7-12 Section 7 - Boilers and Thermal Oil System
Fig. 7.7 Values of coefficient for the design of dihed ends
-
Section 7 - Boilers and Thermal Oil Systems 7-13
Fig. 7.8
Fig. 7.9
4.3.3 Reinforcement of openings in the sphericalsection
Openings in the spherical section are deemed to beadequately
reinforced if the following expressionrelating to the relevant
areas is satisfied.
(7)pc10
ApA
12
perm
The area under pressure Ap and the supportingcross-sectional
area A are shown in Fig. 7.8.
For calculation of reinforcements and supportinglengths the
formulae and prerequsites in 2.3.4 areapplicable.
The relationship between respective areas of cutoutsexerting a
mutual effect is shown in Fig. 7.9.
The edge of disk-shaped reinforcements may notextend beyond 0,8
D a .
In the case of tubular reinforcements, the followingwall
thickness ratio is applicable:
sS c
sA c 2
4.4 Design calculation for external pressure
4.4.1 The same formulae are to be applied toend-plates under
external pressure as to those subjectto internal pressure. However,
the safety factor usedto determine the allowable stress in
accordance with1.4.1 is to be increased by 20 %.
4.4.2 A check is also required to determine whetherthe spherical
section of the end-plate is safe againstelastic buckling.
The following relationship is to be applied:
(8)pc 3,66 EtSk
s c
R
2
The modulus of elasticity Et for steel can be takenfrom Table
7.6.
The safety coefficient Sk against elastic buckling andthe
required safety coefficient Sk' at the test pressureare shown in
Table 7.8.
Table 7.8 Safety coefficient against elasticbuckling
s - cR
Sk1) Sk'1)
0,001 5,5 4,0
0,003 4,0 2,9
0,005 3,7 2,7
0,01 3,5 2,6
0,1 3,0 2,21) Intermediate values should be interpolated
-
7-14 Section 7 - Boilers and Thermal Oil System
Fig. 7.10
Fig. 7.11
4.5 Weakening factor
The weakening factor can be taken from Table 7.4 in2.3.3. Apart
from this, with welded dished ends-except for hemispherical ends -
a value of v = 1 maybe applied irrespective of the scope of the
testprovided that the welded seam impinges on the areawithin the
apex defined by 0,6 Da (cf. Fig. 7.10).
4.6 Minimum allowable wall thickness
The minimum allowable wall thickness for weldingneck end-plates
is 5 mm. Smaller minimum wallthicknesses are allowed for
non-ferrous metals andstainless steels.
5. Flat surfaces
5.1 Scope
The following Rules apply to stayed and unstayed flat,flanged
end-plates and to flat surfaces which aresimply supported, bolted,
or welded at their peripheryand which are subjected to internal or
externalpressure.
5.2 Symbols
pc [bar] design pressures [mm] wall thicknesss1 [mm] wall
thickness in a stress
relieving groove
s2 [mm] wall thickness of a cylindrical orsquare header at the
connectionto a flat end-plate with a stressrelieving groove
Db [mm] inside diameter of a flat, flangedend-plate or design
diameter ofan opening to be provided withmeans of closure
D1, D2 [mm] diameter of circular platesDl [mm] bolt-hole circle
diameter of a
plate subject additionally to a
bending moment
de [mm] diameter of the largest circlewhich can be described on
a flatplate inside at least threeanchorage points
da [mm] outside diameter of expandedtubes
a, b [mml clear supporting or designwidths of rectangular or
ellipticalplates, b always designating theshorter side or axis
tl, t2 [mm] pitch of uniformly spaced staysor stay bolts
e1, e2 [mm] distances between centers ofnon-uniformly spaced
stays andstay bolts
f [mm2] cross-sectional area of ligamentrK [mm] inner corner
radius of a flange,
or radius of a stress relievinggroove
h [mm] inner depth of a flat,welding-neck end-plate
C [-] design coefficienty [-] ratioperm [N/mm2] allowable stress
(see 1.4)c [mm] allowance for corrosion and
wear
5.3 Design calculation of unstayed surfaces
5.3.1 Flat, circular, flanged, unpierced
end-plates(cf.Fig.7.11).The necessary wall thickness s is given by
theexpression:
(9)s C ( Db rK ) p
c
10 perm c
5.3.2 Circular plates
-
Section 7 - Boilers and Thermal Oil Systems 7-15
Fig. 7.12a - 7.12d
Fig. 7.13
Fig. 7.14
Fig. 7.15
Fig. 7.16 Fig. 7.17
The required wall thickness s is given by theexpression :
(10)s C Db p
c
10 perm c
5.3.3 Rectangular and elliptical plates.
The required wall thickness s is given by theexpression:
(11)s C b y pc10 perm
c
5.3.4 Welding-neck end-plates.
The thickness of the plate s is determined by applyingformula 10
or 11 as appropriate.
In the case of end-plates with a stress relievinggroove,
provision must be made for the effectiverelieving of the welded
seams. The wall thickness s1in the stress relieving groove must
therefore satisfythe following conditions, cf. Fig. 7.17:
For round end-plates : s1 0,77 s2For rectangular end-plates : s1
0,55 s2Here s2 represents the wall thickness of the cylindricalor
rectangular header in [mm]. In addition, provisionmust be made to
ensure that shear forces occurring inthe cross-section of the
groove can be safelyabsorbed.
It is therefore necessary that for round end-plates:
(12)s1 p
c
10
Db2
rK 1,3perm
and for rectangular end-plates:
(13)s1 p
c
10
a ba b
1,3perm
-
7-16 Section 7 - Boilers and Thermal Oil System
Fig. 7.18 Fig. 7.19
Fig. 7.20
Fig. 7.21
Radius rK shall be at least 0,2 s and not less than5 mm. Wall
thickness sl must be at least 5 mm.
Where welding-neck end-plates in accordance withFig. 7.16 or
Fig. 7.17 are manufactured from plates,the area of the connection
to the shell is to be testedfor lamination, e. g.
ultrasonically.
5.4 Design calculation of stayed surfaces
5.4.1 For flat surfaces which are uniformly bracedby stay bolts,
circular stays or stay tubes, cf. Fig. 7.18.
The required wall thickness s inside the stayed areasis given by
the expression:
(14)s C pc ( t21 t
22 )
10 perm c
5.4.2 For flat plates which are nonuniformlybraced by stay
bolts, circular stays and stay tubes, cf.Fig. 7.19.
The necessary wall thickness s inside the stayed areasis given
by the expression:
(15)s C e1 e22
pc
10 perm c
5.4.3 For flat plates which are braced by gussetstays, supports
or other means and flat plates betweenarrays of stays and tubes,
cf. Fig. 7.20.
The design calculalion is to be based on the diameterde or a
circle, or on the length of the shorter side b ofa rectangle which
can be inscribed in the free un-stiffened area, the least
favourable position from thepoint of view of stress being decisive
in each case.
The required wall thickness s is given by theexpression:
(16)s C de
pc
10 perm c
or
(17)s C b y pc10 perm
c
The higher of the values determined by the formulaeis
applicable.
5.4.4 Flat annular plates with central longitudinalstaying, see
Fig. 7.21.
The required wall Thickness s is given by theexpression:
(18)s 0,25 ( D1 D2 rK1 rK2 ) p
c
10 perm c
5.5 Requirements for flanges
5.5.1 Application of the above formulae to flangedend-plates and
to flanges as a means of staying issubject to the provision that
the corner radii of theflanges should have the following minimum
values inrelation to the outside diameter of the endplate (cf.Table
7.9).In addition, the flange radii rK (Figs. 7.11, 7.20 and7.21)
must be equal to at least 1,3 times the wallthickness.
5.5.2 In the case of welding-neck end-plateswithout a stress
relieving groove for headers, theflange radius must be rK 1/3 s,
subject to aminimum of 8 mm, and the inside depth of theend-plate
must be h s, s for end-plates withopenings being the thickness of
an unpierced
-
Section 7 - Boilers and Thermal Oil Systems 7-17
end-plate of the same dimensions, cf. Fig. 7.16.
Table 7.9 Minimum corner radius of flanges
Outside diameter of endplate[mm]
Corner radius offlanges[mm]
over 500over1400over 1600over 1900
up to 500up to 1400up to 1600up to 1900
3035404550
5.6 Ratio y
The ratio y takes account of the increase in stress, ascompared
with round plates, as a function of the ratioof the sides b/a of
unstayed, rectangular and ellipticalplates and of the rectangles
inscribed in the free,unstayed areas of stayed, flat surfaces, cf.
Table 7.10.
Table 7.10 Values of ratio y
Shape Ratio b/a 1)1,0 0,75 0,5 0,25 0,1
Rectangle 1,10 1,26 1,40 1,52 1,56
Ellipse 1,00 1,15 1,30 --- ---1) Intermediate values are to be
interpolated linearly.
5.7 Coefficient C
Coefficient C takes account of the type of support, theedge
connection and the type of stiffening. The valueof C to be used in
the calculation is shown in Tables7.11 and 7.12.
Where different values of C are applicable to parts ofa plate
due to different kinds of stiffening accordingto Table 7.12
coefficient C is to be determined by thearithmetical value :
C = (C1 + C2 ......Cn) / n
5.8 Minimum ligament with expanded tubes
The minimum ligament width depends on theexpansion technique
used. The cross-section f of theligament between two tube holes for
expanded tubesshould be for :
steel f [mm2] = 15 + 3,4 dacopper f [mm2] = 25 + 9,5 da
Table 7.11 Values of coefficient C for unstayedsurfaces
Type of end-plate or cover C1)Flat, forged and-plates or
end-plates withmachined recesses for headers and flat,flanged
end-plates 0,35Encased plates tightly supported and boltedat their
circference
Inserted, flat plates welded on both sided
Welding-neck end plates with stress re-lieving groove
0.40
Loosely supported plates, such as man-holecovers; in the case of
closing appliances, inaddition to the working pres-sure,
allowanceis also to be made for the additional forcewhich can be
excerted when the bolts aretightened (the permitted loading of the
bolt orbolts) distributed over the cover area).
0,45
Inserted, flat plates welded on one side
Plates which are bolted at their circum-ference and are thereby
subjected to anadditional bending moment according to theratio
:
Dl/Db = 1,0
= 1,1
= 1,2
= 1,3
Intermediate values are to be interpolatedlinearly
0,45
0,50
0,55
0,60
Table 7.12 Values of coefficient C for stayedsurfaces
Type of stiffening and/or end-plate C
Boiler shell, header or cumbustion chamberwall, stay plate or
tube area
0,35
Stay bolts in arrays with maximum stay boltcentre distance of
200 mm
0,40
Round stays and tubes outside tube arraysirrespective of whether
they are welded-in,bolted or expanded
0,45
5.9 Minimum and maximum wall thickness
5.9.1 With expanded tubes, the minimum platethickness is 12 mm.
Concerning safeguards againstthe dislodging of expanded tubes, see
6.3.2.
5.9.2 The wall thickness of flat end-plates shouldnot exceed 30
mm in the heated portion.
5.10 Reinforcement of openings
-
7-18 Section 7 - Boilers and Thermal Oil System
Fig. 7.22 - 7.24
Where the edges of the openings are not reinforced,special
allowance is to be made when calculatingthickness for cutouts,
branches etc. in flat surfaceswhich lead to undue weakening of the
plate.
6. Stays, stay tubes and stay bolts
6.1 Scope
The following Rules apply to longitudinal stays, gus-set stays,
stay tubes, stay bolts and stiffening girdersof steel or copper and
are subject to the requirementsset out in C.5.
6.2 Symbols
pc [bar] design pressureF [N] load on a stay, stay tube or
stay
bolt
A1 [mm2] c a l c u l a t e d r e q u i r e dcross-section area
of stays, staybolts and stay tubes
A2 [mm2] supported area of expandedtubes
Ap [mm2] plate area supported by onestay, stay bolt or stay
tube
da [mml outside diameter of stay, staybolt or stay tube
di [mm] inside diameter of stay tubelo [mm] length of expanded
section of
tube
a1 [mm] weld height in direction of loadperm [N/mm2] allowable
stress
6.3 Design calculation
The supporting action of other boiler parts may betaken into
consideration when calculating the size ofstays, stay tubes and
stay bolts. Where the boundaryareas of flanged end-plates are
concerned, calculationof the plate area Ap is to be based on the
flat surfaceextending to the beginning of the end-plate flange.
In the case of flat end-plates, up to half the load maybe
assumed to be supported by the directly adjacentboiler wall.
6.3.1 For stays, stay bolts or stay tubes, thenecessary
cross-sectional area is given by:
(19)A1 Fperm
6.3.2 Where expanded tubes are used, a sufficientsafety margin
must additionally be applied to preventthe tubes from being pulled
out of the tube plate. Sucha safety margin is deemed to be achieved
if thepermissible load on the supporting area does notexceed the
values specified in Table 7.13.
For the purpose of thecalculation, the suppor-ting area is given
bythe expression : A2 = (da - di) losubject to a maximumof : A2 =
0,1 da lo
Table 7.13 Loading of expanded tube
Type ofexpandedconnection
Permissible load onsupporting area
[N/mm2]
Plain F / A2 150
With groove F / A2 300
With flange F / A2 400
For calculating the supporting area, the length of theexpanded
section of tube (lo) may not be taken asexceeding 40 mm.
6.3.3 Where longitudinal stays, stay tubes or staybolts are
welded in, the cross-section of the fillet weldsubject to shear
shall be at least 1,25 times therequired bolt or stay tube
cross-section:
da a1 1,25 A1 (20)
6.4 Allowable stress
The allowable stress is to be determined in accordancewith
1.4.1. In departure from this, however, a value of
is to be expected in the area of the weld in theR
e,H,t
1,8case of stays, stay tubes and stay bolts made of rolledand
forged steels.
7. Boiler and superheated tubes
7.1 Scope
The design calculation applies to tubes under internalpressure
and, up to an outside tube diameter of 200
-
Section 7 - Boilers and Thermal Oil Systems 7-19
mm, also to tubes subject to external pressure.7.2 Symbols
pc [bar] design pressures [mm] wall thickness da [mm] outside
diameter of tubeperm [N/mm2] allowable stressv [-] weld quality
rating of
longitudinally welded tubes
7.3 Calculation of wall thickness
The necessary wall thickness s is given by theexpression :
(21)s da pc20 perm v pc
7.4 Design temperature t
The design temperature applied is to be as specified inTable
7.3.
In the case of once through forced flow boilers, thecalculation
of the tube wall thicknesses is to be basedon the maximum
temperature expected in theindividual main sections of the boiler
under operatingconditions plus the necessary added
temperatureallowances.
7.5 Allowable stress
The allowable stress is to be determined in accordancewith
1.4.1.
For tubes subject to external pressure, a value of is to be
applied.
ReH,t
2,07.6 Quality rating of weld, vFor longitudinally welded tubes,
the value of v to beapplied shall correspond to the approval
test.
7.7 Wall thickness allowances
In the case of tubes subject to relatively severemechanical or
chemical attack an appropriate wallthickness allowance shall be
agreed which shall beadded to the wall thickness calculated by
applyingformula (21). The permissible minus tolerance on thewall
thickness (see 1.1.2) need only be taken intoconsideration for
tubes whose outside diameterexceeds 76,1 mm.
7.8 Maximum wall thickness of boiler tubes
The wall thickness of intensely heated boiler tubes(e.g. where
the temperature of the heating gas exceeds800 C) shall not be
greater than 6,3 mm. Thisrequirement may be dispensed with in
special cases,
e. g. for superheater support tubes.
8. Plain rectangular tubes and sectionalheaders
8.1 Symbols
pc [bar] design pressures [mm] wall thickness2 m [mm] clear
width of the rectangular
tube parallel to the wall inquestion
2 n [mm] c l e a r w i d t h o f t h erectangular-tube
perpendicularto the wall in question
Z [mm] coefficient according toformula (23)
a [mm] distance of relevant line ofholes from center line of
side
t [mm] pitch of holesd [mm] hole diameterv [-] weakening factor
for rows of
holes under tensile stress
v' [-] weakening factor for rows ofholes under bending
stress
r [mm] inner radius at cornersperm [N/mm] allowable stress (see
1.4)8.2 Design calculation
8.2.1 The wall thickness is to be calculated for thecenter of
the side and for the ligaments between theholes. The maximum
calculated wall thickness shallgovern the wall thickness of the
entire rectangulartube.
The following method of calculation is based on theassumption
that the tube connection stubs have beenproperly mounted, so that
the wall is adequatelystiffened.
8.2.2 The required wall thickness is given by theexpression
:
If there are several different rows of holes, thenecessary wall
thickness is to be determined for eachrow.
(22)s p
c n
20 perm v
4,5 Z pc
10 perm v,
8.2.3 Z is calculated by applying the formula:
(23)Z 13
m 3 n 3
m n
12
(m 2 a 2 )
-
7-20 Section 7 - Boilers and Thermal Oil System
Fig. 7.25
Fig. 7.26
Where Z has a negative value, the sign is to be disre-garded
when incorporating the term into formula (22).8.3 Weakening factor
v
8.3.1 If there is only one row of holes, or if thereare several
parallel rows not staggered in relation toeach other, the weakening
factors v and v' are to bedetermined as follows :
v t d
t
for wholes where d < 0,6 mv v t d
t
for wholes where d > 0,6 mv t 0,6 m
t
8.3.2 In determining the values of v and v' forelliptical holes,
d is to be taken as the clear width ofthe holes in the longitudinal
direction of therectangular tube. However, for the purpose
ofdeciding which formula is to be used for determiningv', the value
of d in the expressions d > 0,6 m andd < 0,6 m is to be the
clear width of the holeperpendicular to the longitudinal axis.
8.3.3 In calculating the weakening factor forstaggered rows of
holes, t is to be substituted in theformula by t for the oblique
ligaments (Fig. 7.25).8.3.4 For oblique ligaments, the value of Z
to beused in formula (22) is that determined by applyingformula
(23), with a = 0, and multiplying by cos .
8.4 Stress at corners
In order to avoid undue stresses at corners, thefollowing
conditions are to be satisfied :
r 1/2 s, subject to a minimum of:3 mm for rectangular tubes with
a clear width of up to50 mm.
8 mm for rectangular tubes with a clear width of80 mm or
over.
Intermediate values are to be interpolated linearly.The radius
shall be governed by the arithmetical meanvalue of the nominal wall
thicknesses on both sides ofthe corner. The wall thickness at
corners may not beless than the wall thickness determined by
applyingformula (22).
8.5 Minimum wall thickness and ligamentwidth
8.5.1 The minimum wall thickness for expandedtubes shall be 14
mm.
8.5.2 The width of a ligament between twoopenings or tube holes
may not be less than 1/4 of thedistance between the tube
centers.
9. Straps and girders
9.1 Scope
The following Rules apply to steel girders welded tothe
combustion chamber crown.
9.2 General
The supporting girders are to be properly welded tothe
combustion chamber crown at all points. They areto be arranged in
such a way that the welds can becompetently executed and the
circulation of water isnot obstructed.
9.3 Symbols
pc [bar] design pressureF [N] load carried by one girdere [mm]
distance between center lines of
girders
l [mm] free length between girdersupports
b [mm] thickness of girderh [mm] height of girderW [mm3] section
modulus of one girderM [Nmm] bending moment acting on
girder at given load
z [-] coefficient for section modulusperm [N/mm2] allowable
stress (see 1.4)9.4 Design calculation
9.4.1 The simply supported combustion chambergirder shown in
Fig. 7.26 is to be treated as a simplysupported beam of length l.
The support afforded bythe plate material crown may also be taken
intoconsideration.
-
Section 7 - Boilers and Thermal Oil Systems 7-21
9.4.2 The required section modulus of a combus-tion chamber
crown is given by:
(24)W M
max
1,3 perm z
b h 2
6
The coefficient z for the section modulus takesaccount of the
increase in the section modulus due tothe combustion chamber crown
plate forming part ofthe girder. It may in general be taken as z =
5/3.
For the height h, a value not exceeding 8 b is to beinserted in
the formula.
9.4.3 The maximum bending moment is given bythe expression :
(25)Mmax F l
8
where
(26)F p
c
10 l e
10. Bolts
10.1 Scope
The following Rules relate to bolts which, as forcetransmitting
connecting elements, are subjected totensile stresses due to the
internal pressure. Normaloperating conditions are assumed.
10.2 General
Necked-down bolts should be used for elastic boltedconnections,
particularly where the bolts are highlystressed, or are exposed to
service temperatures ofover 300 C, or have to withstand internal
pressuresof 80 bar or over. All bolts > M 30 (30 mm
diametermetric thread) must be necked-down bolts.Necked-down bolts
are bolts to DIN 2510 with ashank diameter dS = 0,9 dk (dk being
the root dia-meter). In the calculation special allowance is to
bemade for shank diameters < 0,9 dk.
Bolts with a shank diameter of less than 10 mm arenot
allowed.
Bolts may not be located in the path of heating gases.
At least 4 bolts must be used to form a connection.
To achieve small sealing forces, the jointing materialshould be
made as narrow as possible and preferenceshould be given to the
tongue and groove system.
Where standard pipe flanges are used, the strengthrequirements
for the bolts are considered to besatisfied if the bolts used
comply with DIN 2500 andconform to the specifications contained
therein inrespect of the materials used, the maximum allowable
working pressure and the service temperature.
10.3 Symbols
pc [bar] design pressurep' [bar] test pressureFS [N] total load
on bolted connection
in service
F'S [N] total load on bolted connectionat test pressure
FSo [N] total load on bolted connectionin assembled condition
with nopressure exerted
FB [N] load imposed on boltedconnection by the
workingpressure
FD [N] force to close joint underservice conditions
FDo [N] force to close joint inassembled condition
FZ [N] additional force due to stressesin connected piping
Db [mm] mean jointing or bolt pitchcircle diameter
di [mm] inside diameter of connectedpipe
ds [mm] shank diameter of anecked-down bolt
dk [mm] root diameter of threadn [-] number of bolts forming
connection
perm [N/mm2] allowable stress [-] surface finish coefficientc
[mm] additional allowancek1 [mm] jointing factor for service
condition
ko [mm] jointing factor for assembledcondition
KD [N/mm2] jointing material deformationfactor
10.4 Design calculation
10.4.1 Bolted joints are to be designed for thefollowing load
conditions:
a) Service conditions(design pressure pc and design
temperaturet),
b) Load at test pressure
-
7-22 Section 7 - Boilers and Thermal Oil System
(lest pressure p', t = 20 C) andc) Assembled condition at zero
pressure
(p = 0 bar, t = 20 C).10.4.2 The necessary root diameter of a
bolt in abolted joint comprising n bolts is given by :
(27)dk 4 F
s
perm n c
10.4.3 The total load on a bolted joint is to becalculated as
follows :
a) For service conditionsFS = FB + FD + FZ (28)
(29)FB D 2b
4
pc
10
(30)FD Db k1 p
c
10 1,2
(Where the arrangement of the bolts deviateswidely from the
circular, due allowance is tobe made for the special stresses
occurring)The additional force Fz due to connectedpiping must be
calculated from the stressespresent in these pipes. Fz is 0 in the
case ofbolted joints with no connected pipes. Whereconnecting pipes
are installed in a normalmanner and the service temperatures
are< 400 C, Fz may be determined, as anapproximation, by
applying the expression :
FZ d 2i
4
pc
10
b) For the test pressure:
(31)Fs
pp
c
FB FD1,2
FZ
For calculating the root diameter of thethread, Fs is to be
substituted by F's informula (27).
c) For the zero-pressure, assembled condition:FSO = FDO + FZ
(32)FDO = Db ko KD (33)For calculating the root diameter of
thethread, Fs is to be substituted by FSo informula (27).In the
zero-pressure, assembled condition,the force FDO is to be exerted
on the bolts
during assembly to effect an intimate unionwith the jointing
material and to close thegap at the flange bearing surfaces.
If the force exerted on assembly FDO > FS,this value may be
replaced by the followingwhere malleable jointing materials with
orwithout metal elements are used :
(34)FDO 0,2 FDO 0.8 FS FDO
Factors ko, k and KD depend on the type and design ofthe joint
and the material used. The relevant values areshown in the Tables
7.16 and 7.17.
10.4.4 The bolt design is to be based on the greatestroot
diameter of the thread determined in accordancewith the three load
conditions specified in paragraphs10.4.1 a) to 10.4.1 c).
10.5 Design temperature t
The design temperatures of the bolts depend on thetype of joint
and the insulation. In the absence ofspecial proof as to
temperature, the following designtemperatures are to be
applied:
Loose flange steam temperature - 30 C+ loose flange
Fixed flange steam temperature - 25 C+ loose flange
Fixed flange steam temperature -15 C+ fixed flange
The temperature reductions allow for the drop intemperature at
insulated, bolted connections. Fornon-insulated bolted joints, a
further temperature re-duction is not permitted because of the
higher thermalstresses imposed on the entire bolted joint.
10.6 Allowable stress
The values of the allowable stress perm are shown inTable
7.14.
Table 7.14 Allowable stress perm
Condition for necked-down bolts
for full-shank bolts
Servicecondition
Re,H,t
1,5R
e,H,t
1,6
-
Section 7 - Boilers and Thermal Oil Systems 7-23
Test pressureand zero-pressureassembledcondition
Re,H,20
1,1
Re,H,20
1,2
10.7 Surface finish coefficient
10.7.1 Full-shank bolts are required to have asurface finish of
at least grade mg to DIN 267.Necked-down bolts must be machined all
over.
10.7.2 In the case of unmachined, plane-parallelbearing
surfaces, = 0,75. Where the bearing sur-faces of the mating parts
are machined, a value of =1,0 may be used. Bearing surfaces which
are notplane-parallel (e. g. on angle sections) are
notpermitted.
10.8 Additional allowance c
The additional allowance c mm shall be as shown inTable
7.15.
Table 7.15 Additional allowances c
Condition c [mm]For service conditions :
up to M 24M 27 up to M 45M 48 and over
35 - 0,1 . dk
1
for test pressure 0
for assembled conditions 0
E. Equipment and Installation
1. General
1.1 The following requirements apply to steamboilers which are
not constantly and directlymonitored during operation. Note is also
to be takenof the official regulations of the flag country of
thevessel, where appropriate.
1.2 In the case of steam boilers which are monitoredconstantly
and directly during operation, some easingof the following
requirements may be permit ted,while maintaining the operational
safety of the vessel.
1.3 In the case of steam boilers which have amaximum water
volume of 150 litres, a maximumallowable working pressure of 10 bar
and where theproduct of water volume and maximum allowablewater
pressure is less than 500, an easing of thefollowing requirements
may be permitted.
1.4 With regard to the electrical installation andequipment also
the Rules for Electrical Installations,Volume IV and Rules for
Automation,Volume VII areto be observed.
2. Safety valves
2.1 Any steam boiler which has its own steam spaceis to be
equipped with at least two reliable, spring-loaded safety valves.
At least one safety valve is to beset to respond if the maximum
allowable workingpressure is exceeded.
In combination, the safety valves must be capable ofdischarging
the maximum quantity of steam which canbe produced by the steam
boiler during continuousoperation without the maximum allowable
workingpressure being exceeded by more than 10 %.
2.2 Any steam boiler which has a shut-off but whichdoes not have
its own steam space is to have at leastone reliable, spring-loaded
safety valve fitted at itsoutlet. At least one safety valve is to
be set to respondif the maximum allowable working pressure
isexceeded. The safety valve or safety valves are to bedesigned so
that the maximum quantity of steamwhich can be produced by the
steam boiler duringcontinuous operation can be discharged without
themaximum allowable working pressure being exceededby more than 10
%.
2.3 External steam drums are to be fitted with atleast two
reliable, spring-loaded safety valves. At leastone safety valve is
to be set to respond if theallowable working pressure is exceeded.
Incombination, the safety valves must be capable ofdischarging the
maximum quantity of steam which canbe produced in continuous
operation by all connectedsteam generators without the maximum
allowableworking pressure of the steam drum being exceededby more
than 10 %.
2.4 The closing pressure of the safety valves shallbe no more
than 10 % below the response pressure.
2.5 The minimum flow diameter of the safety valvesmust be 15
mm.
2.6 Servo-controlled safety valves are permittedwherever they
are reliably operated without anyexternal energy source.
2.7 The safety valves are to be fitted to the saturatedsteam
part or, in the case of steam boilers which donot have their own
steam space, to the steam-wateroutlet of the boiler.
2.8 In the case of steam boilers which are fitted
withsuperheaters with no shut-off capability, at least twosafety
valves must be located at the discharge from thesuperheater.
Superheaters with shut-off capability areto be fitted with at least
one safety valve.
Safety valves which are located at the discharge fromthe
superheater must be designed for at least 25 % ofthe required
blow-off capacity. When designing safetyvalves, allowance is to be
made for the increase in the
-
7-24 Section 7 - Boilers and Thermal Oil System
volume of steam caused by superheating.
2.9 Steam may not be supplied to the safety valvesthrough pipes
in which water may collect.
2.10 Safety valves must be easily accessible andcapable of being
released safely during operation.
2.11 Safety valves are to be designed so that nobinding or
jamming of moving parts is possible evenwhen heated to different
temperatures. Seals whichmay prevent the operation of the safety
valve due tofrictional forces are not permitted.
2.12 Safety valves are to be set in such a way as toprevent
unauthorized alteration.
2.13 Pipes or valve housings must have a drain facilitywhich has
no shut-off capability fitted at the lowestpoint on the blow-off
side.
2.14 Combined blow-off lines from several safetyvalves may not
unduly impair the blow-off capability.
The discharging mediums are to be drained awaysafely.
3. Water level indicators
3.1 Steam boilers which have their own steamchamber are to be
fitted with two devices giving adirect reading of the water
level.
3.2 Steam boilers which have their own steam spaceheated by
exhaust gases whose temperature does notexceed 400 C, are to be
fitted with at least one devicegiving a direct reading of the water
level.
3.3 External steam drums of boilers which do nothave their own
steam space are to be fitted with twodevices giving a direct
reading of the water level.
3.4 Cylindrical glass water level gauges are notpermitted.
3.5 The water level indicators are to be fitted so thata reading
of the water level is possible when the shipis heeling and during
the motion of the ship when it isat sea. The limit for the lower
visual range must be atleast 30 mm above the highest flue, but at
least 30 mmbelow the lowest water level. The lowest water levelmay
not be above the centre of the visual range.
The water level indicators must be well illuminatedand visible
from the boiler control station.
3.6 The connection pipes between steam generatorand water level
indicators must have a inner diameterof at least 20 mm. They must
be run in such a way thatthere are no sharp bends in order to avoid
water andsteam traps, and must be protected from the effects ofthe
heated gases and against cooling.
Where water level indicators are linked by means ofcommon
connection lines or where the connectionpipes on the water side are
longer than 750 mm, the
connection pipes on the water side must have an innerdiameter of
at least 40 mm.
3.7 Water level indicators are to be connected to thewater and
steam chamber of the boiler by means ofeasily accessible, simple to
control and quick-actingshut-off devices.
3.8 The devices used for blowing through the waterlevel
indicators must be designed so that they are safeto operate and so
that blow-through can be monitored.The discharging mediums are to
be drained awaysafely.
3.9 Remote water level indicators and displayequipment of a
suitable type to give an indirectreading may be approved as
additional displaydevices.
3.10 In place of water level indicators, once-throughforced flow
boilers must be fitted with two mutuallyindependent devices which
trip an alarm as soon aswater flow shortage is detected. An
automatic deviceto shut down the heating system may be provided
inplace of the second warning device.
3.11 The cocks and valves of the water levelindicators which
cannot be directly reached by handfrom floor plates or a control
platform must be have acontrol facility using pull rods or chain
pulls.
4. Pressure gauges
4.1 Each steam boiler is to be fitted with twopressure gauges
which are linked to the steam space.The allowable maximum working
pressure is to bemarked on the dial by means of a permanent
andeasily visible red mark. The display range of thepressure gauge
must include the test pressure. Onepressure gauge must be located
on the boiler andanother at the machinery control station or at
someother appropriate site.
Where several steam boilers are incorporated on oneship, the
steam chambers of which are linked together,one pressure gauge is
sufficient at the machinerycontrol station or at some other
suitable location, inaddition to the pressure gauges on each
boiler.
4.2 The pipe to the pressure gauge must have awater trap and
must be of a blow-off type. Aconnection for a test gauge must be
installed close tothe pressure gauge. In the case of pressure
gaugeswhich are set off at a lower position the testconnection must
be provided close to the pressuregauge and also close to the
connection piece of thepressure gauge pipe.
4.3 Pressure gauges are to be protected againstradiant heat and
must be well illuminated.
5. Temperature gauges
5.1 A temperature gauge is to be fitted to the fluegas outlets
of fired steam boilers.
-
Section 7 - Boilers and Thermal Oil Systems 7-25
5.2 Temperature gauges are to be fitted to theexhaust gas inlet
and outlet of steam boilers heated byexhaust gas.
5.3 Temperature gauges must be fitted at theoutlets from
superheaters or superheater sections, atthe inlet and outlet of
attemporators, and also at theoutlet of once-through forced flow
boilers, where thisis necessary to assess the behaviour of the
materialsused.
6. Regulating devices (Controllers)6.1 With the exception of
boilers which areheated by exhaust gas, steam boilers are to
beoperated with rapid-control, automatic firing systems.In main
boilers, the control facility must be capable ofsafely controlling
all rates of speed and manoeuvresso that the steam pressure and the
temperature of thesuper-heated steam stay within safe limits and
thesupply of feed water is guaranteed. Auxiliary boilersare subject
to the same requirements within the scopeof potential load
changes.
6.2 Steam pressure must be automatically regu-lated by
controlling the supply of heat. The steampressure of boilers heated
by exhaust gas may also beregulated by condensing the excess
steam.
6.3 In the case of boilers which have a specifiedminimum water
level, the water level must be regu-lated automatically by
controlling the supply of feedwater.
6.4 In the case of forced-circulation boilerswhose heating
surface consists of a steam coil andonce-through forced flow
boilers, the supply of feedwater may be regulated as a function of
fuel supply.
6.5 In the case of steam boilers which are fittedwith
superheaters, the temperature of the superheatedsteam must be
automatically regulated unless thecalculated temperature is higher
than the maximumattainable temperature of the superheater
walls.
7. Monitoring devices (Alarms)7.1 A warning device is to be
fitted which istripped when the specified maximum water level
isexceeded.
7.2 In exhaust-gas heated boilers, a warningdevice is to be
fitted which is tripped when themaximum allowable working pressure
is exceeded.
7.3 In exhaust-gas heated boilers with a specifiedminimum water
level, a warning device is to be fittedwhich is tripped when the
water falls below this level.
7.4 Exhaust gas boilers with finned tubes are tohave a
temperature monitor fitted in the exhaust gaspipe which trips an
alarm in the event of fire. Cf.Rules for Automation, Volume
VII.
7.5 Where there is a possibility of oil or greasegetting into
the steam or condensate system, a suitableautomatic and
continuously operating unit is to beinstalled which trips an alarm
and cuts off the feedwater supply if the concentration at which
boileroperation is put at risk is exceeded.
7.6 Where there is a possibility of acid, lye orseawater getting
into the steam or condensate system,a suitable automatic and
continuously operating unitis to be installed which trips an alarm
and cuts off thefeed water supply if the concentration at which
boileroperation is put at risk is exceeded.
7.7 It must be possible to carry out function test-ing of the
monitoring devices, even during operation,if an equivalent degree
of safety is not attained byself-monitoring of the equipment.
7.8 The monitoring devices must trip visual andaudible fault
warnings in the boiler room or in themachinery control room or any
other suitable site. CfRules for Automation, Volume VII.
8. Safety devices (Limiters)8.1 The suitability of safety
devices for marineuse is to be proven by type testing.
8.2 Fired boilers are to be equipped with a reli-able pressure
limiter which cuts out and interlocks thefiring system when the
maximum allowable workingpressure is exceeded.
8.3 In steam boilers on whose heating surfaces ahighest flue is
specified, two reliable, mutuallyindependent water level limiters
must respond to cutout and interlock the firing system when the
waterfalls below the specified minimum water level. Thewater level
limiter must also be independent of thewater level control
devices.
8.4 The receptacles for water level limiterslocated outside the
boiler must be connected to theboiler by means of lines which have
a minimum innerdiameter of 20 mm. Shut-off devices in these
linesmust have a nominal diameter of at least 20 mm andmust
indicate their open or closed position. Wherewater level limiters
are connected by means ofcommon connection lines, the connection
pipes on thewater side must have an inner diameter of at least40
mm.
Operation of the firing system may only be possiblewhen the
shut-off devices are open or else, afterclosure, the shut-off
devices must reopenautomatically and in a reliable manner.
Water level limiter receptacles which are locatedoutside the
boiler are to be designed in such a waythat a compulsory and
periodic blow-through of thereceptacles and lines can be carried
out.
8.5 In the case of forced-circulation boilers with
-
7-26 Section 7 - Boilers and Thermal Oil System
a specified lowest water level, two reliable,
mutuallyindependent safety devices must be fitted in additionto the
requisite water level limiters, which will cut outand interlock the
heating system in the event of anyunacceptable reduction in water
circulation.
8.6 In the case of forced-circulation boilerswhose heating
surface consists of a single coil andonce-through forced flow
boilers, two reliable,mutually independent safety devices must be
fitted inplace of the water level limiters in order to provide
asure means of preventing any excessive heating of theheating
surfaces by cutting out and interlocking thefiring system.
8.7 In steam boilers with superheaters, atemperature limiter is
to be fitted which cuts out andinterlocks the heating system if the
allowablesuperheated steam temperature is exceeded. In thecase of
boiler parts which carry superheated steamand which have been
designed to long-term resistancevalues, one temperature recording
device is adequate.
8.8 The safety devices must trip visual andaudible alarms in the
boiler room or in the machinerycontrol room or any other
appropriate site. Cf. Rulesfor Automation, Volume VII.
8.9 The electrical devices associated with thelimiters are to be
designed in accordance with theclosed-circuit principle so that,
even in the event of apower failure, the limiters will cut out and
interlockthe systems unless an equivalent degree of safety
isachieved by other means.
8.10 To reduce the effects due to swell, waterlevel limiters can
be fitted with a delay functionprovided that this does not cause a
dangerous drop inthe water level.
8.11 The electrical interlocking of the firingsystem following
tripping by the safety devices mayonly be cancelled out at the
firing system controlpanel itself.
8.12 If an equivalent degree of safety cannot beachieved by the
self-monitoring of the equipment, thesafety devices must be
subjected to operational testingeven during operation. In this
case, the operationaltesting of water level limiters must be
carried outwithout the surface of the water dropping below
thelowest water level.
8.13 For details of additional requirementsrelating to
once-through forced flow boilers, see 3.10.
9. Feed and circulation devices
9.1 For details of boiler feed and circulation de-vices, see
Section 11, F. The following requirementsare also to be noted:
9.2 The feed devices are to be fitted to the steamboiler in such
a way that it cannot be drained lower
than 50 mm above the highest flue when the non-re-turn valve is
not tight.
9.3 The feed water is to be introduced into theboiler in such a
way as to prevent damage occurring tothe boiler walls and to heated
surfaces.
10. Shut-off devices
10.1 Each steam boiler must be capable of being shutoff from all
connected pipes. The shut-off devices areto be installed as close
as possible to the boiler wallsand must operate without risk.
10.2 Where several boilers which have differentmaximum allowable
working pressures give off theirsteam into common lines, it is
necessary to ensure thatthe maximum working pressure allowable for
eachboiler cannot be exceeded in any of the boilers.
10.3 Where there are several boilers which areconnected by
common pipes and the shut-off devicesfor the steam, feed and drain
lines are welded to theboiler, for safety reasons while the boilers
arerunning, two tandem shut-off devices which are to beprotected
against unauthorised operation are each tobe fitted with an
interposed release device.
11. Scum removal, sludge removal, drain andsampling devices
11.1 Boilers and external steam drums are to be fittedwith
devices to allow them to be drained and thesludge removed. Where
necessary, boilers are to befitted with a scum removal device.
11.2 Drain devices and their connections must beprotected from
the effects of the heating gases andcapable of being operated
without risk. Self-closingsludge removal valves must be lockable
when closedor alternatively an additional shut-off device is to
befitted in the pipe.
11.3 Where the scum removal, sludge removal ordrain lines from
several boilers are combined, a non-return valve is to be fitted in
the individual boilerlines.
11.4 The scum removal, sludge removal or drainlines, plus valves
and fittings, are to be designed toallow for the maximum allowable
working pressure ofthe boiler.
11.5 With the exception of once-through forced flowboilers,
devices for taking samples from the watercontained in the boiler
are to be fitted to steam boilers.
11.6 Scum removal, sludge removal, drain andsampling devices
must be capable of safe operation.The mediums being discharged are
to be drained awaysafely.
12. Name plate
12.1 A name plate is to be permanently affixed toeach steam
boiler, displaying the following
-
Section 7 - Boilers and Thermal Oil Systems 7-27
information:
Manufacturer,
Build number and year of construction,
Maximum allowable working pressure in bar,
Steam production in kg/h or t/h,
Permitted temperature of super-heated steam inC provided that
the boiler is fitted with asuper-heater with no shut-off
capability.
12.2 The name plate must be permanently attached tothe largest
part of the boiler or to the boiler frame sothat it is visible.
13. Valves and fittings
13.1 Materials
Valves and fittings for boilers must be made of ductilematerials
as specified in Table 7.1 and all theircomponents must be able to
withstand the loadsimposed in operation, in particular thermal
loads andpossible stresses due to vibration. Grey cast iron maybe
used within the limits specified in Table 7.1, butmay not be
employed for valves and fittings which aresubjected to dynamic
loads, e.g. safety valves andblow-off valves.
Testing of materials for valves and fittings is to becarried out
as specified in Table 7.2.
13.2 Design
Care is to be taken to ensure that the bodies of shut-off gate
valves cannot be subjected to unduly highpressure due to heating of
the enclosed water. Valveswith screw-on bonnets must be safeguarded
to preventunintentional loosening of the bonnet.
13.3 Pressure and tightness tests
13.3.1 All valves and fittings are to be subjected toa
hydrostatic pressure test at 1,5 times the nominalpressure before
they are fitted. Valves and fittings forwhich no nominal pressure
has been specified are tobe tested at twice the working pressure.
In this case,the safety factor in respect of the 20 C yield
strengthvalue may not fall below 1,1.
13.3.2 The sealing efficiency of the closed valve isto be tested
at the nominal pressure or at 1,1 times theworking pressure, as
applicable. Valves and fittingsmade of castings and subject to
operatingtemperatures over 300 C are required to undergo oneof the
following tightness tests:
a) Tightness test with air (test pressure approxi-mately 0,1 x
working pressure; maximum 2 bar);
b) Tightness test with saturated or superheatedsteam (test
pressure may not exceed themaximum allowable working pressure);
c) A separate tightness test may be dispensed withif the
pressure test is performed with petroleumor other liquid displaying
similar properties.
14. Installation of boilers
14.1 Mounting
Boilers must be installed in the ship with care andmust be
secured to ensure that they cannot bedisplaced by any of the
circumstances arising whenthe ship is at sea. Means are to be
provided toaccommodate the thermal expansion of the boiler
inservice. Boilers and their seatings must be easilyaccessible from
all sides or must be easily renderedso.
14.2 Fire precautions
See Section 12.
F. Testing of Boilers
1. Constructional test
After completion, boilers are to undergo aconstructional
test.
The constructional test includes verification that theboiler
agrees with the approved drawing and is ofsatisfactory
construction. For this purpose, all parts ofthe boiler must be
accessible to allow adequateinspection. If necessary, the
constructional test is to beperformed at separate stages of
manufacture. Thefollowing documents are to be presented: material
testcertificates covering the materials used, reports on
thenon-destructive testing of welds and, whereapplicable, the
results of tests of workmanship andproof of the heat treatment
applied.
2. Hydrostatic pressure tests
2.1 A hydrostatic pressure test is to be carried out onthe
boiler before the insulation is fitted. Where onlysome of the
component parts are sufficientlyaccessible to allow proper visual
inspection, thehydrostatic pressure test may be performed in
stages.Boiler surfaces must withstand the test pressurewithout
leaking or suffering permanent deformation.
2.2 The test pressure is generally required to be 1,5times the
maximum allowable working pressure,subject to a minimum of PB + 1
bar.2.3 In the case of continuous-flow boilers, the testpressure
must be at least 1,1 times the water inletpressure when operating
at the maximum allowableworking pressure and maximum steam output.
In theevent of danger that parts of the boiler might besubjected to
stresses exceeding 0,9 of the yieldstrength, the hydrostatic test
may be performed inseparate sections. The maximum allowable
workingpressure is then deemed to be the pressure for which
-
7-28 Section 7 - Boilers and Thermal Oil System
the particular part of the boiler has been designed.
2.4 For boiler parts subject to internal and externalpressures
which invariably occur simultaneously inservice, the test pressure
depends on the differentialpressure. In these circumstances,
however, the testpressure should at least be equal to 1,5 times
thedesign pressure specified in D.1.2.4.
G. Hot Water Generators
1. Design
Hot water generators with a permissible dischargetemperature of
> 120 C, which are heated by solid,liquid or gaseous fuels or by
exhaust gases or electri-cally are to be treated in a manner
analogous to thatapplied to boilers. The materials and
strengthcalculations for hot water generators which are heatedby
steam or hot liquids are subject to the requirementsin Section 8
(Pressure Vessels).2. Equipment
The safety equipment of hot water generators issubject to the
requirements contained in DIN 4752with due regard for the special
conditions attaching toshipboard operation.
3. Testing
Each hot water generator is to be subjected to amanufacturing
test and to a hydrostatic pressure test at1,5 times the maximum
allowable working pressuresubject to a minimum of 4 bar.
H. Exhaust Gas Economizers
1. Definition
Exhaust gas economizers are preheaters connected tothe exhaust
gas side of boiler heating surfaces whichare used, without steam
being produced in them inservice, to preheat the feedwater and
which can beisolated from the water side of the boiler.
The surfaces of the preheater comprise the waterspace walls
located between the shut-off devices plusthe casings of the latter.
Water may be taken from theeconomizer only if the boiler feed
system is speciallydesigned for this purpose.
2. Materials
See under B.
3. Design calculation
The formulae given under D are to be applied in thecalculation.
The design pressure is to be at least thamaximum allowable working
pressure of the
economizer.
The design temperature is the maximum feedwatertemperature plus
25 C for plain tube economizersand plus 35 C for finned tube
economizers.