Piping to Nozzle to Vessel

Piping to Nozzle to Vessel

Piping Engineer vs. Vessel FabricatorDid you check the nozzle for loads

Alright.., Give me actual loads

My Nozzle is good for Pressure

But, the analysis is not finished yet

Ok, give me Maximum Loads your nozzle can withstand

What !, there are infinite combinations...

Saga of Nozzle loads

• What came first,

Or

Some Ideas for resolution

• Use “standard” Nozzle Loads

• Provides a “standard” level of strength

Some Ideas for resolution

• Get a “Maximum” Nozzle load set

• Indicate if you want a bigger Mx, My etc..

Resolutions ….

• Model Nozzle flexibilities in Piping model

• Ask for the loads in categories SUS, EXP, OCC– Thermal Expansion – Self-limiting, so higher

allowable– Occasional – 20% increase in allowable

Stresses near Nozzles

2. Some methods employed: • Welding Research Council Bulletin (WRC) 107

Local Stress Analysis

• Welding Research Council Bulletin (WRC) 297

• PD5500 (British code), Annex- G

• Finite Element Analysis (FEA)• Welding Research Council Bulletin (WRC) 368

WRC107

• 1965, updated in 1979, Prof. Bijlaard work

• Provides stress in Cylinder and Spheres

• Gives verifiable solution, used for a long time.

• Based on Un-penetrated shell

• Gives stresses in header only

• Consists of charts and fill in tables.

Radial Force PLongitudinal Force VL

VL

Circumferential Force VC

VC

MC

P

Circumferential Moment MCLongitudinal Moment ML

ML

Torsional Moment MT

WRC 107 CONVENTION MT

AU

DUBU

CUAL BLCLDL

Lots of charts to look up

Then fill in tables

12

x, )

1 + 2)/2

Max Shear Stress

Stress Intensity

1x y x y

24

2

2

2x y x y

24

2

2

x

y

1 - 2

Then Use, Mohr Circle

Stress Combinations

• Next, Combine stresses in categories

– General Primary Membrane (Pm)– Local Primary Membrane (Pl)– Secondary Stresses (Q)

• Compare to allowables

Primary Stresses

• “load-controlled” – pressure, weight• Not self-limiting• Tighter limits (1.5*S)

Secondary Stresses

– “Strain-controlled” – thermal Exp., bending at gross discontinuities

– Self-limiting – stress can reduce after local yielding.

– Higher allowable (approx 3*Savg)

Some limitations of WRC107• Re-pad not considered• Assumes a 90° (radial nozzle)

• Spherical Shells– di/Di 1/3 but less if Dm/T between 20-55– U 2.2 (U = ro / ((Rm T)0.5, for nozzle)– 0.25 t /T 10– 5 rm /t 50

• Cylindrical Shells:– d/D ¼ for cylinders or < 0.6 with significant warnings– D/T 600– L/D 1.5– ¼ C1 /C2 4

WRC 297

• Based a different, thin shell theory (Prof. Steele)

• For cylindrical nozzles on cylinders• Extends the range of WRC 107 (d/D 0.5)• Gives stresses both in header and branch• Also provides Nozzle Flexibilities

A

B

D

A

B

DC

Vessel Orientation +y directionNozzle Orientation +x direction (toward vessel)B to A Convention In the direction of the vessel

x

y

z

GLOBAL COORDINTES

x

y

z

A

B

D

A

B

DC

Fx force P RADIALLY INWARDFy force VL FROM B -> AFz force -VC FROM C - > D Mx moment -MT TORSIONALMy moment -MC CIRCUMFERNETIALMz moment -ML LONGITUDINAL

P

VL

-VC

-MT

-ML

-MC

A WAY TO REMEMBER TO DIRECTIONS:

P IS RADIALLY TOWARD THE VESSEL

VL IS FROM B -> A

VC IS FROM D-> C

MT IS RADIALLY OUTWARD

MC IS FROM D->C

ML IS FROM B -> A

Example Geometry1. Shl: 144 in. ID, 1.5 in. thk, 240 in Len., SA-516 70

2. Noz: 24 in. ID, 1 in. thk., 10 in Len, SA-516 70.

3. Internal Pressure: 200 psi4. Loads: P = 5400 lbs, VL = 2100 lbs, ML = 3500 ft-lbs.

5. Radial Nozzle in the shell center.

WRC Parameters for this example:

1. d/D: 0.167 ( < 0.3 )2. L/D: 1.67 ( > 1.5 )3. D/T: 96 ( <= 600)4. d/T: 16 ( >= 5 )5. d/t: 24 ( > 20 )

• Within ranges of 107 and 297.

PD5500 Convention

Pressure Thrust

• Force on the vessel-nozzle junction due to pressure

Pressure Thrust

• Nozzle with a blind-

• Typically, a more flexible system, more thrust load on nozzle.

Entire thrust load

Pressure Thrust and WRC107

Pressure Thrust and WRC 107

• Use WRC 368 or FEA and watch for WRC 107 limits

Missing data, Curve exceeded

WRC Bulletin 368: Stresses due to Pressure and Pressure Thrust

• Max. Stress Intensities for nozzle-cylinder junction due to

Internal Pressure.

• Derived from the FEA data.

• Loadings include Internal Pressure + Pressure Thrust

• More Accurate way of modeling Pressure Thrust (PT)

• But, does not combine well with stress due external loads

• Use as a tool for pressure only case

FEA interface1. FEA Interface to “NozzlePro” program from

Paulin Research Group (www.paulin.com).

2. Reuse input from 107, blends in with CodeCalc/PVElite.

3. Additional capabilities- geometric, analysis.

WRC vs. FEA

• Accurate modeling – repad, hillside/Y-angle nozzles

• No limitation of d/D, etc.

• Accurately combine Pressure and stresses due to external loads.

• Accuracy is not limited on the geometry

Results and Comparison1. The ASME check: Design Pressure 200 psi

Method MAWP (psi)

Area of Replacement(UG-37)

232

CodeCase 2168 306

WRC 368: Shell

Nozzle252233

2. 107 v/s 297 v/s PD5500: Max. Stress Intensity.

* Stress intensity in ksi

Method Au Bl Cu Dl

107 8.02 9.86 8.12 10.56

297 8.05 9.98 7.71 11.16

PD5500 26.1 28.3 27.6 28.9

2.b Stresses from PD5500:

Method Pressure stress

107 9.5

PD5500 27.7

27.7/(Pressure Stress SIF) = 27.7/2.864 = 9.7 ksi.

3. 107 v/s 297 v/s PD5500 v/s FEA:

* Stress intensity in ksi

Method Pm + Pl stress Allow

107 9.52 30

107 + PT 15.58 30

107 + PSI 31.03 30

PD5500 27.75 29.6

FEA 20.53 30

4. Location of highest stress ?

Method Location

107Shell B inner (PM + PL) C, D inner (PM+PL+Q)

297 Nozzle C, D inner !

368 Nozzle

PD5500 Shell Q1, Q4 inner

FEAShell (PM + PL),

Nozzle (PM+PL+Q) !

Conclusions1. WRC 107/297 are good tools when used within their

limits.( e.g when d/D > 0.33.)

2. It provides good first step.

3. Be aware of its limitations, Re. pads, hillside nozzles, inside projection – use FEA for accurate stress pattern

4. Always check Nozzle per ASME code first.

5. Stresses in Nozzle can be higher than Shell stresses:- WRC 297, FEA.

6. Input loads in categories (Sustained, Expansion..) to take full advantage of the code allowables.

References1. WRC bulletins 107, 297 & 368. Pressure Vessel

Research Council www.forengineers.org/pvrc/index.htm.

2. Mechanical Engineering Newsletter articles- July 2001, June 2000 and June 1997. Available at www.coade.com.