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piping
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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.