Simulation of Nozzles for Fatigue (ASME VIII-2)
Simulation of Nozzles for Fatigue (ASME VIII-2)
(OP)
Hello,
I'm looking at doing a fatigue analysis for a pressure vessel in accordance with ASME VIII-2. As such, I'm most interested in determining peak stresses, particularly around nozzles, supports, and attachments.
The nozzles for this vessel would be attached as detailed in ASME VIII-1 Fig. UW-16-1(c) or ASME VIII-2 Table 4.2.10 Detail 3 (set-in nozzle, full pen to shell c/w external fillet weld). If I were to recreate the ASME VIII-1 detail in Solidworks Simulation, I would model it as follows:
Some thoughts that I've had were:
Thank you for any help/suggestions you can provide!
Marty
I'm looking at doing a fatigue analysis for a pressure vessel in accordance with ASME VIII-2. As such, I'm most interested in determining peak stresses, particularly around nozzles, supports, and attachments.
The nozzles for this vessel would be attached as detailed in ASME VIII-1 Fig. UW-16-1(c) or ASME VIII-2 Table 4.2.10 Detail 3 (set-in nozzle, full pen to shell c/w external fillet weld). If I were to recreate the ASME VIII-1 detail in Solidworks Simulation, I would model it as follows:
- 1/8" fillet to model grinding the inside corner
- equal leg chamfer to model the external fillet weld
Some thoughts that I've had were:
- Add a small fillet at the toes of the chamfer (how small is appropriate?)
- Model the fillet as an equal leg fillet rather than a chamfer (this would represent less overall weld material, is this conservative?)
- Another method of back-calculating the peak stresses? Does anyone have recommendations?
Thank you for any help/suggestions you can provide!
Marty






RE: Simulation of Nozzles for Fatigue (ASME VIII-2)
Welds in simulation is always a problem. Mostly because you have issues with actual welds vs what we model. I remembered that Solidworks used to have a set of Simulation Tutorials by Vince Adams. I'll attempt to attach the weld one here. The whole series is a great read if you can find them online somewhere.
http://files.engineering.com/getfile.aspx?folder=2...
I also had this other discussion of welds. Not sure where I got this one.
http://files.engineering.com/getfile.aspx?folder=b...
Good luck.
RE: Simulation of Nozzles for Fatigue (ASME VIII-2)
Yeah I've seen a lot of discussion on welds in general, but it's been a bit tougher to find stuff in relation to fatigue analysis of welds.
I've been doing a lot of digging around on this subject to try and figure out how best to perform this analysis. There are a bunch of different methods to determine an appropriate peak stress, some of which would be brutal in terms of meshing requirements and run-times.
I dug up a paper by the International Institute of Welding titled "Recommendations for Fatigue Design of Welded Joints and Components". In this paper it discusses a method of surface extrapolation in which stresses on the surface of the base plate are taken at varying distances from the toe of the weld, and the stress is extrapolated back to the toe of the weld using either a linear or quadratic formula.
Does anyone have familiarity with this method and know whether this type of extrapolation is widely accepted as an appropriate method for determining peak stresses per ASME VIII-2? In particular, these calculations may need to be submitted to ABSA (Alberta boiler branch) for review, so I need to know if this is a common approach.
Thank you,
Marty
RE: Simulation of Nozzles for Fatigue (ASME VIII-2)
RE: Simulation of Nozzles for Fatigue (ASME VIII-2)
pressure vessels and welds have to be checked analytically using the correct code, as they have to adhere to relevant standards (safety, etc).
relying only on FEA data and yield strength is a recipe for a potential disaster and litigation.
http://en.wikipedia.org/wiki/Pressure_vessel#List_...
RE: Simulation of Nozzles for Fatigue (ASME VIII-2)
As I stated, we are performing our fatigue analysis in accordance with ASME VIII-2, which is the applicable code in this situation.
The issue is that ASME VIII-2 does not explicitly explain how to determine peak stresses at weld toes, so I am asking how others approach this area of analysis.
Do you have any recommendations?
Marty
RE: Simulation of Nozzles for Fatigue (ASME VIII-2)
Another method include the hot spot method where points are taken a distance from the toe and the stress is curve fit and extrapolated to the toe of the weld and the stress is then used to determine the cycles. You mentioned this method I believe.