marty007
Mechanical
- Mar 8, 2012
- 622
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:
[ul]
[li]1/8" fillet to model grinding the inside corner[/li]
[li]equal leg chamfer to model the external fillet weld[/li]
[/ul]
This however creates an issue when trying to determine the peak stresses for the fatigue analysis since a chamfer has sharp corners at the toes. These sharp corners would create a singularity in Simulation, and I would obtain higher and higher stress results as I make the mesh smaller and smaller. If I could exempt this vessel from fatigue analysis using the ASME VIII-2 exemption criteria, none of this would be a problem, but that's not an option. How do some of you handle this singularity issue?
Some thoughts that I've had were:
[ul]
[li]Add a small fillet at the toes of the chamfer (how small is appropriate?)[/li]
[li]Model the fillet as an equal leg fillet rather than a chamfer (this would represent less overall weld material, is this conservative?)[/li]
[li]Another method of back-calculating the peak stresses? Does anyone have recommendations?[/li]
[/ul]
I've used a nozzle attachment as an example, but the issue of modelling fillet welds for fatigue analysis is true for all attachment fillet welds (vacuum ring, lifting lugs, etc...).
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:
[ul]
[li]1/8" fillet to model grinding the inside corner[/li]
[li]equal leg chamfer to model the external fillet weld[/li]
[/ul]
This however creates an issue when trying to determine the peak stresses for the fatigue analysis since a chamfer has sharp corners at the toes. These sharp corners would create a singularity in Simulation, and I would obtain higher and higher stress results as I make the mesh smaller and smaller. If I could exempt this vessel from fatigue analysis using the ASME VIII-2 exemption criteria, none of this would be a problem, but that's not an option. How do some of you handle this singularity issue?
Some thoughts that I've had were:
[ul]
[li]Add a small fillet at the toes of the chamfer (how small is appropriate?)[/li]
[li]Model the fillet as an equal leg fillet rather than a chamfer (this would represent less overall weld material, is this conservative?)[/li]
[li]Another method of back-calculating the peak stresses? Does anyone have recommendations?[/li]
[/ul]
I've used a nozzle attachment as an example, but the issue of modelling fillet welds for fatigue analysis is true for all attachment fillet welds (vacuum ring, lifting lugs, etc...).
Thank you for any help/suggestions you can provide!
Marty