ASME VIII, div 2: Elastic vs. plastic FEA

[subseapilot]

In ASME B31.3 chapter VI paragraph 345 it is "clearly" stated what maximum stresses are allowed for pressure testing conditions. For a plastic analysis on the other hand, the allowed limits for testing condition is not as obvious. Does anybody know where stress limits (or more likely allowed percentange of the collapse load) can be found that applies for a plastic analysis?

I would be more that happy for any information about this!

 

[TGS4]

Stress limits have no relevance in a plastic analysis. What are you trying to achieve? Is your question about B31.3 or Section VIII, Division 2?

 

[subseapilot]

The choosen code for design is B31.3 which later referes to sec VIII div 2 for stress analysis in my case.

"Stress limits have no relevance in a plastic analysis", I totally agree, that's why I wrote "(or more likely allowed percentange of the collapse load)".

In a elastic analysis, Section VIII division 2 describes allowed stress limits for operating conditions. In addition, B31.3 chapter VI paragraph 345 lists less conservative stress limits for pressure testing conditions. I was just wondering if there are any corresponding "testing condition requirements" for a plastic analysis?

 

[TGS4]

Simply put - NO. If you meet the requirements, in the design condition, of the plastic analysis with the appropriate design margins stipulated in Appendix 4 of Section VIII, Division 2, then there need not be any additional restriction on stresses/strains for the test condition.

CAVEAT - Testing at a pressure significantly in excess of the minimum test pressure may cause local yielding and permanent deformation. It is up to you to decide of this is acceptable or not. It shouldn't affect the pressure integrity of the pipe, but there are always additional requirements in addition to pressure integrity (dimensional stability, equipment loads, etc) that need to be considered.

Also, you will note that any limits on testing stress refers only to the general membrane stress. That was an intentional choice. For an elastic analysis, there are no limits on any stresses that cannot be classified as general primary membrane stress.