von Mises vs Sec VIII, div 2 fig 4-130.1

[tr6]

Not sure if this is the correct forum for this question, or if the FEA forum would be better, but will give it a try.

Having performed an FEA on a perforated plate welded inside an ASME vessel, the FEA results are von Mises stress equivalent. The next step is to determine the material's "allowable" as allowed by the Code as it relates to the FEA results.

Is it acceptable to use the Code's allowables (S), as listed in the material tables, or is Sec VIII, Div 2 fig 4-130.1 (attached), applicable?

Perhaps the basic question is, "How does the von Mises stress equivalent relate to the Code's allowable stresses?".

Thanks,

 

[TGS4]

You need to wade through ALL of Part 5 (for the 2007 and later editions of Division 2). If you're stuck with a 2006 or older vessel, then von Mises isn't for you - you're stuck with Tresca. And read ALL of Appendix 4 (for 2006 and older) while you're at it.

Search these fora and you'll find this (and similar) topics discusses in depth.

 

[tr6]

OK TGS4, I have completed my assignment. I did obtain a copy of 2007, read the entire section, and studied section 5.2.2, so here is how I understand it as it relates to my original question:

1. Section 5.2.2 - Elastic Stress Analysis Method - applies to FEA analysis.

2. Section 5.2.1.b: "The maximum distortion energy yeile criterion shall be used to establish the equivalent stress,. In this case, the equivalent stress is equal to the vaon Mises equivalent stress...".

3. From 5.2.4.c: "...a detailed stress analysis using a numerical method such as finite element analysis typically provides a combination of Pl + Pb and Pl + Pb + q + F directly" and in the following section 1. "...the computed equivalent stresses shall be used to directly represent the Pm, Pl + Pb, or Pl + Pb + Q".

Therefore, the FEA output in the form of von Mises equivalent stress, can be used directly with fig 5.15 of Div 2, 2007. And depending on the loading conditions: Primary, Secondary, Peak, and combinations there-in, determines whether the allowable stress is "S" of "1.5S".

Am I close in my understanding?

 

[TGS4]

Close.

One thing that you'll have to note is that the linearization that is required to be performed for comparison against the stress limits for the various stress categories is performed at the component level. See Annex 5.A.

From your reading, does the classification and categorization of stresses make sense to you?