I've got a bit of a debate going on here and I need some more facts to work with.

Specifically, the WRC-107 module calls for Smc and Smh to be inputed from ASME Section VIII, Division 2.

These allowables are higher than those given in Division 1, which most vessels are designed to. The justification for the higher allowables of Division 2 are, first, a more rigorous design and analysis procedure, and second, higher quality control and inspection requirements.

Now, while it can be argued that running a WRC-107 or FEA on a nozzle connection constitutes a more rigorous analysis, you aren't guaranteed to get the higher QC in fabrication.

So, the basic question is - what is the justification for a blanket statement of using the Div 2 allowables, particularly in the case of a Div 1 vessel, or even a large piping connection designed to B31.1, which has even lower allowables?

Dear Mr. Klein,

Ultimately, the choice of allowables is up to you. One thing to realize of course that WRC 107, 297, BS-5500 Annex G, etc. compute stress intensities. ASME table 1A and table 2A contain listings of allowable stress versus temperature. ASME VIII Div. 1 is a Code that is based on the Maximum Principal Stress theory of failure. On the other hand, Division 2 is based on the Maximum Shear Stress theory of failure which is slightly more complex. Since a WRC 107 analysis is Code independent, we feel it is more accurate to compare computed stress intensities to stress intensity allowables for that material. Other Codes such as PD(BS)5500 also are based on more complicated theories than the one used for Division 1. A user of a foreign pressure vessel code may not have access to the lower allowables.

All in all, we believe that it is more appropriate to use stress intensity allowables as a comparison base to computed stress intensities.

If you have other ideas or views on this subject, please share them with us.


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Scott Mayeux
COADE Inc.