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.