Well flexmen our opinions on this have been put to one side by the collective opinion of the B31.3 comitee... If the work you have performed as you proposed to do it was under the jurisdiction B31.3 your questionable method does not meet the rquirements of the B31.3 code, B31.1 has been given the following interpretation and will render their verdict at a later date, but I doubt that it will be significantly different in philosophy....

B31.3 05-13065

In accordance with ASME B31.3-2004, when a piping system operates at multiple sets of coincident operating temperatures and pressures, and the system may at any random moment be loaded with an occasional load such as earthquake, wind, or pressure relief, should all coincident operating pressures and temperatures expected during operation be considered and shall the basic allowable stress used in para. 302.3.6 be based on the applicable temperature for each condition?

Reply Yes.

TG B originally turned down the request as a consulting question... in other words the question was the responsibilty of the designer (who should be qualified as outlined in B31.3) but after looking over this thread and asking me why I sent in the RFI TG A provided the question and response!