Dan,

I was typing faster than I was thinking. Thank you for your correction.

This may help.

Appendix P was established to address uncertainty in the value used for SL in B31.3 equation (1b). Appendix P is an alternative to evaluating the expansion stress range. Appendix P has no effect on the requirements to satisfy the requirements for longitudinal stress (SL) due to sustained loads.

In nonlinear situations, SL may change. For SL, you may want to check this stress in all support configurations.

I claim that running an (operating case) minus (all expansion effects) will give SL in nonlinear cases as well.