Please can anyone add comment to the schools of thought regarding the temperatures and pressures used for stress analysis of a piping system.
1. Should Design Temps and Pressures quoted for the system be used?
2. Should Worst case coincident Operating Temps and Pressures be used?
ASME B31.3 302.2.4 does state " the most severe conditions of coincident pressure and temperature should be used to determine the design conditions"

If the designs are used in place of actual worst case operating you result in an overdesigned system and unrealistic values for stresses and subsequent loads on restraints and equipment?

This has been answered here on the forum many times. Try the following thread:

http://www.coade.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=11680&page=4