Having a system with maximum design temperatures (hot) and minimum design temperature (cold, below zero), what is the best way to access the themal stress range?

Some people's approach is:
(1) W+T1+P1 (OPE)
(2) W+T2+P1 (OPE)
(3) DS1-DS2 (EXP)
T1: hot temperature
T2: cold temperature

Others would change the ambient temperature to match the minimum design temperature and do the following cases:

(1) W+T1+P1 (OPE)
(2) W+P1 (SUS)
(3) DS1-DS2 (EXP)
T1: hot temperature

What is the best approach?

I think you will get an insight into the wrong and right approach by reading COADE Mechanical Engineering News - May 1993 pages 32 to 34. This can be accessed via Support / Newsletters options on this website.

Happy Reading.

Thank you Dave.

Spot on