OK, I have to quit posting in the AM before I have had my coffee. From the above I finally understand your question. Its all about allowable stress limits. Sorry that I misunderstood.

But now that I understand "a little" I am left to wonder what is the "event" that you are evaluating as your "occasional" load. Can that event happen at only 25 degrees? Can that event happen at any time the system is operating?

Regards, John.