External pressure on an ellipsoidal head ASME VIII div 1 (UG-33-1b) 1

You are not missing anything. You are simply not permitted to use that material at that temperature under any external pressure. You would need to generate a Code Case (with all the supporting documentation and calculations - of course) to extend Fig CS-2. That said, I would do a search through the Code Cases to see if someone has already done that for your material.

If that doesn't work, you have to choose a different material.

Thanks TGS4. Not the answer I was hoping for, but thanks anyway.

TGS4 is correct. Paragraph UG-20(c) states that you cannot exceed the maximum temperature limits shown on the external pressure charts.

Is it possible that you could use a lower design temperature for the external pressure case?

-Christine

Raaden-

TGS4's response is correct. Christine's solution may work for you. Often the external pressure requirement is accompanied by a different design temperature.

Do a search for Code Cases as TGS4 suggested. You may find something useful there.

Another option since your temperature is fairly close to the 900°F limit is to put a relatively thin refractory layer in the head - say 1" (25mm) or so. You'll have to run the calc's to determine the expected metal temperature, but I'd bet that 1" (of even a hard face, relatively high conductivity) refractory would work.

jt