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

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

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

(OP)
I have run into a little problem. I am supposed to calculate a formed head of a semi ellipsoidal shape that is under a external pressure. This is my first time doing this calculation so this might be a really stupid question, but anyway: I have followed the steps and arrived in subpart 3 of ASME II, part D. My head is of A-387 22Cl.2 material, so I should look at Fig. CS-2. But when I look in the diagram I see only graphs for up to 900°F and my design temperature is 560°C (1040°F). Is there a way around this or am I missing something totaly obvious?

Thanks

Pontus

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

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.

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

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

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

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

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

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

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