Pressure vessel or bellows test pressure!? 1

[chillwynston]

Hi guys,

I have a question, in my company we make bellows, we test the bellows to a standard test pressure of 1.5 times the design pressure. I was reading some of EJMA the expansion joints manufacturers association stds book and a paragraph confused me. When testing products with an extremely high design temperature, we would generally use a lower test pressure than 1.5 times the design pressure. Why is this? I asked a colleague who informed me there is a test pressure calculation with the ASME standards yet he seems to think the calulation would suggest a higher test pressure at an elevated temperature. Can anybody tell me why test pressure should be lowered at high temperature and if anyone knows the formula for the test pressure?! thanks for listening...

 

[chaulklate]

I agree with your colleague. In ASME Section VIII, the hydrotest would be higher for vessels in elevated temperatures. Refer to paragraph UG-99(b). The formula is:

1.3 x MAWP x test stress / design stress

This would in fact give you a higher hydrotest pressure. I don't know anything about bellows and I am unaware of any situation that would give a lower test pressure.

 

[doct9960]

chillwynston,

have a look at this thread in the ASME (mechanical) Code Issues forum... thread292-25903