Burst Pressure Calculation

I would think the hoop stress equation is the one to use. Whether you use the yield stress or ultimate stress of the metal depends on what you consider failure. I would consider failure to be stress beyond the yield point of the material.

Another factor which could affect the answer is fatigue. If you are stressing and de-stressing the material cyclically, eventually the material will fail at much lower stress levels. How much lower depends on the frequency of the cycles.

There is quite a bit of information available on the internet. Here is one link which may be helpful.

This is an evaluation of an existing seal pot that burst so I'm looking at tensile strength.

Fatigue is certainly a possibility but I don't know if we have enough operational data to determine if it was fatigue or simply overpressure. We are just looking at the overpressure case for now though.

Thanks for the input though.

You do not need the operational data, you need the fracture surface. Send it for analysis to determine if it was a fatigue failure or not.

I would have to concur with using a hoop stress equation and substituting tensile strength for yield strength to calculate burst pressure. yield strength will only bring you to the point of permanent deformity. Aside from that I believe your equation should be the same.

If tensile strength is used in the hoop stress equation, the change in diameter should be considered as the strain becomes very large near ultimate.