Can anyone explain the meaning behind UG-99(c)? When would you use this paragraph instead of UG-99(b)?

Chaulkate,
When your client wants you to show that the pressure vessel is capable to withstand pressure which induces stresses of S value in parts, you may conduct this kind of test, but you must carefully calculate the test pressure value for each component of your vessel. Usually this is not possible only using formulas of SecVIII-1, because some of them (like flanges) are not likely to rebuild so you can easily calculate this value. And there's always some weakest part, which gets stressed with S value much quicker than most other parts. Of course, you can make the design in such a way, that all parts get stressed with S value at the same test pressure value, but I never saw such a demand. Does any PV software give such possibility?

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Konrad Anikiel