Fatigue is only a problem if there are cyclic loads present. If the loads are constant static loads then fatigue will not be an issue.
If the loads do cycle then the principal stress ranges need to be determined and the fatigue life can then be calculated.
A good example is in appendix C of...
Thanks Adrian.
We do have regs etc in the UK (BS5500) but this problem is more of a fit for purpose requirement and does not come into any code. I know ASME VIII specifies minimum number of threads to be engaged for pipe threads but to satisfy my self that the plug will not shear I wanted to...
How is the shear stress calculated in a threaded plug subject to internal pressure (fitted into a pressure vessel). What force would actually strip the thread if only say 5 threads were engaged.
Cheers