Hello,

I have read the reason why the piping codes consider Sustained and expansion (collapse and fatigue mechanisms).

But why they also use Operating, which includes both the above load cases? I mean why they sometimes separated and sometimes combined.Like 31.3 normally Sus and Exp, but now they add appendix P. what is the reason for this? the code says Appendix P is more comprehensive but the given reason seems not so clear.

And I dont understand, base on what reason people require many load case to be considered when analyzing pipe stress.

Thank alot for any reply