Hi,erveybody!

I have a doubt on the Load cases comb method of "Hot sustained stress" mentioned in the 6 Chapter of Technical Reference Manual:
L1 = W + T + P （OPE）
L2 = W + P (SUS)
L3 = T (EXP)
L4 = L1-L2 (EXP)
L5 = L1-L3 (SUS)

Above,They use L5 to calculate the "hot sustained stress",But,I do not think this is a suitable method.
When the piping system is a nonlinear system，This approach will cause the stress which is generating by the nonlinear(which is secondary) to be included in the primary stress.
Many previous analysis of the pipeline, is now running very well for several years , but after analysis using this method, the primary stress is always not pass ,but even beyond 300%。

In my opinion, weight is also a limiting factor on the temperature，the virtual weightless Load case will lead the force of pipeline system (which one end is fixed,the other end is free) to be zero,In this state，all +Y support will lift off,and then,if you add the weight and pressure,the pipeline will sag back to the support,but the stress by the lift off gap will be included primary stress in this case. it will casuse a lot of pipeline system to be failure, even a lot of pipeline system which don't have support to lift off also don't pass and exceed a lot than the code stress .

in fact ,the weight is always earlier to exist in the piping system than the temperature，and later to unload.

if the fact is temperature is always earlier to exist in the piping system than weight,and later to unload,so the L5 is right,but it is not the fact,so i think it is not suitable to calculate the hot sus stress using this method.

this is why we can use (w+P+T+wind)-(w+p+T) to get wind ,because the wind is Generally to load after Terperatue.
For nonlinear systems, the sequence of loading is critical。

My English is very bad, I could not express what I mean。

But I eagerly want to know, how should we do, if you must do it according to this method, I think a lot of piping systems will not pass，You did not encounter the same problem？

In the Technical Reference Manual, if coade recommend to use this method, or not recommend, because i am bad in english , I do not know what they mean.

i have read some topics about this question in this forum,but different people have different views, I want to know coade's view