I am new in CAESAR II …

I couldn’t find clear answer for my question, from previous posts.

When we see lift off in OPE we need to remove lifted off supports for SUS stress check. But what shall we do for supports that haven’t been lifted off, but the loads on supports have changed?

If we only remove the lifted off supports and don’t consider change in loads on other supports we can’t get correct SUS stress.

Read the discussion in the CAESAR II documentation on "Hot Sustained Stress".

We do not subscribe to the idea that a support should be removed from the model. That may (or may not) be correct for one load case only. Your model must address all conditions of the piping system.

I believe you are digging deeper than most here. The Codes say very little about nonlinear response in evaluating stress. One of the more recent interpretations (issued by B31.3?) states that longitudinal stress shall be evaluated in all support configurations. So, if a pipe lifts off a support due to thermal strain, rerun the sustained case with those "missing" supports removed.
We here at ICAS (old COADE) have always promoted our recommended load cases as adequate. If the pipe yields under sustained load, the pipe will relax and once again rest on the support - a strain event that we believe belongs in the expansion stress range calculation.
If you want to include that change in sustained load that you mention, run an operating case minus the strain case (the indicated case below):
L1: W+T1+P1+D1 (OPE)
L2: W+P1 (SUS)
L3: T1+D1 (EXP)
L4: L1-L2 (EXP)
L5: L1-L3 (SUS) <==

Thank you Richard and Dave,

From your answers I noticed that if we have nonlinearity in system, it is better to ues L5 instead of L2, but if we use only L2 (and removing lifted off supports) it is not in conflict with code 31.3

I think we need to model a system as accurate as possible, because this model will be constructed and we need to see the results of analysis in the actual case. because of that how can we rely on B31.3 that separeted sustain and expansion stresses?

Hello NZE,

I'm my modest opinion, the key is not "instead", i think is better to say here "and also".., so: "...It is better to uses L5 and also L2...", code 31.2 tell us that we must evaluate sustained stresses under all the positions of our pipe system, in "cold position" and also in "hot/operation position".

If we remove lifted off supports in the same calculus, the expansion stress would be affected.., so here were leaving the accurace that we need...

I suggest that if you want to use the way of deleting lifted supports.., do in a only-sustained-stress calculus.., just to verify the sustained stress..., and use another calculus with all of the supoports that you're planing to realy uses in order to check the expansion/occ stress..

I found a lot of helping tips searching with "hot-sustained" in the forum.., also in the Technical Manual this tip is very well explained too.

Regards