Refer to technical discussion topic "sustained stresses and non linear restraints ". As explained in this topic , if we make case for hot sustained check , the value of SL obtained in this case is used for calculating SA . When liberal is "ON" this affects SA value in the sense SA is lowered as SL in hot sustained case is higher than W+P (SUS) case.
Do we have an option in CAESARII to use SL from W+P (SUS) case instead of that from hot sustained case when we make such case ?
This is because secondary stress range shall be worked out from W+P ( SUS) case i.e. the profile in installation case. From this profile , the system reaches W+P+T profile and completes one cycle when returns to W+P (SUS) profile.
Even the technical discussion has note that "There is no corresponding confusion on the question of calculating expansion stresses , because the codes are explicit in their instructions that the expansion stress range is the difference between the operating and cold stress positions , both of which are known.
I am presently handling cryogenic plant systems at -170 Deg C and find that in a model where hot sustained case is made system sometimes is overstressed in EXP case
i.e. {(W+P+T , OPE)} -{(W+P ,SUS)} case.
But same system passes in {(W+P+T ,OPE)}-{(W+P, SUS } case when hot sustained case is not there in model.

No, there is no way of selecting which, of several, sustained stress cases will be used in the expansion stress range limit. CAESAR II will use the maximum sustained stress here.
An easy way to use the sustained case you want is to re-specify the other (SUS) cases as, say, (OCC).
If the piping code you are using has the same stress equations for sustained and occasional you can eat your cake and have it too by this:
- re-specify the other (SUS) cases as (OCC)
- change the occasional load factor in the Load Case Options tab (far to the right) for these cases to 1.0
: now those other SUS cases are OCC but the OCC limit is now 1.0*Sh (it used to be 1.33Sh in your previous B31.3 analysis).

Is it possible that the hot sustain case made as per CAESARII guidelines can show negative displacement at non acting rest supports which will be much more than the +ve displacement in W+P+T case? Suppose W+P+T case shows 3 mm upward movement at certain support, is it possible that (W+P+T)-(T) case, i.e. Hot sustain case can show a displacement of say -6 mm? Then it should be interpreted as in operating scenario sustained contribution is to that much tune. It does not mean pipe will sag and touch the support again.
please advice.

I guess your results show that it is possible.
First, is it significant? I suggest you compare your hot sustained results with a second sustained stress analysis where you make all your nonlinear supports match their linear state from the operating condition. That is what the hot sustained case intends to mimic.
Second, what's the cause? One issue I have with hot sustained involves friction. That "-(T)" component does not have the dead weight component to the normal load at supports with friction. Without this normal load, friction supports may "slip" rather than "stick" and this will alter the displacements found in "-(T)". This would be my first guess.

= = = = =

B31.3 2014 now says that the allowed expansion stress range (1b) shall use the maximum sustained stress (SL) considering all support conditions. Running a separate "hot sustained" case does not get a higher SL back into the allowable expansion stress range used in the original analysis. To address this, the next release of CAESAR II will include the capability to reuse the operating support configuration to recalculate sustained stress. We are calling this an Alternate Sustained Stress. The highest SL from all analyses will be used in (1b). Stay tuned...

Yes , there is significant downward displacement sometimes in HOT SUSTAINED CASE as compared to upward displacement in operating case . One case I have seen -18 mm in HOT sus case and +3 mm in operating at support node.
My only question is it should not be interpreted as pipe would sag back and rest on the support. It should be interpreted as SUS contribution in HOT case.

Thanks for the response.
regards,

Would you be able to clarify my interpretation. We have full faith in CAESARII and their team, we users , all are not of the same caliber as Richard and Dave. We try to interpret what COADE guides us.
At times we are required to explain it to our juniors . Presently I am making a presentation on Hot sustained check and want to pass on my interpretation to them, provided I get a corroborating statement from someone like Richard or Dave.
Requested to clarify whether my understanding that the sag in HOT SUS case ( (W+P+T)-(T)) is not the physical sag , but contribution of sustained load in hot or operating situation which will be used to work out the stresses in that case.

Thanks again for always giving a satisfying guidance.

Regards,
bag_piper ( bagpiper is some brand of liquor in India)

The purpose of the "hot sustained" case is to estimate the magnitude of the sustained stress based on the operating support configuration (rather than the installed support configuration). I would also expect the displacements from this case to show the dead weight sag. But as you point out here this sag appears different. I say this change is related to the changes in the support configuration.
You can learn more about your specific situation by replicating the hot support configuration (in a duplicate model) and see how those weight plus pressure numbers line up with your "hot sustained" load case.

I will make a model as advised.Since the program has already calculated the operating profile which means the support is not taking load. Then obviously the sag in the absence of expansion is theoretically the contribution of dead weight for that profile and even though it shows -'ve displacement > than +'ve upward movement, that does not mean that physically the pipe will rest back.

Also remember that the displacements you see for the Hot Sus case are relative to the operating case. Thus you will see negative displacements at some support points. The disp. are NOT absolute, they are relative. I am quite sure this is correct. See for yourself at uplift points. But then again I may be wrong but I doubt it.

The displacements in HOT SUS case are global displacements and NOT relative to operating profile. They are to be interpreted like any other SUS case displacements.
Someone correct me if I am wrong.

In my opinion, the displacements from the HOT SUS case are used ONLY as a means to calculate (approximate?) the sustained stress distribution based on the operating support configuration. HOT SUS is not an examination of a physical state of the piping system.