Dears,

Is it neccessary to check the system in Occassional stresses while checking system for lift-off case?
As per my understanding,during lift off case we remove support(which are lifting in operating & Ope+Occ.) and check the system in sustained case.
As sustained case allowables are compared with Hot-stresses,if the stresses in Sustained case is within the allowables then in Occassional case where we are having 1.33times the Basic alllowables stress gives us the liniency not to check stresses in Occassional case during lift-off check.
Is my understanding right?,please suggest me.

Dear Pipeswami,

c2TR.pdf>Chapter 6: Technical Discussions>Sustained Stresses and Nonlinear Restraints and Notes on Occasional Load Cases is the reference for it.

Thanks Mr.Samsul for the reference,but i am confused to co-relate the importance of Sustained case with the occasional case.
Please clarify if i am right with the below understanding.
1)As per the ASME.B31.3(2004),says the sum of Longitudinal stresses(SL)& the stresses produced by occasional case may be 1.33times the basic allowables for the particular material.
Can i above co-relate to my understanding that if the system is passing in sustained case for piping lift-off check then there is no need to check for occasional stress(in piping lift-off check) as the ocassional stresses are 1.33 times the basic allowables.
2)If my stresses while Piping lift case in sustained case is passing then there is no need to check the occasional stresses in Piping lift-off case as the sustained case(force driven) remains constant even after the thermal growth(displacement driven) during the life of the piping system and hence we can assume that the scalar summation of occasional case(difference between W+P+T-W+P+T+OCC.CASE(WIND OR SEISMIC)=pure wind & Pure seismic) & sustained case will be safe.

Please clarify if i am wrong or any alternate explanation so that i can understand thoroughly.

Regards.

1) No

2) No

As the responsible engineer for a stress analysis report, you have to review all of the required load cases. It's what you get paid for; if you decide the effort required to fulfill this obligation is too much for you I'm sure you can find a less taxing, lower-paying career path. I'm sure there are many discussions of lift-off on this board.

Checking for overstresses due to lift-off is one of the reasons for reviewing the "hot sustained" load case report. By tagging this load case as "OCC" for your occasional load case, you can arrange to compare the calcualted stresses with the increased allowables specified by your Code. I know you can find many discussions of "hot sustained" loac case on this board.