Hello,
In my calculation work, I have met a problem about seismic.
I have set the load case just like the following shows in the easy way.
L1=W+P+T（OPE）
L2=W+P+T+U（OPE）
L3=W+P（SUS）
L4=L1-L3（EXP）
L5=L2-L1（OCC）
L6=L3+L5（OCC）
when checking the nozzle load, the loads at the case L1 ,L2and L3 should be considered, but if the load at case L6 should be considered? Why?
If the case L7=W+P+U can indictate the Maintenance status of the plant and seismic happening simultaneously? This case should be OPE , SUS or OCC? Should be considered in the nozzle load check?
Looking forward for your reply.
Thanks a lot.


Best regards,
Hongxiasu

Case 6 provides the stresses for the Code's requirement (the sum of the occasional stresses and the sustained stresses). The stresses are the only useful information from this load case. You would not need to evaluate loads or displacements from this load case.

As you indicated above, a 7th case can be constructed for load/maintenance evaluation. This case however is NOT a stress compliance case (it may yield different stress results from case 6 based on the non-linear boundary conditions of the system). Therefore, since this is not a stress compliance case, you could specify that the load case stress type is OPE. Assuming you're running B31.1 or B31.3, this will produce a stress report (which you shouldn't really look at) with ZERO allowable values. This way, no one can mis-interpret the stress results.

hello Richard Ay,
Thanks you very much.
Here has another question for nozzle check.
When using Nozzle-Pro checking the nozzle loads, normally need the weight loads, operating loads and occasional loads. It is clear that the weight loads related to L3, the operating loads related to L1/L2. And the occasional loads should be related to case L5? Or one new case need to be made for the occasion loads?
When using WRC107/297, need loads at SUS, EXP and OCC case. SUS should be related to L3, EXP to L4, So OCC should be related to L5?
Thanks for your reply.


best regards,
hongxiasu

Yes, you want Case 5.

Richard,
In the seismic case 6 above, the thermal expansion T is not included, yet the most likely seismic event is during operation at T. Is the premis that the pipe has already expanded and T stress has dissapated or balanced and does not endanger the pipe once the pipe is stable, so only the added seismic OCC is stressing the pipe? (That implies cycling of the pipe T is worse than operating at the elevated temp.In an operating steam system that cycles only once a year, it implies T doesn't matter if it is within the material's T allowables.) Or is the T considered in the seismic case as if the seismic is applied to an already stressed pipe. Logically The T and seismic occur simultaneously. How Is Caesar or the code handling it?

They typical piping code says, that for flexibility analysis of occasional loads, you sum the stresses from the OCC event with the stresses from the SUS event.

You may have other reasons for evaluating an OPE+OCC case: maximum restraint loads, maximum excursion, etc.

But for (typical) Code Compliance, you want case 6 above.