modeling compressor nozzles - static analysis according with Nema SM23 without taking into consideration gravity (only pressure, temperature loads, and gas gravity) ?

Question

I have a basic question regarding modeling piping in a compressor station. 
 Typically, the compressor is installed first and properly levelled and grouted. The pipe (discharge and suction) is installed next and all adjustments to the piping are performed until the mating faces of the pipes and the compressor nozzles are accurately aligned. At this point all the gravity load from the empty pipe is carried by the supports on the pipes and no load is transferred to compressor nozzle. After assuring that the pipe and the nozzles are accurately aligned, the pipe is connecetd to the compressor nozzles. At this instant no load from the pipe is carried by the compressor nozzle. When the system is in operation the compressor nozzle will be subjected to all the loads (temperature, pressure, gas in the pipe) that occur in the system subsequent to the initial connection bewteen the pipe and the nozzle. Does it mean that during static analysis to check nozzle allowable acording to Nema SM23 or API 617, the gravity load is not taking in the static analysis, in addition taking into consideration the fact that compressor nozzles are modeled as a rigid? 
 
 Regards 
 Bob

Maciej Rydlewicz - CS Softdesk · Accepted Answer

I was asked by Bob to comment more so here I am with my opinion. I think that the solution proposed by Mike may be difficult to apply when it comes to inserting such small values of a free pipeline end displacement. Values of this order can also be "method errors" especially when it comes to non-linear analysis. I am opting for the variant I propose. Please, take into account that in case of non-linear analysis, the initial conditions for thermal analysis are the results of gravity analysis (in the assumed sequence GR > T1 > P1; the order of P and T can be changed). We have a discussion regarding 'model splitting' somewhere else in the community and that subject seems to be not quite clear and solved as well. Topic open...

Mike Dattilio · Answer

Hello Bob, 
 Suggest that you model your piping up to the compressor location but do not model an Anchor or nozzle element for the compressor it self at this point in time. Analyze the model, using the results grids copy the exact displacement and Rotation of the node point location representing the compressor. 
 Note: By clicking in the grid fields see the exact value used by AutoPIPE in the calculations instead of the rounded off value in the output report. . 
 Insert an anchor to represent the compressor connection, then insert Import Support displacement on the anchor, using the values recorded above for Translation X,Y,Z and Rotation X,Y,Z, run your Analysis and check the Equipment sub-report. Loads due to gravity should be fairly low, if not Zero. 
 
 See example attached model to prove concept. If remove anchors A02 and B02, The gravity displacement = the impose displacements. 
 Rotating equip-pump.zip 
 Note: attached model created by AutoPIPE 12.02.00.14 
 Regards, 
 Mike Dattilio Bentley Systems Design Analyst Design Engineering Analysis group ===================================================

modeling compressor nozzles - static analysis according with Nema SM23 without taking into consideration gravity (only pressure, temperature loads, and gas gravity) ?

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