I am running a pipeline tie-in spool model with various expansions etc applied to the model. I initially had 4 loadcases, operating conditions with waves from 4 directions. I then added 8 more loadcases to assess two different potential pipeline expansion values (again for 4 different wave directions) giving me 12 loadcases. When I run the first four loadcases on their own the stresses are within allowable limits, however when I run all twelve I get a failure in the first four loadcases. Can anyone advise what may be occurring here? Thanks
Could it be something to do with this? The first four loadcases have a displacement, while the additional loadcases have a displacement and a rotation. But the first loadcase uses D1, while the additional expansions use D2 and D3?
Load Cases with Pitch and Roll: In offshore piping evaluation there is often platform movement or relative movement between two platforms with inter-connected piping. This also applies to FSPO and other ship-board piping systems. For these applications the pitch and roll displacements are applied to Cnodes on each affected restraint similar to settlement. Use displacement vectors not in use to describe thermal displacement boundary conditions. Usually there is a positive displacement and a negative displacement to describe the peak pitch and roll conditions. Consider the state of the platform at its peaks to determine the worst two conditions for relative displacement between piping separated by the largest distance along the line of wave travel. D3 and D4 are used in this example to describe two peak pitch conditions. D1 is thermal displacement.
I have 7 displacement loadcases, all applied at the same cnode (D1-D7). d1-displacement(y) d2-displacement(y) d3-displacement(y) d4-rotation(+rx) d5-rotation(-rx) d6-rotation (+rz) d7-rotation (-rz)
The first four loadcases passed stress checks until i added the other loadcases, it then fails and I can't figure out why. I have deleted all of the additional loadcases and then reran the first four and again it passes. Could anyone offer any advice?
I've been playing around with it over the weekend and it definitely appears to be something to do with having multiple displacement/rotation loadcases, do you know whether the later displacement/rotation loadcases can modify the restrain conditions used in the earlier one? That appears to be whats happening. If I run the loadcases in separate models the problem is resolved. I just end up with heaps of models.
Registered: 12/13/99
Posts: 6226
Loc: Houston, Texas, USA
This really shouldn't happen for that piping code. (This can happen if you're dealing with the "maximum sustained stress" used to compute the Expansion allowable - more SUS cases can change the allowable for other load cases.)
Please open a Support Request on Smart Support and send in the model so the Tech Support group can review this issue.
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Regards, Richard Ay - Consultant
Registered: 12/14/99
Posts: 2382
Loc: Houston, TX, USA
Tell me, are there nodes and directions common to D1, D2 & D4? An example, an X displacement defined at node 10 in both D1 and D2. A zero entry counts.
Apologies I've just seen this response. Yes there were, I was restraining it it some axis, could this be the issue? I just ended up creating different models to run the different loadcases. Thanks
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