Piping design in an offshore platform - Relative displacements between modules

[4r4ujo]

I'm designing a piping in a offshore platform. This piping is interconnected between more than one structural modules and these modules are supported by four stools. I have to define the load combination to use on the analysis. However I dont know how to combine the directions of environmental loads. I have to create a coherent combination to take into account the inertia forces and the relative displacements between the modules acting on the anchor points. These relative displacements is obtained from the modules structural analysis and there are several combination used by the structural engineer team. The question is: what I can do to reduce the number of the load combination on my piping flexibility analysis? Is there a methodology to select an worse direction to cut off the number of load combination on my analysis? I apologize for my english mistakes.

 

[DSB123]

I presume the displacements are due to wind and wave action. You need to perform a fatigue analysis of the pipework taking into account the wind/wave distribution. Bear in mind that the stress intensification factors given in the piping Code (presumably B31.3) are 50% of the actual SIF values for piping components such as bends and branches. You need to effectively double the stresses calculated by any pipe stress analysis program you are using.

 

[4r4ujo]

The structural displacements are due to DOC (Operation Condition) and DEC (Extreme Condition). I’m aware that I have to perform the fatigue design considering the cyclic load only. For this, I’m going to subtract the static portion. For others conditions I have to evaluate the piping loads considering eight directions (0º, 45º,90º,135º,180º,225º,270º,315º and 360º). The problem is that I must create a lot of load combination per direction on CAESAR (accelerations and displacements) which is very difficult to perform on CAESAR. So, my question is: Is there a simplest way to evaluate the most unfavorable direction instead of evaluating the 8 directions? Thanks for your reply.