I agree whole heartedly with the previous post, also I suggest that you take time out to do a literature search on this subject matter.

I commend you for realizing that the beam element model is giving you "funny" results. I wish more people looked at output reports and though about what they were saying.

However, by declaration of your state of puzzlement you also indicate being outside the depth of your knowledge, I am certain however that you can fill in you voids.

Check API RP 579, its pricey at $600, but it looks like it may adress some of these issues (No I have not yet been willing to cough up $600, but I know I will sooner or later, I hope to attend a seminar on this this fall)

Other points to ponder ASME B31.3 and B31.1 are "design codes" for new design and their coverage does not directly adress this type of evaluation. Although B31.3 has some discussion of settlement in it.

And finally, the B31.3 and B31.1 codes will sometimes allow the calculated secondary displacement stresses to go beyond the yield of the material, however they and all "pipe stress analysis, beam element programs" provide only one-dimensional beam elements that act elastically even beyond the yield point. This "simplified" method when combined with the codes has demonstrated time and again to provide a safe design for most (but not all) piping systems.

Hope this helps, and one more thing despite the twisted and magled condition of the pipe, if it does not have to undergo a significant amount of cycles or very rigorous duty it might be OK as is, hence the phrase "Fitness for Service" evaluation.

Best Regards,

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Best Regards,

John C. Luf