A while ago I was asked to check an above ground pipeline model. The pipeline was a 16 NPS High Pressure Steam line (320°C, 11240kPa), several kilometers long with 1000mm of growth into the expansion loops. The expansion loops were typical with the lateral legs at 45° to save material.

The problem I had was that the analyst had put large gaps at the guides near the loops to reduce stresses and structural loads. Typically we specify 6 mm gaps to prevent binding in the guides, but these ones had 50 mm gaps.

A model only simuluates what happens in the first cycle, so the calculated guide loads are 25% lower than with a no gap model. But what happens after the next cycle? The pipe isn't going to return to it's original position is it?

I was able back then to check 3 cycles in sequence using AutoPIPE because you can sequence the load cases in the one of the advanced dialogues. I haven't figured out how to do this in Caesar. I recall after 3 cycles the calculated guide loads were just as high as with no gaps and I want to be able to prove this critical fact with Caesar as I no longer use AutoPIPE.

I've seen too many failures in above ground pipelines as a result of structural deflection and binding in guides. I need to be able to prove my theory to convince future analysts from continuing to use this naive approach to reducing structural loads. I am developing a paper/article/presentation on this subject so the more evidence I can get the better.

Any guidance or references you know of would be much appreciated.