Here's a half-baked idea:

Say you have a short line you're tying into a really long existing header that has expansion loops and the like.

If you wanted to model that header with accuracy, you'd include every support.

If you wanted to subtract some accuracy and add some speed, you might count supports between important features (anchors, loops, etc) and then split into even increments.

If you wanted to speed things up further, you might replace the previous step with a uniform load equal to the weight of the pipe, effectively making it weightless, and requiring far fewer nodes - just at anchors and expansion joints.

What issues would you speculate you would encounter with either of these methods?

Do you have alternative methods for estimating displacements of header tie-in locations?

Michael,

I understand you are trying to cross run (hot tap) on to a hot above ground piping which you call it header.

I think there is no short-cut for estimating header thermal displacement and the effect of new piping attachment. If you are lucky you can find an anchor support close to the attachment location and pipe guided against lateral movement, lateral rotation under thermal load. Otherwise you should model up to the thermal neutral location on the header to be able to answer future questions which may arise.

Main header will be hot under the operating temperature, the new piping will be cold. So you may be forced to see the effect off the shut down of combined piping in case the temperature significant(?).

I know this was not the answer you were not expecting. However it may help you rethink.

Michael,

For me it sounds effective. About alternatives, no more than manual estimations. Anyway knowing anchors or axial stops on "existing" is often difficult.