If you take the supports out of the model, then the Expansion case will be incorrect. To properly evaluate the "extreme displacement stress range" (the expansion case), you have to be able to evaluate each condition of the piping system. In the shut-down case, if the pipe is sitting on the supports, they must be in the model. The same holds true for these supports in a model where a section is off (spared) for subsequent use.

For primary stress evaluation (sustained), you may want to perform a "hot sustained" evaluation (CAESAR II by default performs a "cold sustained evaluation"). There is a write-up in the Technical Reference Manual on how to do this.

Once you evaluate all of these conditions, you can decide between a "hard support" and a "spring".