For high temperature lines, (greater than 300ºC) one task in the analysis is to stipulate the Hot Elastic Modulus of the material for the expansion stresses.  B31.1 and B31.3 both require that expansion stresses "Se" be calculated using the Cold Modulus Ec, however for high temperature lines you can reference the B31.3 code section 319.2.2(b)(4) to use the hot modulus instead.  What this affords you is lower loads and displacements in your Operating case, which can help prove out a troublesome analysis.  The side effect of activating this hot modulus is that you cannot consider the stresses on the piping system to be accurate for your expansion case, which is the difference in allowable stress between the operating and sustained case. 

The stress adjustment that is not performed here is multiplying the "hot" stress range by the ratio of the cold to the hot modulus, Ec/Eh.  For this reason, to invoke the hot elastic modulus you must have two separate load cases as shown:

In this example, L1 is my operating case with Ec, the cold modulus selected.  L2 will be my operating case with my hot modulus.  To access either modulus to be calculated for that load case, I need to go to the "Load Case Options" tab.

Here on the load case options tab, I've selected Eh as the operating modulus for L2.  

Additionally, I'm going to modify the output of my L2 case, so that I don't have stresses output with this load combination, since they aren't valid anyway.

That's it!  Now when I review my results for each Operating case, those results will be valid, for that case.  Additionally, you may want to modify the load case name, for easier review of results.