I am currently working on a piping system which is subject to cyclic operating conditions; I wonder if someone could confirm this for me:
assuming that the only cyclic condition occurring on this system is the fluctuation of temperature, is it still necessary that on top of the relevant (EXP) stress case with the proper "f" (stress reduction factor), a (FAT) stress case would have to be made? I have checked this in various calculations and the (EXP) case has been always the decisive case.
please advise.

thanks in advance

The ASME code is set up for "typical" use, which by its nature is subject to some cycling, but isn't precisely defined.

As a result, it is commonly the end user's decision as whether to treat it as a "high cycle" analysis or not. Some people might say the cut-off is 1 million cycles.

If you have the cycles information, I'd say just do it. If you don't have cycling design criteria, then press the end-user / project manager that if they want it, they need to provide the information.