Hi Richard, I can understand this in case of the uplift of a +Y support, as small plastic deformation can bring the pipe back on its rest.
In my case the stresses occur after a bend in a long line. Due to friction from this long line on its supports I need to combine the load cases. In such a case the difference between W and WNC is not a secondary stress, although the resulting stresses after the bend are thermal stresses of course.
I'm now puzzling myself. I'll overthink it once again.

Thanks for your reply.