If we have a piping system that is subject to temperatures T1 & T2; which results in thermal range of D1=T1-T2.
My question is; since we are analyzing the piping system statically, doesn’t make a difference how fast the system’s temperatures change from T2 to T1, as long as we are considering the number of cycles?! Please, advise.

So far as I know, rate of change is not generally addressed. It is clearly significant when for instance, considering an overhead line off a tall vessel, where the heat-up and cool-down rates of pipe and vessel may radically differ and thus could cause relative expansion problems.