Is there a clear statement/interpretation about stress classification due to ground settlement
in B31.1?

We have a steam line with difference displacements at supports, caused by the different
settlement of two pipe racks. The effect is limited to some supports but passes a tee piece.

What are arguments for sustained or expansion stress check and is there room for interpretations?
The difference displacement cause self limiting stresses, is the increase of the thermal expansion
stress range a possible/sufficent stress check?