Sam,

I just repeat for the third time my question
"Do you mean your system is qualified by B31.3 with SE< =SA and still has troubles due to thermal strain?" The only thing to add is I would like to know SE has been calculated considering stress due to axial loads.

My additional question would be you intend to share your case and listen to other opinions or you prefer to say in different forms - I have a crack in weld and I have also the solution which is to consider everything as primary load and stress, hence the Code must be changed because, BTW, "We never doubt in code!" but we'd like to change it?