Good Morning.

I made an analysis for preinsulated burried piping as per ASME B31.3;I have a question regarding hoop stress. Why is that the result of Operating Case (W+T1+P1) is different from Sustained Case (W+P1) with regards to the HOOP STRESS considering they have the same pressure (P1) applied?

Thank you very much for the help. Greatly appreciate it.