Good Morning.

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.

What specific code did you applied?

it was for Burried Preinsulated Piping as per ASME B31.3

My guess (I'm away from the office) is, the sustained stress (W+P1) uses corroded wall in Z while operating stress uses uncorroded wall. Run another (W+P1) but call it (OPE) to test.