Dear Sam,

I am not sure if this is the answer relates to your posting. I just try to. Internal pressure in pipe cause 1) hoop stress Sh = P*D/2t ; 2) longitudinal pressure stress Slp=P*D/4t . Hoop stress used for minimum wall thickness calculation. It is a local effect. It will generate fail in the thinnest part of pipe wall, assumed not in all metal part. That’s why not considered as code stress. If our minimum pipe wall thickness is enough = pressure thickness (due to hoop) + CA, we don’t worry to hoop stress. If our pressure thickness is not enough, Caesar will remind us during error checker in warning. You can try trial. Longitudinal pressure stress occurs in all surface area and considered as part of code stress.

It is recommended to use design pressure rather than operating pressure regarding to both stresses.