Hi

As you know for rectangular section pressure vessel (ASME sec.VIII Div.1 Appendix 13) maximum allowable stress for Membrane & Bending is 1.5 x S.
moreover it seems membrane & bending stresses always exist in pressure parts of a rectangular pressure vessel. Since sometimes 1.5S is greater than yield stress(Sy), I want to know if any plastic deformation (though very small) occurs in pressure parts?

For example for SA240-316L allowable stress is 115.1 Mpa $ Sy is 143Mpa. In the other hand 1.5S is 172.7 which is grater than 115.1 Mpa.

Thanks
Arash