Dear All,

I am working on calculation of Rpad thickness using Roarks equation.

These are the terms in that equations.

1. Hoop stress due to pressure, σhp - General Primary membrane stress, Pm

2. Circumferential membrane stress, σ2 - Local Primary membrane stress, PL

3. Circumferential Bending stress, σ ́2 - Secondary stress, Q

According to ASME Section VIII Div-2. Pm + PL + Q = 3 Smavg

Based on ASME B 31.3 for sustained allowable is only Sh. In sustained we are considering Due to pressure, Due to axial and Due to Bending then Why in ASME 31.3 has less allowable compared with SECTION VIII –DIV 2??

Please correct if I am wrong.