I' d like to know if is it possible to use allowable stresses written in ASME B31.3 at para. 304.5.1.b to verify flanges by Caesar II "Flange Leakage/Stress Calculations":

- SUSTAINED LOADS + PRESSURE < Sh (where Sh is allowable stress at
design temperature)

- EXPANSION LOADS < f (1.25 Sc + 0.25 Sh) (where Sc is allowable stress
at minimum metal temperature and Sh is allowable stress at design
temperature).

I ask this because as written in ASME Sect. VIII - Division I App.2 at para 2-1 "These rules provide only for hydrostatic end loads and gasket seating". In these cases I agree to use the allowable stress that Code requires.

But if I want to verify the flange with operating condition loads (SUS + EXP + Pressure) is it correct to use at least 1.5 Sh (where Sh is allowable stress at design temperature) to compare stresses?

According to me using 1.0 Sh to verify operating condition loads(SUS + EXP + Pressure) is too restrictive because moments and axial force due to temperature can be enough high and the analysis seldom will be satisfied.

If I can use an higher allowable stress for pipe (as B.31.3 allows) and generally pipe is weaker than a rigid element like a flange why can't I use a higher allowable?

Thanks

Regards