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

The article beginning on page 6 of this Newsletter should answer your questions.

Thanks Richard, the article has been very useful. But nothing is written about allowable stress for ANSI B31.3. Do you know anything about it? How can I justify an increase in allowable using ANSI B31.3?

Regards

I'd like to know your opinion about allowable stress when you verify flanges with operating moment and axial loads (SUS + EXP + Pressure) using ANSI B31.3.

Thanks

Regards

Flange stress analysis is covered (in the US) by the ASME BPVC. Trust me, you don't really want to go there.

what do you mean by this, Craig?

The calculations are very time-consuming, and you are highly unlikely to find an overstress within the flange unless the piping is badly overstressed locally.

We just assume, in piping, that the flanges will leak before breaking. So, we do a leakage check - if it passes we are OK. This assumption is validated by many years of operating experience with many millions of flange pairs - the flanges themselves normally do not fail.

So, in your opinion, should it be enough to check only leakage and not mechanical load from piping?

Do you know an answer about allowable stress to use when you verify flanges with operating moment and axial loads (SUS + EXP + Pressure) using ANSI B31.3?

Thanks

Can some of you advise me about what written above?

Thanks
Regards

Other than referencing flanges as listed components for pressure classification, B31.3 provides little input on flange load limits. B31.3 allows "more rigorous analysis" and evaluating flange stresses in accordance with ASME Section VIII Division 1 Appendix 2 (or equivalent) may be useful. Leakage is best addressed through material selection and bolt tightening. If you want to do more analysis, try FEA methods.

Thanks Richard, but when I verify flange according to ASME Section VII Div.1 Appendix 2 I'd like to know if I can use an higher allowable stress when I have to verify operating axial force and moment (SUS + EXP + Pressure) applied to the flange

According to me using 1.0 Sf (where Sf is allowable stress at
design temperature)to compare SR (radial flange stress),ST (tangential flange stress), (SH+SR)/2 with operating condition loads(SUS + EXP + Pressure) is too restrictive.

Infact 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 anything is written about allowable stress when operating (SUS + EXP + Pressure) loads are applied to flange.

For example B31.1 allow to increase allowable up to 1.5 Sf for longitudinal hub, tangential and radial stress as stated in 4.2.3.

When I use B31.3 and I have to verify a flange, is it allowed to increase allowable stress stated by ASME Section VII Div.1 Appendix 2? If yes, what is the limit?

I hope I have made myself clear about my doubt.

Thanks

Regards

I can't give you a "yes" or "no" answer to this one. This is between you, the owner, and the inspector. This subject (which allowable to use) was discussed in the Newsletter article I mentioned above.

Link is dead, please advise. Thank you!

Unfortunately the COADE newsletters have not been transitioned to the new Hexagon website. You will have to file a Support Request on Smart Support and ask for this newsletter.