Pressure rating of ANSI 150 304 system at 120degC

[scorer]

Dear All

I hope that one of the materials experts may be able to help me.

One of our piping specifications uses 304 StStl ANSI 150 flanges (or more accurately ASME B16.5 A182-F304)
Our spec states that it is rated for 17.0barg pressure at up to 120degC.

My question is how do we get the 17.0barg limitation.

If I look at the flange pressure ratings for 304 in ASME B16.5 then table 2.2.1 gives a pressure rating barg at 100degC and of 14.2barg at 150degC. By interpolating I get 15.1barg at 120degC. Should this be the limit on our piping spec.

Towards the end of B16.5 (annex B) there is the table on ceiling pressures. This suggests 17.7barg at 100degC and 15.8barg at 150degC. By interpolating this becomes 16.94barg at 120degC.

Is this where the 17barg comes from, and is it correct?

Hope someone can help clear this up for me.

Kind regards

Scorer

 

[Duwe6]

It probably is where it came from. However, it is extremely poor engineering practice to have a piping spec that goes all the way to the MAWP of flanges. And if your calc's are correct, 17barg at 120°C is slightly past the 16.94barg MAWP. Engineering-wise and 'go-to-court' legal-wise, that spec is indefensible. Fails to meet "good engineering practices".

 

[LittleInch]

Should 15.1 be your limit - Until you have actually completed the equation in A2-1 for your particular material then yes.

Remember the ceiling value is exactly that - a ceiling / maximum. The appendix A allows you to use particular stress of your material to calculate the MAWP rather than the lowest SMYS of group 2.1.

Without undertaking and filing the calculation in appendix A, you are IMHO on very thin ice... you can't just use the ceiling value without demonstrating that it is actually the ceiling for your particular material at your max temperature.

If there is no practical impact from reducing the design pressure then I would just go to the table 2.2.1. saves everyone a lot of bother.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[scorer]

Dear All

Thanks for the advice.

Kind regards

Scorer