What's behind ANSI B16.5 Class Ratings
What's behind ANSI B16.5 Class Ratings
(OP)
I've always been curious into what's behind an ANSI B16.5 flange pressure rating and the "class" that it's normally referred to. For example, and CL600, or 600#, flange actually is rated for about 1,440 PSI in typical materials and services. Where did the 600# come from?
Thanks
Thanks





RE: What's behind ANSI B16.5 Class Ratings
You have overlooked the fact that all material (and pressure) -test in ASME code are done at high temperature (temperature where material yields without additional force). Other values at lower temperature are derived from these high temperature results .( Thus the basis of ASME are these high tmeperature values.) This temperature-point is for standard Fe materials 800-850 °F.
Look at this in mind at the pressure temperature ratings in B16.5 for materialgroup 1.1, 1.2, 1.3, 1.4,...
For example 600# ==> you will see that for 850°F the pressure is +/- 600 psi (600#). The same counts for all tables. (This high temperature point is for every material different!)
The only exception is the 150# class. The reason for this is for me still a misery.
RE: What's behind ANSI B16.5 Class Ratings
Today, the gap is closing/not as great.
Don't know if that is the original reason, but it may be one reason why people specify 150#.
RE: What's behind ANSI B16.5 Class Ratings
RE: What's behind ANSI B16.5 Class Ratings
I am not sure what xcrosby meant by "As materials improved the actual pressure ratings increased but the class designation remained.".
ANSI flange tables have a whole host of materials, and temperature/pressure relationships. Different materials, of course have different temperature/pressure relationships - not so much better/worse, just different.
Also keep in mind, the ANSI flange tables by class has taken into account that different pressure class flanges are constructed differently (eg 300# flanges are much more stout, have more material, than 150# flanges, and different bolting patterns too).
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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RE: What's behind ANSI B16.5 Class Ratings
"... comments from users and changes in the ASME Boiler and Pressure Vessel Code led to significant revisions in the Class 150 rating basis, and, in the ratings of stainless steel and certain alloy steel flanges and flanged fittings in all rating classes. Extensive public review comments led to addition of considerations for flanged joints, for bolting and gaskets, and of marking requirements. To avoid
frequent and confusing changes in ratings as further changes in Code allowable stresses are made, it was agreed with Subcommittee N to leave ratings alone unless the relevant Code stress values are changed by more than 10%."
RE: What's behind ANSI B16.5 Class Ratings
As to how the original classes were chosen... I also believe that it goes back to steam pressures/temperatures.
jt