Flange Rating

I don't know the best reference to tell you for this. Roughly speaking, "Class 150" corresponds to a pressure of 150 psi (not to a force of 150 lb). However, this rating must be adjusted by temperature conditions (and possibly some other criteria). For example, a Class 150 valve might be suited for 150 psi at temperatures up to say 300°C, some lesser pressure up to 600°C, etc. This is just a "toy" example, and there are charts and other data that explain these adjustments. Lower temperatures can allow higher pressure ratings, down to the point that brittle fracture comes into play. There are no "one size fits all" formulas for this.

ASNI ANSI Class 150.

It is not Lbs pressure or force. Once upon a time it used to be Lbs pressure (ie PSI) but the times have changed when designers realised that the strength of materials are highly dependant on temperature.

So Now it is called rating and has different rated pressure for different temperatures.

Best source is the ANSI standard itself B16 series has different fittings including flanges. Say ANSI 16.5 or 16.47

If you google "ANSI Flange rating" you will have several hits on this subject eg this

www.gaumer.com/Resources/RefANSITempR.pdf

http://www.ebaa.com/PDF/Connections.FL-01.pdf

Wiki too will have its article on it

First, forget the "150"....it is both unfortunate and rerehensible that the esteemed ASME/ANSI organization continues to use this confusing misnomer. Many piping newbies are confused by this

The "150" really has little to do with the actual flange pressure ratings.

It would be better if a flange constructed to this particukat group of pressure/temperature limitations were called a "Class Alpha - Group I" flange....or something similar.

Higher rated flanges could be "Beta", "Gamma" etc...etc