what is pressure class & how is it related to working pressure & rated pressure?

Answer 1

If you are talking about piping pressure classes, the 150# class that Jeffery S talked about is good for different pressures depending on the materials of construction and the design temperature of the system it is being used in.

I don't have the current ANSI ratings for the steel 150# class but it is about 285 psi at 100 degrees and is derated up to about 95 psi at 750 degrees F. Carbon steel (A105) is not recommended for sustained use above 750 degrees or so.

For steel there are other classes such as 300#, 600#, 900#, 1500# and 2500#. There are also classes for cast iron, ductile, some plastics and other materials.

The maximum working pressure is usually considered the same as the design pressure. That pressure is the maximum you should normally operate the system at. The code usually allows some brief pressure excursions above the design pressure.

Answer 2

If your talking about pipe, then pressure class is the rated pressure at which the pipe can safely function at (ie. 150 # pipe has a rated pressure of 150 psi). Your working pressure or the pressure of the process or fluid the pipe carries should be less then the rated pressure.