Common Sense of Flange Rating

There are three types of American-standard flanges most commonly applied in pipeline industry: ASME B16.5 flanges,ASME B16.47 Series A and Series B flanges.

In all these standards, flanges are grouped in classes by pressure ratings according to there design pressure. Generally speaking, there are 7 classes: Class 150, Class 300, Class 400, Class 600, Class 900, Class 1500, Class 2500. In common practice, people speak for example of "a 300 pound flange" instead of "a class 300 flange". This is just a non-standard customary nomenclature. However, you must keep in mind that a class 300 flange doesn't mean that the flange rated pressure is 300 psi. The formula is:

PT = Pr ST / 8750

PT = rated working pressure for the specified material at temperature T, psi

Pr = pressure rating class index

ST =flange material allowable stress at temperature T, psi

As a rule of thumb, at ambient temperature, the maximum operating pressure of a carbon steel flange of class X is approximately 2.4X. This rule works particularly well for class 300 and heavier ratings. For example, a class 300 carbon steel flange will have a design pressure of 2.4 x 300 = 720 psi at ambient temperature.

Views: Author：hbmetals Date:15/05/20