*Flanges are often rated according to a system of “pressure classes” defined in the ANSI (American National Standards Institute) standard -These pressure classes are designated by numerical values followed by “pound”, “lb”, or “#”. -Common ANSI ratings include the 150#, 300#, 400#, 600#, 900#, 1500#, and 2500# pressure classes. -It should be noted that these class numbers do not refer directly to pressure ratings in units of PSI, but that they do scale with pressure (i.e. a 600# flange will have a greater pressure rating than a 300# flange, all other factors being equal). -Pressure ratings not only vary with the “class” of the flange, but also with operating temperature, as metals tend to weaken at elevated temperature. *Originally, the ANSI class designations were based on the ratings of these flanges in steam line service. A 250# flange, for instance, was rated such because it was designed to be used in piping service where the fluid was steam at 250 PSI (and 400 degrees Fahrenheit). -EBAA Iron Sales, Inc published a two-page report in 1994 summarizing the history of flange “pound” ratings, from the ASME/ANSI B16 standards.
Posted on: Tue, 15 Oct 2013 08:07:43 +0000