What is a pressure class?
A pressure class is a designation given to a group of similarly designed components that have the same pressure rating.
In other words, a 2” 150 A105 blind flange will have the same pressure/temperature limits as a 24” 150 blind flange. It is important to note the pressure/temperature limits are dictated by the combination of the material grade and design specification. The design specification will state the allowable pressures at a given temperature for each material. This is referred to as the pressure/temperature chart.
It is also important to note that not all the pressure-temperature ratings will be the same from different specifications. So a class 150 flange will not have the same pressure-temperature rating as a class 150 malleable iron.
The following is a partial list of design specifications with their pressure classes.
|
Design Specification |
Class |
Comments |
|
ASME B16.1 – Cast Iron Pipe Flanges and Flanged Fittings |
25, 125, 250 |
This covers pressure-temperature ratings, materials, dimensions, |
|
ASME B16.5 Pipe Flanges and Flanged Fittings |
150, 300, 400, 600, 900, 1500, 2500 |
This covers pressure-temperature ratings, materials, dimensions, |
|
ASME B16.47 – Large Diameter Steel Flanges: NPS 26 through NPS |
75, 150, 300, 400, 600, 900 |
This covers pressure-temperature ratings, materials, dimensions, |
|
ASME/ANSI B16.36 – Orifice Flanges |
300, 400, 600, 900, 1500, 2500 |
This covers dimensions, and tolerances for orifice pipe flanges. |
|
ASME B16.11 – Forged Steel Fittings, Socket-Welding and Threaded |
2000, 3000, 6000, 9000 (AKA 2M, 3M, 6M, 9M) |
This covers ratings, materials, dimensions, and tolerances for forged |