Design Specification

Class

Comments

ASME B16.1 – Cast Iron Pipe Flanges and Flanged Fittings

25, 125, 250

This covers pressure-temperature ratings, materials, dimensions,
and tolerances for Iron flanges and valves. 125 is the most common followed
by 250 and 25 respectively.

ASME B16.5 Pipe Flanges and Flanged Fittings

150, 300, 400, 600, 900, 1500, 2500

This covers pressure-temperature ratings, materials, dimensions,
and tolerances for pipe flanges and valves with flange diameters ≤24”.
The most common is 150 and generally decreases as the class number increases.

ASME B16.47 – Large Diameter Steel Flanges: NPS 26 through NPS
60

75, 150, 300, 400, 600, 900

This covers pressure-temperature ratings, materials, dimensions,
and tolerances for pipe flanges in sizes 26” to 60”. There are two different
designs covered and they are not interchangeable. Series A which is the old
MSS SP-44 and Series B which is the old API 605. Series A is more common.

ASME/ANSI B16.36 – Orifice Flanges

300, 400, 600, 900, 1500, 2500

This covers dimensions, and tolerances for orifice pipe flanges.
This specification refers to B16.5 for materials and pressure-temperature
ratings.