Flange Size Chart, Pressure Classes & Standards

ASME B16.5 Class 150 flange dimensions

Millimetre values are converted from the inch dimensions in ASME B16.5. Flange thickness and hub dimensions differ by flange type, so they are not listed here. Ask us for the dimension sheet of the exact type you are buying.

ASME B16.5 Class 300 flange dimensions

Class 300 flanges are larger and heavier than Class 150 of the same size, with a bigger PCD and often more bolts, so the two classes never bolt together.

Pressure class is not the pressure

A Class 150 flange is not limited to 150 psi. The class is a rating step, and the allowed working pressure depends on the material group and the temperature. For carbon steel ASTM A105 (material group 1.1) between −29 °C and 38 °C:

As temperature rises, the allowed pressure falls, and stainless and alloy grades have their own tables. Always check the ASME B16.5 rating for your material at your design temperature.

Table E, IS 6392 and PN flanges

• BS 10 Table D, E, F, H: drilling tables from an old British standard. BS 10 has been withdrawn, but Table E is still the most common MS flange in Indian trade. The letters go up with pressure: D is the lightest and H the heaviest.
• IS 6392: the Indian Standard for steel pipe flanges, rated by nominal pressure (PN). Often specified on Indian infrastructure and government work.
• EN 1092-1 PN 6, 10, 16, 25, 40: the European system, where PN is the nominal pressure in bar at reference temperature. PN drilling is metric and is generally not interchangeable with ASME classes.

If you are not sure which system an old flange follows, measure the OD and PCD, count the holes and measure one hole. Those four numbers identify it. See MS flanges and plate flanges for the Indian-trade drillings.

Flange faces: RF, FF and RTJ

• Raised face (RF): a raised ring around the bore that concentrates gasket pressure. Standard on ASME steel flanges.
• Flat face (FF): the whole face is flat. Used against cast iron, FRP and plate flanges, where a raised face could crack the mating flange.
• Ring type joint (RTJ): a machined groove holding a metal ring gasket, for high pressure and temperature.

Bolt a raised-face flange to another raised-face flange, and a flat-face flange to a flat-face flange.

How to write a flange enquiry

Give six things and you will get an accurate quotation the first time:

1. Type: weld neck, slip-on, blind, socket weld, threaded, lap joint or plate
2. Size: NPS or NB, plus pipe OD for slip-on and socket weld
3. Standard and class or table: for example ASME B16.5 Class 300, or Table E
4. Pipe schedule, for weld neck and socket weld bores
5. Material grade and facing: for example A105 RF, or F316L RF
6. Quantity and delivery location

Example: 4" WNRF, ASME B16.5 Class 300, A105, bore Sch 40, 20 nos, delivery Pune.