Class 150 flanges are the lightest pressure class in ASME B16.5 (NPS ½" to 24") and ASME B16.47 (NPS 26" to 60"). They are used on the largest share of all piping by length: cooling and firewater, utilities, tank connections, low-pressure process lines and the many systems where pressure stays below about 20 bar. Class 150 flanges are thinner and lighter than higher classes and use fewer, smaller bolts, which makes them the most economical flanged joint.
Raaj Fittings manufactures Class 150 flanges in every type, from ½" to 60", in stainless steel, duplex, nickel alloys, carbon, low-temperature and alloy steel at our two plants in India, for EPC contractors, fabricators and stockists across the Middle East, Europe and the Americas.
The class is not a pressure in psi: each class has a pressure–temperature rating that depends on the material group and falls as temperature rises.
| Material group (example grade) | −29 to 38 °C | 200 °C | 400 °C |
|---|---|---|---|
| 1.1 (ASTM A105) | 19.6 | 13.8 | 6.5 |
| 2.2 (ASTM A182 F316) | 19.0 | — | — |
| 2.3 (ASTM A182 F316L) | 15.9 | — | — |
At 38 °C, a Class 150 carbon steel flange is rated 19.6 bar (285 psig), but at 400 °C only about a third of that. Above roughly 200 °C the rating drops quickly, so a hot system that looks "low pressure" may still need Class 300.
| NPS | Flange OD, mm | Bolts | Bolt size |
|---|---|---|---|
| 2" | 152.4 | 4 | ⅝" |
| 4" | 228.6 | 8 | ⅝" |
| 6" | 279.4 | 8 | ¾" |
| 8" | 342.9 | 8 | ¾" |
| 12" | 482.6 | 12 | ⅞" |
Class 150 flanges bolt only to other Class 150 flanges of the same size. They do not match Class 300 drilling, and they do not match EN 1092-1 PN 16 flanges in most sizes.
Every heat is PMI-verified and its chemistry and mechanical properties are confirmed against the material specification before the flanges are released. Each piece is marked with grade, size, rating and heat number for traceability to its EN 10204 3.1 mill test certificate. EN 10204 3.2 certification and inspection by the buyer's nominated third-party agency are available on request, as are PED 2014/68/EU compliance for European projects and IBR certification for Indian boiler applications.
It depends on material and temperature. A carbon steel (A105) Class 150 flange is rated 19.6 bar (285 psig) at up to 38 °C, falling to about 13.8 bar at 200 °C. Stainless steel ratings are a little lower at ambient temperature. Use the ASME B16.5 tables for your material.
No. Class 300 flanges of the same size have a larger outside diameter, a larger bolt circle and usually more or larger bolts, so the holes do not line up.
No. They have similar pressure capability at ambient temperature, but EN 1092-1 PN 16 flanges have different dimensions and drilling in most sizes and are not interchangeable with ASME Class 150.
Use flat face flanges with a full-face gasket when mating with cast iron, ductile iron or plastic equipment flanges. A raised face would bend and crack such flanges when the bolts are tightened.