ASME B16.5 is the American standard for pipe flanges and flanged fittings from NPS ½" to NPS 24". It sets pressure–temperature ratings, materials, dimensions, tolerances, facings, marking and testing for seven pressure classes, from Class 150 to Class 2500, and it is the flange standard most often named in process-plant and pipeline specifications around the world.
Raaj Fittings manufactures ASME B16.5 flanges in every common type and in stainless steel, duplex, nickel alloy, carbon and alloy steel, at our two plants in India. Flanges are made and marked to B16.5 and the material specification, and shipped with EN 10204 3.1 certificates to buyers across the Middle East, Europe and the Americas. Larger sizes, from 26" to 60", are covered by ASME B16.47.
The class number is not a pressure in psi. Each class has a pressure–temperature rating that depends on the flange material group and falls as the temperature rises. B16.5 sorts materials into groups: Group 1 for carbon and low-alloy steels, Group 2 for austenitic and duplex stainless steels, and Group 3 for nickel alloys. For example, A105 carbon steel is in Group 1.1, F316 in Group 2.2 and F316L in Group 2.3.
As a guide, the maximum working pressures for Material Group 1.1 (such as A105) at −29 °C to 38 °C are:
| Class | bar | psig |
|---|---|---|
| 150 | 19.6 | 285 |
| 300 | 51.1 | 740 |
| 400 | 68.1 | 990 |
| 600 | 102.1 | 1480 |
| 900 | 153.2 | 2220 |
| 1500 | 255.3 | 3705 |
| 2500 | 425.5 | 6170 |
For each size and class, B16.5 fixes the flange outside diameter, thickness, bolt-circle diameter, number and diameter of bolt holes, hub dimensions and bore, together with tolerances for each. Bolt holes are always in multiples of four and straddle the centrelines. Because these dimensions are fixed, any two B16.5 flanges of the same size and class bolt together, whatever their type or maker. Weld neck flanges are bored to match the pipe schedule and bevelled for welding to ASME B16.25.
Each B16.5 flange is marked with the manufacturer's name or mark, the material grade, the pressure class, the B16 designation, the size and, where required, the heat number and the ring groove number for RTJ flanges. The material must meet its ASTM specification. B16.5 requires a hydrostatic shell test for flanged fittings; flanges themselves are tested only where the purchase order asks for it. Our flanges are supplied with EN 10204 3.1 mill test certificates, with 3.2 certification and third-party inspection by the buyer's nominated agency on request.
| Standard | Covers | Interchangeable with B16.5? |
|---|---|---|
| ASME B16.47 Series A / B | NPS 26" to 60", Class 75 to 900 | Takes over above 24". Series A (MSS SP-44) and Series B (API 605) are not interchangeable with each other. |
| ASME B16.36 | Orifice flanges with pressure taps, Class 300 and above | Based on B16.5 weld neck, slip on and threaded flange dimensions. |
| EN 1092-1 | European flanges designated by PN | No. Bolt circles and drillings differ for most sizes. |
| JIS B2220 | Japanese flanges designated by K rating | No. |
ASME B16.5 covers pipe flanges and flanged fittings from NPS ½" to NPS 24" in Classes 150 to 1500, and up to NPS 12" in Class 2500. Flanges from NPS 26" to 60" are covered by ASME B16.47 Series A and Series B.
The class is a pressure rating designation, not a pressure in psi. Each class has a pressure–temperature rating that depends on the flange material group and falls as temperature rises; the values are tabulated in ASME B16.5.
Generally no. EN 1092-1 flanges are designated by PN and have different outside diameters, bolt circles and bolt holes for most sizes, so they do not bolt to B16.5 flanges. Match the flange standard to the mating equipment.
The raised face is 1.6 mm (0.06") high for Class 150 and 300 flanges and 6.4 mm (0.25") for Class 400 and above. Check how the flange thickness is quoted for each class when comparing drawings.
B16.5 requires a hydrostatic shell test for flanged fittings, not for flanges. Flanges can be hydrostatically tested when the purchase order or project specification requires it.