Class 900 flanges to ASME B16.5 are used for high-pressure hydrocarbon, gas injection, boiler feedwater and high-pressure steam service. They are thick, heavy forgings with large-diameter bolting, and in Class 900 most oil and gas specifications call for ring type joint (RTJ) facings, although 6.4 mm raised-face flanges with spiral wound gaskets are also common in steam and process service.
Raaj Fittings forges and machines Class 900 flanges at our two plants in India, in NPS ½" to 24" (ASME B16.5) and 26" to 48" (ASME B16.47), in carbon, low-temperature and chrome-moly steel, stainless steel, duplex and nickel alloys, for EPC contractors and plant owners across the Middle East, Europe and the Americas.
| Material group (example grade) | Max. pressure at −29 to 38 °C |
|---|---|
| 1.1 (ASTM A105) | 153.2 bar (2,220 psig) |
| 2.2 (ASTM A182 F316) | 148.9 bar |
As with every ASME class, the number is a designation, not a pressure: the allowable pressure depends on the material group and the design temperature. Class 900 has exactly 1.5 times the rating of Class 600 for the same material and temperature.
Every Class 900 flange is made from PMI-verified material, dimensionally inspected against the ordered standard and marked with material, size, rating and heat number. Orders are supplied with EN 10204 3.1 certificates; EN 10204 3.2 certification and inspection by the buyer's nominated third-party agency are available on request.
For carbon steel (A105), Class 900 is rated 153.2 bar (2,220 psig) at up to 38 °C, falling as temperature rises. Other materials have different ratings in the ASME B16.5 tables.
Both are used. RTJ is common in oil and gas and wherever metal-to-metal seals are specified; raised face with spiral wound gaskets is common in steam and process service.
Class 900 flanges are covered in NPS ½" to 24" (ASME B16.5) and 26" to 48" (ASME B16.47).
No. Mating flanges must be the same class and size; other classes have different outside diameters, bolt circles and bolting.