Raised face (RF) flanges have a gasket surface raised above the bolting circle face. Concentrating the bolt load on the smaller raised area increases the gasket stress and makes a reliable seal, which is why raised face is the most widely used flange facing in process, utility, refinery and power piping.
Raaj Fittings manufactures RF flanges in every type and material, to ASME B16.5, B16.47, EN 1092-1 (facing type B), DIN, BS and JIS standards, at our two plants in India.
| Standard / class | Raised face height |
|---|---|
| ASME B16.5 Class 150 and 300 | 1.6 mm (0.06") |
| ASME B16.5 Class 400 to 2500 | 6.4 mm (0.25") |
| EN 1092-1 (type B) | Varies with size, typically 2 to 5 mm |
In ASME B16.5, the published flange thickness of Class 150 and 300 flanges includes the 1.6 mm raised face; for Class 400 and above, the 6.4 mm raised face is in addition to the published thickness. Check this when comparing drawings or calculating face-to-face dimensions.
RF gasket surfaces are machined with a concentric or spiral serrated finish, typically 3.2 to 6.3 µm Ra (125 to 250 µin). The serrations grip spiral wound and soft gaskets and prevent them blowing out. Smoother finishes are specified for some metallic gaskets; radial scratches across the face must be avoided because they create leak paths.
Every RF 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.
ASME B16.5 Class 150 and 300 flanges have a 1.6 mm (0.06") raised face; Class 400 and higher have 6.4 mm (0.25").
It is not recommended, especially against cast iron or plastic flanges, because tightening the bolts bends the flat-face flange around the raised face and can crack it. Use flat face flanges on both sides.
A serrated concentric or spiral finish, typically 3.2 to 6.3 µm Ra (125 to 250 µin), suits spiral wound and soft gaskets.
Concentrating the bolt load on a smaller gasket area gives a reliable seal with a wide range of gaskets, at a lower cost than RTJ or confined facings.