Flange facing types: RF, FF, RTJ and more

The face is the part of a flange the gasket sits on. The facing type decides which gasket you use and how high a pressure the joint can seal.

Raised face (RF)

The most common facing. A raised ring concentrates bolt load on a smaller gasket area. ASME B16.5 sets the raised face height at 1.6 mm (1/16 in) for Class 150 and 300, and 6.4 mm (1/4 in) for Class 400 and above. For Class 150 and 300 the 1.6 mm is included in the listed flange thickness; for higher classes it is added on top. Spiral-wound and compressed-fibre gaskets are typical.

Flat face (FF)

The gasket covers the whole face, out to the OD. Required when mating with cast-iron, ductile-iron or FRP flanges and valves, because a raised face could bend and crack a brittle mating flange as bolts are tightened. Use full-face gaskets.

Ring type joint (RTJ)

A machined groove holds a solid metal ring gasket (oval or octagonal, ASME B16.20). The ring is crushed into the groove to form a metal-to-metal seal, so RTJ is used for high pressure and temperature — typically Class 600 and above, and in oil and gas wellhead and hydrocarbon service. The groove hardness must exceed the ring hardness.

Tongue and groove, male and female

Matched pairs where one face fits into the other, trapping the gasket so it cannot blow out. Used on heat exchanger covers, pump covers and some valve bonnets. Both flanges must be ordered as a pair.

Surface finish

RF and FF faces are normally supplied with a concentric or spiral serrated finish of 3.2–6.3 µm Ra (125–250 µin), which grips soft and spiral-wound gaskets. Smoother finishes are specified for metallic gaskets; RTJ grooves need about 1.6 µm Ra or finer. Always check the project specification.

Last updated 2026-11-02