The raised ring is 1/16 inch high on Class 150 and 300 flanges and 1/4 inch on Class 600 and above, with a spiral serrated finish that grips the gasket. Concentrating bolt load on that narrow ring seals better than a full flat face. Raised face is the default in process piping; flat face is used on cast iron, ductile iron and fiberglass flanges, and an RF steel flange bolted hard to a flat-face cast iron flange can crack it.
Pump's got a flat-face cast iron nozzle, machine the raised face off the mating flange and use a full-face gasket.
Also heard as
- RF
- RF flange
Do not mix it up with
- RTJ: A raised face uses a flat gasket on a serrated surface; an RTJ face has a machined groove holding a solid metal ring.
Related terms
RTJ
Ring type joint: a flange face with a machined groove that holds a solid metal ring gasket for high pressure.
Spiral wound gasket
A flange gasket made of a V-shaped metal strip wound with a soft filler, held between an outer ring and usually an inner ring.
Pressure class
The standardized rating step, such as 150, 300 or 600, that sets a valve or flange's allowable pressure at each temperature.
Two-holing
Orienting a flange so two bolt holes straddle the top centerline instead of one hole sitting dead on top.