Raised Face Smooth Finish
More than several years ago, the standard finish on raised face flanges was around 500 microinch roughness. Some users and licensers desired a smoother flange finish for services like hydrogen to get a better flange seal when used with spiral wound gaskets. The term RFSF was used to differentiate these smooth face flanges from those with the rougher standard finish. When an RFSF flange is specified, the required finish should also be defined, for example 63-125Ra or 125-250Ra.
In recent editions of ASME B16.5, the standard finish is defined as 125-250 Microinch average. Because the standard finish is now much smoother than before, the RFSF requirements have pretty much been abandoned. You'll find that the smooth finish requirement for flanges and valves in most old piping specifications are equivalent or close to the standard finish for flanges today.
Tags: Pipe Flange Gaskets