What is Flange Face and Finish?
The “Flange Face” refers to the mating surface of a flange that comes into contact with another flange during the assembly of a pipeline or other system. The flange face must be smooth, flat, and parallel to ensure a proper seal between the two flanges, and prevent leakage of the fluid or gas being transported. The type of flange face used depends on the application, pressure, and temperature of the fluid or gas being transported.
The most common types of flange faces are:
Flat Face (FF) – a smooth, flat surface that provides a broad contact area for the flange to seal against.
Raised Face (RF) – a flat surface with a raised ring around the perimeter that compresses against the gasket when the flanges are bolted together, creating a tight seal.
Ring Joint (RTJ) – a special type of flange face with a groove machined into the surface to hold a metal ring gasket that seals against the flange face of the mating flange.
The “Flange Finish” refers to the surface roughness of the flange face, which affects the ability of the gasket to seal against the flange. The finish is typically measured in units of Ra (roughness average) or RMS (root mean square) and is specified in the flange standards. A smoother finish generally provides a better seal, but can also increase the risk of gasket damage during installation. The flange finish is often specified in conjunction with the gasket type and material to ensure a reliable seal.