Flange Types
Raised Face Flanges
The most common flange facing for industrial piping applications.
Raised face (RF) flanges are the most common flange facing type used in industrial piping. The raised face is a circular area on the flange face that is machined to a height of 1/16" above the bolt circle for Class 150 and 300, and 1/4" for Class 400 and above. This raised surface concentrates the bolt load onto a smaller gasket area, producing higher gasket seating stress for a better seal.
The face finish on raised face flanges is typically a concentric serrated pattern with a surface roughness of 125 to 250 microinch Ra (AARH). This roughness profile provides the necessary "bite" for soft gasket materials like spiral wound (with graphite or PTFE filler) and compressed non-asbestos sheet gaskets. Smoother finishes may be specified for special gasket types.
Raised face flanges are the default facing for ASME B16.5 flanges in Classes 150 through 2500 when mating with other steel flanges. They should not be used when connecting to cast iron (ASME B16.1) flanges, which require a flat face to prevent cracking the brittle cast iron. Flanges.IO stocks raised face flanges in all standard sizes, classes, and materials. Contact us for inventory availability.
