RAISED FACE (RF) FLANGE
RF flanges seal with a flat gasket, formerly made of asbestos but now made of more environmentally friendly material, designed for installation between the raised faces of two mating flanges (both with raised faces). The raised faces have a prescribed texture to increase their gripping and retaining force on this flat gasket. Some users of raised face flanges specify the use of spiral wound gaskets. These gaskets may often have an inner ring on their I.D. and an outer disc around their O.D. This feature will hold the gasket concentric with the bolt circle and bore to make precise assembly easier with the gasket centered on the flange sealing surfaces. See an explanation of Spiral Wound Gaskets below
SPIRAL WOUND (SPWD) GASKET
SPWD identifies a flat gasket used between two RF flanges (without ring grooves). SPWD gaskets contain a "spiral wound" metallic filler forreinforcement.
RING TYPE JOINT (RTJ) FLANGE
RTJ flanges have grooves cut into their faces which accept steel Ring Gaskets. RTJ flanges seal when tightened bolts compress the gasket between the flanges into the grooves, deforming (or "Coining") the gasket to make Intimate Contact inside the grooves, creating a metal to metal seal.
An RTJ flange may have a raised face with a ring groove machined into it. This raised face does not serve as any part of the sealing means. For RTJ flanges that seal with BX ring gaskets, the raised faces of the connected and tightened flanges may contact each other. In this case the already coined gasket will not bear additional load beyond the bolt tension, vibration and movement cannot further crush the gasket and lessen the connecting tension.
