To:
Subject: The Meaning of "RF",
"SPWD", and "RTJ"
Question:
Can you describe the difference between an RF flange
and an RTJ flange? What type of gasket do the different flanges require? What does SPWD
mean when referring to a gasket?
Answer:
RF means "Raised Face."
SPWD means "Spiral Wound."
(Referring to a gasket for RF flanges)
RTJ means "Ring Type Joint."
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 for reinforcement.
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 compressed gasket will not bear additional load beyond the
bolt tension, vibration and movement cannot further crush the gasket and
lessen the connecting tension.
To see a more complete explanation for why flanges
that seal with BX gaskets have raised faces,
Click Here: Q & A 42, When and Why Have Raised Faces on API Flanges?
To find good information about RTJ
flanges, with illustrations, click here:
Flange Make-up, Stand-off and Drift
For extensive information about ring gaskets, click
here:
Q & A 21 Ring Gasket Evaluation.
Follow the links at the bottom of the page.
To identify API Spec 6A flanges and determine the
correct ring gasket to use with any API Spec 6A flange click here:
Flange Slide Rule.
