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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.

 

 




For engineering details about flange connected pressure joint,
using these gaskets, click here


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.

 

 

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.

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WOODCO USA provides Web Site Tools for identification, estimating, and reference only. Do not use this information for manufacturing or inspection. Users of these tools should not use them as a substitute for professional engineering advice.  Anyone making use of the information presented does so at his own risk and assumes any and all liability resulting from such use.

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www.woodcousa.com
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