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Raised face flange to FRP flat face flange.

Raised face flange to FRP flat face flange.

Raised face flange to FRP flat face flange.

How do you guys handle a case where a raised face flange (say a lined valve or lined fitting) has to be connected to an FRP flange, which is flat face.  The gap between the flanges due to the raised face would set up a bending moment that would break the FRP flange, when applying the torque necessary to seal the lined valve or fitting.  Given that it is an issue of the FRP flange, do the FRP manufacturers make any type of support rings or such that allow the installer to use sufficient torque values to seal the lined valve or fitting?

RE: Raised face flange to FRP flat face flange.


The most common fix I have seen is to grind off the raised face...alternately, you can simply replace the flange with a FF version.

Yes, there would be an excessive bending monment, and yes you can break a GRP flange....the "clasic" field installation mistake, however, is connecting a RF (steel) flange to a FF (cast iron) flange on a pump.

The "Piping Handbook" by Nayyar cautions against making this mistake...



RE: Raised face flange to FRP flat face flange.

Grinding off the raised face is not an option when it is a lined component like plastic lined pipe or valves.  These are and must be raised face by definition, since the liner comes out over the flange face and forms a gasket sealing surface.  This insures that all wetted parts of the lined component are lined.

RE: Raised face flange to FRP flat face flange.

They'd have to use with a flat-faced flange, and apply the liner material over the entire face of the flange, to give the same effect as a full-face gasket.

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