Backing Rings for Fiberglass Pipe Flanges?

[brazilianjj]

At one time, backing rings were recommended for frp pipe flanges.

Large frp manufacturers such as Ameron and Fibercast have told me that backing rings are not necessary because of the better quality in flange production.

Can provide me with the reason why they are not used anymore? Also, I'm curious why the backing rings were recommended in the past? Were there problems with failure in the flanges, etc.???

Thanks

 

[gwn]

I assume you're talking about full face fiberglass pipe flanges. Steel backing rings on these have not been common for many years. Two things to look out for..
1) You can get cracking in the fillet radius on back of flange. It's often cosmetic and not a structural concern.
2) Check mating flange faces for flatness. Over-tightening flange bolts to stop a leak can fracture the flange. I suspect that backing rings were used to try to seal a flange that was too light or not flat.
Choose a good FRP fabricator.

 

Steel backup rings are recommended for FRP flanges when you are using a gasket not recommended by the FRP flange manufacturer when the gasket you are using requires higher bolt torques to seal the gasket than the recommended FRP bolt torques of the manufacturer. You must use the recommended FRP manufacturers bolt torques or risk breaking the flange.

 

[Endoyeti]

Backing rings are specified and used for the following reasons;
1) Improves installation time to compensate for poor alignment of valves etc. Especially when retrofitting into metallic pipelines.
2) Is usually cheaper than full face flanges especially when dealing with 400NB and above even more so at 16bar+
3) It negates bending effects especially when connecting to raised face flanges.

I would like to think that poor manufacturing techniques have been irradicated, but there are better and more cost effective jointing techniques for pipe-pipe connections and that stub flanges with backing rings should typically be used for those installations where drilling detail is subject to change or alignment can be less than ideal.