Peening Compression Limiting Rings to Stop Flange Leaks

[Bambie]

In my plant, a number of 900# 4"nps blind flanges have 30 year old spiral wound asbestos filled gaskets with outer compression limiting rings that are beginning to leak.
The process can be de-pressurized but not drained, so the following proposal is presented for comment.

1) remove a single stud
2) mill out the compression limiting ring between the two adjacent studs and flush to the raised face
3) replace the stud and torque
4) repeat until all studs are replaced, torqued and excess compression limiting ring is removed
5) peen the remnant (.158" wide x .125" thick) compression limiting ring face 360 degrees
6) check torques on all studs and adjust if necessary

Could this be successful?

 

[MikeHalloran]

That sounds like a lot of work for an uncertain result.

How about mocking up a similar joint with new parts, and see if you can make the proposed process work even once? Or, better, ten times?





Mike Halloran
Pembroke Pines, FL, USA

 

[Bambie]

Mike, I agree, a mock-up is needed - perhaps someone out there has tried this before.

I have spoken with several pipeline leak specialty company representatives and they endorse the idea but indicate that sealant injection with tongue clamps or wire dams retained by peening the flange edges is a proven solution - so why bother.

 

[MikeHalloran]

If you're not prepared to just outsource the work to the specialists you contacted, then it doesn't matter what someone else has done; you have to come up with a process that _your_ crew of peen-nuts can accomplish reliably and safely.



Mike Halloran
Pembroke Pines, FL, USA

 

[Bambie]

Mike,

Engineering must demonstrate that the risks to safety are acceptably small and the confidence of success is high.

At our plant, installing a leak mitigating device is a very temporary modification to the pressure boundary that would have to be removed before the process can be drained - we need a 'permanent' repair until that time.

Torques have been increased to 70% yield and it is likely that the .175" thick asbestos gasket has lost its resilience and is now .125" thick with the result that further torque will cause the flanges to rotate around the compression limiting ring, dishing the flanges and off-load the gasket.

Peening has acquired a bad reputation in some parts of industry but that should not detract from it's usefulness.

 

[rconner]

While I have no experience with repairing asbestos gasketed joints (and certainly not machining in the area of same with such high pressure flanges etc.); however, I was just curious if there is any chance to some how "encapsulating" the leaking flanged joints? [I have heard of devices made, basically to totally encircle variously leaking flanged process joints.]

 

[Bambie]

rconner,

Yes, leak mitigation devices include sealant injected tongue clamps that fit between flanges and enclosures that surround the flanges and can prevent flange joint separation if the stud condition is in doubt.

The beauty of compression limiting ring removal and peening the remnant is that stud stresses can be immediately confirmed by checking torques and then reducing (if necessary) before the flanged joint is re-pressurized.

The problem with enclosures and tongue clamps is that the system pressure can move outside the registered pressure boundary (which is inside the gasket) and increase stud and flange stresses.