Gasket cupping question
Gasket cupping question
(OP)
Hi,
This is my first post here at eng-tips.com, so if I have missed any information that you need to help me, please ask and I will do my best to find answers.
We are in the midst of commissioning a new facility and as part of the hydrotest walkdown team we have encountered numerous cases of "gasket cupping" or "radial buckling" of gaskets.
Our primary concern is figuring out whether or not this buckling is acceptable. Beyond that, we are trying to understand what is causing the buckling; is it a result of 1)improper torquing 2)misalignment of the flange faces, 3)incorrect gaskets, 4) incorrect installation etc etc.
Please see the attached pictures and provide any input you may have. Again, if you require additional information regarding the specs we are following and that sort of stuff, please ask and I will post that information.
This is my first post here at eng-tips.com, so if I have missed any information that you need to help me, please ask and I will do my best to find answers.
We are in the midst of commissioning a new facility and as part of the hydrotest walkdown team we have encountered numerous cases of "gasket cupping" or "radial buckling" of gaskets.
Our primary concern is figuring out whether or not this buckling is acceptable. Beyond that, we are trying to understand what is causing the buckling; is it a result of 1)improper torquing 2)misalignment of the flange faces, 3)incorrect gaskets, 4) incorrect installation etc etc.
Please see the attached pictures and provide any input you may have. Again, if you require additional information regarding the specs we are following and that sort of stuff, please ask and I will post that information.





RE: Gasket cupping question
RE: Gasket cupping question
Do the joints leak? Did they pass hydrotest? That's the only real criteria for a gasket.
Radial buckling? Are the gaskets deflecting radially? I see axial displacements, but your photos don't show radial displacements.
Why does it happen? You are compressing a ring axially, the rubber has got to go somewhere, so it squeezes out of the joint radially. The gasket has a lot of stiffness radially, but very little axially, so it deforms (squirms or buckles) by axial displacements. The "free" or unconstrained rubber outside the seal faces does nothing for the job of of the gasket, which is to seal between the contact faces. You could cut the free rubber away and the joints will still seal; the gasket will stay put (if properly torqued) by friction forces alone.
RE: Gasket cupping question
Much appreciate your response.
To quickly answer your first two questions, of all the joints that have been tested, everything is ok. The untested joints, joints that were used as test limits during hydrotesting, have yet to be tested and we will have to wait until startup.
You are correct, we are not experiencing any radial buckling just axial deflection. My mistake.
Thanks for the input! Much appreciated
RE: Gasket cupping question
This problem got so bad at on time we actually had our sheet metal shop set up to notch out for the studs.
RE: Gasket cupping question
Very good point and I believe that suggestion was brought forward. I will take a closer look tomorrow myself to see if that is contributing to our problems.
Also, you mentioned that you had your sheet metal shop set up to notch out the studs. Was this a result of a request from the client or were you just tried of dealing with the oversized gaskets.
RE: Gasket cupping question
This problem doesn't normally affect the sealing ability of the spirals as in some applications we don't have the outer ring. With the proper flange a spiral wound gasket is more forgiving than one would think.
RE: Gasket cupping question
Johnny Pellin
RE: Gasket cupping question
While I will not profess to be an expert in all types of proprietary flange gaskets and applications/installations, if it is just rubber I would think some degree of outward extrusion might be normal as others have stated, and I think the degree to which this extrusion occurs around a joint could be influenced by many factors, including but perhaps not limited to the following:
Specific proprietary or type of gasket (sheet or molded "rubber" of some type and hardness, is it "reinforced" or not, and if so with what and where is the reinforcement placed oriented on the area of the gasket etc.?)
The nature and mating orientation of the both flange and gasket contact faces (are they basically flat, smooth, serrated, and has any kind of lubricant been applied in assembly by the contractor etc. – if the gaskets are basically just rubber, I in general kind of like "clean and dry" assembly myself, though you might find many differences of opinion here among at least mechanics?)
The effective bolting force level, and uniformity, of bolt tightening accomplished by the installer (if the extrusion is reasonably uniform around the joint, one would be suspicious of at least uniform tightening!)
Presence of extreme beam load on the piping (e.g. due to settlement or transverse movement/deformations of the piping system under pressure?)
I hope you can tell by the nature of my questions the kind of conditions (perhaps among others?) that might influence the degree and location of outward gasket extrusion.
RE: Gasket cupping question
I just wanted to acknowledge your replies and let you know that I am tracking down as many answers to your questions as I can and will post later.
RE: Gasket cupping question
- 1/8" thick
- 316SS windings w/ flex graphite filler
- Carbon steel outer ring