Rubber gasket failure
Rubber gasket failure
(OP)
We have had a rubber gasket fail as shown in the photographs. A supplier is suggesting the gasket was misaligned when assembled and bolts were hit through the gasket to form the new holes (hence his photograph). I believe this is impossible. Even the most incompetent fitter would not and could not do this.
The gasket is in a full face to half face joint.
There appears to be a crease in the inside diameter of the gasket. I believe this caused a leak to occur. The resultant flow of water, going from 8.5 bar (g) to 0 bar (g) cavitated and caused the damage to the gasket within 100 hours of operation. The holes in the gasket are where the shoulder of the half face flange is, so will be where there is a high pressure drop in the leaking fluid.
The gasket is PN16 200mm nb.
Does anyone have any experience of this and what the mechanism of failure is likely to be?
Many thanks
The gasket is in a full face to half face joint.
There appears to be a crease in the inside diameter of the gasket. I believe this caused a leak to occur. The resultant flow of water, going from 8.5 bar (g) to 0 bar (g) cavitated and caused the damage to the gasket within 100 hours of operation. The holes in the gasket are where the shoulder of the half face flange is, so will be where there is a high pressure drop in the leaking fluid.
The gasket is PN16 200mm nb.
Does anyone have any experience of this and what the mechanism of failure is likely to be?
Many thanks





RE: Rubber gasket failure
RE: Rubber gasket failure
RE: Rubber gasket failure
BS EN 1092 refers to them as raised face flanges. That is what I need to start referring to them as.
I should have refered to the full face flange as a flat face flange.
RE: Rubber gasket failure
RE: Rubber gasket failure
RE: Rubber gasket failure
I have seen those exact same crease marks on NCAF gaskets on large diameter, low pressure steam piping systems (Usually the exhaust end of a steam turbine). Initially all is well but over a very short time the gasket joint fails.
RE: Rubber gasket failure
The gasket doesn't seem to cover much of the raised face area at all, and if you are going to bolt up a flat face to a raised face flange then you need an adaptor as the flat face flange could be of more brittle material than the raised face and possibly crack when tightened up. Could the flat face flange be thin enough to have bowed as it was tightened up to the raised face, thereby helping the gasket to failure?
RE: Rubber gasket failure
The gasket is the right size for the flange. The second photo shows the supplier demonstrating his hypothesis that the fitters incorrectly fitted the flange by pushing bolts through the rubber rather than through the bolt holes. When the correct bolt holes are used, the flange and gasket look normal. I don't know what the actual fitting the supplier is demonstrating on, it looks like a sharp reducer. It is probably all they had lying around in their workshop.
pch1, a star for you. There is a slight pinch/fold in the gasket near where all the damage happened. I suspected this was the origin of the problems, with the flow of water causing the further damage. It is good to hear somebody else has seen this damage and knows the cause for it in his circumstances.
It is worth noting, this is the bottom flange on a borehole pump rising main, between the pump and the main. It is therefore not possible to pressure test this joint following assembly and the gasket may have been leaking from day 1.
RE: Rubber gasket failure
I agree with everyone about not fixing a flat face to a raised face. Should not be done. I know about the problems with the flat face cracking, but hadn't thought about the bowing.
It's one of the joys of my job, the project managers don't involve the engineers until something goes wrong, then want to know why their projects are not working as they should have.
RE: Rubber gasket failure
I aAm just curious also of how did the leak failure/blow-out?failure actually manifested itself? [Is it possible the gasket for some reason just "blew out" (moved radially outward as if moved outward by pressure from between normal confinement at least in the half flange annular area) -- I ask this due to the rather large what appear to be stress marks radiating inward from adjacent gasket bolt holes, in fan or seashell shaped fashion, as if by great force or movement against the bolt shank at the two gasket bolt holes in the first photograph)?]