I don't know the degree of importance and of risk of your application.
Anyway a possible solution is to use double gaskets, venting the space between the gaskets to a suitable treatment plant.
prex
motori@xcalcsREMOVE.com
Where do you get the info. that a gasket is never perfectly tight?
Leaks occur or do not occur for a huge variety of reasons. If your gasket/seal ring/rtj etc. is not perfect and you have no leak it may just be that the potential leak path is too small to allow a leak (smaller than the particle size of your content).
If leakage or potential leakage is a problem there are various methods of leak detection prior to service.
Thank you Jonralph. But, when the gasket is perfectly tight (zero leakage), the tightness parameter will be infinity: it means we will need a infinite gasket stress to seal?
We must remember that the issue of leak tightness is driven by two standards
1. Laboratory - Specs we all use M and Y factors etc,API etc
2. Field experience, having just finished a flange
monitoring program, flange leakage is uncommon
especially if you measure against EPA standards ie PPM
So a "leak" or tightness depends on your point of view
I can't speak to "tightness parameter", I just know how gasket leakage is analyzed for Powertrain analysis. In that situation, a "leak" is defined as a path of zero-pressure which exists across the cross-section of the gasket.
Nowhere in that definition (which is what is used for automotive powertrain) is the implication of infinite gasket stress; rather the implication is non-zero gasket stress.
If you don't agree with my assessment; please clarify your statement. I know that this is the way that it is done, but I am not completely attuned to some of your terms. For that reason, I may be misinterpreting what you are stating.
Since the tightness parameter is meaured using a helium mass spectrometer to measure leakage of helium at eigher 400 or 800 PSIG, this is why there is no such thing as a "leak proof" gasket. Helium is notoriously difficult to seal, and the mass spectrometer can measure leakage as small as 10^-9 cm^3/s.
After reading it, I am not clear what specific gasket applications they are testing for.
My more educated response to the original question would be that these tests are certainly worst-case--many gaskets operate in much lower differential-pressure environments. Also, they are required to hold materials which have significantly larger molecular size than helium.
Other than hydrogen, I would expect that no molecule would elicit greater 'porosity' across a gasket than helium. Since this test is essentially worst-case, wouldn't it be logical that a 'fail' under these conditions may still be effectively leak-proof for many applications?
Therefore, a seal which is not 'perfectly tight' by this standard may be in fact leak-proof for in-service conditions.
After going through the trail, I am getting interested with my leakage problem. We use rubber O-rings with metal to metal joint. The joint does not leak for some time and after some time, we observge leakage.
Can some one suggest a book for studying leak science which gives various parameters for seal technology.
