On the Use of Gas Flow Models to Predict Leak Rates Through Sheet Gasket Materials

Abstract

The prediction of leak rate through porous gaskets for different gases based on test conducted on a reference gas can prevent bolted joint leakage failure and save the industry a lot of money. This work gives a basic comparison between different gas flow models that can be used to predict leak rates through porous gasket materials. The ability of a model to predict the leak rate at the micro and nano levels in tight gaskets relies on its capacity to incorporate different flow regimes that can be present under the different working conditions. Four models based on Navier-Stokes equations and incorporate the boundary conditions of the appropriate flow regime considered. The first and second order slip, diffusivity and molecular flow models are used to predict and correlate leak rates of gases namely helium, nitrogen, SF6, methane, argon and air passing through three frequently used nanoporous gasket materials which are flexible graphite, PTFE and compressed fiber. The methodology is based on the determination experimentally of the porosity parameter (N and R) of the micro channels assumed to simulate the leak paths present in the gasket using helium as the reference gas. The predicted leak rates of different gases at the different stresses and pressure levels are confronted to the results obtained experimentally by measurements of leak rates using pressure rise and mass spectrometry techniques. The results show that the predictions depend on the type of flow regime that predominates. Nevertheless the second order slip model is the one that gives better agreements with the measured leaks in all cases.