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 lots 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 nanolevels in tight gaskets relies on its capacity to incorporate different flow regimes that can be present under different working conditions. Four models based on Navier–Stokes equations that incorporate different boundary conditions and characterize specific flow regime are 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 porous gasket materials which are flexible graphite, polytetrafluoroethylene (PTFE), and compressed fiber. The methodology is based on the determination experimentally of the porosity parameter (N and R) of the microchannels assumed to simulate the leak paths present in the gasket using helium as the reference gas. The predicted leak rates of different gases at 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.