On the inception of leakage : Effect of hydrostatic pressure on the sealing interface

Abstract: The seal is a commonly used machine element to prevent leakage and maintain fluid pressure. A static seal without leakage is subjected to the hydrostatic load from the pressurized fluid. The fluid pressure consistently applied to the seal has multiple effects. On one hand, it is utilized as a complementary source of the contact force to tighten the sealing surfaces, since the contact force generated by the pre-tension and interference can not be designed too high for the ease of seal installation. On the other hand,  the sealing edges of the contact zone are not flattened most of the time and exhibit curvature, it leaves a gap between the contacting surfaces. The fluid filling this area will provide a force that opens up the sealing. One failure reason for the new static seal design is that the seal can not survive the elevated fluid pressure. A significant leakage is observed when the fluid pressure passes a certain critical value, and the transition from zero to a finite leakage flow rate is observed in the experiments. This transition is not continuous and often in connection with little material failure. It is a design problem closely related to the contact pressure distribution at the sealing interface. The critical pressure is of interest in the seal design,  and it is closely related to the hydrostatic load from the sealed fluid. In this work, the contact mechanics at the sealing interface is studied incorporated with the hydrostatic load from the sealed fluid. We first study the case where the sealed fluid pressure both contributes to the total contact load and the contact opening force with the finite element method for a 2D contact case. Then a new boundary element method is implemented to study the case of the complicated contact surfaces. The newly developed method is utilized to study the critical pressure that leads to leakage for 2D and 3D contact cases. The results have shown that the critical pressure of bulk leakage can be acquired from the surface's dry contact state with a dimensionless correction factor, and the hydrostatic load at the contact interface leads to a different critical area ratio and critical solid-solid contact load when compared with the case without the hydrostatic load.