To quantitatively predict the leakage rates of static metal seals, it is important to observe the real contact area at seal surfaces because the leakage path consists of the noncontact portions between the flange and gasket surfaces. In a previous study, we observed the real contact situation using a thin polymer film 1 μm in thickness. In the present study, we observed the real contact area on gasket surfaces using a laser microscope with a wide field of view. With this method, observation time over the whole gasket surface could be greatly reduced compared with conventional methods. The observations indicated that the leakage paths on the gasket surfaces were in the radial direction perpendicular to a lathe-turned groove and the circumferential direction along the groove. As the closing loads increased, the leakage paths in the radial direction disappeared and only the leakage path in the circumferential direction remained. When the closing loads increased further, the widths of the leakage paths at both the inside and outside on the gasket surface became narrower. The critical contact pressure where the leakage paths in the radial direction disappear was determined from the observation of the contact surface of the gasket. The leakage rates obtained from the experiments showed good agreement with the calculated values under the assumption of laminar flow along the turned groove over the critical contact pressure.

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