Thorough Observation of Real Contact Area of Copper Gaskets Using a Laser Microscope With a Wide Field of View

Abstract

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.

Influence of Grease on High-Pressure Gas Tightness by Metal-to-Metal Seals of Premium Threaded Connections

“…Nitta et al [5] observed the real contact portions over the entire apparent contact area using a laser microscope. They determined the critical contact pressure at which the leakage flow in the radial direction ceases.…”

An Enhanced Stochastic Two-Scale Model for Metal-to-Metal Seals

“…These choices are motivated to ensure a sufficiently large domain to achieve convergence and a sufficiently fine mesh to resolve correctly the smaller wavelengths. The second topography used is one that is typical in metal-to-metal seals, i.e., a turned surface which has undergone mild wear [2,8,[25][26][27]. The surface has been measured using white light interferometry and then filtered by truncating any frequency higher than 1/(8∆x).…”

Prediction and Measurement of Sealing Properties of Joints Between Wavy Metal Surfaces

“…Equations (6) to (10) refer to a diffusive problem for which local transmissivities, h(r,θ) 3 12 , form an heterogeneous field [12,15] which is obtained from contact simulation. The computation of the pressure and local fluid flow (p, q v ), solution of the above boundary value problem, is carried out with a numerical code based on an integral formulation of Eqns.…”

“…The computation of the pressure and local fluid flow (p, q v ), solution of the above boundary value problem, is carried out with a numerical code based on an integral formulation of Eqns. (6) to (10) and a boundary element method (see Chap. 7 in [21]).…”

“…It was further proven from direct measurements [2,7,8] carried out on an experimental setup [9] designed for measurement of fluid flow-rate through a contact of rough metal surfaces. More recently, a direct in-situ observation of contact areas was reported [10], allowing the identification of radial and circumferential flow paths while increasing the clamping load.…”