A long-term life prediction method for a compressed fiber sheet gasket under a high-temperature environment is studied. Non-asbestos compressed fiber sheet gaskets are now being used as a substitute for asbestos in the bolted flange joint, for instance chemical plants and oil plant facilities. Consequently, there is a real need for a technology to predict the lifetime of non-asbestos compressed fiber sheet gaskets quantitatively. We have previously reported that the facing surface which was formed the gasket and flange was visualized with scanning acoustic tomography (SAT). Voids were observed on the facing surface of the gasket and increased with the increase in exposure time at high temperature. If a leakage path for inner fluids was created by the increasing number of voids, the leak occurs on the facing surface of the gasket surface. The probability of a leak due to voids and the lifetime of this gasket were predicted by applying the percolation theory, which describes the connectedness of voids and clusters. In this report, the influence of internal pressure of test flange joint upon the rate of increase is studied.

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