Masahiro Hagihara

Evaluation of Leakage Probability of Non-Asbestos Fiber Sheet Gasket at Elevated Temperature Based on Percolation Theory: Characteristics Under Internal Pressure

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.© 2011 ASME

Effect of Creep of Non-Asbestos Sheet Gaskets at Elevated Temperature on Relaxation Behavior of Bolted Flange Joints

Gaskets in bolted flange joints experience creep when used for long periods of time. Since gaskets are often used at elevated temperatures, the clarification of their high-temperature creep behavior is essential. Relaxation of bolted flange joints is caused by creep in the gaskets, and may result in leakage of internal fluids. Therefore, the ability to predict relaxation in bolted flange joints due to the effects of creep in gaskets would allow the lifetime of the gaskets to be estimated and thus prevent leakage of internal fluid. In the present study, the creep behavior of non-asbestos sheet gaskets and the relaxation behavior of these gaskets in bolted flange joints at room/elevated temperature were investigated using four-inch flanges. The test conditions were 180 °C for 360 hours (approximately 2 weeks). The test samples were four types of non-asbestos sheet gaskets, two types of compressed fiber sheet gaskets and two types of PTFE sheet gaskets. The differences in creep behavior between the two types of compressed fiber sheet gaskets and between the two types of PTFE sheet gaskets were clarified. The creep strain at the end of the test was always larger than that just after reaching the test temperature for all gasket materials. On the other hand, the creep strain in the PTFE sheet gaskets just after reaching the elevated temperature was approximately equivalent to the total creep strain after the test has been completed. Thus, the creep behavior of each test gaskets was clarified under aging. In addition, the time for replacement of gaskets was estimated using the relaxation behavior in bolted flange joints by defining the time to reach the minimum design seating stress of the test gasket.Copyright

Evaluation of Leakage Probability of Non-Asbestos Fiber Sheet Gasket at Elevated Temperature Based on Percolation Theory

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 petrochemical factories. Consequently, there is a real need for a technology to predict the lifetime of non-asbestos compressed fiber sheet gaskets quantitatively. In this report, the facing surface of the gasket and flange is 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 is created by the increasing number of voids, the leak occurs on the facing surface of the gasket. The probability of a leak due to voids and the lifetime of this gasket are predicted by applying the percolation theory, which describes the connectedness of clusters.Copyright