It has been well known that a scatter in axial bolt forces of pipe flange connections tightened by the torque control method is substantial. It is necessary for evaluating the sealing performance of the pipe flange connections with the gaskets subjected to internal pressure to know the contact gasket stress distributions due to the scatter of the axial bolt forces in the connections tightened by the torque control method. Especially, when gases are used in the pipe flange connections with gaskets at a high temperature, it is necessary to evaluate the amount of gas leakage. In this study, when bolts and nuts in a pipe flange connection were tightened using a torque wrench, the axial bolt forces were measured and then the amount of gas leakage in the pipe flange connection at 50,100,150 and 200 °C was measured under internal pressure. Leakage tests were performed using Helium gases. In addition, the thermal stress distributions at the interfaces between pipe flanges and the gasket under heat condition (temperature 50,100,150 and 200 °C) and internal pressure were calculated by using the finite element method (FEM) taking into account hysteresis in the stress-strain curves of a spiral wound gasket. By using the calculated contact stress distributions and the results of the leakage tests, the sealing performance was evaluated.

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