FEM Stress Analysis and Mechanical Characteristics of Bolted Pipe Flange Connections With PTFE Blended Gaskets Subjected to External Bending Moments and Internal Pressure

In designing of pipe flange connections with gaskets, it is important to examine the mechanical characteristics of the connections subjected to external bending moments due to earthquake such as the changes in hub stress, axial bolt forces and the contact gasket stress distribution which governs the sealing performance. One of the authors developed the PTFE blended gaskets and the authors examined the mechanical characteristics of the connections with the PTFE blended gaskets under internal pressure. However, no research was done to examine the mechanical characteristics of the connections with the newly developed PTFE blended gasket subjected to external bending moment due to earthquake. The objectives of the present study are to examine the mechanical characteristics of the connection with PTFE blended gasket subjected to external bending moment and internal pressure and to discuss the difference in the load order to the connections between the internal pressure and the external bending moments. The changes in the hub stress, the axial bolt force and the contact gasket stress distribution of the connection are analyzed using FEM. Using the obtained the gasket stress distribution and the fundamental data between the gasket stress and the leak rate for a smaller test gasket, the leak rate of the connection with the gasket is predicted under external bending moment and internal pressure. In the FEM calculations, the effects of the nominal diameter of pipe flanges on the mechanical characteristics are shown. In the experiments, ASME class 300 4 inch flange connection with 2m pipes at both sides is used and the test gasket is chosen as No.GF300 made by Nippon Valqua Industries, ltd. Four point bending moment is applied to the connection. The FEM results of the hub stress and the axial bolt forces are in a fairly good agreement with the experimental results. In addition, the FEM results of the leak rate are fairly coincided with the measured results.