Stress Analysis and Sealing Performance Evaluation of Pipe Flange Connections under Internal Pressure (Effects of Scatter in Bolt Preloads)

Abstract

The effects of scatter in bolt preloads of pipe flange connections with gaskets subjected to internal pressure are examined. The scatter in the bolt preloads tightened by a torque wrench was measured in the experiments. The contact gasket stress distributions at the interfaces of the pipe flange connections with the gaskets were calculated under the measured bolt preloads using elastoplastic finite element method (FEM) taking into account hysteresis and non-linearity in the stress-strain curves of the gaskets. The effects of the scatter in the bolt preloads on the gas leakage were also exmained using actual pipe flange connections. As the result a difference in an amount of measured gas leakage was found to be substantial between our study and PVRC (ASME) procedure. By using the calculated contact gasket stress distributions in the connections under the internal pressure and the results of the leakage tests, the sealing performance was evaluated. The effect of the scatter in the bolt preloads is found to be substantial on the leakage. It is found that the sealing performance is worse in the actual pipe flange connection than that evaluated by PVRC procedure. The tightening efficiency was proposed taking account the leakage due to the scatter in bolt preloads.