FEM Stress Analysis of Long-Term Sealing Performance for Bolted Pipe Flange Connections With PTFE Blended Gaskets Under Elevated Temperature

Abstract

Mechanical characteristics of bolted pipe flange connections with PTFE blended gaskets under elevated temperature are examined using FEM calculations and experiments. Firstly, the basic characteristics of the PTFE blended gaskets are measured such as the stress-strain curves, the thermal expansion coefficient and the relationship between the contact gasket stress and the leak rate at room temperature and some high temperature. The leak rates of the gasket at the averaged gasket stress are measured using the rigid platen. In addition, the creep characteristics of the gaskets are measured using the rigid platen under elevated temperature. Then, using the gasket basic characteristics measured above, the FEM calculations are carried out to analyze the mechanical characteristics such as 1) changes in axial bolt forces (the load factor), 2) the contact gasket stress distributions, 3) flange hub stress. Then, the sealing performance of bolted pipe flange connections is predicted using the contact gasket stress distributions obtained from the FEM calculations and the relationship between the gasket stress and the leak rate. In the FEM calculations, the value of the load factor due to the internal pressure is obtained as φg = 0.12. Furthermore, the sealing performance in long-term is estimated using the change in the axial bolt forces (creep) and the contact gasket stress distributions under heat cycle and internal pressure. For verification of the FEM calculations, the experiments were performed to measure the load factor (change in axial bolt forces), the leak rate of the connection at each temperature, and the hub stress. The FEM results are in a fairly good agreement with the measured results. In addition, the reduction in the contact gasket stress due to the heat cycle, internal pressure and the creep is demonstrated and the effect of the nominal diameter of pipe flanges on the sealing performance is shown.