Sealing performance evaluation of pipe flange connection with spiral wound gasket under cyclic thermal condition

Although a lot of pipe flange connections are exposed to elevated temperature during long-term plant operation, a sealing performance of the pipe flange connections at elevated temperature is not well understood because of the experimental difficulty and the analytical problems which result from the lack of the materials properties of gaskets at elevated temperature. The authors have been evaluating the effects of the material properties of spiral wound gaskets (SWG) and the sealing performance of the pipe flange connections at elevated temperature with numerical and experimental analysis. The gasket stress induced by the mismatch of the thermal expansion between the gasket and flange/bolt increased as increasing the temperature in the case that the thermal expansion coefficient of the gasket was larger than that of bolt/flange material and the sealing performance of the pipe flange connection was improved. However, the thermal expansion coefficient declines at temperatures higher than 210°C. In addition, the binder compositions of SWG vaporize and the mechanical properties slightly change at high temperature such as higher than 200°C. Therefore, the sealing performance of pipe flange connection with SWG might decline more than 200°C. The sealing performance and long-term durability of pipe flange connection with SWG at elevated temperature were evaluated in this study. The long term leakage test with heat cycle revealed that the sealing performance of pipe flange connection didn't show any degradation for 21 days. The compression tests for the new, the thermal aged and the used gaskets were done to investigate the effect of material characteristics on the long term sealing performance. In addition to the leakage test and the compression tests, the thermal characteristics of SWG were evaluated by the Thermogravimetry/ Differential Thermal Analyzer (TG/DTA) measurement. The measurement showed the weight loss of SWG more than 130°C. According to those experimental results and FE analysis, the effect of temperature on the sealing performance was discussed.