Characterization of PTFE-Based Gaskets at High Temperature

The objective of this work is to analyze the hot blow-out test procedure (HOBT) used to determine the maximum operating temperature of Teflon-based gaskets. The study focuses on the effect of thermal cycles and a few considerations that can be made to improve the characterization procedure for better prediction of the long-term performance of these types of gaskets at high temperature. The determination of their safe operating temperature limit requires a good knowledge of their capacity to resist creep-relaxation due to temperature exposure in the short and long terms. The study investigates the effects of the cumulative gasket deformation due to thermal cycling, gasket stress level, and holding time on the relaxation of these materials. In parallel, an experimental fixture has been developed to measure the thermal expansion coefficient and the short-term creep resistance of such materials. Based on this study, the introduction of thermal cycling in the HOBT test procedure shows that ratcheting damage has some impact on the reduction of the gasket lower bound stress and therefore on the temperature limit of polytetrafluoroethylene (PTFE) gaskets. The effect of holding temperature for a short period of time is also investigated. The modified HOBT rig allows measurement of the gasket deflection during the test in order to accurately quantify the cumulative permanent deformation. Tests on small size PTFE-based gaskets are conducted to demonstrate the above mentioned effects.