The objective of this work is to improve the HOt Blow-out Test procedure (HOBT) to determine the maximum operating temperature of Teflon-based gaskets. The study aims to analyze the relaxation of these gaskets due to creep at high temperature. The determination of their safe operating temperature limit requires a good knowledge of its capacity to resist creep-relaxation due to temperature exposure in the short and long term. This work investigates the effects 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 a previous work, the introduction of a fixed number of cycles of heating and cooling in the HOBT test procedure has shown that ratcheting damage may have some impact on reduction of the gasket stress and the temperature limit of PTFE. The effect of holding temperature for a short period of time will also be investigated. The modified HOBT rig allows measurement of the gasket deflection during the test in order to accurately quantify the cumulative permanent deformation. Several types of PTFE-based gaskets will be tested in order to cover a wide range of gaskets to justify the generalization of the modified procedure.
