Stress Analysis of PTFE Sleeves in Industrial Valves

Abstract: The polymer PTFE has become an important and widely used sealing material in the valve industry in recent years. It provides good strength and low friction, but it is sensitive to stress relaxation, i.e. loss of stiffness with time. This in turns may cause problems with leaking seals. The objective of this master’s dissertation is to perform a stress analysis of the PTFE sleeve used in an industrial plug valve. The analysis is performed in cooperation with Fluoroseal Valves Inc, a Canadian company situated in Montréal. The master’s dissertation comprises study of the properties of PTFE and measurements on the sleeve. A finite element model of the valve is developed in ABAQUS, and special attention is drawn to the stress relaxation of PTFE, in order to predict leakage. It is found that an inhomogeneous stress field occurs in the sleeve upon loading, and that the stress relaxation causes the sleeve to loose a great deal of its load bearing capacity. High plastic strains are observed at the actual leakage sites and the finite element analysis is confirmed by the measurements.