Analysis Of Newly-Developed Textured Ptfe Gaskets Subjected To Creep Relaxation

The ability of a gasket to maintain sealability over a long period of time is the primary consideration for pressure vessel and piping designers. While service conditions such as temperature, internal pressure, gasket stress, and the caustic nature of the transport media are all important parameters, factors such as the gasket material, gasket dimensions, and flange torque procedure have generally been viewed as the most influential. Viscoelastic gaskets are attractive as intermediate layers between bolted flanges because they conform to the inherent imperfections between mating flange faces. They display time-sensitive relaxation responses over the long term. Next generation gaskets, termed EPX and manufactured by Garlock, have been designed with a dual-face, raised honeycomb pattern to confer more rapid stabilization compared to existing non-textured products. Historically, a re-torque is conducted at approximately 24 hours after initial torqueing. The consequence of the secondary load is a significant boost in the load retention response, especially for more compliant materials. Preliminary studies reveal that the viscoelastic properties exhibited by ceramic-filled PTFE materials can achieve a nearly identical post-re-torque response with a one-hour dwell in place of the day-long dwell. The gaskets having a textured-style (i.e., EPX), however, were found to require no re-torque whatsoever. Gasket efficiency, η%, defined in earlier studies, is used to measure both stress relaxation and load carrying capability of gaskets. A design of experiments (DoE) approach is applied to characterize the factors that influence load relaxation response of the both candidate (EPX) and existing (Legacy) gasket styles. Experimental data are used to develop modeling constants associated with the Burger viscoelasticity model. With the use of finite element modeling, stress distributions within the gasket are revealed. The collection of efficiency measurement methods, approach to re-torque optimization, and modeling convey a novel framework that designers can invoke to facilitate improved flange performance