Thermo-Mechanical Behavior of a Stainless Steel Threaded Fitting With a Pre-Compressed Gasket

Abstract

This paper investigates the clamp load loss in threaded fittings with a collapsible metal gasket for elevated temperature application. Firstly, the joint is tested at room temperature to find the correlation between the joint clamp load, the tightening torque, and the angle of turn. Secondly, a mathematical model for clamp load loss of the bolted joints under temperature cycling is proposed for predicting the clamp load variation. Although the bolt and the joint would normally undergo linear elastic deformation at room temperature, they are more likely to exhibit nonlinear behavior at high temperature due to the reduced material strength. The plastic or creep deformation of the bolt, gasket, and joint would cause permanent clamp load loss that may lead to joint leakage, part separation, or plastic thread deformation that would significantly increase the cost of fitting replacement and/or maintenance. A non-linear finite element model is used with temperature dependent material properties. The FEA model is used to investigate the clamp load loss of the threaded fittings due to plastic and creep behavior. Some measures for enhancing the threaded fitting reliability at elevated temperature are proposed.