When flanged connections are used at a high temperature, one of the issues is the reduction of bolt forces, especially in the cases where PTFE-based gaskets are employed. Bolt forces significantly reduce when flanged connections are heated and re-torque is necessary in many cases. It is important to estimate the residual bolt forces under thermal loading to ensure the integrity of flanged connections.
In this paper, the behavior of bolt force changes under thermal loading was experimentally examined using a flanged connection with expanded PTFE sheet gaskets. The flanged connection was heated and then cooled in an electric oven and the changes of the bolt forces were measured. It is found that the bolt forces reduce at the first thermal loading due to the gasket flow. Once the gasket is settled, the bolt force changes depend on the difference of thermal coefficients of the bolts and the gasket. It is also clarified that thinner gaskets and spiral wound gaskets are effective for elevated temperature applications.