The deflections of gaskets after initial tightening largely affect the residual bolt forces and the tightness of bolted flanged connections. The bolt forces decrease significantly due to the deflections of gaskets after initial tightening in the cases where expanded PTFE gaskets are used. The visco-elastic characteristic of the gaskets is the main cause for the phenomenon. It was shown in the paper PVP2012-78694 that the tightness improved even if the bolt forces reduced in the long term. This is because the gasket becomes packed under a high gasket stress. It is important to estimate the thickness change of gaskets to evaluate the tightness of bolted flanged connections.
In this paper, an analytical model of a bolted flanged connection, in which the flanges, the bolts and the gasket are represented by spring constants, is proposed. Experiments were carried out to measure the creep characteristic of the expanded PTFE gasket. The residual bolt forces and the deflection of the gasket were estimated based on the analytical model of the bolted flanged connection and the creep characteristic of the gasket. Thus, the relationship between gasket deflection and the tightness of the bolted flanged connection are clarified.