Estimation of Bolt Creep Characteristics and Sealing Performance of Flanged Joints

In the published standards, selection criteria for bolt materials for high temperature and high pressure environments (exceeding 540°C (1000°F) and 300 lb) has not been specified. In addition, it seems that there are few studies that summarize how the initial bolt load and the flange nominal diameter affect the change over time of the bolt load under a high temperature environment. This paper proposed formulas to calculate the changes over time in bolt stress and gasket stress easily due to bolt creep by applying the mechanical relationship of bolted flange joint. The changes over time in the bolt stress and the gasket stress calculated by the proposed formulas were fairly good agreement with the FEM and the experiments. By utilizing proposed formulas, it is possible to predict when retightening should be carried out for bolted flange joints operated continuously for a long period of time. Furthermore, in the present paper, the effects of initial bolt load, internal pressure, bolt materials, and flange nominal diameters on the sealing performance under high temperature environments are clarified by utilizing proposed formulas and FEM. As a result, this paper shows that the increasing initial bolt load against bolt creep under a high temperature environment can not be expected to be effective, and that the size of internal pressure and flange nominal diameter has small effects on the change over time of bolt load.