Bolted connections inserting gaskets such as box-shape flange connections have been widely used in mechanical structures, nuclear and chemical industry, and so on. They are usually used under internal pressure. In designing the box-shape flange connections with gaskets under internal pressure, it is important to clarify the gasket stress distribution for evaluating the sealing performance of these connections. However, no research in which the sealing performance of these connections is examined under internal pressure has been carried out. Thus, the design for box-shape connection such as thickness of flange cover, number of bolts, gasket width and so on is not clarified. In this paper, the contact gasket stresses of these connections under internal pressure are analyzed using the finite element method (FEM), taking into account a hysteresis in the stress-displacement curve of the gasket. And then, using the contact gasket stress distributions obtained from FE analysis and the relationship between gasket stress and leak rate obtained from a gasket sealing test (JIS B2490), method for estimating an amount of leakage is examined. The leakage tests were also conducted to measure an amount of gas leakage using an actual box-shape flange connection with a gasket. The estimated results are in a fairly good agreement with the experimental results. In addition, the effect of gasket width, flange cover thickness and flange cover material is examined on the sealing performances of box-shape flange connections under internal pressure. The effects of the above factors are discussed on the sealing performance in designing box-shape flange connections.

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