Recently bolting procedures for flanged connection is one of the important research topics, and several procedures for bolting process are proposed or about to be issued. These procedures are based on bolting experimental and/or analytical results, namely by Finite Element Analyses. Among these researches, only a few are addressing the relationship between bolt tension scatter and gasket contact stress distribution. Bolt tension scatters in nature due to elastic interaction of the bolts as the bolts are tightened one by one. In order to obtain a uniform, or nearly uniform, tension along all the joint bolts, many “rounds” or “passes” are necessary to eliminate this elastic interaction. If the installer does not iterate this tightening process, gasket stress will be distributed undesirably due to the bolt tension scatter. The bolt tension scatter is now mostly calculated using the analysis programs that are developed by research laboratories themselves. In this paper, the author suggests to use a general purpose finite element analysis code for bolt stress, gasket stress and flange stress, which accommodates such advanced functions as bolt pretension and gasket plastic behavior. The author will show that it is possible to analyze the bolt tension, gasket stress and flange stress at the same time using a market sold analysis code, ABAQUS, and examine how many “rounds” are necessary to achieve uniform gasket contact stress. This paper also describes the relationship between the gasket contact stress and the bolt tension scatter, and the effect of internal pressure of piping or pressure vessels. Based on these results, the tightness parameters are estimated and the methods in the standards are verified in the aspect of allowable and achieved leakage.

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