FEM calculations and leakage experiments are carried out for bolted flanged connections with metal flat gaskets. It is found that the sealing performance of bolted flanged connections with raised face metal gaskets under internal pressure is improved significantly when the contact gasket stress reaches the gasket yield stress. In our FEM calculations it is demonstrated that the contact gasket stress at the outside diameter is bigger than that at the inside diameter due to the flange rotation. It is also found from the leakage test results and the FEM calculations that the sealing performance of the bolted flange connections with metal flat gasket is better than that of the metal gasket in platen device tests,. In addition, the contact stress in the joints with RTJ (ring type joint) gasket is examined and 4 stress peaks on the oval type and 8 peaks on the octagonal type are found. From the obtained results, a method for determining the bolt preloads in the bolted joints using flat metal gaskets and RTJ gaskets under internal pressure is proposed taking account the given allowable leak rate. Finally, the leak rates for bolted flanged connections tightened under internal pressure are compared with the experimental results. The new method can be proposed for determining the bolt preload for bolted flange connections with metal gaskets under internal pressure at room temperature.

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