This paper deals with the safety evaluation of bolted flange connections subjected to combined loads of axial load and external bending moment. Bolted flanged connections sometimes experience bending moments exerted by the wind load or earthquakes under working conditions. Under these circumstances, leakage accidents may occur. Therefore, it is important to understand the sealing capacity under the combined load of axial load and bending moment.

The purpose of this study is to examine the minimum gasket stress to maintain the tightness of bolted flange connections when subjected to combined loads of axial load and bending moment. Bolted flange connections with gaskets were prepared for this purpose. The bolted flange connection was pressurized and subjected to the combined load. The pressure decays were measured with a pressure transducer and the leak rates were also measured using a mass flow meter. The relationship between the measured results and the combined load were examined and the combined load when large leakage caused was determined. The effects of gasket type and flange type were also examined.

The finite element analysis of the contact stresses of the bolted flange connection was carried out using ANSYS. The gasket stress distribution when the tightness of flange connection is lost was clarified. Summarizing the experimental and analytical results, the initial tightening force to maintain the tightness under combined load of axial load and an external bending moment is discussed.

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