An Estimation of the Load Factor and Sealing Performance Evaluation for Bolted Pipe Flange Connections With Gaskets Under Internal Pressure

In designing bolted pipe flange connections with gaskets, It is necessary to know the actual residual gasket contact stress in the connections under internal pressure. However, the actual reduced gasket stress in the connection has not been sufficiently estimated. In estimating the actual residual contact gasket stress more precisely, it is needed to know the load factor (the ratio of an increment in axial bolt force to the axial force due to the internal pressure per bolt) of the connections with gaskets. The new formula for obtaining the load factor was proposed by one of the authors using the tensile spring constant K_tg and the compressive spring constant K_cg, while the spring constant of bolt-nut system is designated as K_t. In the present paper, for estimating the load factor of the connections with gaskets, the circular plate theory is applied for obtaining the values of K_cg and K_tg and then the load factor is obtained for pipe flanges specified JIS 10K flanges and ASME B 16.5 flanges. The obtained results are in a fairly good agreement with the FEM results. Using the obtained load factor for the connections, a design method is demonstrated taking account of the allowable leak rate. Using the residual contact gasket stress and the fundamental gasket leak rate, an amount of gas leakage is predicted. The predicted amount of gas leakage for 3” and 20” pipe flange connections is fairly coincided with the experimental results and the FEM results. In addition, a design method for determining the bolt preload for a give allowable real rate is demonstrated using the simple method for obtaining the load factor.