Elasto-Plastic FEM Stress Analysis and Mechanical Characteristics of Pipe Flange Connections with Non-Asbestos Gaskets under Internal Pressure

Abstract

The effects of the nominal diameter of pipe flange connections with non-asbestos spiral wound gaskets(SWG) under internal pressure on the mechanical characteristics such as the contact gasket stress distribution which governs the sealing performance, the load factor and the hub stress of the connections were evaluated. The stresses in the connections with the nominal diameters from 3” to 24” under internal pressure are analyzed using the elasto-plastic(EP) FEM analysis taking account the hysteresis and non-linearity of deformation behavior of the non-asbestos SWG. As a result, it is found that the variations in the contact gasket stress distributions are substantial due to the flange rotation in the connections with the larger nominal diameter. Leakage tests were conducted to measure the axial bolt forces (the load factor) and the hub stress. The results obtained from the EP-FEM analyses are fairly consistent with the experimental results concerning the variation in the axial bolt forces (the load factor) and the hub stress. Using the obtained contact gasket stress distributions and the fundamental relationship between the amount of leakage and the contact gasket stress, the amount of the leakage of the connections is estimated. It is observed that the sealing performance of the connections with larger nominal diameter is worse than that of the connection with smaller nominal diameter because of the flange rotation. The estimated results are in a fairly good agreement with the measured results. The difference in the hub stress between the EP-FEM and ASME code is demonstrated and the differences in the load factor and the sealing performance of the connections are shown between the asbestos and non-asbestos gaskets.