Abstract
The effects of scatter in bolt preloads and the nominal diameter (3inch and 20inch) of pipe flange connections with gaskets subjected to internal pressure are examined. The scatter in the bolt preloads tightened by a torque wrench was measured for smaller and larger pipe flange connections (3inch and 20inch) . The contact gasket stress distributions of the pipe flange connections are calculated with the measured bolt preloads using elasto-plastic finite element method (FEM) taking into account the hysteresis and the non-linearity of the stress-strain curves of the gaskets. The effects of the scatter in the bolt preload on the sealing performance are also examined for the pipe flange connections. The bolts were tightened using torque wrenches according to JIS B 2251 and ASME PCC-1 procedure. By using the calculated contact gasket stress distributions in the pipe flange connections under the internal pressure and the measured results from the leakage tests, the sealing performance is evaluated. The effect of the scatter in the bolt preload is found to be substantial on the sealing performance. The difference in the leakage is found to be small between JIS and ASME tightening procedures. The assembly efficiency η based on the amount of leakage is newly proposed as η =0. 65 for bigger nominal diameter pipe flange connection while η =0. 8 for smaller nominal diameter pipe flange connection.
