Study on the Standard of Tightening Procedure of Pipe Flange Connections and Evaluation of its Sealing Performance by Computational Mechanics

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1.Optimal Tightening Procedure of Pipe Flange ConnectionsIntroducing "Elastic Interaction Coefficient Method" into 3-D FEA, two numerical methods have been proposed, which can estimate the scatter of bolt preloads when tightening the clamping bolts with an arbitrary sequence and provide an optimal tightening sequence that gives uniform bolt preloads in the final state.2.Mechanical Behaviors of Pipe Flange Connections using Soft GasketsBy incorporating the stress strain relationship of asbestos joint sheet gasket that were obtained experimentally into FE analysis, an optimal tightening sequence, mechanical behaviors under external loads and its sealing performance have been analyzed systematically.3.Elucidation of Mechanical Properties of the Disassembly Process of Pipe Flange ConnectionsVariations of bolt clamping forces and contact pressure distributions on the gasket interface have been systematically analyzed using FE approach developed above.4.Proposal of a Robust Tightening Proced … More ure of Pipe Flange ConnectionsTo suppress the scatter in final bolt clamping forces, an effective tightening sequence is to clamp the four bolts simultaneously, which are apart ninety degrees each other, and then tighten the other bolts simply in the clockwise pattern.5.Effects of Short Bolt Clamping Force on the Sealing Performance of Pipe Flange ConnectionsIt has been found that the missing of two bolts causes 1.6 times initial clamping force in the remaining bolts in the case of 20 inch flanges.6.Relationship between the scatter in bolt preloads and gasket contact stresses from the view point of sealing performanceThe scatter due to torque control method is found to be fairly smaller than that due to the elastic interaction of bolt deformations caused by the successive tightening operation.7.Evaluation Procedure of Leakage Performance based on Computational MechanicsIt has been shown that the leakage rate can be estimated by means of the maximum contact stress occurred along the outer diameter of gasket.A part of the achievements of this study has been published from High Pressure Institute of Japan (HPI) as "A Guideline for Pipe Flange Tightening. Z103TR-2004". Less