Research On The Tightening Procedure Of Bolted Flange Joints With Corrugated Flexible Graphite Metal Gasket

Flange joints are widely used in petroleum,petrochemical,electric power,nuclear,metallurgy and other industries because of their simple structure and easy disassembly.The leakage is a common failure of pressure equipment,which usually causes serious accidents.An important reason of the leakage failure is the lack of effective management in installation process of flange joints.In this paper,the effect of three structural parameters on the mechanical properties of flange joints with flexible graphite corrugated metal gasket is analyzed by ANSYS software.These parameters include the wave depth(0.5mm,0.8mm,1.3mm),wave width(0.2mm,0.6mm,1.0mm)and graphite layer thickness(1.5mm,2.0mm,2.5mm,3.0mm,3.5mm).Results show that the order of importance is the graphite layer thickness,the wave depth and the wave width.Based on the analyses of metal layer stress distributions,compression rate and resilience rate,an optimized parameter combination of 1.3-0.6 is obtained which means the graphite layer thickness is 1.3mm and the wave depth 0.6mm respectively.Then the optimized gasket is applied in four kinds of flange joints,whose specifications are PN100 DN50,PN100 DN100,PN100 DN200 and PN100 DN300.For these flange joints,bolts tightening processes are simulated under the crisscross procedure and sequential procedure.Results show that the bolt force distribution under the crisscross procedure takes a shape of W,while under the sequential procedure it takes a shape of N.Besides,the interactions among bolts increase with the flange size and the number of bolts,though they are not affected by bolt tightening procedures and bolt tightening forces.Through further analyses on the interaction,a new tightening process is proposed by increasing the tightening force on bolts,the former tightening effects of which are weakened.Results show that under the new procedure the bolt forces reach more than 98% of the target force after the fifth tightening round,and the proportions are 10%~20% higher than the ASME PCC-1 bolt tightening procedure.Besides the gasket contact stress is improved significantly,and the uniformities of bolt force and gasket contact stress are also improved.