Study Of The Influencing Factors On The Leakage Of Bolt-flange-gasket Joint

Bolt-flange-gasket joint is a common type of static seal connection in pressure vessels.Because of its simple structure and convenient assembly,the structure has been widely used in petrochemical plants.However,the sealing failure of bolt-flange-gasket joint is one of the main causes for petrochemical engineering accidents,and thus,a lot of attentions have been paid to reduce the leakage rate of the joints.In this thesis,finite element analyses together with experiments were carried out on a bolt-flange-gasket joint and a flexible graphite and stainless steel wound gasket for studying the tightness of the bolt-flange-gasket joint.Main work and results are as follows:(1)A finite element model for the whole bolt-flange-gasket was established and the deformation of the joint as well as the compressive stress distribution on the gasket in the pre-tighting and operation cases.It is found that as the result of the flange deflection,the distribution of the compressive stress on the gasket is not uniform with the maximum at the outer edge of the gasket which determines the leakage of the joint.(2)Influences of parameters such as flange thickness,number of bolts,working pressure and pre-tighting force on the flange deflection and leakage of the joint were investigated.Results show that different parameters yield different effects of the flange deflection on the joint leakage.(3)The compression-rebound property of the flexible graphite and stainless steel wound gasket is studied numerically and experimentally.A so-called equivalent elastic modulus of the flexible graphite was defined.Numerical simulated compression-rebound curves well agreed with those obtained by experiments.(4)Effect of the metal-band angle of the gasket on flange deflection and leakage rate was studied.It is found that with increasing the angle,the compressive stress on the gasket decreases and as a result,the leakage rate of the joint increases.