The Test And Analysis Of Flange Connection’s Bolt Load And Gasket Contact Stress

Flange connection system is a simple and reliable sealing structure,which can be widely used in petrochemical,aerospace and nuclear industries.Statistical data of petroleum and chemical industry department pointed out that the pressure vessel and pipe failure in the flange connection seal leakage accounted for 48%.The medium of chemical equipment has the characteristics of high temperature,high pressure,inflammable and explosive.Once the leakage accident occurs,the loss will not be estimated.The appropriate bolt load and gasket contact stress is the key factor to ensure the sealing of flange connection.Gasket specific pressure y and gasket coefficient m which recommended in the traditional flange connection design method has not been validated and updated since 1943.In the actual engineering installation of flange connection,there are some technical problems that pretightening force can not be accurately applied to the bolt.In this paper,the test device of the bolt load and the gasket contact stress is established by taking the PN25/DN300 flange joint with the neck as an example.The preload and operating conditions of the flange connection are simulated by the use of a pointer type torque wrench and a manual pressure test pump.Real-time detection of bolt load and gasket contact stress under different working conditions is realized.The correspondence between the tightening torque and the bolt load and the specific pressure of the gasket is obtained.The reliability of the sealing effect of the traditional flange connection design method is verified,and the effectiveness of gasket specific pressure y and gasket coefficient m is examined and discussed.Taking the bolt,flange and gasket as the research object and the nonlinear contact relation of each element is considered.The finite element analysis is carried out by using the solid element,the pre-tightening element and the contact element,and the numerical simulation of the preloading process and the operation process of the flange connection system is realized.The numerical solutions of the bolt,flange and gasket under different loading conditions are obtained,including the stress and strain nephogram,displacement nephogram and contact pressure nephogram.The corresponding relationship between the bolt pre-tightening load and the contact pressure is obtained by the finite element numerical simulation,and the test results are in good agreement with the finite element analysis results.Based on bolt load and gasket contact stress test and finite element numerical simulation,the application of wireless measurement technology is introduced to verify the reliability and accuracy of wireless strain measurement,and the wireless measurement of bolt load and gasket contact stress is realized.The influence of the friction force of the flange on the preload torque transmission is discussed.It is found that the use of end bearing to reduce friction can be a good way to reduce energy consumption and increase the torque transmission,and it causes the bolt axial load to increase by nearly 150%.The effect of uneven bolt load on the contact pressure of the gasket is discussed.The distribution of the contact pressure of the gasket under different working conditions is obtained.It is found that when a bolt is broken or not pre tightened,the sealing contact surface of the gasket is partially separated and the leakage failure occurs.The test and finite element analysis in this paper provide reliable data basis for the design of the traditional flange connection,and it has practical significance to the actual installation of bolt.