Finite Element Simulation Of The Influence Of Complex Changing Conditions On The Strength And Sealing Of The Bolted Flange Joint

Bolted flanged joints are widely used in petrochemical equipment and pipelines.A variety of extremely complex and changing conditions put forward more stringent requirements for its strength and sealing performance.The research object of this paper is a bolted flange joint with a flexible graphite spiral wound gasket,and the APDL in ANSYS is used to establish its full cycle three-dimensional finite element model.Considering the nonlinear compression rebound constitutive relation of gasket and the elastic interaction between bolt groups,the thermal structure indirect coupling method is used to simulate the whole process of flange connection from installation to operation and maintenance.Finally,the distribution of displacement and stress of flange connection under a series of complex combined working conditions of preloading,pressurization,temperature rise,creep,start-up after emergency stop and additional load are obtained,and the strength and sealing performance of flange connection under different working conditions are analyzed.The stress distribution of the bolted flange joint is uneven along the circumference in the whole process.The maximum stress of flange is sinusoidal,and the stress decreases slightly under internal pressure.The stress value increases greatly under temperature.After 10000 hours of creep,the stress decreases to the lowest value,and then increases gradually.The maximum stress is at the first and last screwed bolt,the outer wall of upper flange nozzle and the tension side of upper flange.The bolt stress increases first and then decreases in the whole process.The stress is the largest under the pressure condition,and the maximum stress of bolts under each condition appears in the last tightened bolt.In practical engineering application,it should focus on the first and last screwed bolt,the outer wall surface of the upper flange nozzle and the tension side of the upper flange to prevent the strength failure.The deflection angle of flange increases first,then decreases and then increases with the superposition of working conditions.It reaches the minimum value after the temperature load,and reaches the maximum value under external load.The deflection angle of the flange fluctuates sinusoidal along the circumferential direction,and the maximum value appears at the third tightened bolt and the tension side of the bending moment,but it is lower than the standard value.The compressive stress of gasket is tight inside and loose outside,and it gradually decreases with the load accumulation.The minimum stress occurs on the inside of bolt 2 and bolt 24 and on the tension side of bending moment.In the process of emergency stop and start-up,the minimum stress of gasket is lower than the minimum sealing pressure for about 4.5 hours,and the flange joint has sealing failure.These provide the prediction of the possible strength failure and leakage location and time for the engineering application of flange connection,which has important engineering guiding significance.