Research On Damage And Failure Modes At Tube-tubesheet Joint Of Heat Exchangers Under Pressure Loads

In modern industrial production,shell and tube heat exchanger is widely used and has a large market share.The heat exchanger accounts for about 40%of the total equipment investment of plant.Tubesheet is one of the important components of heat exchanger.At present,the design and application of heat exchanger show the trend of high temperature,high pressure,high heat flux,and large-size heat exchangers.The research on the damage and failure mechanism of the heat exchanger becomes more and more important for the safety and stabilization during in-service operation.The joints connecting the tubesheet and the tubes are the frequent failure positions.There are three main failure modes:strength failure under static load;alternative plastic failure and fatigue failure.In this thesis,strength failure based on the value of perforation weakening factor(E~*/E)is studied.The stress and strain at the tubesheet are simulated with FEA and are compared with the results in the two standards:ASME and GB/T 151.The rationality and accuracy of the value E~*/E for perforated tubesheet is analyzed.The stress-strain curves and the mechanical parameters of the material are obtained,through the tensile test and tension-compression cycle test.Simulation and analysis of conventional type for figuration of tubes welded to the backside of the tubesheet and the new type for figuration of tubes extend through the tubesheet.The strain and stress distribution characteristics of the tube sheet under the pulsating load condition and the symmetrical cyclic load condition are studied.The mechanical response characteristics of the two tubesheet structures under the Multilinear isotropic hardening(MISO)with pulsating cyclic loads and the Multilinear kinematic hardening(MKIN)with cyclic loading and unloading are simulated.At the same time,the influence of expansion joint on the mechanical response characteristics of tubesheet is analyzed.Through numerical simulation,the structural damage characteristics of different positions near the tube hole under fluctuating pressure load and cyclic pressure load are obtained,which provides a reference for cyclic plastic strain failure and fatigue failure for heat exchangers.