The Study Of Crevice Corrosion For Weld Joint Between Heat Exchanger Tubes And Tube Sheet

Heat Exchangers are widely used in petrochemical industry.However,since the contact medium of heat exchangers is complex and highly corrosive,corrosion and leakage happened frequently in production process.And the corrosion on weld crack between tube and tube sheet account for 80% in this issue.Therefore,it is significant on prolonging the service life of heat exchangers and increasing economic benefit of enterprises to research the corrosion behavior on weld crack between tube and tube sheet and the influence factors come from the galvanic couple which are made up of different materials.The main content of this paper can be divided into three parts:(1)Simulating the corrosion on weld crack in circulating water by using the Comsol Multiphysics softwore,select corrosion,three Nernst-Planck as the physical interface,while choose steady-state study as the prefabricated solution type.Then build the geometric model based on valid assumptions for the struct of corrosion happened on weld crack.For the object316 L stainless steel which is in the circulating water,this model helps to provide the prediction of chloride ion concentration,pH value and electric potential distribution for the weld of the object.The result of experiment provides scientific basis for simulating the solution in occlusion area of weld crack in circulating water,in addition,it shows the change of chemical environment of weld crack under different chloride ion concentration and pH value.(2)Researching the cathode process of stainless steel in the simulated solution by using the method of testing polarization curve,as well as the anodic dissolution process through electrochemical impedance spectroscopy.Besides,I also make the study on how different chloride ion concentration and pH value influence the corrosion speed.Those results show that,the acidification of the solution play a leading role in accelerating corrosion and autocatalytic corrosion,and the influence comes from pH value is bigger than that comes from chloride ion concentration.(3)Testing the open circuit potential of tube,tube sheet and weld metal in simulated solution,more specifically,testing the galvanic current and galvanic potential under different area ratio of cathode and anode and different temperature for several galvanic couples those are made up of different materials.The result of experiment shows that the influence of arearatio of cathode and anode and temperature on the changes of galvanic potential is not obvious while it is obvious on changes of galvanic potential.The study of corrosion behavior on weld crack in circulating water between tube and tube sheet and the influence factors of galvanic corrosion made by numerical simulation and electrochemical test,provides a theoretical basis for solving the issue of corrosion happened on weld crack of struct that made up of different materials and the galvanic corrosion in recirculating cooling water system for refinery.