Study On Mass Transfer And Electrochemical Synergy Of Crevice Corrosion In Tube Plate Hole Of Heat Exchanger

Heat exchangers are widely used in petrochemical industry.Corrosion leakage is one of the main causes of heat exchanger failure.It is found that crevice corrosion in the environment of multi-material and complex medium consisting of heat exchanger tubes,tube sheets and their welds leads to a large proportion of corrosion leakage.Corrosion is controlled by many factors,and the environment inside the crevice is complex.It is very important to study crevice corrosion and prevent it from destroying the heat exchanger system.In this study,the crevice corrosion of heat exchanger tube-sheet holes in circulating water system is studied:In the experiment,304 stainless steel material was selected as the self-made crevice model.The corrosion in crevice was studied by electrochemical method in different weak acid and alkali environments.During the experiment,the chloride ion concentration and electrode potential were monitored at different positions in crevice at different time points.The variation rule of them in crevice was obtained,and the phenomena in weak acid and alkali environments were also studied.Line comparison and analysis.Using COMSOL multi-physical field coupling software,a two-dimensional model which is more close to the actual situation of heat exchanger is established based on the characteristics of axisymmetric tube-plate aperture.The mass transfer process and electrochemical reaction of 304 stainless steel in 3.5% NaCl solution are simulated.The reaction obtained the change of the concentration of chloride ions at different positions in the gap and the distribution of the electrode potential as well as the corrosion current density and the amount of corrosion loss.In this study,through experiment and numerical simulation method to study the mass transfer and electrochemical synergy under the action of heat exchanger tube sheet hole crevice corrosion behavior,the gap in the chloride ion concentration increases with the increase of test time,at the beginning of the test,the increase of chloride ion speed is relatively fast,weak acidic medium,crevice corrosion more more intense,as the reaction progresses,different location of the chloride ion concentration also gradually tends to be stable;The occurrence of slot corrosion leads to the decrease of potential inside the slot,and the potential of the sample at the slot position is the highest,while that at the bottom of the slot is the lowest.Finally,according to the loss image produced by corrosion,the most serious corrosion at the joint was obtained.The research in this paper is of certain reference value for the further study of corrosion of heat exchangers under the condition of circulating water,and also provides an important reference for the revision of the standard of heat exchangers.