Corrosion Behavior Of Dissimilar Connection Between 316 Stainless Steel And Copper In Bromine Refrigerator

When absorption chillers operate in a high temperature,high concentration lithium bromide environment,there are problems with corrosion of the metal components inside them,and corrosion of the metal components by lithium bromide is considered the main factor affecting the operation of the chillers.The tubes of the heat exchangers in absorption chillers are mainly made of metallic copper.Copper tubes are usually used as refrigerant tubes in refrigeration equipment to connect its indoor unit to the outdoor unit.However,copper metal is expensive,which greatly increases the production cost of the absorption chillers.On the other hand,316 stainless steel is inexpensive and has better corrosion resistance due to chromium,forming a passivation film on its surface.Therefore,the use of 316 stainless steel tubes to replace part of the red copper tube can significantly reduce the cost of manufacturing refrigeration equipment and ensure the corrosion resistance of refrigeration equipment.However,in some specific parts of the refrigeration equipment,the stainless steel tube needs to contact the red copper tube.Due to the difference in material corrosion potential,galvanic corrosion will be at the joints of stainless steel and red copper tubes.In order to ensure reliable contact between red copper and stainless steel tubes,it is,therefore,necessary to evaluate the corrosion resistance of the joints of stainless steel and copper heterogeneous connections systematically to obtain the electrochemical corrosion parameters of each component after the welding connection of the two metals and provide theoretical guidance for engineering applications.The main research content of this thesis is as follows:(1)The corrosion behavior of Cu,316 stainless steel,and welds in lithium bromide solution at different temperatures was evaluated by polarization curves and electrochemical impedance spectroscopy techniques.The surface morphology and elemental content of various materials before and after corrosion were compared by Scanning Electron Microscope(SEM),Energy Dispersive Spectrometer(EDS),X-ray Photoelectron Spectroscopy(XPS),and other characterization means to reveal their corrosion mechanisms;the effect of temperature on the galvanic corrosion was studied by Zero Resistance Amperometry(ZRA)technique.The effect of temperature on the corrosion mechanism of electric couples between different couples was investigated by the ZRA technique.The corrosion rate of the material was measured by evaluating the corrosion of the material in 850 g/L lithium bromide solution through a corrosion weight loss test.The results show that:with the increase of temperature,the corrosion resistance of copper and weld gradually deteriorated,316 stainless steel is more prone to pitting corrosion;the degree of galvanic corrosion of all the couples pairs with the increase of the temperature and enhance.The first two couples are 316 stainless steel as the cathode,copper or weld as the anode of galvanic corrosion;for copper-weld couples,the weld corrosion priority is at room temperature.When the temperature at 50℃ and 75℃,the polarity reversal phenomenon in the electric couple pair,copper is corroded.The corrosion loss test showed that the weld showed corrosion resistance close to or slightly better than copper in the lithium bromide solution.(2)The corrosion behavior of Cu,316 stainless steel,and weld seam in different concentrations of lithium bromide solution was evaluated by polarization curve and electrochemical impedance spectroscopy techniques.The influence mechanism of lithium bromide concentration on the corrosion behavior of the three materials was analyzed.In addition,the influence mechanism of lithium bromide concentration on the galvanic coupling corrosion between different coupling pairs was studied by the ZRA technique.The results show that:with the increase of lithium bromide concentration,the corrosion resistance of copper and weld gradually deteriorates,and 316 stainless steel is more prone to pitting corrosion;the degree of galvanic corrosion does not change significantly with the increase of lithium bromide concentration,and in the 316 stainless steel/copper galvanic couple pair,copper is always the anode material(the electrode where corrosion occurs);in the 316 stainless steel/weld galvanic couple pair,the weld is always the anode material.In the copper/weld couple pair,the weld is always the anode material.