Research On Corrosion Characteristics Of Stray Current In Grounding Grid

As high intensity stray current roams in soil,the grounding grid metals would be suffered seriously corrosion.The stray current is derived from substation discharge and railway track leakage flow.The research and protection work about stray current corrosion was developing lately in China,and there were no standards about stray current corrosion for ground grid.Therefore research on corrosion characteristics of stray current in grounding grid is of great significance.The corrosion properties and regularities of Q235 flat steel,Q235 galvanized flat steel and copper were studied,which affected by stray current in soil.Influencing corrosion factors for soil were also researched,which including moisture content,chloride ion and sulfate ion.The research methods included electrochemical method,weight-loss measurement and micro-analysis,the experimental results were as following.The results showed as follow.(1)All of the electrochemical impedance spectroscopy was characterized by an eccentric semicircle with a certain dispersion effect.As stray current was small(5mA),EIS response frequency of Q235 flat steel and copper was affected by moisture content.Q23 5galvanized flat steel gave priority to diffusion control in different moisture content and its response frequency wasn't affected by moisture content.EIS response frequency and mass transfer of metal materials were influenced by different stray current in same chlorine and sulfate ion content.Different chlorine(0.005%?0.05%)and sulfate ion(0.05%?0.5%)content in soil with same stray current only affected the mass transfer processes of cathode and anode of metal materials.(2)The corrosion rate of materials increased with increasing stray current in same moisture content,chloride ion and sulfate ion content in soil.Comparing with three kinds of materials,the corrosion rate of copper was the least and Q235 flat steel was largest.(3)Microscopic analysis results of grounding grids in 20%moisture content soil after 30d with 5mA stray current showed that:the size of corrosion products of Q235 flat steel were larger compared with other two kinds of materials,which were mainly Fe3O4.The size of corrosion products of Q235 galvanized flat steel and copper were small,smooth and uniform distribution.Corrosion products of Q235 galvanized flat steel were mainly Zn(OH)2,ZnO and Fe3O4 respectively,and corrosion products of copper were mainly CuO and Cu2O.(4)Microscopic analysis results of grounding grids in 0.05%Cl" content soil after 30d with 40mA stray current showed that:the corrosion products of Q235 flat steel were mainly Fe3O4,Fe2O3 and FeCl2.Corrosion products of Q23 5 galvanized flat steel were Zn(OH)2 and FeCl3·5H2O.Corrosion products of copper were CuO,Cu2O and Cu2Cl(OH)3.Microscopic analysis results of grounding grids in 0.5%SO42-content soil after 30d with 40mA stray current showed that:corrosion products of Q235 flat steel were mainly Fe3O4 and Fe2(SO4)3.Corrosion products of Q235 galvanized flat steel were Zn(OH)2,ZnO and ZnFe(SO4)2-7H2O.Corrosion products of copper were CuO,Cu2O,Cu4(SO4)2(OH)6 and CuSO4-H2O.(5)To sum up,corrosion of grounding grid materials caused by stray current was very severe.Copper had better resistant to stray current corrosion compared with Q235 galvanized flat steel and Q235 flat steel.The anti-corrosion properties of Q235 galvanized flat steel were better than Q235 flat steel.But Q235 galvanized flat steel would occur electrolytic corrosion in presence of stray current,thus it couldn't obviously improve its anti-corrosion performance.Comparing with other two kinds of materials,copper had better anti-corrosion performance in soil environment,but it had some environmental problem and its price was a little more expensive.Thus,choosing the corresponding grounding grid materials should be based on the actual situation in presence of stray current.