Study On The Effect Of Soil Chemistry On Stray Current Corrosion Of Buried Metals In Urban Rail Transit

In recent years,urban rail transit has become the main means of transportation in many large and medium-sized cities in China because of its punctuality,fast and safety.However,with the convenience brought by urban rail transit,the stray current generated by it has become a problem that cannot be ignored.The long-term existence of stray current will corrode the buried metal along the line,cause huge economic losses,and bring huge security risks to the maintenance personnel.Aiming at the problems existing in the current research on stray current,this thesis studies the effects of soil chemical properties(soil salt content and soil p H)and buried depth on the corrosion of buried metals by stray current based on the method of combining experiments with COMSOL multiphysical field simulation.Firstly,this thesis introduces the research status of stray current and its corrosion in urban rail transit at home and abroad,and the generation principle and harmfulness of stray current.Secondly,based on the traditional resistance distribution network,the mathematical model of the stray current in the rail-drainage-ground structure is established without ignoring the change of soil resistivity,and the analytical expression of the stray current in the ground is obtained through derivative calculation.Thirdly,according to the mathematical model,the experimental model of rail-drainage-ground resistance network distribution and a small stray current testing platform used in the experiment are built.The leakage current value in the ground are measured under different traction currents based on the unilateral power supply mode,and the stray current value are obtained by calculation.Finally,the maximum stray current corresponding to the traction current of 3A in the experiment is selected as the external input current for the buried metal corrosion experiment.The effects of soil salt content,soil p H,and buried depth on buried metal corrosion are experimented and simulated respectively,and the experimental results are compared and analyzed with the simulation results to ensure the accuracy of the research results.Through the comparison and analysis of the experimental and simulation results,we can draw the following conclusions.The leakage current and stray current in the ground will increase with the increase of traction current,and the stray current will reach the maximum in the middle of the power supply interval and gradually decrease to both sides.Under the same soil environment,the corrosion degree of buried metal increases with the increase of soil salt content.In the same soil environment,when there is stray current interference,the deeper the buried depth of the metal,the lighter the corrosion degree of buried metal,and when there is no stray current interference,the buried depth of the metal will not affect the metal corrosion degree.Under the same soil environment,the corrosion degree of buried metal is the most serious in acidic soil environment,and the stronger the soil acidity,the more serious the corrosion degree of buried metal,followed by alkaline soil environment,and the stronger the soil alkalinity,the more serious the corrosion degree of buried metal,and the least corrosion degree of buried metal in neutral soil environment.Under the interference of the stray current,the buried metal presents obvious local corrosion phenomenon,that is,the anode area of the buried metal is seriously corroded,while the cathode area is hardly corroded.But under the absence of stray current interference,the buried metal presents uniform corrosion characteristics,and no local corrosion phenomenon occurs.Under the same soil environment and experimental conditions,the corrosion of the buried metal is more serious under the interference of stray current,and even obvious corrosion deformation and perforation phenomena will occur.However,without the stray current interference,the corrosion degree of the buried metal is very light and small,indicating that the existence of stray current will seriously aggravate the corrosion degree of the buried metal,reduce its structural properties,and shorten its service life.