| Under the influence of stray current leaked from electrical equipment,the pipelines nearby are out of the natural corrosion state and enter accelerated corrosion,which leads to the reduction of the normal life span of the pipelines,as well as environmental pollution and energy waste.This article focuses on the corrosion of pipelines caused by stray currents.Through COMSOL simulation,the main factors affecting pipeline potential fluctuations and the effectiveness of cathodic protection under specific subway operating conditions are analyzed.Laboratory experiments are conducted to explore the impact of specific DC interference and AC interference on accelerated corrosion of pipelines in different environments.The specific research results are as follows:Through the simulation of the equivalent model of rail-pipe-soil,it is found that during subway operation,the rise of rail potential causes the pipeline potential to deviate from the natural state,and the stray current flow caused by rail leakage determines the degree of pipeline corrosion.The increase in locomotive traction current and rail longitudinal resistance leads to an increase in rail and pipeline potential fluctuations and an increase in rail leakage current,while the rail to ground transition resistance mainly affects the rail leakage current.Under simulated working conditions,only pipelines with a maximum length of no more than20% are in cathodic protection state.Analysis suggests that higher soil resistivity or pipeline anti-corrosion layer resistivity has a certain mitigating effect on stray current corrosion of pipelines.The increased DC stray current leads to an increase in the corrosion rate of X70 pipeline steel.Corrosion is more likely to occur in strong alkaline environments with a pH of 10.0when DC is less than 30 m A,and weak acidic solutions with a pH of 4.0 when DC is greater than 30 m A have a higher corrosion rate.The increase in chloride ion concentration promotes ion migration in the electric field,accelerates the corrosion of X70 steel,and weak acidic environments are more conducive to cross corrosion between chloride ions and DC.An increase in AC stray current or chloride ion concentration leads to an increase in the corrosion current density of X70 steel.However,there is a threshold value for the accelerated AC corrosion effect of chloride ions on X70 steel.Before reaching this threshold value,the increase in chloride ion concentration leads to greater and greater corrosion.After this threshold value,chloride ions will no longer be the main factor in accelerating pipeline corrosion.Comparing the corrosion caused by pH,chloride ion concentration,and stray current,it can be seen that in a solution with the same salt ion composition,when DC interference is applied,the degree of corrosion impact varies from large to small: DC stray current>chloride ion concentration>pH;When applying AC interference,the degree of influence of three parameters on pipeline corrosion dissolution ranges from large to small: AC stray current>chloride ion concentration>pH.In the AC corrosion interference experiment,the threshold value of chloride ion concentration accelerating corrosion is smaller than that in the DC corrosion interference experiment.Under the same interference conditions,the corrosion caused by AC interference is weaker than that caused by DC interference. |
