| During the operation of the subway,the current of the train’s power supply system will leak into the ground through the track,and this part of the leakage current is called stray current.As subway lines and buried pipelines inevitably cross and parallel,stray current will interfere with nearby pipelines,causing abnormal pipeline potential fluctuations,pipeline cathodic protection failure and electrochemical corrosion of pipelines.Therefore,it is of great significance to study the influence of stray current on pipeline potential and the influence of stray current on corrosion behavior.Stray current is dynamic pulse current.Since the propagation speed of the electric field is almost equal to the speed of light,it can be defined as an instantaneous constant current when using electromagnetic finite element analysis.In the stray current corrosion test,direct current cannot be used to replace the stray current.Therefore,it is feasible to simulate and analyze the distribution of stray current and the change of pipeline potential in the finite element electromagnetic field module.It is also necessary to use the current with fluctuating characteristics to conduct the stray current corrosion test.Based on a large number of domestic and foreign literatures,this paper introduces the stray current detection method and evaluation method in detail,and the stray current item of the pipeline is detected on the spot,and the track-soil-pipe finite element model is established and simulated in accordance with the actual situation.According to the pipeline potential changes obtained by simulation,the corresponding interference voltage fluctuation range is set,and the stray current corrosion test is performed to study the corresponding relationship between the pipeline metal surface potential fluctuation range and the corrosion behavior.The main contents are as follows:(1)Taking a high-pressure gas pipeline in Guangzhou as an example,short-term and long-term testing of the on/off potential of the 12 test piles of the pipeline were carried out by using the test piece power-off method and the cathodic power-off potential tester,and the protection of the pipeline was done according to the test results.Make an evaluation to determine the direction of stray current and the location of pipeline corrosion.(2)Establish a rail-soil-pipe stray current distribution model in ANSYS finite element software,and discuss the distribution of pipeline protection potential under different parameters.The results show that the crossing angle of the track and the pipeline will affect the location of the maximum potential of the pipeline.When the crossing angle is between 0°and 90°,the greater the crossing angle,the closer the location of the maximum potential of the pipeline is to the crossing point.Under different soil media,pipe-rail spacing and track load,the pipeline potential is different,and the maximum value of the pipeline potential is the same.(3)A stray current corrosion test is done in this paper.In order to simulate the potential change of the pipeline where the stray current flows into and out of the area,an interference voltage with a fluctuation range of 0～E_u(|E_u|>0)is applied to the metal surface of the pipeline.The results show that the metal corrosion potential during interference has an oscillating effect.With the continuous increase of|E_u|,both the charge transfer resistance and the polarization resistance will increase.The corrosion products,corrosion morphology and corrosion rate of metals in the inflow and outflow areas of stray current are different. |
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