Research On The Interference Mechanism And Protection Of The Stray Current Of DC Tram On The Corrosion Behavior Of Pipelines

With the rapid development of Chinese national economy,more and more buried pipelines and trams have been built and put into use,and the speed of planning and construction is faster and faster,and they begin to develop from first-tier cities to provincial capital cities and then to third and fourth-tier cities.These trams and underground pipelines will inevitably cross or parallel at close distance,thus forming a "common corridor".In this case,the possibility of leakage current from tramway track into adjacent damaged buried pipelines is increased.At the outlet of stray current at the pipeline-soil interface,the pipeline will produce serious corrosion.Once these buried pipelines are corroded and cracked,they will cause fire and explosion,cause environmental pollution,threaten personal safety and cause huge economic losses.Therefore,this paper carries out research on the interference rule and protection of stray current of DC tram on pipeline corrosion behavior,in order to reveal the interference mechanism of stray current of DC tram on pipeline corrosion,and provide corresponding reference for pipeline protection.In this paper,the following aspects of work are specifically carried out:(1)The existing methods of stray current interference detection are analyzed.The on-line potential method and the test piece power-off method are selected to carry out field testing and field monitoring.The interference of leakage current on the ground potential of buried pipeline during the operation of DC tram and subway is analyzed.The results show that stray current of rail transit changes the ground polarization potential of pipeline and shows obvious dynamic state.The characteristics of direct current interference have great influence on pipeline.(2)The current leakage law of DC tramcar and its influence on tube-to-ground potential were studied.Based on the circuit principle,the theoretical model of track stray current leakage of double-sided DC tram is established.The model is validated by solving,analyzing and designing experiments with MATLAB.The results show that the leakage of track stray current is proportional to the size of track potential.Based on COMSOL Multiphysics,the earth and pipe-ground potential distribution models are established,which can greatly disturb the stray current.The distribution of ground potential and the distribution and change of pipe-ground potential are analyzed.The analysis shows that when the pipeline-rail is parallel,the interference of pipe-ground potential is the greatest at the running position of DC tram and at the substation.When the rail-tube is orthogonal,the interference of pipe-ground potential is the greatest at the intersection point.When the rail-tube is crossed at a small angle,the interference of pipe-ground potential is the greatest at the intersection point and near the DC tram and substation.The ground potential change curve of the same point tube is similar to the sinusoidal curve.The horizontal position will affect the amplitude of the potential change,and the vertical position will affect the offset value of the potential change.(3)Experiments on electrochemical corrosion behavior of DC tram stray current on pipeline were carried out.The magnitude,frequency and offset of the characteristic parameters of pipe-to-ground potential variation were analyzed.The effects of different pipe-to-ground potential variation parameters on the corrosion behavior and mechanism of pipeline metal were studied by electrochemical platform test,and the corrosion weight loss experiment was carried out.Through the analysis of open circuit potential,polarization curve,AC impedance spectroscopy,corrosion rate and morphology,the results show that the bigger the change amplitude of pipe-to-ground potential,the more serious the corrosion is,and the corrosion is more serious under low frequency interference,and the offset will accelerate the corrosion.(4)The pipeline corrosion risk section and protective control measures under stray current interference of DC tram are studied.By analyzing the operation parameters of different DC trams and the parameters related to the location of pipelines,it is considered that the increase of station spacing of DC tram track substation and the acceleration of DC tram speed will promote corrosion.The corrosion of pipelines passing through DC tram substation is the most serious,which should be avoided as far as possible.The protection of rail-pipe intersection needs to be strengthened.Polyethylene three-layer structure anticorrosive layer and row can be used.Flow protection and cathodic protection are combined to protect pipelines.The research results provide theoretical guidance for reducing the stray current interference of the pipeline and ensuring the safe operation of the pipeline.