| With the continuous development of modern new cities,the laying of gas pipelines and subway lines in cities is also gradually updated,and inevitably there will be gas pipelines and subway lines crossing or parallel.As the track cannot be completely insulated from the earth,part of the current will leak from the track,exacerbating the corrosion of adjacent gas pipelines.Therefore,it is necessary to study the distribution law of stray current leakage in subway,strengthen the detection of stray current in subway,clarify the stray current interference environment where the pipeline is located,and carry out stray current protection measures to provide guarantee for the safe operation of gas pipeline.The stray current distribution models under single and bilateral different power supply modes are established,and the stray current expression in the model is deduced,and the stray current distribution law is obtained.Based on the ideal assumption conditions,the track longitudinal resistance and transition resistance are regarded as uniform resistance,and the resistance distribution model is obtained.The micro-element part of the resistance distribution model is taken,and the differential equation is listed by using Kirchhoff’s law and other knowledge,and the stray current expression is solved.With the help of MATLAB software,the influence factors of the expression are simulated and analyzed by the control variable method.The results show that the factors such as traction current value,track longitudinal resistance and transition resistance have great influence on the stray current distribution,while the other factors have little influence.In order to clarify the stray current interference environment in the pipeline.A number of subway interference sections were selected,test points were arranged on site,test piece simulation measurement method was adopted,stray current was detected through the test data,and the severity of stray current at test points was determined according to the relevant specifications.The tube ground potential fluctuation value of48 test points all exceeded 350 m V.In the tube ground potential migration test of three types,the judgment result of stray current severity at many test points was "strong".In the soil potential gradient test,the soil potential gradient value of 31 test points exceeded 5 m V.The results show that there is strong stray current in the area adjacent to subway track or subway station.The interference source of stray current is confirmed and the validity of detection is verified.By selecting non-subway interference section to detect and compare the stray current,and analyzing the test results of subway interference section in detail,including the influence of typical interference time characteristics and distance on the degree of interference,it is clear that the stray current comes from subway.The pipes in Nigang East section and Minkang Section in the area with serious stray current were selected to excavate at the damaged point of anticorrosion coating.The pipes in Nigang East Section had corrosion defects of about 3mm in depth,and the pipes in Minkang Section had 6 corrosion defects in total,and the most serious pit depth reached 3.42 mm.The results show that the pipeline in the area with serious stray current is easily disturbed and corroded,which verifies the validity of the detection.The protection measures of stray current in subway are put forward.According to the study of stray current distribution law,some measures to reduce stray current generation in subway system are obtained.Based on the stray current drainage method,drainage points were set up in the pipe section in the severely disturbed area,and the method of combining polarity drainage with grounding drainage was adopted to restore the pipes at the 7 abnormal test piles from the under-protection state to the normal protection state.The results show that the effect of stray current on gas pipeline can be significantly reduced by taking effective drainage measures. |
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