Research On Corrosion Prediction Of Buried Steel Gas Pipeline By Stray Current In Subway

The subway provides power for the metro locomotive.When the power supply current flows through the rails,part of the current leaks to the earth to form the stray currents.For buried steel gas pipelines laid around the subway,when stray currents flowing into the pipeline may cause electrochemical corrosion,affecting the use of the pipeline,and even causing corrosion perforation to cause leakage and fire and explosion accidents.Therefore,it is of great significance to analyze the causes of stray currents and corrosion mechanisms,study the stray current distribution,and construct stray current corrosion prediction models.Based on a large number of domestic and foreign literatures,this paper builds a stray current distribution model and simulates it based on the stray current distribution of the subway.It combines the stray current corrosion evaluation criteria to evaluate the measured data and proposes protective measures.Then,the stray current corrosion prediction model was established to predict the corrosion of buried pipelines.The main contents of the thesis include:(1)By studying the distribution of stray currents,distribution models of ''Running rails-Metal mesh'' and ''Running rails-Discharging nets-Metal mesh'' were established respectively.The distribution formulas of walking rail current,walking rail voltage,stray current and current in draining net are deduced respectively.(2)Using MATLAB to simulate the stray current distribution,the effect of drainage network and the influence of different influencing factors on stray current distribution were studied.The results show that: there were about 72% of the stray currents can be collected by the drainage network;the stray current is linearly related to the supply current and the longitudinal resistance of the traveling rails;when the distance between substations exceeds 2km,the discharge rate is significantly lower than the increase rate of stray current;when the transition resistance is greater than 11?·km,the stray current decay rate decreases and remains at a relatively small value.(3)Integrating stray current corrosion evaluation criterias,corrosion assessment of buried pipelines along the Guangzhou-Foshan line was conducted,and the stray current inflow,outflow,and corrosion locations were deterimined.Based on the simulation results of stray current distribution,the control of the source of the subway system,the drainage control of the circulation process and the corrosion protection measures of the buried pipeline were proposed.(4)An ANFIS corrosion prediction model and a BP neural network corrosion predictionmodel were established respectively.The grey correlation analysis was used to determine the model input,and the fluctuation of pipeline potential was used as the model output,the prediction errors of training data and test data were studied respectively.The prediction errors of training data and test data were studied respectively.For the test data prediction,the ANFIS prediction error is basically less than 10%,and has better generalization performance.