Research On Corrosion And Protective Measures Of Buried Gas Pipeline By Stray Current

As people’s living standards gradually increase,the demand for natural gas will increase greatly.In order to meet the needs of the people’s convenient travel,many cities are vigorously building urban rail transit projects.The traction current of rail transit leaks from the rail into the soil and enters the gas pipeline,which will accelerate the corrosion of the gas pipeline,and the corrosion rate will increase to several dozen times than natural corrosion.The geological conditions of different regions are quite different,and the areas which gas pipelines are densely buried,usually have many urban rail transit lines.Therefore,the problem of stray current protection in urban rail transit is very complicated and has many influencing factors.If the protective measures are adopted blindly,it may cost a lot but not the expected results.This paper analyzes the law of stray current leakage and diffusion in urban rail transit by using equivalent circuit diagram.Based on the knowledge of graph theory,the path of stray current diffusion is simplified into points and directed line segments,and the graph is formed.The current values existing in each part of the graph are calculated by Matlab software,and the factors of stray current leakage and diffusion processes are analyzed.Based on COMSOL Multiphysics simulation software and boundary element method,the simulation model of the gas pipeline network in the core area of a city is built.The simulation data is compared with the measured data to verify the feasibility of the simulation.The protection measures for some sections of pipelines that are subject to high interference is optimized.And the protective effects of different protective measures is considered.For the entire area pipe network,several protective measures are combined in different ways to propose a more effective protection scheme.Suggestions for the protection of stray currents in the core areas of the city is provided.According to the dynamic analysis method,the economics of programs is calculated,and the most effective one is found.The conclusions obtained are as follows:(1)The rail to soil transition resistance has the greatest influence on the stray current of the buried pipeline.The coating resistivity has a great influence.The distance between the tunnel and the gas pipeline is less affected,and the soil resistivity of the surrounding environment has the least influence.(2)The forced grounding drainage station has obvious protection effect on the drainage of the gas pipeline network in the core area of a certain city.Pipes closed to the drainage station are prone to hydrogen embrittlement and peeling of the coating due to the large negative deviation of the tube ground potential.Some sections that are subject to strong interference or are far away from the drainage station need to take further protective measures.(3)The protective range of deep well forced grounding drainage is larger compared with magnesium anode polarity grounding drainage.When both two measures are available at the same time,priority should be given to forced ground drainage.For the pipeline with strong interference,the drainage protective effect of polarity ground drainage is better than the forced ground drainage.The replace of the pipeline coating cannot effectively suppress the stray current interference.If the pipeline coating is replaced on the basis of the drainage protection measures,the stray current interference of the gas pipeline can be greatly improved.Reasonable optimization design of the buried scheme saves material costs and construction costs,and also has a good protection effect against stray current interference.(4)In the core area of a city,which the surrounding subway lines are densely distributed,when polarity ground drainage and forced ground drainage is combined to prevent the stray current interference in the buried steel gas pipeline in the area,it costs less and produces less interference to the surrounding structures.