Study On Corrosion And Protection Measures Of Buried Metal Pipeline Around Dc Grounding Electrode

Recent years,with fast economy and society development in China,the demand for electrical energy and fossil fuel continues to grow.Accompanying this are the escalated number of projects for high voltage direct current(HVDC)transmission and oil/gas pipelines.As major consumers of power and oil/gas often overlap,there are chances DC grounding electrodes are located inevitably close to metal oil/gas pipelines.In this scenario,the grounding current of DC electrodes could induce electrochemical corrosion of the pipelines.Additionally,the pipelines are also affected by soil corrosion.Considering both factors,appropriate protection measures are essential to bring the corrosion rate to a controllable level.This is of great importance to ensure safe operations of the buried metal pipelines around DC grounding electrodes.According to Faraday’s laws of electrolysis,the amount of electrochemical corrosion of a pipeline is proportional to the leakage current density.The MALZ module of CDEGS software can simulate metal conductors under various soil types and calculate the leakage current density on the surface of each section of the conductor.In this dissertation,firstly,equivalent circuit model,simulation experiment platform and CDEGS simulation model of a buried metal pipeline around DC grounding electrode were established.By comparing theoretical,experimental and simulation results of the leakage current density of the pipeline,the accuracy of this CDEGS simulation model was validated.Secondly,in order to reduce the influence of electrochemical corrosion on the pipeline,effects of four frequently-used protective measures on reducing the leakage current density of pipeline were studied based on CDEGS simulations.These protective measures are piecewise insulation protection,mitigation wire protection,concentrative grounding drainage protection and cathode drainage protection.Thirdly,based on damage rate of pipeline anti-corrosion coating,pipeline inspection cycle,inspection technology for damage points of anti-corrosion coating and grounding electrode operation condition,this dissertation proposed a calculation method of electrochemical corrosion rate at the damaged point of the pipeline anticorrosive coating,and studied the effect of soil resistivity on different protective measures.Finally,according to the residual wall thickness evaluation standard in oil/gas pipeline industry,on the premise of superposing pipeline soil corrosion,a threshold of pipeline electrochemical corrosion rate was proposed.From this,the selection of pipeline protective measures and the formulation of protection scheme in different soil environments were further studied.This dissertation could provide theoretical and practical references for calculation of metal pipeline corrosion rate,selection of protective measures and formulation of protection scheme in the early stage of engineering designs.