Study On Corrosion Behavior And Protection Measures Of Buried Oil And Gas Pipelines Under DC Grounding Pole Interference

With the increasing demand for energy in China,the construction of long-distance oil and gas pipelines and high-voltage DC transmission projects has become inevitable in order to realize the transmission of oil and gas and long-distance large-capacity electricity,and the similarity of the routing of the two leads to local pipelines being disturbed by the corrosion of high-voltage DC grounding electrodes into the ground current.In this paper,we use experimental simulation and computational simulation to study the corrosion behavior of buried oil and gas pipelines and protective measures for the actual situation that cannot be studied by field test due to the uncertain size of high-voltage DC grounding electrode inlet current,uncertain discharge duration and uncertain size of pipeline anticorrosive layer breakage point and other factors.Using experimental simulation methods to study the interference voltage,interference duration,the size of the corrosion protection layer breakage point and the impact of cathodic protection potential on the corrosion behavior of X70 pipeline steel.The results show that:under different interference voltage,with the increase of interference voltage,the specimen current density increases,corrosion rate is a linear increase,and different interference voltage specimen corrosion rate test measured value and Faraday theory calculated value is basically the same;in different interference length,the specimen current density are decreasing stable trend,and corrosion rate is first increase and then decrease trend;interference voltage is certain,multiple discharge cumulative interference When the interference voltage is certain,the accumulated interference time and a continuous discharge time on the specimen produced roughly the same risk.Different anticorrosive layer breakage point area,corrosion rate and anticorrosive layer breakage point area is a linear decreasing relationship,that is,the same interference voltage,the smaller the anticorrosive layer breakage point area,the greater the current density,the greater the corrosion rate;specimens in-1.6 V_CSE cathodic protection potential,belongs to the over-protected state,corrosion rate significantly reduced,specimens if long-term in the cathodic protection potential under insufficient conditions(cathodic protection potential of-0.8 V_CSE),the annual corrosion rate of the specimen will increase,in order to reduce the risk of pipeline corrosion,should make the pipeline cathodic protection potential is within a reasonable range.Computational simulation methods were used to study the effects of horizontal zinc strip,segmental insulation and forced drainage protection measures on the corrosion protection mitigation rate of X70 pipeline steel.The results show that:when the grounding current is set to 1000 A,2000 A and 4000 A respectively,the grounding current and the pipe interference voltage under the condition of no protection measures are linearly increasing,and the mitigation rate under the condition of horizontal zinc strip protection measures is approximately linearly decreasing with the size of the grounding current;the mitigation rate under the condition of segmental insulation protection measures is approximately linearly increasing with the grounding current,and the mitigation rate under the condition of Under the condition of forced drainage protection measures,the mitigation rate tends to decrease linearly with the magnitude of incoming current;under the condition of incoming current of 2000 A,the mitigation effect gradually increases with the increase of zinc strip diameter,but the increase is smaller,and the mitigation rate of horizontal zinc strip laid on both sides of the pipe（inside of the pipe and grounding pole,outside of the pipe and grounding pole）is basically the same;under the condition of incoming current of 2000 A,the mitigation rate of insulated joints installed in the interference Under the condition of incoming current of 2000 A,the mitigation rate when insulating joints are installed at the middle value of the interference potential is higher than that at the position of 0 V.Installing insulating joints at the middle value of the interference potential,the interference potential along the pipeline decreases significantly as the number of insulating joints installed increases,and installing multiple insulating joints can effectively reduce the interference voltage along the pipeline.In this paper,the corrosion behavior of buried oil and gas pipelines and the factors influencing the mitigation rate of protective measures are studied by combining experimental and computational simulations of DC grounding electrode inlet currents,and the results have certain theoretical significance and practical application value for the laying of horizontal zinc strips and the installation of insulating joints in buried oil and gas pipelines.