Numerical Simulation Of Stress Corrosion Cracking Of High-strength Pipeline Steel In Soil Environment

Pipeline transportation has become the main way of oil and gas energy transportation due to its good safety and economy.The demand for energy in economic and social development has increased significantly.The development direction of pipeline transportation is to use large diameter,high pressure and high strength pipeline steel.Buried pipelines are often used,and stress corrosion occurs under the action of soil environment and stress,which seriously threatens the safe operation of pipelines.This paper mainly studies the stress corrosion of high strength pipeline steel in the soil environment,taking X90 pipeline steel as the research object,through the electrochemical corrosion experiment,analyze the corrosion resistance characteristics of X90 pipeline steel,and obtain the electrochemical parameters of X90 steel corrosion;The corrosion behavior of X90 pipeline steel under different stress and strain,pipeline defects and environmental parameters is analyzed by finite element numerical simulation on the basis of experiment,which provides reference for the application of X90 pipeline steel corrosion protection.The main research contents are as follows:The corrosion electrochemical behavior of X90 pipeline steel in soil simulated solution was studied by an electrochemical workstation using a dynamic polarization curve and AC impedance spectroscopy.Corrosion electrochemical parameters such as corrosion potential,corrosion current density,Tafel slope of cathode and anode,electrochemical impedance,and polarization resistance were obtained at different polarization times,concentrations of different ions(Cl^-,HCO₃^-,SO₄^2-)and different temperatures.The results indicate that with the passage of polarization time,the corrosion current density first decreases,then increases,and then decreases again;With the increase of Cl^-,HCO₃^-concentration,and temperature,the corrosion current density gradually increases.With the increase of SO₄^2-concentration,the corrosion current density generally increases,reaching the maximum value at 0.0025mol/L SO₄^2-corrosion current density,and then the corrosion current density firstly decreases and then slightly increases and then decreases.The corrosion electrochemical parameters obtained from the experiment are applied to the COMSOL multi-physical field coupling simulation software.Based on the mechanical-electrochemical coupling equation,a finite element stress corrosion model is established to study the impact of strain,pipeline internal pressure,pipeline defects,ion concentration and temperature factors on stress corrosion.The degree of stress corrosion is characterized by the stress,plastic strain,corrosion potential,corrosion current density and other parameters at the defect.The results show that,in the elastic strain stage,the mechanical-electrochemical effect is not obvious due to the small stress at the defect,and the corrosion degree at the center and both ends is basically the same;When the strain is plastic deformation,the stress at the center of the defect is concentrated,the mechanical-electrochemical effect is obvious,and the corrosion at the center of the defect is more serious than that at both ends.