X80管线钢在NaHCO_3溶液中的阳极电化学行为

ANODIC ELECTROCHEMICAL BEHAVIOR OF X80 PIPELINE STEEL IN NaHCO_3 SOLUTION

采用动电位极化曲线、动电位电化学阻抗谱(DEIS)和SEM研究了X80管线钢在NaHCO_3溶液中的阳极电化学行为,结果表明:随着HCO_3^-浓度增加,X80管线钢腐蚀速率呈现先增加、后减小的趋势,X80管线钢"钝化"的临界HCO_3^-浓度为0.009 mol/L.随着HCO_3^-浓度增加,极化曲线阳极电流峰发生变化,当HCO_3^-浓度低于0.009 mol/L时,无阳极电流峰;当浓度在0.009—0.05 mol/L时,有一个阳极电流峰;当浓度增加到0.1 mol/L时,出现两个明显的阳极电流峰,且第1峰与第2峰的峰值电流比随浓度的增大而逐渐增大,DEIS结果与动电位极化曲线完全对应,二者相结合可以很好地研究在不同电位下NaHCO_3溶液中X80管线钢的腐蚀行为,同时对其腐蚀产物和腐蚀机理进行了分析。

X80 steel has the potential to be widely used for building the gas transmission pipelines because of its high-intensity and high-toughness.Its corrosion performance is a key problem for the life expectancy,especially in soil environment.The anodic electrochemical behavior of X80 pipeline steel in NaHCO3 solution was studied using potentiodynamic polarization curve,dynamic electrochemical impedance spectroscopy（DEIS） as well as SEM observation.The results show that the shape of the polarization curves changes with HCO3^-concentration.The corrosion rate of X80 pipeline steel first increases and then decreases with the increase of HCO3^-concentration.0.009 mol/L is the critical concentration of HCO3^-for forming the ＇passive＇ film of the X80 pipeline steel.There is no anodic current peak in the solution when HCO3^-concentration is below 0.009 mol/L,and one anodic current peak below 0.05 mol/L and two anodic current peaks above 0.1 mol/L.The results of the DEIS measurements are in complete agreement with the potentiodynamic polarization curve.The corrosion products change with polarization potential and two equivalent circuits are used to explain the experimental spectra of X80 pipeline steel in the whole corrosion process.Therefore,the combination of dynamic polarization curve and DEIS methods can be well used to investigate the corrosion behavior of X80 pipeline steel in NaHCO3 solution at various potentials.In addition,different corrosion products forming at various potentials and the corrosion mechanisms of X80 pipeline steel are briefly analyzed.