通过交流腐蚀模拟实验考察了X70钢在4种环境介质中的交流腐蚀行为,获得了X70钢在4种介质中的腐蚀速率K_d。结果表明,腐蚀速率\begin{array}{c}{K}_{\mathit{d}\left(\mathit{NaCl}\right)}\end{array}>\begin{array}{c}{K}_{\mathit{d}\left(N\right.a_{2}S{O}_4)}\end{array}>\begin{array}{c}{K}_{\mathit{d}\left(\mathit{CaC}{l}_2\right)}\end{array}>\begin{array}{c}{K}_{\mathit{d}\left(\mathit{MgC}{l}_2\right)}\end{array}。采用SEM、EDS和XRD对腐蚀产物膜的表面/截面微观形貌、元素和物相成分进行了表征与分析,探讨了X70钢在相同交流电流密度下,不同介质中腐蚀速率差异的原因：在Na₂SO₄和NaCl介质中,腐蚀产物膜比较疏松,侵蚀性离子SO₄^2-和Cl^-的存在会加速X70钢的腐蚀,Na⁺不会影响腐蚀产物膜的形成;在MgCl₂和CaCl₂介质中,Ca²⁺和Mg²⁺的存在有利于形成保护性好的致密腐蚀产物膜。

During the past decades, more buried oil or gas pipeline failures have been attributed to alternating current (AC) interference, and finally, those corrosion failures were investigated and the AC current density was identified as the critical influence parameter. There is general agreement on AC current density as a chief factor in determining metal wastage condition or assessing the AC corrosion risk for any type of soil in the presence of AC corrosion. Different degrees of AC corrosion may occurr if long distance pipelines pass through different kinds of soil environments, however, the effect of soil ions on pipeline steel without cathodic protection is still not well understood. Therefore, it is imperative to study the AC corrosion behaviors of pipeline steel in different soil environments. In the AC corrosion simulation experiment, by investigating the AC corrosion behaviors of X70 steel in 4 kinds of environmental media, the corrosion rates (K_d) were obtained, whose order was \begin{array}{c}{K}_{\mathit{d}\left(\mathit{NaCl}\right)}\end{array}>\begin{array}{c}{K}_{\mathit{d}\left(N\right.a_{2}S{O}_4)}\end{array}>\begin{array}{c}{K}_{\mathit{d}\left(\mathit{CaC}{l}_2\right)}\end{array}>\begin{array}{c}{K}_{\mathit{d}\left(\mathit{MgC}{l}_2\right)}\end{array}. SEM, EDS and XRD were used to characterize and analyse the microscope morphologies, elements and phase compositions of the corrosion product films surfaces/cross-sections. Under the same AC current density, the reasons of differences of X70 steel's corrosion rate in different media were discussed. The presence of corrosive ions SO₄^2- and Cl^- would accelerate the corrosion rate, Na⁺ would not affect the formation of corrosion product film in NaCl and Na₂SO₄ solution media, however, the presence of Ca²⁺ and Mg²⁺ were helpful to form protective corrosion product films in MgCl₂ and CaCl₂ solution media.