利用浸泡实验分别模拟了低合金钢3Cr和X70在含有超临界CO₂的3.5%NaCl溶液和溶解有NaCl溶液的超临界CO₂相中的缝隙腐蚀行为。采用SEM、EDS和3D显微镜分析了腐蚀产物膜的形貌和成分,运用失重法测试了不同环境下低合金钢的腐蚀速率。结果表明,在超临界CO₂环境下低合金钢在缝隙内部腐蚀较轻,在缝隙边缘处发生了明显的腐蚀。这种缝隙腐蚀现象是由于缝隙内部与外部之间形成的电偶效应引起的。2种钢在超临界CO₂相中的均匀腐蚀速率均低于局部腐蚀速率,在NaCl溶液中的情况则相反。在超临界CO₂环境中,3Cr钢的耐均匀腐蚀性能优于X70钢,而耐局部腐蚀性能则劣于X70钢。2种钢缝隙腐蚀行为的差异主要是Cr含量不同造成的,而Cu在3Cr钢缝隙边缘处的富集可能对缝隙腐蚀过程起到了促进作用。

With the exploitation of high pressure gas fields and the development of carbon capture and storage (CCS) techniques, the corrosion problem of steels under CO₂ environment has been paid more and more attention. To transportation easier and cost reduction, CO₂ in pipelines and containers is usually pressured to a high pressure, such as supercritical state. The supercritical CO₂ corrosion environment includes the CO₂-saturated aqueous phase and the water-saturated supercritical CO₂ (SC CO₂) phase. Moreover, corrosive ions such as Cl^- usually exist in CO₂ corrosion environment, which could accelerate the occurrence of corrosion. Low alloy steels, widely used as pipelines and construction materials in oil/gas and CCS industries, are susceptible to corrosion in the aggressive environment that contains high-concentration ions and acidic gases, especially to severe localized corrosion. In this work, the crevice corrosion behavior of 3Cr and X70 steels exposed in supercritical CO₂-saturated 3.5%NaCl solution and NaCl solution-saturated supercritical CO₂ phase was investigated. SEM, EDS and 3D laser microscopy were used to analyze the corrosion product scale on the steel surface. The results show that both the steels occurred crevice corrosion on the edge of crevice, but slightly occurred corrosion inside the crevice. The crevice corrosion occurred due to the galvanic effect of areas inside and outside the crevice. In supercritical CO₂ phase, 3Cr steel exhibited a higher uniform corrosion resistance than X70 steel, while the crevice corrosion resistance of 3Cr steel was lower than that of X70 steel. The different crevice corrosion behaviors between X70 and 3Cr steels might be attributed to the synergistic effect of elements Cr and Cu on enhancing the crevice corrosion.