针对油气管道CO₂腐蚀环境,研究了Cr含量为1%~5% (质量分数)的5种低铬钢的阳极极化行为,讨论了半钝化行为受Cr含量的影响规律。测试了不同pH值下5种低铬钢的极化曲线,探究了不同Cr含量的低铬钢出现明显半钝化的临界pH值。利用Raman光谱,对比了在不同pH值溶液中极化生成的腐蚀膜的成分。结果表明,随着Cr含量的升高,低铬钢半钝化特征变得更加明显。在CO₂环境下,溶液pH值的升高对Cr(OH)₃沉积有利,基体中Cr的溶解导致低铬钢表面生成了Cr(OH)₃膜,在极化曲线测试过程中,显示出半钝化的特征。

More than 60% corrosion failure of oil/gas pipeline happened in carbon steel pipeline transporting fluid containing CO₂. Adding appropriate amount of Cr to carbon steel can greatly suppress localized corrosion. So, anti-CO₂ low Cr steel and its corrosion mechanism become research hotspot. This work found that active-passive transition region occurred when low Cr steel was anodic polarized. But stable broad passive region like typical passivation was not found. This phenomenon was called semi-passivation. The anodic polarization behavior of low Cr steels with Cr content of 1%~5% and the effect of Cr content on semi-passivation in CO₂ corrosion environment had been studied and discussed respectively. The anode potentiodynamic polarization curves of five kinds of low Cr steels in solutions with different pH values had been tested, subsequently the critical pH value which made the occurrence of the semi-passivation of low Cr steels with different Cr contents had been explored. The components of the corrosion product films on the low Cr steel samples polarized in solutions with various pH values had been compared through the Raman spectroscopy. The results showed that with the increase of Cr content, the semi-passivation characteristics was more obvious. The pH value of solutions in the CO₂ environment contributes to the precipitation of Cr(OH)₃. The Cr³⁺ ions dissolved from the substrate generate the corrosion films of Cr(OH)₃ on the surface, resulting in the semi-passivation characteristics in the tests of anode potentiodynamic polarization.