Ca~(2+)和Mg~(2+)对CO_2环境中点蚀形貌的影响

研究了 CO2 环境下 P110油管钢在不同介质中的点蚀形貌。结果表明 :点蚀形貌与腐蚀介质组成密切相关。在不含可生成难溶性碳酸盐的金属阳离子的介质中 ,P110油管钢的点蚀形貌为典型的 V形点蚀坑 ;在含 Ca2 +或 Mg2 +的介质中 ,点蚀则表现为 V形、半球形和闭口圆球形 3种形貌并存。蚀坑腐蚀产物的 SEM分析证实 ,Ca2 +、Mg2 +影响点蚀形貌的重要原因是 :这些离子的难溶性碳酸盐在点蚀坑上部优先沉积 ,有效地抑制了点蚀坑上部的金属溶解速度。试验中还发现 ,Cl-的存在并不是 CO2 环境中发生点蚀的必要条件 ,但 Cl-会加速点蚀的发展

Effect of Ca~(2+) and Mg~(2+) on Pitting Morphology in CO_2 Environment

The pitting morphology for P110 tubular steel in CO 2 bearing solutions with different composition was investigated. Results indicate that there is a very close relationship between pitting morphology and solution chemistry. In the solution without any metallic cations being able to form insoluble carbonate, the P110 steel presents typical V shape pitting. Whereas in the solution containing Ca 2+ or Mg 2+ ions, the V shape together with semi spherical and closed spherical pitting are appeared. The SEM analysis of the corrosion products in pitting indicated that insoluble carbonate formed from Ca 2+ and Mg 2+ ions are preferentially precipitated at the upper part of pitting, which can significantly reduce the in situ corrosion rate as the key factor contributing to the change of pitting morphology. Test results also show that pitting could occur in CO 2 environment without Cl -, but Cl - really promotes pitting.