温度对5Cr钢在模拟油田高温高压环境中CO_(2)腐蚀行为的影响

Effect of Temperature on CO_(2)-inducedCorrosion Behavior of 5Cr Steel in a Simulated Oilfield Produced Hightemperature and High-pressured Water

采用丝束电极技术、形貌表征和EIS测试相结合,研究5Cr钢在不同温度条件下的CO_(2)腐蚀特性。利用XRD、SEM和EDS等技术表征不同条件下腐蚀产物,利用高温高压电化学中阻抗测试技术对5Cr钢CO_(2)腐蚀行为进行研究,并采用丝束电极(WBE)技术分析腐蚀产物/金属界面局部腐蚀电位、腐蚀电流的分布规律。结果表明,电极腐蚀电位整体随腐蚀温度的增加有不同程度的负移,5Cr钢发生腐蚀的倾向增加,腐蚀速率随温度的增加而变大。5Cr钢的电化学阻抗谱中形成半径较大的容抗弧,腐蚀产物膜覆盖程度和致密性增加,等效电路中电荷传递电阻呈变大趋势,电化学反应阻力明显增加。5Cr钢表面局部阳极区形成、扩展使其有产生点蚀的倾向,且形成于腐蚀初期产物膜空隙通道处。腐蚀产物逐渐沉积在点蚀坑内壁,在坑内壁形成了有明显的Cr富集的保护性表面层,原发生点蚀区域由原阳极活性点位转变为阴极区,对其发展起抑制作用。被腐蚀产物膜覆盖下的5Cr钢区域电流发生由阴极向阳极的极性转变现象,产物膜存在孔隙使得5Cr钢基体金属被腐蚀,从而导致阳极电流的出现。

The CO_(2)-induced corrosion of 5Cr steel in a magnetically driven autoclave with a simulated oilfield produced water at different temperatures and pressures was assessed by means of XRD,SEM and EDS as well as electrochemical measurement and wire beam electrode(WBE)technique.The results show that with the increasing temperature,the corrosion potential of the electrode as a whole has different degrees of negative shift,the corrosion tendency and the corrosion rate of 5Cr steel all increase;meanwhile,the capacitive impedance arc with a large radius emerged in the electrochemical impedance spectrum of 5Cr steel,the film coverage degree and compactness of the corrosion product increase,the charge transfer resistance tends to increase,and the resistance of the electrochemical reaction increases significantly.The formation and expansion of the local anode area on the surface of 5Cr steel has the tendency to cause pitting corrosion,which may be preferred to form at defects on the film formed in the early stage of corrosion.The corrosion products are gradually deposited on the inner wall of the pit,then a protective surface layer with obvious Cr enrichment is formed on the inner wall of the pit,thereby,the original pitting corrosion area is transformed from the active sites on the original anode to the cathode area,therefore,the pitting expansion is inhibited.The polar transformation phenomenon of the corrosion current of the local sites of the 5Cr steel beneath the corrosion product film occurs,namely,from cathodic ones turn to anodic ones,and the defects in the corrosion product film make the 5Cr steel substrate corroded,resulting in the appearance of anodic current.