碳钢高温高压CO2腐蚀产物膜的形成机制

利用高温高压反应釜模拟了N80钢在CO2分压1MPa、温度90℃、流速1ms-1条件下地层水中不同时间的腐蚀行为,并应用SEM、EDS和XRD等微观分析手段研究了腐蚀产物膜的微观形貌、成分和结构特征,探讨了腐蚀产物膜的形成机制. 结果表明:在腐蚀开始阶段(8h),腐蚀产物主要为Fe3C,并有少量的FeCO3形成. 随着腐蚀的进行(72h后),腐蚀产物膜基本上为FeCO3. 腐蚀产物膜由内外两层构成:内层膜是溶液中HCO-3不断透过膜进入膜/基界面与基体反应形成,并使膜/基界面不断向内推进;外层膜是由于溶液中Fe2 和CO2-3的浓度超过FeCO3的容度积,FeCO3晶体在内层膜表面形核并长大而形成. 外层膜的晶粒比较细小、致密. 内层膜与外层膜的界面结合比较弱,而内层膜与基体的结合比较强.

Formation mechanism of corrosion scales of carbon steel by CO2 corrosion under high temperature and high pressure

The corrosion behaviors of carbon steel exposed to CO2-containing water under high temperature and high pressure for different intervals of time were measured by using an autoclave.The morphology and microstructure of the CO2 corrosion scale were investigated by SEM,EDS and XRD,and its formation mechanism was discussed.The results indicate that the corrosion scale is mainly composed of Fe3C and a little FeCO3 in the beginning period(8 h),and with the process of corrosion(after 72 h)it changes to FeCO3.The corrosion scale consists of inner and outer scales.HCO-3 penetrates the scale,reaches the scale/substrate interface and reacts with substrate to form the inner scale,while the formation of the outer scale is attributed to the concentration of Fe2 and CO2-3 in the solution exceeding the solubility of FeCO3.The grain size of the outer scale is smaller and denser than that of the inner scale.The adhesion intensity between the inner and outer scales is weak but that between the inner scale and substrate is strong.