含O2高温高压CO2环境中3Cr钢腐蚀产物膜特征

采用高温高压反应釜分别开展3Cr钢在CO2和O2共存、单独CO2和单独O2三种气体条件下的腐蚀实验,利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能量色散X射线能谱(EDS)和电化学方法研究了3Cr钢在高温高压含有O2的CO2环境中的腐蚀产物膜特征.结果表明,在含有O2的CO2的条件下,3Cr钢表面腐蚀产物膜疏松多孔,主要成分为FeCO3、Fe3O4和Fe2O3,腐蚀产物中未见明显Cr元素富集,3Cr钢表现出点蚀的腐蚀形态.3Cr钢在高温高压含O2的CO2腐蚀条件下内外膜层电阻(Rf1、Rf2)和电荷传递电阻Rt均比仅含有CO2腐蚀环境的低,双电层电容(Cdl)和内外膜层电容(Cf1、Cf2)均比仅含有CO2腐蚀环境的高.含有O2的CO2条件下,其保护性显著低于单一CO2条件下形成的腐蚀产物膜.提出了在含O2的CO2气体条件下,3Cr钢表面存在由多种物质组成的腐蚀产物,这导致腐蚀产物疏松多孔,不会形成单一CO2条件下存在的显著提高腐蚀产物膜保护性的Cr(OH)3层,从而促进了3Cr钢的析氢腐蚀和酸性介质中的吸氧腐蚀的机理.

Characteristics of Corrosion Scale of 3Cr Steel at High Temperature and Pressure in an O2 and CO2 Environment

The corrosion behavior of 3Cr steel in atmospheres composed of only O₂ or CO₂ or a combination of O₂ and CO₂ was investigated using an autoclave. The characteristics of the corrosion scale of the 3Cr steel were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), and electrochemical methods. The corrosion scale developed in the combined O₂ and CO₂ atmosphere was composed of FeCO₃, Fe₂O₃, and Fe₃O₄, and had a loose texture with a large number of pores. The surface and subsurface corrosion film resistance (R_f1, R_f2) and charge transfer resistance (R_t) were all lower than those found in samples treated in only CO₂ or O₂ atmospheres. The double-layer capacitance (C_dl) and corrosion film capacitance (C_f1, C_f2) were higher for the sample treated in the combined O₂ and CO₂ atmosphere than for those treated in only CO₂ or O₂ atmospheres. The resistance to formation of a corrosion film on the 3Cr steel in the combined O₂and CO₂ atmosphere was significantly lower than in the CO₂ only atmosphere. The corrosion mechanism of 3Cr steel is proposed: In the O₂ and CO₂ environment the corrosion is proceed by the formation of several corrosion products causing a loose film to develop. The Cr(OH)₃ layer which can greatly improve the protection of the corrosion film formed in a CO₂ only corrosion environment is not found in the O₂ and CO₂ environment, thus promoted the corrosion process of hydrogen evolutional and oxidation corrosion in acid medium.