Wear Resistance of CO_2 Corrosion Product Scale Formed at High Temperature

To investigate the correlation between structure characteristics and wear resistance of CO2 corrosion product scales at high temperature and high pressure, an autoclave was used to prepare CO2 corrosion product scales on N80 steel in carbon dioxide corrosion environment. The correlation between wear resistance of the scales and many other factors, such as temperature, pressure, morphology, structure, velocity of fluid medium, sand grain size, and so on, was comparatively analyzed by a self assembled wear device, and the scale morphologies before or after being worn were observed by scanning electron microscope （SEM）. And then the surface grain size and thickness of scale were measured. The results showed that the cross-section of the corrosion scale was of a double-layer structure, the outer layer of which was composed of regular crystals, whereas the inner layer was a thin scale of fine grains. The outer grain size and thickness of scale varied with temperature, and the initial wear loss was consistent with the surface grain size; at the same time, the total wear loss corresponded to the thickness of scale. Compared to wear resist- ance in different depths of the scale, it was found that the structure of scale was a double-layer structure in cross-section, and the wear resistance of inner layer was better than that of the outer layer; the closer the scale to the matrix, the greater was the wear resistance of scale; and the larger the size or the higher the rotary speed of solid grain in multiphase flowing medium, the more was the wear loss of scale.

Anticorrosion performance of the coating/metal system by electrochemical impedance spectra

In order to investigate the anticorrosion performance of the organic coating/metal system, electrochemical impedance spectra （EIS） were measured in the 3.5wt% NaCl solution, the chemical component and the formation of corrosion products scale were analyzed by laser Raman microspectroscopy, and the pattern of the organic coating/metal system was observed by scanning electron microscopy （SEM）. The characteristics and the delamination process of the organic coating/metal system were investigated systematically, and the emphases were on the transportation of the corrosive medium and the changes of the coating/metal interface. The results show that the impedance decreases at the initial immersion, then increases at the middle-immersion, and again decreases at last, which is related to the corrosion products scale. The concentration of Cl in the coating, which destroys the corrosion products scale, increases with the immersion time.