The Structure and Composition of Corrosion Product Film and its Relation to Corrosion Rate for Carbon Steels in CO2 Saturated Solutions at Different Temperatures

For carbon steels immersed in CO2 saturated solutions at different temperatures, the structure and the composition of corrosion product film formed on the steel surface were studied by scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The corrosion rate of the steel was evaluated by potentiodynamic polarization, and the relation between the corrosion rate and the film property was discussed. The corrosion rate of the steel was very closely associated with the structure and the composition of corrosion product film, which were affected significantly by the solution temperature. From 30 to 60 ºC, the corrosion product film composed of FeCO3 was porous and poorly adherent, and the corrosion rate increased with the rise of temperature. At 70 and 80 ºC, the corrosion product film was also composed of FeCO3 and presented a compact and dense cubic crystal structure, resulting in the decrease on the corrosion rate. The corrosion rate increased once again when the temperature was up to 90 ºC, which was attributed to the negative effect of high temperature water vapor corrosion on the grain coarsening and the part exfoliation for the FeCO3 film.