Effect of Cr Content on Corrosion Resistance of Low Alloy Steels in a High Temperature, High Pressure and High Salinity Environment

The characteristics and corrosion behavior of the corrosion product films of low alloy steels with Cr mass fraction from 1% to 5% were studied in a high temperature, high pressure and high salinity environment by 60 d corrosion immersion experiment in combination with scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results show that with the increase of Cr content, the uniform corrosion rate and localized corrosion rate of the low alloy steels decreased. The uniform corrosion rate decreased to less than 0.026 mm/a when 3% Cr was added. The localized corrosion sensitivity decreased significantly with the increase of Cr content. The effect of Cr content on corrosion behavior was due to the change of structure and composition of the corrosion product films. With the increase of Cr content in matrix, the corrosion product films mainly composed of deposition products changed from calcium-ferrous carbonate salt to the structure mainly composed of ferrous carbonate, and the effect of Ca²⁺ ions in solution on the product films decreased.