（Corrosion and Protection Center, Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China）
Electrochemical corrosion behavior of carbon steel and Cr-Cu-Ni low alloy steel with rust forming in simulated CO2–O2–H2S–SO2 wet–dry environment of cargo oil tanks of crude oil tankers for 98 days were investigated using corrosion rate by mass loss method, scanning electron microscope, X-ray diffraction, and electrochemical measurement. The results showed that the corrosion rate of Cr-Cu-Ni low alloy steel was higher than carbon steel in initial period, while with the increase of corrosion time, it was tend to be lower than carbon steel. The corrosion current density of Cr-Cu-Ni low alloy steel reduced greatly from 67.4μA/cm2 to 11.7μA/cm2 in comparison with a little special of the decreasing of carbon steel corrosion current density. The rust layer of carbon steel existed the larger cracks throughout the cross-section of it. Cracks existed throughout the cross-section of rust layer of carbon steel, while the rust of Cr-Cu-Ni low alloy steel was compact due to the small size of rust particles, leading to smaller crack in cross-section of the rust. The rusts of both carbon steel and Cr-Cu-Ni low alloy steel were composed of amorphous corrosion products, α-FeOOH, small account of γ-FeOOH, Fe3O4 and element S. However, no obvious difference between the phase compositions of the two kinds of steel rust existed. Compared to the rust of carbon steel, the rust of Cr-Cu-Ni low alloy steel had high content of the amorphous corrosion product and high α/γ value, i.e. the content ratio of α-FeOOH to γ-FeOOH, leading to high rust compactness.