Influence of chromium on corrosion behavior of low-alloy steel in cargo oil tank O2-CO2-SO2-H2S wet gas environment

As international maritime organization (IMO) draft 289 was adopted to develop a low-alloy anti-corrosion steel for the deck of cargo oil tank and to understand corrosion mechanism, corrosion behavior of a low-alloy steel with chromium contents was studied in O2-CO2-SO2-H2S wet gas environment. Corrosion rate was measured, and the microstructure and morphology of corrosion product film were characterized by scanning electron microscopy (SEM). The phase and chemical composition of the corrosion product film were investigated by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS), respectively. The effect of misorientation distribution on corrosion resistance of steel was evaluated by electron backscattered diffraction (EBSD). The results showed that corrosion rate decreased with increasing chromium content in the low-alloy steel, and the corrosion type was general corrosion. The phenomenon of chromium enrichment was found in corrosion product film consisting of α-FeOOH, γ-FeOOH, sulphur, FeS2 and Fe1−xS. The increase of chromium content decreases the amount of high-angle grain boundaries, thus resulting in the improvement of corrosion resistance.