Abstract:

In order to reveal the corrosion mechanism of the bottom plate environment of cargo oil tanks and to developnew low-alloy steels under such environment,a home-made cargo oil tank corrosion simulation device with thestrong-acid Cl- solution corrosion on the bottom plate,was used to investigate the corrosion behaviors of low-alloysteels with different Cr contents.Specifically,the average corrosion rates of the steels in the corrosion test weremeasured with the corresponding morphology observation,and the micromorphologies and element distributions ofthe steels were characterized respectively by means of SEM and EDS.Moreover,the effect of the steel microstructureon the corresponding corrosion-resistance was analyzed by means of EBSD ( Electron Backscattered Diffraction)and TEM,and the polarization curves and AC impedance spectroscopy of the steels with different Cr contents weretested.The results show that ( 1) when the Cr content increases within a range of 1% ～ 3% in the bottom plate environment,the corrosion rate gradually increases and the surface pitting phenomenon becomes obvious; ( 2) withthe increase of the Cr content,the proportion of small-angle low-energy grain boundary and the dislocation densityboth improve,and the changes of the two microstructures both play their roles in the increase of the corrosion rate;and ( 3) the corrosion test results accord well with the electrochemical analysis results.

Key words: low-alloy steel, cargo oil tank, bottom plate environment, corrosion resistance, corrosion rate