Investigation of Q235 low-carbon steel corrosion under simulated ballast water tank conditions

Abstract

To study the corrosive effect of an inert flue gas deoxygenation treatment of ship ballast water on ballast tanks, a total immersion corrosion test was employed. Under the simulated corrosive environment of the ship ballast tank, different corrosive media with a dissolved oxygen (DO) degree of 0.5 mg/L, a pH value of 6, a DO concentration of 0.5 mg/L and a pH value of 6 were used to simulate seawater. After the marine low-carbon steel Q235 was immersed in different media for 792 h, the corrosion law of the low-carbon steel Q235 was explored for ships with the most suitable conditions for inactivating microorganisms by inert flue gas deoxygenation. Specifically, the dissolved oxygen content of ballast water was 0.5 mg/L and the pH value was 6. The results show that in the ballast water treated with inert flue gas N2 and CO2 with a DO concentration of 0.5 mg/L and a pH value of 6, the corrosion rate of the sample was reduced by 69.02% compared to that of the sample in the simulated seawater. There were fewer corrosion products and little black pitting, of which the open circuit potential was relatively positive, and the resistance to corrosion was better. The polarization curve shifted to the right, and the tendency of corrosion was significantly reduced. Under the optimal process conditions for the inert flue gas treatment of microbes in ballast water, that is, a DO concentration of 0.5 mg/L and a pH value of 6, the ballast water after the inert flue gas treatment reduced corrosion in the ballast tank.