Cathodic protection criteria of ship hull steel under flow condition in seawater

The effect of flow velocity on the cathodic protection criteria of ship hull steel was studied in synthetic seawater. Sufficient protection could not be obtained at -800 mV versus SCE (-781 mV versus Ag/AgCl) under the flow condition. The anodic Tafel lines were used to determine the protection potential at each flow condition. The protection potential was shifted to the more negative value as the flow velocity increased. From the surface analysis, the change of cathodic protection potential criteria was due to the formation of the magnetite (Fe₃O₄) on the surface under the flow condition. There was a good agreement between electrochemical impedance spectroscopy (EIS), weight loss and numerical simulation results.