Effects of electropolishing and plasma ion nitriding on UNS S31603 corrosion in ship scrubber water

Abstract

Marine scrubbers use seawater as washing water and are damaged by sulfur oxides and chlorides during desulfurization. Therefore, surface treatments to enhance corrosion and pitting resistance of scrubber materials must be investigated. This investigation conducts cyclic potentiodynamic polarization experiments to analyze the effects of electropolishing and plasma ion nitiriding of UNS S31603 in washing water. The corrosion current density (0.186 μA cm-2) of electropolishing is significantly lower than mechanical polishing (1.125 μA cm-2), but plasma ion nitriding is higher (18.995 μA cm-2). Electropolishing forms a uniform and dense passivation film, increasing corrosion resistance, whereas plasma ion nitriding reduces corrosion resistance due to CrN formation. All specimens present local corrosion. Electropolishing reduces the maximum damage depth by 110.13 μm and increases pitting potential by 0.32 V compared to mechanical polishing. Plasma ion nitriding reduces maximum damage depth by 46.59 μm due to suppression of local acidification during hydrolysis.