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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.

Abstract In this investigation, electropolishing and plasma ion nitriding are applied to super austenitic stainless steel for the purpose of improving its corrosion and pitting resistance. Electrochemical experiments are conducted with washing water collected directly from the ship’s scrubber. After electropolishing, the surface roughness is improved by about 73.6% compared to mechanical polishing. After plasma ion nitriding, CrN (precipitate), Fe4N (compound), and γN (solid solution) are observed on the surface. The thickness of the layer formed on the surface is measured to be about 10 μm. A hysteresis loop is observed in the cyclic potentiodynamic polarization curves of mechanical polishing and electropolishing, and the areas are calculated as 23.33 mW cm−2 and 0.17 mW cm−2, respectively. The polarization curve of plasma ion nitriding presents perfect passivation characteristics. Accordingly, mechanical polishing and electropolishing reveal local corrosion, whereas plasma ion nitriding presents a tendency towards general corrosion. In the mechanical polishing, electropolishing, and plasma ion nitriding, the corrosion current densities are 0.665 μA cm−2, 0.093 μA cm−2, and 16.47 μA cm−2, respectively, and the maximum damage depth is observed to grow progressively smaller from plasma ion nitriding to electropolishing and then mechanical polishing.

In this study, we investigated the performance and reliability of commercial corrosion sensors for monitoring the integrity of piping systems in various fluid environments as an alternative to ultrasonic transducers. To this end, we investigated pipes’ wall-thinning using commercial electrical resistance (ER), linear polarization resistance (LPR), and ultrasonic transducer (UT) sensors under various operating environments. A pilot-scale closed-loop test bed was built to simulate a real pipeline flow situation, from which the sensor data were collected and analyzed. Experimental results indicate that, in the case of the LPR sensor, it is challenging to accurately measure the corrosion rate when a specific measure exceeds the threshold in a severe corrosion environment. In contrast, the ER sensor could measure metal loss under all conditions and reflect the corresponding characteristics. The metal loss (about 0.25 mm) of the real pipe after the experiment was confirmed to be equal to the metal loss (0.254 mm) measured by the sensor. Furthermore, the regression analysis revealed a high correlation between the results obtained from the ER and UT sensors. Thus, evaluating the remaining thickness of the piping system using the commercial ER sensor is deemed to be effective and reliable.