Effect of Temperature and Concentration Rate of the Mother Liquor in Salt Production by Ion Exchange Membrane on Pitting Corrosion of Austenitic Stainless Steel and Nickel Alloy

• Published in: Bulletin of the Society of Sea Water Science, Japan Vol. 77; no. 3; pp. 130 - 139
• Main Authors: NAKAJIMA, Kiyomi, NAKAHARA, Satoru, NAKAMURA, Akio, MASAOKA, Koji
• Format: Journal Article
• Language: Japanese
• Published: The Society of Sea Water Science, Japan 2023
• Subjects: austenitic stainless steel; Localized corrosion; nickel alloy; Pitting potential; Salt production
• ISSN: 0369-4550; 2185-9213
• DOI: 10.11457/swsj.77.3_130

The pitting potentials of various metals in different solutions of modified actual mother liquor, which were assumed to be possible compositions in a salt production process, were measured. The target metals of test pieces were UNS S31600, S31254, S32053, N08354, and N06022, from which evaporators are fabricated. Experimental conditions in the study for austenitic stainless steels（S31600, S31254, S32053, and N08354） were divided into two categories: situations where pitting corrosion occurred on surface of test pieces and situations where pitting corrosion did not occur but instead water decomposition reaction（oxygen evolution reaction） occurred mainly, thus suggesting that the potential for oxygen evolution couldnʼt be influenced by concentrations and temperatures of mother liquor and metals but pitting potential could be influenced. Therefore, prediction equations were developed using the acquired data, with pitting potential and limit concentration of pitting corrosion as response variables, and concentrations and temperatures of mother liquor and pitting index of metals as explanatory variables. However, in the study, pitting corrosion did not occur but instead transpassive dissolution occurred on the surfaces of test piece for nickel alloy（N06022）, suggesting that the transpassive dissolution potential could also be influenced by concentrations and temperatures of the mother liquor. Consequently, a prediction equation was developed using the acquired data, with transpassive dissolution potential as the response variable, and concentrations and temperatures of the mother liquor as explanatory variables. These prediction equations should allow for estimating pitting potential and limit concentration of pitting corrosion in the mother liquor of salt production by ion exchange membrane, which may contribute to selecting metal materials used for evaporators.