Elucidation of Corrosion Mechanism in a Simulated Potable Water of 304 stainless steel for Water Storage Tank
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Drinking water storage tanks are essential for maintaining water quality in distribution systems, and their stability is crucial. STS 304 stainless steel, known for its excellent corrosion resistance, is commonly used in water supply facilities and storage tanks. However, localized corrosion has been observed in STS 304 tanks, likely due to local enrichment of chloride (Cl-) or residual chlorine (OCl-) ions caused by evaporation and condensation. This study evaluated the corrosion behavior of STS 304 base metal and weld metal in simulated potable water containing 50 ppm, 200 ppm, or 400 ppm Cl- and 2 ppm, 4 ppm, or 8 ppm OCl- at temperatures of 20oC, 35 oC, and 50 oC. To assess corrosion resistance, we conducted cyclic polarization, open-circuit potential (OCP) measurements, and electrochemical impedance spectroscopy (EIS). While increases in Cl and OCl- ions had minimal impact on pitting and protection potentials, higher temperatures led to a decrease in pitting potential. The addition of OCl caused a rapid increase in OCP to a level between the protection and pitting potentials, indicating that the corrosion observed in 304 tanks is linked to the potential-raising effect of OCl- ion addition.
Abstract
Drinking water storage tanks are essential for maintaining water quality in distribution systems, and their stability is crucial. STS 304 stainless steel, known for its excellent corrosion resistance, is commonly used in water supply facilities and storage tanks. However, localized corrosion has been observed in STS 304 tanks, likely due to local enrichment of chloride (Cl-) or residual chlorine (OCl-) ions caused by evaporation and condensation. This study evaluated the corrosion behavior of STS 304 base metal and weld metal in simulated potable water containing 50 ppm, 200 ppm, or 400 ppm Cl- and 2 ppm, 4 ppm, or 8 ppm OCl- at temperatures of 20oC, 35 oC, and 50 oC. To assess corrosion resistance, we conducted cyclic polarization, open-circuit potential (OCP) measurements, and electrochemical impedance spectroscopy (EIS). While increases in Cl and OCl- ions had minimal impact on pitting and protection potentials, higher temperatures led to a decrease in pitting potential. The addition of OCl caused a rapid increase in OCP to a level between the protection and pitting potentials, indicating that the corrosion observed in 304 tanks is linked to the potential-raising effect of OCl- ion addition.