Corrosion Science and Technology

The Corrosion Science Society of Korea (한국부식방식학회)
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Effect of Seawater Concentration on Electrochemical Corrosion of Duplex Stainless Steel

  • Ho-Seong Heo (SNNC) ;
  • Hyun-Kyu Hwang (Department of marine engineering, Graduate school, Mokpo national maritime University) ;
  • Dong-Ho Shin (Department of marine engineering, Graduate school, Mokpo national maritime University) ;
  • Seong-Jong Kim (Division of marine system engineering, Mokpo national maritime university)
  • Received : 2024.03.03
  • Accepted : 2024.03.12
  • Published : 2024.08.30
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Abstract

Duplex stainless steels (UNS S32205, UNS S32750) are used in various environments. The potentiodynamic polarization tests were conducted at 30 ℃ in order to study the electrochemical corrosion behaviors of duplex stainless steels under different seawater concentrations (fresh water, seawater, mixed water). The results of Tafel analysis in seawater showed that UNS S32205 and UNS S32750 had the highest corrosion current densities at 6.12 × 10-4 mA/cm2 and 5.41 × 10-4 mA/cm2, respectively. The pitting potentials of UNS S32205 and UNS S32750 were comparable to or higher than the oxygen evolution potential in fresh water, mixed water, and seawater. The maximum damage depths and surface damage ratio caused by pitting corrosion increased with chloride concentration. The synergy effect of molybdenum and nitrogen enhances the concentration of Mo, Ni, and Cr at the interface of the metal-electrolyte. In particular, in the case of nitrogen, NH3 and NH4+ are formed to compensate for the pH drop in the pitting region, thereby strengthening the repassivation of the film. The excellent corrosion resistance of UNS S32750 is attributed to the strengthening effect of the chromium oxide film due to the presence of molybdenum and nitrogen.

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References

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