Effect of Dissolved Oxygen and Hydrogen Ion on Corrosion Rate and Passivation of Carbon Steel Boiler Tube

H. T. Kim; C. H. Paik; W. I. Cho; B. W. Cho; K. S. Yun; Y. H. Kim; J. B. Ju; J. S. Kim; M. S. Kang; J. S. Ha; K. Y. Kim

Journal of Industrial and Engineering Chemistry, Vol.3, No.1, 51-55, March, 1997

H. T. Kim, C. H. Paik¹, W. I. Cho¹, B. W. Cho¹, K. S. Yun¹, Y. H. Kim¹, J. B. Ju, J. S. Kim², M. S. Kang², J. S. Ha², and K. Y. Kim²

HongIk University, Seoul 121-160 Korea
¹Korea Institute of Science and Technology, Seoul 130-650, Korea
²Korea Electric Power Research Institute, Taejon, 305-380 Korea

The corrosion rate of carbon steel was characterized at various concentrations of dissolved oxygen and pH by potentiodynamic method. In pH 7, the corrosion rate was found to be minimum at 2 ppm O₂. This minimum was likely due to a difficulty of passive film formation below 2 ppm O₂; oxygen reduction is enhanced above 2 ppm O₂. In pH 10, corrosion rate was found to be low when the oxygen concentration was below 2 ppm O₂ a result of stabilization of passive film which acted as a barrier to O₂ diffusion toward the metal surface. The pH effect was also investigated by incorporating HCI, NaOH, NH₄OH, Na₃PO₄, or their combination. For below pH 5, the corrosion rate was found to increase resulting from sufficient hydrogen and chloride ions. For pH between 5 and 10, the corrosion rate was found to be low and constant due to the barrier (passive film) of O₂ diffusion. For pH above 10, as passive film was more stable, the corrosion rate was found to be lower.

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[1] Mann GMW, Br. Corrs. J., 12 (1977)

[2] Gabrielli F, Mater. Performance, June, 51 (1988)

[3] Hargrave RE, Mater. Performance, Aug., 51 (1994)

[4] Cotton IJ, Mater. Performance, Mar., 41 (1987)

[5] Lindsley D, "Boiler Control System," 35, McGraw-Hill (1992)

[6] Uhlig HH, "Corrosion and Corrosion Control," 3rd ed., 280, John Wiley (1991)

[7] Fontana MG, "Corrosion Engineering," 3rd ed., 462, McGraw-Hill (1987)

[8] Jones DA, "Principle and Prevention of Corrosion," 357, Macmillan (1992)

[9] Whitman W, Ind. Eng. Chem., 16, 665 (1924)

[10] Sheir LL, "Corrosion," 3rd ed., Butterworth (1994)