An electrochemical criterion for galvanic protection of steel exposed to marine environments

CIM Bulletin, Vol. 83, No. 935, 1990

B.E. Wilde, Fontana Corrosion Center, Department of Metallurgical Engineering, The Ohio State University

Zinc has been used for many years as a galvanic coating for the protection of steel. Electrochemical measurements show that zinc actually overprotects steel. The corrosion rate of DQSK (drawing quality semi-killed) steel in air saturated salt water was determined as a function of applied cathodic potential. The resulting data indicate that at a critical cathodic overpotential of - 0.725 Vsce an acceptably low corrosion rate of less than 1 mpy occurs. Using the developed criterion, alloys of Zn/X and AL/X were produced and evaluated in galvanic contact with steel in a standard laboratory test. The results indicate that Zn/Mn, Zn/Co, Al/Mg/Si andAl/Mg/Ge alloys offer excellent galvanic protection along with (a) no hydrogen evolution, and (b) improved dissolution life over Zn coatings.

Keywords: Corrosion, Marine industry, Galvanic protection.