Current requirement and calcareous scale properties on carbon steel were investigated as a function of applied potential, flow rate, and time in natural seawater. The current requirement was dominated by oxygen reduction during the initial stage of polarization after application of cathodic protection, However, as the calcareous scale deposited, oxygen reduction reaction rate decreased and hydrogen evolution became the dominating cathodic process. Furthermore, the rate of hydrogen evolution appeared to become catalyzed by the presence of the calcareous scale deposit. At a given flow rate, a maximum was obtained when the Ca/Mg ratio measured in the calcareous deposit was plotted as a function of applied potential. The maximum became larger and shifted to more active potentials with increasing flow rate, as determined by the pH and potential-dependent competing kinetics of calcium hydroxide (Ca[OH]2) and magnesium hydroxide (Mg[OH]2) deposition. The applied potential giving the maximum Ca/Mg ratio in the calcareous deposit provided the best protection and minimum current requirement at a given flow rate.
Significance of hydrogen evolution during cathodic protection of carbon steel in seawater
Bedeutung der Wasserstoffentwicklung während des kathodischen Schutzes von Kohlenstoffstahl in Meerwasser
Corrosion, Houston ; 63 , 9 ; 857-865
2007
9 Seiten, 10 Bilder, 1 Tabelle, 11 Quellen
Article (Journal)
English
kohlenstoffreicher Stahl , Meerwasser , Meerwasserkorrosion , kathodischer Korrosionsschutz , Inkrustierung , Verkalkung , Stromdichte , kathodischer Strom , kathodische Reaktion , Wasserstoff , Strömungsfeld , Strömungsgeschwindigkeit , Nusselt-Zahl , Reynolds-Zahl , Schmidt-Zahl , Diffusionsschicht
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