Carbon steel coupons were set in the tidal zone of a French seaport for 7 years with or without cathodic protection. The average corrosion rates decreased from 90 µm yr-¹ to 9 µm yr-¹ under cathodic protection. The phenomena occurring on the steel surface under CP, or during an interruption of CP, depend on those occurring at OCP. Cathodic protection induces a significant decrease of the corrosion rate (one order of magnitude), which demonstrates the efficiency of the protection (the lifetime of the seaport structure is multiplied by 10). The residual corrosion process leads to the formation of a thin film of corrosion products under the thick calcareous deposit. This film is mainly composed of magnetite, i.e. the main corrosion product at OCP. This suggests that CP mainly induces a decrease of the rate of the corrosion process without drastic changes of the mechanisms. Accordingly, the interruption of CP proved to simply induce a re-acceleration of the corrosion process.The corrosion product layers covering the unprotected coupons, characterized by Raman spectroscopy and X-ray diffraction, were mainly made up of magnetite and Fe(III) oxyhydroxides, with magnetite being clearly predominant. The products of the residual corrosion process under cathodic protection, similar to those observed at open circuit potential, formed a thin layer on the steel surface under the calcareous deposit.
Corrosion and cathodic protection of carbon steel in the tidal zone: Products, mechanisms and kinetics
Korrosion und kathodischer Schutz von Kohlenstoffstahl in der Gezeiten-Zone: Produkte, Mechanismus und Kinetik
Corrosion Science ; 90 ; 375-382
2014
8 Seiten, 9 Bilder, 33 Quellen
Aufsatz (Zeitschrift)
Englisch
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