When two dissimilar metals are connected in an electrolyte such as seawater, a corrosion cell is formed in which one metal becomes an anode and suffers corrosion, while the other metal becomes the cathode and remains preserved. Current flows through the electrolyte from the anode to the cathode, resulting in electrolytic corrosion. Anodic and cathodic areas exist on the surface of all steel structures due to slight variations in material composition, local stresses, differences in coating condition and the availability of oxygen.
Ships' hulls, cargo tanks and submerged fixed structures are all vulnerable to corrosion (details).
Cathodic protection works within this natural process to help put you in control of what corrodes and what does not.
The principle of cathodic protection involves the introduction of a metal that is more electro-negative than the existing anodic and cathodic areas. This additional metal becomes the anode and will corrode while providing current to the metal it is protecting, thereby overcoming the local anodic areas and making them cathodic.
This time-tested solution utilizes a material such as zinc or aluminum, which will sacrifice itself in protecting the cathode.
Zinc anodes are cast from 99.995% purity ingot, to US Mil Spec A-18001K, and will yield 780 ampere hours per kilogram.
Aluminum anodes are cast from a special mercury-free alloy, yielding 2700 ampere hours per kilogram, resulting in longer life, higher output and lighter weight (for easier installation).
Wilson Walton International manufactures sacrificial zinc and aluminum anodes in its own U.S. foundry for superior quality, reliability and value.
In the case of ship hulls, the optimal solution includes
Wilson Walton's Aquamatic III Impressed Current
Cathodic Protection (ICCP) system.
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