Preventing Corrosion with Sacrificial Anodes

Since the first metal hulls went to sea over 150 years ago, ship owners and operators have waged a constant battle with corrosion. Today, effective and efficient methods are available to mariners to resist this corrosion. Simple and reliable, cathodic protection of ships and marine infrastructure is the method of choice for preventing corrosion for owners and operators around the globe.

As corrosion of metals is an electrochemical process, technologies have developed to harness the naturally occurring processes in a manner that ultimately protects the valuable asset. Called a galvanic anode or sacrificial anode, a piece of metal which is naturally more electrochemically active than the protected material is attached to the material to be protected. Zinc, aluminum, and copper are popular anode choices for marine systems. The anode works by ensuring that the component to be protected has a uniform electrical potential. When submerged in the corrosive fluid, electrons flow from the anode to the protected component due to the difference in the electrochemical potential. While the protected component remains physically unchanged, the anode loses mass over time and must be replaced with a new anode to ensure that the protection is maintained.

Cathodic Protection Of Carbon Steel Material By Sacrificial Anode

Zinc sacrificial anodes are widely used in salt water environments due to their high electrochemical potential, low cost, and common availability. The same element used to galvanize steel for corrosion protection, zinc sacrificial anodes may be designed as streamlined bars bolted to a ship’s hull, a solid plug attached to a prop, or plates for large structures.

Zinc Sacrificial Anode

Zinc Sacrificial Anode

 

Similar to zinc sacrificial anodes, aluminium sacrificial anodes provide efficient protection of carbon steel, brass, bronze, and cast iron components in a corrosive environment. Lighter weight and with greater electropotential capacity than zinc, these anodes provide long life with minimal influence on components. While slightly less reactive than zinc in a pure form, alloys of aluminium and zinc which combine positive attributes of both metals are readily available at low cost.

Though less common than either zinc or aluminium sacrificial anodes, copper sacrificial anodes are available and are particularly useful in providing protection of cast iron components. Copper sacrificial anodes should be selected carefully however as many common metals are more reactive than copper and will in turn act as the anode instead of the copper when electrically connected.

In summary, protecting vessels and marine structures from corrosion can be accomplished with rugged, passive, and well provide catholic protection components. As noted in the discussion of copper anodes though, careful consideration of the materials and environment is required to maximize the protection of the vessel or structure. For more information on cathodic protection and to contact experts in the marine corrosion field with a global reach, visit the website of Cathodic Marine Engineering Pte Ltd at www.cathodicme.com.

Knowledge base: Marine Growth Prevention System on Water Vessels.


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