Corrosion is one of the greatest enemies of the ship and its machinery. A ship is continuously in contact with water and moisture laden winds which makes it highly susceptible to corrosion. The other body of the ship (mainly hull) is continuously in contact with water, making it extremely vulnerable to corrosion. It is for this reason sacrificial anodes are used to protect the parent material.
In the case of a ship, sea water acts as an electrolyte and transfers the electrons from the anode by oxidizing it over the steel plate and making a protecting layer. If the metal is more active it will be easily oxidized and will protect the metallic compound by making it act as cathode. The anode will corrode first sacrificing itself for the other compound and it is thus called sacrificial anode.
Sacrificial anodes works on the principle similar to electrolysis, according to which if an anode and a metallic strip are dipped in electrolytic solution, anode electron will dissolve and deposit over the metallic strip and make it cathode.
Anode materials such as: Magnesium (Mg), Aluminum (Al), Zinc (Zn), Chromium (Cr), Iron (Fe), Nickel (Ni). These metals are preferred because they are easy and cheap to replace the anodes rather than complete a large sheet of metal. The most common metals used for sacrificial anode is zinc.
These anodes are used in various applications such as:
1) Protecting the ship’s hull.
2) Protecting the ballast tanks corrosion.
3) Protecting the heat exchangers.
4) Sea chests