Magnesium Disc Anodes

Coatings are the first barriers to protect vessel hulls against corrosion. Due to microscopic pinhole defects in the coating and damage to it whilst in service localised pitting will occur. Disc anodes are usually mounted on rudders and are used to complement the coating at areas of exposed steel prolonging the life of the coating. Zinc is the only material that has an official specification, the American MIL-A-18001 K spec. Zinc is a well-proven anode material and its capacity is virtually unaffected by the operating current density, although the driving voltage diminishes with increasing temperature therefore it has limited application. If zinc is not to this specification i.e. commercial purity zinc, it will have a limited use as an anode material because of excessive polarisation due to iron present as an impurity.