If a magnesium sacrificial anode has a 50% efficiency rating, where does the other 50% go?

In the context of a magnesium sacrificial anode with a 50% efficiency rating, it indicates that only half of the anode's potential is effectively used for cathodic protection of the metal surfaces it is designed to safeguard. The other 50% of its activity is dissipated due to self-destruction through electrochemical corrosion.

This means that while some of the anode successfully protects the vessel's hull by corroding itself, a significant amount of the anode's mass is consumed due to direct electrochemical reactions without providing the desired protective effect. These reactions can include processes that do not contribute to cathodic protection but rather to the dissolution of the anode material into the surrounding water as unproductive corrosion.

Understanding this concept is crucial in assessing the effectiveness and efficiency of sacrificial anodes in marine environments, as it emphasizes the importance of selecting adequately sized and rated anodes to ensure optimal performance for corrosion protection.