Tank api; plane of sacrificial anodes. the interior surface of a container containing fresh water or formation water is susceptible to attack by corrosion. the use of coatings is the first step taken to combat corrosion; as the coatings are not perfect, the cathodic protection should be used as a complement. all coatings may suffer deterioration over time; therefore the use of them is not enough to ensure proper control of corrosion. cathodic protection is effective in controlling corrosion only on surfaces wetted by the electrolyte.