Anodic Protection

In circumstances where cathodic protection is not practical, such as in strongly alkaline or acidic environments, anodic protection is a useful corrosion control technique. Specifically, in metal-environment conditions where active-passive behaviour is demonstrated, anodic protection is usually effective. In practise, the metal-environment potential is held in the passive region by polarizing the structure in the electropositive direction. Historically, anodic protection has the widest application in the process industries and in particular on mild or stainless steel equipment use for concentrated sulphuric acid storage. Equipment, such as pulp and paper mill digesters and recausticizing (white, green & black) liquor clarifiers and storage tanks have also been effectively protected.
Here the metal potential is shifted to the passive zone from the active region by the application of a direct current.

Source: http://www.westcoastcorrosion.com/service%20anode%20Protection.htm