Cathodic protection (CP) is a technique used to control the
corrosion of a metal surface by making it the
cathode of an
electrochemical cell. A simple method of protection connects the metal to be protected to a more easily corroded "
sacrificial metal" to act as the
anode. The sacrificial metal then corrodes instead of the protected metal. For structures such as long
pipelines, where passive galvanic cathodic protection is not adequate, an external DC electrical power source is used to provide sufficient current.