Cathodic protection example, using sacrificial anodes. These sacrificial anodes are often referred to as Magnesium anode bags.

In cathodic protection with sacrificial anodes, metals with a more negative electrode than steel is used, than the structure they shall protect. The anodes consist of zinc, aluminum or magnesium, depending on the conditions. The sacrificial anode is connected to the pipe, which causes a positive current to flow from the anode into the pipe, such that the entire steel surface becomes more negatively charged, which is a cathode. Because of the potential difference between the anodal area (less noble) and cathodal area (steel), the positively charged metallic ions exit from the anodal surface, and the electrons exit the cathodal surface.

By electrically connecting the metal being protected with the most anodic (electronegative) metal, we ensure the anode will sacrifice itself by preferentially corroding to its cathodic counterpart. The latter metal, commonly called the galvanic or sacrificial anode, has less negative electrochemical potential than a piece of regular steel. Hence, the main reason the more positive metal will obtain protection.

Commonly used to protect several structures, such as pipelines, ships, tanks, and offshore oil platforms, cathodic protection works by allowing the more reactive, sacrificial metal to corrode in place of the protected metal. This way, you control the corrosion process actively. Not passively, which you do with a coating or a paint.

The water & gas distribution alongside with the oil and gas industry uses cathodic protection systems to prevent corrosion of pipelines, steel storage tanks, offshore platforms, and well casings. Benefits are many.