Understanding Cathodic Protection


Cathodic protection is used to lessen the damage caused by corrosion to active metal surfaces. It is used all around the world to protect water treatment plants, pipelines, ship hulls, underwater and above water storage tanks, reinforcement bars in piers, offshore production platforms, and more.

Essentially, cathodic protection joins a sacrificial metal to the base metal. This metal corrodes instead of the base metal. The metal is preserved because a highly active metal acts as an anode with free electrons. Because of these free electrons, the ions of the active metal are sacrificed. Thus, the less active metal is not as susceptible to corrosion.

What Causes Corrosion?

Even though corrosion is a natural process, the deterioration it causes to metal structures can lead to costly damage for your company. Corrosion occurs when four elements are present. First, there is a host site that is the origin of the current flow. Next, there is a destination site without any current flow. There must also be a conductive medium, such as soil, concrete, or water, as well as a metal path that goes between the destination and the host sites.

When ions on the surface of metal transfer with another substance electrochemical corrosion takes place. This other substance is known as a depolarizer, which is a less active metal or substance. The depolarizers may be acids, oxygen, or cations of more passive metals.

Types of Cathodic Protection

Basically, there are two different types of cathodic protection, which are impressed current and galvanic. With galvanic cathodic protection, a coating of protective zinc is applied to the metal to prevent rusting. The corrosion will affect the zinc instead of the base metal.

With impressed current cathodic protection, anodes are connected to a source of power, which provides a perpetual flow of electricity. This method provides protection because the anode is a more active metal that provides sacrificial ions.