How It Works: What Is Cathodic Protection And How Does It Protect The Pipeline?

Cathodic protection technology plays a crucial role safeguarding Colonial’s pipeline from corrosion. For some of you, however, it may only be a term and you may not have heard an explanation about how the technology works. This article provides a basic introduction.

The first line of defense against pipeline corrosion across the Colonial system is its coating which may consist of asphalt, polyethylene or epoxy depending on the technology available at the time of the pipeline installation. The purpose of the coating is to act as a barrier against the pipeline’s corrosive environment or ​“electrolyte” which typically consists of soil and water. Along the course of its life as the coating deteriorates or becomes disbonded from the pipeline a coating defect or ​“holiday” forms. Colonial’s cathodic protection system can effectively mitigate the corrosion process that would normally occur at these coating defects.

A power source – also known as a rectifier – provides a direct current that travels through the ground looking for a return path on the pipeline. This return path is found at coating defects where the metallic surface of the pipeline is in contact with the ground thus completing the circuit through a wire that’s connected to the pipe and power source. The electrical current, which flows through an anode, initiates a chemical reaction which generates hydrogen ions at the interface of the coating defect creating a passive environment for the pipeline. This phenomenon is also referred to as cathodic polarization.

You can think of a cathodic protection system as a kind of giant battery with positive and negative terminals. The pipeline acts like the cathode (positive terminal) and a ​“sacrificial” metal serves as the anode (negative terminal). This process corrodes the anode – or sacrificial metal – but not the cathode (pipeline). Cathodic protection is also the basic principle behind zinc galvanization used in nails and fences and is also used to extend the life of hot water heaters used in most homes.

A crucial benefit of cathodic protection systems is that the current is able to constantly ​“seek out” locations on the pipeline where corrosion is most likely to occur and neutralize corrosion process before it begins. This not only increases the safety and reliability of pipelines, but it also indefinitely extends their useful lives. Colonial employs the technology across its entire system.

Below is a graphical depiction of how the process works.