What is Cathodic Protection?

Cathodic protection is a technique used to protect underground metal pipes or structures from corrosion. It involves the application of a protective electrical current or the use of sacrificial anodes, which helps extend the service life of the structures.

Corrosion occurs when metals are exposed to moisture, soil, and other environmental factors. This process leads to the degradation and weakening of the metal, eventually resulting in structural damage, leaks, and failure. Cathodic protection is employed as a preventive measure to counteract the corrosive forces.

There are two main methods of cathodic protection:

1. Impressed Current Cathodic Protection (ICCP): In this method, a power supply, typically a rectifier, is used to convert alternating current (AC) into direct current (DC). The DC current is then applied to the underground structure, such as a pipeline or tank, through anodes. The anodes release electrons, which are attracted to the metal surface, causing it to become the cathode of an electrochemical cell. By supplying a protective current, the structure’s potential is shifted in a negative direction, preventing corrosion. The rectifier controls and regulates the output current to maintain the desired level of protection.
2. Sacrificial Anode Cathodic Protection: This method involves the use of sacrificial anodes made of more electrically active metals, such as zinc, aluminum, or magnesium. These anodes are strategically placed in contact with the underground metal structure. When the electrolyte (soil or water) comes into contact with the anode and the metal structure, a galvanic cell is formed. The anode corrodes sacrificially, releasing electrons that protect the metal structure from corrosion. Over time, the sacrificial anodes gradually corrode and need to be replaced.

The choice between impressed current cathodic protection and sacrificial anode cathodic protection depends on factors such as the size of the structure, the soil conditions, and the level of corrosion protection required.

Cathodic protection systems require careful design, installation, and monitoring to ensure their effectiveness. Factors such as the size and composition of the structure, soil resistivity, and current distribution need to be considered during the design phase. Regular monitoring of the system’s performance, including the measurement of electrical potentials and currents, is necessary to ensure proper protection. Maintenance activities, such as anode replacement or rectifier calibration, may be required periodically to keep the system functioning optimally.

Cathodic protection is widely used in various industries, including oil and gas, water and wastewater, transportation, and infrastructure, to safeguard underground metal structures and prolong their service life.