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Underground pipelines play a critical role in water supply systems, natural gas transmission, oil transportation, and urban infrastructure. Once buried, pipelines are continuously exposed to soil environments containing moisture, oxygen, dissolved salts, acids, alkalis, and microorganisms. These factors create favorable conditions for electrochemical corrosion of metal pipelines.
Protective coatings are widely used as the first line of defense. Their main function is to form a physical barrier that isolates the steel surface from the surrounding environment. However, in real engineering practice, coating defects are inevitable.
When coating defects occur, a typical “large cathode–small anode” corrosion cell forms. The exposed metal area becomes the anode, while the surrounding coated area acts as the cathode. This imbalance significantly accelerates corrosion at the damaged location.
Cathodic protection provides an effective electrochemical solution. By shifting the potential of the pipeline surface to a cathodic state, corrosion reactions can be greatly reduced or even suppressed.
This is achieved either by attaching a metal with a more negative potential, known as a sacrificial anode, or by applying an external power source through an impressed current system.
Sacrificial anode cathodic protection is commonly used in environments with low soil resistivity and relatively small current demand. Impressed current systems are better suited for long-distance pipelines or high-resistivity soil conditions.
Combining coating systems with cathodic protection has proven to be the most reliable
long-term corrosion control strategy for underground pipelines.
