How does cathodic protection prevent corrosion of subsea wellhead equipment?

Cathodic protection (CP) prevents corrosion of subsea wellhead equipment by making the metal structure the cathode in an electrochemical cell, thereby suppressing the anodic reactions that cause corrosion. Corrosion is an electrochemical process where metal atoms lose electrons and become ions, leading to the degradation of the metal. CP works by supplying electrons to the metal structure, shifting its electrical potential to a more negative (cathodic) level. This makes it thermodynamically unfavorable for the metal to corrode. There are two main types of CP: sacrificial anode cathodic protection (SACP) and impressed current cathodic protection (ICCP). SACP involves attaching a more electronegative metal (anode) to the structure to be protected. The anode, typically made of aluminum, zinc, or magnesium, corrodes sacrificially, releasing electrons that flow to the steel structure, protecting it. ICCP uses an external power source to drive current from an anode to the structure. The anodes are typically made of materials like platinized titanium or mixed metal oxides. The power source maintains a negative potential on the structure, preventing corrosion. In subsea wellhead equipment, SACP is commonly used because it is simple, reliable, and requires no external power source. Sacrificial anodes are strategically placed on the wellhead structure to provide uniform protection. The anodes are designed to corrode at a predictable rate, providing protection for a specified period. Regular inspections are conducted to monitor the condition of the anodes and to replace them when necessary. CP is essential for protecting subsea wellhead equipment from corrosion, as it can significantly extend the equipment's lifespan and reduce the risk of failures.