What is the function of sacrificial anodes in a seawater cooling system?

The function of sacrificial anodes in a seawater cooling system is to protect the metallic components of the system from corrosion, specifically galvanic corrosion. Seawater is an electrolyte, meaning it conducts electricity. When dissimilar metals, such as steel and bronze, are in contact with each other in seawater, they form a galvanic cell. The more electrochemically active metal (the anode) will corrode preferentially to protect the less active metal (the cathode). This is galvanic corrosion. Sacrificial anodes are made of a highly electrochemically active metal, typically zinc, aluminum, or magnesium. These anodes are strategically placed within the seawater cooling system, electrically connected to the components that need protection, such as heat exchangers, pumps, and piping. The sacrificial anode corrodes instead of the protected metal components. As the anode corrodes, it is "sacrificing" itself to protect the other metals in the system. The anodes need to be periodically inspected and replaced as they are consumed. By using sacrificial anodes, the lifespan of the seawater cooling system components is significantly extended, reducing maintenance costs and downtime.