In a sacrificial anode CP system, what provides the protective current?

• A. External power supply
• B. Galvanic current from more active metals
• C. Renewable energy
• D. None

Answer: (B)

In a sacrificial anode system, protection comes from a natural galvanic reaction between dissimilar metals in the electrolyte. The sacrificial anode is made from a metal that is more electrochemically active (less noble) than the metal being protected. When they are electrically connected in a corrosive environment, the more active metal corrodes (oxidizes) first, releasing electrons. Those electrons flow to the protected structure, making it the cathode in the couple, which suppresses its oxidation. The current that flows from the anode to the structure is the protective current.

There is no external power source driving this protection—it's all due to the galvanic potential difference between the anode and the structure. The anode gradually dissolves and must be replaced as part of maintenance. Options like an external power supply or renewable energy describe other systems (impressed current CP) and don’t apply here.