What is impressed current protection and how is it different from sacrificial anodes?

• A. An external power source applies current to make the structure the cathode; unlike sacrificial CP, the anodes are not sacrificed.
• B. A sacrificial CP relies on an external power source to drive corrosion away.
• C. Impressed current protection uses sacrificial metals that corrode preferentially.
• D. Impressed current protection stops all corrosion instantly.

Answer: (A)

Impressed current protection uses an external DC power source to drive protective current into the metal structure, making the structure the cathode. By supplying electrons from the power source, the structure is held at a cathodic potential, which slows or stops its anodic dissolution and reduces corrosion. The current is carried by inert or slowly corroding anodes (such as MMO-coated titanium or graphite), so those anodes aren’t sacrificed as they are in other systems. In sacrificial CP, a more active metal acts as the anode and corrodes preferentially, protecting the structure through galvanic action. The external power in impressed current systems lets you adjust current to suit large or complex structures and varying conditions, whereas sacrificial CP relies on natural potential differences and requires replacing the sacrificial anodes over time.