Which of the following is NOT an indicator of CP under-protection?

• A. High corrosion rate
• B. Insufficient protection potential
• C. Anode depletion
• D. Hydrogen-induced cracking

Answer: (D)

Under-protection means the protective system isn’t driving the metal to a sufficiently negative potential to suppress corrosion. That shows up as a higher corrosion rate because the surface isn’t in the protective range. If the anode is depleted, the protection current drops and the potential becomes less protective, clearly indicating under-protection. Hydrogen-induced cracking, however, is tied to excessive cathodic protection and hydrogen embrittlement, a sign of over-protection rather than under-protection. So the first three reflect inadequate protection, while hydrogen-induced cracking points to too much protection, not insufficient protection.