How do inhibitors reduce corrosion in cooling water systems?

• A. They scavenge aggressive species only.
• B. They form protective films.
• C. They form protective films, scavenge aggressive species, and maintain favorable water chemistry to slow corrosion.
• D. They simply increase water temperature.

Answer: (C)

Inhibitors reduce corrosion in cooling water systems by three coordinated actions that together slow the electrochemical reactions at the metal surface. First, they form protective films on the metal, creating a barrier that limits direct contact between the metal and the corrosive water. Second, they scavenge aggressive species, such as dissolved oxygen, which are drivers of corrosion reactions. Third, they help maintain favorable water chemistry—controlling pH and alkalinity and often adding complexing or buffering species—to keep the surface environment less conducive to corrosion. Because using all three mechanisms provides the most comprehensive protection, the best approach is the combination of film formation, scavenging, and chemistry control. Relying on only one mechanism—like just scavenging or just film formation—leaves other avenues for corrosion to proceed. And changing temperature alone typically accelerates corrosive processes rather than suppressing them.