What are common inhibitors used in cooling water or closed-loop systems?

• A. Filming inhibitors, passivators, and sometimes nitrite-based or other corrosion inhibitors.
• B. Oxygen scavengers only.
• C. Surfactants only.
• D. No inhibitors are used.

Answer: (A)

In cooling water and closed-loop systems, keeping metal surfaces from corroding is about using inhibitors that protect the surface in different ways. Filming inhibitors rapidly adsorb onto the metal to form a thin, protective film that blocks water contact and slows the diffusion of corrosive species. Passivators promote or sustain a passive, protective oxide layer on the metal, reducing the tendency for corrosion to proceed. Nitrite-based inhibitors, and other corrosion inhibitors used in combination, help maintain a protective film—especially on iron-based components—by contributing to a stable surface environment and, in some cases, scavenging reactive species. Together, these types of inhibitors address both the surface barrier and the chemistry of the loop to keep corrosion rates down. Relying on oxygen scavengers alone, surfactants alone, or using no inhibitors would not provide the same comprehensive protection in these systems.