What is corrosion?

Corrosion is the destruction of a metal by chemical or electrochemical reaction with its environment. In cooling systems, corrosion causes two basic problems. The first and most obvious is the failure of equipment with the resultant costs of replacement and plant downtime. The second is decreased plant efficiency due to loss of heat transfer, the result of heat exchanger fouling cause by the accumulation of corrosion products.

Corrosion occurs at the anode, where metal dissolves. Often, this is separated by a physical distance from the cathode, where a reduction reaction takes place. An electrical potential difference exists between these sites, and current flows through the solution from the anode to the cathode. This is accompanied by the flow of electrons from the anode to the cathode through the metal.

What is corrosion control in water treatment?

Corrosion control requires a change in either the metal or the environment. The first approach, changing the metal is expensive. Also, highly alloyed materials, which are very resistant to general corrosion, are more prone to failure by localized corrosion mechanisms such as stress corrosion cracking.

The second approach, changing the environment, is a widely used, practical method of preventing corrosion. There are three ways to effect a change in environment to inhibit corrosion.

• Form a protective film of calcium carbonate on the metal surface using the natural calcium and alkalinity in the water.
• Remove the corrosive oxygen from the water, either by mechanical or chemical deaeration or add corrosion inhibitors.