Corrosion Inhibitors

Corrosion Inhibitors in cooling towers are chemicals that are added to the water circulation system to prevent or slow down the occurrence of corrosion (rusting) on metals that are in direct contact with water, such as pipes, heat exchangers, and other tower components.

Why is it needed?

Water in cooling towers is generally corrosive because it contains dissolved oxygen, mineral salts (Ca, Mg, Cl-, SO₄²-), and fluctuations in pH and temperature. Without protection, these conditions will accelerate the deterioration of metal materials resulting in:

• Leaks in pipes and equipment.

• Decreased heat transfer efficiency.

• High maintenance costs and downtime.

How Corrosion Inhibitors Work

There are two main mechanisms:

1. Forming a protective layer (film-forming): the chemical substance sticks to the metal surface and forms a thin film that blocks direct contact between the metal and oxygen/water.

2. Controlling the chemical state of the water: e.g. stabilizing the pH, binding corrosion-causing ions, or changing the chemical properties of the solution so that it is less aggressive towards the metal.

Types of Corrosion Inhibitors in Cooling Tower

• Anodic inhibitors: e.g. phosphates, nitrites, molybdate. Forms a protective oxide layer on the metal surface.

• Cathodic inhibitors: e.g. zinc or calcium salts. Reduce the cathodic reaction in the corrosion process.

• Organic film-forming inhibitors: such as amines or imidazolines, form a thin organicfilm on the metal surface.

• Blended inhibitors: a combination of several types for more comprehensive protection.

Important Notes

• The use of inhibitors should be controlled by monitoring (e.g. pH, conductivity and coupon corrosion tests).

• Overdosing or misapplication can cause scaling or foaming.

• Usually used in conjunction with scale inhibitors and biocides to maintain overall cooling tower water quality.