Glossary

Uniform corrosion is the most common and predictable form of metallic corrosion, characterized by the even and consistent attack of a metal surface over a large area. In this process, the corrosion reaction occurs uniformly across the exposed surface, causing the metal to thin gradually and evenly rather than developing localized pits or cracks.

This type of corrosion happens when the entire surface of the metal is exposed to a corrosive environment—for example, air, moisture, acids, or salts—and when the chemical or electrochemical conditions are consistent across that surface. Each microscopic area of the metal alternates between acting as an anode (where metal atoms oxidize and dissolve) and a cathode (where reduction reactions occur), resulting in an overall uniform rate of material loss.

A classic example is the rusting of unprotected carbon steel exposed to air and moisture, which produces iron oxides (Fe₂O₃) or hydrated rust evenly across the surface. Over time, this leads to surface roughening, scaling, and uniform wall thinning, which can weaken structural components like pipes, tanks, or machinery parts.

The general electrochemical reactions for uniform corrosion of iron in the presence of oxygen and water are:

- Anodic reaction: Fe → Fe²⁺ + 2e⁻

- Cathodic reaction: O₂ + 2H₂O + 4e⁻ → 4OH⁻
The resulting Fe²⁺ ions combine with hydroxide ions to form Fe(OH)₂, which oxidizes further into rust (Fe₂O₃·xH₂O).

Uniform corrosion rates can be measured and predicted relatively easily by weight loss tests, electrochemical methods, or thickness measurements. The rate depends on environmental factors such as humidity, temperature, pH, oxygen concentration, and the presence of salts or pollutants.

Although it is the least dangerous type of corrosion in terms of sudden failure—because the material loss is gradual and visible—it can still cause significant structural weakening over time if left untreated.

Prevention typically involves:

- Protective coatings (paints, platings, or galvanizing) to isolate the metal from the environment.

- Corrosion inhibitors added to liquids or systems.

- Cathodic protection, particularly for buried or submerged structures.

- Material selection, using corrosion-resistant metals or alloys such as stainless steel, aluminum, or titanium.