What is a corrosion class?
A corrosion class (or corrosivity category) indicates how aggressive an environment is towards unprotected steel and other metals. The classes are defined in the standard EN ISO 12944 and range from C1 (very low) to CX (extreme). The corrosion class determines which protective system is required.
Classification
| Class | Severity | Example environment |
|---|---|---|
| C1 | Very low | Heated, dry interiors |
| C2 | Low | Unheated buildings, rural outdoors |
| C3 | Medium | Urban or mildly industrial outdoor climate |
| C4 | High | Industrial or coastal environment |
| C5 | Very high | Heavy industry, coast with high humidity |
| CX | Extreme | Offshore, chemical industry, permanent immersion |
Applications
- Steel structures — the class determines the paint system (number of coats, thickness, paint type)
- Specifications — the corrosion class is prescribed in the project specification
- Cladding work — higher classes may require aluminium or stainless steel
- Maintenance cycles — the higher the class, the more frequent inspection and maintenance
Choosing a protection system
Higher corrosion classes call for thicker coatings, more expensive paint systems (epoxy, polyurethane) or alternative methods such as hot-dip galvanising or the use of weathering steel.
Related terms
- Corrosion
- Steel
- Galvanising
- Weathering steel
- Preservation
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