The Corrosivity Categories

ISO 12944 is a globally recognised standard that provides guidelines on the protection of assets from corrosion. It covers the protective paint systems designed for application to abrasive blasted steel, hot dipped galvanised steel and thermally sprayed zinc steel.

The classification of the environment is given as per table:

Corrosivity Category

Application Area – OutdoorsApplication Area – Indoors

C1 (Very low)

Not ApplicableInside heated rooms – offices, commercial buildings, schools, hotels

C2 (Low)

Low pollution, mostly rural areasUnheated buildings where condensation may occur – storage, facilities, sport centres

C3 (Medium)

Urban and industrial areas, moderate pollution, coastal regions with low salt concentrationHigh humidity rooms with some air pollution – breweries, dairies, food production facilities
C4 (High)Industrial areas, coastal regions with moderate salt concentrationChemical plants, swimming pool, boat houses above sea water

C5 – I (Very high)

Industrial areas with high humidity and aggressive atmospheresBuilding and areas with ever present condensation and heavy pollution
C5 – M (Maritime)Coastal and offshore regions with high salt concentrationBuildings and areas with ever present condensation and heavy pollution

The durability categories of corrosion protection are as follow:


MediumHighVery High
Up to 7 years7-15 years15-25 years

More than 25 years

To find out more information, please contact Exnovo’s team of experts to discuss the best surface protection for your transformer needs.