Corrosion categories acc. ISO 12944-5

Be aware that your steel is to be addressed to the correct corrosion category

It is requirement to life span in a concrete environment that determines the choice of the corrosion category a given steel structure to be treated for.

Steel structures must be used/placed under different climatic conditions:

  • Low corrosion categories of protected environments such as indoor use
  • High corrosion categories of vulnerable and coastal surroundings

Corrosion categories are divided into 6 different categories according to ISO 12944-5by their scope:




C1: Very low


Heated buildings with production, such as offices, shops, schools, hotels, etc.

C2: Low

Environments with low levels of polutionMainly rural setting

Unheated buildings where condensation can occurFor example, warehouses, depots, sport facilities and similar.

C3: Medium

City and industrial environments with moderate sulfur dioxide pollutionCoastal areas with low salinity

Production areas with high humidity and some air pollution. For example, industrial plantslaundries, breweries, food production, etc. 

C4: High

Industrial areas and coastal areas with moderate salinity

Chemical industry, ship- and boat yard.

C5I: Very high

Industrial areas with high humidity and aggressive environment

Buildings and areas with almost permanent condensation and with high pollution impact. 

C5M: Maritime

Coastal environment and off-shore installations with high salt content

Buildings and areas with a high degree of condensation and with high impact of pollution.