Aluminium corrosivity categories

Aluminium plate under attack
Aluminium plate under attack

The overview below shows how steel is classified in relation to standard EN/ISO9223:2012 in connection with corrosivity categories. Since there is no equivalent standard for aluminium, this is often the standard used as basis in the classification of aluminium in relation to corrosivity categories.

Because the characteristics of aluminium differ from the characteristics of steel, a number of conditions must be taken into account. We therefore recommend that you read the reservations and guidelines under the table before using it.

Corrosivity category Corrosivity Typical indoor environments Typical outdoor environments
C1 Very low Offices, schools and museums. Certain deserts, Central Arctic and Antarctica. 
C2  Low Storage rooms/premises and sport halls. Rural areas and small towns, deserts and subarctic regions.
C3  Medium Food processing plants, laundries, breweries and dairies. Urban areas and a few coastal areas with low effect from the sea.
Subtropical and tropical zones with low pollution in the atmosphere.
C4  High Industrial processing plants and swimming pools.  Contaminated urban areas, industrial areas, certain coastal areas, areas exposed to strong de-icing salts.
Subtropical and tropical zone, atmosphere with medium pollution. 
C5  Very high Mines, caverns for industrial purposes, unventilated sheds in subtropical and tropical zones. Industrial areas, coastal areas in general, sheltered positions on coastlines.
CX  Extreme Unventilated sheds/buildings in humid tropical zones exposed to outdoor factors to an extent that is particularly corrosion-stimulating. Extreme industrial areas, coastal and offshore areas, areas often exposed to contact with salts.

Reservations before using the table

Whether the aluminium can live up to the various corrosivity categories depends on an assessment of the specific environment, and the situation in which the material is to be used.

1) As a starting point, it is problematic to apply this standard to aluminium because corrosivity categories are assessed together based on both indoor and outdoor conditions. Aluminium primarily has the best durability in environments with changing conditions, which most often occurs outdoors. For example, it is not a problem if the aluminium surface is exposed to rain and the like as long as it has the opportunity to dry up again, thereby regenerating itself. On the other hand, aluminium cannot withstand, for example, enclosed environments where the material is constantly exposed to moisture.

2) At the lowest corrosivity categories - C1 and C2 (see table) - it is unproblematic for all aluminium alloys to be corrosion resistant in both indoor and outdoor conditions.

3) Corrosivity category C3 (see table) covers, in connection with indoor conditions, laundries and brewers, among other things. Here it is important to take into account a number of factors: How often cleaning takes place, what cleaning agents are used and are there any acids and bases in the environment? These have an impact on whether aluminium can be included in the environment. At the same time, the outdoor conditions classified as C3, are unproblematic for alloys for marine applications and certain other alloys, provided that they have undergone correct surface treatment.

4) In the remaining corrosivity categories - C4, C5 and CX (see table) - indoor conditions are problematic in relation to aluminium. For example, mine operation often involves the use of a wide range of powerful chemicals that can dissolve aluminium. At the same time, seawater resistant alloys can be included in coastal environments just fine, without aluminium breaking down.