Exposure class C1: Very mild
Dry indoor spaces.
Climate exposure
If you spend a lot of time outdoors, at sea, in the rain and in the sun, you know firsthand how the climate takes its toll. The sun burns, the wind dries, and sea air weathers. But not only you, everything. Vehicles, nature, buildings. How much the climate wears things down is affected by emissions from traffic and factories, temperature and humidity, in other words climate exposure. When climate exposure wears down building materials made of steel, it is called corrosion: corrosion, or rusting.
When constructing, it is necessary to know what kind of climatic exposure the building will be subject to. To take the corrosiveness of the climate into account, climatic exposure has been divided into six different classes according to intensity. These climatic exposure classes are described in the SFS-EN 12944-2 standard. The climatic exposure class can be determined in two different ways.
First, the climatic exposure of the area can be measured. In this case, metal test specimens are placed at two test sites. After one year, the corrosion is measured. The obtained figures are compared with the table values in the EN 12944-2 standard, and the climatic exposure class of the area is determined.
Another way of determining climatic exposure is through assessment. In this case, the time of wetness and the deposition of sulphur and chlorine salts at a specific location are assessed. Based on these values, the climatic exposure class of the area is determined.
A roofing screw, like all other construction products, must withstand the climatic exposure in which the building is located. (SFS-EN 1993-1-3+AC). In Finland, the most common climatic exposure class is C3, an urban and industrial climate, which includes approximately 80% of buildings.
Exposure category C2: Mild
Unheated indoor spaces, dry and clean outdoor air, and a rural climate.
Corrosivity category C3: Moderate
Urban and industrial atmosphere with moderate sulphur dioxide pollution. Coastal areas with low salinity. Indoors, production facilities with high humidity and air pollution.
Corrosivity category C4: High
Outdoors, industrial areas and coastal areas with moderate salinity. Shipyards on the coast. Indoors, chemical industry production facilities, swimming halls and pools.
Corrosivity category C5-I: Very severe industrial environment
Industrial areas with high humidity and a corrosive atmosphere. Indoor areas where condensation is almost continuous and the levels of air pollution are high.
Corrosivity category C5-M: Very severe marine environment
Marine environment with high salt content. Indoor buildings or areas where condensation is almost continuous and air pollution levels are high.
Microclimate
A microclimate, or local corrosive environment, may also contain factors that increase the atmospheric corrosivity beyond that of the surrounding environment.
If there are many pollutants in the area originating, for example, from your own chimney or a nearby production facility, the atmospheric corrosivity is higher. Sulfur can form corrosive sulfur compounds together with moisture and other factors. Similarly, salt compounds corrode many metals, and soot collects moisture from the air, increasing the risk of corrosion.
How is suitability for a specific atmospheric corrosivity demonstrated? Read more ›