Corrosion types
Corrosion Types © Zsolt Palatinus The types of corrosion for metals can vary in a number
Corrosion rates for metals will vary dependent upon metal type and the environment that it is exposed to.
When most metals come into contact with certain substances in the air or water, they undergo a chemical change which decreases the integrity of the metal. This process is called corrosion. Oxygen, sulfur, salt, and other materials can all lead to corrosion.
When a metal corrodes or deteriorates, it cannot hold the same loads as it did before corrosion began. At a certain point, corrosion can lead to dangerous conditions.
Metal used in construction is all subject to corrosion. Because of this, it is important to monitor and manage corrosion to avoid structural collapse.
The rate of corrosion is the speed at which any given metal deteriorates in a specific environment.
The rate, or speed, is dependent upon environmental conditions as well as the type, and condition, of the metal.
Corrosion rates are normally calculated using µpy (microns per year). In other words, the corrosion rate is based on the number of microns (thousands of a millimetre) it penetrates each year.
In order to calculate the rate of corrosion, the following information must be collected:Â
Corrosion rates determine the lifespan of metal-based structures. This dictates the choice of metals used for different purposes, and in different environments.
It also determines the maintenance requirements for structures: a metal structure in a wet and/or polluted environment may require more frequent maintenance than a similar structure in a drier or unpolluted environment.
Maintenance schedules are developed based on the types of calculations described above.
Heated buildings with clean atmospheres like offices, shops, schools and hotels, represent a low corrosivity category and risk, with a very low-carbon steel thickness loss – less than 1.3µm/per year.
Also in a low risk atmospheric corrosivity category and risk with an annual corrosion rate between 1.3µm and 25µm are rural areas, areas with a low level of pollution and the interior of the buildings that are unheated and where condensation may occur (e.g. depots, sports halls).Â
Corrosion rates in a medium risk category will be between 25 and 50µm for urban and industrial atmospheres with moderate sulphur dioxide pollution, coastal areas with low salinity, or the interior of production rooms with high humidity and some air pollution (e.g. food processing plants, laundries, breweries, dairies).
Corrosivity category and risk | Low carbon steel Thickness Loss (µm)* | Examples of typical environments in a temperate climate (informative only) | |
---|---|---|---|
Exterior | Interior | ||
C1 very low | ≤ 1.3 | – | Heated buildings with clean atmospheres, e.g. offices, schools, shops, hotels. |
C2 low | > 1.3 to 25 | Atmospheres with low level of pollution. Mostly rural areas. | Unheated buildings where condensation may occur, e.g. depots, sports halls. |
C3 medium | >25 to 50 | Urban and industrial atmospheres, moderate sulphur dioxide pollution. Coastal area with no salinity. | Production rooms with high humidity and some air pollution, e.g. food processing plants, breweries, laundries, dairies. |
C4 high | > 50 to 80 | Industrial areas and coastal areas with moderate salinity. | Chemical plants, swimming pools, coastal ship and boatyards. |
C5-I very high (industrial) | > 80 to 200 | Industrial areas with high humidity and aggressive atmosphere. | Buildings or areas with almost permanent condensation and high pollution. |
C5-M very high (marine) | > 80 to 200 | Coastal and offshore areas with high salinity. | Buildings or areas with almost permanent condensation and high pollution. |
CX extreme | > 200 to 700 | Offshore areas with high salinity and industrial areas with extreme humidity and aggressive atmosphere and subtropical and tropical atmospheres. | Industrial areas with extreme humidity and aggressive atmosphere. |
* 1µm (1 micron) = 0.001 mm
** The thickness loss values after a year of exposure. Losses may reduce after subsequent years.
*** The loss values used for the corrosivity categories are identical to those give in BS EN ISO 9223.
**** In coastal areas in hot, humid zones, the mass or thickness losses can exceed the limits of category C5-M. Special precautions must therefore be taken when selecting protective paint systems for structures in such areas.Â
Corrosion Types © Zsolt Palatinus The types of corrosion for metals can vary in a number
Corrosion process Reaction Corrosion reaction One example for the occurrence of corrosion is when steel reacts
What is corrosion https://vimeo.com/285102710© Construct Films All materials weather, dependent upon the environmental conditions that they
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