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What is Corrosion?
Corrosion Is a Serious Issue for Construction and Safety
What is Corrosion?
Corrosion is the breakdown of materials due to chemical reactions. It is usually oxidation with air molecules and often in the presence of water. Corrosion also occurs when an acidic or basic material touches another material. When a material corrodes, its physical properties change. Problems with corrosion are mostly with metal, though other materials can corrode. Corrosion is a form of erosion.
Do All Metals Corrode?
All metals can corrode. Some, like pure iron, corrode quickly. Stainless steel, however, which combines iron and other alloys, is slower to corrode and is therefore used more frequently.
All small group of metals, called the Noble Metals, are much less reactive than others. As a result, they corrode rarely. They are, in fact, the only metals that can be found in nature in their pure form. The Noble Metals, not surprisingly, are often very valuable. They include copper, palladium, silver, platinum, and gold.
Types of Corrosion
Many structural alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pit or crack, or it can extend across a wide area more or less uniformly corroding the surface. In fact, there are many different reasons for metal corrosion. Some can be avoided by adding alloys to a pure metal. Others can be prevented by a careful combination of metals or management of the metal's environment. Some of the most common types of corrosion are described below.
- General Attack Corrosion: This very common form of corrosion attacks the entire surface of a metal structure. It is caused by chemical or electrochemical reactions. While general attack corrosion can cause a metal to fail, it is also a known and predictable issue. As a result, it is possible to plan for and manage general attack corrosion.
- Localized Corrosion: This corrosion attacks only portions of a metal structure. There are three types of localized corrosion:
Pitting: the creation of small holes in the surface of a metal.
Crevice corrosion: corrosion that occurs in stagnant locations such as those found under gaskets.
Filiform corrosion: corrosion that occurs when water gets under a coating such as paint. Weakness.
- Galvanic Corrosion occurs when two different metals have physical or electrical contact with each other and are immersed in a common electrolyte, or when the same metal is exposed to electrolyte with different concentrations. In essence, one metal's molecules are drawn toward the other metal, leading to corrosion in only one of the two metals.
- Environmental Cracking: When environmental conditions are stressful enough, some metal can begin to crack, fatigue, or become brittle and weakened.
Protection from corrosion
Various treatments are used to slow corrosion damage to metallic objects which are exposed to the weather, salt water, acids, or other hostile environments. Some unprotected metallic alloys are extremely vulnerable to corrosion, such as those used in neodymium magnets, which can spall or crumble into powder even in dry, temperature-stable indoor environments unless properly treated to discourage corrosion.
- Surface treatments
- Applied coatings
- Reactive coatings
- Anodization
- Biofilm coatings
- Controlled permeability formwork
- Cathodic protection
- Sacrificial anode protection
- Impressed current cathodic protection
- Anodic protection
- Rate of corrosion
Corrosion Prevention
The World Corrosion Organization estimates the global cost of corrosion to be about US$ 2.2 trillion annually, and that a large portion of this - as much as 25% - could be eliminated by applying simple, well-understood prevention techniques. Corrosion prevention should not, however, be considered solely a financial issue, but also one of health and safety. Corroded bridges, buildings, ships, and other metal structures can and do cause injury and death.
