Types of Corrosion

When materials react with the surrounding environment or medium, electrochemical and chemical reactions destroy the material. This is called corrosion of materials. Most of the time, the term corrosion is used in the case of metals. Rusting of Iron is the best example of Metal corrosion. Corrosion may inhibit all the good properties of a material, and gradually it will destroy the whole material. There are different types of corrosion according to varying conditions of the material. In this article, we will briefly explain different types of corrosion and some established ideas for preventing or reducing the rate of degradation. 

Corrosion is an unwanted reaction that happens when materials react to the surrounding environment or medium because the electrochemical and chemical reactions will destroy the material.

Types

There are several types of corrosion, some are:-

• Pitting Corrosion
• Uniform Corrosion
• Metal Dusting
• High-temperature Corrosion
• Microbial Corrosion
• Galvanic Corrosion
• Intergranular Corrosion
• Crevice Corrosion

Pitting Corrosion: Pitting corrosion is difficult to find because these types of corrosion are unpredictable. When compared with other types of corrosion, pitting corrosion shows more damage. That’s why this corrosion is termed as Most dangerous corrosion. At first, a small localized scratch is formed at a point, leading to the formation of a hole or a pit. When a pit or cavity is visible, the corrosion starts faster and penetrates the surface. The corrosive products may settle inside the cavity. Thus, the corrosion will be hard to detect. Pitting corrosion is so dangerous if left undetected that it can be a reason for the complete malfunction of an engineering system.

Uniform Corrosion: When talking about uniform corrosion, it’s one of the common types of corrosion. When the whole surface of the metal comes into contact with the corrosive environment, it leads to loss of metal uniformly from the surface which came into contact. This will make the metal thin, and after some time, the metal will ultimately lose its features. When compared with other types of corrosion, uniform corrosion is easily detectable. So it can be prevented by early detection. Uniform corrosion is seen in copper, steel, aluminum and other common materials. The best example of uniform corrosion is a rusty bolt. If uniform corrosion is left undetected, it will cause a failure to any metals.

Metal Dusting: This is also a very destructive type of corrosion. On coming in contact with the atmosphere having high amounts of carbon activities, the materials at risk become the victims of metal dust. Metal dusting can convert metals into metal powders. The primary mechanism seen here is, from the carbon monoxide (vapor state), deposition of graphite takes place on the surface of the metal. Then the formed graphite layer will change into a metastable form, which goes away from the surface of the metal. In other words, we can tell that the whole metallic surface is converting into a layer of graphite. Metal dusting is a prominent issue in the petrochemical industries, especially in Furnaces and reforming units.

High-temperature Corrosion: This type of corrosion of materials is due to excess heating (high temperature). When there is the presence of gasses like sulfur, oxygen, and other gasses in the hot atmosphere, metal’s chemical deterioration can occur quickly because of oxidation. High-temperature corrosion mainly affects gas turbines, machinery, furnaces and diesel engines that have direct contact with hot gasses. Any component is potentially at risk when exposed to higher temperatures in a non-inert environment. At higher temperatures, most of the alloys and metals corrode and oxidize. The acceleration of the corrosion when exposed to higher temperatures is because a rise in the temperature results in the increase of the active center of corrosion in material or metal. Thus, protecting equipment and metal products from higher temperatures are necessary. Coating metals with a high-temperature structural coating will help prevent corrosion due to higher temperatures. 

Microbial Corrosion: This is a type of corrosion that happens due to the presence of microorganisms. This is also termed MIC (microbiologically influenced corrosion). The most common microorganisms that cause microbial corrosion are chemoautotrophs. Even in the presence or absence of oxygen, this corrosion can happen. Microbial corrosion occurs in metallic and non-metallic materials. This type of corrosion is prevented by regular checking and cleaning of all the equipment and by the standard application of chemicals with biocides.

Galvanic Corrosion: In this type of corrosion, galvanic corrosion will happen if the metals are in an electrolytic environment and there is an electric contact with metals dissimilar electrochemically. This phenomenon will result in the degradation of one metal at any point.

• Intergranular Corrosion: This type of corrosion happens when there are pollutants or impurities in the grain boundaries, which are formed due to metal alloy solidification. This also occurs when there is an increase or decrease in the amount of alloy at the grain boundaries. 

Prevention of Corrosion

Corrosion is an undesirable event that happens to metals and other materials. The corrosion phase may be slow, but it will affect the core of the metal and decrease the stability. There are different methods to overcome corrosion, some are: 

• Painting
• Enameling
• Tarring
• Galvanizing 
• Electroplating
• Tin plating 

Conclusion

Corrosion is an undesirable event that happens to metals and other materials. Corrosion may impact the metal partially or wholly. Corrosion may result in the complete malfunction of equipment or a machine. Corrosion may inhibit all the good properties of a material, but gradually it will destroy the whole material. There are different types of corrosion according to varying conditions of the material. This article discussed different kinds of corrosion and their effect on the materials.