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It is deterioration of a metal as a result of chemical reaction between it and the surrounding environment. Both the type of metal and the environment condition, particularly gases that are in contact with the metal, determine the form and rate of deterioration.

Types of Corrosion

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 metal’s environment.

1. General Attack Corrosion :
This is very common form of corrosion that attacks the entire surface of a metal structure. It is caused by chemical or electrochemical reactions.

2. Localized Corrosion :
Localized corrosion attacks only portions of a metal structure; there are three types of localized corrosion.
(a) Pitting — the creation of small holes in the surface of a metal.
(b) Crevice corrosion — corrosion that occurs in stagnant location such as those found under gaskets.
(c) Filiform corrosion — corrosion that occurs when water gets under a coating such as paint or weakness.

3. Galvanic Corrosion :
Galvanic corrosion can occur when two different metals are located together in a liquid electrolyte such as salt water. In essence, one metal’s molecules are drawn towards 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.

Corrosion Prevention

In virtually all situations, metals corrosion can be managed, slowed, or even stopped by using the proper techniques.

Corrosion prevention can take a number of forms depending on the circumstances of the metal being corroded. Corrosion prevention techniques can be generally classified into 6 groups.
1. Environmental modifications
2. Metal selection and surface conditions
3. Cathodic protection
4. Corrosion inhibitors
5. Coating
6. Plating

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