Types of Corrosion Classification

Over the years, corrosion engineers and researchers have found that metal corrosion occurs in various types that have certain similarities and are divided into specific groups, many of which are not unique. The most familiar classification of metal corrosion types was presented by Fontana and Green. The basis of this classification is the appearance of the corroded metal.

Corrosion Classification Based on Appearance (Fontana and Green)

In this classification, eight types of corrosion are mentioned as the most important types of metal corrosion, which are:

1. Uniform corrosion
2. Gritting corrosion
3. Galvanic corrosion
4. Intergranular corrosion
5. Selective separation
6. Abrasive corrosion
7. Stress corrosion
8. Hydrogen damage

The above classification is based on the appearance of the attack of corrosive agents on the metal surface. It is worth noting that it is not possible to determine a clear boundary between the types of metal corrosion, because a number of types of corrosion overlap.

The incidence of each type of metal corrosion varies, and the importance of each type will vary among different systems and environments. On the other hand, there are striking commonalities in the distribution of damage from corrosion in similar industries, which, when compared, show that corrosion problems in similar industries are very similar.

Classical Classification of Corrosion (Ulick and Evans)

Some corrosion scientists, such as Ulick and Evans, have avoided using a specific classification framework and have simply examined the classical corrosion types according to the type of metal or alloy in question. Ulick has described the types of metal corrosion as follows:

1. Bimetallic corrosion
2. Localized corrosion
3. Stress corrosion
4. Microbial corrosion
5. Fatigue corrosion
6. Abrasive corrosion
7. Flow corrosion
8. Atmospheric corrosion
9. Corrosion in soil
10. Hydrogen cracking and stress cracking in the presence of sulfur

Types of metal corrosion

Among the important types of corrosion - without providing a specific division and grouping - the following corrosions can be mentioned:

1. Uniform corrosion
2. Bimetallic corrosion
3. Corrosion by oxygen
4. Intergranular corrosion
5. Selective corrosion
6. Bubble corrosion
7. Hydrogen damage
8. Stress corrosion
9. Microbial corrosion

As can be seen, different researchers and scholars have introduced different types of metal corrosion as the most important corrosion mechanisms. Therefore, a uniform classification for the types of metal corrosion has not been provided by different authors and scholars, and only the types of corrosion have been introduced in a simple way.

Types of Metal Corrosion Based on Origin and Appearance

The Corrosion Reference Book from ASM Publications, one of the most authoritative references on corrosion science, divides corrosion into the following five main categories based on their origin and appearance:

1. Uniform corrosion:This type of corrosion includes atmospheric corrosion, bimetallic corrosion, molten metal corrosion, and high-temperature corrosion.
2. Localized corrosion:Includes filamentary corrosion, crevice corrosion, pitting corrosion, and localized corrosion due to the activity of living organisms.
3. Corrosion caused by metallurgical factors:Includes intergranular corrosion, selective segregation or dealloying, and crevice corrosion in carbon steel.
4. Corrosion caused by mechanical factors:Includes erosion, frictional corrosion, blistering and water droplet impact corrosion, fatigue corrosion, stress corrosion, hydrogen damage, and embrittlement due to contact with molten metal.
5. Corrosion caused by environmental factors:Includes stress corrosion and cracking. In addition to the above-mentioned groupings, some scientists have considered other indicators and criteria for classifying types of corrosion and have presented different classifications from a different perspective. For example, corrosion can be divided into corrosion in wet environments and corrosion in dry environments according to the environment in which it occurs:

5-1 Corrosion in wet environments:includes bimetallic corrosion, selective corrosion, pitting and crevice corrosion, concentration pitting, grain boundary corrosion, intergranular corrosion, selective separation, abrasion corrosion (turbulence and impact velocity), blister corrosion, and crevice stress corrosion (stress concentration, fatigue, environmental cracking).

2-5 Corrosion in dry environments:includes high-temperature corrosion and high-temperature oxidation. High temperature corrosion is divided into three different categories:

1. 1. Low temperature (temperatures below 180 ° C, which cause hot corrosion in the boiler outlet)
   2. Medium temperature (temperatures around 1200 ° C, which cause corrosion of superalloys in gas turbine blades.)
   3. High temperature (temperatures around 1200 ° C, which cause corrosion of superalloys in gas turbine blades.)

Types of metal corrosion based on the equipment required to evaluate and identify corrosion

Another type of corrosion classification is based on the equipment required to evaluate and identify corrosion, which is divided into the following major groups:

a) Corrosions that can be detected by normal inspection and with the naked eye, such as uniform corrosion, pitting corrosion and bimetallic corrosion.

b) Corrosions that may require additional tools for detection, such as erosion corrosion, blister corrosion and grain boundary corrosion.

c) Corrosions that require more detailed microscopic (optical or electron) inspection, such as selective delamination, stress corrosion cracking, and fatigue corrosion.

Sometimes another classification of corrosion types is presented based on microscopic and macroscopic observations.

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