Corrosion leads to the deterioration of materials and affects resources, which is a significant problem. One step towards solving this problem is understanding the different types of corrosion.
In this post, we will cover 19 different forms of corrosion to help you understand them faster, and when to distinguish them.
- Uniform (General) Attack Corrosion
- Localized Corrosion
- Selective Leaching Corrosion/De-alloying
- Erosion Corrosion
- Fretting Corrosion
- Intergranular Corrosion
- Galvanic Corrosion
- Stress Corrosion (S.C.C.)
- Corrosion Fatigue Occur
- High-Temperature Corrosion
- Microbial Corrosion (a.k.a. Biological corrosion)
- Exfoliation Corrosion
- Stray Current Corrosion
- Lamellar Corrosion
- Caustic Agent Corrosion
- Impingement Corrosion
- Cavitation Corrosion
- Atmospheric Corrosion
- Aqueous Corrosion
Despite their differences, they have one common characteristic. All types of corrosion weaken materials. Weakening occurs because of oxides and salts.
Keep reading to learn more.
1. Uniform (General) Attack Corrosion
This is the uniform attack corrosion is a type of corrosion that attacks most metals. Some of the metals it attacks include lead, aluminum, and zinc. Uniform or general attack corrosion leads to a lot of tonnage wastage.
Uniform corrosion occurs when a chemical reaction affects a whole exposed surface. Usually, it happens when you expose metals to open atmospheres such as water, air, and soil. Affected metals become thinner and then fail in the end. Even though the uniform attack corrosion affects most metals, it is easy to spot. Once detected on time, it is possible to manage.
2. Localized Corrosion
Localized corrosion is the opposite of general attack corrosion. It is a type of corrosion that attacks some parts of metal surfaces while leaving other parts intact.
This type of corrosion is further categorized into different forms discussed below.
This corrosion is one of the most destructive. It is also not easy to predict or detect this type of corrosion. The name “pitting” originates from the pits or holes the corrosion leaves on the metal surfaces it attacks. Pits penetrate downwards into the surface.
Pitting can originate from a chemical attack. An example of a pitting attack is when aerated water gets into contact with steel. It can also originate from a mechanical attack like an impact that destroys the oxide film – a protective layer.
Crevice corrosion occurs when shielded areas get exposed to corrosive environments. It takes place in areas with an inadequate flow of oxygen, like under bolt heads. The difference in ion concentration in the two areas is the leading cause of this corrosion.
Another name for this localized corrosion is “under-film corrosion.” It occurs underneath a coating and manifests itself as threadlike fibers. Oxygen concentration cells cause filiform corrosion.
This corrosion occurs when metallic areas accumulate different forms of debris and dirt. Wheel wells are an example of where poultice corrosion is most likely to occur.
In this type of localized corrosion, deposits of a more noble metal get deposited on the less noble metal. These deposits then encourage pitting.
For example, water can pass through a copper pipe and collect some copper ions. Deposition corrosion will occur when those ions are deposited in an aluminum pipe.
3. Selective Leaching Corrosion/ De-alloying
When different metallic surface areas are different metallurgically, selective leaching corrosion is most likely to occur.
De-alloying occurs when an alloy loses one of the elements. For instance, Brass, which contains copper and zinc, experiences de-alloying when the zinc is removed, leaving behind the copper.
4. Erosion Corrosion
High-velocity movements between corrosive fluids and metal surfaces cause erosion-corrosion. This type of corrosion occurs because of the mechanical abrasive action that comes with the rapid movement.
5. Fretting Corrosion
Fretting corrosion, commonly associated with contact surfaces, is induced by the repetition of relative surface motion. For instance, vibration can cause this type of corrosion. Apart from vibration, weight and repeated wearing also cause fretting corrosion. Bolted joints are common victims of fretting corrosion.
6. Intergranular Corrosion
Also known as intercrystalline corrosion, intergranular corrosion affects grain boundaries. Impurities at the boundaries cause intergranular corrosion. Depletion and enrichment of an alloying element at these boundaries can also cause this type of corrosion.
7. Galvanic Corrosion
This type of corrosion also goes by the name two-metal corrosion. When two, unlike metals, are electrically connected, the more active one corrodes faster than the other.
The active metal becomes the anode, and the other the cathode. The corrosion rate of the anode usually increases when the metal connects with the other metal.
8. Stress Corrosion (S.C.C)
Stress corrosion (S.C.C) occurs when there is a combination of a corrosive medium and tensile stress. A material can exist in an inert environment where a corrosive medium exists, but only when stress is applied will corrosion occur.
For this reason, stress corrosion is particularly hazardous. Stress corrosion usually causes the material to fail without little or no warning.
9. Fatigue Corrosion
Somehow similar to stress corrosion, corrosion fatigue involves the premature fracturing of metal because of being exposed to a corrosive environment. Cyclic loading, vibrations, and pressure fluctuations also causes corrosion fatigue.
10. High-Temperature Corrosion
Just like the name suggests, heat is the cause of high-temperature corrosion. It is a type of corrosion that is not dependent on liquid electrolytes.
In this type of corrosion, instead of metals reacting to ions in solutions, they react with the atmosphere’s vaporous particles. Examples of machinery that suffer from this type of corrosion include gas turbines and furnaces.
11. Microbial Corrosion (Biological Corrosion)
Biological corrosion, also known as microbial corrosion or microbiologically induced corrosion, occurs due to microorganisms’ presence.
The metabolic activity of microorganisms is what deteriorates materials. Microorganisms create biofilms, then alter the environment at the surface of the metal. After the alteration, deterioration begins to occur.
12. Exfoliation Corrosion
It is a more severe form of intergranular corrosion. In this type of corrosion, metal gets divided into layers along the grain boundaries. Exfoliation corrosion leads to the loss of surface material.
13. Stray Current Corrosion
As the name suggests, stray current corrosion occurs when current flows through a different path other than the intended one.
When electrical currents enter metals from other sources, corrosion accelerates. Reducing the currents that flow through nearby systems is one way of preventing this type of corrosion.
14. Lamellar Corrosion
Lamellar corrosion is more or less the same as exfoliation corrosion. However, lamellar corrosion usually applies when talking about a broader exfoliation.
This broader exfoliation is that which occurs in light metals with low densities. Examples of light metals include aluminum and magnesium.
15. Caustic Agent Corrosion
Some household agents, like drain cleaners, contain caustic agents. These agents can destroy tissue. When misused, these agents can cause caustic agent corrosion to pipes. Caustic agent corrosion affects old metal pipes.
Old pipes that have already been exposed to corrosion and have developed pits can hold the caustic agents found in cleaners, thus, increasing corrosion.
16. Impingement Corrosion
Like erosion-corrosion, impingement corrosion relates to velocity. The impact sustained from the impingement of high-velocity flowing particles causes this type of corrosion.
17. Cavitation Corrosion
This type of corrosion occurs from an abrupt creation and collapse of vacuums and bubbles.
Therefore, cavitation corrosion is a combination of cavitation and corrosion. Turbulence in a liquid is what causes the sudden creation and collapse of bubbles and vacuums.
Metal surfaces with pits are a sign of cavitation corrosion. The roughness of surfaces is also a sign of cavitation corrosion.
18. Atmospheric Corrosion
This is an electrochemical type of corrosion. Air and the pollutants contained in air cause corrosion. Habitually, in the form of a thin film, electrolytes form on surfaces under certain atmospheric conditions.
Only when a certain level of humidity is reached does the film form, and these levels depend on the type of metal.
Once electrolytes form, corrosion occurs by balancing cathodic and anodic responses.
19. Aqueous Corrosion
Aqueous corrosion occurs when a material with the potential for corrosion stays immersed in an electrolyte of moisture. Oxygen must also be present for this type of corrosion to occur. The wet environment is the leading cause of aqueous corrosion. Pitting and rust are two appearances associated with aqueous corrosion.
Understanding the types of corrosion is one step towards managing corrosion.
For instance, caustic agents are not a good match for old metal pipes. It would be best to avoid household products that contain these agents.
Additionally, remember that reducing the current flowing through systems adjacent to metal surfaces is a wise way of preventing stray current corrosion.
Have you encountered one or more of these forms of corrosion listed above?
Or maybe you met the forms that I didn’t mention here.
Let me know in the comments or on LinkedIn