7 Types of Corrosion
Corrosion is the natural and gradual deterioration of materials, most commonly metals. This comes as a result of chemical reactions with the environment, for example with oxygen or water. But did you know that there are different types of corrosion? Yes, as one of the enemies of sheet metal fabricators across the land, corrosion has many different forms.
If left untreated, corrosion can:
- Weaken structures and components
- Reduce the lifespan of equipment
- Lead to costly repairs or replacements
- Pose safety risks in industrial or structural settings
To prevent this, it’s important to understand the different types of corrosion, so we’ve compiled a handy list of corrosion examples for you in this blog post. Carry on reading for more information on the 7 types of corrosion and some tips on how to avoid them.
Different types of corrosion example
1. Uniform Corrosion
Also known as general corrosion, this is the most common and widespread of corrosion examples. It occurs evenly across a metal surface, typically as a result of direct chemical exposure, such as contact with acids. The initial sign is usually a dulling of the metal, which can progress to a rough, frosted texture if left unchecked.
Although uniform corrosion affects appearance more than structural integrity, it’s still important to address as soon as you can, or as soon as you see it. Protective coatings or corrosion-resistant materials can help prevent it from developing.
2. Pitting Corrosion
This is a highly localised form of corrosion where small pits or cavities form on the surface of the metal. These pits can deepen very quickly, compromising structural integrity while leaving most of the surface seemingly intact. This can make spotting it a little harder, as it can come on subtly and out of sight initially.
Pitting is often caused by defects in coatings, inconsistent metal surfaces or damage to the protective oxide layer. It’s commonly seen in aluminium, stainless steel and nickel alloys. Early detection and proper surface finishing are key to prevention.
3. Galvanic Corrosion
Galvanic corrosion happens when two dissimilar metals come into electrical contact with each other. An electrolyte must also be present, such as saltwater. One metal (the anode) will then corrode quicker than it would alone, while the other (the cathode) is protected. This issue is a common one in marine environments or with chemical processing equipment.
4. Crevice Corrosion
Crevice corrosion develops in confined spaces where stagnant fluids can accumulate, such as between washers, flanges, or metal overlaps. Crevices often have limited oxygen flow, which creates acidic conditions that break down protective oxide layers. This is what leads to corrosion. Improved joint design and careful assembly practices can help minimise the risk of this often hard to detect corrosion type.
5. Fretting Corrosion
This is essentially caused by repeated small movements between two metal surfaces that are under load. This vibration wears away the protective oxide layer, exposing fresh metal that quickly oxidises. The resulting debris gets trapped in the contact area, accelerating both wear and corrosion.
Fretting corrosion examples typically occur in mechanical joints, bearings and bolted assemblies. You can help to prevent this with vibration damping, tighter tolerances and protective powder coatings.
6. Stress Corrosion Cracking (SCC)
This is a result of two factors combining – tensile stress and a corrosive environment. This often occurs at higher temperatures or as a result of expansion and contraction as a result of fluctuating temperatures. It may also be caused by residual stress from the manufacturing process, for example, welding, machining, or cold forming.
With stress corrosion, most of the surface area usually remains intact. But fine cracks do appear in the microstructure, which makes these types of corrosion hard to detect. Choosing appropriate materials for a given environment can help to avoid potential failures.
7. Intergranular Corrosion
This occurs along the grain boundaries of a metal. These boundaries, which separate individual grains within the metal’s crystalline structure, are often more chemically reactive than the grains themselves. This is due to impurities or uneven solidification during alloy formation. This form of corrosion typically happens when a material experiences high temperatures, such as during heat treatment or welding.
In these conditions, carbide precipitation can occur, which reduces the corrosion resistance at the grain boundaries. As a result, the metal becomes more vulnerable to corrosive agents, even if the grain interiors remain intact.
How to prevent corrosion
Here are some general tips you can follow to ensure you avoid the different types of corrosion.
- Select corrosion-resistant metals: Materials like aluminium and stainless steel offer durability and are well-suited to various environments.
- Apply laser treatments: Laser technology can alter surface structure to enhance corrosion resistance.
- Use non-metallic coatings: Grease, plastics, carbon fibre, paint, and oil can act as effective barriers against moisture.
- Opt for specialist coatings: Modern powder coatings provide durable, UV-resistant protection without fading, chalking, or the need for multiple layers.
- Control moisture: Use drying agents in equipment and storage areas, and regularly check for signs of damp or leaks.
- Maintain regularly: Inspect metal surfaces often and repair any damage to protective coatings as soon as possible.
Contact Salamander Fabrications for more information or support
If you would like more information on how to protect your metal projects from the different types of corrosion, please contact us, call us on 01484 843599 or send an email to sales@salamanderfabs.com.
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