What are the different types of corrosion?
- General Attack Corrosion
- Galvanic Corrosion
- Localized Corrosion
- Environmental Cracking
- High-Temperature Corrosion
Metal and stainless steel in the Philippines are widely used as a primary material for many industries. They’re tough, readily available, and can be used for various applications. Though metals aren’t indestructible, they have one major weakness. Corrosion may be caused by many different conditions and factors, let’s take a look at a few different types of corrosion:
General Attack Corrosion
This is the most common type of corrosion; it is also commonly known as uniform corrosion. It is considered to be an even attack of oxidation across the surface of a metal material. This form of corrosion is usually easy to determine because it is relatively simple to replicate and reproduce its effects with consistency. Usually, causes of this form of corrosion are due to chemical exposition or from an electrochemical reaction.
From this point, general attack corrosion will render the full deterioration of the metal to the point of structural failure. As mentioned earlier, it’s the most common type of corrosion, which correlates to this type of corrosion accounting for the greatest amount of metal destruction via corrosion. Since it’s common, it isn’t difficult to prevent and predict. Oftentimes, a metal that succumbs to this type of corrosion is still manageable and even preventable.
Galvanic corrosion, often times called dissimilar metal corrosion happens when two dissimilar metals are in contact with one another and in the presence of an electrolyte. This usually happens at metal structural locations such as joints or weld spots. To know how this type of corrosion occurs involves taking a deeper look at metals from a molecular level.
Three conditions must be met in order for this type of corrosion to occur. First, the metals in contact must be electrochemically different. Second, the metals in contact must be electrically connected. Third, the metals must be exposed to an electrolyte. When these conditions are met, one metal starts giving its electrons to the other metal or it becomes an anode, while the other receives the electrons or becomes a cathode.
In Galvanic corrosion, the anode will begin to rapidly rust with the cathode will become more resistant to corrosion. A common example of this is when copper and steel are linked together and suddenly become exposed to salt water.
Under localized corrosion, we have three types: pitting, crevice, and filiform corrosion. These types of corrosion target a specific area in a metal’s structure.
- Pitting Corrosion – is one of the most difficult types of corrosion to spot. It happens when a cavity is formed in the metal. What happens in the cavity is that the exposed area experiences a loss in electrons, the anodic area then becomes more susceptible to a localized form of galvanic corrosion. This cavity will weaken the structure of the metal from within, leading to potential failure.
- Crevice Corrosion – crevice corrosion is similar to pitting corrosion but it doesn’t involve any electron loss. This type of corrosion happens when a cavity, small hole, or crevice in a metal becomes exposed to a stagnant microenvironment. Because of the acidic environment or the exhaustion of oxygen in a crevice, this will lead to corrosion.
- Filiform Corrosion – One of the subtlest corrosions that can slip under the guise of many, filiform corrosion is a form of corrosion that happens under any form of coating. Common instances that because filiform corrosion is when a coating breach occurs and water slips in between the metal and its coating. This form of corrosion spreads underneath paint, epoxy, and many other forms of coating to cause structural weakness.
Environmental cracking is a common form of corrosion that occurs to metals exposed to various environmental conditions. Oxidation, temperature change, and chemical exposure are a few factors that contribute to various structural damages such as stress corrosion cracking, metal embrittlement, corrosion fatigue, and hydrogen induced cracking.
Often caused by high-temperature oxidation and carbonization, high-temperature corrosion typically happens in vehicle’s turbochargers, diesel engines, and exhaust pipes. This happens due to the fuels used in these types of machines; during combustion, various compounds attach themselves to the metal and quickly corrode the surface. At times, even stainless steel may rust due to high-temperature corrosion.
In the Philippines, stainless steel products that are exposed to high-temperature corrosion usually don’t mean that structural integrity will be compromised. Typically, in older engines, you may notice that the exhaust side of a turbocharger will always be more rusted compared to the intake side, but it still works well.
Knowing the different types of corrosion can help you determine whether your metal structure, parts, or components can be saved and how they can be remedied. With this knowledge, you can somehow pinpoint the causes of corrosion and prevent them from happening. If you want high-quality stainless steel that can combat the harshest effects of corrosion, click here to learn more about One Sky Philippines.