Most people have dealt with corrosion in one form or another; whether it’s rust on bolts, screws, or flat washers used on outdoor furniture or the build-up that can accumulate on metal battery terminals. There is a reason why manufacturers, builders, and fastener distributors purchase flat washers that are HDG for external settings and placements that need additional resistance. The reason is the corrosion. This natural reaction occurs in many different circumstances, and that’s because there are many different types of corrosion. Regardless of the type of corrosion, in most cases; prevention is critical for maintaining the integrity of a structure, piece of equipment, or other items.
Understanding 5 Most Common Types of Corrosion
To choose the most effective option for resisting or repairing the effects of corrosion; it’s helpful to know the most common types of corrosion and the circumstances where they are most likely to occur.
Galvanic corrosion is sometimes called bimetallic corrosion. It’s caused by the interaction of two different metals; which react when an electrolyte is present. The likelihood of galvanic corrosion varies based on the electrode potentials of two metals and whether they will interact as an anode and cathode. When galvanic corrosion is allowed to persist; the metal acting as the anode will begin to deteriorate, while the metal acting as the cathode will not lose integrity.
You can prevent galvanic corrosion by checking the electrolyte potentials of any metals that you must combine for an application. For example, steel fasteners used in aluminum sheets will result in galvanic corrosion; if they can make direct content, and you can avoid it. You can introduce the combination, or a buffer element; like using plated zinc flat washers or HDG flat washers instead of plain steel USS flat washers or SAE flat washers.
Pitting corrosion is a destructive form of deterioration that appears as small holes and pits in the metal’s surface. It will occur in metals with structural inconsistency, foreign deposits, or poor coating on their surface. When these factors are present, moisture can allow for an anode-cathode relationship; which causes a corrosion cell that rapidly penetrates the material.
Since pitting corrosion starts with flaws in the material, it cannot be easy to predict and prevent in every case. Checking the integrity of all coatings and buffers and ensuring no foreign deposits or build-up can help prevent the circumstances that lead to pitting.
Intergranular corrosion mainly affects a metal’s grain boundaries; while the rest of the material is unaffected. This type of corrosion occurs if problems during the heat treating process interfere with passivation along the grain; which means corrosion resistance properties are weaker.
Intergranular corrosion is more likely to affect some materials than others. You can avoid it by selecting lower carbon or stabilized materials; or ensuring all heat treatments are correctly performed.
Uniform corrosion is a common type of material deterioration that occurs; when metal is subjected to a corrosive chemical; or other substance that causes an electrochemical reaction. Rusted steel caused by exposure to saltwater is just one example of uniform corrosion.
This problem is relatively easy to prevent by utilizing materials inherently resistant to rust and other types of corrosion; such as stainless steel or materials that have been coated or treated to incorporate added resistance. Painted, coated, or galvanized parts, for example, will resist uniform corrosion; if these protective treatments are maintained.
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Stress cracking can be identified by the appearance of small or fine cracks in portions of a metal’s surface. It occurs when too much tensile stress allows corrosive factors in an environment to penetrate the material.
Issues during welding, heat treatments, and deformations can contribute to the development of residual stresses that create this problem. Controlling the material’s hardness; and carefully evaluating its performance in the specified environments are a few ways to prevent stress corrosion cracking.
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