When you install a fastener, you expect that fastener to stand the test of time. For all types of projects, fasteners serve as the joining element that holds together numerous pieces to create a structure or object built with integrity. Lurking in the shadows there is one enemy that can threaten that integrity and the strength of metal fasteners though; CORROSION. Corrosion is a big deal and it demands action; it is not something you can just wish away and hope for the best. In fact the earlier you remediate the situation the more cost effective it is and prevents the corrosion from spreading. That’s why you must either do something to prevent corrosion or do something to fix the problem should it occur. Here’s a look at why corrosion occurs and how to prevent it.
Why Corrosion Occurs
Corrosion happens when metal’s inherent properties begin to degrade. All metal, including the metal used in
fasteners, holds electric potential. Various metals have different types of electric potential, and when two metals interact with water, which is an electrolyte, a galvanic cell is created and an electric current begins to flow between the two metals. This low-energy galvanic flow begins to degrade the one with the higher electric potential. The higher-potential metals are known as “anodes,” and the anode metal’s atoms actually lose electrons to the lower-potential metal, known as the “cathode” metal. This transfer of electrons creates what we know as rust in the higher-potential metal.
How to Prevent Corrosion
The good news is that we have the knowledge and technology to prevent corrosion, or at least limit its effects. Initial steps include insulation, coatings or paint to seal fasteners that are a different metal than the material they will be installed into. These dielectric coatings can help limit the occurrence corrosion. It is vital to strategically select the materials used in manufacturing and construction. The flow of electricity and the rate of corrosion are greater when flowing from a smaller object to a larger area. You wouldn’t want to use steel zinc plated screws to fasten together higher grade stainless materials. If you did, the large gap in electric potential would quickly degrade the steel zinc plated screws, which would then weaken the structure or type of construction built.
Different Types of Corrosion
Corrosion can occur in different places and present itself in different appearances, depending on the environment. Here’s a look at different types of corrosion to keep an eye out for:
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Galvanic Corrosion: This is the type of corrosion mentioned previously. It occurs when two different types of metal are joined, and electricity flows from one to the other, leaving behind corrosion.
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Uniform Corrosion: This occurs across the entire surface area of a fastener when it’s not properly coated or plated.
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Crevice Corrosion: Crevice corrosion appears in small gaps and openings in your fasteners that are not ventilated as they should be.
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Pitting Corrosion: Pitting corrosion is when tiny holes appear in a fastener, so small that they are difficult to detect. Pitting corrosion is most likely to occur in noble materials like nickel and chromium, but can be prevented by keeping surfaces clean.
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Intergranular Corrosion: Ever wonder why welders quickly plunge parts into water to cool them down? This is done to prevent intergranular corrosion, which occurs in stainless steel when it reaches extremely high temperatures. Reheating a welded component during multi-pass welding is a common cause of this problem.