When you intend to use fasteners such as alloy 20 carriage bolts en masse, it’s normally important to understand how corrosion is going to affect them. Adopting an overly simplistic view of corrosion might seem simple enough, but the problem is that using this to make decisions on how to prevent it might not work. […]

types of fastener corrosion
When you intend to use fasteners such as alloy 20 carriage bolts en masse, it’s normally important to understand how corrosion is going to affect them. Adopting an overly simplistic view of corrosion might seem simple enough, but the problem is that using this to make decisions on how to prevent it might not work. This is primarily due to the fact that there are many types of corrosion that can occur, and the steps you need to prevent this from happening might vary depending on the type you expect.

A better way to prevent corrosion, therefore, would be to examine the circumstances under which you will use the fasteners. You can then figure out the type of corrosion that is most likely to occur, and then put in place measures to prevent this. However, this will only work if you understand the different types of corrosion in the first place. Some of the most common include:
Uniform corrosion
This is the most prevalent type of corrosion. It normally turns the fastener red, and is distributed along the entire length of the fastener as the name might suggest. This pattern of corrosion can be particularly destructive. Since it affects the entire fastener, it could cause complications such as making it more difficult to undo the fastener. One of the ways of preventing this would be by using fasteners made of a material that is not corrosive, such as Inconel hex tap bolts. This type of corrosion can also be prevented by preventing water from accumulating around a fastener.

 
Crevice corrosion
This type of corrosion occurs within small cracks and crevices in a fastener. Such spaces tend to retain moisture, which will then react with the metal leading to corrosion. The risk of crevice corrosion increases with the number of joint faces the fastener has. The best way of preventing this type of damage is by minimizing the use of washers. You will also need to ensure that all joint surfaces are as smooth as possible to eliminate any potential space between them.
Galvanic corrosion
This occurs when two different metals are placed in contact with each other in the presence of moisture. The resulting chemical reaction leads to damage to one or both metals. Strategies you can use to prevent it include using plastic washers to fasten the joints. You should also avoid using copper, zinc or stainless steel fasteners if they are going to be in contact with a surface of a different type of metal.
Stress corrosion cracking
This results when the corrosion occurs in areas where the material is under tension. As a result, the weakening caused by the corrosion leads to cracking. Periodic inspection of the critical parts that are fastened together is necessary to ensure that such cracking does not go undetected.
The type of corrosion that is likely to occur will be determined by the circumstances under which you use the fasteners. Keeping this in mind will make it easier for you to come up with better anti-corrosion measures.

About the Author

Larry Melone
By Larry Melone
President

Started my career in the fastener world in 1969 at, Parker Kalon Corp. a NJ based screw manufacturer located in Clifton, NJ working in inventory control, scheduling secondary production and concluding there in purchasing. In 1971 I accepted a sales position at Star Stainless Screw Co., Totowa, NJ working in inside sales and later as an outside salesman, having a successful career at Star I had the desire with a friend to start our own fastener distribution company in 1980 named: Divspec, Kenilworth, NJ. This was a successful adventure but ended in 1985 with me starting Melfast in August 1985 and have stayed competitive and successful to date. Melfast serves the OEM market with approximately 400 accounts nationally.

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