What is salt corrosion?

It's the sixth most abundant element on Earth and is a key component to health bodily functions. In its purely chemical form, however, it's also among the most destructive elements on Earth. What is it? Sodium chloride, more commonly known as salt. This destruction manifests itself as corrosion, on metals, ceramics, steel, stainless steel and several other surface materials.

While salt corrosion is virtually impossible to prevent entirely, the more you know about it and its development, the more you can do to delay its growth.

How does salt affect corrosion?
Corrosion occurs when chemical and biological compounds, which are naturally conflicting with one another, combine. Salt is an electrolyte, and is an extremely important one for the human body, affecting muscle function, fluid balance and cellular reactions.

But when salt attaches to metal and similar surfaces, it strips away electrons that protect metals. Any movement of electrons is called oxidation, the key ingredient of corrosion. Without oxidation, corrosion doesn't occur.

"Salt is among the top 10 most abundant elements on Earth."

Given that salt is among the top 10 most abundant elements on Earth, you can understand why corrosion is so commonplace. It's found in the ocean, spread on road surfaces (on average, over 48 billion pounds of it each year, according to reporting from USA Today) in the winter months to enhance tire traction, as well as in the Earth's soil and in the air.

Does salt corrode steel?
Metal workers know that while steel is often mischaracterized as a metal, it's actually an alloy of iron and a number of other smaller carbons. As such, some may wonder whether salt corrodes steel.

Since iron is a metal and steel is an alloy of iron, yes, steel can and does corrode. The rate at which corrosion takes place can vary significantly, depending on the surface, its environment and the type of steel. For example, stainless steel is used in many industries and is valued for its resistance to corrosion. But if it's continuously exposed to liquids with a high saline concentration – such as seawater, as opposed to fresh water – then stainless steel will corrode. How quickly it develops depends on a number of different factors, such as how much chromium the stainless steel contains, oxygen in the air and the wetness of the environment. Chromium almost serves as a protective layer when present in stainless steel. It doesn't prevent corrosion from occurring, but when it combines with oxygen, it acts as a barrier to ongoing deterioration.

Does aluminum corrode in salt air?
One of the more resistant elements to salt corrosion is aluminum, the most abundant element in the Earth's crust. Aluminum is completely free of iron, making it impossible for it to rust, since rusting as a process is exclusive to steel and iron. It's somewhat similar to chromium in that once oxidation occurs in the presence of water, the thin film that forms serves as a deterrent to ongoing corrosion. 

"The combination of wetness, oxygen and aluminum surfaces creates aluminum oxidation."

Aluminum reacts similarly in salt-saturated air. The combination of wetness, oxygen and aluminum surfaces creates aluminum oxidation, which is a form of corrosion. As noted by Aluminum Handrail Direct, aluminum oxide produces a white, chalky substance and creates pitting. As noted by NACE International, pitting corrosion is a localized form of corrosion that can bore holes into hard surfaces. Pitting corrosion is considered to be the most dangerous kind because it can affect the structural integrity of surfaces used for weight-bearing purposes.

How can you prevent salt corrosion?
As previously mentioned, it's pretty much  impossible to prevent corrosion entirely, given that the environment is composed of chemical compounds and elements that can't be altered.

However, there are strategies you can implement that will slow its development. Chief among them is leveraging coatings, such as paints, powders like epoxy and nylon or certain varieties of plastics. These literally act as a defensive barrier to metal and iron-based surfaces and make it harder for water and salt to penetrate them.

Another strategy is something called hot-dip galvanization. As its description suggests, this method is used on steel products and surfaces and involves dipping them into molten zinc, which is liquefied. Once allowed to cool, the iron that is a natural ingredient of zinc forms a protective layer, deterring corrosion on an ongoing basis.

Whether you're looking for coating or corrosion testing services, turn to Auto Technology. We are the top producer of corrosion test equipment in the United States and are fully equipped to meet your needs.