Corrosion Basics

If you live on planet Earth, you have seen or experienced the effects of corrosion. Rusty cars, corroded bolts, and swollen rebar are all telltale signs of this global, never-ending challenge. Rust never sleeps, and corrosion is possible wherever oxygen and metal exist together, causing untold problems every day.

What are the consequences? According to the NACE IMPACT study, the estimated direct cost of corrosion is 2.5 trillion USD (3.275 trillion USD in 2025, adjusted for inflation in 2025). This equals 3.4% of the global GDP (2013). With corrosion control offering a potential savings of 15-35% on corrosion costs, the value of corrosion mitigation is obvious and proactive prevention is pivotal.

In order to effectively fight corrosion, it is important to understand the enemy, its weak points, and the allies that you can enlist to help you.

In simple terms, corrosion is metal going back to nature. To make iron and steel, workers must mine iron ore (which basically contains rust in its natural form) and heat it to extreme temperatures. This purifies the metal and gives it the strength and other properties needed to be used for nails, car parts, bridges, and more. Unfortunately, as metal is exposed to air, water, and salt, it is under a constant pull to return to its natural state. Sooner or later this results in rust that starts to “eat” away at the metal until it loses strength and function.

The simplest way to stop or slow down corrosion is to break the “corrosion triangle.” As mentioned above, corrosion often requires three components—metal, oxygen, and an electrolyte—to start. Taking away any of those parts can break the corrosion triangle. Remove oxygen and you break the triangle. Remove moisture and you break the triangle. Remove metal itself and you break the triangle. There are many ways to do so, including the use of desiccants, barrier coatings, rust preventatives, corrosion inhibitors, rust preventatives, or non- metallics. The choice of a corrosion prevention method will depend on a variety of factors including environment, duration, budget, ease of application, and other concerns.

Corrosion is a problem because it usually ends in metal deterioration. One of the most iconic examples of corrosion is a car with large rusty orangish-brown patches or holes where the rust has broken through. However, corrosion appears almost anywhere metal is used—on metal structures, fences, tools, fasteners, rebar, and industrial equipment. Corrosion compromises the integrity of the metal—“eating” away at it until it is weak or contains holes and looks bad. The result can be damaged goods, equipment failures, dangerous leaks, structural collapses, extra repairs, and downtime. For some metals such as copper and aluminum, oxidation creates its own protective layer that slows down corrosion on the metal. But in most cases, one spot of corrosion leads to another, starting a vicious cycle that reduces the value of the metal.

Rust refers to the oxidation of ferrous metals such as steel and iron and usually presents a familiar orangish-brown color. Corrosion is the broader term used for oxidation of ferrous and non-ferrous metals (e.g., yellow metals like copper or bronze) and may appear in the well-known patina color of oxidized copper as seen on the Statue of Liberty (this is one case where oxidation works to the metal’s advantage by producing a protective layer).

Testing can be an important part of choosing the right corrosion protection strategy for your metal parts, equipment, or structures. Tests such as ASTM B117 (salt fog chamber testing) and ASTM D1748 (humidity chamber testing) expose protective coatings to aggressive conditions that allow you to compare the performance of different rust preventatives or corrosion inhibiting paints. ASTM G180 testing allows chemical formulators or specifying engineers to screen and compare different chemistries for potential use as corrosion inhibiting concrete admixtures. ASTM D4627 can be used to determine the ideal concentration of rust preventative to balance cost and effectiveness for a specific application.

Laboratory testing can also be used to confirm the effectiveness of your current corrosion protection strategy or troubleshoot failures. For example, a manufacturer experiencing corrosion on new metal parts being shipped to the customer in VCI (vapor corrosion inhibitor) bags can send samples of the parts and packaging to Cortec Laboratories® for testing to see if the packaging contains active corrosion protection or is deficient. The results can provide vital information to help you improve your corrosion prevention process and ensure quality control.