Corrosion is one of the most common causes of structural damage. Corrosion often leads to reduced usefulness of the affected structure and, ultimately, brings repairs and operational costs to the facility.
Corrosion commonly affects metal or steel surfaces. When corrosion protection coatings fail for these substrates, corrosion comes in the form of a nearly-undetectable chemical reaction attacking the surface. Eventually, corrosion will lead to the loss of surface integrity, and will be visible as stains, discolorations or irregularities in the surface.
Pitting corrosion, in particular, penetrates deeply in certain surface locations, creating irregular surface profiles and crevices. Another type of corrosion is due to microbiological organisms thriving in certain environmental conditions, such as areas constantly exposed to humidity and moisture, and where certain elements support the growth of microorganisms. They bring widespread damage and usually involve major repairs and clean up, and even then the microorganisms may not be completely eradicated.
Barrier Coatings for Effective Corrosion Control
One type of effective corrosion protection coatings are commonly known as barrier coatings. These coatings act as protective film, shielding the surface from any foreign elements that can trigger corrosive chemical reaction. Most barrier coatings are oil- or solvent-based and work to keep out water and other elements from reacting with the metal surface. Recently, water-based corrosion protection coatings have been developed as a cleaner and more environment-friendly alternative. But since water-based barrier coatings only work to inhibit metal oxidation, solvent- and oil-based coatings still have a wider range of applications.
Barrier coatings commonly applied to metal structures are heavy-duty corrosion protection coatings that can be installed with minimal surface preparation. While surface cleaning is still recommended prior to application, this tough corrosion protection coatings can be applied even to rusty surfaces, and can last for many years. Protective films differ from product to product, and may either be soft, hard, transparent or colored. The application method and the removal of these barrier coatings also vary. It is best to check the manufacturer’s data sheet (MDS) for the correct application methods to use.
Sacrificial Coatings for Effective Corrosion Control
Another form of corrosion protection coatings are sacrificial coatings. These coatings are so-called because they uniquely contain elements such as zinc, iron or manganese, which prevents corrosion through sacrificial oxidation. Instead of corrosive elements reacting with the surface itself, these sacrificial elements are the ones taking part in chemical oxidation, leaving the surface corrosion free.
Variations of sacrificial corrosion protection coatings contain inorganic phosphates that render the metal surface indifferent to any chemical reactions, thereby inhibiting corrosion.
An example of corrosion protection coatings application that are sacrificial in nature are aluminum or zinc thermal sprays. When molten sacrificial zinc materials are sprayed onto the surface, they adhere layer by layer onto the substrate to form a porous coating system. The sacrificial zinc lay within the substrate, ready to oxidize when coming into contact with corrosive agents.
Some Application Considerations
For successful installation of effective corrosion protection coatings, there are several factors that must be considered. The most important is the material composition of the surface to be protected, because different materials react with corrosion in different ways. Another is the degree of protection required by the substrate, or the desired length of time that the protective coating is effective. Environmental factors, health and safety requirements, are also considered. These, and many other factors, will require specific solutions to address them. There is no one solution that works for all conditions.