Protective coatings are performance-driven systems that extend the useful service life of many of the facilities that are key to daily living and economic growth—power generation, oil and gas production, water treatment facilities, refinery and petrochemical plants, and commercial buildings and infrastructure.
But what makes protective coatings able to do their job? To answer that question requires a deeper look into what a typical protective coatings system looks like.
It’s important to realize that protective coatings must be viewed as a total system, starting with the type of environment in which they will be applied and used; what they will protect against; and the substrate being protected. After those factors are determined, the types of coatings to be used can be considered. Anticorrosive performance is most often associated with protective coatings, but weathering, thermal, hydrolysis and chemical resistance are sometimes the key drivers for required performance and the tests that coating systems must pass.
To understand the service environment better, here are four primary questions to ask:
- Will the coating be for interior or exterior service? This dictates the need for weathering resistance.
- How corrosive or chemically aggressive is the environment and will it be incidental or continuous exposure? This will dictate the need for corrosion or chemical resistance.
- What temperatures will the coating face? Ambient is great, but an extremely hot or cold environment will raise challenges in application, adhesion and longevity.
- Will the article be submerged in any way? This will help define the required hydrolysis resistance properties of the coating.
After considering the service environment, knowing the substrate is critical. The obvious first question is what is being protected—metal, concrete or plastic? Protecting metal typically garners the most attention, but we know from market studies that protecting concrete and other systems can be as much as 40 percent of the market for these coatings.
Using a metal substrate as an example, the next considerations are the type of metal (hot-rolled steel, cold-rolled steel, aluminum or galvanized, etc.) and if a pretreatment was employed (shot-blasting, phosphatizing, zirconium silane pretreatments, etc.).
The Application System
After understanding the substrate, it is then necessary to understand the application system. Most protective coatings are field applied by human operators. This is especially true in renovation or restoration projects (i.e., maintenance). This makes understanding how a coating’s application and subsequent curing will be impacted by changes in temperature and humidity, as well as the impact of “less-than-consistent” film coverage due to operator tendencies or error.
That said, not all protective coatings are field applied. In many instances, especially in new projects or first-time installations, a piece of equipment will be shop-primed in a factory setting where application environment and operator tendencies are more controlled.
This brings us finally to the coating system itself. The severity of the service environment will drive three main decisions:
- The number of coatings components
- The number of coats
- Coating chemistry complexity
In general, as the service environment goes from less demanding to more demanding and as the risk associated with a potential coating failure goes from low to high, the number of coating types used in the total system goes up, the number of coats and overall thickness of the coating system is increased, and the types of coatings used gets more complex and costly
Number of Coating Components
In less severe environments, a single type of coating applied directly to the substrate where the coating is acting both as the primer and top coat is sufficient. In more aggressive environments, one type of coating may be used as the primer, another as the intermediate coat and even a third as the top coat to offer the maximum protection.
Number of Coats and Coating Thickness
Again, as the severity of the environment increases, the number of coats applied and the film thickness of each layer goes up. The single biggest cost of a protective coating system is the application labor, so trying to manage this to a minimum is critical. However, end users also want to manage coatings inventories. If they can use the same coating for different environments simply by adding more layers or applying it thicker, they will often consider it.
As severity of service increases, so does the requirement for more sophisticated technologies to resist degradation. This is also true where a specific concern, like high-temperature service, may be required. In less severe environments, tried and true coatings like alkyds and acrylics are sufficient. As severe environment requirements increase, the technology moves into Zinc-rich primers, epoxies and polyurethanes, and even inorganic coatings based on silanes, silicones or ethyl silicates.
If this seems complicated, it certainly can be. There are many factors to consider in understanding the breadth of coatings choices for a good protective coating system. But there is help. At Lubrizol, we can work directly with protective coatings formulators to ensure product offerings are aligned to meet specific formulation needs and the needs of end-use customers.
Contact us for information about Lubrizol’s innovations in resins, dispersants and specialty additives that contribute to corrosion protection, aesthetic appeal and toughness for the protective coatings industry.