Abrasion resistance often takes a back seat to corrosion resistance in the coatings selection process. But because abrasions erode a protective coating system over time —resulting in premature corrosion and failure of assets—designers and owners must consider abrasion resistance when choosing coatings.
The role abrasion resistance plays in protecting your assets
The ultimate goal of any coating system is to protect your asset. And as the leading cause of asset failure —costing the U.S. nearly $300 billion each year— corrosion is naturally the primary concern when choosing a coating system. But in order control corrosion, the coating system must be able to withstand the stresses of its environment without suffering premature failure itself.
Proper surface preparation and application contribute to the longevity of a coating system, but the system must also be able to stand up to in-service impact and abrasion. Otherwise, the coating will crack (as with forceful impact) or slowly wear away (as with a constant flow of water or sand), exposing your substrate to water, salt and, ultimately, corrosion. Typically, failure due to abrasion manifests itself as corrosion affecting a generalized area where there’s a loss of coating protection.
Here are a couple examples of abrasion-related corrosion failures we’ve seen in the field:
- Impacts against coating
Think about the deck of a ship. Heavy foot traffic, dropped equipment and other impacts will take their toll on your coating system. Over time, this can crack and wear away the coating, exposing unprotected steel to the elements.
- Slow degradation of coating
Applications where wind-blown sand and water turbulence are common occurrences (think coastal bridges or water treatment plants) are prone to erosion of the coating. If the coating system erodes away to the point that steel is exposed, corrosion will follow.
- Other extenuating circumstances
Occasionally, we see assets that have been hit by a single, high-velocity impact — such as being hit by an 18-wheeler. While the steel surface might look good initially, except for a couple scratches and scuffs, within a couple weeks corrosion will emerge at the spot of the impact because the coating has been compromised.
We’ve found that abrasion resistance is an afterthought for many owners. And that’s a big reason why abrasion-related corrosion of assets is a core problem on most of the structures we repair and maintain.
Modifying your coating selection process to account for abrasion resistance
Protective coating systems are selected based on service environment, desired lifespan of the asset, longevity of the coating system, ease of maintenance and budget. And while abrasion-resistant coatings better withstand heavy-duty environments, extend the service life of your asset and last longer — they tend to be significantly more expensive, both in material and labor costs.
Still, for some applications the benefits justify the cost difference. For instance, a department of transportation might choose a more premium coating for a major metropolitan bridge so they don’t have to shut that bridge down again to do a full replacement of the ramps for 30 years, if not more. Locks and dams are also very expensive to shut down for a coating replacement, making them good candidates for more expensive abrasion-resistant coatings.
Not every application requires a high level of abrasion resistance — and for many applications, it’s cost-prohibitive. But it’s important for designers and owners to evaluate their application’s risk and choose their coating system accordingly. When in doubt about whether or not your application would benefit from abrasion resistance, it’s important to consult an SSPC-certified coatings contractor.
What properties make a coating system abrasion resistant?
Abrasion resistance refers to a coating’s ability to resist wear due to erosion or impact, allowing for the system to continue to provide comprehensive protection to the substrate. Generally speaking, coatings that are hard, flexible, smooth and thick tend to be the best at preventing coating wear.
Hardness and flexibility work together. If a coating isn’t hard enough, an impact may fracture the system down to the substrate. But the harder you make a coating, the more brittle it becomes, so hardness must be balanced with flexibility. The smoothness of a system is important, as abrasion is caused by two rough surfaces coming into contact. The rougher the surface of the coating, the more vulnerable it is to abrasion. And the thicker the overall coating system, the more wear is required to expose the substrate to its environment. Together, these four properties make a coating system more resistant to impact and erosion.
Several abrasion-resistant coating types to consider
It’s impossible to make a definitive coating recommendation without knowing the budget and project-specific parameters of your project, but we can walk you through some coating types known for their abrasion-resistant properties.
Polyurethanes are a good, cost-effective option for abrasion resistance. When applied correctly, they’re relatively smooth, allowing would-be abrasive materials to easily slide off the surface. But they’re also thinner than a lot of other coating types, meaning they’re more prone to wear.
Epoxy coatings are known for their slick and durable film properties, making them good at resisting abrasion. When exposed to UV, however, epoxies will chalk and abrade more easily, so they’re best in applications that aren’t exposed to sunlight.
Polysiloxane coatings tend to be a step above both epoxies and polyurethanes, but are as much as two to three times as expensive. These coatings provide excellent UV protection, abrasion resistance and perform better overall. Because of the added value polysiloxanes provide, the United States Coast Guard has been using the system for almost 20 years, according to Good Painting Practice from the Society for Protective Coatings (SSPC).
Of course, there are dozens of other generic coating types that also provide good abrasion resistance. Metallizing, for example, is good for abrasion resistance but comes with an astronomical cost increase and is much more time-intensive to apply.
The most important thing to remember when choosing an abrasion-resistant coating system for your application is to know the parameters of your application. Otherwise, you run the risk of over (or under) designing your coating system, which can result in unnecessary expense or asset failure. Before selecting a coating, system, talk to us. We’ll help determine the best coating type for your project, while keeping cost to a minimum.