Barrier coating or alloy for corrosion protection? Tony Collins explores the best options for protecting steel from corrosion
Corrosion is an ever-present threat for any industry working with steel. The most popular form of corrosion protection is barrier coatings, which involves covering steel surfaces with a layer of protective paint. For many, barrier coatings are more than the industry standard: they’re the only option. However, there’s another form of corrosion protection that offers stronger and longer-lasting protection: alloy.
Alloys chemically bond to steel surfaces rather than simply cover them. So why aren’t more people turning to alloys for protection? Are they really that much better than barrier coatings? Let’s compare the two and see how alloys deliver a level of corrosion protection many people don’t even realise is available.
The appeal of barrier coatings
People tend to develop habits and repeat them for no other reason than routine. In that way, businesses are just like people and will often remain with products and processes that are outdated or unproductive. For most asset owners and managers, traditional barrier coatings are the only steel-protection method that they are familiar with. For some, this is the only method they’ve ever heard of.
This is no coincidence. The barrier coatings industry has played a role in keeping their methods top-of-mind with consumers. For the past 50 years, the industry has spent hundreds of millions of dollars advertising that their coatings are the only option.
This isn’t to say barrier coatings aren’t helpful. They provide years of protection and meet the expectations that paint companies and customers have come to accept. Let’s take a closer look to see the science behind barrier coatings.
Barrier coatings: the pros and cons
Traditional barrier coatings work like a tarp by adding a protective layer over the steel. Just like a tarp bonds to a steel picnic table in your backyard, these coatings mechanically bond to the steel. As long as the paint holds, the steel is protected.
This brings us to a major drawback of barrier coatings. Once chipped or scratched, the barrier coating leaves the steel open to moisture. Moisture leads to the formation of corrosion cells. Corrosion spreads as the moisture and other chemicals transit between the barrier coating and the steel. Instead of serving as a protective tarp, the paint coating now acts like a greenhouse, trapping the moisture underneath. So your steel isn’t only at risk for complete corrosion - it’s guaranteed to corrode.
It’s important to note that barrier paint coatings were never intended as a permanent solution against steel corrosion. Let’s think about today’s cell phones and computers: we replace them every few years with newer models because they weren’t designed to last forever. Paint wears out and needs to be replaced, which results in repeat customers. Whether it’s a business model you agree with or not, paint wear has certainly helped keep the paint coating industry alive for more than a century. Planned obsolescence has made them a fortune.
The alloy solution
Unlike a paint coating that acts as a protective layer, an alloy layer chemically bonds to steel. In fact, it becomes part of the steel. Moisture or oxygen can’t cause corrosion simply because the alloy is part of the steel itself.
So how exactly do alloy solutions work?
Every steel surface has small valleys that aren’t visible to the naked eye. While paint coatings cover over these valleys, an alloy fills these valleys. In other words, the entire surface area of the steel is chemically bonded to the alloy layer.
In the case of chemically bonded phosphate ceramics, a ceramic layer forms over the alloy, protecting the alloy layer and providing a phosphate reservoir. This is important for two reasons. First, if the ceramic layer is damaged it does not affect the alloy underneath. Second, if a deep gouge cuts through both the ceramic and the alloy layer - all the way down to the steel - the ceramic layer supplies the phosphate needed to re-form the alloy layer. The two levels of protection offered by the alloy layer and the ceramic layer make this solution ideal for industrial tanks, pipelines, and other equipment exposed to harsh conditions.
The drawback to alloys
If an alloy is a better solution than layers of paint, why aren’t more companies using alloys? Historically, the main prohibition has been price. Alloying has been prohibitively expensive. Advanced alloys such as Hastelloy can sell for as much as US$30,000 per ton. But while many businesses assume that all alloy solutions are cost prohibitive, in fact there are alloying solutions that are comparable in price to traditional industrial coatings.
In the past, the alloying process could only take place in a factory environment when equipment was first being fabricated. There was no viable, cost-effective method for field alloying. But now, there are solutions that you simply spray on steel, and an alloy layer forms. So assets can be field alloyed. And those steel assets will be immune to corrosion.
There’s no doubt that barrier coatings and alloys are both viable solutions for corrosion protection. Choosing one over the other just because it’s the status quo isn’t a good reason for deciding which solution to embrace. Alloy layer products offer protection for years longer than barrier coatings. Unlike barrier coatings, some alloy solutions don’t contain harmful volatile organic compounds (VOCs) or hazardous air pollutants (HAPs) and have zero flame spread. While barrier coatings are the familiar option, it might be time for a change — you may be surprised at the corrosion protection results of an alloy solution.
Tony Collins is CEO of EonCoat.