Save your assets: Corrosion prevention based on environment
Save your assets: Corrosion prevention based on environment
Corrosion is a scourge of industry and infrastructure.
It totals billions of dollars in damages every year throughout the U.S. economy and places at risk our most important public and private assets such as bridges, tunnels and pipelines, according to NACE International.
There are many causes and solutions, but it is important to know which line of defense is best for your assets and the environment in which they are located. If done right, NACE International estimated that the country could save 25-30% of our annual corrosion costs through improved management practices.
This article explores common types of corrosion and how it places assets at risk. We then dive into some of the most effective preventative measures based on the conditions to which assets are exposed.
Common Types of Corrosion
Corrosion is the natural degradation of a metal surface when exposed to the atmosphere. It occurs when iron contacts oxygen and moisture, causing rust to form, which slowly wears the metal away.
Generalized corrosion
There are two broad categories of corrosion: generalized and localized. Generalized corrosion attacks the entire surface area of an asset, while localized corrosion is limited to certain areas of a particular asset.
Generalized corrosion—also known as general attack or uniform corrosion—appears over the surface, causing relatively uniform thinning of the material. This often occurs when protective coating systems breakdown.
It is predictable, treatable and fairly easy to detect, so it usually only causes minor issues. However, it can lead to more serious types of corrosion if permitted to progress.
Localized corrosion
Localized corrosion can be more difficult to detect and is more likely to occur even with protective measures. According to NACE, the most common localized corrosion types are:
- Pitting corrosion, which is caused by localized failures in a coating system. Small holes form at points of failure and expand if not addressed. Pitting can cause serious degradation. It is often difficult to spot and can occur on assets that owners consider adequately protected.
- Crevice corrosion, which is sometimes called contact corrosion, occurs in micro-spaces between touching materials. This could be a metal-on-metal or metal against non-metal point of contact but usually occurs around bolts, gaskets, washers or other fasteners.
- Filiform corrosion, which occurs when moisture penetrates the small gap between a coating and substrate, usually at a natural edge on the substrate or at a defect in the coating system. It’s often distinguishable by bubbles forming beneath the coating.
- Pack rust, which is generally caused when steel components develop an exposed crevice. It is common in bridges where rust builds up between two meeting surfaces.
- Galvanic corrosion, which is damage induced by different materials electrically contacted under water, resulting in rapid deterioration of the surface metal. This corrosion is generally prevented through prior design measures.
- Lamellar corrosion, which creates a layered appearance in the metal by progressing along planes parallel to the surface and is also referred to as layered corrosion or exfoliation. It most commonly affects extruded aluminum alloys. It is often prevented through heat treatment control rather than protective coatings.
Corrosion prevention with resistant coatings
Selecting the appropriate corrosion prevention methods depends on the conditions your assets endure. Environmental factors such as acid rain, humidity, chemical salts, oxygen and high temperatures can affect the pace of corrosion.
Corrosion resistant coatings are among the most reliable and cost-effective prevention methods for most forms of corrosion.
Here’s a top-level breakdown of the strategies most of our industrial coating products use to battle corrosion:
Sacrificial coatings
Sacrificial coatings tend to make excellent primers. They’re typically an extremely thin layer of metal, such as zinc or nickel applied directly to the asset.
Zinc primers are excellent examples of sacrificial coatings. They corrode preferentially to the asset at a slower rate than many other sacrificial coatings, leading to longer intervals before a recoat is necessary.
Sacrificial primers can effectively fight corrosion, but you’ll need to pair it with a topcoat barrier system.
Barrier coatings
Barrier coatings probably come to mind when most people think of industrial coatings. They keep oxygen and moisture from a substrate and protect it from harmful chemicals like soluble salts.
According to NACE, the following are the most important properties for a barrier coating:
- Protects against the surrounding chemical environment
- Resists moisture
- Resists vibration and minor impacts
- Exhibits strong adhesion even in moist conditions
- Exhibits strong wetting properties for a smooth, even film build
Different environments stress barrier coatings in different ways. In areas experiencing prolonged exposure to sunlight, a high UV-resistant coating will be a priority. In marine environments, a coating’s ability to protect against the corrosive effects of soluble salts will be especially important. Chemical resistance will be necessary in chemical factories and other processing facilities that house harsh and reactive materials.
That’s why we offer on-site surveys as part of our corrosion services so you know exactly which system is best for your asset’s environment.
A project’s specification sheet should address any special circumstances surrounding an asset, including any extreme pressures it will encounter. A NACE-certified coatings inspector can help determine how to address these issues, such as if a highly corrosive environment will require a urethane topcoat rather than an alkyd.
It’s also important to consider where a generic coating comes from. Many manufacturers cut corners to produce what many qualify as an “epoxy primer” or a “polyurethane finish”. Inferior resins along with cheap fillers and extenders can yield a less expensive product at the expense of performance.
Having your asset examined by a coatings specialist beforehand will also help with that all-important second step in keeping corrosion at bay: a well thought out maintenance plan.
Coatings maintenance
The worst time to discover your corrosion prevention system hasn’t been maintained is when an asset fails. Corrosion prevention must be a regular process. Elements degrade. Chemicals erode. Moisture seeps in. But, with a coatings maintenance plan in place, regular wear over time needn’t be a significant setback.
A full-scale failure as a result of damage caused by corrosion could be catastrophic. Leaking chemical pipelines and unsound structural steel threaten lives as well as financial stability. We’ve seen how much corrosion costs the economy, and regular coating’s maintenance is one of the best fundamental strategies we have for reducing those expenditures.
A spot coating as a part of a regular coatings maintenance plan can prevent the spread of localized corrosion and delay a full-blown recoat for years.
Reach out to get specific recommendations
Contact US Coatings for help with your corrosion prevention needs. You can request an on-site survey for asset evaluations and specification consulting to be certain that you have the right coating for your assets based on the conditions and pressures of the environment.
As you’ve learned, there are many causes and forms of corrosion that influence the best prevention strategies. Our NACE-certified experts want to hear about your project and its exact requirements. We can also help with placing product orders or simply talk about your coatings and lining needs.
