With all the talk about sustainability and renewable resources, one thing that gets overlooked is the assets themselves. Not as in what is a wind turbine, geothermal, or a solar panel or a nuclear power plant or even tidal power. It is the protection of those particular assets as they pertain to functioning in the setting that they are used. In all cases, the assets are exposed to the elements as is an industrial coating, which is exterior and generally corrosive. In addition, they may have some unique performance properties that are required.
Renewable energy sources (i.e., biomass, geothermal, hydropower, solar, wind) accounted for approximately 20% of net domestic electrical generation during 2019, according. A year earlier, renewables’ share was 18%.
30 years ago it wouldn’t have been possible to consider powder or thermal coatings for painting applications. And in many cases, aftermarket coatings still continues to be liquid. But the efficiency of powder and the performance of it and thermal are making it difficult to ignore them as competition for the liquid market. In addition, several paint manufacturers claim that they are able to get the same performance with two coats versus three coats. Ultimately, paint companies desire one coat. With costs of painting an asset split nominally 70 to 90% in labor and the remainder in the paint itself, obviously fewer coats are desired, especially in offshore applications such as wind turbines, tidal power, etc.
Different types of industrial coatings have dissimilar chemical and physical properties —corrosion resistance, performance when exposed to UV, etc.— but no coating provides all the protection a structure needs. That’s why assets are coated with multiple coating types to form a total protective coating system, or a system providing all the chemical, physical and galvanic protection required to protect the substrate from its environment.
Understanding the most common generic coating types —and how they work together to form a total protective coating system— allows designers and owners to choose the system best-suited for their prevailing service location
Solar panel coatings serve a vital but sometimes ignored purpose. Solar panels attract the sun to generate renewable energy for the connected property. These solar panels endure improbable amounts of natural erosion from water and wind, as well as ultraviolet degradation. With solar panel coating, you will see a large reduction in thermal shock in cases that solar panels overheat, as well as prevent water and ultraviolet degradation. As a result, you can enjoy the longevity and stability of your solar panels and their energy.
In wind turbine coatings there are three environments that are of note. On land, you mostly have to worry about bugs and the acidity of them. In the extreme northern climates, there is the formation of ice and ice accretion, and offshore as well. No one really produces multiple coatings for different environments, so you would look at the most extreme environment. Off shore coatings are serviced by a multitude of coatings that have a long history of employment. Companies such as International Paint, PPG, Sherwin-Williams, etc. have been supplying industrial coatings to the industrial market for a long time. Therefore, you have the longevity of knowing that they will last, but the specific needs of the different coatings in different environments.
Epoxy coatings are typically comprised of an epoxy base and a curing agent. A wide variety of coating properties can be achieved by manipulating either of these components: Epoxy polyamide coatings offer great moisture resistance, epoxy mastic coatings offer exceptional film thickness and phenolic epoxy coatings offer good chemical resistance. And due to this versatility, you’ll find epoxies used as a primer, intermediate coat or even a topcoat depending on the needs of the application. Epoxies are appropriate for use in industrial marine applications and onshore uses such as wind turbines and solar panel superstructures.
The most notable limitation of the epoxy family of coatings is their poor performance in UV — which is why epoxies are most often used in interior or submerged industrial applications. You might find epoxies protecting steel inside a nuclear power plant. Advantages of epoxies include abrasion resistance, chemical resistance, good performance in non-UV situations, film build and flexibility of formulation. The disadvantages include chalking with exposure to UV light and poor flexibility.
Polyurethane coatings are extensively used —often as a topcoat— in applications where durability and abrasion resistance are key considerations. Polyurethanes generally fall into two categories: Aliphatic and aromatic. Aliphatic polyurethanes provide excellent color retention and perform well in sunlight, making them well-suited to exterior environments. Aromatic polyurethanes, on the other hand, better lend themselves to submerged environments — they’ll chalk and weather when exposed to sunlight. Aromatics are used mostly in foams.
Most often, polyurethanes are chosen as the topcoat of a total protective coating system. For example, polyurethane might be applied as a topcoat above a zinc-rich primer and epoxy intermediate coat on a highway bridge. Or even as a topcoat on the concrete walls and floors of a nuclear power plant. Other possible applications include locks and dams. The advantages of these coatings are abrasion resistance, high gloss and color retention, low VOC possible and UV resistance with aliphatic chemistries. Disadvantages include isocyanate inclusion (-NCO).
Polysiloxane coating systems provide excellent abrasion and weather resistance, as well as appearance retention benefits — but fail to provide the flexibility and corrosion resistance industrial environments require. Combining the benefits of epoxies with polysiloxanes —into epoxy polysiloxane coatings— provides industry-leading abrasion, weather, UV, chemical and corrosion resistance. Although epoxy polysiloxane hybrid coatings cost more than epoxies and polyurethanes, they can be applied more quickly and last longer — providing better long-term value for many applications. Advantages include excellent resistance to abrasion and weather, two-coat application, excellent color and gloss retention, and the cost reduction of applying two coats versus three.
As a generic coating type, zinc-rich coatings refer to organic (i.e., containing epoxy or polyurethane binders) or inorganic (i.e., containing silicate binders) coatings with high loadings of zinc dust. The zinc provides galvanic protection of the steel surface, meaning that it will corrode instead of the steel beneath it. As the zinc-rich coating corrodes it forms a barrier between the steel and its environment
Inorganic zinc-rich coatings tend to provide better galvanic protection and abrasion resistance than do organic zinc-rich coatings but require a much higher level of surface preparation. Both variations perform well as a primer in a multi-coat system, as they adhere well to the steel surface.
Zinc-rich primers will often be applied as part of a two-coat (zinc-rich primer, polysiloxane topcoat) or three-coat (zinc-rich primer, epoxy intermediate coat, polyurethane topcoat) system. You’ll find zinc used in a wide range of highly corrosive environments, including bridges, coal plants and the topside of ships. The advantages are that it provides both galvanic and barrier protection to steel, abrasion resistance and highly durable. The disadvantages include a very clean surface prior to application to ensure adherence, low resistivity to acids and alkali and almost all the coatings have to be top coated.
Industrial coating systems provide steel structures with long-term protection against their environment. To do this, the coating system must be well-equipped to handle the environmental conditions of its environment, whether that’s heat, sunlight, contact with chemicals or constant abrasion.
Although it is impossible to completely eliminate all corrosion, the organization of suitable corrosion control strategies is promising for significantly mitigating its impact. The need for protection and the task of ensuring its adequacy has exponentially grown, especially with high-temperature environments, such as power plants and biomass use are involved. This has necessitated the need for improved corrosion protection, and it is clear that further significant advancements can only be achieved through the use of advanced protective coatings as the first line of corrosion attack.
Although most of the discussion has involved steel structures and corrosion, let’s circle back to solar panels. The panels themselves are typically coated on the surface with a very thin fluoropolymer. This is to protect the elements from UV and also give it some hydrophobicity with water.
Tidal power was not discussed as the requirements are the same for submerged superstructures as they are for FPSO. There is a requirement for abrasion resistance as well as corrosion.
Nuclear power is considered a renewable resource and has many requirements relating to isotopic radiation. Most of the utility is governed by the NREL and coatings are typically approved for use and on a Qualified Products List for use. For more information on coatings and types of coatings used for these applications, refer to UL prospector recommended formulas.
Resources:
https://worldofrenewables.com/events/
https://www.ulprospector.com/knowledge/9714/pc-bio-based-resins/# Wally Kesler
https://www.ulprospector.com/knowledge/7354/pc-chemistry-of-resins-and-hardeners/ Ron Lewarchik
https://www.ulprospector.com/knowledge/3281/pc-industrial-coatings-resins-polyurethanes-part-2/ Marc Hirsch
https://www.ulprospector.com/knowledge/2343/pc-bio-based-resins-for-coatings/ Ron Lewarchik
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