Moisture-Cured Urethanes Offer Simplicity and Durability
At petroleum-chemical facilities, recoating steel is a necessary evil — it’s complicated, expensive, and almost always interrupts production. But corrosion is a constant threat to steel pipes, equipment and framework, and neglecting it can lead to shutdowns, lost productivity, and in the worst-case scenarios, catastrophic failures.
Recoating steel at petro-chemical facilities is a challenge, but aluminum-impregnated, moisture-cured urethane coatings can reduce the time and expense, while yielding long-lasting results.
Aluminum-impregnated, moisture-cured urethane coatings, such as U-104 from Coatings for Industry, make coating of steel structures — both new and existing — easier, while providing long-lasting results, potentially extending the coating’s life cycle. Following are reasons that many contractors and maintenance engineers choose these coatings over conventional recoating methods.
Why They Work Better
By their very nature, petroleum-chemical facilities, including refineries, chemical plants, power plants, transfer stations and even offshore oil rigs, are prone to corrosion. They are often located in coastal areas, such as Louisiana and Texas, where high humidity and salty air wreak havoc on all steel surfaces. Also, the chemicals, solvents, and heat/cool cycles found in the plants exacerbate the problem, often speeding the corrosive effects of the environment.
Combatting corrosion is a nonstop endeavor. To prevent unplanned shutdowns and service interruptions, professionals at these facilities will typically plan to recoat portions of the plant on a rotating basis.
For decades, the go-to system has been an epoxy primer and either an epoxy or urethane topcoat. Applying these traditional coatings demands careful, often meticulous preparation of the steel surface, usually by aggregate blasting to rid it of existing rust to meet a specified standard.
By using U-104 or similar highly penetrating primers impregnated with aluminum, maintenance engineers and contractors at petro-chemical facilities can realize several advantages over conventional coatings.
U-104 can be applied directly to a rusted surface, eliminating the need for aggregate blasting and making surface prep faster.
Ease of Use + Speed
Using aluminum-impregnated, moisture-cured urethane coatings all but eliminates the blasting step, because they bond to existing corroded steel. Surfaces can typically be prepared by removing loose scale and rust and assuring the surface is dry by using an agent such as acetone.
Because U-104 doesn’t require a topcoat, that step can also be eliminated, if desired. Two 2-3 mils DFT coats offer about a decade of corrosion protection, even in tough splash-zone environments. A topcoat, included for color, can provide additional long-term protection — typically 5 or more years.
Overall, surface preparation and application of U-104 is a far easier process than other conventional methods and can significantly reduce the amount of production downtime due to recoating.
In any production facility, time is money, and petroleum-chemical plants are no exception. When equipment has to be taken offline for recoating, that amounts to lost productivity and lost revenue.
In addition, the overall cost of surface prep and painting can be significant. The cost of labor to prepare and coat the complex steel surfaces generally found at a petroleum chemical plant can often dwarf the cost of the coating itself.
Because U-104 requires dramatically less surface preparation effort and equipment, the overall cost to apply it may be significantly less. And its effectiveness may extend the recoat lifecycle, potentially making recoatings less frequent.
Microscopic cross-section shows how U-104 penetrates the existing rust, bonds it to the good steel beneath, and essentially halts further corrosion.
Under the conventional recoating method, after blasting a steel surface, moisture in the air begins the oxidation process anew almost immediately, especially in the absence of dehumidification. It works particularly fast in areas of higher humidity, where many petroleum-chemical facilities are located.
Moisture attacking freshly blasted steel sows the seeds for corrosion to occur under the coating just a few years later. Conventional epoxy primers make this worse by trapping moisture.
Products like U-104, with its innovative chemical composition, work by consuming moisture on the surface of the steel, while curing the aluminum flake and bonding it to the surface at the same time.
How They Work
Aluminum-impregnated, moisture-cured rust-preventive coatings like U-104 work by bonding existing corroded surface molecules in the substrate steel to the aluminum flake, forming a nearly impenetrable barrier. Made with a combination of resins and solvents, the coating penetrates into the corrosion that’s on the surface, binding it together, and in the process, scavenging for and consuming existent moisture that may be present in the surface. This helps eliminate one of the key conditions necessary for corrosion to continue.
Moisture-cured, rust-preventive coatings have an added layer of protection from the elements: the aluminum-flake pigment that forms a barrier. In addition to giving the coating its color, the aluminum flakes lie flat on top of each other within the coating. This creates a multi-layer, “labyrinth” barrier that makes it difficult for additional moisture to navigate its way to the steel.
The combination of the moisture curing and the corrosion bonding in this multi-layered barrier coating gives this family of coatings superior corrosion resistance, even if the surface is not prepared by blasting.
When using these coatings, contractors can limit their surface preparation to removing loose rust, scale and debris; this can even be done with hand tools. Then, to a dry surface, simply applying two to three coats of 2-3 mils DFT will give the steel proven, long-term corrosion protection. The result is a barrier coating with a hard, uniform surface that resists the elements and, if desired, can easily accept a variety of topcoats.
Panels treated with U-104 shown after 14,000 hours of ASTM Salt Fog test, nearly 6 times the ASTM standard, with no rust undercutting.
Independent Performance Testing
Though they’ve been on the market for some time, aluminum-impregnated, moisture-cured, aluminum-flake, rust-preventive coatings are relatively new to many contractors and specifying engineers at petroleum-chemical facilities. But these coatings have proven their value. They have been shown in industry salt fog tests to effectively resist corrosion for up to 14,000 hours (more than 6 times longer than the relevant ASTM test) without corrosion creeping under the coating at the scribe.
More important, the coatings have proven their value in real-world applications, including bridges, water tanks and other steel structures. In one case, U-104 was used to recoat a bridge that endured constant punishment from the weather and winter road salt. Twenty years after the recoating, independent tests demonstrated less than two percent corrosion.
Coatings like U-104 have also been shown to endure the harsh environments of petroleum-chemical facilities. U-104 can withstand prolonged exposure to many solvents and petroleum-based products, as well as splash and spill exposure to most organic and inorganic acids. It even has a proven history of retaining its properties when immersed in gasoline.
With two coats of 3-mil DFT, facilities can count on a decade or more of corrosion protection under most conditions. An additional 4-mil topcoat of CFI’s U-166 in any specified color can add another five or more years of protection when properly applied.
The product has excellent flexibility for fixed equipment that moves, and maintains its corrosion-resistant properties from -25°F to 250°F.
For many petro-chemical facilities, aluminum-impregnated, moisture-cured coatings offer an ideal alternative to conventional coating methods, requiring potentially far less surface preparation and labor, while offering long-term performance.
*Claims or positions expressed by sponsoring authors do not necessarily reflect the views of TPC, PaintSquare or its editors.