The concept of tried and true exists for good reason—it signifies a method that has stood the test of time. However, as new technologies emerge, even the most reliable methods must be revisited. Spanish chemist Alex Yagüe Marrón did just that, reaffirming that zinc-rich coatings remain the best solution for protecting offshore steel structures from corrosion.
Yague, senior scientist with coatings solutions provider Hempel in Barcelona, Spain, authored the AMPP conference paper “Benefits of Using Zinc-Rich Primers in Offshore Environments.”
His study tested various coating systems, with and without zinc, in real offshore conditions for six to 12 months. The results, he says, show that zinc-rich coatings offer significantly better protection against corrosion, proving they are still the best choice for offshore environments.
“In this study, we have aimed to demonstrate that systems containing a zinc-rich primer provide superior corrosive protection than any other liquid coating in these harsh, offshore environments and validate it in real-life conditions,” Yagüe explains. “These types of coatings can also be used in the splash and tidal zones with excellent performance.”
The Problem
Offshore structures—whether they be oil rigs, wind towers, or platforms—are exposed to some of the most aggressive environments on Earth. Marine environments, especially those close to the coast, combine high salinity, humidity, and intense exposure to ultraviolet (UV) radiation, all of which contribute to rapid corrosion.
As such, corrosion protection is critical to ensure the longevity and structural integrity of these massive structures.
The environments that offshore structures face are categorized into different zones: atmospheric (exposed to air), immersion (underwater), and tidal (where the structure is submerged and exposed to air due to tides). Each zone has different levels of corrosiveness, and it’s important to choose the right coating based on these conditions.
Coating Systems in Offshore Environments
In offshore environments, Yagüe’s paper explains, corrosion protection systems are not just about aesthetics or surface coating; they are about ensuring the structure’s long-term viability and minimizing maintenance costs.
Typically, a three-layer system is used: a primer, a midcoat, and a topcoat. Zinc-rich primers—either organic or inorganic—have been the industry standard for many years. Their success lies in the galvanic (sacrificial) protection they provide. Zinc dust acts as an anodic material, offering cathodic protection to the underlying steel. This ensures that even if the coating is damaged, the zinc will corrode before the steel, protecting the integrity of the structure.
However, due to the growing demand for cost-effective solutions, some in the industry have turned to non-zinc primers, which, although meeting basic standards like ISO 12944-9, don’t deliver the same high-level protection, the author writes. This shift could ultimately result in a higher cost of ownership due to more frequent maintenance and shorter service life, says Yagüe, who has a bachelor’s degree in chemistry and a master’s in nanotechnology from the University of Barcelona.
Yagüe has more than 10 years of experience in paints, adhesives, and polymers in technical positions and joined Hempel in 2015. Over the last five years, he has specialized in zinc-rich primers, especially in zinc epoxy coatings.
A Matter of Cost
Maintenance in offshore structures is challenging and costly to perform, so it is crucial that the coating scheme reduces or eliminates the need for major maintenance during the life cycle of the structure, expected to be 25 years, the author writes.
Yagüe’s paper explains that the cost of coating onshore structures ranges between €15 and €25 ($15.55 to $25.93 in U.S. dollars) per square meter, while the cost of coating repair work performed on-site on offshore structures could be up to 10 times higher. When all job-related costs are accumulated, in offshore cases, the cost can increase to €1,000 ($1,036.69) per square meter, up to 50 times more than the initial application cost.
“We think that this is much more feasible when using novel zinc-rich epoxy technology as the primer,” he says.
The study highlights the importance of considering long-term costs when selecting a coating system. While non-zinc coatings may seem like an attractive option due to their lower initial cost, they often fall short in performance. Without the galvanic protection of zinc-rich primers, these systems tend to degrade faster, requiring more frequent maintenance and shorter operational lifespans, Yagüe notes.
The corrosion products of zinc, such as zinc oxide and zinc carbonate, are stable and adhere well to the steel surface, he says, and form an additional protective layer that further inhibits corrosion, enhancing the longevity of the protection.
“This effect is even more relevant for severely corrosive environments such as atmospheric offshore and splash zones,” Yagüe says.
The true cost of a coating system isn’t just the price at the time of application. It’s the combined cost of installation, maintenance, repairs, and downtime throughout the life of the offshore structure. When these factors are considered, zinc-rich primers offer superior value by minimizing the need for expensive repairs, especially in challenging environments like the splash zone.
Testing Procedure
Accelerated aging tests simulate real-life conditions in a short time, but they don’t always predict how coatings will perform in actual offshore environments, Yagüe says. While coatings might perform similarly in lab tests, zinc-based coatings provide better protection in real-life offshore conditions. Therefore, actual field data is crucial for assessing the effectiveness of coatings.
To test the primers, Yagüe exposed several commercially available solutions to real offshore conditions for six and 12 months. He selected two different locations: the floating platform-laboratory HarshLab, located at Biscay Bay in Spain, and the Marine Corrosion Test Site El Bocal on the coast of Cantabria, Spain.
He tested panels made of carbon steel by cleaning them with abrasive blasting to create a textured surface. He made a 50 mm scratch on each panel to simulate a coating defect, which would speed up rusting by exposing the metal underneath. He tested the panels for one year at HarshLab in areas exposed to air and for six months at El Bocal, where they were splashed with seawater.
He then measured rust under the scratch to see how well the coatings protected the metal. He also conducted a test to determine how strongly the coatings stuck to the steel by pulling at the coating and measuring how much force it could handle before coming off.
Key Findings
Zinc-rich coatings performed the best in preventing rust from spreading under the scratch thanks to a galvanic effect where zinc helps protect the metal. Other coatings without zinc showed five to 10 times more rust creep compared to the zinc-rich coatings.
In the splash zone, coatings with glass flakes added also performed well, and coatings with high thickness didn’t always outperform those with lower thickness.
All coatings had strong adhesion initially, with most getting stronger after being exposed for a year. The coatings did not show major failures, such as the coating peeling off the metal, a good sign of durability.
His findings showed the zinc-rich primers offered:
Superior corrosion resistance: In both atmospheric and splash zone tests, coatings with zinc-rich primers exhibited significantly better corrosion resistance. In the splash zone, for example, systems with zinc-rich primers had rust creep values up to eight times lower than other systems, even when the non-zinc coatings were applied at much greater thicknesses. This demonstrated that higher thickness does not always correlate with better protection, especially when the underlying primer cannot offer galvanic protection.
Improved adhesion: Coatings with zinc-rich primers also showed superior adhesion characteristics. In the HarshLab tests, coatings with zinc primers maintained high pull-off adhesion strength even after a full year of exposure. Conversely, the zinc-free system showed signs of degradation under real-world exposure.
Lower maintenance costs: While zinc-rich primers are often more expensive up front, they can ultimately save costs in the long run by significantly extending the service life of offshore structures and reducing the need for frequent repairs. In extreme environments like the splash zone, the galvanic protection provided by zinc-rich primers helps prevent extensive damage to the steel substrate, reducing corrosion-related maintenance work.
“I recommend that offshore structure owners understand the importance and the long-term implications of selecting a scheme with enhanced corrosion protection to offer potential savings in operational costs,” Yagüe says. “Here, a shift in thinking is sometimes needed—lifecycle payout instead of short-term costs.”
Editor’s note: This article first appeared in the April 2025 print issue of Materials Performance (MP) Magazine. Reprinted with permission.
