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The superior corrosion resistance of inorganic zinc-rich (IOZ) primers is beyond debate.
Too bad they only come in zinc-dust gray.
If that color was permitted in jurisdictions mandating bright white for tanks and piping in liquid terminals, we’d see a lot more assets covered in IOZ primers and nothing else, and the terminal owners would see a lot of time and money saved.
But it is possible to greatly improve corrosion protection for storage tanks that must be bright white. And the recipe is no mystery. The coatings industry has known how to do it for decades.
It starts with the inorganic zinc-rich coatings which already are an industry mainstay. And it ends with an inorganic finish coat—yes, the Armorlast system comes in white—that simply lets zinc be zinc.
Inorganic resins maximize zinc’s potential
The reaction between zinc and the atmosphere is an essential factor in the extended corrosion protection zinc-rich coatings provide. But the coating’s resin type also influences its performance.
Immediately on its exposure to the environment, zinc reacts with oxygen, moisture and CO2 in the air to form numerous reaction products. These reaction products fill in microscopic pockets in the coating film over time, a process which continually reinforces the structure of the coating and is essential to its overall protective properties.
IOZ primers are typically based on silicate resins that cure to form comparatively permeable coating films compared to organic resins. That allows moisture to move through the film for continued curing of the silicate resins as well as reacting with zinc to continually reinforce the coating.
Zinc compounds fill the pores in the silicate resin matrix, creating a physical barrier between the substrate and its environment. The zinc also reacts with the silicate resin and the iron in steel to form a chemically bound complex. The presence of moisture closes the circuit and activates cathodic protection.
And, unlike organic counterparts which weaken over time under UV radiation, IOZ primers are unaffected and strengthen with age.
But in some locations, storage tanks and piping are legally required to be white. That means any zinc-rich primer, which comes in only one color, must be top coated. So, owners turn to a traditional system: a zinc primer under one or two organic epoxy or urethane coats.
Organic resin based coatings are less permeable vs. inorganic ones. Application over an IOZ primer insulates some of the zinc, impeding that vital interaction with the atmosphere.
Compounding the problem is that all organic resins eventually break down under UV radiation. The corrosion-protective performance of an IOZ primer is handicapped by the introduction of an organic resin on top of it.
And even if an IOZ primer is liberated when organic mid- or topcoats wear away, remember the rule about the asset being white. A fine is owed if it’s not.
Beachside Test Panels
Photo of NASA’s beachside corrosion test site at Kennedy Space Center in Florida. The panels marked 312 and 320 are coated in an inorganic zinc-rich primer. The two panels to their right are coated in organic resin based materials. Both sets of panels were set out for testing at the same time.
Comparing IOZ primers vs. galvanizing
No discussion of high-performance corrosion protection should exclude mention of galvanizing. The process has been around for centuries. It is well understood and effective at achieving long-lived corrosion protection.
How do liquid-applied coatings compare? It’s hard to offer a scientifically valid performance comparison for two reasons:
• Galvanizing is not subject to the same rigorous performance testing as paint; paint is held to a different and higher standard
• Variability in assets, surface preparation, application techniques, formulas, environmental exposures and other influences mean control conditions are difficult to achieve in the field
With that said, ample laboratory testing and historical field performance indicate IOZ primers are equal or superior in performance to galvanizing, which is usually marketed as a 50-year corrosion protection solution.
It’s worth noting that the structural steel in NASA’s Vehicle Assembly Building in coastal Florida was coated in a single layer of Carbozinc 11 in 1966. It was observed in excellent condition as recently as February 2025, 59 years later.
Cost, application properties and health and safety concerns are easier to compare:
• Galvanizing is slower to apply and requires stationary equipment
• The high heat and dangerous chemicals used in galvanizing pose greater health and safety risks to workers
• Galvanizing costs more, sometimes as much as twice the cost per square foot vs. painting
A note about floating roofs
Storage tank floating roofs present a more complex challenge because they encounter additional exposures that can compromise protective coatings: steel movement, petrochemical fallout and ponding water.
Two familiar strategies attempt to address these.
One is to apply a comparatively thin-film, two-coat epoxy system that resists exposure to commodities and periodic immersion in water. But these often fade and crack after just a few years.
Another is to apply a thick-film liner to the roof. These materials withstand immersion and commodity exposure but add a great deal of weight to roofs, become brittle over time and are quite a bit more costly to repair or remove.
Could two-coat inorganic systems take over?
Their thin-film formulas add less weight to roofs, they are inert against UV exposure, and our chemical resistance and immersion testing suggests good performance in periodic immersion or in contact with commodities.
Two-coat inorganic systems are the best of both worlds for storage tanks
Third-party testing has shown that adding an inorganic coating layer over an IOZ primer may increase the system’s durability and resistance to impact damage while still offering excellent galvanic protection.
Test panels coated in Carboline’s Armorlast two-coat inorganic system have shown virtually no degradation following exposure in back-to-back-to-back ISO 12944-9 cyclic aging tests. A single test cycle simulates 25 years in the harshest, most corrosive conditions.
NASA ML-2 Module
The Armorlast two-coat inorganic coating system protects the structural steel of NASA’s ML-2 launcher. Designed to support NASA’s Artemis program, the launcher is currently under construction at Kennedy Space Center in Florida. Image courtesy of Bechtel.
And then there’s color.
Carboline’s Armorlast I inorganic finish coat comes in a range of colors including bright white. Liquid terminals can now achieve the triple objectives of improved corrosion protection, reduced coating maintenance, and compliance with regulations on color.
The Armorlast system has now opened the door to being a game-changer for sites across the U.S. As these case histories describe, corrosion engineers around the country are more and more in favor of specifying an inorganic-based system that could potentially last twice as long or more as a glossy organic-topcoat system more suited for beauty contests than for long-lived, low-maintenance service.
Lifetime performance, a lower cost to own and the right color: The Armorlast two-coat inorganic system sends a message tank and pipe asset owners hear loud and clear.
For more information, visit carboline.com.
