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As the world embraces hydrogen and related energy alternatives, new details meet the old challenge of corrosion protection. Is the “hydrogen economy” finally here? Consider the signs: An S&P analysis from July 2023 suggested that the ammonia market will triple by 2050 — not because of agriculture, but on the strength of its potential as a lower-impact energy source.
In June of this past year, The American Bureau of Shipping and Lloyd’s Register granted initial approval to a shipping consortium’s design for ammonia-fueled container ships. And speaking of shipping, Maersk wouldn’t have ordered 10 very large ammonia carrier (VLAC) vessels if the writing on the wall did not clearly spell out a need for increased transport capacity.
It is also important to note that ammonia is a convenient carrier for hydrogen, which itself is advancing as an alternative fuel. The tiny size of its atoms and very cold temperatures needed for its storage and transport make hydrogen very challenging to handle on its own.
Meanwhile, governments seeking to meet climate pledges are fully involved: In the U.S., a $7 billion federal investment supports new production, processing and use of hydrogen fuel, according to a World Pipelines report.
It’s all solid evidence that the hydrogen economy is here. But what does that mean at ground level? As this story of agreeing on the right corrosion protection coating systems for a new bulk ammonia tank illustrates, the emergence of this new era has a lot to do with individual people working out some critical technical details.
A case in point in Texas
If Texas City, Texas, has a skyline, it consists of the sprawl of stacks and storage tanks all over the south side of town. And at first glance, a recent addition to that skyline — a tall white storage tank completed in late 2022 just spitting distance from the Barge Canal — was nothing new.
Protecting ammonia tanks in the new hydrogen economy
But this bulk anhydrous ammonia storage tank is unique. At 110 feet tall and 212 feet in diameter, it was the largest bulk ammonia tank in the world at the time it was built, according to its owner. The commodity it holds is made at a nearby processing plant, and the tank’s waterside location is crucial for loading the ammonia onto tanker ships for global export.
Significant industrial assets require significant corrosion protection, especially in a humid coastal climate. Again, nothing new for Texas City. But anyone proximate to industry here knows paint isn’t just paint. High-performance protective coatings must be chosen carefully and applied correctly. The failures that could result if either side of that equation falls short would be disastrous for workers, neighboring residents and fragile local ecosystems. Expensive, too, when one tallies the cost of cleanup and lost business. And despite the uncountable number of coated steel storage tanks around the world, it is not as if the industry has perfected corrosion protection.
Characteristics of a stored commodity, the commodity’s required storage conditions, and myriad external influences like weather, climate or the risk of chemical exposure or physical impact all influence how a tank should be protected.
In this case in Texas City, some of those influences were the subject of fascinating technical exchanges among the tank’s owner, its builder and coating contractor, and the coating manufacturer before corrosion protection systems for the roof and tank shell exterior were agreed upon.
Debating tank shell corrosion protection
Protecting the tank shell was more challenging than an ordinary crude oil tank because this one is insulated. The part anyone sees from the outside is merely the insulating jacket. A few inches of air separate the jacket from the actual shell of the tank.
The coating contractor’s tank shell corrosion protection package proposal consisted of the following Carboline coatings:
- A primer coat of Carbozinc 11, shop-applied at 2-3 mils DFT prior to construction
- Then, after sections were welded together, the shell exterior would receive a stripe coat of Carboguard 890, a surface-tolerant epoxy mastic
- A mist coat of Carboguard 890 at 1-2 mils DFT would come next, followed by another full coat of the same
Because the tank was to be insulated, an owner’s representative realized that the interface between the tank shell coating and the insulating air would be considered an immersion environment.
First, the thermal cycling inherent to bulk ammonia passage and storage would likely create condensation on the outer surface of the tank shell. Second, though the insulating jacket installed around the shell is intended to be weather-tight, weather-tightness is impossible to guarantee, especially given the turbulent weather common on the Texas coast. Moisture always finds its way in.
So the owner contacted a Carboline Technical Service representative to propose swapping out the zinc-rich primer for an alternative that is normally specified as an interior lining. They were concerned that a zinc-rich primer under immersion would reverse its polarity.
Polarity reversal can occur in zinc-protected steel assets in immersion at high temperatures (140° to 180°F or 60° to 82°C) when dissolved oxygen, bicarbonates and nitrate ions are present. When it happens, steel corrodes preferentially to zinc instead of the opposite.
But the Carboline representative concurred in the contractor’s proposal for the two-coat zinc-epoxy system. The ammonia stored inside the tank would be held at -20°F (-29°C); even when it was empty, the tank shell exterior would not exceed ambient temperatures. Absent the elevated heat, there would be no risk of polarity reversal.
Application method drove material selection for roof coatings
Settling on a corrosion protection package for the roof was a bit more complicated, partly due to local environmental conditions, but also because of how the tank was to be erected and the way its roof would be coated.
The contractor’s initial corrosion protection proposal for the roof consisted of:
- One coat of Carbozinc 11 shop-applied at 2-3 mils DFT prior to erection
- One stripe coat of Carboguard 890, field-applied over the roof’s weld seams
- A subsequent mist coat of Carboguard 890 over the whole surface of the roof at 1-2 mils DFT
- An intermediate coat of Carboguard 890 at 4-6 mils DFT to the whole surface
- A finish coat of Carbothane 134 HG, a high-gloss, highly weatherable polyurethane at 2-3 mils DFT to the whole surface
Subsequent discussion among stakeholders led to two important changes. The first one addressed the need to protect the roof’s weld seams. Aware of the humid coastal location of the tank, the Carboline Representative proposed replacing the Carboguard 890 weld seam stripe coat with Carbozinc 859, an organic zinc-rich epoxy primer.
This change, he reasoned, was necessary even though a zinc-rich primer already would have been applied in the shop prior to construction. Construction would involve welding roof plate sections together, a process that would leave exposed steel at the seams. The Carbozinc 859 would give that exposed steel the same cathodic protection as the rest of the surface.
Far more complex circumstances drove the second change. The slope of a domed tank roof becomes steeper and steeper the farther out from the center a painter goes. A variety of safety and fall protection systems are available, and the contractor chose the one its crews felt safest using: angled incline safety platforms.
Using this type of platform meant the paint crews would be standing on a level surface no matter the angle of the domed roof. And while painting from angled incline safety platforms can be comparatively slow, this project was to be completed by brush and roll anyway. On a job site adjacent to a waterway and with wildlife refuges nearby, spray application of coatings was prohibited.
The superintendent said getting the job done right the first time meant his crew wouldn’t be back to fix avoidable and expensive mistakes later. So what has that to do with coating material selection?
The contractor understood that painters’ careful pace of work meant it was possible that they would miss the recoat window of the Carboguard 890, which is as little as a few hours in warm weather. If they missed this window, they risked adding an unplanned surface preparation step to the project’s schedule.
Instead, in consultation with the Carboline representative, the contractor suggested Carboguard 60. The product offers similar performance to Carboguard 890, but its recoat window is far longer — a handful of weeks, even in a Texas summer.
Here’s why: Carboguard 60 is based on polyamide epoxy resin technology that forms comparatively less dense molecular bonds when it cures. Carboguard 890 is an amine epoxy, which forms comparatively denser bonds. Paint adheres to substrates better if there is more surface area on the substrate for it to stick to. But what happens when that substrate is a coat of paint?
Carboguard 60’s lower bond density means that, at a molecular level, there is more surface area onto which a second coat can bite. This change was agreed, too, and the tank was coated.
Global implications
All of that just to paint one tank. One. But the careful, unhurried approach of technical experts will be necessary if we hope to minimize the turbulence of today’s energy transition. The world will need more ammonia tanks. And because those tanks won’t all be in Texas City, stakeholders will have their own versions of the conversations examined here.
Those conversations will mark the opening chapters of future success stories like this one if owners, contractors and manufacturers alike lean on one another’s expertise to specify corrosion protection packages that work for the commodity and withstand local exposures. Close contact and open communication, in other words. Everyone involved in building and protecting the new ammonia tank in Texas City understood that. They understood that when the energy transition comes to town, nothing new for Texas City is actually nothing short of game changing.
For more information, visit carboline.com.
