Corrosion protection is vital for tank maintenance
VScarbon steel corrosion may require early tank replacement and maintenance, as well as pose a safety risk in terms of potential leaks, spills and even fire and explosion, effective protection against corrosion is therefore essential.
“We clean just about any tank transportation product or waste on road or rail,” said Joe Svehlak, facilities manager at DFW Tank Cleaning, a Dallas-Fort-based full-service tank cleaning facility. Worth, Texas, specializing in chemical cleaning. “Corrosion protection is vital in such tanks, as it is in the flushing tanks at our facilities.”
According to Svehlak, effective corrosion resistance is essential in cisterns because they hold wastewater from the first flushes of the tanks the company cleans, which may include residual chemicals, until they are treated. . This equates to thousands of different residual chemicals being retained in flush tanks every year – from petroleum products and saltwater brine to fluoride, caustic soda and a variety of acids.
In the face of these tank corrosion problems, traditional polymer paints and rubber-like coatings have long been used as physical barriers to keep corrosion promoters such as water and oxygen away from steel substrates. This works until the paint is scratched, chipped or punctured and the corrosion promoters enter the gap between the substrate and the coating.
Tank trucks or tank cars transporting waste, including sand and sediment, can be particularly prone to scratching, chipping or chipping. When this happens, the coating can act like a greenhouse – trapping water, oxygen and other corrosion promoters – allowing corrosion to spread.
Although stainless steel can be used for tanks to resist corrosion, it can be up to six times more expensive than carbon steel, as well as difficult to weld, fabricate and maintain. A new generation of anti-corrosion coating, called chemically bonded phosphate ceramic, is now available.
“Our corrosion protection for our 10,000 gallon flush tanks has to be particularly robust because we mix the sewage so it doesn’t stratify, and sand, rocks and even metal shavings can be present in the waste trailers we service,” Svehlak said. “Corrosion protection must also withstand the high temperature and high pressure water that we often work with.”
To control corrosion, the tank cleaning facility chose to have the insides of two flush tanks coated by DC Metal Construction, a private company specializing in steel construction and facility construction projects. industries, based in Ennis, Texas. The cisterns were coated with a spray-applied inorganic coating called EonCoat from the company of the same name based in Raleigh, North Carolina. EonCoat represents a new class of chemically bonded phosphate ceramics (CBPC) that can stop corrosion.
Unlike traditional polymer coatings which sit on the substrate, the corrosion resistant coating bonds through a chemical reaction with the substrate, and slight surface oxidation actually enhances the reaction. An alloy layer is formed. This prevents corrosion promoters such as oxygen and moisture from penetrating behind the coating as they can with ordinary paints. The corrosion barrier is coated with a ceramic shell that resists corrosion, fire, water, abrasion, chemicals and temperatures up to 400 degrees.
Although traditional polymeric coatings mechanically bond to substrates that have been extensively prepared, if gouged moisture and oxygen will migrate under the coating film on all sides of the gouge.
In contrast, the same damage to the ceramic coated substrate will not propagate corrosion because the carbon steel surface is transformed into an alloy of stable oxides. Once the steel surface is stable (as noble metals like gold and silver are), it will no longer react with the environment and corrode.
Visible in scanning electron microscope photography, EonCoat leaves no gap between the steel and the coating because the bond is chemical rather than mechanical. Since there is no gap, even if moisture were to enter the steel through a dent, the moisture has nowhere to go. The only place that can corrode is the drawn line itself, eliminating the possibility of corrosion migration.
“Unlike traditional methods, corrosion resistant coatings for mild steel have a double layer of protection,” said Bobby Hobbs, foreman at DC Metal Construction. “The tough ceramic outer coating does not flake like paint and requires sanding to remove. The chemically bonded layer stops corrosion and does not allow corrosion promoters to spread.
“EonCoat held up well to everything from chemicals and salty brine to abrasion, high pressure water and heat,” Svehlak said. “I believe this will double the life of our tanks while significantly reducing maintenance costs and downtime.”
According to Svehlak, the coating’s robust anti-corrosion properties could also benefit a wide range of transportation-related businesses.
“Tanker and railroad operations can benefit from the reliability of the anti-corrosion coating,” Svehlak said. “Its abrasion resistance would be a huge benefit for sewage haulers or vacuum super truck operators with vacuum tanks who may encounter metal shavings, glass shards, etc. when cleaning sumps. It would also resist tank corrosion when transporting petroleum products or even used restaurant waste such as oil, grease or grease.
Another benefit of CBPC coatings is a quick return to service that minimizes equipment downtime, Svehlak said.
“For corrosion protection projects using typical polymer paints such as polyurethanes or epoxies, the cure time can be days or weeks before the next coat of traditional three-part systems can be applied, depending on the product,” Svehlak said. “Cure time is necessary for each coat to achieve its full properties, even though it may feel dry to the touch. In contrast, a corrosion resistant coating for carbon steel using the single layer ceramic coating requires virtually no curing time. Return to service can be completed in as little as an hour.”
After proper tank preparation, “we have found that if we spray EonCoat in the morning, the tank can be returned to service the same day because it applies in one coat and dries quickly,” Hobbs said.
EonCoat consists of two non-hazardous components that do not interact until applied by a multiple spray system such as those commonly used to apply polyurethane foam or polyurea coatings. As the coating is inorganic, there are no VOCs, no PAHs and no odor. This means the coating can be applied safely even in confined spaces, according to the company.