The DFW Tank Cleaning facility in Waxahachie, Texas, specializes in chemical cleaning, and essential to that process are the internal flush tanks at the home base. These tanks hold the untreated wastewater from the first flushes of tanks that the company cleans during any given job. This cleaning process, though, creates its own “dirt:” It leaves behind residual chemicals that can potentially corrode the carbon steel (CS) flush tanks at the facility.
Luckily for the client, a contracting crew at DC Metal Construction in nearby Ennis, Texas — located just south of Dallas — was ready for the challenge. “There’s no telling what’s liable to be in that tank, all at the same time,” said Bobby Hobbs, a job foreman with DC Metal Construction. “It is definitely a harsher environment.” They came armed with a recent innovation in coating technology that could help prevent further corrosion.
So when the three-person crew from family-owned DC Metal Construction got to the job site earlier this year to clean one of the 14-foot by 14-foot (4.3 m x 4.3 m) tanks, they immediately recognized the challenge. Having already coated three other tanks at the facility, they were acutely aware of the conditions and had a solution ready.
Preparing the Tank Surface
DC Metal Construction, which specializes in metal construction fabricating and erecting metal buildings, currently has 11 employees. This particular job called for a three-person crew.
“It takes one person to operate the spray gun, one to maintain the spray machine, and one to do damage control,” Hobbs said.
On the first morning of the two-day job, the crew contracted out to nearby Metro Transit Sandblasting from Argyle, Texas, to help prep the 600-square-foot (55.7 m²) tank by commercial blasting. All foreign materials are removed in order to allow the tank surface to degrade, or flash rust. Only metal or light iron oxide (Fe3O4) can remain on the surface during coating, since previously-painted surfaces require removal of the paint in order for the new coating to form a molecular bond with the steel.
The crew blasted the surface to achieve an anchor profile of at least 1-to-2 mils (25.4–50.8 microns), and then they removed the spent abrasive by vacuum cleaning. Hobbs went into the tank that first afternoon to inspect the surface. “I go in and look, just to see if there are any holes or bad thin spots,” he said.
On this particular job, no patches to the tank were needed prior to the application of the coating; however, during prior jobs on adjacent tanks, Hobbs said that he came across other tanks that were in “rough shape” and that required several patches on the floor to fix pitting. With a patch not needed, the crew was able to begin applying the coating early the next morning.
Getting the Job Done
Wearing gloves, goggles, a cloth face mask, and Tyvek coveralls, the crew began applying the EonCoat system. They used a fan at the bottom hatch of the tank to promote circulation, which when combined with a natural opening at the top hatch, gave enough ventilation that respirators were not needed. The crew used a ladder to access hard-to-reach areas.
The EonCoat works as a two-part surface treatment coating. The A side is the acid side, which brings the iron out in the steel to cause a chemical reaction. The EonCoat must physically touch the metal in order to alloy it. Meanwhile, the B side is the outer shell of the coating, which creates a ceramic-like outer layer. Because it is a two-part coating, the system requires using both a plural-component spray machine from Cosmostar and a two-part gun. The machine has two hoppers and two pumps on it.
Holding the spray gun perpendicular to the surface at a distance of 24 to 30 inches (60–75 cm), the crew sprayed the interior of the tank with the machine set at a working pressure of between 1,500 psi (10.3 MPa) and 1,800 psi (12.4 MPa). A separate line hooked directly to the spray gun worked with a pressure of 30 psi (0.20 MPa) to 40 psi (0.27 MPa).
“You have to have an even amount of chemical come out at all times,” said Hobbs, who added that stripe coats were applied locally to welds, fasteners, and external corners after the full coat went down.
Applying the coating at a thickness between 10 and 20 mils (254.0–508.0 microns), it took the crew about three and a half hours to complete the first step, and it took another 15 to 20 minutes for the coating to dry to the touch.
“I give it about two hours to dry, just to make sure that everything has bonded and that we have no problems with the coating,” Hobbs said.
After waiting the duration of the cure time, the crew went back in to inspect the coating and found two small spots that looked like cracked paint. Those spots meant that the coating had not sufficiently bonded in those areas, so the crew then went into investigation mode.
Because a member of the crew was watching the spray machine at all times, they were able to rule out a problem with the spraying process. Similarly, because the coating had worked throughout the tank except in two small spots, they knew the problem was not bad product. Other possible contributing factors to the lack of bonding could have been high heat, humidity, or winds — but since the job was done on a picturesque day, with temperatures at 70° F (21.1° C), 65-percent humidity, and little wind, Hobbs suspected that weather was not a factor.
The most logical conclusion, according to the crew, was that something had gotten into the tank. EonCoat needs a clean surface to chemically adhere to the steel. Oil, grease, dirt, dust, or standing water on the tank would have inhibited that adhesion. Accordingly, the crew cleaned those two problem spots and recoated those areas.
“This was the only time that I have run across this situation,” Hobbs said. “So we prepped the surface for patching, patched it, and it worked just fine.”
By the end of the second day, Hobbs and his crew had completed the entire job.
Decrease in Downtime
The combination of enhanced protection and greater time efficiency has Hobbs optimistic about his prospects for more EonCoat-based jobs in the future. A quick solution in a short time period is a win/win for DC Metal and its clients.
“After appropriate tank preparation, we’ve 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. “Quick return to service like this can be particularly important in production-focused industries like oil and gas. Since the coating has no VOCs [volatile organic compounds], HAPs [hazardous air pollutants], or odor, we were able to spray during work hours, so the facility could stay in full production in adjacent areas while we coated the tanks.”
In fact, within the next year, Hobbs already has an order from a different client to coat six new tanks in Texas in a similar manner. If Hobbs and his crew keep it up, Texas might find that high-performance coatings are deep in its heart.