For multinational steel manufacturer POSCO, corrosion can be an occupational hazard. Because steel mills require sufficient raw materials to produce, they are often located near marine terminals — where both raw material and finished products can be easily shipped.
That has long been the case for POSCO at its steel plant in Pohang, South Korea, where its processing equipment and infrastructure must be coated to withstand atmospheric corrosion from the high humidity and salty air of the coastal area. Any coating also needs to protect against corrosion under insulation (CUI), which can result from exposure to moisture from sources such as steam, wash downs, sprinkler systems, or the frequent condensation and evaporation of atmospheric moisture.
Though prior coating applications at the site were successful, POSCO found that it had to reapply coatings every few years based on coastal conditions. As such, this increased their maintenance costs and production downtime. So when POSCO sought to recoat several of its corroded assets in April 2018, they put a premium on finding both the right coatings contractor and the right coatings technology.
“POSCO benefits when they can safely extend the lifespan of their steel assets with less maintenance,” said Sungjun Ahn, general manager at Korean coatings contractor Dong-buk E&C, which ultimately earned the assignment. “Without frequently repainting, they can more productively invest in further product and process innovation.”
To protect its steel assets and improve its environmental performance, POSCO turned to EonCoat, a spray-applied inorganic coating. When the coating is applied, it forms an alloy layer that chemically bonds with the steel’s surface, effectively preventing intrusion from moisture and other potential corrosion promoters. The EonCoat system also forms a ceramic outer layer that further resists corrosion, water, abrasion, impact, chemicals, and high temperatures. Many of those were especially desirable characteristics at this jobsite, considering the coastal location.
“That’s a really tough environment for traditional paint to withstand, because effectively, you’ve got salt water, humidity, wind, and significant temperature variations,” said Merrick Alpert, president of EonCoat. “With us, rather than lay a traditional tarp over it, you’re passivating the steel.”
The unique features of the technology, though, can require specialized applicator expertise. So before turning Ahn and his crew loose on this or any other jobsite, some training from the coatings manufacturer was a prerequisite.
“We train the applicator, and we’re there with the applicator for the first job,” Alpert said. “From there, they go out and do it and don’t need us. Our business is to manufacture the coating and to ship it, and we send out the technical support to train and advise the customer’s applicator, who applies the material.”
“EonCoat is a really sensitive product compared to other conventional coatings,” Ahn added. “It reacts really fast in hot temperatures, and it’s also fast enough with just normal temperatures, too. But it reacts really slowly under cold conditions. It’s much faster or slower than an epoxy, for example. In the past, we had trouble since it’s either a fast reaction or a slow reaction. There’s plugging of the gun, a wrong mixing ratio caused by a pump problem, no curing under 0 °C [32.0 °F], and many other problems can occur if you don’t pay attention to the details. You need to prepare all the equipment and products very carefully before you start to spray to prevent any trouble. But when you use it correctly, it’s a good product with excellent quality.”
For the April 2018 assignment, POSCO chose the EonCoat system with an aesthetic topcoat for the four boiler dust-collection “hoppers” at the facility. Due to the system’s inorganic properties, chemical resistance, and its ability to withstand temperatures up to 500 °C [932.0 °F], it is useful in such high-temperature areas, where it can help prevent CUI.
“The corrosion inside the dust-collection hopper was severe due to the sulfuric and nitric acid of the line,” Ahn said. “The older plates were too thin because of corrosion. Although not all plates were thinned, random spots with low thickness could cause a collapse.”
Because POSCO opted to replace the carbon steel plates entirely, a separate welding contractor prepared the surface of the new plates offsite via dry grit blasting to achieve a NACE No. 3/Society for Protective Coatings (SSPC) Surface Preparation (SP) 6: Commercial Blast Cleaning standard and then installed the plates inside each hopper. From there, it was time for the Dong-buk E&C team to get to their portion of the assignment.
The initial priority, of course, was accessing the entirety of the 6,500-square-foot (603.9 m2) structure. A scaffolding system was set up to reach higher areas, while personal protective equipment (PPE) for the four-person crew began with a clipped fall protection vest belt to lock each person’s body to the scaffolding. Other PPE gear included dust masks, goggles, safety boots, gloves, helmets, and ankle protection.
For the application, the crew used Cosmostar PF100 plural spray pumps and a Graco G40 airless spray gun with an XHD535 RAC switch tip. That was with a Swagelok remote mix manifold and a 1/4-inch (0.64 cm) hydraulic whip hose with a static mixer from On-Site Hose Inc. The EonCoat product was applied at an average thickness of 20 mils (508.0 microns) and dried within minutes, allowing for the quick application of a topcoat for aesthetics. On this job, the topcoat was the Yeolcoat QT6612 heat-resistant silicone acrylic resin-based coating from Korean manufacturer KCC Corp., applied at an average of just 1 mil (25.0 microns) dry film thickness (DFT).
“I was the sprayer, and the rest of them were supporters,” Ahn said of the crew. “One was mixing and taking care of the pump, and one was looking after hoses since we're spraying inside the hopper. The last supporter was standing by me while controlling the valve and holding the heavy hoses.”
Because the two-component EonCoat system is inorganic, nontoxic, and non-flammable, this meant the crew could apply the system safely in confined spaces. Considering the hoppers, the confined spaces aspect of the POSCO job actually helped the crew, because the sealed shape prevented wind from disrupting their spraying. “And because of the compatibility of EonCoat with moisture, rainy weather was not an important factor,” Ahn added.
The crew diligently coated two hoppers each week, and by the end of week two, the Dong-buk E&C team had successfully hopped away from the jobsite after completing the assignment. The client was happy with the work, and barring any unexpected snags, both the client and contractor aren’t anticipating seeing the results again any time soon.
“The job was done successfully, but we’re unable to see how it’s holding up inside,” Ahn said, “because it must run continuously during the next four years.”
POSCO is also using EonCoat on a variety of other equipment at its Pohang steel plant, such as storage tanks and dock pilings, including the splash zone and beneath the waterline. Based on the system’s chemical resistance, it is additionally being considered as a primer for equipment in contact with sulfur dioxide and nitrogen dioxide gases, which result from burning fossil fuels and smelting mineral ores.
The system certainly has its technical benefits, but its complexity requires strong teamwork and communication between the manufacturer and applicator. Fortunately for the client on this job, EonCoat and Dong-buk E&C had both the expertise and steely resolve to answer any challenges that came their way. Kudos to the crew for hopping to it!