When Arlington Water Utilities and the Trinity River Authority realized a pipe actively supplying drinking water to the people of Arlington, Texas, USA, needed refurbishment and upgrades, they called on general contractor (GC) Archer Western. From there, nearby contractor Corrosion Control Resources, Inc. was brought in during early 2021 for the coating component.
Located just outside of Dallas, the city of Arlington could only shut down the pipe for 28 days without causing a significant disruption to local supply. Archer Western needed to complete some repairs first, leaving 21 days for Corrosion Control Resources to coat 225 linear feet (68.6 m) of 60-inch (1.5 m) steel pipe, or approximately 3,500 square feet (325.2 m2).
Factoring in cure time, the contractor viewed the project’s expected time window as tight but achievable, assuming everything went according to plan with removing what was believed to be an existing coal tar epoxy coating. Then, they would apply three new coats.
Expect the Unexpected
Upon arriving at the jobsite, though, the coatings crew encountered one unexpected problem. It wasn’t coal tar epoxy! During the project scoping phase, a coupling that connected the pipe and pump was removed, and they confirmed it had epoxy on it. But on day one, Archer Western discovered the existing coating was, in fact, coal tar enamel.
The epoxy they were expecting to remove would have been about the thickness of 10 sheets of paper. Instead, the enamel they found was 0.5 inches (1.3 cm) thick. After getting “the call” from the GC, general manager Drew Johnson knew he had to check things out, in person.
“I could tell right off the bat that this was not what we were expecting, and we had a pretty big problem,” Johnson says. “That was not what anybody wanted to hear on day one. Coal tar enamel is a very thick lining that has been phased out over the last couple decades. We were looking at having to remove a lot more material using hand blasting with coal slag abrasive.”
Knowing he had to convey the significant impact this would have on the project’s timeline, he brought over the blaster while gathering the GC and engineer.
“I took the coupling with epoxy and blasted a 100-pound [45.4 kg] bag of blast media on it, and the same on the enamel,” Johnson says. “The epoxy cleared about 20 square feet [1.9 m2]; the enamel didn’t even clear one. That’s when it became evident that we were looking at one-twentieth of the expected production rate.”
As if that wasn’t enough, the carcinogenic components in the coal tar enamel significantly increased safety controls. The debris needed to be manually removed from the pipe without contacting the skin, eyes, or lungs. It then had to be placed in skid pans and disposed of, following local regulations. Covers or blinds were placed over openings to avoid having material fall directly into the water while keeping debris in the pipe.
Technology Transfer
After a test blast using ordinary blasting equipment and coal slag abrasive, Johnson estimated it would require more than 20 semi-trucks worth of abrasive media, all while extending the project’s time frame to 20 weeks. Understandably, this was not acceptable to the client! Thus, on day one, the project received a new work scope and methodology.
The clock was already ticking. Since adding those additional weeks to the project’s schedule was not an option, the stakeholders agreed the best strategy was turning to technology. A few years prior, Johnson had learned about Sponge-Jet’s 470SJ feed unit with a Robotica blasting robot, and he believed it might be a solution here.
After consulting with product representatives, it was determined to be a perfect use case for the technology. To speed up the learning curve on a new tool, the Sponge-Jet team sent Ed Zaharias, senior manager, to the site to train crew members on how to operate the robot directly.
Johnson describes Sponge-Jet as an invaluable resource. “The unit removed the coal tar enamel lining about three times as fast as conventional blasting,” he says. “With the light weight of the media, it sped up manual debris and media removal between runs, and the reduced dust helped improve productivity. Seeing the soft/spongy media eat away at the coal tar enamel was amazing. We also used a tenth of the media that would have been needed using coal slag.”
“The robot speed varied, but we ran most of the time at 2.2 in (6.0 cm) per minute,” Johnson says. “With the 60-in diameter pipe, that equates to 2.87 ft² [0.27 m²] per minute. To compare, it took 2 minutes, 32 seconds to remove under 1 ft² (0.1 m²) of liner when hand-blasting with coal slag. Even if you account for the robot having two nozzles, it is still safe to say that using sponge media and Robotica was approximately three-to-four times as fast as conventional hand blasting.”
Crew Considerations
Robots can do a lot, but they still need an operator and a crew to clear debris. That meant additional personal protective equipment (PPE) for workers and air monitoring inside the pipe. For that, United Rentals stepped up as a source of hard-to-find 1,600 CFM (45.3 m³/min.) air compressor units and a 5,000 CFM (141.6 m³/min) dehumidification unit.
The crew ordered boxes of PPE, including RPB Nova 3 blast hoods, Tychem suits, and Thickster gloves. They used a second 375 CFM (10.6 m³/min) compressor solely for supplying breathing air, just in case the 1,600-CFM compressor powering the Sponge-Jet unit broke down.
“We didn’t have to worry at all about confined space entry,” Johnson says. “The robot was operated from a pendant… that allowed us to remotely adjust drive speed, direction, and blast arm rotation.”
Working hunched over in a 5-foot (1.5 m) pipe, however, was challenging on its own. Factor in working in the Texas heat in Tychem suits that don’t breathe, and the conditions were near unbearable at times. Every 10 to 15 minutes, crew members took breaks to stretch, rehydrate, and change out their sweat-drenched suits.
To avoid wearing anyone out, project managers brought in another crew to provide a rotation schedule. On most days, the crew averaged about five people in size, though it expanded to as much as 10 or slightly more during critical steps.
When blasting, they were able to alternate running the Robotica with manually removing debris, which allowed things to move forward even when crew members were on break. They continued this rotation and, both literally and figuratively, worked their way down the pipeline.
Early on, another challenge was thrown the contractor’s way when jobsite power was lost. The pump station itself was being revamped and upgraded with new equipment, and it just so happened they needed to cut power from the station while the pipe was being worked on. Fortunately, thanks to good communication, Corrosion Control Resources had planned to use generators to self-sustain all of their lights, fans, and electrical equipment. This hurdle required extra personnel to monitor gas levels and other related maintenance.
They were also made aware in advance that the pump station’s roof was damaged and leaking. “As they were stripping things out of the roof, it only worsened,” Johnson says. “When it rained, water would flood in, so we had to build temporary coverings over pots and other critical equipment… and put out catch buckets to collect as much rainwater as possible.”
Coating Champions
Luckily, with all the challenges they had already faced, the coating selection and installation was able to proceed as planned. Based on a longstanding relationship with the manufacturer, they had selected Sherwin-Williams and its Tank Clad HS epoxy lining as the appropriate technology. The semi-gloss lining resists chemicals and abrasion, and it can be applied directly to metal.
According to the contractor, the project’s tight timeline was a major factor. Corrosion Control Resources needed a high-solids, quick-curing, easy-to-use coating system with a fast turnaround to return the pipe to service. Additionally, the product needed to be an approved system for potable water by the
American Water Works Association and certified by
NSF.
After about 50 years of operation, much of the pipe’s steel substrate remained in good condition with no signs of corrosion, though severe pitting was present at Ts, flanges, and joints. Most of the pitting was around 0.125 in (0.3 cm) in depth, with a few areas near 0.25 in (0.64 cm). For the worst areas, the engineer approved using Sherwin-Williams’ Steel-Seam FT910 epoxy patching compound to fill in and smooth out the surface, prior to coating.
Using a Graco Xtreme King X70 airless sprayer, the Tank Clad HS was applied in three layers, each at approximately 4-7 mils (101.6 to 177.8 microns) of wet film thickness (WFT). To help move through the pipe evenly and in a clean manner, they used an assistant to help the spray operator with the hose and to continuously check WFT readings.
The project’s conditions and timeline were challenging at the onset, and they only became more so as it continued. But through innovation, technology, good communication, and support from multiple vendors, they pulled together as a team and ultimately finished the project on time!
“The city was glad to have this critical phase of work completed on time, despite the unforeseen challenges that arose,” Johnson concludes. “Because we were able to revise our plan of attack and source the specialized equipment and materials almost immediately, we were able to meet the original deadline, which felt great.”
Editor’s note: This article first appeared in the September 2023 digital lineup of CoatingsPro Magazine. Reprinted with permission.