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¢ Replace highly corroded steel and install upgrades ¢ Spray-apply three 4- to 6-mil (101.6 microns to 152.4 microns) DFT coats of Carboline Carboguard 891 to a total 12 to 18 mils (304.8 microns to 457.2 microns) DFT ¢ Gaps filled with Sikaflex polyurethane caulk SAFETY CONSIDERATIONS: ¢ Working on scaffolding and swing stages required fall protection ¢ Rooftop fall protection precautions where needed ¢ Forklifts and other motorized equipment used inside the tank were fitted with catalytic converters to lessen noxious emissionsThe Sherwin-Wil- liams Macropoxy 646 is spray-applied to the entire area at a thickness of 5.0 to 10.0 mils (127 microns to 254 microns). ¢ Sherwin-Williams Acrolon 218 HS polyurethane top coat is spray- applied at a thickness of 3.0 to 6.0 mils (76.2 microns to 152.4 microns). SAFETY CONSIDERATIONS: ¢ The crew wears custom coveralls, eye protection, gloves, boots, and North respirators or Nova 2000 Blast Hoods. ¢ All OSHA regulations are followed, especially those for the removal of an existing lead-based coating. ¢ Fall protection is required for all traffic control work, as well as work on the box truss sections of the bridge. entire project generated only ten 45-gallon (170.34L) drums of waste, states Soper. "The ARS units are not cheap, " Soper says, "but they can be a worthwhile investment when you factor cost of purchasing new blast media and landfill tipping fees. Getting rid of 400 tons (362,873.9kg) of waste can be cost-prohibitive. Plus, it's good for the environment." Whi le the bot tom line is important, nothing is more important than the health and well-being of your crew. Rising ambient temperatures inside the tank had Soper's attention. Sand blasting is a hard job, but even with the 20-ton AC unit running 24/7, midday temps inside the dome soared past 120°F (48°C). Soper had a trick up his sleeve that called for more sand blasting. Blast hoses galore! "These roofs get pretty hot," Soper says. "So one way to bring down interior temperatures is to blast and prime the roof, then lay down the intermediate coat. The original coat and primer are dark, but the intermediate coat is white, which reflects heat a lot better." The trick worked! As the crew worked, interior blasting began to reveal a host of unforeseen problems, mainly at the tank's central high point where chlorine fumes accumulated over the years. The 48"-wide (121.92cm), 45'-long (13.7m) beams were too far gone to take paint. The discovery necessitated a change order, which took time and threatened to put a major kink in the schedule. "Finding problems is no fun," opines Soper. "Change orders take time to process and approve. Things you find in the middle of the job are often hard to deal with because you already have a rhythm and sequence going, and sometimes $10,000 worth of extra work keeps you from earning $100,000 in revenue by the time you go through all the approval processes. I understand procedures and policies are important, but I'd just as soon not 58 CoatingsPro J July 2012 run into change orders." To keep the project flowing, Blastco brought in a welding team from Houston-based Blackstone Welding and Fabrication. Including tank upgrades, such as new roof vents and a more modern cathodic protection system, the interior welding took Blackstone's five-man-crew about 45 days. "There was a lot of work and not a lot of time," says Blackstone owner and project manager, Jim Lee. "We had to push hard, especially after initial inspection when they handed us our punch list. We run a small crew, but my guys are tough, and they got the job done on time." PUMPED UP! With the tank interior finally prepped to NACE No. 2/SSPC-SP10 Near White Metal Blast at 3-mil (76.2 microns) anchor profile, the Blastco crew was pumped up. They switched on their Graco Xtreme 56-1 airless sprayers (#419 tips) and prepared to apply the first of three 4- to 6-mil (101.6 microns to 152.4 microns) DFT coats of Carboline Carboguard 891. After power mixing the two-part cycloaliphatic amine epoxy (1:1 ratio, A to B), the first pass was applied direct to metal. The coating's relatively short cure time permitted subsequent passes within hours. By way of example, a 4- to 6-mil (101.6 micron to 152.4 micron) coat of Carboguard 891 dries to recoat in as few as two hours at 90°F (32°C), according to BELOW The crew used a FasterBlaster remote-controlled blasting robot to prep the exterior tank walls with a steel shot and grit mixture, bringing the surface to NACE No. 3/SSPC-SP6 Commercial Blast standard with a 2.5-mil (63.5 microns) anchor profile.