CoatingsPro Magazine

NOV 2016

CoatingsPro offers an in-depth look at coatings based on case studies, successful business operation, new products, industry news, and the safe and profitable use of coatings and equipment.

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Page 32 of 68

32 NOVEMBER 2016 COATINGSPROMAG.COM BY JACK INNIS, CONTRIBUTING EDITOR PHOTOS COURTESY BOSWELL'S CONSULTING TESTING SERVICES Jacked Up Tank Job raig Winter and his Blastco coatings crew were jacked up! W hile his team brings its "A" game to every project, this particular 10-million-gallon (~37.8 million L) steel water tank was special. ey had a history with it. e 231-foot-diameter by 35-foot-tall (70.4 m x 10.7 m) tank — built in 1988, owned by the City of Austin, Texas, and operated by Austin Water — was last coated by Blastco. e 17-year-old coating system had seen better days. In addition to sporting a drab overall appearance, recent exterior inspections revealed areas of failed adhesion between primer and finish coats. Inside, things were worse. Rust stained the roof plates, bloomed between rafter tops and roof plates, and even caused a garden-hose-sized leak in the tank 's 24-inch-diameter (60.9 cm) overflow pipe. Hey! Water is scarce in Texas. No one wants to stand around twiddling their thumbs watching a leak grow larger! Rarin' to Go! Project manager Winter and his crew were rarin' to go on this 205,000-square-foot (19,045.1 m²) project. Little did they know they'd be in an even bigger hurry to beat the 160-day deadline! "We've done similar tanks for Austin Water and know what to expect," said Blastco General Manager Steve Wissing. "Austin Water needs these projects completed during low demand season. We begin in early January so the tanks are up and running before summer." T he 10 - to 15 -man Wood lands, Tex as-based Blastco crew got of f to a fast star t by attack ing the exter ior tank wa l l w ith a FasterBlaster 32 robotic abrasive blaster. T he R BW Enter pr ise's FasterBlaster compr ises a robotic blast element that goes up and dow n tank wa l ls on cables. A wheeled w inch r ig tethered to a tie dow n at the center of the roof helps it move around the per imeter. A g round operator w ith a remote control paces the robot 's ver tica l jour ney whi le a man on the roof moves the w inch af ter each completed ver tica l pass. If this a l l sounds like f un and games, achiev ing the specif ied NACE No. 2/Societ y for Protective Coatings (SSPC) Sur face Preparation (SP) 10: Near-W hite Blast C leaning w ith a 3.5 -mi l (88.9 microns) minimum anchor prof i le actua l ly ta kes a lot of work! Since the thickness and toughness of coatings varies from project to project, it took considerable trial and error to find the perfect aggregate. In this case, the crew settled on a 70/30 blend of Ervin steel shot and steel grit. e grit comprised a 25 and 40 mix. "We combine shot and grit to make the coating come off faster," said Winter. "If you run straight steel grit, you risk taking off too much, cutting too deep, and wasting paint. It's counterintuitive, but steel shot keeps the substrate from getting over-profiled." W hile a FasterBlaster remote control operator could conceivably do his job sitting in a lawn chair, it takes a small army of fervent workers to keep the blast job on pace. "e aggregate comes in 55-gallon [208.2 L] drums, so the ground crew uses small buckets to keep the hopper full," said Winter. "Between loading, recycling, vacuuming, and moving everything around the tank perimeter to keep up with the FasterBlaster, at the end of a 12-hour shift, the ground crewmen really know they've been working." W hile all this was going on, crewmen on the roof ran the same aggregate through their Blastrac EBE 500 walk-behind abrasive blaster. Others used a Schmidt 6-ton (5,443.1 kg) blast rig filled with MineralTech 30/60 garnet to attack areas that the FasterBlaster and EBE 500 couldn't reach. No one wants to run the risk of f lash rust destroy ing exterior prep work. Virtually ever y time the blast crew stopped, they used Graco 33:1 airless guns armed w ith #417 tips to spray apply 3 to 4 mils (76.2–101.6 microns) dr y film thickness (DFT) in a single pass of Dimetcote 9H inorganic zinc silicate primer. PPG's Dimetcote 9H is a solvent-borne system, so the three components ( liquid, powder, and activa- tor) were agitated w ith air-powered mi xers to prevent electric sparks from igniting the solvent vapor. POLYURETHANES STEEL EPOXY TANK

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