CoatingsPro Magazine

MAY 2018

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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46 MAY 2018 COATINGSPROMAG.COM glass/garnet mix, the men set out to bring the tank walls to NACE No. 2/Society for Protective Coatings (SSPC) Surface Preparation (SP) 10: Near-W hite Blast Cleaning with an approx- imate 4-mil (101.6 microns) anchor profile. But the old epoxy coating wasn't giving up without a fight! e Texans needed help. Peel Them "We could either stand around or shoulder together and help," said Carlisle. "is blast took all nine of us two full days. I'm not sure what the existing 20- to 30-mil [508.0‒762.0 microns] epoxy was, but it was tough! In a lot of areas, the blast media would just bounce right off. In those places, our guys used Milwaukee Sawzalls, blades laid flat, to cut edges into the coatings. We'd then physically peel them up once piece at a time. e pieces were tiny; you'd be happy to get a 5-inch [12.7 cm] section. W hen they blasted, the nozzle man took care not to spend too much time on one spot. e topcoat was well-ad- hered to the primer, so the idea was to try not to remove all the primer. Doing so could actually damage the steel by taking it way beyond the 4-mil [101.6 microns] anchor profile specified." It was Saturday afternoon, and the 9-man crew had their hands full with the abrasive blast when bad news arrived. Weather radar showed a thunderstorm bearing down on the Simplot plant, due to arrive in less than 24 hours. e crew hustled to finish blasting, headed home, and set their alarm clocks early. Sunday at daybreak, they spent four hours covering the freshly blasted tank walls with plastic sheeting. Anything to keep moisture out! Right on cue, the storm came through. But the weatherman had it wrong! Rather than rain, the storm packed 30 to 40 mph (48.3‒64.4 kph) winds. "It's one of those things I have to laugh about, otherwise I'd be crying," said Carlisle. "e thunderstorm came through — more a raging dust storm — and completely ripped up all the plastic. It was gone. To this day I have no idea where all those 10- by 20-foot [3.0 m x 6.1 m] sheets ended up. I'm just glad they didn't wind up on the highway somewhere wrapped around someone's car." e dust storm caused another setback Monday when the blast crew had to hit the walls with a light blast (NACE No. 4/ SSPC-SP-7: Brush-Off Blast Cleaning) to knock off any surface corrosion that may have formed. Flash rust can materialize in hours on bare metal. And a bad Monday was about to turn into a bad Tuesday! "e abrasive blast uncovered several rough patches that needed welding," said Quenzer. "W hen the tank is running, which is most of the time, it's full of murky liquid, so you really can't see what's going on with the coatings. We had to address that issue then and there." e clarifier's interior walls need to be smooth because the rotating weir (aka rake-like device) arms are tipped with squee- gees. If the squeegees were to come into repeated contact with a grossly uneven spot, they could abrade and tear up the coatings. e prospect of a major clarifier tank failure is so daunting that Simplot keeps entire steel replacement panels, pre-bent to the proper circumference, in inventory. ankfully, none were needed on this project. Three Eyes With welding and prep complete, Carlisle rigged up his Graco EXP-2 with an AP Fusion gun armed with a #37 round tip. W hen held approximately 48 inches (121.9 cm) from the substrate, the #37 produces the 18-inch diameter (45.7 cm) round pattern Carlisle likes to see. is hard-working project manager was dog tired, but with only one day to spray the wall, and one to do the trough, he'd just have to suck it up. Now, spraying polyurea can get pretty wild. "e chemicals come out so fast and are so heav y that if you squeeze the trigger and the gun's not moving, and you're not at least 4 feet [1.2 m] away, it will puddle instantly," said Carlisle. "You really need three eyes. One to see what you're currently spraying, another to check what you just sprayed, and the third to watch where you're about to spray." The client needed the steel walls to be smooth so that the squeegees on the end of the rotating weir (aka rake-like device) didn't tear up the coating. That meant smoothing welded spots. Especially when spray applying the 80-100 mils (2,032.0-2,540.0 microns) dry film thickness (DFT) of the polyurea, the crew wore personal protective equipment (PPE), including Tyvek suits, gloves, respirators, and eyewear. Wastewater Tank

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