CoatingsPro Magazine

JAN 2019

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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42 JANUARY 2019 COATINGSPROMAG.COM e water in this tower was drained for about eight weeks, the duration of the project. e wet bowl is where the crew started. ey began by abrasive blasting to achieve NACE No. 2/Society for Protective Coatings (SSPC) Surface Preparation (SP) 10: Near-White Blast Cleaning to prep the steel, which results in a surface that is free of dust, dirt, mill scale, rust, coating, and oxides. W hile one crewmember manned the blast nozzle, another member of the crew filled the Clemco pots with Black Beauty 20/40 grit. Once the blasting was done, the crew shoveled out any remaining spent abrasive material from the tank 's interior, removed it from the site to have it tested and disposed, and then took an air nozzle to blow any dust off the walls. e crew was sure to wear full air-fed blast hoods when blasting and full-face respirators when shoveling. With the metal prepped, the crew moved on to spray applying the primer, Tnemec 94-H₂O Hydro-Zinc. at is a moisture-cured, zinc-rich primer that has been used in the industry for more than 20 years. It can be used as a primer both inside and outside of water tanks, as it has been approved in accordance with NSF/American National Standards Institute (ANSI) 61: Drinking Water System Components – Health Effects. e crew would blast every day and then get the priming done immediately afterward in case the dew point dropped or it rained. Any amount of moisture can cause the steel to flash rust, which is clearly a problem. e crew used a Davis weather machine and pyschrometers to measure the dew point. After applying the primer throughout the tank 's interior at an average of 3 mils (76.2 microns) dry film thickness (DFT), the crew applied two coats of Tnemec N140 at 4–6 mils (101.6– 152.4 microns) DFT each. "We have used Tnemec's products for many years and are very happy with the quality," said Penny. e feeling appears to be mutual: Ozark received Tnemec's Tank of the Year award in 2014 and was a runner-up in 2015. In total, the crew covered the approximately 6,400 square feet (594.6 m²) of steel that created the wet bowl using equip- ment from Graco. Rising to the Top A dry riser of a water tower is normally used by firefighters. It is a typically empty pipe that can be externally connected to a pressurized water source. It's where the ladder, landings, and belly of the tank are located. For PWSD #1's tower, the entire dry riser is 5,100 square feet (473.8 m²). e crew blast-cleaned the area using NACE No. 4/SSPC-SP 7: Brush-Off Blast Cleaning. ey spot primed using Tnemec N140 and then applied a full coat of N140 at 4–6 mils (101.6–152.4 microns) DFT. T he interior access tube is the dr y cylinder area that runs through the wet bowl and allows someone to climb up to the top of the tank. T his tube is approximately 3 feet (0.9 m) in diameter and 50 feet (15.2 m) tall, and it's approximately 700 square feet (65.0 m²). It was prepped to NACE No. 3/SSPC-SP 6: Commercial Blast Cleaning, and then the crew spray applied one coat of Tnemec 94 -H₂0 at an average of 3 mils (76.2 microns) DFT. It's very common to have moisture inside this area of the water tower, which leads to quicker steel deterioration and corrosion. e tank is pumping water from ground level. In the summer months especially, the ground water might be 55 ° F (12.8 °C) whereas the tower temperature could be 100 °F (37.8 °C). W hen this cooler water enters the dry riser, it can cause the pipes to sweat, and more moisture forms. To combat the moisture, the Ozark team applied two coats of Tnemec's Series 971 Aerolon Acrylic to the access tube and the belly of the tank (aka the rounded bottom that's exposed to the interior dry riser), covering approximately 1,900 square feet This was the crew's first time applying the Aerolon coating, so the crew headed to Tnemec's headquarters in Kansas City to receive training. It was spray applied using an airless pump. The crew needed to use a variety of equipment on this job, including the spray equipment for the coatings and tools to measure dew point. Missouri Water Tower

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