Lining System Enables Fast Return to Service for Minnesota Water Storage Tower

Situation
When the time came to restore the 500,000-gallon Sterling Ave. water tower serving the Maplewood, Minnesota, community, the project team was interested in a fast return to service to minimize the tower’s time offline. Time was also of the essence with a frigid Minnesota winter coming close on the heels of the project’s start. Given these constraints, a team including utility provider Saint Paul Regional Water Services, consulting services firm Short Elliott Hendrickson Inc. (SEH®), restoration contractor TMI Coatings, Inc. and Sherwin-Williams Protective & Marine brainstormed solutions. The team ultimately arrived at applying a 100% solids, glass-flake reinforced lining system that enabled a fast return to service. This was the first tower to feature this interior lining system.

Execution
The team chose to apply Sherwin-Williams Dura-Plate® 6000, a durable, 100% solids glass-flake reinforced lining system that offered a return-to-service time of just 10 hours following the final application. The high-build, high-strength reinforced epoxy lining system had just completed NSF/ANSI/CAN 600 testing, making it an excellent choice for a potable water tower lining. With the project commencing in September, the fast-curing coating would enable TMI Coatings to complete the lining application in late fall in Minnesota. In addition, the glass-flake reinforced lining would also provide a life expectancy greater than a conventional three-coat zinc/epoxy/epoxy system due to the coating’s extremely low permeability and excellent abrasion resistance.

To install the lining system inside the spheroidal Sterling Ave. tower, a crew from TMI Coatings first prepared the interior tank surfaces to the SSPC SP-10/NACE No. 2 near-white metal blast cleaning standard. Next, crewmembers applied a stripe coat of Sherwin-Williams Corothane® I GalvaPac 1K Zinc Primer to welds before spraying a full coat on the interior surfaces at 2 to 4 mils dry film thickness (DFT). This moisture-curing urethane zinc-rich primer provides resistance to corrosion and enables cathodic protection to help protect the tank’s steel from deteriorating. Applicators then sprayed the reinforced Dura-Plate 6000 lining at 30 to 40 mils DFT in a single coat using plural spray equipment, with the ability to spray up to 125 mils DFT to fill in any pits. TMI Coatings had the option to spray the high-build coating using single-leg equipment but opted to spray the tank using a plural component spray pump due to the elevation inside the tank and the number of gallons needed for the project.

Aesthetics were the focus for the water tower’s exterior, prompting the team to specify Sherwin-Williams Acrolon™ Ultra for the tank’s top coat. The high-performance acrylic polyurethane offers exceptional long-term color and gloss retention, as well as excellent resistance to corrosion and weathering. It can also be applied at thinner DFTs of just 2 to 3 mils compared to 3 to 5 mils for conventional polyurethanes. Applicators from TMI Coatings first prepared the tank’s exterior to the SSPC SP-6/NACE No. 3 commercial blast cleaning standard and then applied a 2- to 4-mil DFT primer coat of Corothane I GalvaPac. Next, they applied an intermediate coat of Macropoxy® 646 Fast Cure Epoxy at 4-6 mils DFT as a protective layer before adding the Acrolon Ultra topcoat. For the finishing touches, applicators hand painted a logo featuring the Maplewood community name and an artistic maple leaf drawing. To ensure long-term color and gloss retention for the brown and maroon logo, applicators used Fluorokem® HS 100, a premium, ultra-durable fluoropolymer urethane finish that offers superior exterior durability.

Outcome
Upon completion of the coating applications, the tower rehabilitation project faced its final test – a discerning panel of taste testers that had to approve water samples from the newly lined and filled tank before it could be approved for servicing the Maplewood community. No tank has passed the panel on the first try in about 15 years. If the panel expressed any taste or odor concerns, Saint Paul Regional Water Services would need to drain and refill the tank – perhaps multiple times – until the panel approved the new samples, with each draining of the tank wasting water, time and money. Given the 100% solids lining system’s chemistry, the project team had no worries about the test. Still, the team was relieved to learn the panel passed the first samples without hesitation, enabling Saint Paul Regional Water Services to place the tank online immediately thereafter.

The utility provider returned the tower to service just 30 days after starting the restoration. This timing was possible due to the easy application and fast-curing properties of Dura-Plate 6000 for the lining, as well as the streamlined exterior coating system application. In addition, the taste panel’s approval of water samples from the first tower fill enabled immediate service, proving the project team made the right choice in specifying the new lining system.