What Works: Damp pipes not a problem to polyurethane coating

June 4, 2008
In this "What Works" installment, a moisture-cured coating renews protection of pipes at the Hammond Water Filtration Plant in Hammond, Ind.

When maintenance was required inside the Hammond Water Filtration Plant in Hammond, Ind., more than 35,000 square feet of piping and valves were coated with a moisture-cured polyurethane system.

The plant, which was built in 1936 and renovated in 1950 and 1970, posed numerous repainting challenges. Some of the pipes had never been coated, producing serious corrosion problems. There were no coating records, but it was likely that lead was present. It was imperative to remove the rust and any lead-based paint before any recoating, but cold water piped into the plant caused significant condensation, making coating extremely difficult. There was no chance of shutting down or taking any of the pipes out of service since the plant filtered 70 million gallons of water per day.

In October 2004, Hammond called upon Dixon Engineering (www.dixonengineering.net) to evaluate the project and make recommendations. Ira Gabin, vice president for Dixon, says, “Performance and aesthetics were the major considerations – they wanted the job to last and look good 15 to 20 years from now. It was a huge project, and it was going to take a really experienced coatings contractor. The crew would be limited to working in winter months when pipe sweating is minimal. In late spring and summer, you’d get huge differentials in water temperature, and it would be like walking through a waterfall in there.”

Dixon Engineering specified a moisture-cured urethane (MCU) system formulated from raw materials manufactured by Bayer MaterialScience LLC (www.bayermaterialsciencenafta.com). They called on Sherwin-Williams (www.sherwin-williams.com), which agreed to deliver the paint within a week’s time. The Sherwin-Williams system consisted of two different Corothane primers to be used on two types of pipes, plus an intermediate coat of Corothane I IronOx B, and a Corothane I aliphatic topcoat. Given the conditions inside the plant, Gabin noted that “The MCU system opened a bigger painting window for us.”

Specifications were sent to 17 paint contractors, and 14 came to the site for a mandatory pre-bid walk-through. Eight companies submitted bids. In January, 2005, Era Valdivia Contractors, Chicago, was awarded the job. Project Manager Greg Bairaktaris says, “We walked this plant twice just to make sure we were comfortable with the logistical challenges. The bottom line was going to be proper planning and execution.”

Work was scheduled to be completed in two phases so it could be performed in the cooler months. Era Valdivia began Phase I in March 2005. Work needed to be done upstairs and downstairs, and the painting crew had to carefully stage their hoses and other equipment around the plant staff’s work area. Plant Superintendent Gary Williams admits he was nervous about protecting valves, controls and other vulnerable equipment.

Greg Bairaktaris notes that the surface preparation was particularly challenging. Dehumidification was necessary to remove condensation from the pipes to hold the blast. If dehumidification was not used, flash rusting would have occurred.

The substrate was mostly steel, to be blasted to SP10 specification before it was coated with Corothane I GalvaPak. Cast iron pipes were prepped to SP6, then coated with Corothane I MIO Zinc. The moisture-cured Corothane system compensated for some of the on-site problems, because it could be applied to damp pipes and could handle some flash rusting. “It was hard to get the surface clean enough and moisture-free,” Bairaktaris says. “You couldn’t get that cast iron to near-white. But the moisture-cured system solves problems on the engineering side, as well as on the application side.”

Once the primer was applied, the intermediate and topcoats followed. Since all the pipes needed to be color-coded, the topcoats were made with six pigments. And because the Corothane I aliphatic topcoat emitted a low (3.5) VOC, the plant could remain in operation even during the final stages of the maintenance project. “It was a difficult application,” Bairaktaris says. “We needed to use a combination of brush, roller and spraying techniques. We’d spray the piping system first, then cut around it for the color-coded piping. It wasn’t a straightforward job.”

Era Valdivia completed one room at a time during Phase I, before tackling Phase II in January 2006. Both phases were completed on time. In all, the project spanned two years and took 900 gallons of coating. “We’re very happy with the way it turned out,” Hammond’s Gary Williams says.

“This was the only project of this scope that we had done with MCUs,” says Ira Gabin of Dixon. “But in an environment like this, I would spec this MCU system again without concern.”

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