The Right Coatings Make All the Difference in Storing and Protecting a Water Plant's Critical Equipment

Manual surface preparation and humidity-tolerant coatings enable in-service rehabilitation of equipment in a water plant pipe gallery.

The Right Coatings Make All the Difference in Storing and Protecting a Water Plant's Critical Equipment

For the first step of the restoration, CMT crew members performed solvent cleaning. 

“The pipes were sweating so much they looked like they had just finished running a race.”

That’s how David Van Zee, co-owner of Carolina Management Team (CMT), described the steel pipes serving the filter pipe gallery at the Kerr Lake Regional Water Treatment Plant in Henderson, North Carolina.

Located inside a temperature-controlled building, the pipes sweat nearly continuously as cool water pulled from the John H. Kerr Reservoir (Kerr Lake) runs through the plant. The warm environment is ripe for condensation on the pipes and surrounding equipment. The condensation was an obstacle Van Zee and his infrastructure rehabilitation team had to overcome as they planned to restore protective coatings on the pipe gallery equipment.

The Kerr Lake Regional Water System last restored the gallery’s pipes, valves, pumps, motors and other equipment in 1996. After 20 years in the humid environment, the coatings had begun to deteriorate and flake, showing visible signs of substrate corrosion. Without preventive steps, corrosion would continue.

Full rehabilitation was needed, from removing existing coatings to priming and topcoating the surfaces, and the 10 mgd facility needed to stay in full operation throughout the project to serve some 50,000 customers. No part of the pipe gallery could be taken out of service for maintenance, meaning condensation would be ever-present. Furthermore, the ideal surface preparation method of abrasive blasting was not an economical option.

Faced with these challenges, the crew performed manual surface preparation and then applied two moisture-tolerant coating technologies from Sherwin-Williams Protective & Marine Coatings. This ensured minimal disruptions to plant operations, while providing a quality, durable finish. The successful restoration earned CMT and the City of Henderson an honorable mention in the 2017 Sherwin-Williams Impact Award program, which recognizes outstanding water and wastewater projects.

Manual preparation

Due to numerous hardware connections and sharp edges on the assets being restored, abrasive blasting would have been ideal for surface preparation. However, blasting in an operational water plant requires an extensive temporary containment system to protect equipment and plant personnel. The time-intensive setup was impractical.

Instead of sandblasting, the four-member crew followed a two-step surface preparation process. First, they soda-blasted the surfaces following SSPC-SP1 Solvent Cleaning guidelines, removing a significant amount of rust and the existing coating. The slurry of water and baking soda lightly abraded any coating that remained on the surfaces to provide a good bonding profile for the adhesion of new coatings.

Next, the crew used hand and power tools to clean the many pipes, nuts, bolts, and flanges, removing all loose mill scale, rust, and coatings to leave an SSPC-SP2/SP3 surface. The crew also lightly abraded and profiled any remaining coatings to create smoother transitions from uncoated to coated areas so that the new coatings would provide a smooth finish with sufficient film builds and edge retention.

Coating the wet assets

After surface preparation, the crew next had to prime and coat the pipe gallery assets, some with damp exteriors due to condensation. The best way to stop the condensation would have been to shut the systems down, but that was not an option.

The next option was to dehumidify the pipe gallery and reduce the temperature to 5 degrees below the dew point to mitigate the condensation. However, this would be costly and potentially ineffective during February, with the plant drawing in cold lake water.

To overcome the challenge of coating the wet substrates, CMT selected two moisture-tolerant coatings from Sherwin-Williams. The products react with moisture in the air and on substrates, curing in place to form a durable protective coating film. They require moisture to cure, making them highly suitable for the conditions within the gallery.

“You typically don’t coat an asset when it’s wet, so we came up with a system to address this environmental issue,” Van Zee says. “Using two moisture-tolerant technologies enabled us to restore the pipes and surrounding components with minimal disruptions to plant operations.”

For the primer coat, CMT selected Dura-Plate 301K, a surface- and moisture-tolerant epoxy product that can be applied with no dew-point restrictions over marginally prepared surfaces, including damp steel and flash-rust. CMT specified the high-solids epoxy for its ability to be used on damp substrates. In addition, its high edge-retention properties (70 percent) helped ensure a sufficient film build on the sharp edges of numerous nuts, bolts, and flanges. The crew applied this base coat at 4 to 8 mils dry film thickness.

Metal protection

Before applying the subsequent coating layers, CMT needed to protect the exposed steel between multiple flanges throughout the pipe gallery. The steel in these zones where pipes are bolted together needs to be left uncoated to permit future maintenance. In those voids, crew members applied Stampede polyurethane sealant, a caulking material with 100 percent solids that resists shrinking.

Finally, CMT applied two coats of Corothane I HS at 3-5 mils DFT per layer for the intermediate coat and topcoat. The moisture-cured urethane is designed for high-humidity applications. The single-component, high-gloss coating offers high color and gloss retention to provide a durable, aesthetically pleasing look. The coating allowed CMT to color-code equipment, including coating valves orange and pumps and piping blue.

“The Corothane I HS coating has a wet look that doesn’t dull out, almost like an automotive finish,” Van Zee says. “The completed filter pipe gallery looks very professional. The coating looks as good as it protects.”

Because CMT did not set up a containment system for surface preparation, the crew applied the coatings manually to avoid overspray that could potentially be taken up by running motors or fans. Brushing on the coatings also ensured 100 percent coverage on surfaces throughout the gallery.

Complete restoration

Despite the inability to use best practice surface preparation methods and the need to coat sweating pipes and equipment, CMT restored the filter pipe gallery to like-new condition while the plant stayed in operation.

“Carolina Management Team delivered a coating restoration project that was minimally disruptive to our operations, while overcoming significant surface preparation and moisture challenges,” says Christy Lipscomb, water system director. “The plant now has a filter pipe gallery that is visually stunning with a high-gloss, wet-looking finish. We look forward to showing it off during future plant tours.” 


About the author

Kevin Morris is market segment director, Water & Wastewater for Sherwin-Williams Protective & Marine Coatings. He is a NACE Level III Certified Coatings Inspector, a Certified Concrete Coatings Inspector with the Society of Protective Coatings, and an instructor for the Society of Protective Coatings – Concrete Coatings Basics and Concrete Coatings Inspector Programs. He can be reached at kevin.l.morris@sherwin.com. 



Discussion

Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.