MAGNA-Coat Industrial Coatings, Georgetown, TX, has developed what it says is an effective method of preventing this problem. The company can extend the service life of new and existing cooling towers by spraying the inside of the towers with an elastomeric polyurethane coating from Bayer Corp., Pittsburgh, PA. The result is cost savings, as well as fewer headaches, for building owners and managers.
With 25 years experience in the hvac industry, Mike Swearingen, president of MAGNA-Coat, saw how the inside of cooling towers could corrode prematurely. He also noted how attempts to protect towers had mixed results, in part because the linings used had difficulty withstanding harsh conditions inside the tower and adhering for an extended period of time. “Adhesion is the key,” he explained.
HOLDING HARSH CONDITIONS AT BAYSwearingen experimented with several polyurethane products, surface preparation techniques, and spraying conditions. He found a solution in the Baytec® SPR polyurethane spray elastomer system from Bayer's Polyurethanes Division.
With a Shore hardness of at least 66A, as well as added ultraviolet (UV) stabilizers, the Baytec SPR system is used in spray applications to improve the corrosion, weather, and abrasion resistance of metal, concrete, wood, and plastic materials. Typical uses include protective layers for wood and industrial surfaces, and liners for pipes and tanks.
The long-term corrosion protection and adhesion of the system has been proven in field use. The deck of a Norwegian fishing vessel sprayed in 1967 was still intact and preventing corrosion 17 years later in 1984. In Germany, sheet steel profiles on a sea wall were still in good condition 14 years after they were lined, beneath layers of algae and barnacles.
“In addition to its excellent adhesion properties, it is also easier to apply,” said Swearingen. “In fact, I haven't found a polyurethane product that is as forgiving as Baytec SPR in regard to the ambient conditions, such as humidity, dewpoint, and temperature, under which you can spray.” Swearingen applies the polyurethane elastomer to the inside of cooling towers using a computerized, metered spraying system equipped with electronic temperature control. While spraying time varies by project, he said it typically takes three to four hours to coat the inside of a cooling tower. The polyurethane dries to the touch in just a minute or two, and fully cures in approximately 24 hours, he related.
While the coating system is a constant in the equation, Swearingen evaluates other variables (such as tower age, condition, and manufacturer) on a project-by-project basis, tailoring his proprietary preparation method accordingly. “No two towers are exactly alike,” he explained.
COATING MAKES THE SAVEAccording to Swearingen, his lining process can markedly extend the service life of deteriorated cooling towers for approximately a quarter of the cost of installing a new tower.
Ken Anderson, chief engineer at Regency Office Center in Austin, TX, called upon MAGNA-Coat when his complex's 360-ton, two-cell cooling tower started to pit and deteriorate less than six months after installation.
The facility drained the 12- by 15-ft tower, and Swearingen sprayed the polyurethane elastomer inside. Now, more than a year later, the polyurethane lining is holding up very well, according to Anderson.
“The beauty of this elastomer system is that you can take something that is rusting and greatly extend its life,” he said, adding that lining the 22-year-old evaporator coil drain pan of the complex's cooling tower is now under consideration.
In fact, Swearingen recently completed this type of project for Dobie Center, a multi-use facility incorporating a 30-story dormitory, retail complex, and six-story parking garage on the University of Texas campus. The factory service arm of Carrier Corp. contacted Swearingen to line the condensate pan for the 30-year-old air-handling unit in the dormitory's cafeteria.
“In places, the pan was rotted through and was leaking,” explained Jack Preston, Carrier service manager.
The pan was cleaned, patched, and sprayed, saving Dobie Center the expense of replacing the entire unit. As a preventive measure, Swearingen also sprayed the water basin and associated parts of two new outside makeup air units that service the cafeteria's kitchen. Larry Dougherty, chief facility engineer for Dobie Center, is pleased with the results. “I was especially impressed with how the polyurethane adhered to the corroded pan,” he said, adding that he plans to have MAGNA-Coat apply the elastomer to the pans for the Center's 20-year-old cooling tower during the next scheduled maintenance shutdown. “For patching and repairing, I don't think you could find a better product.”
CHURCH IS A BELIEVERIllustrating the effectiveness of the coating and his proprietary lining process, Swearingen also sprayed the drain pan of Tarrytown Baptist Church's nearly 50-year-old wooden cooling tower, in Austin, TX. Other contractors considered the tower a lost cause, but Swearingen had faith in the polyurethane system.
“He was the first to tell us that it was worth saving,” said Beth Frank, minister of education and administration.
Swearingen lined the pan in May 1999, and it has held up “incredibly well, and saved us a huge expenditure,” said Frank, adding that, as a preventive measure, the church may ask MAGNA-Coat to spray the wooden slats around the cooling tower as well.
The latest application of this technique was a 400-ton cooling tower that served 80% of a hospital's hvac system in the Austin, TX, area. Over the course of a single weekend, Swearingen drained and cleaned the tower, then lined it with the polyurethane elastomer. His assessment was that the tower had approximately three years of service life remaining due to heavy corrosion. By coating the tower, he estimates it could remain in service “for as long as 25 more years.”
Swearingen added, “Facilities that have purchased a new cooling tower recently, or that plan to purchase one soon, should also consider coating the new tower to help prevent corrosion from developing.”
For more information on the lining process for cooling towers from MAGNA-Coat, visit www.nocorrode.com. For more information on the polyurethane spray elastomer system from Bayer, visit www.bayer.com/polymers-usa.
Publication date: 07/09/2001