Pittsburgh, November 29, 2007 - In 1986, a powerful twister ripped through the Port Neal Power Plant owned by Iowa Public Service Company, now MidAmerican Energy. The path of destruction was huge and needed immediate attention. Not only was a large coal-conveying unit destroyed, but roofing was torn off and siding was ripped away. One entire side of the facility in Sergeant Bluff, near Sioux City, was virtually sandblasted by wind-blown gravel.
Rebuilding and repairing the many tanks, structural members and trusses was no easy task. But 20 years after the fact, there's still a powerful story to tell - and it revolves around the selection of what was then a revolutionary new coating system.
When the project was put out to bid, the public utility specified a four-coat, conventional alkyd system, similar to the one used when the plant was constructed in 1976. But coating manufacturer Tnemec Company of Kansas City, Mo., had a better idea.
Instead of the slow drying and extremely labor intensive alkyd system, Tnemec recommended a two-coat polyurethane system that would provide better long-term protection as well as significant cost savings in application time and labor.
H.M. Watkins Company of Omaha was selected as the paint contractor and immediately went to work. Wherever possible, surfaces were sandblasted in accordance with SSPC-SP6 commercial blast cleaning. Next, airless spray guns were used to apply 3 mils of Tnemec Series 90-97 Tneme-Zinc, a moisture-cured zinc-rich primer that incorporated an aromatic polyisocyanate from Bayer MaterialScience. The Watkins crew applied a 3 mil topcoat, using Tnemec's Series 73 Endura-Shield, a high-build, acrylic polyurethane finish, which was manufactured using Desmodur N aliphatic polyisocyanate from Bayer MaterialScience. In all, nearly 4,000 gallons of primer and topcoat were sprayed and brushed on more than 550,000 square feet of tanks, silos, coal conveyors and other steel structures at Port Neal.
Four years after the application, a report noted that the durable finish looked "practically as good as new." Follow-up inspections showed good gloss and color retention and no signs of chipping, peeling or weathering. Today, more than 20 years after the polyurethane coating system was applied, the finish remains in excellent condition. A visual survey in April 2007 shows that corrosion has been minimal, and very little maintenance has been required.
According to Carl Angeloff, P.E., Head - NAFTA Business Development and Manager - BD Corrosion, Bayer MaterialScience, "There couldn't have been a better choice for this application. The polyurethane coating system is designed to out-perform epoxies and alkyds, and stand up to severe conditions. Even the harsh combination of sub-zero Iowa winters and red-hot fly ash likely won't affect this durable finish."
The public utility was so pleased with the coating system used on their Port Neal facility, they specified a similar two-coat polyurethane system for a sister plant upstream. "With a conventional four-coat system, labor costs would have been significant," says Tnemec's local coating consultant Kevin Greteman, with Schmit-Greteman Associates of Omaha. "The two-coat polyurethane system provided dramatic labor savings, which contributed to an overall cost reduction of about 20 percent." Better yet, MidAmerican Energy is now achieving even greater savings now that they see the long-term durability of the polyurethane system.
Bayer MaterialScience LLC is one of the leading producers of polymers and high-performance plastics in North America and is part of the global Bayer MaterialScience business with nearly 14,900 employees at 30 sites around the world and 2006 sales of 10.2 billion euros from continuing operations. Our innovative developments in coatings, adhesive and sealant raw materials, polycarbonates, polyurethanes and thermoplastic urethane elastomers enhance the design and functionality of products in a wide variety of markets, including the automotive, construction, electrical and electronics, household and medical industries, and the sports and leisure fields. Our inorganic basic chemicals unit produces chlorine and related essential products for the chemicals industry. Let us give life to your vision. Bayer MaterialScience - Where VisionWorks.
Bayer Corporation, headquartered in Pittsburgh, is a subsidiary of Bayer AG, an international health care, nutrition and innovative materials group based in Leverkusen, Germany. In North America, Bayer had 2006 net sales of 7.8 billion euros and employed 17,200 at year end. Bayer's three subgroups, Bayer HealthCare, Bayer CropScience and Bayer MaterialScience, improve people's lives through a broad range of essential products that help prevent and treat diseases; protect crops and enhance yields; and advance automobile safety and durability.