Praxair News, July/August 2004
New Life for Old Turbines
TAFA-Sprayed Surface Lasts Five Times Longer Praxair Surface Technologies’ TAFA subsidiary in Concord, New Hampshire, has a uniqueapplication for hydroelectric companies that operatein areas where the water contains high particulateconcentrations and is very abrasive. Insteadof repairing the worn-out turbine wheelsevery three or four weeks, why not spray them with a coating that allows them to operate for more than six months without a repair? The process not only extends the operating life, butsaves thousands of dollars in weld-repair and labor costs for each water wheel. TAFA’s Equipment & Services Business Unit Manager Richard Thorpe developed the solution for coating the pelton wheel, a water turbine used by many hydroelectric companies, in 1996. Each pelton wheel has 21 arms, with a “bucket” at the end of each arm. Water is channeled into the turbine, hitting the wheel at high pressure and causing it to spin and generate electricity. In contrast to the United States or Europe, in some regions, such as Peru, Chile, China, India and Nepal, the water has extremely high levels of quartz and silica, which quickly erode the wheel’s surface and decrease its generating efficiency.
“Power companies try to keep the turbines’ generating efficiency high by constantly rotating and servicing the wheels,” Thorpe explained. “When the wheels are sprayed with a tungsten-carbide- type material, they last five times longer.”
TAFA’s first customer was Chilgener, an electric company in Chile, located in Santiago. “The coating extended the life of our turbine from 40 to over 200 days,” said Chilgener Production Manager Juan Moggia, “and we needed only 660 pounds of stainless steel for weld repair instead of 2,200 pounds.”
Thorpe explains how the process works. “We take a powder made of 86 percent tungsten carbide, 10 percent cobalt and four percent chromium, which is manufactured at our Indianapolis, Indiana, powder facility,” he said. “We run it through our high-velocity, oxy-fuel spray gun, Richard Thorpe says he’s trying to expand the coating’s use to India and other developing countries that need more power. where it’s semi-melted, accelerated to 500 to 700 meters per second velocity and then applied to the wheel’s surface.
The coating formed is extremely dense and hard, so it protects the wheel from damage for much longer period of time.” The initial success at Chilgener led to sales of the spray systems and coating solution to customers in Peru, India and Nepal. “Hydroelectric power is less expensive than oil and nuclear power,” Thorpe said. “We’re trying to expand the coating’s use throughour distributors to India and other developing countries thatneed more power.”
Praxair and the Flowing Airstream design are trademarks or registered trademarks of Praxair Technology, Inc. in the United States and/or other countries. Other trademarks used herein are trademarks or registered trademarks of their respective owners. The information contained herein is offered for use by technically qualified personnel at their discretion and risk without warranty of any kind.
