A Protective “Lozenge” for Steam Turbines

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Study: Film-Forming Products Can Mitigate Corrosion and Deposition of Contaminants During Power Plant Shutdowns

Film-forming products may soon become the trusted “throat lozenges” for power plant steam turbines. In a first-of-its-kind field study, EPRI demonstrated that these chemicals’ ability to form a protective layer on metal surfaces can significantly reduce corrosion in low-pressure turbines during plant shutdowns and layupslayups. This finding supports their use in the steam/water cycle prior to shutdown.

Plant shutdowns may alter steam chemistry in the phase transition zonephase transition zone

In a test loop deployed at Duke Energy’s Marshall Steam Station Unit 3, researchers installed strips of carbon steel and a stainless steel alloy containing chromium (similar to that used in steam turbines). They injected film-forming products from several manufacturers, along with corrosive contaminants such as chloride and sulfate, into low-pressure steam as it was diverted from the Marshall unit into the loop. After the loop was cycled on and off for two weeks, researchers assessed the steam’s corrosivity based on the number and size of pits on the strips. Results demonstrated the film-forming products’ superior protective ability to arrest pitting on the strips during plant shutdown and layup conditions relative to conventional steam chemistry.

The study’s authors point to the importance of carefully evaluating each film-forming product before use because some may contain constituents that could adversely impact steam/water cycle components.