Best Practices: Improved steam-piping reliability off-peak

LH 1-3Tenaska Lindsay Hill Generating Station (2007)

Challenge. During off-peak periods the plant’s capacity factor goes down, but the power purchase agreement requires the plant to be available for dispatch. This situation results in steam piping being exposed to atmospheric conditions for long periods of time. The high humidity in our region is corrosive to piping system internals. Resulting corrosion also affects valve internals with tight clearances and causes valves to stick. This can compromise facility reliability.

Solution. We developed a cost-effective way to protect the steam lines that did not impact unit start times. Plant instrument air was routed to each steam section—high (HP), intermediate (IP), and low pressure (LP)—to provide dehumidified air to the plant’s steam piping (Figs 1-3). The air is checked using a dew-point analyzer. The readings are taken at the air-compressor dryer outlet and at the end of the steam lines. A comparison is made between the two readings to ensure dry air is being fed to the entire steam system. The dew point is maintained at approximately -30F. This removes the water component from the oxygen and water corrosion reaction.

Results. Compared to previous years, the number of steam valves stuck or sticking after admitting dry air to the steam piping was reduced. Steam chemistry quality is also obtained faster after the plant has been down for long periods.