Erosion Wear Caused by Coarse Particles in the Flow-Through Part of the Medium-Pressure Stage of T-250/300-240 Turbines

Abstract

The problem of erosion wear of the first stages of IPC-1 of T-250/300-240 turbines by solid particles is briefly described. It is shown that solid particles arriving at the flow-through part of intermediate-pressure cylinders form as a result of decomposition of an oxide film in the convective superheater piping of supercritical boilers. Fracture of the oxide film is intensified due to the temperature mode of the boiler and changes in the water chemistry. A general picture of wear of the flow-through part including guide and moving blades, shroud seals, and elements of the peripheral zone of the first intermediate-pressure stages by solid particles is presented. Wear of the flow-through part reduces the service life of the blading to two interrepair periods and substantially worsens the efficiency of operation of the intermediate-pressure part. The mechanism of motion of solid particles in the flow-through part is described and the ways to decrease the wear by removing solid particles from the hot reheat line, shutoff valves, and the first intermediate-pressure stage are considered. The latter method has been realized in the form of a protection system containing continuous or periodic double-loop blow. The first loop extracts a steam sample with solid particles from the steam-in box and the second loop removes solid particles from the increased blade clearance of the first stage into a separator-accumulator from which the cleaned steam is returned to the nearest extraction of the turbine. The operating experience of such a system confirms its expedience.