Solid-particle erosion and protective layers for steam turbine blading

Abstract

Solid particle erosion of steam path surfaces is a major concern in steam turbines. This is mainly due to the formation of magnetite on the inside of boiler tubes. This builds up, spalls and travels along with the steam causing erosion in areas where steam velocities are the highest. The steam velocities are the highest in the high pressure sections of steam turbines. The erosion depends upon the base material and steam flow conditions. The base material is generally protected by plasma/detonation sprayed and thermo-chemically formed diffusion coatings. In this paper prevention and visualisation of erosive wear of two dimensional steam turbine 12Cr steel blading under similar Reynolds number to that of steam turbines is described. For erosion visualisation, a rotating disc apparatus has been used. From the study, it was observed that erosion of complicated steam turbine blading depends upon the flow conditions especially flow separation, reattachment and boundary layer growth. The flow visualisation was obtained from the replicas which were etched on the aluminium disc due to erosive wear. Further, to control the erosive wear of steam turbine blading, these were given a hard diffusion layers based upon boronising. The performance of these hard diffused layers along with erosion visualisation of 12Cr steam turbine blading are reported in this paper.