Microstructure analysis and crack detection in turbine blades after prolonged exposure in plant

Abstract

Turbine blades are one of the most important machine parts in every power generator. Corrosion and/or erosion attack on blades are also available in moisture atmosphere, because the wet water vapour is an usual working media in low pressure turbine. After long time in service, the initial structure is changed Some pores were metallographically detected and their aggregation combined with probable coagulation around non-metallic inclusions is observed Those pores can lead to the crack formation. Serious problems may arise due to these non-metallic inclusions since they are surrounded by a number of individual pores or even characteristic "clouds" of pores are formed around inclusions. From the aspect of blade vibrations, the crack will be expected only at some positions. This kind of crack usually is initiated at the blade surface. In another case, when an aggregation process of pores occurs, the coagulation and coarsening of pores may provoke the crack initiation not on the surface, but in the bulk of the blade material. Metallographic investigations were performed using light microscope.