The location of the component for in-situ metallography is carefully chosen based on the knowledge about the operating conditions and stress analysis. The selected area is polished using a portable grinding machine or by electrochemical means. Subsequently, the polished surface is etched to reveal the microstructure. Examination of the polished surface directly and also the etched surface gives the useful information regarding the microstructural degradation, if any.

Inspection carried out on the labyrinth seal and curtis wheel of a 9.2 MW turbine rotor, which was under continuous operation for more than 30 years revealed normal tempered martensite microstructure. However, decarburisation, an indication for strength reduction was observed in the primary superheater outlet pipeline which carried steam at 42 kg per sq. cm at a temperature of 673 K. Microstructural degradation in the form of graphitisation was also noticed in one of the attemperator shell. Also, in yet another instance, absence of coolant through a reheater pipeline resulted in overheating of the shell damaging its surrounding insulation. In-situ metallography carried out near the damaged region revealed extensive grain growth and grain boundary oxidation. In all these cases, in-situ metallography clearly revealed microstructural degradation which helped in taking decision on the continued operation/replacement of the component