The creep lives of enhanced high-temperature strength and creep resistance of 9%Cr 1%Mo P91 steels in boiler and piping systems of high-temperature plants are limited by the formation of cavitation. P91 steels are characterised by various secondary phases and a complex grain boundary microstructure which leads to regions of increased stress accumulation resulting in the initiation of cavities. In order to predict and possibly extend the creep lives of P91 structure components in energy applications, it is important that the processes promoting the initiation and early growth of cavities are understood. This paper employs microscopy techniques as well as image segmentation tools in order to quantify and characterize the cavitation and the secondary phases present in ex-service and creep tested P91 samples.
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