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Abstract:
Ferritic–martensitic P91 steel is widely used in high-temperature power plant components due to its excellent creep resistance and mechanical stability. However, long-term service exposure and improper heat treatment can lead to progressive microstructural degradation, resulting in a reduction of mechanical properties and component lifetime. Reliable, non-destructive methods capable of detecting such microstructural changes are therefore essential for condition monitoring and life assessment. In this study, the influence of controlled heat treatment at temperatures ranging from 200 °C to 600 °C on the eddy current (EC) response of P91 steel was investigated. Eddy current measurements were performed over a range of probe operating frequencies, and changes in resistance and reactance components were quantitatively analyzed. The EC results were correlated with detailed microstructural observations, revealing a strong relationship between electromagnetic response and recovery and tempering phenomena, including dislocation density reduction, martensite lath degradation, and carbide coarsening. The findings demonstrate that eddy current testing is highly sensitive to thermally induced microstructural evolution in P91 steel and shows significant potential as a non-destructive tool for assessing thermal exposure and material degradation in power plant components.

Keywords:
Non-destructive testing, Power engineering steels, Eddy current, Coil impedance,