The use of Grade 91 steel for high-temperature power plant applications can result in substantial reductions in component thickness compared to weaker alloys, resulting in reduced thermal stresses and improved service life. Although Grade 91 offers superior resistance to thermal fatigue and creep, this is dependent on the creation and maintenance of a specific microstructure, which can be altered through routine component fabrication, installation and maintenance. Electromagnetic inspection has the potential to assess the level of degradation in steel components through in-situ measurements at elevated temperatures. In this work, measurements are carried out on sections of Grade 91 power station tube, heat treated to simulate in-service conditions and mis-heat treatment and compared to measurements from machined Grade 91 samples exposed to the same heat treatments. Correlations are drawn between microstructural changes in the samples and electromagnetic properties including, coercivity, incremental permeability and magnetic Barkhausen noise. The results demonstrate the viability of electromagnetic methods for inspection of power station tubes in-situ.
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