Damage evaluation of fossil fuelled power plant boiler tubes through magnetic Barkhausen technique

Abstract

The failure mechanism of two economizer tubes of a fossil fuelled 260MWpower plant has been investigated through the magnetic Barkhausen emission (MBE) technique along with the conventional and established materials characterization and evaluation techniques (like microstructures, mechanical properties and X-ray diffraction). The longer service exposer period results in the breaking of ferrite–pearlite structure and spheroidization lamellar cementite in ferrite matrix, associating with high magnetic r.m.s. voltage for former structure. The failure mechanism was governed by the cold end corrosion process with the presence of sulfates, and the subsequent erosion through hard quartz particles leads to a localized thinning of outer surface. Accordingly, the hoop stress was operative in tube walls and failed through fish-mouth opening. The MBE r.m.s. voltage response and pulse height distribution throw light on microstructural changes with duration of service exposure as well as leaked and non-leaked regions of economizer tubes.