The super-heater and re-heater tubes of the boilers used in thermal power plants are subjected to unacceptable levels of surface degradation by the combined effect of erosion–corrosion mechanism, resulting in the tube wall thinning and premature failure. The nickel-based superalloys can be used as boiler tube materials to increase the service life of the boilers, especially for the new generation tra-supercritical boilers.
The aim of the present investigation is to evaluate the erosion–corrosion behaviour of Ni-based superalloy Superni-75 in the real service environment of the coal-ﬁred boiler of a thermal power plant. The cyclic experimental study was performed for 1000 h in the platen superheater zone of the coal-ﬁred boiler where the temperature was around 900°C. The corrosion products have been characterized with respect to surface morphology, phase composition and element concentration using the combined techniques of X-ray diffractometry (XRD), scanning electron microscopy/energy-dispersive analysis (SEM/EDAX) and electron probe micro analyser (EPMA). The Superni-75 performed well in the coal-ﬁred boiler environment, which has been attributed mainly to the formation of a thick band of chromium in scale due to selective oxidation of the chromium.