Investigating short-term overheating failures in secondary superheater outlet of boiler steam power plant

• Scale exfoliation inside the secondary superheater hanger tube led to steam flow blockage, triggering localized overheating. • The overheating caused the loss of the protective magnetite layer, increasing susceptibility of corrosion and accelerating material degradation. • As a result, the tube wall thinned up to 1.3 mm, accompanied by microstructural changes such as pearlite spheroidization and grain coarsening. • These degradations reduced hardness from 253 HVN to 185 HVN, weakening the tube's ability to withstand internal pressure and causing ductile rupture. • To prevent such failures, predictive maintenance strategies—such as steam flow optimization, oxide scale monitoring, and thermal imaging—are essential. Short-term overheating is a critical failure mechanism in boiler components, particularly in the secondary superheater outlets of steam power plants, where high temperatures and pressures prevail. This study investigates a failure in the outlet section of a hanger tube supporting the secondary superheater, characterized by a fish-mouth rupture, significant wall thinning, and the presence of corrosion scale on both the inner and outer tube surfaces—indicating a combined effect of overheating and corrosion. A comprehensive metallurgical investigation was carried out using Scanning Electron Microscopy (SEM), Optical Emission Spectroscopy (OES), Vickers microhardness testing, X-Ray Diffraction (XRD), and Energy Dispersive Spectroscopy (EDS). The failure was primarily triggered by the exfoliation of magnetite scale, which obstructed steam flow and caused localized heat accumulation. This led to the loss of the protective oxide layer, exposing the tube to high-temperature corrosion and accelerating material degradation. Microstructural analysis revealed pearlite spheroidization and grain coarsening at the rupture site, accompanied by a significant reduction in hardness—from 253 HVN in the unaffected region to 185 HVN in the degraded zone. Wall thinning of up to 1.3 mm was also observed, confirming mechanical weakening under sustained internal pressure, which ultimately resulted in ductile rupture. The findings emphasize that steam flow blockage due to scale accumulation is a key contributor to overheating failures. Preventive measures such as optimizing flow distribution, maintaining water chemistry, monitoring oxide scale thickness in-situ, and conducting periodic thermal imaging inspections are essential for enhancing predictive maintenance and extending boiler component lifespan.