Mohammad Ali Mohtadi Bonab

This study presents a comprehensive investigation of a failed 12Cr1MoV super-heater tube that had been in long-term service. Several characterization techniques such as confocal laser scanning microscopy, scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, and electron backscatter diffraction (EBSD) were utilized to analyze the microstructure and surface of the failed steel and to investigate the effect of microstructural components on crack initiation and propagation. The investigations indicate that the formation of various types of deposits which is very common during service may act as insulation on tube surfaces. In this case, increasing the furnace temperature is necessary to regulate the steam temperature in the tubes resulting in the development of local hot spots on the outer surface of the steel which facilitates crack initiation. EBSD measurements revealed that the cracks propagated in both intergranular and transgranular manners with no preferred orientation, propagating through differently oriented grains. Furthermore, the results showed that the presence of hard and brittle chromium carbide around the crack propagation path assists the crack growth. The findings provide valuable insights into the complex mechanisms of crack propagation in super-heater tubes and can be incorporated into the development of the studied material as well as designing the failure mitigation strategies for operating power plant tubes.