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.