The failure of feed water pump shaft failure uesed in HRSG (heat recovery steam generator) of 9F class gas turbine generator unit has been systematically investigated in terms of visual inspection, fractographic, chemical component, micro structure and mechanical properties analysis using optical microscope (OM), scanning electron microscope (SEM) equipped with energy-dispersive X-ray (EDX) analysis, transmission electron microscope (TEM), elemental analyzer and universal tensile testing machine, respectively. Results suggest that the failure of feed water pump shaft was typical multiple-origin fatigue fracture resulting from torsion stress, owing to the lower mechanical properties caused by the less alloying element and alloy strengthening phase (epsilon-Cu,eta-Ni). A detailed analysis of the micro structure revealed the existence of severe microsegregation and coarse M23C6 carbide at the grain boundaries, which accelerated the nucleation of micro holes and led to the formation of microcracks at the junction of micro holes. This failure analysis can help identification of root cause and its elimination with corrective measures undertaken.
