Premature Failure of Gas Turbine Blade
A set of first stage stationary blade of gas turbine was prematurely replaced due to severe cracking after 5,000 hours in operation. Failure investigation was conducted on damaged blades by non-destructive penetrant inspection, microstructure examination, chemical analysis, hardness mapping and fracture surface observation. The blade material, verified as IN738LC nickel superalloy, exhibited presence of elongated grain boundary carbides, TCP phases formation, and grain boundary creep void on the airfoil. Morphology of γ' precipitation, however, was normal throughout the blade with size of approximately 1μm and no significant coarsening. Presence of welding structure and possible brazing layer on the airfoil was detected suggesting that the blade was previously refurbished. Primary crack occurred on previous welding repair and propagated in transgranular mode. It was concluded that the blade failure was caused by improper welding repair despite evidence of base material degradation.
Ahmad Kamal Ariffin, Shahrum Abdullah, Aidy Ali, Andanastuti Muchtar, Mariyam Jameelah Ghazali and Zainuddin Sajuri
Z. Sajuri et al., "Premature Failure of Gas Turbine Blade", Key Engineering Materials, Vols. 462-463, pp. 325-330, 2011