Premature damage of the second stage nozzle guide vanes of a gas turbine made of Inconel 738LC

摘要

In this work, premature damage of the second stage nozzle guide vanes (NGVs) of a gas turbine engine made of nickel-base Inconel 738LC superalloy has been studied. To determine the cause of damage, evaluations including visual inspections, microstructural investigations, and finite element method (FEM) analyses were carried out on the damaged nozzle. The microstructural investigations were performed through evaluation of the microstructure near the damaged area using optical and scanning electron microscopes. The FEM analyses performed to determine the temperature and stress distribution at different points of the nozzle. The results of visual inspections and microscopic investigations revealed the signs of microstructural degradations and hot corrosion near some of the cracks on the trailing edge of the NGVs. The results of the FEM analyses showed that due to the temperature gradient, thermal stresses are arisen in the nozzle components and caused thermal fatigue occurrence. Based on the analyses, it was concluded that the thermal fatigue is the dominant mechanism for premature damage of the second stage nozzle guide vanes of the gas turbine. Moreover, the simultaneous occurrence of microstructural degradations and hot corrosion on the NGVs, has a supplementary effect on the propagation of the cracks in addition to thermal fatigue.