Metal degradation of thermally loaded elements of power plants during operation in the North

Abstract

The study of structural and phase changes and processes of destruction of heat-resistant nickel alloys is necessary to solve urgent problems of improving the serviceability and reliability of parts of the hot path of gas turbine installations, including under severe temperature and power operating conditions in the North. The purpose of this work is to study the high-temperature degradation of metal and the nature of operational failures of parts of the hot path (heat insert, blades) of gas turbine units operating in an extremely cold climate. Using the methods of optical, scanning and transmission electron microscopy the morphological changes were revealed in the strengthening γ’-phase and other symptoms of instability in structural state of the alloys from which the failed parts had been made. The insufficient level of structural stability of alloys in non-stationary operating conditions of gas turbine installations in the North which sharply increase the load on the parts is revealed. The degradation of alloys was developed in the depletion of the solid solution by the intermetallide phase, the softening of intermetallide particles by internal defects, the development of intra-grain porosity, and the weakening of grain boundaries by precipitates and pores. The fracture of the heat insert (made of a deformable nickel alloy) was realized by the creep mechanism, the fracture of the working blades (made of a casting alloy) – by the thermal fatigue mechanism. A limited resource of the studied parts is caused by the insufficient level of service properties for the considered operating conditions as well as error modes of the gas turbines caused the overheating of parts. The improving of materials for gas turbine installations in the North requires the adapted optimization of alloys compositions and the development of technologies for manufacturing parts taking into account operating conditions.