The impact of unevenness and instability of flue gas temperature on the technical condition of gas turbine blades

Gas turbines are used in the power sector, aviation, pump houses, and other technical systems. Such a broad range of application is associated with favourable indicators: high power, rather low weight per unit of power, significant efficiency, as well as high durability. All of these indicators greatly depend on the combustion chamber flue gas temperature. It is important for the flue gas temperature to be uniform around the turbine perimeter and stable over time. This condition is extremely important also in the case of frequent temperature variations associated, e.g. with a variable operating range of a manoeuvre aircraft turbojet engine. The paper analyses the causes for the unevenness and instability of combustion chamber flue gas temperature. The impact of the fuel quality, the technical condition of the fuel supply system, as well as the operating conditions of the combustion chamber-turbine assembly was shown. The issues regarding the presence of various types of damage to turbine elements, their blades in particular, were defined. The main cause behind the damage is the unevenness and instability of flue gas temperature, resulting in the presence of overheating, creeping, thermal fatigue, high-temperature corrosion of blade material. The forms of that damage, especially the first turbine stages, were presented. Blade material microstructure test results showed increased layer thickness, grain-size, and especially, adverse modification of the strengthening γ' phase in the temperature function. It was concluded periodic diagnostics of turbine blades with the optical method enables the non-invasive evaluation of their technical condition and drawing conclusions in terms of their durability.