Gas Turbine Seminar Report

CHAPTER-1 INTRODUCTION
1.1. About Gas Turbine:
The gas turbine has become an important, well-known, and reliable device in the area of transportation, power generation and other applications. A gas turbine is an internal combustion engine; it can burn a variety of fuels to drive the engine as well as to generate power in industrial applications.
Gas turbine works on Brayton Cycle consist of the following four processes:
a) Adiabatic, quasi-static compression at the inlet of compressor.
b) Constant pressure fuel ignition (or constant pressure heat addition).
c) Adiabatic, quasi-static expansion in the turbine and exhaust nozzle.
d) Constant pressure heat rejection.
*In actual, processes a) & c) are not completely isentropic.

It is typically a problem associated with machines that have been in operation for several years. In this situation, minute flaws grow into cracks that, upon attaining critical size, rupture. Cracks also develop in the nozzle sections to some extent, this is to be expected under normal operation and cycling service.

THERMOCHEMICAL FATIGUE
Thermomechanical fatigue (TMF) is associated with thermal stresses, e.g., differential expansion of hot section components during start-up and shutdown, and is particularly severe during rapid starts and full load emergency trips. The stress levels induced may initiate cracks, if they exceed the material yield stress. Temperature variations as high as 360°F (200°C) per minute are often experienced in hot section blading. This is the reason why full load trips are so detrimental in terms of life reduction, consuming as much as 200 equivalent hours per trip.

ENVIRONMENTAL

Methodology
In this work we examined the cause of failure of gas turbine blade by SEM techniques and analysed the failure modes of turbine blade using modal analysis. But here we mainly focused over the modal analysis of gas turbine blade using experimental modal analysis (EMA) and computational modal analysis (CMA) and then correlating their results in order to identify the percentage variation of the EMA with CMA. Before working on the blade directly we first did with a cantilever beam of mild steel, then verifying the results of EMA and CMA for validation and then switching over turbine blade.
In this way we will be able to rely on computational method for modal analysis of gas turbine blade and can say that this result is true upto maximum extent as per the applied boundary conditions.

1.4.1. Scanning Electron Microscopy (SEM):
This technique is used by various researchers to identify the failure cause and mode of failure from the failed specimen. Here specimen of fractured portions was taken and then Fractographic analysis of the fractured region has been done. This shows the region of high cycle fatigue, corrosive fatigue, crack propagation and generation, thermal corrosive fatigue failure