Most failures of compressor and turbine blades in gas turbines and axial-flow compressors are due to high-frequency fatigue (neglecting the rare instances of foreign-object ingestion). Fatigue is the result of vibration of the blade, either in resonance or in flutter. With mature machines, the user can avoid the possibility of most resonant-vibration failures by a program of performance monitoring. Flutter can be avoided only if there is reason (such as experience) to expect it in a certain operating regime. Examples of a simple performance-monitoring procedure are given.

A mathematical model of a constant-speed single-shaft gas turbine was devised using a typical compressor map. Performance calculations were performed at various ambient temperatures based on a standard temperature control system for a number of possible component deterioration modes. The effects on compressor operating line were determined. It was found that only two modes of deterioration; reduction of compressor flow capacity either through fouling or through erosion and closing of turbine nozzle diaphragms, moved the operating line toward surge. Inlet filter clogging must also be minimized in order to avoid surge because resulting distortion can induce stall and surge.

Data on the distribution by size of generator-drive gas turbines insured by Allendale Insurance, Arkwright and Protection Mutual insurance companies is presented. Similar data on loss costs is included. The principal failure modes are shown and described. Finally, a comprehensive table outlining the causes of these failure modes, and the optimum approaches to their prevention, is given.

The concept of performance monitoring for prevention of certain serious failures in gas turbines is described. The use of compressor mapping as the key to avoiding surge is developed, and an example is presented showing how the compressor in a steam-injected gas turbine can be much closer to surge in one of two nearly-identical operating points on a steam-injection control envelope than the compressor in the other. The technique of monitoring blade-path temperature spread in the exhaust of a gas turbine is then described, and examples of its value in preventing combustor burnout and turbine blade failures in high-frequency fatigue are given. Next, a concept of diagnosing internal deterioration by recognizing patterns of deviation of operating parameters from baseline data is described, and illustrated for a single-shaft generator-drive gas turbine. Finally, the use of a modern computer-controlled data acquisition system to perform the above monitoring functions in real time is demonstrated.

This paper opens with a discussion of the various mechanisms of cracking and fracture encountered in gas turbine failures, and discusses the use of metallographic examination of crack and fracture surfaces. The various types of materials used in the major components of heavy-duty industrial and aeroderivative gas turbines are tabulated. A collection of macroscopic and microscopic fractographs of the various mechanisms of failure in gas turbine components is then presented for reference in failure investigation. A discussion of compressor damage due to surge, as well as some overall observations on component failures, follows. Finally, a listing of the most likely types of failure of the various major components is given.