This paper presents the analysis and corrective action taken to solve a flow induced non-synchronous vibration failure problem encountered in the last stage rotating blade in a large industrial combustion turbine. A description of the fatigue failures and of temporary operation restrictions that precluded further failure is given. The results from a strain gauge telemetry test are presented which show that failure was due to high vibratory stress excursions from fundamental mode vibration, which resulted from broad band buffeting excitations and very low aerodynamic damping at high levels of power and mass flow. From these data, design criteria were developed for designing a retrofittable blade that removed the operating restrictions. Telemetry test results (from the same turbine), which verified the new design, are also briefly presented and discussed. This investigation shows that the design of future high performance exhaust end combustion turbine blading must take into account non-synchronous excitation (buffeting) and the aeroelastic interaction between blade structure and flow, in addition to the synchronous excitations traditionally allowed for in the design process.

This paper presents the analysis and corrective action taken to solve a flow-induced nonsynchronous vibration failure problem encountered in the last-stage rotating blade in a large industrial combustion turbine. A description of the fatigue failures and of temporary operation restrictions that precluded further failure is given. The results from a strain gage telemetry test are presented which show that failure was due to high vibratory stress excursions from fundamental mode vibration, which resulted from broad band buffeting excitations and very low aerodynamic damping at high levels of power and mass flow. From these data, design criteria were developed for designing a retrofittable blade that removed the operating restrictions. Telemetry test results (from the same turbine), which verified the new design, are also briefly presented and discussed. This investigation shows that the design of future high-performance exhaust end combustion turbine blading must take into account nonsynchronous excitation (buffeting) and the aeroelastic interaction between blade structure and flow, in addition to the synchronous excitations traditionally allowed for in the design process.

High reliability and availability of current production combustion turbines have been achieved only after the identification and the resolution of past operating anomilies. Technological advances in fields such as aerodynamics, metallurgy, cooling, and computer capability have played important roles in these solutions as well as in the development of new advanced heavy duty combustion turbines. This paper discusses experiences with the W501 and the MW 701D combustion turbines and how this background influenced the design of the 501F advanced heavy duty combustion turbine.

One common method of reducing the NOx emissions from industrial gas turbines is to inject water into the combustion process. The amount of water injected depends on the emissions rules that apply to a particular unit. Westinghouse W501B industrial gas turbines have been operated at water injection levels required to meet EPA NOx emissions regulations. They also have been operated at higher injection levels required to meet stricter California regulations. Operation at the lower rates of water did not affect combustor inspection and/or repair intervals. Operation on liquid fuels with high rates of water also did not result in premature distress. However, operation on gas fuel at high rates of water did cause premature distress in the combustors. To evaluate this phenomenon, a comprehensive test program was conducted; it demonstrated that the distress is the result of the temperature patterns in the combustor caused by the high rates of water. The test also indicated that there is no significant change in dynamic response levels in the combustor. This paper presents the test results, and the design features selected to substantially improve combustor wall temperature when operating on gas fuels, with the high rates of water injection required to meet California applications. Mechanical design features that improve combustor resistance to water injection-induced thermal gradients also are presented.