A very comprehensive technology of on-line rotor crack detection and monitoring has been developed. The technique, based on the vibration signature analysis (VSA) approach, can detect incipient transverse rotor cracks in an “on-line mode.” The technique is generic and is applicable to all machines whose rotors are subjected to some kind of bending load. These machines include turbines, generators, pumps and motors, etc. The technique is based on the analytical modeling of the dynamics of the system. The basic idea is that through the modeling approach, the crack symptoms can be determined in terms of characteristic vibration signatures. These signatures are then used to diagnose the flaw in real life situations. A 3-D finite element crack model and a nonlinear rotor dynamic code have also been developed to accurately model a cracked rotor system. This program has been used to develop a variety of unique vibration signatures indicating a rotor crack. Both the analytical crack model and the crack signature analysis techniques have been experimentally validated. A microprocessor-based on-line rotor crack detection and monitoring system has been developed. The system has successfully detected cracks of the order of 1 to 2 percent of shaft diameter deep in an “on-line” mode in a series of large-scale laboratory tests. The system has been installed on a turbine-generator set at a utility in the field in October 1986 and has since been operating continuously, both in on-line as well as in coast-down modes, essentially, flawlessly. The system has also been applied in a crack detection program for nuclear reactor vertical coolant pumps. This paper describes all aspects of the development, starting from the technical concept to the commercial field applications.

As gas turbine (GT) temperatures have increased, thermal barrier coatings (TBCs) have become a critically important element in hot section component durability. Ceramic TBCs permit significantly increased gas temperatures, reduced cooling requirements, and improve engine fuel efficiency and reliability. TBCs are in use throughout the GT hot section with turbine blades, vanes, and combustion hardware, now being designed with TBCs or upgraded with TBCs during component refurbishment (Miller, 1987, “Current Status of Thermal Barrier Coatings,” Surf. Coat. Technol., 30(1), pp. 1–11; Clarke et al., 2012, “Thermal-Barrier Coatings for More Efficient Gas-Turbine Engines,” MRS Bull., 37(10), pp. 891–898). While the industry standard 6–9 wt. % yttria stabilized zirconia (7YSZ) has been the preferred ceramic composition for the past 30+ yr, efforts have been underway to develop improved TBCs (Stecura, 1986, “Optimization of the Ni–Cr–Al–Y/ZrO2–Y2O3 Thermal Barrier System,” Adv. Ceram. Mater., 1(1), pp. 68–76; Stecura, 1986, “Optimization of the Ni–Cr–Al–Y/ZrO2–Y2O3 Thermal Barrier System,” NASA Technical Memorandum No. 86905). The principal development goals have been to lower thermal conductivity, increase the sintering resistance, and have a more stable crystalline phase structure allowing to use above 1200 °C (2192 °F) (Levi, 2004, “Emerging Materials and Processes for Thermal Barrier Systems,” Curr. Opin. Solid State Mater. Sci., 8(1), pp. 77–91; Clarke, 2003, “Materials Selection Guidelines for Low Thermal Conductivity Thermal Barrier Coatings,” Surf. Coat. Technol., 163–164, pp. 67–74). National Aeronautics and Space Administration (NASA) has developed a series of advanced low conductivity, phase stable and sinter resistant TBC coatings utilizing multiple rare earth dopant oxides (Zhu and Miller, 2004, “Low Conductivity and Sintering-Resistant Thermal Barrier Coatings,” U.S. Patent No. 6,812,176 B1). One of the coating systems NASA developed is based on Ytterbia, Gadolinia, and Yttria additions to ZrO2 (YbGd-YSZ). This advanced low conductivity (low k) TBC is designed specifically for combustion hardware applications. In addition to lower thermal conductivity than 7YSZ, it has demonstrated thermal stability and sintering resistance to 1650 °C (3000 °F). The Electric Power Research Institute (EPRI) and cincinnati thermal spray (CTS) have teamed together in a joint program to commercialize the YbGd-YSZ TBC coating system for GT combustion hardware. The program consists of validation of coating properties, establishment of production coating specifications, and demonstration of coating performance through component engine testing of the YbGd-YSZ TBC coating system. Among the critical to quality coating characteristics that have been established are (a) coating microstructure, (b) TBC tensile bond strength, (c) erosion resistance, (d) thermal conductivity and sintering resistance, and (e) thermal cycle performance. This paper will discuss the coating property validation results comparing the YbGd-YSZ TBC to baseline production combustor coatings and the status of coating commercialization efforts currently underway.

Whenever the operations and maintenance economics so dominate the operation of a particular power producer, engineering insight is the plant’s vanguard in maintaining and managing costs. To provide a basis for operators to confront the spiraling parts replacement costs that are so closely tied to the durability of the hot section, EPRI has developed the Gas Turbine Life Management Platform (LMP), an effort which has been directly supported by F-Class turbine operators. Tested and verified on the advanced 7FA and 9FA class of turbine designs, the LMP provides unprecedented detail on temperatures and stresses throughout a selected hot section component. In turn, the platform relies on explicit details of stress and temperature to track the damage due to creep, coating oxidation and TMF (thermal mechanical fatigue). Supplied with operating data, it graphically represents the recent practices of either base load or peaking service. The platform supplies the engineering data needed by operators to make informed decisions regarding the disposition (continued use, repair, or scrap) of these most advanced and expensive parts. In this paper, the procedures of predicting temperature/life and how well these predictions correlated with field observations will be discussed in detail.

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This paper describes the current status and anticipated improvements in the Cascaded Humidified Advanced Turbine (CHAT) technology. With these improvements, CHAT will provide an alternative approach to achieving the goals of the Department of Energy’s Advanced Turbine Systems (ATS) project of a 60% thermal cycle efficiency for natural gas fired combined cycle power plants. The traditional approach to increasing the efficiency of simple cycle and combined cycle power plants was to increase the firing temperature and pressure of the basic Brayton cycle. However, every increase in the CT firing temperature required progressively higher development cost, associated with new materials and cooling techniques, and increased NOx control challenges. CHAT is a gas turbine based cycle with intercooling, reheat, recuperation and humidification. It is based upon the integration of an existing design heavy duty combustion turbine with an additional high pressure shaft comprised of industrial compressors and expander. The current CHAT plant design includes an HP expander inlet temperature of 871 C (1600 F), which represents the level of the combustion turbine technology of the late 1960’s – early 1970’s. The expander on the power generation shaft (LP) is based upon current combustion turbine technology with turbine inlet temperature of 1400 C (2550 F). One of the most effective ways to increase the CHAT plant efficiency is to increase the HP expander inlet temperature. By increasing this temperature to a relatively low 1150 C (2100 F), and maintaining the current inlet temperatures on the LP expander, the CHAT plant could achieve the ATS program target efficiency. The paper presents the current CHAT plant’s performance and cost characteristics, and the initial findings of a project co-sponsored by the Electric Power Research Institute (EPRI) and Energy Storage and Power Consultants, (ESPC) for the development of an HP expander with increased inlet temperatures.