Terutaka Fujioka

Elastic-Route Estimates of Strain Range for Notched Components Under Thermal Loading Without Performing Linearization of Stresses

This paper describes simplified methods for estimating the strain range produced in notched components under thermal loading for the purpose of fatigue, creep, and creep-fatigue damage assessment. The methods presented are based on the previously proposed stress relaxation locus and the elastic follow-up factor combined with a newly proposed method for evaluating primary-plus-secondary stress limit. The procedures contained in the methods do not need the linearization of stresses. The proposals are validated by performing elastic-plastic finite element analysis of notched components subjected to cyclic thermal loading.Copyright

Numerical Analysis of Temperature Distribution of a Film-Cooled and TBC Coated Blade

In order to contribute to assessment of structural integrity of a gas turbine cooled-blade, numerical estimation of temperature distributions of the blade was conducted. Steady-state simulations by means of one-way coupling of a CFD calculation with thermal conduction analysis were developed and executed to estimate the temperature distributions with using a realistic blade model. Thermal protection schemes applied to the target blade analyzed are external surface film cooling, internal convective cooling and thermal barrier coating (TBC). Non-conformal multi-block meshes were adopted in the analyses for the purpose of reducing turnarounds required in the simulations of real blades, so as to cope with a compound domain including film-cooling holes of various directions. The CFD was applied to flow fields inside and outside of the blade in order to estimate thermal loads imposed on the blade. The temperature distribution of the blade was calculated with the thermal conduction analysis under the conditions based on the CFD calculation. The calculated temperature profiles are in reasonable agreement with local temperature which was estimated on the basis of micro-structural observations of an ex-service blade. The present calculations can also predict influence of lower internal cooling performance on the temperature distribution of the blade.Copyright

Development of Risk-Based Maintenance Software for Gas Turbines

Risk-based maintenance software has been developed to perform risk-based maintenance and inspection planning on gas turbine hot gas path components. The software allows the user to easily prepare a risk matrix, plotting every active damage mechanism for each hot gas path component. Based on the result of the risk assessments the components can be ranked, allowing inspection plans to be focused and prioritized and aiding the user to identify the most appropriate and effective risk mitigating activity within the software. Risk assessments are performed on a component-by-component basis, with the software’s scope including all combustor and turbine hot gas path components. The software also contains comprehensive help documents to aid the user in identifying and assessing peculiar damage mechanisms and prescribing the most effective inspection methods for gas turbines.Copyright

Derivation of Temperature-Estimation Equation Based on Microstructural Changes in Coatings of In-Service Blades of Gas Turbines

A CoNiCrAlY-coated blade of an in-service gas turbine is analyzed, and a diffusion layer is formed along the boundary between the coating and the substrate due to the interdiffusion in the middle and tip of the blade. Such a layer is not observed in the vicinity of the blade root because of a comparatively low temperature during the operation. Coated specimens are prepared from the portions of the blade devoid of the diffusion layers, and the specimens are exposed to a high temperature in air. On the basis of the increase in the diffusion layer thickness, an equation for estimating the temperature of the blade is derived. An analysis of another in-service blade with a thermal barrier coating is carried out. The aluminum content decreases below the bond coat surface due to Al diffusion caused by the Al-oxide formation. This results in the formation of an Al-decreased layer (ADL) along the leading and trailing edges. The ADL is not observed at the center of the blade chord. The specimens are extracted from the portions of the blade that are devoid of ADL, and they are subjected to a high temperature in air. On the basis of the increase in the ADL thickness, a temperature-estimation equation is derived.

Development of Non-Destructive Heat Resistance Evaluation System for TBC on Gas Turbine Blade

The use of thermal barrier coatings (TBCs) is the key technique for realizing high-efficiency gas turbine combined cycles. Hence, TBCs are applied to various hot gas path components such as combustors, blades, and vanes. The application of a TBC causes a significant decrease in the temperature of the base metal surface. Consequently, the lifetime of the component is increased. However, it is reported that under high-temperature operating conditions, the heat resistance of the TBC decreases gradually because of sintering and erosion of the TBC layer. Accurate evaluation of changes in the TBC heat resistance is very important for evaluating the residual lifetime of a given component. We have previously developed a nondestructive technique for measuring the heat resistance of TBCs applied on the inner surface of a combustion liner. In this technique, the TBC surface is heated by a laser beam, and the temperature change of this heated point is measured by an IR camera. The heat resistance is calculated from the measured temperature. On the basis of this concept, we have made improvements to this technique so that it can be used to measure the heat resistance of a TBC layer on a blade surface. However, several difficulties are encountered whenusing this technique for the abovementioned purpose. For example, the blade has a three-dimensional (3D) surface and complex internal cooling paths, as opposed to the combustion liner, which has a simple cylindrical shape. Hence, it is difficult to keep the same heating condition at any surface. To overcome these difficulties, we propose a new concept and develop a system for measuring the heat resistance of the TBC layer on a blade. This system is mainly composed of a carbon dioxide laser, a robot arm, and an IR camera. In this paper, we present an overview of the developed system. Copyright

Development of Gas Turbine Hot Gas Path Parts Maintenance Planning Support System

Since the hot gas path parts such as combustors, blades, and vanes are subject to extremely severe working conditions, the parts must be inspected and repaired at relatively short intervals. Therefore, it is essential to reduce the maintenance costs for economic reasons. Furthermore, since the hot gas path parts have cooling structures with advanced design and coated with various types of coatings, the prices of parts are usually very high. Therefore, using the parts efficiently and extending the service life of the parts are needed to significantly reduce the maintenance costs. In such a situation, a platform free system of “Gas Turbine Hot Gas Path Parts Maintenance Planning Support System” has been developed. This system can be used to decrease parts disposal loss by optimizing parts rotation plans. In this paper, main functions of this system and the results of some case studies by this system are described.Copyright

Development of Management Support System for Gas Turbine Hot Gas Path Parts

The combined cycle power plants operating in Japan are normally provided with two or more gas turbines and spare parts in quantities as required by the number of gas turbine units in operation. Since the quantity of hot gas path parts installed in a gas turbine is massive, the parts required for a gas turbine are arranged in groups so as to simplify the control of parts inventory. These parts groups are replaced and repaired at each inspection. Furthermore, since the costs of hot gas path parts are very high, using the parts efficiently and implementing measuring to prolong the life of the parts are very important. Detailed parts rotation schedules are prepared to properly rotate the spare parts groups. In doing so, the length of service life, quantity of spare parts, schedules for using the parts for several years to come, and time required for maintenance and repairs must be taken into consideration. Special characteristics of respective power plants such as plans for prolonging the service life of parts and various costs must be taken into consideration. Since it is difficult to prepare the schedules for rotating parts automatically, skilled workers are carrying out most of work manually at present. Against such a backdrop, the authors have developed the “Management Support System for Gas Turbine Hot Gas Path Parts”. This system can be used to reduce the maintenance and repair costs by optimizing parts rotation schedules. The basic concepts of the development are as follows. 1) Some parts can be shared among plural number of power plants with the gas turbines of the same model. A user freely sets models of the gas turbines, categorization of parts, and numbers of the parts dealt with. 2) The unit of the part management is done based on not groups but serial numbers. Moreover, replacing parts is enabled. 3) The program is modulated according to the functions. Addition, change, and deletion of these functions are facilitated. The total system is developed platform-free.Copyright