Gas Turbine Technology Service Center

Incheon, South Korea

Gas Turbine Technology Service Center

Incheon, South Korea

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Shin I.-H.,Sungkyunkwan University | Koo J.-M.,Sungkyunkwan University | Seok C.-S.,Sungkyunkwan University | Yang S.-H.,Gas Turbine Technology Service Center | And 2 more authors.
Surface and Coatings Technology | Year: 2011

Plasma-sprayed thermal barrier coatings (TBCs) are applied to protect the blades of a gas turbine system from high-temperature gas and to lower the surface temperature of the blades. The failure of TBC is directly connected to the failure of the blades because the spallation of a ceramic layer leads to the acceleration of local corrosion and oxidation at the location of failure. Therefore, the spallation life of TBC is very important in the evaluation of the reliability of a gas-turbine blade.In this study, thermal fatigue tests were performed at 1100 °C and 1151 °C. Then, c-scanning and bond strength tests were performed for TBC specimens that were thermally aged by thermal fatigue tests. From the results, an empirical equation based on the ratio of the delamination area and the thermal cycle number was presented and the spallation life of a TBC specimen could be roughly estimated using the relationship between the delaminated area and the number of cycles. © 2011 Elsevier B.V.


Kim H.-I.,University of Delaware | Park H.-S.,KEPCO E&C | Koo J.-M.,Sungkyunkwan University | Seok C.-S.,Sungkyunkwan University | And 2 more authors.
Journal of Mechanical Science and Technology | Year: 2012

To enhance the gas turbine efficiency, the inflow temperature of the first-stage blade of the turbine system is raised to an ultra-high temperature of more than 1300°C. When the gas turbine blade is used at high temperature for a long time, its base material can become damaged. To prevent such damage, regenerative maintenance is performed after the equivalent operating hours so that the quality of the part may be restored for its reuse. After the first-cycle operation, nondestructive testing and a durability diagnosis of material quality are performed to determine whether the gas turbine blade should be reused or scrapped. For the recovery of the material properties, heat treatments are performed. So, this study aimed to analyze the condition of the heat treatment and to evaluate the influence of microstructure variation with this heat treatment for degraded superalloys. We studied the influence of HIP (hot isostatic processing) and post-heat treatment. HIP treatment has the effect of the elimination of cavities and cracks. The heat treatment processes removed the inhomogeneity of the creation and the growth of the γ′ phase due to the temperature gradation during the welding. © 2012 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.


Kim H.-I.,University of Delaware | Park H.-S.,KEPCO E&C | Koo J.-M.,Sungkyunkwan University | Seok C.-S.,Sungkyunkwan University | And 2 more authors.
Journal of Mechanical Science and Technology | Year: 2012

A Ni-based super-alloy is widely used in manufacturing the first stage blade of high power land-based gas turbines as these first stage blades operate under high temperature and high pressure. The blade of a gas turbine must withstand the most severe combination of temperature, stress, and environment. After continued operation, the blade may be damaged by the turbine operation mode. To recover its initial mechanical properties, the blade of the Ni-based super-alloy undergoes a replacement repair process. Typical repair processes include blending, welding, re-machining and precision grinding. In this paper, the effects of manual overlay and laser cladding were investigated as part of the welding characteristic evaluation. Results are compared with those for post-heat treatment known as hot isostatic processing (HIP). © 2012 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.


Kim D.-J.,Sungkyunkwan University | Shin I.-H.,Sungkyunkwan University | Koo J.-M.,Sungkyunkwan University | Seok C.-S.,Sungkyunkwan University | Lee T.-W.,Gas Turbine Technology Service Center
Surface and Coatings Technology | Year: 2010

The aim of this study is to investigate the failure mechanisms of coin-shaped plasma-sprayed thermal barrier coatings (TBCs) for gas turbine blades due to cyclic thermal fatigue. For this purpose, cyclic thermal fatigue tests at 1100 °C were performed for a commercial TBC system that was used for the first-stage blade of a gas turbine. The failure location was near the interface between the top coat and the thermally grown oxide (TGO). For thermally aged TBC specimens, bond tests were performed to investigate the failure modes and to observe the decrease in the bond strength. The spallation of a TBC was preceded by external crack initiation at the edge of a specimen, and the bond strength gradually decreased with increasing thermal cycles due to the expansion in the delaminated zone. Through the thermal stress analysis it was found that edge delamination originated from repeated "cooling shock", which occurs right after forced air quenching, where the normal stress the edge increases sharply within a few seconds. © 2010 Elsevier B.V.


Kim Y.,Sungkyunkwan University | Seok C.-S.,Sungkyunkwan University | Lee S.-Y.,Sungkyunkwan University | Koo J.-M.,Sungkyunkwan University | And 2 more authors.
International Journal of Precision Engineering and Manufacturing | Year: 2014

Thermal barrier coatings (TBC) protect the components of gas turbines from severe environments by reducing the surface temperature of the substrate. Therefore, an accurate prediction of the temperature gradient (temperature drop) in TBC is an important issue when estimating the exact life of the components. Material properties of bulk ceramic are often used for the analysis. However, Bulk materials do not have the same material properties as thin ceramic layers due to differences in processing and micro structure. Bulk materials also have different interfacial properties since the ceramic is sprayed on different materials with highly conductivity. Therefore, it is necessary to develop a thermal barrier performance test method using a TBC applied to real gas turbine. In this study, a thermal barrier performance test method was developed using the TBC applied to real gas turbine. The thermal gradient of a real gas turbine was analyzed by FEA, using measured conductive heat transfer coefficients. A simple equation that can predict thermal gradient conditions of the components in a gas turbine from measured temperature of the test is proposed. Finally, Thermal barrier performance tests on various TBCs were conducted. The test method was verified by comparing the tested data with reference data. © 2014 Korean Society for Precision Engineering and Springer-Verlag Berlin Heidelberg.


Koo J.-M.,Sungkyunkwan University | Seok C.-S.,Sungkyunkwan University | Kang M.-S.,Sungkyunkwan University | Kim D.-J.,Sungkyunkwan University | And 2 more authors.
Transactions of the Korean Society of Mechanical Engineers, A | Year: 2010

The thermal barrier coating of a gas turbine blade was degraded by isothermal heating in a furnace and by varying the exposure time and temperature. Then, a micro-Vickers hardness test was conducted on the cross section of the bond coat and Ni-based superalloy substrate. Further, the thickness of TGO(Thermally Grown Oxide) was measured by using an image analyzer, and the changes in the microstructure and element contents in the coating were analyzed by using an optical microscope and by performing SEM-EDX analysis. No significant change was observed in the Vickers hardness of the bond coat when the coated specimen was degraded at a high temperature; delamination was observed between the top coat and the bond coat when the coating was degraded for 50 h at a temperature 1, 151°C.


Kim K.M.,Yonsei University | Park J.S.,Yonsei University | Lee D.H.,Yonsei University | Lee T.W.,Gas Turbine Technology Service Center | Cho H.H.,Yonsei University
Engineering Failure Analysis | Year: 2011

Prediction of heat transfer coefficients and stresses on blade surfaces keys a role in thermal design of a gas turbine blade. The present study investigates heat transfer and stress in a gas turbine blade with 10 circular internal cooling passages. 3D-numerical conjugated simulations using a FVM and FEM commercial codes, CFX and ANSYS are performed to calculate distributions of the heat transfer coefficients and the stresses, respectively. The heat transfer coefficient is the highest on the stagnation point of leading edge due to impingement of incoming gas flow. It is the lowest at the trailing edge on both pressure and suction sides due to development of thermal boundary layer. However, the maximum material temperature and the maximum thermal stress occur at the trailing edge near the mid-span. Therefore, the failure of turbine blade should be predicted by total stress resulted from the combination of thermal load and cooling. © 2011 Elsevier Ltd.


Kim K.M.,Yonsei University | Yun N.,Yonsei University | Jeon Y.H.,Yonsei University | Lee D.H.,Yonsei University | And 2 more authors.
Journal of Mechanical Science and Technology | Year: 2010

Prediction of temperature distributions on hot components is important in development of a gas turbine combustion liner. The present study investigated conjugated heat transfer to obtain temperature distributions in a combustion liner with six combustion nozzles. 3D-numerical simulations using FVM commercial codes, Fluent and CFX were performed to calculate combustion and heat transfer distributions. The temperature distributions in the combustor liner were calculated by conjugation of conduction and convection (heat transfer coefficients) obtained by combustion and cooling flow analysis. The wall temperature was the highest on the attachment points of the combustion gas from combustion nozzles, but the temperature gradient was high at the after shell section with low wall temperature. © 2010 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.

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