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윤완노,최병호,강명수,정남근,김준성 한국정밀공학회 2012 International Journal of Precision Engineering and Vol. No.
Gas turbine engines are being widely used for power generation recently because of their high efficiency and versatility. However, it is occasionally reported that a gas turbine under normal operation fails even though careful inspections were scheduled. In this paper, the recent failure of the gas turbines of a cogeneration plant is analyzed by focusing mainly on the crack initiation mechanism of blade fracture. Damage of several blades of the compressor was observed after a gas turbine was disassembled, and the root causes of the damage were investigated in detail by scanning electron microscopy as well as optical microscopy. The defects observed at the crack initiation site have been characterized by comparison with previous studies. The fracture of the blade was supposed to be initiated by a crack due to concentrated stresses around a preexisting defect which was possibly formed before the turbine was operated, e.g., a forging defect during the three-step forging process for blades manufacture.
유한요소해석을 이용한 가스터빈 압축기 블레이드 피로균열 해석
윤완노(Wan No Yun),김준성(Jun Sung Kim) Korean Society for Precision Engineering 2010 한국정밀공학회지 Vol.27 No.12
A gas turbine consists of an upstream compressor and a downstream turbine with a combustion chamber, and also the compressor and the turbine are generally coupled using a single shaft. Large scale gas turbine compressor is designed as multi-stage axial flow and the blade is fantype which is thick and wide. Recently radial cracking happens occasionally at the compressor blade tip of large scale gas turbine. So, FEM was performed on the compressor blade and vibration modes and dynamic stresses were analyzed. According to the analysis, 9th natural frequency mode of the blade, which is 2 strip mode, is near the vane passing frequency by the vane located at the upstream of the blade.
초음파탐상 검사를 이용한 증기터빈 블레이드 루트 휭거 균열 탐지기법 개발
윤완노(Wan No Yun),김준성(Jun Sung Kim),강명수(Myung Soo Kang),김덕남(Duk Nam Kim) Korean Society for Precision Engineering 2011 한국정밀공학회지 Vol.28 No.6
The reliability of blade root fixing section is required to endure the centrifugal force and vibration stress for the last stage blade of steam turbine in thermal power plant. Most of the domestic steam turbine last stage blades have finger type roots. The finger type blade is very complex, so the inspection had been performed only on the exposed fixing pin cross-section area due to the difficulty of inspection. But the centrifugal force and vibration stress are also applied at the blade root finger and the crack generates, so the inspection method for finger section is necessary. For the inspection of root finger, inspection points were decided by simulating ultra-sonic path with 3D modeling, curve-shape probe and fixing jig were invented, and the characteristics analysis method of ultrasonic reflection signal and defect signal disposition method were invented. This invented method was actually executed at site and prevented the blade liberation failure by detecting the cracks at the fingers. Also, the same type blades of the other turbines were inspected periodically and the reliability of the turbine increased.
강명수(Myung-soo Kang),윤완노(Wan-no Yun),정남근(Nam-gun Jung),김준성(Jun-sung Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
The vibration increased suddenly during the normal operation of the gas turbine in cogeneration plant. The subsequent disassembly showed one blade of compressor 5th stage fractured and many downstream blades were damaged. The OEM redesigned and replaced the 5th blades already, because the 5th blade failure had occurred before. Optical microscope and scanning electron microscope inspection of the blade which had the same indication by the non-destructive test showed the forging defect at the same location with the fractured blade. The forging defect might be induced by the insufficient removal of surface crack and scale or foreign object inclusion in the process of hot forging. The defect existed at the highly stressed area and the crack initiated at the point. And the crack propagated by the high cycle fatigue and fractured finally. This paper describes the root cause analysis and countermeasures for the gas turbine compressor blade damage of the cogeneration plant.
최우성(W.S. Choi),윤완노(W.N. Yun),강명수(M.S. Kang) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
A gas turbine is called a combustion turbine and has an upstream compressor coupled to a downstream turbine, and a combustion chamber. Several cracks were oftenly observed at flange area between compressor casing and turbine casing in case of Westinghouse 501F series gas turbine. This component was made 1Cr1Mo0.25V steel such as conventional steam turbine casing. In this study, heat transfer and stress analysis using finite element analysis was performed in order to identify causes of flange cracking failure. Also, repairing method for effective maintenance was proposed.