• 대한기계학회논문집A
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• 제26권11호
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• pp.2421-2428
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• 2002

In this study, the failure probability of the degraded LP turbine blade steel was performed using the Monte Carlo simulation to apply variation of applied stress and strength. For this purpose, applied stress under the service condition of steady state was obtained by theoretical stress analysis and the maximum Von-Mises stress was 219MPa. The fatigue strength under rotating-bending load was evaluated by the staircase method. Furthermore, 3-parameter Weibull distribution was found to be most appropriate among assumed distributions when the probabilistic distributions of tensile and fatigue strength were determined by the proposed analysis. The failure probability with various loading conditions was derived from the strength-stress interference model and the characteristic factor of safety was also estimated.

• 대한기계학회논문집A
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• 제40권4호
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• pp.423-428
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• 2016

저압터빈 최종 단 블레이드는 응축 증기 내 농축된 불순물에 의해 조성되는 부식환경 하에서, 고속회전에 따른 높은 응력이 부가되어 응력부식 균열에 의한 파손이 빈번히 발생된다. 이러한 가혹 환경 하에서 블레이드의 안정적 사용을 위해서 내식성과 고 강도 특성 등을 갖춘 12% Cr 마르텐사이트계 스테인레스 강을 널리 적용한다. 본 논문은 마르텐사이트계 스테인레스 강으로 제작된 최종 단 블레이드가 정상운전 중 갑작스럽게 파손되어, 원인진단을 위해 파손 및 건전 블레이드를 대상으로 기계적 물성, 파단면 및 미세 조직 검사를 수행한 결과를 기술한 내용이다. 파손된 블레이드의 기계적 물성 시험결과 재질 사양서 기준에 비해 충격치는 낮고 경도는 높은 전형적인 재질 취성화 특성이 확인되었다. 또한, 파단면 검사결과 가지(branch)형태의 균열이 입계를 따라 진전하였고, 표면에서 Cl, S 등의 부식성분이 검출되었다. 이상의 결과들을 토대로 블레이드의 파손원인은 응력부식 균열임을 알 수 있었다.

• 한국신뢰성학회:학술대회논문집
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• 한국신뢰성학회 2002년도 정기학술대회
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• pp.199-204
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• 2002

본 연구에서는 저압 증기 터빈블레이드의 안전성 확보를 위하여 작용응력 및 강도의 변동성을 고려한 확률론적 해석을 수행하였다. 정상상태에서 작용응력은 이론 및 유한요소해석에 의해서 얻을 수 있으며, 최대 von-Mises 응력은 215.4MPa이다. 회전굽힘 하중하에서의 피로한도는 응력비 R= -1에서 계단식 시험법을 이용하여 구하였으며, 이의 확률론적 특성에 가장 적합한 분포는 3 모수 와이블 분포이다. 그리고 신뢰성에 미치는 다양한 인자들의 영향은 영향계수(sensitivity factor)를 이용하여 정량적으로 평가하였다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1998년도 강연회 및 연구개발 발표회 논문집
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• pp.11-28
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• 1998

Crack initiation and propagation of blades is a serious matter in turbomachinery. Outages are common due to these problems that occur during the service of the machine resulting in a huge loss of revenue. Once in a while, the problems become serious and cause major shutdowns which can in some cases result in the loss of the whole machine in a catastrophic manner. In this presentation, we will discuss the crack initiation studies of a hydraulic machine runner blade by local stress strain approach and crack propagation at the root of a low pressure stage steam turbine blade by means of stress intensity factor approach. In both the cases, we will show how the present day technologies can predict actual field observations.

• 대한기계학회논문집
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• 제19권3호
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• pp.784-795
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• 1995

This paper represents the results of the experiments of the three-dimensional flow and the aerodynamic loss caused by the three-dimensional flow within the plane bucket blades. To research the secondary flow and the aerodynamic loss, the large-scale plane bucket blade of lst-stage in the low pressure steam turbine is made of FRP. The detailed investigation of the secondary flow and the aerodynamic loss using 5-hole pressure probe within turbine cascade has been carried out in the low speed wind tunnel. The limiting streamlines of the suction and endwall surface have been visualized by the oil film method. The flow visualization of the secondary flow has been performed by the laser light sheet technique and image processing system. By using the method mentioned above, it is possible to observe the evolution of the pitchwise mass-averaged flow deviation angle and total pressure loss coefficient, the secondary flow, and the aerodynamic loss through the cascade.

• 대한기계학회논문집B
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• 제36권2호
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• pp.171-179
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• 2012

고온부에 해당하는 터빈 노즐과 로터의 냉각은 가스터빈의 성능에 큰 영향을 미친다. 본 연구에서는 냉각 공기의 예냉각이 가스터빈과 복합화력 발전 성능에 미치는 영향을 알아보았다. 계산에 사용된 모델은 F-Class 가스 터빈이며 냉각을 고려한 터빈의 구성요소를 사용해 냉각공기의 변화에 대해 보다 정확한 모사를 구사하였다. 냉각공기의 예냉각에 따른 가스터빈의 성능변화를 나타내기 위해 탈설계 해석이 수행되었다. 노즐 및 로터의 냉각에 따른 성능 변화를 보다 정확하게 나타내기 위해 열역학적 냉각모델과 속도삼각형을 고려한 모델이 고려되었다. 또한 복합발전의 경우 냉각공기에서 추출된 열을 하부사이클에서 회수하여 스팀터빈을 구동하는데 추가적인 열을 공급하는 시스템이 구성되었다. 복합발전 시스템의 모든 냉각공기의 온도를 200K 예냉각하는 경우에 주유동가스의 유량증가로 인해 약 1.78%의 출력 증가를 나타내었으며 동일한 터빈 입구온도 유지를 위한 연료소모의 증가로 효율은 0.70% 포인트 감소하였다.

• Corrosion Science and Technology
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• 제10권4호
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• pp.151-155
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• 2011

The iron oxide particles could be resulted from the corrosion of the circulating water system of a power plant. Because it may be one of the trouble materials which affect the power generation efficiency due to the deposition on steam generator tube and turbine blade, the continuous observation of its concentration is very important. The laser induced break-down detection (LIBD) technology was applied to monitor continuously the concentration of corrosion products with the detection limit of ppb level. The measurement system consists of a Nd:YAG pulsed laser, a polarizing beam splitter, a flow-type sample cell, an acoustic emission sensor, a high speed data acquisition board, a personal computer, etc.. The performance test results confirmed that this technology can be effective to monitor the corrosion product concentration of the circulating water system of a power plant.

• Journal of Mechanical Science and Technology
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• 제18권3호
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• pp.407-418
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• 2004

Prandtl-Meyer expansion flow with homogeneous condensation is investigated experimentally and by numerical computations. The steady and unsteady periodic behaviors of the diabatic shock wave due to the latent heat released by condensation are considered with a view of technical application to the condensing flow through steam turbine blade passages. A passive control method using a porous wall and cavity underneath is applied to control the diabatic shock wave. Two-dimensional, compressible Navier-Stokes with the nucleation rate equation are numerically solved using a third-order TVD (Total Variation Diminishing) finite difference scheme. The computational results reproduce the measured static pressure distributions in passive and no passive Prandtl-Meyer expansion flows with condensation. From both the experimental and computational results, it is found that the magnitude of steady diabatic shock wave can be considerably reduced by the present passive control method. For no passive control, it is found that the diabatic shock wave due to the heat released by condensation oscillates periodically with a frequency of 2.40㎑. This unsteady periodic motion of the diabatic shock wave can be completely suppressed using the present passive control method.

• 한국표면공학회지
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• 제37권4호
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• pp.226-233
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• 2004

The residual stresses on the surfaces of low carbon 12Cr steels used as a nuclear steam turbine blade material have been studied by controlling the flame hardening surface treatments. The temperature cycles on the surfaces of 12Cr steel were controlled precisely as a function of both the surface temperature and cooling rate. The final residual stress state generated by flame hardening was dominated by two opposite competitive contributions; one is tensile stress due to phase transformation and the other is compressive stress due to thermal contraction on cooling. The optimum processing temperatures required for the desirable residual stress and hardness were in the range of $850^{\circ}C$ to $960^{\circ}C$ on the basis of the specification of GE power engineering. It was also observed that the high residual tensile stress generated by flame hardening induced the cracks on the surfaces, especially across the prior austenite grain boundaries, and the material failure virtually, which might limit practical use of the surface engineered parts by flame hardening.

• 대한기계학회논문집A
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• 제25권6호
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• pp.965-971
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• 2001

To estimate the reliability of 12Cr alloy steel, the material of turbine blade in the steam power plant, Its corrosion susceptibility and fatigue characteristics in NaCl and Na$_2$SO$_4$solution with the difference of concentration and temperature was investigated. The polarization tests recommended in ASTM G5 standard for corrosion susceptibility in the various corrosive solutions was estimated. It showed that the higher temperature, the faster corrosion rates and corrosion rates were the fastest in 3.5 wt.% NaCl and 1M Na$_2$SO$_4$solution. From these results, the degradation conditions were determined in distilled water, 3.5 wt.% NaCl and 1M Na$_2$SO$_4$solution at room temperature, 60$\^{C}$ and 90$\^{C}$ during 3, 6 and 9 months. Its surface had a few pits for long duration. But, it was not susceptible in sulfide and chloride condition of several temperatures. If the degraded 12Cr alloy steel and non-degraded one were compared with fatigue characteristics, Any differences were not found regardless of temperature and degradation period.