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유지시간 효과를 고려한 12Cr 내열강의 열피로 및 저주기 피로 특성
하정수(J. S. Ha),고승기(S. K. Koh),옹장우(J. W. Ong) 한국자동차공학회 1995 한국 자동차공학회논문집 Vol.3 No.1
Isothermal and thermal-mechanical fatigue characteristics of 12Cr heat resisting steel used for high temperature applications were investigated including hold time effects. Isothermal low cycle fatigue test at 600°C and in-phase, out-of-phase thermal-mechanical fatigue test at 350 to 600°C were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.0l5. Regardless of thermal-mechanical and isothermal fatigue tests, cyclic softening behavior was observed and much more pronounced in the thermal-mechanical fatigue tests with hold times due to the stress relaxation during the hold time. The phase difference between temperature and strain in thermal-mechanical fatigue tests resulted in significantly shorter fatigue life for out-of-phase compared to in-phase. The differences in fatigue lives were dependent upon the magnitudes of plastic strain ranges and mean stresses. During the hold time in the strain-controlled fatigue tests, the increase in the plastic strain range and the stress relaxation were observed. It appeared that the increase in plastic strain range per cycle and the introduction of creep damage made important contributions to the reduction of thermal-mechanical fatigue life with hold time, and the life reduction tendency was more remarkable in the in-phase than in the out-of-phase thermal-mechanical fatigue. Isothermal fatigue tests performed under the combination of fast and slow strain rates at 600°C showed that the fatigue life decreased as the strain rate and frequency decreased, especially for the low strain ranges.
현중섭(J. S. Hyun),송기욱(G. W. Song),박정현(J. H. Park),하정수(J. S. Ha) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.8
The piping system of fossil power plant is subject to a severe thermal range and usually operates well into the creep range. Cyclic operation of the plant subjects the piping system to mechanical and thermal fatigue mechanisms and poor or defective support assemblies can impose massive loads onto the system. In order to prevent the serious damage and failure of the critical pipe system in fossil power plants, 3-dimensional displacement measurement system was developed for the on-line monitoring. Two types displacement measurement systems were developed with LVDT type sensor and rotary encoder type sensors. These systems were installed and operated on the piping system of fossil power plant successfully.
변형률에너지법에 의한 1Cr-0.5Mo-0.1V강의 피로손상평가
고승기(S.K. Koh),나의균(E.G. Na),하정수(J.S. Ha) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
In order to represent and evaluate the fatigue damage of 1Cr-0.5Mo-0.1V steel used for high strength pressure vessels, strain-controlled fatigue tests using uniaxial specimens were performed. Based on the fatigue test results from different strain ratios of -2, -1, 0, 0.5, 0.75, the fatigue damage of the steel was evaluated by using a strain energy density. Mean stress relaxation depended on the magnitude of the applied strain amplitude. The high pressure vessel steel exhibited the cyclic softening behavior. Total strain energy density consisting of the plastic strain energy density and the elastic tensile strain energy density described fairly well the fatigue life of the steel, taking the mean stress effects into account. Fatigue lives predicted by the strain energy density correlerated very well with the experimental fatigue lives within factors of 3 to 4, compared to other fatigue damage parameters.
정훈(H. Jeong),하정수(J.S. Ha),장성호(S.H. Chang),유근봉(K.B. Yoo),강명수(M.S. Kang) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
Nowadays, the various components in the fossil power plants are very complicated. So, it is difficult to establish the proper maintenance management policies for each plant that has its own management policy by different operating environment and culture. The advantages of maintenance optimizing method for a certain power plant would be unsuitable to others. In this paper, several method of optimizing maintenance management for plant are reviewed with merits and demerits, especially fossil power plant. Finally, how to optimize deciding or changing the maintenance period and the method for each equipment (system) with RCM (Reliability Centered Maintenance) are explained.
송기욱(G.W. Song),현중섭(J.S. Hyun),하정수(J.S. Ha),조선영(S.Y. Cho) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
Most domestic fossil power plant have exceeded 100,000 hours of operation with the severe<br/> operating condition. Among the critical components of fossil power plant, high temperature steam pipe<br/> system have had a many problems and damage from unstable displacement behavior because of<br/> frequent start up and shut down. In order to prevent the serious damage and failure of the critical<br/> pipe system in fossil power plant, 3-dimensional displacement measurement system were developed for<br/> the on-line monitoring system. 3-D Measurement system was developed with using the LVDT type<br/> sensor and rotary encoder type sensor, this system was installed and operated on the real power plant<br/> successfully. In the future time, network system of on-line diagnosis for critical pipe will be designed.
송기욱(G.W. Song),김의현(E.H. Kim),하정수(J.S. Ha),김종영(J.W. Kim) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
화력발전 기술은 점차 대형화, 고온고압화하는 경향으로서 고효율/ 환경친화성 뿐만 아니라 안전성과 높은 신뢰성이 요구되기 때문에 1000㎿ 급의 초초임계압 발전설비의 개발이 요구되고 있다. 국내에서는 그동안 확보된 기술을 바탕으로 각종 실증 신뢰성 평가 기술을 개발하고자 한다. 아울러 기존의 초임계압 발전설비에서 얻어진 손상기구 및 수명평가 기술을 상호 보완하기 위하여 실험실적 기계 및 재료 특성을 구하는 것은 물론 실증 신뢰성 평가 기술을 확보하고자 한다. 이를 위하여는 보일러 설비는 가공성 및 용접성, 내식성 등의 특성 실험을 실제 규모의 모델로 수행하고자 한다. 터빈 설비에서는 고온에서 실험할 수 있는 시험용 로타를 설계하였다. 크리프 특성을 고려하기 위하여 500시간 운전이 가능한 고온 시스템을 구상하였다. 또한 핵심 부속기기의 실증 신뢰성 평가를 위하여 실제 운전조건에서 시험할 수 있는 시험계통을 설계 제작하고자 한다. As a result of the fuel cost increasement and the competitive environmental condition for the power plants, it became highly desirable to have a plant of high efficiency. The research and the development to raise the temperature and the pressure of steam have been actively undertaken to improve the efficiency of power plants in the world. The development plans of the Ultra Super Critical (USC) power plant system is undergoing. To develop those system, it is necessary to get the field evaluation tests for the reliability of new components and materials. This paper introduces the fundamental technologies for the life and the reliability test and a conceptional design test.