• Steel and Composite Structures
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• 제32권6호
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• pp.701-715
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• 2019

Using first-order shear deformation theory (FSDT), a semi-analytical solution is employed to analyze creep damage and remaining life assessment of 304L austenitic stainless steel thick (304L ASS) cylindrical pressure vessels with variable thickness subjected to the temperature gradient and internal non-uniform pressure. Damages are obtained in thick cylinder using Robinson's linear life fraction damage rule, and time to rupture and remaining life assessment is determined by Larson-Miller Parameter (LMP). The thermo-elastic creep response of the material is described by Norton's law. The novelty of the present work is that it seeks to investigate creep damage and life assessment of the vessels with variable thickness made of 304L ASS using LMP based on first-order shear deformation theory. A numerical solution using finite element method (FEM) is also presented and good agreement is found. It is shown that temperature gradient and non-uniform pressure have significant influences on the creep damages and remaining life of the vessel.

• 한국정밀공학회지
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• 제16권6호
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• pp.100-107
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• 1999

This paper describes a probabilistic remaining life assessment program for the creep crack growth. The probabilistic life assessment program is developed to increase the reliability of life assessment. The probabilistic life assessment involves some uncertainties, such as, initial crack size, material properties, and loading condition, and a triangle distribution function is used for random variable generation. The resulting information provides the engineer with an assessment of the probability of structural failure as a function of operating time given the uncertainties in the input data. This study forms basis of the probabilistic life assessment technique and will be extended to other damage mechanisms.

• 한국항공우주학회지
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• 제49권7호
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• pp.565-572
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• 2021

본 연구에서는 국방 분야에서 분리장치로 사용되고 있는 파이로 장치 중 장기간 보관된 폭발볼트의 성능 및 노화에 관한 연구를 수행하였다. 연구를 위해 약 10년간 무기체계에 탑재되어 있던 폭발볼트를 확보하였으며, AIAA Standard 및 MIL-STD를 기반으로 성능 및 수명 평가 절차를 수립하였다. 성능 평가를 위해 먼저 비기능 검사를 수행하여 외적인 변화나 고장이 발생하였는지 확인하였으며, 내부 회로 및 구조에 이상이 없는지 회로검사와 X-ray 검사를 수행하였다. 비기능 검사가 통과된 시료에 대해서 작동 확인을 위한 성능 시험을 실시하였다. 성능 시험을 통해 폭발볼트의 분리 여부 및 분리시간을 측정하였으며, 일부 시료의 경우 잔여 수명 및 연장 가능성을 확인하기 위해 고온저장시험 후 성능 시험을 실시하였다. 마지막으로 시험 결과와 아레니우스 모델을 바탕으로 잔여 수명 및 신뢰도를 예측하였으며, 수명에 따른 신뢰도를 확인하였다.

• KEPCO Journal on Electric Power and Energy
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• 제8권2호
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• pp.73-77
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• 2022

Recently, as the number of years of operation has increased for more than 30 years, interest in evaluating the remaining life of major power facilities such as transformers and ultra-high voltage cables is increasing. In particular, the risk of failure is increasing because the underground transmission XLPE cable has been built since 1980 and has been operating in excess of 30 years of design life or close proximity. Therefore, it is necessary to develop an algorithm to evaluate the residual life of the XLPE cable considering the load to determine the risk of failure. Since load data is large amount of data, it is necessary to make the variable load information equivalent to the time unit first in order to calculate the remaining life of the system quickly. In overseas literature, transformers are reported to be standardized for variable load equivalent conversion formulas, but they have not been reported for ultra-high voltage cables. Therefore, in this paper, whether the equivalent conversion formula of a transformer can be applied to XLPE cables was reviewed through accelerated degradation tests under equivalent and variable temperature conditions, and considerations were studied when evaluating the remaining operating life of XLPE cables based on the experimental results.

• 한국강구조학회 논문집
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• 제14권2호
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• pp.365-373
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• 2002

이 논문에서는 교량의 수명을 예측하기 위한 시스템 신뢰성 이론이 설명되고, 생애 분포 함수를 이용하여 현존하는 교량의 잔존 수명을 예측하는 방법이 설명된다. 시스템 이론과 생애함수 (survivor functions) 를 이용하여 LIFETIME 이라는 프로그램을 개발하였다. Survivor functions은 주어진 시간 t에 대해 신뢰성을 산출한다. 이 프로그램을 이용하여 콜로라도주에 있는 교량의 수명을 예측하였다. 이 교량은 직렬과 병렬로 구성된 시스템으로 컴퓨터 모델링 되었으며 이 모델을 이용하여 시스템 파괴 확률을 시간에 대해 계산하였다.

• Steel and Composite Structures
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• 제28권3호
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• pp.349-362
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• 2018

This paper presents a semi-analytical solution for the creep analysis and life assessment of 304L austenitic stainless steel thick truncated conical shells using multilayered method based on the first order shear deformation theory (FSDT). The cone is subjected to the non-uniform internal pressure and temperature gradient. Damages are obtained in thick truncated conical shell using Robinson's linear life fraction damage rule, and time to rupture and remaining life assessment is determined by Larson-Miller Parameter (LMP). The creep response of the material is described by Norton's law. In the multilayer method, the truncated cone is divided into n homogeneous disks, and n sets of differential equations with constant coefficients. This set of equations is solved analytically by applying boundary and continuity conditions between the layers. The results obtained analytically have been compared with the numerical results of the finite element method. The results show that the multilayered method based on FSDT has an acceptable amount of accuracy when one wants to obtain radial displacement, radial, circumferential and shear stresses. It is shown that non-uniform pressure has significant influences on the creep damages and remaining life of the truncated cone.

• 콘크리트학회논문집
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• 제12권5호
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• pp.69-80
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• 2000

This paper presents the prediction of remaining service life of the concrete due to steel corrosion caused by the following three cases; carbonation, using sea sand and using deicing salts. The assessment of initiation period was generalized considering the existing perdiction models in the literature, corrosion experiment and field assessment. To evaluate the prediction equation of rust growth, the corrosion accelerating experiments was performed. The polarization resistance was measured by potentiostat and the conversion coefficient of polarzation resistance to corrosion rate was determined by the measurement of real mass loss. Chloride content, carbonation, cover depth, relative humidity, water-cement ratio(W/C), and the use of deicing salts were taken into account and the resulting prediction equation of rust growth was proposed on the basis of these properties. The proposed equation is to predict the rust growth during any specified period of time and be effective in particular for predicting service life of concrete in the case of using sea sand.

• 한국산업보건학회지
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• 제18권3호
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• pp.204-215
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• 2008

Many researches for service-life of chemical cartridges of respirators have been performed in many countries. On the result of these researches a few softwares programs were eventually developed to be used. In spite of that, it is difficult to apply these researches and softwares practically in the work spot because of too many factors that influence on service-life of chemical cartridges. This study was the first of two conducted for the purpose of developing program for estimating exchange period or service-life of chemical cartridges available feasibly in the workplaces. Collecting plan of cartridges discarded after use is in principle that three cartridges from three workers at a time, three steps of 1/2 exchange time due to smelling, just routine exchange time and 1.2 to 1.3 expanded time of routine exchange, total nine cartridges are collected in the same job site. 33 cartridges for organic vapor were collected in paint spray process of ship yard and paint factory, and 6 cartridges for acid were collected in plating process. These cartridges were analysed the remaining breakthrough time in 3M Innovation Center. Challenge vapor and breakthrough concentration were complied with Korean regulation for chemical cartridge respirators. Estimated breakthrough time was determined from previously used time plus breakthrough time for the remaining. Exchange period of cartridge would be the shortest time among three estimated breakthrough times. On the result breakthrough time for organic vapor was found to be relatively easily estimated, but that for acid aerosol or vapor was difficult to be confident. Even though this method was difficult to be precisely predicted exchange period of cartridge, it could be an alternative program practically available in the job site.

• 에너지공학
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• 제8권4호
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• pp.605-611
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• 1999

화력발전설비 고온요소의 잔여수명평가는 주로 비파괴검사 및 검사결과의 파괴역학적 해석등으로 행해졌다. 그러나 기존 방법은가동중에는 적용되기 어렵고 급작스런 운전이력에 대한 정량적인 손상을 평가할 수 없었다. 따라서 구조물의 형상, 운전이력 및 재료물성에 근거하여 실시간 수명소비율 및 잔여수명을 평가하는 기술의 개발이 요구되고 있다. 본 연구에서는 고온 증기헤더의 수명을 실시간으로 평가하는 감시시스템 소프트웨어를 개발하였다. 고온헤더에 대하여 해석된 온도, 응력, 그린함수를 이용하여 취약부위의 실시간 응력을 계산하고 천이 사이클을 카운트하여 크리프 및, 피로수명을 계산하였다. 본 소프트웨어를 개발함으로써 운전이력에 따른 소비수명을 실시간으로 평가하고 운전정보를 기록하여 향후 운전계획, 보수주기 및 교체시기를 결정하는데 지침이 되도록 하였다.

• Nuclear Engineering and Technology
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• 제52권9호
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• pp.1998-2008
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• 2020

Solenoid operated valves (SOV) play important roles in industrial process to control the flow of fluids. Solenoid valves can be found in so many industries as well as the nuclear plant. The ability to be able to detect the presence of faults and predicting the remaining useful life (RUL) of the SOV is important in maintenance planning and also prevent unexpected interruptions in the flow of process fluids. This paper proposes a fault diagnosis method for the alternating current (AC) powered SOV. Previous research work have been focused on direct current (DC) powered SOV where the current waveform or vibrations are monitored. There are many features hidden in the AC waveform that require further signal analysis. The analysis of the AC powered SOV waveform was done in the time and frequency domain. A total of sixteen features were obtained and these were used to classify the different operating modes of the SOV by applying a machine learning technique for classification. Also, a deep neural network (DNN) was developed for the prediction of RUL based on the failure modes of the SOV. The results of this paper can be used to improve on the condition based monitoring of the SOV.