• Nuclear Engineering and Technology
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• 제45권1호
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• pp.99-106
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• 2013

Thermal fatigue is a significant long-term degradation mechanism in nuclear power plants. In particular, as operating plants become older and life time extension activities are initiated, operators and regulators need screening criteria to exclude risks of thermal fatigue and methods to determine significant fatigue relevance. In general, the common thermal fatigue issues are well understood and controlled by plant instrumentation at fatigue susceptible locations. However, incidents indicate that certain piping system Tee connections are susceptible to turbulent temperature mixing effects that cannot be adequately monitored by common thermocouple instrumentations. Therefore, in this study thermal fatigue evaluation of piping system Tee-connections is performed using the fluid-structure interaction (FSI) analysis. From the thermal hydraulic analysis, the temperature distributions are determined and their results are applied to the structural model of the piping system to determine the thermal stress. Using the rain-flow method the fatigue analysis is performed to generate fatigue usage factors. The procedure for improved load thermal fatigue assessment using FSI analysis shown in this study will supply valuable information for establishing a methodology on thermal fatigue.

• Tribology and Lubricants
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• 제30권2호
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• pp.124-129
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• 2014

The piping system accounts for a large portion of the machinery structure of a plant, and is considered as a very important mechanical structure for plant safety. Accordingly, it is used in most energy plants in the nuclear, gas, and heavy chemical industries. In particular, the piping system for a nuclear plant is generally complicated and uses the reactor and its cooling system. The piping equipment is exposed to diverse loads such as weight, temperature, pressure, and seismic load from pipes and fluids, and is used to transfer steam, oil, and gas. In ultrasound infrared thermography, which is an active thermography technology, a 15-100 kHz ultrasound wave is applied to the subject, and the resulting heat from the defective parts is measured using a thermography camera. Because this technique can inspect a large area simultaneously and detect defects such as cracks and delamination in real time, it is used to detect defects in the new and renewable energy, car, and aerospace industries, and recently, in piping defect detection. In this study, ultrasound infrared thermography is used to detect information for the diagnosis of nuclear equipment and structures. Test specimens are prepared with piping materials for nuclear plants, and the optimally designed ultrasound horn and ultrasound vibration system is used to determine damages on nuclear plant piping and detect defects. Additionally, the detected images are used to improve the reliability of the surface and internal defect detection for nuclear piping materials, and their field applicability and reliability is verified.

• 한국농공학회:학술대회논문집
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• 한국농공학회 2001년도 학술발표회 발표논문집
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• pp.344-350
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• 2001

Piping is a phenomenon where seeping water progressively erodes or washes away soil particles, leaving large voids (Pipes led to the development of channels) in the soil. Piping failure caused by heave can be expected to occur on the downstream side of a hydraulic structure such as fill dams when the uplift forces of seepage exceed the downward forces due to the submerged weight of the soil. The way to prevent erosion and piping and to reduce damaging uplift pressures is to use a protective filter or to construct cutoff wall/imperious blanket. Therefore, all the hydraulic structures faced/with soil materials should be taken the safety against piping into consideration.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.480-485
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• 2011

In this study, the seismic analysis of power plant piping system was performed using finite element model. This study was performed by ANSYS 12.1. For qualification of power plant piping system, the response spectrum analysis was performed using the given operating basis earthquake(OBE) and safe shutdown earthquake(SSE) floor response spectrum. The maximum stresses of power plant piping system were 166 MPa under OBE condition and 281 MPa under SSE condition. Thus, it can shown that the structural integrity of tpower plant piping system has a stable structure for seismic load conditions.

• 한국지반공학회논문집
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• 제39권9호
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• pp.51-61
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• 2023

본 연구의 목적은 보 구조물 기초지반의 파이핑 안정성을 모니터링할 수 있는 지표를 선정하고, 선정 지표를 활용한 파이핑 안정성 모니터링 방법을 제시하는 데에 있다. 기존 연구 결과에 대한 검토와 침투모사 수치해석 결과로부터 보 기초지반에서의 간극수압 변화를 파이핑 모니터링 지표로 선정하였다. 운영 중인 보에서 간극수압계의 설치 상황을 감안하여, 간극수압계가 보 기초 하부에 1개 또는 2개 설치된 경우 각각에 대해, 다양한 상류 저수위 조건에 따른 침투해석을 수행하였다. 침투해석 결과로부터 파이핑 모니터링 방안을 이러한 각각의 경우에 대하여 제안하였다. 아울러, 제안된 모니터링 방안을 운영 중인 보에 시범 적용하였고 이를 통해 그 실효성을 확인하였다.

• 대한조선학회논문집
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• 제55권2호
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• pp.124-135
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• 2018

In order to secure manufacturing competitiveness of offshore plants, piping process is one of the most important processes. This study is about the design of management system for piping materials manufacturing of the offshore plant. As a result of the study, we analyzed the system and algorithms needed for the processing of piping material products and designed the structure of the entire management system. We conducted a process analysis of the design, manufacturing and installation processes. And also we proposed a system structure to improve the various problems that have come out. We also proposed an algorithm to determine the delivery order of the pipe spools, and proposed a raw material management system for the manufacturing of the pipe spools. And we designed a manufacturing process management system to manage the risk of pipe materials delivery. And finally we proposed a data structure for the installation process management system. The data structures and algorithms were actually implemented, and applied the actual process data to verify the effect of the system.

• 한국지반공학회지:지반
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• 제5권4호
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• pp.17-26
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• 1989

토질제체 설계시 piping에 대한 대책으로 현재에 적용되고 있는 creep비는 원래 Masonry 또는 콘크리트 댐의 저면과 기초지반토질과의 접촉면에 따른 침투에 의한 piping의 방지를 위한 기준이었다. 본 연구에서는 이 creep비가 토질로 형성된 제체에서도 적용될 수 있는지의 여부를 모형실험을 통하여 구명하고 현행 creep비기준을 재평가 하였다. 연구결과 토질제체에서 발생되는 piping파괴는 토질제체와 기초지반과의 확측면에서는 발생하 지 않았으며 토질종류에 관계없이 제체내에서만 발생하였다. 따라서 제체를 형성하는 토질과 기초 지반토질중 투수계수가 적은 토질을 기준으로 creep비를 정하는 현재의 설계기준은 불합리함을 알 수 있었다.

• 한국압력기기공학회 논문집
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• 제17권2호
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• pp.101-108
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• 2021

To date, a number of stress intensity factor (SIF) solutions have been proposed for the cylindrical structure with circumferential through-wall cracks. However, each solution has a different format as well as applicable range. It is also known that there is a significant difference in predicted SIF values depending on the shape of the structure and the size of the crack. In this study, the applicability of various SIF solutions was analyzed by comparing the finite element analysis results for the case where a tensile load is applied to the cylindrical structure with circumferential through-wall crack. It is found that the calculated SIF gradually decreases and converges to a certain value with increasing length-to-radius ratio. Therefore, an appropriate length-to-radius ratio should be set in consideration of the dimensions of the actual cylindrical structure. For piping with sufficiently long cylinder, the ASME solution is found to be the most appropriate, and for a short cylinder, the API solution should be applied. On the other hand, the WEC solution requires careful attention to its application.

• 한국유체기계학회 논문집
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• 제7권1호
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• pp.30-35
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• 2004

The HANARO, a multi-purpose research reactor of 30 MWth open-tank-in-pool type, has been under normal operation since its initial criticality in February, 1995. Many experiments should be safely performed to activate the utilization of the HANARO. HANARO flow simulation facility is being developed for the endurance test of reactivity control units for extended life time and the verification of structural integrity of those experimental equipments prior to loading in the HANARO. This facility is composed of three major parts; a half-core structure assembly, a flow circulation system and a support system. The flow circulation system is composed of a circulation pump, a core flow piping, a core bypass flow piping and instruments. The system is to be filled with de-mineralized water and the flow should be met the design requirements to simulate a similar flow characteristics in the core channel of the half-core structure assembly to the HANARO. This paper, therefore, presents an analytical analysis to study the flow behavior of the system. Computational flow analysis has been performed for the verification of system pressure variation through the three-dimensional analysis program with the standard $k-{\epsilon}$ turbulence model and for the verification of the structural piping integrity through the finite element method. According to the analysis results, it could be said that the design requirements and the structural piping integrity of the flow circulation system are satisfied.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.780-785
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• 2005

Vibration has been severly increased at the branch pipe of main steam header since the commercial operation of a nuclear power plant. Intense broad band disturbance flow at the discontinuous region such as elbow, valve or heather generates the acoustical pulsation which is propagated through the piping system. The pulsation becomes the source of low frequency vibration at piping system. If it coincide with natural frequency of the pipe system, excessive vibration is made. High level vibration due to the pressure pulsation related to high dynamic stress, and ultimately, to failure probability affects fatally the reliability and confidence of plant piping system. This paper discusses vibration effect for the branch pipe system due to acoustical pulsations by broad band disturbance flow at the large main steam header in 7nn nuclear power plant. The exciting sources and response or the piping system are investigated by using on site measurements and analytical approaches. It is identified that excessive vibration is caused by acoustical pulsations of 1.3Hz, 4.4Hz and 6.6Hz transferred from main steam header, which are coincided with fundamental natural frequencies of the piping structure. The energy absorbing restraints with additional stiffness were installed to reduce excessive vibration.