• 제목/요약/키워드: quantitative thinning

검색결과 25건 처리시간 0.027초

Development of Wall-Thinning Evaluation Procedure for Nuclear Power Plant Piping-Part 1: Quantification of Thickness Measurement Deviation

  • Yun, Hun;Moon, Seung-Jae;Oh, Young-Jin
    • Nuclear Engineering and Technology
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    • 제48권3호
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    • pp.820-830
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    • 2016
  • Pipe wall thinning by flow-accelerated corrosion and various types of erosion is a significant and costly damage phenomenon in secondary piping systems of nuclear power plants (NPPs). Most NPPs have management programs to ensure pipe integrity due to wall thinning that includes periodic measurements for pipe wall thicknesses using nondestructive evaluation techniques. Numerous measurements using ultrasonic tests (UTs; one of the nondestructive evaluation technologies) have been performed during scheduled outages in NPPs. Using the thickness measurement data, wall thinning rates of each component are determined conservatively according to several evaluation methods developed by the United States Electric Power Research Institute. However, little is known about the conservativeness or reliability of the evaluation methods because of a lack of understanding of the measurement error. In this study, quantitative models for UT thickness measurement deviations of nuclear pipes and fittings were developed as the first step for establishing an optimized thinning evaluation procedure considering measurement error. In order to understand the characteristics of UT thickness measurement errors of nuclear pipes and fittings, round robin test results, which were obtained by previous researchers under laboratory conditions, were analyzed. Then, based on a large dataset of actual plant data from four NPPs, a quantitative model for UT thickness measurement deviation is proposed for plant conditions.

Development of wall-thinning evaluation procedure for nuclear power plant piping - Part 2: Local wall-thinning estimation method

  • Yun, Hun;Moon, Seung-Jae;Oh, Young-Jin
    • Nuclear Engineering and Technology
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    • 제52권9호
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    • pp.2119-2129
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    • 2020
  • Flow-accelerated corrosion (FAC), liquid droplet impingement erosion (LDIE), cavitation and flashing can cause continuous wall-thinning in nuclear secondary pipes. In order to prevent pipe rupture events resulting from the wall-thinning, most NPPs (nuclear power plants) implement their management programs, which include periodic thickness inspection using UT (ultrasonic test). Meanwhile, it is well known in field experiences that the thickness measurement errors (or deviations) are often comparable with the amount of thickness reduction. Because of these errors, it is difficult to estimate wall-thinning exactly whether the significant thinning has occurred in the inspected components or not. In the previous study, the authors presented an approximate estimation procedure as the first step for thickness measurement deviations at each inspected component and the statistical & quantitative characteristics of the measurement deviations using plant experience data. In this study, statistical significance was quantified for the current methods used for wall-thinning determination. Also, the authors proposed new estimation procedures for determining local wall-thinning to overcome the weakness of the current methods, in which the proposed procedure is based on analysis of variance (ANOVA) method using subgrouping of measured thinning values at all measurement grids. The new procedures were also quantified for their statistical significance. As the results, it is confirmed that the new methods have better estimation confidence than the methods having used until now.

The Preference Analysis for Optimum Density and Understory Vegetation Management in Healing Forests

  • Kang, Jeong Seok;Ju, Jeong Deok;Shin, Chang Seob
    • 인간식물환경학회지
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    • 제22권5호
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    • pp.481-488
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    • 2019
  • The purpose of this study is to suggest how to manage healing forests. Field investigation and surveys were conducted to produce results and 313 questionnaires collected from workers in the forestry sector and ordinary people were analyzed. The results were as follows: it is required to preserve flowering plants, scenic trees, and ecological trees in the understory vegetation, and to remove trees that block the forest landscape, leaving about 50 to 60 percent of the understory vegetation. The preferred density order of broadleaf trees was analyzed as follows: Betula platyphylla > Liriodendron tulipifera > Quercus acutissima. The preferred density order of coniferous trees was analyzed as follows: Abies holophylla > Cryptomerias japonica and Chameacyparis obtusa > Larix kaempferi > Pinus densiflora > Pinus koraiensis. The preferred density in healing forests was 81-89% compared to the number of residual trees for quantitative thinning. Specifically, the preferred density were 87% for P. koraiensis, 86% for L. kaempferi, 81% for P. densiflora, 83% for C. japonica, 84% for C. obtusa and 89% for Q. acutissima. In the case of healing forests, it is recommended to periodically conduct a small-scale thinning with different densities according to the species and diameter of trees based on the results of this study.

지역 및 전역 환경에 대한 세선화 기반 위상지도의 작성 (Thinning-Based Topological Map Building for Local and Global Environments)

  • 권태범;송재복
    • 제어로봇시스템학회논문지
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    • 제12권7호
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    • pp.693-699
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    • 2006
  • An accurate and compact map is essential to an autonomous mobile robot system. For navigation, it is efficient to use an occupancy grid map because the environment is represented by probability distribution. But it is difficult to apply it to the large environment since it needs a large amount of memory proportional to the environment size. As an alternative, a topological map can be used to represent it in terms of the discrete nodes with edges connecting them. It is usually constructed by the Voronoi-like graphs, but in this paper the topological map is incrementally built based on the local grid map using the thinning algorithm. This algorithm can extract only meaningful topological information by using the C-obstacle concept in real-time and is robust to the environment change, because its underlying local grid map is constructed based on the Bayesian update formula. In this paper, the position probability is defined to evaluate the quantitative reliability of the end nodes of this thinning-based topological map (TTM). The global TTM can be constructed by merging each local TTM by matching the reliable end nodes determined by the position probability. It is shown that the proposed TTM can represent the environment accurately in real-time and it is readily extended to the global TTM.

위상잠금 광-적외선 열화상 기술을 이용한 감육결함이 있는 직관시험편의 결함 검출 (Defect detection of wall thinning defect in pipes using Lock-in photo-infrared thermography technique)

  • 김경석;장수옥;박종현;;송재근;정현철
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2008년도 추계학술대회A
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    • pp.317-321
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    • 2008
  • Piping in the Nuclear Power plants (NPP) are mostly consisted of carbon steel pipe. The wall thinning defect is mainly occurred by the affect of the flow accelerated corrosion (FAC) of fluid which flows in carbon steel pipes. This type of defect becomes the cause of damage or destruction of piping. Therefore, it is very important to measure defect which is existed not only on the welding partbut also on the whole field of pipe. Over the years, Infrared thermography (IRT) has been used as a non destructive testing methods of the various kinds of materials. This technique has many merits and applied to the industrial field but has limitation to the materials. Therefore, this method was combined with lock-in technique. So IRT detection resolution has been progressively improved using lock-in technique. In this paper, the quantitative analysis results of the location and the size of wall thinning defect that is artificially processed inside the carbon steel pipe by using IRT are obtained.

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전단간섭계를 이용한 직관시험편의 결함 깊이 측정 (Defect Depth Measurement of Straight Pipe Specimen Using Shearography)

  • 장호섭;김경석
    • 비파괴검사학회지
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    • 제32권2호
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    • pp.170-176
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    • 2012
  • 원자력 산업에 있어서 파이프의 감육결함은 수명평가 및 안전평가에 막대한 손실을 발생 할 수 있다. 비파괴검사 기법을 이용하여 변형, 진동, 결함 평가를 수행하고 있지만, 넓은 면적의 결함을 평가하는 기법이 적으며, 시간이 오래 걸리는 단점이 있다. 원자력 발전소의 2차계통에서 주로 사용되는 탄소강 배관을 대상으로 내부에 인공 감육결함을 가공하고 두께를 서로 다르게 하여 제작하여 Shearography를 이용하여 감육결함부의 변형을 측정하였다. 또한 광 계측을 통하여 변형, 진동, 결함 평가뿐만 아니라 압력용기의 결함깊이를 정량적으로 평가하고자 한다. 본 논문은 전단간섭계를 이용하여 파이프의 내부 감육 결함을 측정하고, 압력에 따른 변형을 제시한 기법을 이용하여 정량적인 결함의 잉여두께를 평가하고자 한다. 변형량을 이용하여 잉여두께 예측결과 실제 결함깊이와 약 7%의 오차로 신뢰성을 확보하였으며, 압력에 따른 변형량과 잉여두께의 DB구축을 통하여 원전 배관의 감육부 건전성 평가에 활용될 수 있을 것이다. 따라서, 본 연구에서 제안하는 압력용기 결함깊이 측정법은 원자력배관의 감육결함 예측 및 건정성 평가 기술 개발 등 이론과 실험이 결함된 기초연구로서 압력용기의 안정성, 건전성, 보수성을 증진시킬 수 있는 기반확립에 기여할 것으로 기대한다.

AHP를 이용한 숲가꾸기 사업종별 평가지표 중요도 산정 (Development of Forest Thinning Evaluation Factors using the Analytic Hierarchy Process)

  • 박주원;조승완;정건휘;김보미;우희성;이요한
    • 한국산림과학회지
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    • 제109권3호
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    • pp.350-360
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    • 2020
  • 본 연구는 효율적인 숲가꾸기 사업 모니터링을 위해 숲가꾸기 사업의 작업종별 평가지표의 중요도를 선정하고 이를 적용한 숲가꾸기 사업 평가지표 개발 연구이다. 숲가꾸기 사업의 작업종별 중요도를 산정하기 위하여 Delphi와 AHP를 이용한 전문가 합의를 총 3차례에 걸쳐 진행하였으며, 선정된 사업추진 프로세스 4개 항목(계획 및 설계, 관리·감독, 감리, 작업품질)과 평가 항목 10개를 선정하여 중요도를 산정하였다. 분석결과, 사업추진 프로세스에서는 계획 및 설계가 가장 중요한 숲가꾸기 평가인자로 선정되었으며 관리·감독, 감리, 작업 품질 순으로 중요도가 산정되었다. 최종 종합 가중치 산정결과, 평가 항목별 우선순위에서는 "산림경영계획서 작성의 적절성" 이 가장 중요도가 높은 것으로 사료되었다. 또한 숲가꾸기 사업과 어린나무 가꾸기 사업에서는 "설계서 작성의 적정성", 조림지 가꾸기와 큰나무 가꾸기 사업에서는 "작업 품질"이 숲가꾸기 평가에 있어 중요한 인자로 나타났다. 본 연구 결과에 따르면, 숲가꾸기 계획 및 설계, 산림경영계획서 작성, 설계서 작성의 적정성 등 숲가꾸기 사업을 위한 설계 및 계획단계에서의 성과가 숲가꾸기 사업의 평가에 있어 많은 영향을 미치는 것으로 사료된다.

폴리에틸렌옥사이드 수용액의 정상유동 특성 (Steady Shear Flow Properties of Aqueous Poly(Ethylene Oxide) Solutions)

  • 송기원;김태훈;장갑식;안승국;이장우;이치호
    • Journal of Pharmaceutical Investigation
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    • 제29권3호
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    • pp.193-203
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    • 1999
  • In order to investigate systematically the steady shear flow properties of aqueous po1y(ethylene oxide) (PEO) solutions having various molecular weights and concentrations, the steady flow viscosity has been measured with a Rheometrics Fluids Spectrometer (RFS II) over a wide range of shear rates. The effects of shear rate, concentration, and molecular weight on the steady shear flow properties were reported in detail from the experimentally measured data, and then the results were interpreted using the concept of a material characteristic time. In addition, some flow models describing the non-Newtonian behavior (shear-thinning characteristics) of polymeric liquids were employed to make a quantitative evaluation of the steady flow behavior, and the applicability of these models was examined by calculating the various material parameters. Main results obtained from this study can be summarized as follows: (1) At low shear rates, aqueous PEO solutions show a Newtonian viscous behavior which is independent of shear rate. At shear rate region higher than a critical shear rate, however, they exhibit a shear-thinning behavior, demonstrating a decrease in steady flow viscosity with increasing shear rate. (2) As an increase in concentration and/or molecular weight, the zero-shear viscosity is increased while the Newtonian viscous region becomes narrower. Moreover, the critical shear rate at which the transition from the Newtonian to shear-thinning behavior occurs is decreased, and the shear-thinning nature becomes more remarkable. (3) Aqueous PEO solutions show a Newtonian viscous behavior at shear rate range lower than the inverse value of a characteristic time $1/{\lambda}_E$, while they exhibit a shear-thinning behavior at shear rate range higher than $1/{\lambda}_E$. For aqueous PEO solutions having a broad molecular weight distribution, the inverse value of a characteristic time is not quantitatively equivalent to the critical shear rate, but the power-law relationship holds between the two quantities. (4) The Cross, Carreau, and Carreau-Yasuda models are all applicable to describe the steady flow behavior of aqueous PEO solutions. Among these models, the Carreau-Yasuda model has the best validity.

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레이저 스페클간섭법에 의한 STS430의 열팽창계수 측정 (Thermal Expansion Coefficient Measurement of STS430 by Laser Speckle Interferometry)

  • 김경석;이항서;정현철;양승필
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 2004년도 추계학술대회 논문집
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    • pp.29-33
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    • 2004
  • This paper presents ESPI system for the measurement of thermal expansion coefficient of STS430 up to 1,000$^{\circ}C$. Existing methods, strain gauge and moire have the limitation of contact to object and do not supply the coefficient up to 800$^{\circ}C$. There needs to measure the data up to 800$^{\circ}C$, because heat resistant materials have high melting temperature up to 1,000$^{\circ}C$. In previous studies related to thermal strain analysis, the quantitative results are not reported by ESPI at high temperature, yet. In-plane ESPI and vacuum chamber for the reduction of air turbulence and oxidation are designed for the measurement of the coefficient up to 1,000$^{\circ}C$and speckle correlation fringe pattern images are processed by commercial image filtering tool-smoothing, thinning and enhancement- to obtain quantitative results, which is compared with references data. The comparison shows two data are agreed within 4.1% blow 600$^{\circ}C$ however, there is some difference up to 600$^{\circ}C$. Also, the incremental ratio of the coefficient is changed up to 800$^{\circ}C$. The reason is the phase transformation of STS430 probably begins at 800$^{\circ}C$.

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