침식-부식에 의해 감육된 배관의 파손거동에 미치는 감육위치의 영향

안석환,석금철,남기우 한국해양공학회 2007 韓國海洋工學會誌 Vol.21 No.1

This study on the effects of local wall-thinned location on the fracture behavior of pipes was carried out, and the results were compared with the analytical results. Local wall-thinning for the bending test was machined with various sizes on the outside of pipes, in order to simulate the metal loss,due to erosion/corrosion. In addition, we had carried out FE analysis for the pipes with local wall thinning on the inside, and its results were comparatively studied with that of the outside. Three-dimensional elasto-plastic analyses were able to accurately simulate fracture behaviors of inner or outer wall thinning. Fracture types, obtained from the experiments and analyses, could be classified into ovalization, local buckling and crack initiation,depending on the thinned length and thinned ratio. Based onthe results, the fracture behaviors of pipes with the outer wall thinning can be applied to estimate the fracture behaviors of pipes with the inner wall thinning.1. 서 론현대 산업사회의 에너지 수요는 나날이 가일층 증가하고 있는 경향이다. 특히, 우리나라는 에너지의 수급을 원자력발전에 크게 의지하고 있는 실정이다. 원자력 플랜트의 건설비용에 막대한 재원이 필요하기 때문에, 이에 원자력 플랜트에 사용되는 기기들의 경년열화에 대해 대체방안을 수립함으로 서 사용 기기들의 수명연장을 가져 올 필요성이 있다. 여러 가지 기기들 중 배관은 상당부분을 차지하고 있다. 따라서 배관에 대한 건전성평가를 통하여 플랜트의 안전성을 확보해야만 한다. 그러나 원자력발전 플랜트 배관은 고온고압수나 증기가 고속으로 흐르기 때문에 Erosion/Corrosion 현상에 의한 국소 감육이 발생할 가능성이 많다. 이러한 국소 감육의 발생으로 인하여 배관시스템의 전체의 신뢰성이 떨어질 가능성이 농후하다. 감육에 의해 발생한 대표적인 원전사고로는 1986년에 발생한 미국의 Surry 원자력발전소 사고를 비롯하여 가장 최근에 발생한 일본 Mihama 원자력발전소 사고 등이 보고되고 있다(CNN. com, 2004; Virginia Electric and

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 Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.9

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.

탄소강 배관 티에서의 유동가속부식으로 인한 감육 현상 규명

김경훈 ( Kyung Hoon Kim ),이상규 ( Sang Kyu Lee ),강덕원 ( Kang Deok Won ) 한국분무공학회 2011 한국액체미립화학회지 Vol.16 No.2

When pipe components made of carbon steel in nuclear, fossil, and industry plants are exposed to flowing fluid, wall thinning caused by FAC(flow accelerated corrosion) can be generated and eventually ruptured at the position of pressure boundary. The aim of this study is to identify the locations at which local wall thinning occurs and to determine the turbulence coefficient related to local wall thinning. Experiment and numerical analyses for the tee sections of down scaled piping components were performed and the results were compared. In particular, flow visualization experiment which was used alkali metallic salt was performed to find actual location of local wall thinning inside tee components. In order to determine the relationship between turbulence coefficients and local wall thinning, numerical analyses were performed for tee components in the main feedwater systems. The turbulence coefficients based on the numerical analyses were compared with the local wall thinning based on the measured data. From the comparison of the results, the vertical flow velocity component(Vr) flowing to the wall after separating in the wall due to the geometrical configuration and colliding with the wall directly at an angle of some degree was analogous to the configuration of local wall thinning.

배관계 티에서 유동가속부식으로 인한 난류속도성분과 국부감육의 관계 규명

김경훈(Kyung Hoon Kim),이상규(Sang Kyu Lee),조연수(Yun Su Cho),황경모(Kyung Mo Hwang) 대한설비공학회 2011 설비공학 논문집 Vol.23 No.7

When pipe components made of carbon steel in nuclear, fossil, and industry are exposed to flowing fluid, wall thinning caused by FAC(flow accelerated corrosion) can be generated and eventually ruptured at the portion of pressure boundary. A study to identify the locations generating local wall thinning and to disclose turbulence coefficient related to the local wall thinning was performed. Experiment and numerical analyses for tee of down scaled piping components were performed and the results were compared. In particular, flow visualization experiment which was used alkali metallic salt was performed to find actual location of local wall thinning inside tee components. To disclose the relationship between turbulence coefficients and local wall thinning, numerical analyses were performed for tee components. The turbulence coefficients based on the numerical analyses were compared with the local wall thinning based on the measured data. From the comparison of the results, the vertical flow velocity component(Vr) flowing to the wall after separating in the wall due to the geometrical configuration and colliding with the wall directly at an angle of some degree was analogous to the configuration of local wall thinning.

Buckling and Post Buckling of Thin-walled Composite Columns with Intermediate-stiffened Open Cross-section Under Axial Compression

이재홍,Huu Thanh Nguyen,김승억 한국강구조학회 2009 International Journal of Steel Structures Vol.9 No.3

The thin-walled composite columns with an open cross-section reinforced by intermediate stiffener under axial compression have been considered. The finite element method is employed to study the buckling behaviour of the thin-walled composite column. Eigenvalue analyses are carried out first to predict the buckling load and buckling mode shapes of the column, and then the geometric nonlinear analyses are performed to investigate the nonlinear buckling properties and post-buckling behaviour of the thin-walled structures. The type of angle ply symmetric laminate is used. The investigation is performed over several values of ply arrangement angle and various values of stiffener parameter. The numerical results show a significant effect of the intermediate stiffeners and composite ply angle on loading capacity and buckling behaviour of the thin-walled composite column. The research provides insight into the thin-walled structure and composite laminate, which is employed to enhance the loading capacity of thin-walled composite structures. The thin-walled composite columns with an open cross-section reinforced by intermediate stiffener under axial compression have been considered. The finite element method is employed to study the buckling behaviour of the thin-walled composite column. Eigenvalue analyses are carried out first to predict the buckling load and buckling mode shapes of the column, and then the geometric nonlinear analyses are performed to investigate the nonlinear buckling properties and post-buckling behaviour of the thin-walled structures. The type of angle ply symmetric laminate is used. The investigation is performed over several values of ply arrangement angle and various values of stiffener parameter. The numerical results show a significant effect of the intermediate stiffeners and composite ply angle on loading capacity and buckling behaviour of the thin-walled composite column. The research provides insight into the thin-walled structure and composite laminate, which is employed to enhance the loading capacity of thin-walled composite structures.

탄소강 배관 엘보우에서 유동가속부식으로 인한 난류 속도 성분과 국부 감육의 상관관계

이상규(Sang Kyu Lee),강덕원(Kang Deok Won),김경훈(Kim Kyung Hoon),황경모(Hwang Kyung Mo) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.4

탄소강으로 제작된 산업제의 플랜트 및 발전소의 배관의 내부로 유제가 흐르게 되면 유동가속부식이라는 손상을 받아 국부적으로 두께가 얇아지고 결국에는 파손되는 경우가 많다. 따라서, 본 연구의 목적은 국부감육을 실제적으로 분석하고 그와 관련된 난류매개변수를 밝혀내는데 있다. 축소 제작된 엘보우를 대상으로 실험과 수치해석을 수행하였으며 특히, 실제적인 국부감육 발생 위치를 찾아내기 위해 알칼리 금속염을 사용하여 감육 유로가시화 실험을 수행하였다. 수치해석에 기초한 난류매개 변수와 국부감육 두께를 비교 및 분석하였다. 결과 값 비교를 통하여 반경 방향 유속 Vr이 국부 감육 현상과 가장 연관성이 높은 것으로 나타났다. When pipe components made of carbon steel in nuιlear, fossil , and industry are exposed to flowing fluid, wall thinning caused by FAC(Flow Accelerated Corrosion) can be generated and eventually ruptured. A study to identify the locations generating local wall thinning and to disclose turbulence coefficient related to the local wall thinning was performed. Experiment and numerical analyses for elbow of down scaled piping components were performed. In particular, flow visualization experiment which was used alkali metallic salt was performed to find actual location of local wall thinning. The turbulence coefficients based on the numerical analyses were compared with the local wall thinning thickness. From the comparison of the results, the vertical flow velocity component(Vr) flowing to the wall after separating in the wall due to the geometrical configuration and colliding with the wall directly at an angle of some degree was analogous to the configuration of local wall thinning.

배관 엘보우에서 유동가속부식으로 인한 난류 속도 성분과 국부 감육의 상관관계

이상규(Sang Kyu Lee),조연수(Yun Su Cho),김경훈(Kyung Hoon Kim),황경모(Kyung Mo Hwang) 대한설비공학회 2011 대한설비공학회 학술발표대회논문집 Vol.2011 No.7

When pipe components made of carbon steel in nuclear, fossil, and industry are exposed to flowing fluid, wall thinning caused by FAC(Flow Accelerated Corrosion) can be generated and eventually ruptured. A study to identify the locations generating local wall thinning and to disclose turbulence coefficient related to the local wall thinning was performed. Experiment and numerical analyses for elbow of down scaled piping components were performed. In particular, flow visualization experiment which was used alkali metallic salt was performed to find actual location of local wall thinning. From the comparison of the results, the vertical flow velocity component(Vr) flowing to the wall after separating in the wall due to the geometrical configuration and colliding with the wall directly at an angle of some degree was analogous to the configuration of local wall thinning.

Review paper: Application of the Pulsed Eddy Current Technique to Inspect Pipelines of Nuclear Plants

D. G. Park,C. S. Angani,M. B. Kishore,G. Vertesy,D. H. Lee 한국자기학회 2013 Journal of Magnetics Vol.18 No.3

Local wall thinning in pipelines affects the structural integrity of industries, such as nuclear power plants (NPPs). In the present study, a development of pulsed eddy current (PEC) technology that detects the wall thinning of pipelines covered with insulation is reviewed. The methods and experimental results, which have two kinds of probe with a single and double core, were compared. For this purpose, the single and double core probes having one and two excitation coils have been devised, and the differential probe with two Hall sensors has been fabricated to measure the wall thinning in insulated pipelines. The test sample is a stainless steel having different thickness, laminated by plastic insulation to simulate the pipelines in NPPs. The excitation coils in the probe is driven by a rectangular current pulse, the difference of two Hall sensors has been measured as a resultant PEC signal. The peak value of the detected signal is used to describe the wall thinning. The double core probe has better performance to detect the wall thinning covered with insulation; the single core probe can detect the wall thinning up to an insulation thickness of 18 mm, whereas the double probe can detect up to 25 mm. The results show that the double core PEC probe has the potential to detect the wall thinning in an insulated pipeline of the NPPs

Seismic Response Investigation and Nonlinear Numerical Analysis of Cold-Formed Thin-Walled Steel Tube Truss Shear Walls

Jingfeng Wang,Wanqian Wang,Shuai Pang,Bo Yu 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.5

In order to satisfy the requirements of seismic capacity of cold-formed thin-walled steel structure in low- and multi-rise buildings, an innovative cold-formed thin-walled steel tube truss (CFSTT) shear wall sheathed with both-side oriented strand board (OSB) was proposed in this paper. Five full-scale specimens of CFSTT shear walls which composed of square cold-formed thin-walled steel tubes, tracks, galvanized V-shaped connectors and OSB panels were tested under low-cyclic loading. The seismic performance of CFSTT shear wall was evaluated in terms of hysteretic behavior, envelop curves, ductility and energy dissipation, etc. Then, a practical nonlinear simplifi ed analysis method of CFSTT shear walls under low-cyclic reversed lateral loading was proposed based on the principle of equivalent tie rod model. The double- and fourlimb lattice studs were also simplifi ed as single steel tubes. Besides, a pivot modeling approach was suggested to stimulate the sheathing-to-frame connection. Subsequently, the fi nite element models of CFSTT shear walls were established based on this simplifi ed method and verifi ed by the experimental data. Numerical and experimental results indicated that CFSTT shear walls exhibited excellent seismic performance, and the accuracy of the simplifi ed of lattice stud was verifi ed. Furthermore, the simplifi ed method proposed in this paper will highly facilitate conducting the nonlinear analysis for shear walls.

배관 감육부의 소성 붕괴 강도

안석환(S. H. Ahn),이수식(S. S. Lee),남기우(K. W. Nam) 한국동력기계공학회 2004 한국동력기계공학회 학술대회 논문집 Vol.- No.-

In pipes used at energy plants, those had exposed to various degradations such as fatigue, creep and corrosion etc. in-service periods. Of them, sometimes, the local wall thinning may result from severe erosion-corrosion damage. Therefore, fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear power plant. However, studies on the effects of local wall thinning on strength and fracture behaviors of piping system are rarely. In this paper, so, the monotonic bending test was performed of full-scale carbon steel pipes with local wall thinning. A monotonic bending load was applied to wall thinned straight pipe specimens by four-point loading at ambient temperature without internal pressure. From the tests, fracture behaviors and plastic collapse strength of locally thinned pipes were manifested systematically. The observed failure modes were divided into four types; ovalization, crack initiation after ovalization, local buckling and crack initiation after local buckling. Also, the strength and the allowable limit of piping system with local wall thinning were evaluated.