• 한국해양공학회지
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• 제24권4호
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• pp.38-46
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• 2010

The wall thinning phenomenon of pipes was simulated as metal loss due to erosion and corrosion. Such wall thinning defects in the pipes of power plants are a very important safety consideration. In this study, we analyzed wall thinning defects that occurred by weld bead of weld zone of boost pump recirculation pipe. From the results of the analysis of pipe failures, numerical analysis was performed by Fluent v6.3.26 using the standard k-$\varepsilon$ model of the weld bead shape, such as an elliptical or a spherical shape, on the inner wall of the pipe. Using the results obtained, we showed the overlap effect by cavitations corrosion and erosion-corrosion at the bottom of the wall-thinning defect.

• 대한기계학회논문집B
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• 제34권4호
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• pp.429-435
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• 2010

국내를 포함한 전 세계 50여개 원전의 발전사업자는 유동가속부식에 의한 탄소강 배관 감육을 관리하기 위하여 CHECWORKS 프로그램을 이용하고 있다. CHECWORKS 프로그램은 대구경 배관에만 적용 가능한 것으로 알려져 있기 때문에 소구경 배관에 대해서는 현장 배관감육 관리 담당자의 경험과 판단에 따라 배관을 관리하고 있다. 이에 따라 본 논문에서는 국내 원전 소구경 배관 4개 라인그룹에 대하여 CHECWORKS 프로그램과 FLUENT 코드를 이용하여 유동가속부식과 유동 특성을 분석하였다. 그 결과 현장 배관감육 관리 담당자의 기술력에 따라 CHEC- WORKS 프로그램도 소구경 배관 감육 관리에 이용할 수 있는 것으로 나타났다.

• 대한기계학회논문집A
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• 제36권10호
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• pp.1227-1234
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• 2012

본 연구에서는 감육결함이 가공된 실배관 곡관 시편을 대상으로 10 MPa의 내압과 반복 굽힘하중 조건에서 피로 시험을 수행하였다. 시험에는 감육결함이 곡관의 외호부와 내호부에 존재하는 경우를 고려하였으며, 반복 하중으로는 완전 역방향의 변위제어 형태로 작용되는 In-plane 상의 굽힘하중이 고려되었다. 실험 결과, 감육결함이 곡관의 외호부에 존재하는 경우에는 결함부가 아닌 곡관의 측면에서 축방향 균열이 생성되었다. 또한, ASME Sec.III의 설계 피로곡선에서 예측된 건전 곡관의 피로수명보다 긴 피로수명을 보였으며, 피로수명이 결함 길이에 크게 영향을 받지 않았다. 반면, 결함이 내호부에 존재하는 곡관은 내호부에서 원주방향 균열이 발생하였으며, 피로수명은 ASME Sec.III의 설계 피로곡선에서 예측한 건전 곡관의 피로수명보다 짧은 값을 보였다. 또한, 내호부 감육 곡관의 피로수명은 결함 길이가 감소함에 따라 뚜렷이 감소하였다.

• Journal of Magnetics
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• 제18권3호
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• pp.342-347
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• 2013

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.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.27-28
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• 2006

This study performs to investigate deformation of wall thinning pipe and to find out the position of the internal thinning defect by shearography. Shearography is one of optical methods those have applied to nondestructive testing (NDT) and the strain/stress analysis. This technique has the merit of the directly measuring the first derivative of displacement, sensitivity of which can be adjusted by the handling of optical component in interferometer. In this paper, we tested carbon steel pipe locally wall thinned and loaded internal pressure and developed the nondestructive out-of-plane deformation analysis technique fur internal thinning defect of elbow by shearography. From the results, it was confirmed that this technique is proper to the practical application on the pipe line system with internal defect.

• 대한기계학회논문집A
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• 제30권5호
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• pp.533-542
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• 2006

In order to assess the integrity of pipes with local thinning area, the plastic strain as well as the elastic strain at the root of thinned region are required particularly when fluctuating load is applied to the pipe. For estimating elastic-plastic strain at local wall thinning area in a straight pipe under tensile load, an estimation model with idealized fully circumferential constant depth wall thinning area is proposed. Based on the compatibility and equilibrium equations a nonlinear estimation equation, from which local elastic-plastic strain can be determined as a function of pipe/defect geometry, material and the applied strain was derived. Estimation results are compared with those from detailed elastic-plastic finite element analysis, which shows good agreements. Noting that practical wall thinning in nuclear piping has not only a circular shape but also a finite circumferential length, the proposed solution for the ideal geometry is extended based on two-dimensional and three-dimensional numerical analysis of pipes with circular wall thinning.

• Steel and Composite Structures
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• 제20권4호
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• pp.931-950
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• 2016

Ratcheting deformation of pressurized Z2CND18.12N stainless steel $90^{\circ}$ elbow pipe with local wall thinning subjected to constant internal pressure and reversed bending was studied using finite element analysis. Chen-Jiao-Kim (CJK) kinematic hardening model, which was used to simulate ratcheting behavior of pressurized $90^{\circ}$ elbow pipe with local wall thinning at extrados, flanks and intrados, was implemented into finite element software ANSYS. The local wall thinning was located at extrados, flanks and intrados of $90^{\circ}$ elbow pipe, whose geometry was rectangular cross-section. The effect of depth, axial length and circumferential angle of local wall thinning at extrados, flanks and intrados on the ratcheting behaviors of $90^{\circ}$ elbow pipe were studied in this paper. Three-dimensional elastic-plastic analysis with Chen-Jiao-Kim (CJK) kinematic hardening model was carried out to evaluate structural ratcheting behaviors. The results indicated that ratcheting strain was generated mainly along the hoop direction, while axial ratcheting strain was relatively small.

• Journal of Magnetics
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• 제21권1호
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• pp.57-60
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• 2016

Non Destructive Testing (NDT) methods that are capable of detecting the wall thinning and defects through insulation and cladding sheets are necessary. In this study we developed a Pulsed Eddy Current (PEC) system to detect wall thinning of ferro magnetic steel pipes covered with 95 mm thick fiber glass thermal insulator and shielded with aluminum plate of thickness 0.4 mm. In order to confirm the thickness change due to wall thinning, two different sensors, a hall sensor and a search coil sensor were used as a detecting element. In both the cases, the experimental data indicates a considerable change in the detected pulse corresponding to the change in sample thickness. The thickness of the tube was made to change such as 2.5 mm, 5 mm and 8 mm from the inner surface to simulate wall thinning. Fast Fourier Transform (FFT) was calculated using window approach and the results were summarized which shows a clear identification of thickness change in the test specimen by comparing the magnitude spectra.

• Corrosion Science and Technology
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• 제15권4호
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• pp.182-188
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• 2016

Significant piping wall thinning caused by Flow-Accelerated Corrosion (FAC) and Erosion-Corrosion (EC) continues to occur, even after the Mihama Power Station unit 3 secondary pipe rupture in 2004, in which workers were seriously injured or died. Nuclear power plants in many countries have experienced FAC and EC-related cases in steam cycle piping systems. Korea has also experienced piping wall thinning cases including thinning in the downstream straight pipe of a check valve in a feedwater pump line, the downstream elbow of a control valve in a feedwater flow control line, and failure of the straight pipe downstream of an orifice in an auxiliary steam return line. Cause analyses were performed by reviewing thickness data using Ultrasonic Techniques (UT) and, Scanning Electron Microscope (SEM) images for the failed pipe, and numerical simulation results for FAC and EC cases in Korea Nuclear Power Plants. It was concluded that the main cause of wall thinning for the downstream pipe of a check valve is FAC caused by water vortex flow due to the internal flow shape of a check valve, the main cause of wall thinning for the downstream elbow of a control valve is FAC caused by a thickness difference with the upstream pipe, and the main cause of wall thinning for the downstream pipe of an orifice is FAC and EC caused by liquid droplets and vortex flow. In order to investigate more cases, additional analyses were performed with the review of a lot of thickness data for inspected pipes. The results showed that pipe wall thinning was also affected by the operating condition of upstream equipment. Management of FAC and EC based on these cases will focus on the downstream piping of abnormal or unusual operated equipment.

• Corrosion Science and Technology
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• 제19권3호
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• pp.131-137
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• 2020

A number of piping components in the secondary system of nuclear power plants (NPPs) are exposed to aging mechanisms, such as flow-accelerated corrosion (FAC), cavitation, flashing, solid particle erosion, and liquid droplet impingement erosion. Those mechanisms may lead to thinning, leaking, or rupture of the components. Due to the pipe ruptures caused by wall thinning in Surry unit 2 in the USA in 1986 and Mihama unit 3 in Japan in 1994, pipe wall thinning management has emerged as one of the most important issues in the nuclear industry. To manage pipe wall thinning, a foreign program has been utilized for NPPs in Korea since 1996. As our experience and knowledge of pipe wall thinning management have accumulated, our program needs to reflect our experience, requests from users, and the result of recent experiments using Flow Accelerated Corrosion Testing System (FACTS). FACTS is the empirical experimental facility developed by Korea Atomic Energy Research Institute (KAERI) for tests. Accordingly, KEPCO-E&C developed a 3D-based pipe wall thinning management program called ToSPACE in 2016. This paper describes a comparison between the FAC analysis results using ToSPACE and the experimental results using FACTS to verify their applicability to pipe wall thinning management in NPPs.