• Nuclear Engineering and Technology
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• 제53권5호
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• pp.1580-1586
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• 2021

The application of induction bending processes to industrial pipe production is increasing. The induction bending process has the effect of reducing the number of inspections and preventing leaks by reducing the weld of the pipe. For these reasons, efforts have been made to apply an induction bending process to the pipe of the PGSFR under development in Korea and this is the first attempt in the SFR design. Since the PGSFR pipe has a relatively large diameter-to-thickness ratio, it is difficult to fabricate an induction bending pipe that meets the requirements. In addition, the material properties may change because the pipe heats to a very high temperature during the induction bending process. In this study, P91 pipes were fabricated by induction bending, and the results from analyzing the induction bending process' applicability to the P91 pipe of the PGSFR are examined. The various dimensional measurements of the pipes fabricated by the induction bending process were surveyed to determine whether the requirements of the ASME Code were met. The minimum thickness, ovality, and wall buckling measured in the fabricated pipe met all the requirements. Tensile, impact, and hardness tests at various locations of the fabricated pipe also satisfied the requirements.

• 한국압력기기공학회 논문집
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• 제18권1호
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• pp.26-35
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• 2022

When piping system in a nuclear power plant is subjected to a beyond design seismic condition, it is important to accurately determine possibility of crack initiation and, if initiation occurs, its location and time. From recent experimental works on elbow pipes, it was found that the crack initiation location and crack propagation direction of the SA403 WP316 stainless steel elbow pipe were affected by the pipe thickness. In this paper, the crack initiation location and crack propagation direction for SA403 WP316 stainless steel elbow pipes with different thickness were analyzed via elastic-plastic finite element analysis. Based on FE results, the effect of the pipe thickness on different crack initiation location and crack propagation direction was analyzed using ovality, stress and strain components. It was also confirmed that the presence of internal pressure had no effect on the crack initiation location and crack propagation direction.

• 대한기계학회논문집A
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• 제24권2호
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• pp.279-289
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• 2000

Residual stress induced in U-bending and tube-to-tubesheet joint processes of PWR's row-1 heat exchanger tube was measured by X-ray method and Hole-Drilling Method(HDM). Compressive residual stresses(-) at the extrados surface were induced in U-bending, and its maximum value reached -319 MPa in axial direction at the position of $\psi$ = $0^{\circ}$. Tensile residual stresses(+) of $\sigma_{zz}$ = 45 MPa and $\sigma_{\theta\theta}$ = 25 MPa were introduced in the intrados surface at the position of $\psi$ = $0^{\circ}$. Maximum tensile residual stress of 170 MPa was measured at the flank side at the position of $\psi$ = $90^{\circ}$, i.e., at apex region. It was observed that higher stress gradient was generated at the irregular transition regions (ITR). The trend of residual stress induced by U bending process of the tubes was found to be related with the change of ovality. The residual stress induced by the explosive joint method was found to be lower than that by the mechanical roll method. The gradient of residual stress along the expanded tube was highest at the transition region (TR), and the residual stress in circumferential direction was found to be higher than the residual stress in axial direction.

• 대한기계학회논문집A
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• 제38권7호
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• pp.809-815
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• 2014

최근들어 원자력 발전소에 유도 가열 공정으로 굽힌 배관을 적용하려는 동향이 있다. 이러한 유도 가열 굽힘 공정 동안의 열-기계적 메커니즘에 의해 잔류응력이 발생할 수 있다. 잔류응력은 균열 발생과 성장에 중요한 영향을 미치는 균열 구동력들 중의 하나이다. 그러나, 기존 연구들은 두께 변화, 타원도와 같은 기하학적 형상 변이에 집중하고 있는 반면 공정 변수가 잔류응력에 미치는 영향과 관련된 연구는 찾아보기 힘들다. 본 연구에서는 316 오스테나이트 스테인리스 강으로 제작된 유도 가열 굽힘 배관의 잔류응력 분포에 미치는 공정 변수의 영향을 유한요소 변수 해석을 통해 고찰하였다. 고찰결과, 굽힘 모멘트와 굽힘 각도는 잔류응력에 미치는 영향이 미미한 반면 유도 가열률과 이송 속도는 잔류응력에 상당한 영향을 미침을 확인하였다.

• 대한조선학회논문집
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• 제56권2호
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• pp.175-186
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• 2019

Number of studies on the buckling of thin cylindrical pressure vessels, such as submarine pressure hull and pipe with a large ratio of diameter/thickness, have been carried out in the naval and ocean engineering. However, research about thick cylinder pressure vessel has not been active except for the specific application in nuclear area. There are not many papers for the estimation of buckling and ultimate load capacity of thick cylinders for the deep sea usage. Thus, it is important to understand the theoretical bases of the buckling and collapse process and the derivation process of such loads for the proper design and structural analysis. The objective of this study is to survey the collapse behavior, to analyse and clarify the derivation procedure and to estimate the ultimate collapse load for thick cylinder by analyzing relevant books and papers. It is found that the yielding begins at the internal surface of the thick cylinder and plasticity develops from the internal surface to the external surface to generate collapse. Also the initial imperfection of cylinder develops flattening and consequently accelerates buckling and finally ultimate collapse. By comparing the collapse loads of aluminum thick cylinder by applying equations herein, it is shown that the equations analyzed are appropriate to obtain collapse load for thick cylinder.

• 한국가스학회지
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• 제17권5호
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• pp.64-68
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• 2013

열가소성 플라스틱배관의 전기융착부에 대한 비파괴검사방법은 융착부의 안전성을 확보하고 장기적인 신뢰성을 확보하기 위한 방법이다. 정상적인 방법에 의하여 융착된 접합부에서도 배관의 진원도와 전기융착 소켓과의 진원도 차이 또는 기공 등에 의해 융착부에 결함이 발생할 수 있다. 본 연구에서는 위상배열초음파를 이용하여 손상된 폴리에틸렌 전기융착부의 검사를 수행하였다. 검사 대상인 250mm 직경의 폴리에틸렌 배관 전기융착부는 1994년 12월에 융착되었으며 실제 작동 압력은 2.45kPa이다. 2004년 2월 소켓 이음부 근처에서 가스가 누설되어 수거되었다. 손상된 전기융착부에 대하여 첫 번째로 육안검사를 실시하고 다음에 위상배열초음파를 이용한 비파괴검사를 실시하였다. 그리고 절단 검사를 실시하여 각각의 검사 결과와 비교하였으며 위상배열 초음파를 이용한 검사결과와 절단 검사 결과가 동일함을 확인하였다.