원자로 CRDM 관통노즐 J-Groove 용접부 잔류응력 예측을 위한 유한요소 변수 민감도 해석

배홍열(Hong Yeol Bae),김주희(Ju Hee Kim),김윤재(Yun Jae Kim),오창영(Chang Young Oh),김지수(Ji Soo Kim),이성호(Sung Ho Lee),이경수(Kyoung Soo Lee) 대한기계학회 2012 大韓機械學會論文集A Vol.36 No.10

최근 원자로 압력용기 상부헤드 관통노즐 J-groove 용접부 주변에서 균열로 인한 냉각수 누출사고가 발행하고 있다. 이러한 사고의 원인은 용접에 의한 인장잔류응력, 농축된 붕산수 및 응력부식에 민감한 재료로 인한 일차수응력부식균열(PWSCC : primary water stress corrosion cracking)인 것으로 판명되었다. PWSCC 평가는 원자로 건전성 평가의 주요 관심사로서 용접에 의해 발생되는 잔류응력을 정확하게 예측함으로써 가능하다. 본 연구에서는 유한요소해석을 이용하여 국내 원자로의 일반적인 J-groove 용접부의 해석절차를 소개하고, 용접해석 관련 변수의 민감도 해석을 통해 잔류응력 예측기법을 제시하고자 한다. 이를 위해 2차원 및 3차원 요한요소해석 방법을 바탕으로 변수 민감도 해석을 수행하였으며, 기존 연구결과와 비교를 통해 해석절차 및 방법의 유용성을 검정하였다. In nuclear power plants, the reactor pressure vessel (RPV) upper head control rod drive mechanism (CRDM) penetration nozzles are fabricated using J-groove weld geometry. Recently, the incidences of cracking in Alloy 600 CRDM nozzles and their associated welds have increased significantly. The cracking mechanism has been attributed to primary water stress corrosion cracking (PWSCC), and it has been shown to be driven by welding residual stresses and operational stresses in the weld region. The weld-induced residual stress is the main factor contributing to crack growth. Therefore, an exact estimation of the residual stress is important for ensuring reliable operation. This study presents the residual stress computation performed for an RPV CRDM penetration nozzle in Korea. Based on two and three dimensional finite element analyses, the effect of welding variables on the residual stress variation is estimated for sensitivity analysis.

유한요소법을 이용한 원자로 상부헤드 CRDM 관통노즐 J-Groove 보수용접 영향 분석

김주희(Ju Hee Kim),유삼현(Sam Hyeon Yoo),김윤재(Yun Jae Kim) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.6

국내 가압경수로형 원자로의 압력용기 상부헤드에는 많은 제어봉구동장치(CRDM) 노즐이 분포한다. 이들 노즐은 억지끼워맞춤(Shrink fitting) 방식으로 결합되어 용접 처리 된다. 용접에 의해 발생되는 인장잔류응력은 일차수응력부식균열을 발생시키는 주요 요인이다. 이러한 이유로 최근 15 여 년 동안 관통노즐 용접부 부위에서 균열 발생 사례가 증가하고 있으며, 이를 극복하기 위해 다양한 방안이 모색되고 있다. 또한 용접과정에서 발생되는 불필요한 결함은 일차수응력부식균열(PWSCC)을 가속화 시키는 원인이 되기도 한다. 원자로 제작과정에서 용접에 의한 결함은 보수용접에 의해 즉시 수리가 이루어 진다. 기존의 연구에서는 정상적인 용접과정에서 발생되는 잔류응력을 예측하였으나, 본 연구에서는 용접과정에서 발생되는 결함을 보수하기 위해 실시되는 보수용접이 용접잔류응력에 미치는 영향을 분석하였다. In pressurized water reactors, the upper head of the reactor pressure vessel (RPV) contains numerous control rod drive mechanism (CRDM) nozzles. These nozzles are fabricated by welding after being inserted into the RPV head with a room temperature shrink fit. The tensile residual stresses caused by this welding are a major factor in primary water stress corrosion cracking (PWSCC). Over the last 15 years, the incidences of cracking in alloy 600 CRDM nozzles have increased significantly. These cracks are caused by PWSCC and have been shown to be driven by the welding residual stresses and operational stresses in the weld region. Various measures are being sought to overcome these problems. The defects resulting from the welding process are often the cause of PWSCC acceleration. Therefore, any weld defects found in the RPV manufacturing process are immediately repaired by repair welding. Detailed finiteelement simulations for the Korea Nuclear Reactor Pressure Vessel were conducted in order to predict the magnitudes of the repair weld residual stresses in the tube materials.

FCAW에 의한 590MPa급 고장력압력용기강의 초층편면용접부에서 발생하는 고온균열

김우열,한일욱,유덕상,방한서,안용식,박화순 대한용접접합학회 1999 대한용접·접합학회지 Vol.17 No.5

It is well known that solidification cracking often occurs in welds of root pass for one-side welding under the conditions of high welding currents and speeds. In this study, the solidification in 590MPa class steel for pressure vessels SPPV490 was investigated by using flux-cored arc welding(FCAW) with 4 types of welding wires and welding conditions of 200∼280A and 2.8∼ 4.2mm/sec. In order to compared the result of cracking in SPPV490, 0.2%C steel for welded structure of SWS400 and 0.45%C steel for machine structural SM45C were also used as base metals. As the results, all the cracks formed in some welding conditions were observed near the center of weld bead. The solidification cracks were generally initiated near the upper surface of bead and propagated toward the inner part. The solidification cracking generally increased with welding current and welding speed in the same base metal and welding material. In cracking susceptibility, SPPV490 showed higher cracking susceptibility than SWS400 in all welding conditions and welding materials. It was considered that cracking susceptibility could not be evaluated with the hardness of weld metals. The cracking ratio increased with decreasing of a/b(a and b; the width of the upper surface and the back surface of the bead) as shape factor of bead. The cracking tendency with shape factor of bead was extended under the condition of higher welding currents.

2¼Cr-1Mo강 압력용기 용접이음부의 재열균열에 관한 역학적 연구

권영섭,노찬승,방한서 朝鮮大學校 機械技術硏究所 1999 機械技術硏究 Vol.2 No.2

구조물에 사용되는 각종 압력용기들의 재질은 고온 및 고압에 견딜 수 있도록 요구되고 있다. 따라서, 내열, 내압 및 내부식성이 뛰어난 2¼Cr-1Mo강의 수요가 향후 증대될 전망이다 용접잔류응력은 일반적으로 응접구조물에 각종 악영향을 미치는 것으로 알려져 있다. 이 때문에 용접잔류응력. 확산성 수소제거 및 용접 열영향부의 연화등을 목적으로 용접후열처리(PWHT)를 수행하나, PWHT를 행하면 사용 강재의 종류에 따라 재열균열이 발생하고 있다. 본 연구에서는 2¼Cr-1Mo강에 대하여 실험과 수치해석 기법을 통하여 용접이음부의 재열균열 감수성평가 및 상당크리프 변형율의 재열균열 발생에 판정에 대한 역학적 지표로서의 적용성을 검토하였다. 2¼Cr-1Mo steels are widely used to fabricate pressure vessels. Residual stresses, in general, are known to be harmful to the soundness of the welded structures. PWHT is release residual stresses, which may cause cracks. But, in those PWHT process, 2¼Cr-1Mo steels are apt to occur reheat crack frequently. In this reason, it is strongly needed to analysis and examine the mechanical behavior of welded joints through welding to PWHT process. So, in this study, welded nozzle parts of pressure vessel where reheat cracks are frequently occur are selected for examine the crack-occurrence mechanism.

원자로 상부헤드 제어봉구동장치 관통노즐 형상이 J-Groove 용접잔류응력에 미치는 영향

김주희(Ju Hee Kim),김윤재(Yun Jae Kim),이성호(Sung Ho Lee),허남용(Nam Young Hur),배홍열(Hong Yeol Bae),오창영(Chang Young Oh),김지수(Ji Soo Kim),박흥배(Heung Bae Park),이승건(Seung Geon Lee),김종성(Jong Sung Kim),허남수(Nam Su Huh) 대한기계학회 2011 大韓機械學會論文集A Vol.35 No.10

가압경수로형 원자로의 원자로압력용기 상부헤드에는 많은 제어봉구동장치(CRDM) 노즐이 분포한다. 최근 10 여 년 동안 제어봉구동장치 alloy 600 CRDM 노즐에서 균열 발생 사례가 증가하고 있으며, 이는 용접과 연관성이 매우 깊은 것으로 알려져 있다. CRDM 노즐에서 발생하는 축 및 원주방향 균열은 유럽과 미국의 원자력 발전소에서 발견되었으며, 사고의 원인은 용접 잔류응력 및 작용하중에 기인하는 일차수응력부식균열(PWSCC)임이 확인되었다. 이러한 이유로 본 연구에서는 유한요소해석을 통해 한국형 원자로의 CRDM 관통 노즐 용접부를 대상으로 용접 잔류응력을 예측하였으며, 특히, 관통노즐의 위치와 형상, 용접부 필렛 형상 및 인접노즐 용접에 의한 영향을 분석하였다. In pressurized water reactors (PWRs), the reactor pressure vessel (RPV) upper head contains numerous control rod drive mechanism (CRDM) nozzles. In the last 10 years, the incidences of cracking in alloy 600 CRDM nozzles and their associated welds has increased significantly. Several axial and circumferential cracks have been found in CRDM nozzles in European PWRs and U.S. nuclear power plants. These cracks are caused by primary water stress corrosion cracking (PWSCC) and have been shown to be driven by welding residual stresses and operational stresses in the weld region. Therefore, detailed finite-element (FE) simulations for the Korea Nuclear Reactor Pressure Vessel have been conducted in order to predict the magnitudes of the weld residual stresses in the tube materials. In particular, the weld residual stress results are compared in terms for nozzle location, geometry factor r_o/t, geometry of fillet, and adjacent nozzle.

선박용 휴대형 질소용기(11 kg, 10 L 및 50 bar)의 두께 및 외형 설계

성한샘(Hansaem Seong),김재열(Jaeyeol Kim),엄태진(Taejin Eom),곽효서(Hyo Seo Kawk),이광오(Kwang O Lee),김철(Chul Kim) 대한기계학회 2017 大韓機械學會論文集A Vol.41 No.4

조선소에서 사용되는 대형 셧오프 밸브의 개폐를 위한 용기의 경우, 저압의 고정식 대형 공기탱크가 사용되고 있는데, 이는 먼 거리에 있는 밸브에 공압을 공급해야 할 경우, 추가 배관이 필요하며 수송도중 압력 강하가 발생하는 문제점이 있다. 이에 본 논문에서는 작업자들의 편의성을 증대시키고, 공기누설로 인한 폭발 방지를 위하여 고압의 휴대형 용접식 질소용기(11 kg, 10 L 및 50 bar)의 설계를 수행하였다. 구조적으로 취약한 용접부를 최소화하기 위하여 용기의 외형을 타원형으로 설계하였으며, 기준 무게 및 용적 충족과 사용압력에 대한 구조안전성을 확립하기 위하여 용기의 두께와 장단축 비를 설계하였다. 또한 용접 잔류응력 예측을 위해 APDL(ANSYS Parametric Design Language)을 이용하여 과도 열-구조 연성해석을 수행하였으며, 내압에 의한 구조안전 및 피로수명을 검증하였다. The shipbuilding industry uses large stationary tanks to store low-pressure air, which is used to open and close large shut-off valves. However, when supplying air from the tank to a distant valve, there are problems related to the need for supplementary pipes and the pressure drop during transportation. In this study, a portable welded vessel for storing high-pressure nitrogen (11 kg, 10 L, and 50 bar) was designed to prevent air leakage and improve the convenience of workers. This pressure vessel was elliptical to reduce the number of welded parts, which are structurally weak. The thickness and ratio of the major and minor axes of the pressure vessel were calculated to verify its structure stability at the working pressure (50 bar), and that the proposed weight and capacity were satisfactory. The residual stress caused by the welding process was calculated by performing a transient thermal-structural coupled field analysis using the ANSYS parametric design language (APDL), and the fatigue life of the vessel was verified based on the Goodman criterion.

압력용기 구조물 용접부에서 잔류응력이 피로균열진전거동에 미치는 영향

이연신,차용훈,김덕중,성백섭 朝鮮大學校 機械技術硏究所 1999 機械技術硏究 Vol.2 No.2

This paper is to investigated the influence of welding residual stresses on the fatigue crack growth behaviors in the vertical direction to the weld bead. So, Co₂Automatic welding was performed on the ASTM A5l6 grade 60 Steel. For skip and continuous fillet welding, the specimens of fatigue cracks are initiated at toe end and beginning of welded specimen. The fatigue life of continue fillet welding is greater then that of skip fillet welding. The fatigue lief of as welded specimen is longer than that of PWHT specimen because the compression residual stress are greater than the other zone, which are near the welding toe notch of welded specimen. For skip and continuous fillet welding, da/dN-ΔK relations show retardation at HAZ and increase linearly at the stable growth region.

이종금속의 상온압접에 관한 연구

엄기원,이철구 대한용접접합학회 1987 대한용접·접합학회지 Vol.5 No.3

This paper presents the weldability for cold pressure but welding method in junction of dissimilar metals each other. Although the weldability between the same aluminium metal plate welding has been studied, the study of itthe rod of aluminium and coper has not fully been investigated. The purpose is to suggest the optimal conditions on the rod of those under above method. To obtain the optimal conditions, associated experiments were performed in a various welding parameters. Consequently, it was proved that the mechanical properties such as tensile strength, hardness and bending strength could be obtained excellent particularly under the welding conditions; pressure is $(32~39) {\times} 10^3/kg/cm^2$, time is beyond 70 seconds, stage is higher than fifth stage.

용접구조물 용접토우부의 잔류응력이 피로강도에 미치는 영향 평가

차용훈,김하식,김일수,성백섭 한국공작기계학회 2001 한국생산제조학회지 Vol.10 No.4

This study is to investigate the influence of weld residual stresses on the fatigue crack growth behaviors in pressure ves-sel reinforcement. In order to perform this study, the automatically welded specimens are prepared. The material is ASTM A516 grade 60 steel used in pressure vessel mainly. For pad-on-plate of skip welding, continuous welding and PWHT specimen, fatigue crack initiation is generally initiat-ed at weld starting and end toe zone, and ruptured at weld starting toe zone. Fatigue life of pad-on-plate continuous specimen is increased more than that of pad-on-plate skip fillet welding specimen about 85% under low load, about 20% under high load, and decreased than that of two-pad continuous welding specimen about 85%. In da dN­ΔK curve under low load, pad-on-plate skip fillet welding specimen showed retardation on the initial crack, and the fatigue crack growth rate at the low region of ΔK greater specimen E(3.8 × l0 ^6mm/cycle). And the fatigue life of welding specimen was smaller than that of PWHT specimen.

SM20C摩擦鎔接시 鎔接部 가공에 따른機械的 性質 硏究

이세경,박천봉,민택기 충남대학교 공업교육연구소 2005 論文集 Vol.27 No.1

This study examined mechanical properties according to the change of outer circumference in the friction welding of SM20C, which is one of carbon steel for machine structures used in steel pipes, steel rods, steel plates, bolts, rivets, etc., and SM20C stock with 10 hollow at the center. Welding conditions were fixed at RPM of 2,000, friction pressure of 60㎫, friction time of 1.4 seconds, upset pressure of100㎫ and upset time of 2.0 seconds. The obtained of this study are as follows. According to the tensile strength test, the maximum tensile strength was 585㎫ when the change of outer circumference was 1mm and it corresponds to 94% of 624㎫, the tensile strength of the base material. The result of measuring hardness, hardness appeared to increase at 5mm and then decrease for welding interface, and it was maximum 250HV at D=5mm of the solid shaft. High hardness was observed around 0.5mm of vertical distance from the welding section and relatively low hardness was observed around 2mm. The result of a bending test, the maximum bending strength was 7.701㎫ at L = 5mm in the solid shaft, which is 130% of the bending strength of the base material. The result of examining microstructure, the microstructure grew finer with the change of outer circumference against the welding surface. Namely, as it was closer to the center in the solid shaft, but the microstructure grew finer and then coarser in the hollow shaft.