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이종금속용접부 예방정비 방법에 따른 잔류응력 분포 고찰
송태광,최영환,박정순,정해동,오창영,Song, Tae-Kwang,Choi, Young Hwan,Park, Jeong Soon,Chung, Hae-Dong,Oh, Chang-Young 한국압력기기공학회 2011 한국압력기기공학회 논문집 Vol.7 No.4
This paper presents the effects of preventive maintenance schemes on the residual stress distributions in dissimilar metal welds. Dissimilar metal weld is known susceptible to PWSCC and thus, effective maintenance schemes to prevent PWSCC are needed. Three preventive maintenances schemes, i.e. weld overlay, MSIP and inlay weld which are widely used in nuclear power plants, are selected and their effects on welding residual stresses are investigated via finite element analyses. As results, weld overlay and MSIP were proved effective method to mitigate residual stresses and inlay weld, on the other hand, produces strong tensile residual stresses in the inner surface. Although Alloy 690 known to be resistant to PWSCC are used in inlay weld, continuous careful observation are needed since tensile welding residual stresses are key parameter for PWSCC.
열하중 및 기계하중이 작용하는 원주 방향 균열 배관에 대한 V- 계수 평가
송태광(Tae-Kwang Song),오창균(Chang-Kyun Oh),김윤재(Yun-Jae Kim) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.12
This paper provides V-factor estimation under combined mechanical and thermal load for circumferential cracks. Results are based on finite element analyses and effect of types and magnitudes of the thermal stress, crack geometry, the loading mode and plastic strain hardening on variations of the V-factor are investigated. The results of finite element analyses are compared with R6 values. As a result, it is shown that R6 gives generally conservative results. The conservatism is especially increased for the combination of large mechanical and thermal load. As a result, new estimation method which uses failure assessment line in R6 is proposed for V-factor and gives less conservative results.
용접부 중앙에 원주방향균열이 있는 배관에 대한 강도불일치 한계하중 해석 및 파괴역학 평가
송태광(Tae-Kwang Song),전준영(Jun-Young Jeon),심광보(Kwang-Bo Shim),김윤재(Yun-Jae Kim),김종성(Jong-Sung Kim),진태은(Tae-Eun Jin) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.1
본 논문에서는 유한요소 해석을 통해 용접부 중앙에 원주방향균열이 있는 배관에 대한 강도불일치 한계하중 해석 및 파괴역학 해석을 수행하였다. 강도불일치 한계하중식을 제시하기 위해 강도불일치 비, 용접부 폭, 균열 길이 및 배관 반경비에 대한 체계적인 변수 해석을 수행하였으며 참조응력법을 바탕으로 스테인리스강 및 페리틱 강에 대한 J-적분 계산을 수행하였다. 본 연구에서 제시한 강도불일치 한계하중을 사용하여 참조응력을 정의할 때, 보다 정확한 J-적분 결과를 얻을 수 있었다. In this paper, limit load analyses and fracture mechanics analyses were conducted via finite element analyses for the welded pipe with circumferential crack at the center of the weldment. Systematic changes for strength mismatch ratio, width of weldment, crack shape and thickness ratio of the pipe were considered to provide strength mismatch limit load. And J-integral calculations based on reference stress method were conducted for two materials, stainless steel and ferritic steel. Reference stress defined by provided strength mis-match limit load gives much more accurate J-integral.
용접부 중앙에 표면균열이 존재하는 인장 평판에 대한 강도 불일치 한계하중 해석 및 간략 J-적분 예측
송태광(Tae-Kwang Song),김윤재(Yun-Jae Kim),김종성(Jong-Sung Kim),진태은(Tae-Eun Jin) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.5
In this work, the effect of strength mismatch on plastic limit loads is quantified for similar metal weld plates with cracks under tension load, via three-dimensional, small strain elastic-perfectly plastic finite element analyses. Relevant variables related to plate geometry and crack length are systematically varied, in addition to the weld width. An important finding is that mis-match limit loads can be uniquely quantified through strength mis-match ratio and one geometry-related parameter. Based on the proposed limit load solutions, reference stress based J-integral estimates is also investigated. When the reference stress is defined by the mis-match limit load, predicted J-integral values agree overall well with FE results.
복합응력이 작용하는 균열 배관에 대한 천이 크리프 조건에서의 C(t)-적분 예측 (Ⅱ)
송태광(Tae-Kwang Song),김윤재(Yun-Jae Kim) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.10
In this paper, the estimation method of C(t)-integral for combined mechanical and thermal loads is proposed for elastic-plastic-creep material via 3-dimensional FE analyses. Plasticity induced by initial loading makes relaxation rate different from those produced elastically. Moreover, the interactions between mechanical and thermal loads make the relaxation rate different from those produced under mechanical load alone. To quantify C(t)-integral for combined mechanical and thermal loads, the simplified formula are developed by modifying redistribution time in existing work done by Ainsworth et al..
고리 원전 가압기 노즐 용접부 잔류응력 예측 시 안전단 고려가 이종 금속 용접부 잔류응력 분포에 미치는 영향
송태광(Tae-Kwang Song),배홍열(Hong-Yeol Bae),전윤배(Yun-Bae Chun),오창영(Chang-Young Oh),김윤재(Yun-Jae Kim),이경수(Kyoung-Soo Lee),박치용(Chi-Yong Park) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.8
In nuclear power plants, ferritic low alloy steel nozzle was connected with austenitic stainless steel piping system through alloy 82/182 butt weld. Accurate estimation of residual stress for weldment is important in the sense that alloy 82/182 is susceptible to stress corrosion cracking. There are many results which predict residual stress distribution for alloy 82/182 weld between nozzle and pipe. However, nozzle and piping system usually connected through safe end which has short length. In this paper, residual stress distribution for pressurizer nozzle of Kori nuclear power plant was predicted using FE analysis, which consideded safe end. As a result, existing residual stress profile was redistributed and residual stress of inner surface was decreased specially. It means that safe end should be considered to reduce conservatism when estimating the piping system.
복합응력이 작용하는 균열 배관에 대한 천이 크리프 조건에서의 C(t)-적분 예측 (I)
송태광(Tae-Kwang Song),김윤재(Yun-Jae Kim) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.9
The C(t)-integral describes amplitude of stress and strain rate field near a tip of stationary crack under transient creep condition. Thus the C(t)-integral is a key parameter for the high-temperature crack assessment. Estimation formulae for C(t)-integral of the cracked component operating under mechanical load alone have been provided for decades. However, high temperature structures usually work under combined mechanical and thermal load. And no investigation has provided quantitative estimates for the C(t)-integral under combined mechanical and thermal load. In this study, 3-dimensional finite element analyses were conducted to calculate the C(t)-integral of elastic-creep material under combined mechanical and thermal load. As a result, redistribution time for the crack under combined mechanical and thermal load is re-defined through FE analyses to quantify the C(t)-integral. Estimates of C(t)-integral using this proposed redistribution time agree well with FE analyses results.
예방 용접 Overlay 가 원전 가압기 이종금속용접부 잔류응력 완화에 미치는 영향
송태광(Tae-Kwang Song),배홍열(Hong-Yeol Bae),전윤배(Yun-Bae Chun),오창영(Chang-Young Oh),김윤재(Yun-Jae Kim),이경수(Kyoung-Soo Lee),박치용(Chi-Yong Park) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.10
Weld overlay is one of the residual stress mitigation methods which arrest crack initiation and crack growth. Therefore weld overlay can be applied to the region where cracking is likely to be. An overlay weld used in this manner is termed a preemptive weld overlay(PWOL). In pressurized water reactor(PWR) dissimilar metal weld is susceptible region for primary water stress corrosion cracking(PWSCC). In order to examine the effect of PWOL on residual stress mitigation, PWOL was applied to a specific dissimilar metal weld of Kori nuclear power plant by finite element analysis method. As a result, strong compressive residual stress was made in PWSCC susceptible region and PWOL was proved effective preemptive repair method for weldment.