• Title/Summary/Keyword: Overlay Weld

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Effect of preemptive weld overlay sequence on residual stress distribution for dissimilar metal weld of Kori nuclear power plant pressurizer (고리 원전 가압기 PWOL의 용접 방향이 이종금속용접부 잔류응력 분포에 미치는 영향)

  • Bae, H.Y.;Song, T.K.;Chun, Y.B.;Oh, C.Y.;Kim, Y.J.;Lee, K.S.;Park, C.Y.
    • Proceedings of the KSME Conference
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    • 2008.11a
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    • pp.88-93
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    • 2008
  • Weld overlay is one of the residual stress mitigation method which arrest crack. An overlay weld sued in this manner is termed a preemptive weld overlay(PWOL). PWOL was good for distribution of residual stress of dissimilar metal weld(DMW) by previous research. Because range of overlay welding is wide relatively, residual stress distribution on PWR is affected by welding sequence. In order to examine the effect of welding sequence, PWOL was applied to a specific DMW of KORI nuclear power plant by finite element analysis method. As a result, the welding direction that from nozzle to pipe is better good for residual stress distribution on PWR.

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Effect of Preemptive Weld Overlay on Residual Stress Mitigation for Dissimilar Metal Weld of Nuclear Power Plant Pressurizer (예방 용접 Overlay가 원전 가압기 이종금속용접부 잔류응력 완화에 미치는 영향)

  • Song, Tae-Kwang;Bae, Hong-Yeol;Chun, Yun-Bae;Oh, Chang-Young;Kim, Yun-Jae;Lee, Kyoung-Soo;Park, Chi-Yong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.32 no.10
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    • pp.873-881
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    • 2008
  • 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.

A study on the residual stress relieving for dissimilar metal weld under weld overlay (Overlay 용접을 통한 원전 이종 금속 용접부 잔류응력 완화효과에 대한 연구)

  • Song, Tae-Gwang;Bae, Hong-Yeol;Kim, Yun-Jae;Lee, Gyeong-Su;Park, Chi-Yong
    • Proceedings of the KWS Conference
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    • 2007.11a
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    • pp.260-262
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    • 2007
  • In nuclear power plants, residual stress of dissimilar metal weld propagates cracks in the weld metal which is susceptible to stress corrosion cracking. Overlay welding is a process widely used to mitigate residual stress replacing inside tensile stress by compressing stress. The purpose of this paper is to predict the effect of weld overlay by finite element analysis.

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스테인레스강 Overlay 용접부의 Disbonding에 관한 연구 1

  • 이영호;윤의박
    • Journal of Welding and Joining
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    • v.1 no.2
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    • pp.45-52
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    • 1983
  • Many pressure vessels for the hot H$\sub$2//H$\sub$2/S service are made of 2+1/4Cr-1Mo steel with austenitic stainless steel overlay to combat agressive corrosion due to hydrogen sulfide. Hydrogen dissolves in to materials during operation, and sometimes gives rise to unfore-seeable damages. Appropriate precautions must, therefore, be taken to avoid the hydrogen induced damages in the design, fabrication and operation stage of such reactor vessels. Recently, hydrogeninduced cracking (or Disbonding) was found at the interface between base metal and stainless weld overlay of a desulfurizing reactor. Since the stainless steel overlay weld metal is subjected to thermal and internal-pressure loads in reactor operation, it is desirable for the overlay weld metal to have high strength and ductility from the stand point of structural safety. In section III of ASME Boiler and Pressure Vessel Code, Post-Weld Heat Treatment(PWHT) of more than one hour per inch at over 1100.deg. F(593.deg. C) is required for the weld joints of low alloy pressure vessel steels. This heat treatment to relieve stresses in the welded joint during construction of the pressure vessel is considered to cause sensitization of the overlay weld metal. The present study was carried out to make clear the diffusion of carbon migration by PWHT in dissimilar metal welded joint. The main conclusion reached from this study are as follows: 1) The theoretical analysis for diffusion of carbon in stainless steel overlay weld metal does not agree with Fick's 2nd law but the general law of molecular diffusion phenomenon by thermodynamic chemical potential. 2) In the stainless steel overlay welded joint, the PWHT at 720.deg. C for 10 hours causes a diffusion of carbon atoms from ferritic steel into austenitic steel according to the theoretical analysis for carbon migration and its experiment. 3) In case of PWHT at 720.deg. C for 10 hours, the micro-hardness of stainless steel weld metal in bonded zone increase very highly in the carburized layer with remarkable hardening than that of weld metal.

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A Feasibility Test for Flaw Detection in Overlay Weld of Reactor Upper Head Penetration Using Time of Flight Diffraction Technique (TOFD 기법을 활용한 원자로 상부헤드관통부 오버레이 용접부 결함 검출 가능성 평가)

  • Lee, Jeong Seok;Kim, Jin Hoi
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.10 no.1
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    • pp.15-19
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    • 2014
  • A Failure or degradation of reactor upper head penetration is a recurring problem due to long term operation at nuclear power plants. And a flaw in the reactor upper head penetration has caused unplanned plant shutdown for repair as well as high economic impact on the plants. Consequently, a detection of flaws is of the utmost importance. Prior to the replacement of reactor upper head penetration, some utilities have repaired the flaws of reactor upper head penetration generated by overlay weld. Until now, only the base metal in reactor upper head penetration has been inspected according to 10 CFR 50.55a and ASME code case N-729-1. Accordingly, it is difficult to detect manufacturing defects and repair defects in overlay weld. This paper presents a case study on the application of Time of Flight Diffraction technique for reactor head penetration mockup with artificial flaws in overlay weld. This study offers a way to understand the flaws detected in reactor upper head penetration overlay weld.

Wear Resistance Characteristics of Iron Weld Overlays by Composite Chromium Powders (복합 크롬 분말에 의한 철계 용접 오버레이의 내마모 특성)

  • 김종철;박경채;최창옥
    • Journal of Welding and Joining
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    • v.19 no.5
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    • pp.506-511
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    • 2001
  • Weld overlay has been developed to improve the property of material surface which is used in the severe environment. Weld overlay is the process which uses an arc heat and welds different composition of alloy on the substrate for the improvements of heat resistance and wear resistance. Weld overlay has a lot of advantages which are high hardness, good processing efficiency, easy controlling of layer thickness, good quality and low cost. In this study, weld overlay was performed by MAG welding on the base metal(SS400) with filler metal which contain composite powders(Cr+C+Mn+Mo+NbC) and solid wire(JIS-YGW11). Characterization of hardness and wear resistance were analyzed by EDS, EPMA, XRD and observations of microstructure were performed to investigate characteristics of overlays. The experimental results of overlaid specimens manufactured with Cr+C+Mn+Mo+NbC powders were obtained as fellows. ${\alpha}-phase$, M(Fe, Cr)3C and NbC of overlays were increased with decreasing the wire feed rates and increasing powder feed rates. Also the hardness of overlays were increased and the specific wear were decreased.

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Wear Resistance Characteristics of Iron System MAG Weld Overlays with Chromium and Niobium Carbide Composite (Cr 및 Nb 복합탄화물에 의한 철계 MAG용접 오버fp이의 내마모 특성)

  • 김종철;박경채
    • Journal of Welding and Joining
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    • v.20 no.3
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    • pp.54-59
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    • 2002
  • Overlays is a treatment of the surface and near-surface regions of a material to allow the surface to perform functions that are distinct from those frictions demanded far the bulk of the material. Welding, thermal spray, quenching, carburizing and nitration have been used as the surface treatment. Especially, weld overlay is a relatively thick layer of filler metal applied to a carbon or low-alloy steel base metal for the purpose of providing a wear resistant surface. In this study, weld overlay was performed by MAG welding on the base metal(SS400) with filler metal which contain composite powders($Cr_3C_2+Mn+Mo+NbC$) and solid wire(JIS-YGW11). Characteristics of hardness and wear resistance on overlays were analyzed by EDS, EPMA, XRD and microstructures. Carbide formations were $M(Cr, Fe)_7C_3$ and NbC phases. And carbide volume fraction, hardness and specific wear resistance of overlays were increased with increasing powder feed rate and decreasing wire fred rate. Hardness and wear resistance were almost proportioned to carbide volume fraction of overlay.

Effect of preemptive weld overlay on residual stress of repaired weldment in surge nozzle (예방 용접 overlay 가 밀림관 노즐 보수 용접부 잔류응력에 미치는 영향)

  • Oh, Chang-Young;Song, Tae-Kwang;Bae, Hong-Yeol;Chun, Yun-Bae;Kim, Yun-Jae;Lee, Kyoung-Soo;Park, Chi-Yong
    • Proceedings of the KSME Conference
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    • 2008.11a
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    • pp.94-97
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    • 2008
  • In the welding process, weldments usually include repair weld during the manufacturing process. Repair welds is supposed to cause strong tensile residual stress. Moreover weldments, usually made by Alloy 82/182, is susceptible to PWSCC. Therefore, mitigation of welding residual stress in weldments is important for reliable operating. PWOL is one of the methods for mitigation and verified for over twenty years. In this paper, residual stress distribution of repaired weldments and the effect of PWOL on mitigation is examined for surge nozzle.

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Analysis of Overlay Weld Effect on Preventing PWSCC in Dissimilar Metal Weld (이종금속 용접부의 일차수응력부식균열 방지를 위한 예방정비 용접 효과 분석)

  • Lee, Seung-Gun;Oh, Chang-Kyun;Park, Heung-Bae;Jin, Tae-Eun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.1
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    • pp.97-101
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    • 2010
  • PWSCC(Primary Stress Corrosion Cracking) in Alloy 82/182 butt welds is the problem affecting safety and integrity of nuclear power plant. PWSCC can be occurred in the area that is at high magnitude of tensile residual stress, such as Alloy 82/182 dissimilar metal welds in PZR(pressurizer) nozzles. There have been a number of incidents recently at the dissimilar metal welds in overseas nuclear power plants. Overlay weld is the one of the effective methods to decrease tensile residual stress of inside surface, which will result in preventing PWSCC. In this paper, overlay weld conditions on the purpose of preventing PWSCC was explained and the benefit of the overlay weld was confirmed performing finite element analysis.

Development of Ultrasonic Inspection System and Application to Overlay Weld Flaw Detection (초음파 자동 검사시스템의 개발과 오버레이 용접부의 결함검사)

  • Nam, Young-Hyun;Seong, Un-Hak
    • Journal of the Korean Society for Nondestructive Testing
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    • v.20 no.6
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    • pp.562-567
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    • 2000
  • Many pressure vessels for power and industrial plant are fabricated from low alloy carbon steels. The inner sides of pressure vessels are commonly weld-cladded with austenitic stainless steels to minimize problems of corrosive attack. Disbonding cracks are often detected at the transition region of welding interlayer, which is serious problem to reliability of pressure vessels. We have developed C-scan system to high speed inspection of overlay weld using DSP(digital signal processor). This system consists of signal processing parts (oscilloscope, pulser/receiver, digitizer, DSP), scanner, program and position controller. The developed system has been applied to a practical ultrasonic testing in overlay weld, and demonstrated high speed with precision

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