ASME boiler and pressure vessel codeの許容応力の改訂

This paper provides simulational round robin test results for welding residual stress prediction of safety/relief nozzle. To quantify the welding variables and define the recommendation for prediction and determination of welding residual stress, 6 partners in 5 institutes participated in round robin test. It is concluded that compressive axial and hoop residual stress occurs in dissimilar metal weld and pre-existing residual stress distribution in dissimilar metal weld was affected by similar metal weld due to short length of safe end. Although the reason for the deviation among the results was not pursued further, the effect of several key elements of FE analyses on welding residual stress was investigated in this paper.

Assessment of Round Robin Analyses Results on Welding Residual Stress Prediction in a Nuclear Power Plant Nozzle

Nozzle in nuclear power plant is connected to pipe using safe end. Dissimilar metal weld between nozzle and safe end is followed by similar metal weld between safe end and pipe. And thus residual stress in dissimilar metal weld can be affected by similar metal weld. Similar metal weld impose bending stress on dissimilar metal weld, which is according to the length of safe end. In this study, simple nozzle model which covers various radius to thickness ratios was proposed to quantify residual stress in dissimilar metal weld based on finite element analyses. As a result, short length of safe end was proved to be more effective to mitigate residual stress in dissimilar metal weld and critical effective length of safe end is provided according to the radius to thickness ratio.

https://www.koreascience.or.kr:443/article/JAKO200918839962286.pdf

Effects of Similar Metal Weld on Residual Stress in Dissimilar Metal Weld According to Safe End Length

Recent developing tendency of overlay welding on welding materials are studied by searching of NDSL, Science Direct, KIPRIS and so on. Fe, Co, Ni and WC are selected as welding materials. Development and improvement of various new overlay welding technology, especially improvement of quality and formation of crack are introduced. Also the prospective technologies of overlay welding are anticipated. Key Words : Overlay welding, PTA, Laser cladding, Welding crack, Welding material 1. 서 론 최근 국내 오버레이 용접재료의 연구개발 분야에서는 생산성 향상을 위한 용접시공상의 공법개선, 고에너지 열원을 이용한 첨단기술 및 새로운 합금개발에 대한 기술확립이 절실한 시점에 있다. 특히 국내 기업체의 오버레이 용접재료의 기술확립은 국제경쟁력 확보를 위해서 필수적으로 거쳐야 하는 과제이다. 향후 각종 산업분야에의 오버레이 용접기술의 정착을 위해서는 산학연이 합심하여 공동목적으로 적극적인 지원을 해야 할 것이다. 또한 국내 용접관련 산업 및 용접재료업체의 기술개발 의지가 필요한 이 시점에서, 오버레이 용접기술에 대한 제조기술의 확립과 향후 방향제시를 목표로 하고 있는 정보자료의 출현이 국내산업 발전을 더욱 활성화할 수 있는 촉진제가 될 것이다. 이를 위해 본고에서는 NDSL, ScienceDirect, KIPRIS 등의 검색을 통하여, 국내외 오버레이 용접관련 학술지와 특허자료를 입수하여 체계적으로 분석하였다. 특히 용접재료에 따른 오버레이 용접기술 개발동향을 파악하기 위하여 철계, Co계, Ni계, WC계 재료에 관한 해외 및 국내 오버레이 용접의 기술개발 동향을 파악하고 정성분석하였으며 향후 기술을 전망하였다.

/pdf/recent-study-in-variation-of-welding-materials-for-overlay-123qt0hekg.pdf

Recent Study in Variation of Welding Materials for Overlay Welding

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.

Effect of preemptive weld overlay on residual stress mitigation for dissimilar metal weld of nuclear power plant pressurizer

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. 1. 서 론 최근 들어 V.C Summer, Ringhals 및 Tsuruga 2 등의 원전 이종 금속 용접부(DMW, Dissimilar Metal Weld)에서 (1,2)균열이 발생되었다. 균열의 위치는 상대적으로 운전 압력 및 운전 온도가 높은 원자로(reactor) 및 가압기(pressurizer)의 노즐 용접부로서 균열의 원인은 용접부 금속인 니켈 합금(Alloy 82/182) 재료의 일차수 응력부식균열(PWSCC)로 판명되었다. Alloy 82/182 재료는 응력 부식 균열에 민감하다고 알려져 있으며 주로 이종 금속 용접부 용접 재료로 사용되었다. 응력부식균열은 재료의 민감도, 수화학 환경 및 용접 잔류응력(welding residual stress)의 상호 작용에 의해 발생한다.

http://koreascience.or.kr:80/article/JAKO200824550465170.pdf

Estimation of Residual Stress Distribution for Pressurizer Nozzle of Kori Nuclear Power Plant Considering Safe End

In this study, simplified nozzle geometry was proposed to quantify the effects of adjacent similar metal weld and weld overlay on residual stresses in dissimilar metal weld. Finite element analyses were conducted with various thickness ratios and safe end lengths and corresponding residual stresses were provided. According to the results, residual stresses in dissimilar metal weld were improved after adjacent similar metal welding. The effect of similar metal welding is more evident with shorter length of safe end. Thus, short length of safe end was recommended for new design of nozzle. Appropriate thickness of preemptive weld overlay reduces the conservative thickness recommended by ASME Code.Copyright © 2009 by ASME

Yun Bae Chun

Papers

Estimation of Residual Stress Distribution for Pressurizer Nozzle of Kori Nuclear Power Plant Considering Safe End

Effects of Similar Metal Weld on Residual Stress in Dissimilar Metal Weld According to Safe End Length

Effect of preemptive weld overlay on residual stress mitigation for dissimilar metal weld of nuclear power plant pressurizer

Effect of Adjacent Safe End to Piping Weld and Preemptive Weld Overlay Repair on Residual Stresses on Nozzle to Safe End Weld