• 한국압력기기공학회 논문집
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• 제9권1호
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• pp.56-61
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• 2013

This paper presents the results of integrity assessment for the cracks happened in reactor vessel upper head penetration nozzles. The crack morphology for a boat sample from crack area was analyzed through microscope. The stress condition including weld residual stress around crack was analyzed using finite element analysis. From the results of crack morphology and stress condition, the crack was concluded as primary water stress corrosion cracking. The integrity of the cracked nozzle was assessed by the methodology provided in ASME Section XI. According to the assessment results, the remaining life of the cracked nozzle was 1.43 yrs. and the plant decided to repair it.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.409-412
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• 2003

Fatigue strength. especially crack initiation behavior of high strength steel under marine water environment was investigated. Marine structures were usually constructed by lot of weld joints and were designed by basis of the fatigue strength of weld joints. This study was carried out to mini. The fatigue initiation behavior is more important rather than crack propagation behavior under the design of marine structures, because it is very difficult to find out the crack propagation phenomena and repair the damaged part of welded joints in sea water Then, the new configuration specimen for fatigue crack initiation tests was proposed. Using this new specimen, it is easy to carry out the crack initiation tests with relatively low cycling loading and clearly find out a crack initiation fatigue life.

• 선박안전
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• 통권24호
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• pp.4-20
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• 2008

Stainless steel 304 or stainless steel 630 types using propeller shaft of a small ship or a FRP fishing boat generally restrain localization corrosion and abrasion damage occurrence to shaft bearing or grand packing contact. In general, the residual stress which remains after welding or heat treatment in material can cause the stress concentration or localization corrosion. In case of small ship, stainless steel such as STS304 has long been used for propeller shaft. Meanwhile, crew of small ship tend to reuse damaged propeller shaft after repair by welding and performing heat treatment to save cost. However, it was found that reused propeller shaft by repair often caused troubles in ship's operation. In this study, the basic guideline for maintenance and treatment of propeller shaft are investigated. From the results of investigation, remarkable deterioration of the material properties and corrosion resistance on the welded work part was observed.

• Journal of Welding and Joining
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• 제14권5호
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• pp.49-58
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• 1996

In Korea Gas Corporation, as one of the pipeline repairing methods, damaged pipelines are sometimes treated with a temporally employment of split sleeve. On conducting the repair process, circumferential fillet and longitudinal groove welding usually must be included. For the case of groove welding, a considerable amount of R&D have been carried out related to property changes, while few study on the property change in fillet welding has been conducted. In this paper, so as to confirm the specification of fillet welding in terms of safety and reliability, properties changed by fillet welding were investigated for two welding processes. Qualifying tests such as reviewing macrostructure and nick-break tests were performed according to API 1104 and ASME section IX. In addition, tensile properties and hardness were evaluated according to KS B0841 and BS 4515. The fillet weld prepared by the qualified procedure showed melting depth of 0.8∼1.3mm and heat affected zone of 2.8∼3.4mm length. No crack and lack of penetration were observed. And the results of hardness and nick-break tests satisfied code requirements. The area crossed by fillet and groove welding line was found to have minimal tensile strength.

• Journal of Welding and Joining
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• 제17권1호
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• pp.82-87
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• 1999

The basic remote sleeve repair-welding technology by the pulsed Nd:YAG laser for increasing the lifetime of the steam generator tube in a nuclear power plant has been developed. The relationship between the connection width and welding parameters have been investigated for the fundamental research to apply the sleeve-repair-welding technique to the nuclear industry. The Inconel 600 tube and Inconel 690 sleeve used for high temperature and high pressure service were welded as round lap welding by Nd:YAG laser. It was observed that the tensile shear strength, 340MPa of the welded specimen is equivalent to about 60% of that of the base metal (Inconel 600), 550MPa. The difference between the hardness of the base metal and that of the laser welds was about 10%. Ductile fracture was partly occurred in the weld but the cracking has not been observed. In spite of absence of the crack, the strength of welds was not sufficient in terms of the tensile shear strength.

• Journal of Welding and Joining
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• 제14권4호
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• pp.89-98
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• 1996

This study was performed to establish the characteristics of the heat affected zones from view point of the repair weldability for a damaged CrMoV steam turbine rotor steel. Characterization of the heat affected zones of the weldment was conducted with respect to various of postweld heat treatment temperatures, $566^{\circ}C$, $621^{\circ}C$ and $677^{\circ}C$. The evaluations of the heat affected zones were carried out in terms of microstructural characterization, microhardness measurements, Charpy v-notch impact, tensile and stress-rupture tests. The results indicated that the effect of the postweld heat treatment at $677^{\circ}C$ exhibited the favorable microstructure and mechanical properties for the stability of the heat affected zones. While the heat affected zone of the weldment, produced without postweld heat treatment, displayed the inferior toughness and microstructure indicating localized carbide precipitations on the grain boundary. It was also indicated that the stability of the heat affected zones were deteriorated by the formation of the cavitation on the grain boundaries.

• Journal of Welding and Joining
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• 제28권5호
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• pp.51-57
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• 2010

Brittle microstructure created in a heat affected zone (HAZ) during the welding of low alloy steel can be eliminated by post-weld heat treatment (PWHT). If the PWHT is not possible during a repair welding, the controlled bead depositions of multi-pass welding should be applied to obtain tempering effect on the HAZ without PWHT. In order to anticipate and control the tempering effect during the temper bead welding, the definition of temperature curve obtained from the analytical solution was suggested in this research. Because the analytical solution for heat flow is expressed as a mathematical equation of weld parameters, it may be effective in anticipating the effect of each weld parameter on the tempering in HAZ during the successive bead depositions. The reheating effect by the successive bead layer on the brittle coarse grained HAZ formed by earlier bead deposition was estimated by comparing the overlapped distance between the temperature curves in the HAZ. Three layered weld specimens of SA508 base metal with A52 filler were prepared by controlling heat input ratio between layers. The tempering effect anticipated by using the overlapped distance between the temperature curves was verified by measuring the micro-hardness distribution in the HAZ of prepared specimens. The temperature curve obtained from analytical solution was expected as a good tool to find optimal temper bead welding conditions.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.100-100
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• 2009

본 논문에서는 원자력발전소 1차 계통의 스테인리스강 저합금강 이종금속용접부 및 스테인리스강 동종용접부의 잔류응력을 평가하고 스테인리스강 용접부의 응력부식균열 민감성에 대해 고찰하였다. 노즐 안전단의 이종금속용접부 및 안전단 배관의 동종용접부 제작 및 소재가공에 의행 생성되는 잔류응력을 예측하기 위해 열 탄소성 유한요소법 수치해석을 수행하였으며, 용접공정과 함께 표면의 잔류응력에 기여하는 절삭 및 연삭가공과 소재의 담금질 공정을 열 탄소성적으로 모사하였다. 전산해석 결과, 스테인리스주강의 담금질 잔류응력은 무시할 수 없는 상당한 크기이므로 배관 용접잔류응력 평가 시 소재의 담금질 효과를 고려해야 할 것으로 판단된다. 이종금속 용접과 동종금속 용접공정이 보수용접 없이 정상적인 절차(내면에서 외면으로 적층)로 완성된다면, 냉각재 환경에 노출되는 용접부 내면의 잔류응력은 재료의 응력부식균열 민감성에 영향을 주지 않을 것으로 판단된다. 한편, 안전단 배관 동종용접부의 연삭가공에 의해 내면의 잔류응력이 크게 상승하는 것으로 예측되었으므로, 내면의 연삭가공 이후 표면잔류응력 완화처리(예, 버핑)가 필요하다.

• 한국가스학회지
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• 제20권4호
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• pp.33-43
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• 2016

미국과 유럽의 가스회사에서는 배관의 보수방법으로 그라인딩, 육성용접, 슬리브덮개용접, 복합재료보수, 핫태핑, 클램프 등 다양한 방법을 사용하고 있으며, 배관에 손상이 발생한 경우 사용적합성 평가를 거쳐 배관보수를 실시하고 있다. 또한, 미국과 영국 등에서는 매설된 도시가스배관이 타공사 또는 부식으로 인해 손상을 입은 경우 손상형태별로 적용 가능한 배관보수방법을 규정하고 있다. 국내의 경우에는 노후된 중압배관에 대하여 정밀안전진단을 하도록 하고 있으며, 정밀안전진단결과 발생된 결함의 종류 및 정도에 따라 배관을 보수, 교체 또는 신설하도록 규정하고 있다. 그러나 보수 및 보강 방법에 대하여는 기준이 마련되어 있지 않아 배관에 손상이 발생한 경우 주로 손상된 배관을 절단한 후 단관(短管)으로 교체하는 방법만을 사용하고 있다. 본 논문에서는 미국, 영국 등 국외의 보수방법 및 기준을 조사하고, 국내의 매설배관 검사 방법 등에 대해 조사하고, 보수방법 시험 결과를 분석한 후 국내 실정에 맞는 배관보수기준(안)을 제시하였다. 개발되는 기준에 따라 도시가스사업자가 정밀안전진단 결과의 후속조치로 배관보수를 하는 경우 가스공급을 중단하지 않아도 되므로 가스의 안정적 공급에 기여할 수 있을 것으로 판단된다.

• Corrosion Science and Technology
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• 제7권2호
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• pp.134-137
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• 2008

Cold arc welding of cast iron has been widely used with repair welding of metal structures. However its welding is often resulted in the galvanic corrosion between weld metal zone and heat affected zone(HAZ) due to increasing of hardness. In this study, corrosion properties such as hardness, corrosion potential, surface microstructures, and variation of corrosion current density of welding zone with parameters of used electrodes for cast iron welding were investigated with an electrochemical evaluation. Hardness of HAZ showed the highest value compared to other welding zone regardless of kinds of used electrodes for cast iron welding. And its corrosion potential was also shifted to more negative direction than other welding zone. In addition, corrosion current density of WM in polarization curves was qualitatively smaller than that of HAZ. Therefore galvanic corrosion may be apparently observed at HAZ. However galvanic corrosion may be somewhat controlled by using an optimum welding electrode.