• Corrosion Science and Technology
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• 제9권2호
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• pp.57-66
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• 2010

Since nuclear power plants are being operated under high temperature and high pressure, on-line monitoring technique to detect corrosion could be more effective than off-line method in shut-off period. In this operating condition, electrochemical noise method may be suitable to monitor the corrosion. This paper aims the analysis on the relation between the cracking and electrochemical noise signal of Alloy 600 under U-bending. When electrochemical noise monitoring technique was used during SCC test, it was judge to be obvious that if cracks generate, its generation can be detected by electrochemical current noise. Cracking-related noise was defined as the noise showing 5~10 times greater than the average value of background noise bands. On the base of crack noise, crack initiation time was determined. From SCC test and electrochemical noise monitoring in $25^{\circ}C$, 0.1 M $Na_2S_4O_6$ solution (Reverse U-Bended Alloy 600 SE+), average crack initiation time was obtained as 9,046 seconds and from its initiation time, it could be defined that net crack propagation rate is the crack length divided by ${\Delta}T$(= total test period - crack initiation time). Therefore, average net crack propagation rate was obtained to be $1.18{\times}10^{-9}\;m/s$.

• Nuclear Engineering and Technology
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• 제39권3호
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• pp.231-236
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• 2007

Due to the occasional occurrences of stress corrosion cracking(SCC) in steam generator tubing(Alloy 600), degraded tubes are removed from service by plugging or are repaired for re-use. Since electrodeposition inside a tube does not entail parent tube deformation, residual stress in the tube can be minimized. In this work, tube restoration via electrodeposition inside a steam generator tubing was performed after developing the following: an anode probe to be installed inside a tube, a degreasing condition to remove dirt and grease, an activation condition for surface oxide elimination, a tightly adhered strike layer forming condition between the electro forming layer and the Alloy 600 tube, and the condition for an electroforming layer. The reliability of the electrodeposited material, with a variation of material properties, was evaluated as a function of the electrodeposit position in the vertical direction of a tube using the developed anode. It has been noted that the variation of the material properties along the electrodeposit length was acceptable in a process margin. To improve the reliability of a material property, the causes of the variation occurrence were presumed, and an attempt to minimize the variation has been made. A Ni alloy electrodeposition process is suggested as a primary water stress corrosion cracking(PWSCC) mitigation method for various components, including steam generator tubes. The Ni alloy electrodeposit formed inside a tube by using the installed assembly shows proper material properties as well as an excellent SCC resistance.

• 한국압력기기공학회 논문집
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• 제15권1호
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• pp.28-32
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• 2019

In nuclear power plant operation and spent fuel canisters, it is necessary to provide a sound technical basis for the safety and security of long-term operation and storage respectively. Recently, the peening technology is being discussed and the technology will be adopted to ASME Section III, Division 1, Subsection NX (2019 Edition). The peening is prohibited in current edition, but it will be approved in 2019 Edition and adopted. However, Surface stress improvement techniques such as the peening is used to mitigate SCC susceptible in operating nuclear plants. Although the peening will be approved to ASME CODE, there are no performance criteria listed in the 2019 edition. The Korean International Working Group (KIWG) formed a new Task Group named "Advanced Surface Stress Improved Technology". The task group will develop a CODE CASE to address PWSCC(Primary Water Stress Corrosion Cracking) and CISCC(Chloride Induced Stress Corrosion Cracking) for new ASME Section III components. TG-ASSIT was started to make peening performance criteria for ASME Section III (new fabrication) applications. The objective of TG-ASSIT is to gain consensus among the relevant Code groups that requirements/mitigation have been met.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2000년도 특별강연 및 춘계학술발표대회 개요집
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• pp.326-329
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• 2000

• Journal of Advanced Marine Engineering and Technology
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• 제34권5호
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• pp.661-669
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• 2010

The effects of laser peening on metallic materials have been investigated with water-penetrable frequency-doubled Nd:YAG laser. Laser pulses of 200 mJ energy and 8 ns duration focused on samples underwater with 0.8 mm spot diameter. X-ray study showed that compressive residual stress was imparted on SKD61 from the surface to nearly 2 mm depth. Stress corrosion cracking (SCC) was prohibited for sensitized SUS304 even in a severely corrosive environment fatigue lives of SUS316L and SM490A welded samples were prolonged significantly in the high-cycle regime. Since 1999, laser peening has been applied to prevent SCC in operating nuclear power plants in Japan.

• 비파괴검사학회지
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• 제29권4호
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• pp.374-382
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• 2009

원자력발전소의 1차측 및 2차측 냉각계의 장벽 역할을 하는 핵심 설비중 하나인 증기발생기(steam generator, SG) 전열관은 공공의 사회적 안전성과 효율적인 발전 용량을 유지하기 위해 구조적 건전성을 유지하여야 한다. 또한 결함을 함유하고 있는 전열관은 해당결함을 조기에 검출, 정량적으로 결함을 평가하여 필요한 경우에는 보수조치를 수행하여야 한다. 이러한 결함의 검출 및 정량화를 위해서 검사관련 고시 및 강화된 SG 관리프로그램(SGMP)에 근거하여 와전류탐상검사법(eddy current testing, ECT)을 적용, 검사를 수행하고 있다. SG 전열관에서 검출되고 있는 결함중 응력부식균열(stress corrosion cracking, SCC)은 미세한 경우 결함의 검출이 어려울 뿐 아니라 생성된 결함의 성장속도가 빠르기 때문에 SG 전열관의 건전성을 위협하는 주요결함 기구중 하나로 분류하고 있다. 본 논문에서는 다양한 결함 깊이 및 길이별로 방전가공(electric discharge machining, EDM)된 축방향 ODSCC에 대해 pancake, +point 및 shielded pancake 코일 등이 탑재된 3 coil형태의 +PT MRPC(motorized rotating pancake coils)를 적용하여 결함의 검출가능 여부 및 크기 측정을 위한 검사를 수행하였으며 본 실험결과를 통해 SG 전열관의 건전성 및 원전 운전의 안전성을 진단하는 공학적 평가 자료로써의 활용 가능성 뿐 아니라 와전류탐상검사의 신뢰도 향상을 도모하고자 하였다.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.585-586
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• 2006

Several chemicals were studied to suppress the damage due to stress corrosion cracking (SCC) of steam generator (SG) tubes in nuclear power plants. The effects on the SCC of the compounds, $TiO_2$, TyzorLA and $CeB_6$, were tested for several types of SG tubing materials. The test with the addition of $TiO_2$ and $CeB_6$ showed an effect in decreasing the SCC for the SG tubing material. However, $CeB_6$ caused some more SCC for Alloy 800. The penetration property into a crevice of the inhibitors was investigated by using Alloy 600 specimens with different gap.

• 한국재료학회지
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• 제3권4호
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• pp.361-371
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• 1993

응력부식균열(SCC) 감수성평가를 위한 여러 시험방법들중 저변형율시험방법은 비교적 \ulcorner은 시간내에 금속재료의 SCC감수성을 평가하기 위한 효과적인 시험방법이다. 그러나 저변형율 시험방법만으로 SCC과정의 미시적 파괴거동ㅇ르 분석하는 것은 매우 어렵다. 종래, 음향방출(AE)시험은 재료의 파괴과정시 미시균열의 개시 및 전파거동을 감시하는데 유효한 기법으로 잘 알려져 있다. 그러므로 본 논문에서는 저변형율시험과 음향방출시험을 이용하여 SCC의 전파과정과 AE신호 특성사이의 상호관계를 분석하였다. 실험결과, 재료의 미시파괴 과정에서 발생하는 AE신호들은 뚜렷히 시험환경에 의존하였으며, 인공해수중에서 SCC과정시 발생된 AE신호 특성은 Air상태 보다 상당히 크게 나타났다. 그리고 SCC거동은 AE신호의 진폭인자로서 명확하게 평가할 수 있다.

• 대한기계학회논문집A
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• 제26권5호
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• pp.896-903
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• 2002

The susceptibility of SCC for the weldment and PWHT specimens of HT-60 steel was evaluated using a slow strain rate method under applied potential by means of the potentiostat in synthetic seawater. In case of the parent, anodic polarization voltage was inappropriate in elongating the time to failure(TTF). -0.8V corresponding to cathodic protection range is most effective in improving the SCC resistance against corrosive environment. In case of the weldment, the values of reduction of area(ROA) and TTF at -0.68V corresponding to cathodic polarization value were 45.2% and 715,809sec which were the largest and longest life among other applied potentials. Those were vise versa at -1.1V. In case of the PWHT specimens, TTF and ROA at -0.68V was longest and largest like the weldment. Besides, PWHT is effective in prolonging the time to failure of the welded off-shore structure due to softening of effect. Regardless of the weldment and PWHT specimen, as corrosion rate gets higher, TTF becomes shorter and deformation behaviour for the weldment and PWHT specimen at -1.1V was shown to be irregular. Finally, it was found that specimens showed brittle fracture at -1.1V, but more ductile fracture accompanying the micro-cracks at applied potential of -0.68V.

• 한국가스학회지
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• 제7권2호
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• pp.22-32
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• 2003

Al-황동은 기계적 특성 및 열전도성이 우수하고 해수 중에서 표면 보호피막을 형성하므로 부식저항성이 높아 해수를 냉각수로 사용하는 선박용 열교환기의 세관재로 널리 사용되고 있다 Al-황동 세관은 실제 사용 환경에서 굽힘 등에 의한 소성변형된 상태로 사용되는 경우가 많다. 이와 같은 소성변형에 의한 Al-황동 세관의 균열 파손사례는 선박의 오일탱크 내의 가열코일, 각종 열교환기의 세관 등에서 흔히 찾아 볼 수 있다. 또한 세관의 확관에 의한 밀봉 방법에 따라 세관의 변형에 의한 잔류응력 및 어패류 혼입에 의한 해수 유입부의 국부적인 유속증가 등에 기인하여 Al-황동 세관의 균열 및 침식 등의 파손사례가 보고되고있다. 본 연구에서는 $3.5\%$ NaCl. + $0.1\%\;NH_4OH$ 수용액을 시험편 표면에 5 m/s로 액분사하의 가속실험에서 Al-황동 세관의 응력부식균열 거동에 미치는 응력의 영향에 대하여 고찰하였다.