• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.561-565
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• 1997

증기발생기 전열관 보수를 위하여 sleeve pipe를 삽입하여 레이저 용접을 하는 과정에서 전열관과 sleeve pipe 의 간격을 최소한으로 줄여 용접 품질을 높이고, 균등하게 하기 위하여 sleeve pipe에 대하여 확관이 수행된다. 확관은 sleeve pipe의 상단부와 하단부에 각각 수행되는데 정확한 확관규격을 유지하기 위하여 컴퓨터로 확관압력의 미분치를 비교분석하여 압력펌프를 제어하였다. 압력신호의 변화가 크고 안정되지 못하여 전후신호와 비교분석하여 안정화시킨 후 미분치를 추출하여 제어함으로써 전열관의 확관이 0.02mm 이내가 되도록 하여 전열관의 과도한 확관을 방지하였다.

• Journal of the Korean GEO-environmental Society
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• v.23 no.1
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• pp.39-49
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• 2022

Expandable steel pipe piles are installed by inserting expansion equipment to increase the cross-sectional area of steel pipes, which can improve the pile performance compared to micro-piles. In this paper, a hydraulic expansion device was developed to expand steel pipe piles in practice. A series of laboratory and field tests were conducted to verify the performance of the developed expansion device to expand steel pipes. The expansion capability and expandable range was evaluated by measuring the strain and expansion time at the maximum pressure of the hydraulic expansion device. The thinner steel pipe, the larger strain but longer expansion time required in the test. For example, the 4.0-mm-thick steel pipe showed strain reduction by 30% and a decrease in the required expansion time by 40% compared to the 2.9-mm-thick steel pipe. In addition, in-situ expansion tests were performed to verify the expandability of steel pipes under the ground, and the exhumed specimen showed clear expanded sections. The structural integrity was determined by comparing the material performance the original and expanded specimens.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05c
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• pp.85-91
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• 1996

원전 증기발생기 시제 전열관으로 제조된 Alloy 600 및 690 에 대하여 ASTM 규정 (B163-86a)에 따라 확관실험을 실시하여 평가하였으며, 관 요소에 작용하는 응력을 해석하였다. 실험 결과 시제 전열관은 ASTM에서 요구하는 확관율 30% 및 그 이상의 35% 까지 확관할 경우에도 양호한 확관상태를 보였다. 확관에 따른 유동곡선의 축력은 Alloy 690 이 Alloy 600 에 비해 높았으며, 확관율의 증가에 따라 차이가 점진적으로 크지는 경향을 보였다. 얇은 벽 튜브의 확관에 대한 응력 해석식은 Modified Tresca's Yield Criterion를 도입하여 얻었으며, 소성변형식을 이용하여 확관율에 따른 응력을 예측하였다. 유동곡선의 이론 계산치와 실험치를 비교한 결과 Alloy 600의 경우 이론치는 실험치보다 약간 낮은 값으로 잘 일치되었으나, Alloy 690 경우는 Alloy 600에 비하여 확관율의 증가에 따라 차이가 커지는 경향을 보였다.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1255-1257
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• 2005

본 논문에서는 튜브시트 내, 외부의 여러 다른 위치에서 확관이 이루어졌을 때 절대 및 차동 와전류신호를 유한요소 모델링으로 예측하고, 신호에서 자성 튜브시트로 인한 신호변화와 확관으로 인한 신호변화를 관찰하였으며, 이들에 미치는 주파수의 영향을 조사하였다. 그 결과, 절대 및 차동신호 모두 튜브시트의 위치 파악에는 저주파가 유리하고, 주파수가 높을수록 확관된 내경의 측정 및 확관 천이부의 파악이 용이하였으며, 절대신호가 차동신호에 비해 신호변화가 더 크고 지속적이어서, 확관 품질을 조사하기에 더 적합한 신호형태를 가지고 있음을 알 수 있었다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.216-216
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• 2004

본 논문은 우리가 일상 생활에서 접하는 에어컨의 핵심 부품인 열 교환기의 제작과정 중에서 확관 공정에서의 확관속도 최적화에 관한 것이다 여기서 열 교환기는 구멍 뚫린 박판형태의 방열핀과 이 구멍을 통과하는 구리재질의 관인 헤어핀의 2가지 주요 부품으로 구성되어있다 그리고 확관기(Fig. 1)에 있어서의 확관공정은 Fig. 2에서 보는 바와 같이 소성변형을 통한 관의 반지름 방향의 팽창으로 방열핀과 헤어핀을 결합시켜주는 높은 정밀도를 요구하는 작업이다.(중략)

• Journal of Energy Engineering
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• v.23 no.2
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• pp.149-157
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• 2014

The steam generator tubes of nuclear power plants have various types of corrosion failures during the plant operation. The stress corrosion cracking which occurs on the outer surface of tube is called the secondary side stress corrosion cracking and mainly occurs in the expansion-transition area of tube. The causes are the concentration of impurities by the sludge pile-up related to the geometry of its region and the residual stress by tube expansion in the process of steam generator manufacturing. Especially the directionality and sizes of residual stresses are differed according to the tube expansion methods and the direction and the frequency of tube cracks depend on their characteristics. In bases on the plant experiences, it is notified that circumferential cracks of tubes expanded with explosive expansion method are dominantly occurred compared to those of tubes done with hydraulic expansion one. Therefore in this study, according to tube expansion methods frequencies and sizes of tube cracks with specific direction are compared by means of accelerated immersion test and also the crack morphology and the specific chemicals from water-chemistry environment are observed through the fracture surface examination.

• Journal of Energy Engineering
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• v.21 no.4
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• pp.362-372
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• 2012

The steam generator tubes of nuclear power plants are pressure boundaries, and if tubes are leaked, the coolant with the radioactive materials was flowed out from the primary system to the secondary system and polluted the plant and the air. Recently most crack defects of tubes are stress corrosion cracks and these defects are located in expansion transition area, sludge pile-up region, and U-bend area. The most effective one of crack initiation factors in expansion transition area and U-bend area is the residual stress. According to the experiences of Korea standard nuclear plants(Optimized Power Reactor-1000), they had the stress corrosion cracks at the tube expansion transition area in early operating stage and especially lots of circumferential cracks were occurred. Therefore in this study, the distributions and conditions of residual stresses by tube expansion methods were compared and the dominant reason of a specific direction was examined.

• Journal of Energy Engineering
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• v.22 no.2
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• pp.148-155
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• 2013

The steam generators of OPR-1000 plants have Alloy 600 and Alloy 690 as the tube material and its tube expansion method is the explosive expansion method. According to the experience of these plants, circumferential cracks were largely occurred in steam generator tubes expanded by the explosive expansion method and their locations were the outer surface of tube expansion transition region surrounding with piled-up sludge. But even though tubes have the same conditions, tubes with the hydraulic expansion method shows the prevail trend of axial cracks compared to circumferential cracks. Therefore in this study, in order to identify the difference of such phenomena as above, configurations of tube and tubesheet were modeled and at operating conditions, stress values applied in the tube expansion transition area in accordance with tube expansion methods were calculated by using computational program and the direction and the predominance of cracks were evaluated.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.430-434
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• 2004

Specifically designed mandrel is needed to expand tube of the heat exchanger with inner grooves. Configuration of the expanded tube depends upon the shape and feeding velocity of the mandrel. 3D simulation software LS-DYNA was used to obtain optimum design conditions of the mandrel. We show how configuration of the expanded tube varies with different design parameters such as the approaching angle, diameter , and the feeding velocity of the mandrel. Material property data for analysis were obtained through experiments with SHPB ( Split Hopkinson Pressure Bars ).

• Journal of the Korean Institute of Gas
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• v.16 no.1
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• pp.1-7
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• 2012

The present study has been carried out to analyze the flow characteristics in the inlet expasion duct of a heat recovery steam generator by using numerical flow analysis. The inlet of HRSG corresponds the outlet of gas turbine exit and the flow after gas turbine has strong swirl flow and turbulence. The inlet flow condition of HRSG should be included the exit flow characteristics of gas turbine. The present numerical analysis adopted the flow analysis result of gas turbine exit flow as a inlet flow condition of HRSG analysis. Because the flow characteristics in the inlet duct of the tube bank is strongly related to the performance of a HRSG, it is most important for the optimal design of HGSG to understanding the flow phenomena in the inlet duct of HRSG. From the present study, the position of breakpoint in the inlet expansion duct should be lower than the reference breakpoint position for the optimal flow uniformity before the tube bank.