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A Study on The Strength Evaluation of welded Joints for Degraded Material (열화재 용접부의 강도평가에 관한 연구)

  • 정의정;윤한용
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.705-710
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    • 2002
  • Welding is used not only during the shipbuilding, but also during the repairing of ships. While repairing of ships, it is inevitable to weld new materials with degraded materials. In this case, it is predicted that the strength of both the sections is not identical each other. In this study, the respective welded joints in terms of mechanical properties such as microstructure, mechanical strength and fatigue crack propagation, with the component obtained from the barge used for a long-term period, were analyzed. It was found that the material degradation had a significant effect on the welded joints. The fatigue crack propagation in welded sections showed a big difference. The rate of fatigue crack growth of degraded material for both heat affected zone and parent metal was faster than that of new material. By contrast, The result within identical materials showed that the heat-affected zone was slower than that of parent metal

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Evaluation of Degradation Behavior of the Long-Term Serviced Boiler Header (장기 사용 보일러 헤더의 열화거동 평가에 관한 연구)

  • Gwon, Jae-Do;Bae, Yong-Tak;Choe, Seong-Jong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.7
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    • pp.1673-1680
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    • 2000
  • The degradation of a boiler header constructed by a material, 1Cr-0.5Mo steel in a fossil power plant is observed when the header is exposed for a long period to the high temperature and pressure. The present investigations are for evaluating the effect of the degradation on the material, such as its strength changes. Reheat-treated metal is used to compare the mechanical properties of the degraded and that of reheat-treated materials. Through the investigation, following results are obtained 1) the area ratio of ferrite in the reheat-treated material is larger than that of the degraded material, 2) the hardness and tensile strength of the degraded material are lower than that of the reheat-treated material, 3) the ductile-brittle transition temperature(DBTT) increased toward high temperature region, 4) the fatigue crack growth rate(FCGR) of the degraded material is higher than that of the reheat-treated material in the region of low ΔK value while FCGR of the both materials are similar in high ΔK region.

Initiation and Growth Behavior of Small Fatigue Cracks in the Degraded 2 1/4 Cr-1 Mo Steel (2 1/4 Cr-1 Mo강 劣化材의 微小 疲勞龜裂의 발생 및 진전거동)

  • 곽상국;장재영;권재도;최선호;장순식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.1
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    • pp.53-62
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    • 1992
  • Material can be degraded by using it for a long service under the high temperature and pressure circumstances, Therefore, material degradation can affect the strength of mechanical structures. At present, the life prediction of the degraded structures is considered as an important technical problem. In this paper, the degraded 21/4Cr-lMo steel is the material used for about 10 years around 400.deg. C in an oil refinery plant. The recovered one was prepared out of the above degraded steel by heat treatment for one hour at 650.deg. C. The degradation effect was investigated through the tension test, Hardness test and Charpy impact test. On the smooth surface material, the fatigue crack initiation, growth and coalescence stages of the distributed small cracks were investigated with photographs, and the crack length and density were measured. The measuring results were analyzed by quantative and statistical methods.

A Study on the Strength Evaluation of Welded Joints for Degraded Material (열화재 용접부의 강도평가에 관한 연구)

  • 정의정;윤한용;임명환;김태식
    • Journal of the Korean Society for Precision Engineering
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    • v.19 no.11
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    • pp.75-82
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    • 2002
  • Welding is used not only for the shipbuilding, but also for the repairing of ships. While repairing of ships, it is inevitable to weld new materials with degraded materials. In this case, it is predicted that the strength of both the sections is not identical each other. In this study, the respective welded joints in terms of mechanical properties such as microstructure, mechanical strength and fatigue crack propagation, with the component obtained from the barge used for a long-term period, were analyzed. It was found that the material degradation had a significant effect on the welded joints. The fatigue crack propagation in welded sections showed a big difference. The rate of fatigue crack growth of degraded material for both heat affected zone and parent metal was faster than that of new material. By contrast, the result from identical materials showed that the rate of fatigue crack growth of the heat-affected zone was slower than that of parent metal.

The Evaluation of Partially Degraded Material Using Nonlinear Propagation Characteristics of Ultrasonic Wave (초음파 비선형 전파특성을 이용한 부분 열화 재료의 평가)

  • Kim, Kyung-Cho;Jhang, Kyung-Young;Hisashi, Yamawaki
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.2
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    • pp.214-219
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    • 2001
  • In this paper, the nonlinear behavior of ultrasonic wave in partially degraded material is considered. For this aim, FDM(finite difference method) model for the nonlinear wave equation was developed with the restriction to the 1-D longitudinal wave motion and how the partial degradation in material contributes to the detected nonlinear parameter was analyzed quantitatively. In order to verify the rightness of this simulation method, the relation between the detected nonlinear parameter and the continuous distribution of degradation obtained from simulation was compared with experiment results and the simulation and experiment results showed similar tendency. It can be known from simulation result that the degree of degradation, the range of degradation and the continuous distribution of degradation have strong correlation with the detected nonlinear parameter. As it was possible in these simulations that only special part is assumed as degraded one, the quantitative evaluation of partially degraded material may be obtained by using this method.

Evaluation of corrosion resistance by electrochemical method for Ni-Cr-Mo-V steel (Ni-Cr-Mo-V강의 전기화학적 방법에 의한 내식성 평가)

  • Kwon, Jae-Do;Moon, Yun-Bae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.9
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    • pp.1422-1431
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    • 1997
  • When the structures are exposed to their own an application for a long period, a number of variables such as strength properties and corrosion resistance, so on are expected to change. In the present investigation the corrosion behavior and resistance for the original and degraded materials of Ni-Cr-Mo-V steel were evaluated under the conditions of pH 3, 6, 9 and 12 in a distilled water environment. The electrochemical polarization technique was employed in this investigation. Based upon the experimental results obtained, the following conclusions were drawn. A severe and uniform corrosion was observed for both original and degraded materials under the condition of pH 3. At pH 6 and pH 9, these materials showed the degradation by a pitting corrosion. The materials under pH 12 environment were degraded by a uniform corrosion. The corrosion rate per year were the highest in the pH 3 environment, followed by pH 12, pH 6 and pH 9 environment in order. The corrosion resistance was decreased from the original material, slow cooled material (10.deg. C/hr) and step cooled material in order.

Strength Evaluation and Life Prediction of the Multistage Degraded Materials (다단계 모의 열화재의 재료강도 평가와 수명예측)

  • 권재도;진영준;장순식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.9
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    • pp.2271-2279
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    • 1993
  • In the case of life prediction on the structures and machines after long service, it is natural to consider a degradation problems. Most of degradation data form practical structures are isolated data obtained at the time of periodical inspection or repair. From such data, it may be difficult to obtain the degradation curve available and necessary for life prediction. In this paper, for the purpose of obtaining a degradation curves, developed the simulate degradation method and fatigue test and Charpy impact test were conducted on the degraded, simulate degraded and recovered materials. Fatigue life prediction were conducted by using the relationship between fracture transition temperature (DBTT : vTrs) obtained from the Charpy impact test through the degradation process and fatigue crack growth constants of m and C obtained from the fatigue test.

Experimental Studies on Comparison of Stress Corrosion Cracking Generation Due to Pipe Material Degradation in the Primary Stage of the Nuclear Power Plant (원전 1차 측 배관재질의 열화에 따른 응력부식균열 발생 비교 실험 연구)

  • Park, Kwang-Jin;Lee, Gyu-Young;Bae, Dong-Ho
    • Proceedings of the KSME Conference
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    • pp.108-113
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    • 2007
  • In this report, stress corrosion cracking generation due to pipe material degradation in the primary stage of the nuclear power plant was investigated. Firstly, after artificially degrading the CF8A steel during 2, 4, and 6 months in actual temperature, $400^{\circ}C,$ assessed corrosion susceptibility of the degraded material following ASTM G5 standard. And next, the S.C.C. tests for the degraded material were conducted under the condition of $60^{\circ}C,$ 2wt.% H2BO3+Li70H solution, 0.8 oy. From the results, Corrosion rates linearly increased with degradation period and solution temperature increase. And both the raw material and the degraded materials were not failed in the S.C.C. test condition. In spite of long time test (about 3,900 hrs) under S.C.C. condition, surface pits or surface corrosion by the electro chemical reaction were not observed. And also, even though the nondestructive DCPD and ACPD methods were applied to on-line monitor the S.C.C. failure processes it was impossible because the surface pits and cracks were not generated.

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Capacitance Properties of Degraded Thyristor with Temperature and Voltage (가속열화된 사이리스터의 커패시턴스 특성)

  • Seo, Kil-Soo;Lee, Yang-Jae;Kim, Hyeng-Woo;Kang, In-Ho;Kim, Nam-Kyun
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.131-132
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    • 2005
  • In this paper, the capacitance properties of degraded thyristor with temperature and voltage were presented. As degraded thyristor, 8 thyristors with each other different reverse blocking voltage used. Its impedance and resistance properties were measured from frequency 100Hz to 10MHz applied with bias voltage from 0V to 40V. As a result, at low frequency region, that is, at the frequency 100 - 10kHz, the abrupt increasement of its capacitance was confirmed. And also, at high frequency region, the capacitance peak move toward low frequency in the region of frequency 4 - 6MHz as degradation of thyristor.

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