• Title/Summary/Keyword: corrosion assessment

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Application of Acoustic Emission Technique for Bridge Cable Monitoring (교량 케이블 적용 강연선 모니터링을 위한 음향방출 기법 검토)

  • Kim, Ga-Young;Seo, Dong-Woo
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.22 no.4
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    • pp.121-125
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    • 2018
  • This paper presents the assessment of 7-wire strand monitoring using acoustic emission technique for bridges. 7-wire strand is widely used construction materials to provide additional tensile force to bridges. PSC (PreStressed Concrete) bridge and cable-stayed bridge are representatives for such cases. However, as the bridge aging progresses recently, corrosion problems of strand are emerging. For this reason, various NDT (Non-Destructive Test) methods for cable inspection are being studied and applied to the field. One of the NDT methods, acoustic emission technique, is known as an effective technique to detect cable damage and breakage. In this study, to evaluate the applicability of acoustic emission technique to bridges, acoustic emission signals according to damage of the strand were acquired and analyzed by tensile test. Moreover, The optimal AE sensor type was selected for field application. As a result, it is considered that the acoustic emission technique will be able to detect corrosion breakage and signs of rupture.

Material Integrity Assessment for a Ni Electrodeposit inside a Tube

  • Kim, Dong-Jin;Kim, Myong Jin;Kim, Joung Soo;Kim, Hong Pyo
    • Corrosion Science and Technology
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    • v.6 no.5
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    • pp.233-238
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    • 2007
  • Due to the occasional occurrence of a localizedcorrosion such as a SCC and pitting in steam generator tubing(Alloy 600), leading to a significant economical loss, an effective repair technology is needed. For a successful electrodeposition inside a tube, many processes should be developed. Among these processes, an anode to be installed inside a tube, a degreasing condition to remove any dirt and grease, an activation condition for a surface oxide elimination, a strike layer forming condition which needs to be adhered tightly between an electroforming layer and a parent tube and a condition for an electroforming layer should be established. Through a combination of these various process condition parameters, the desired material properties can be acquired. Among these process parameters, various material properties including a mechanical property and its variation along with the height of the electrodeposit inside a tube as well as its thermal stability and SCC resistance should be assessed for an application in a plant. This work deals with the material properties of the Ni electrodeposits formed inside a tube by using the anode developed in this study such as the current efficiency, hardness, tensile property, thermal stability and SCC behavior of the electrodeposit in a 40wt% NaOH solution at $315^{\circ}C$. It was found that a variation of the material properties within the entire length of the electrodeposit was quite acceptable and the Ni electrodeposit showed an excellent SCC resistance.

Service Life Prediction and Cost Estimation of Repaired Concrete Structures Under Marine Environment (염해 환경 하 보수된 콘크리트 구조물의 사용수명 예측 및 보수 비용 평가)

  • Shim, Hyun Bo;Ann, Ki Yong
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.15 no.1
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    • pp.226-234
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    • 2011
  • The service life of concrete structures exposed to a marine environment can be extended by controlling the amount of chloride in cover concrete. Patching is one of the appropriate maintenance techniques for chloride contamination. Chloride-contaminated cover concrete is removed and replaced with sound one. It can provide less risk of corrosion of steel, so that the structure can be maintained for required service life. In this study, a quantitative assessment of the service life subjected to the chloride attack is proposed to determine the effective repair options such as repair depth, repair material and timing of repair. The Crank-Nicolson based finite difference formulation from Fick's second law is proposed to predict the profiles of chloride ion in a repaired concrete structure, considering ingress of chloride from outer and redistribution of residual chloride from the substrate concrete. Therefore, the repair application times and maintenance cost for the target service life can be estimated. Finally, the numerical examples are presented to ensure its applicability.

Evaluation of PWSCC at Dissimilar Metal Butt Welds in NPP (원전 이종금속 맞대기용접부 PWSCC 균열건전성평가)

  • Lee, Sung-Ho;Lee, Kyoung-Soo;Oh, Chang-Young
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.9
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    • pp.1047-1052
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    • 2012
  • Primary water stress corrosion cracking (PWSCC) instances have been reported in the Alloy 600 reactor pressure vessel head penetration nozzle and the Alloy 82/182 dissimilar metal butt weld nozzle in several PWRs. Therefore, in-service inspection programs have been adopted worldwide to prevent failure at the weld region. If a PWSCC is observed at the dissimilar metal weld region during inspection, its structural integrity should be evaluated; however, this requires considerable time and effort, and this might lead to a decrease in the plant utilization coefficient. To prevent this, KHNP-CRI have established integrity assessment criteria and developed a computer program for the fast evaluation and judgment of PWSCC. In this paper, the results and current status of the same are presented. Through this study, criteria for the structural integrity evaluation of PWSCC have been established, and a computer program has been developed to realize technical means for the evaluation of PWSCC structural integrity.

Modified indirect evaluation method for deterioration assessment of drinking water pipes (상수도 노후도 평가를 위한 수정 간접평가법)

  • Kwon, Hyuk Jaea
    • Journal of Korea Water Resources Association
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    • v.56 no.11
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    • pp.697-703
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    • 2023
  • In this study, a modified indirect evaluation method was developed to predict the deterioration level of water pipes. The accuracy of the modified method was verified by comparing it with the direct method. The weights of index were adjusted by reducing the weight of water quality corrosion, soil corrosion, lay depth and road type according to the importance of the existing evaluation factors and adding the weight of pipe thickness. In the results, the weight of pipe thickness was determined to be 0.1530. Comparing with the direct evaluation method, the accuracy of the modified indirect evaluation method increased by 31.03% compared to the indirect evaluation method. The modified indirect evaluation method will be able to select relatively old pipes more accurately and efficiently than the existing indirect evaluation method when prioritizing the improvement of old water pipes.

Technical Application and Analysis for Reduction of Water Loss in Water Distribution Systems (상수도 관망의 유수율 제고 기술의 적용 및 분석)

  • Kim, Ju-Hwan;Lee, Doo-Jin;Bae, Cheol-Ho;Woo, Hyung-Min
    • Proceedings of the Korea Water Resources Association Conference
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    • 2009.05a
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    • pp.260-266
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    • 2009
  • Non-revenue water reduction(NRW) technologies are implemented to evaluate and manage leakages scientifically in water distribution systems under local governments. A development of quantitative leakage indicator by measuring minimum night flow, pressure control policy by installation of PRV(pressure reducing valve) and the establishment of leakage prevention schemes by residual life modeling of deteriorated water pipes are reviewed and studied. Estimation models of allowable leakage are developed by measuring and analyzing minimum night flow at residential and commercial area in Nonsan city, which is suggested from UK water industry and can improve an existing leakage indicator for the evaluation of non-revenue water. Also, pressure control method is applied and analyzed to Uti distribution area in Sacheon city in the operation aspect. As results, $466\;m^3/day$ of leakage can be reduced and it is expected that 113million won of annual cost can be saved. In the part of corrosion velocity and residual life assessment, non-linear prediction models of residual thickness are proposed by assessment of corrosion velocity based on exposure years, soil and water quality etc., since the deteriorated water pipe play a major role to increase leakage. It is expected that collection data and analyzing results can be applied effectively and positively to reduce non-revenue water by accumulating surveying data and verifying the results in the business field of water distribution systems under local governments.

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Evaluation of Nondestructive Evaluation Size Measurement for Integrity Assessment of Axial Outside Diameter Stress Corrosion Cracking in Steam Generator Tubes (증기발생기 전열관 외면 축균열 건전성 평가를 위한 비파괴검사 크기 측정 평가)

  • Joo, Kyung-Mun;Hong, Jun-Hee
    • Journal of the Korean Society for Nondestructive Testing
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    • v.35 no.1
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    • pp.61-67
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    • 2015
  • Recently, the initiation of outside diameter stress corrosion cracking (ODSCC) at the tube support plate region of domestic steam generators (SG) with Alloy600 HTMA tubes has been increasing. As a result, SGs with Alloy600 HTMA tubes must be replaced early or are scheduled to be replaced prior to their designed lifetime. ODSCC is one of the biggest threats to the integrity of SG tubes. Therefore, the accurate evaluation of tube integrity to determine ODSCC is needed. Eddy current testing (ECT) is conducted periodically, and its results could be input as parameters for evaluating the integrity of SG tubes. The reliability of an ECT inspection system depends on the performance of the inspection technique and abilty of the analyst. The detection probability and ECT sizing error of degradation are considered to be the performance indices of a nondestructive evaluation (NDE) system. This paper introduces an optimized evaluation method for ECT, as well as the sizing error, including the analyst performance. This study was based on the results of a round robin program in which 10 inspection analysts from 5 different companies participated. The analysis of ECT sizing results was performed using a linear regression model relating the true defect size data to the measured ECT size data.

Application of Laser Ultrasonic Technique for Nondestructive Evaluation of Wall Thinning in Pipe (배관부 감육 손상의 비파괴 평가를 위한 레이저 초음파 기술 적용)

  • Hong, Kyung-Min;Kang, Young-June;Park, Nak-Kyu;Yoon, Suk-Bum
    • Journal of the Korean Society for Nondestructive Testing
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    • v.33 no.4
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    • pp.361-367
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    • 2013
  • Many of the nuclear power plant pipe is used in high temperature and high pressure environment. Wall thinning frequently caused by the corrosion. These wall thinning in pipe is expected gradually increase as nuclear power become superannuated. Therefore there is need to evaluate wall thinning in pipe and corrosion defect by non-destructive method to prevent the accident of the nuclear power facility due to pipe corrosion. Especially for real-time assessment of the wall thinning that occurs in nuclear power plant pipe, the laser ultrasonic technology can be measured even in hard-to-reach areas, beyond the limits of earlier existing contact methods. In this study, the optical method using laser was applied for non-destructive and non-contact evaluation. Ultrasonic signals was acquired through generating ultrasonic by pulse laser and using laser interferometer. First the ultrasonic signal was detected in no wall thinning in pipe, then a longitudinal wave velocity was measured inside of pipe. Artificial wall thinning specimen compared to 20, 30, 40 and 50% of thickness of the pipe was produced and the longitudinal wave velocity was measured. It was possible to evaluate quantitatively the wall thinning area(internal defect depth) cause it was able to calculate the thickness of each specimen using measured longitudinal wave velocity.

The effect of crack length on SIF and elastic COD for elbow with circumferential through wall crack

  • Kim, Min Kyu;Jeon, Jun Hyeok;Choi, Jae Boong;Kim, Moon Ki
    • Nuclear Engineering and Technology
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    • v.52 no.9
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    • pp.2092-2099
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    • 2020
  • Many damages due to flow-accelerated corrosion and cracking have been observed during recent in-service inspections of nuclear power plants. To determine the operability or repair for damaged pipes, an integrity evaluation related to the damaged piping system should be performed by using already proven code and standards. One of them, the ASME Code Case is most popularly used to integrity assessment in nuclear power plants. However, the recent version of CC N-513 still recommends the simplified method which means a damaged elbow is assumed as an equivalent straight pipe. In addition, to enhance the accuracy integrity assessment in elbow, several previous studies recommend that the SIF and elastic COD values for an elbow with relatively large crack could be predicted by an interpolation technique. However, those estimates for elbow with relatively large crack might be derived to inaccurate results for crack growth analysis, such as for the allowable crack size and life estimation. Therefore, in this paper, the effect of crack length (0.3≤θ1/π≤0.5) on SIF and elastic COD for elbow is systematically investigated. Then, for large crack in elbow, accurate estimates for SIF and elastic COD, which are widely used to assess the integrity of elbows, are proposed. Those proposed solutions are expected to be the technical basis for revisions of CC N-513-4 through the validation.

Quantitative Risk Assessment for Gas-explosion at Buried Common Utility Tunnel (지하 매설 공동구 내부 가스 폭발에 대한 위험성 평가)

  • Jang, Yuri;Jung, Seungho
    • Journal of the Korean Institute of Gas
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    • v.20 no.5
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    • pp.89-95
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    • 2016
  • Keeping the gas pipelines in the common utility tunnel is useful because it has a lower risk of corrosion than conventional burial, and can prevent from excavating construction. But, explosions in common utility tunnels can cause greater damage from the blast overpressure compared to outdoor explosions, due to nature of the confined environment. Despite this fact, however, research on common utility tunnels has been limited to fire hazard and little has been studied on the dangers of explosions. This study developed scenarios of methane gas explosion caused by gas leak from gas piping within the common utility tunnel followed by unknown ignition; the study then calculated the extent of the impact of the explosion on the facilities above, and suggested the needs for designing additional safety measures. Two scenarios were selected per operating condition of safety devices and the consequence analysis was carried out with FLACS, one of the CFD tools for explosion simulation. The overpressures for all scenarios are substantial enough to completely destroy most of the buildings. In addition, we have provided additional measures to secure safety especially reducing incident frequency.