• Corrosion Science and Technology
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• 제4권4호
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• pp.164-170
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• 2005

Pipelines have the highest capacity and are the safest and the least environmentally disruptive means for transmitting gas or oil. Recently, failures due to corrosion defects have become a major concern in maintaining pipeline integrity. A number of solutions have been developed for the assessment of remaining strength of corroded pipelines. In this paper, a Fitness-For-Purpose(FFP) type limit load solution for corroded city gas pipelines is proposed. For this purpose, a series of burst tests with various types of machined defects were performed. Finite element simulations were carried out to derive an appropriate failure criterion. Based on such solution along with existing solutions, an integrity evaluation program for corroded city gas pipeline, COPAP-CITY, has been developed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.160-165
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• 2004

An effective integrity evaluation system is essential to manage the fitness for service issues on infra-structure because the evaluation processes usually take long times and are detrimental for productivity point of view. In this paper, the key structures and procedures of four integrity evaluation programs which have been developed based on currently available codes and standards are described. The proposed programs are not only flexible to adopt advances in fitness for purpose type assessment methodologies but also convenient for field engineers. The developed programs which will be unified as an integrity evaluation system are expected to play a prominent role for integrity evaluation of major infra-structure.

• Corrosion Science and Technology
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• 제6권1호
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• pp.29-32
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• 2007

The final goal of this study is to develop the core technologies applicable to the design, operation and maintenance of welds in nuclear structures. This study includes predicting microstructure changes and residual stress for welded parts of nuclear power plant components. Furthermore, researches are performed on evaluating fatigue, corrosion, and hydrogen induced cracking and finally constructs systematically integrated evaluation system for structural integrity of nuclear welded structures. In this study, metallurgical and mechanical approaches have been effectively coordinated considering real welding phenomena in the fields of welds properties such as microstructure, composition and residual stress, and in the fields of damage evaluations such as fatigue, corrosion, fatigue crack propagation, and stress corrosion cracking. Evaluation techniques tried in this study can be much economical and effective in that it uses theoretical/semi-empirical but includes many additional parameters that can be introduced in real phenomena such as phase transformation, strength mismatch and residual stress. It is clear that residual stress makes great contribution to fatigue and stress corrosion cracking. Therefore the mitigation techniques have been approached by reducing the residual stress of selected parts resulting in successful conclusions.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.339-344
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• 2001

The transmission pipeline industry spends many millions of dollars annually performing inline inspections, excavating sites of possible corrosion, and repairing or replacing damaged sections of pipe. New criteria for evaluation the integrity of corroded pipe have been developed in recent years to help in controlling these costs. These new criteria vary widely in their estimates of integrity and the most appropriate criterion for a given pipeline is not always clear. This paper presents an overview, comparison and evaluation of acceptability criteria for corrosion defects in pipelines. By full scale burst tests, this paper have assessed the relative accuracy of each of theses criteria in predicting failure and remaining strength. Many of the criteria appear to be excessively conservative and indicate that defects must be repaired when none is needed, based upon burst test data.

• 항공우주시스템공학회지
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• 제6권2호
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• pp.28-34
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• 2012

Structural integrity evaluation is important item in the aircraft certification. Recently, it is designed for limit load, material weakness about fatigue and corrosion, damage by bird strike in flight to evaluate structural integrity of aircraft. And static/fatigue analysis are performed to secure structural integrity, it was verified by static and fatigue tests. To evaluate the structural integrity of small aircraft tail, structural integrity was calculated by the finite element analysis. In the present study, finite element analysis are performed to pick out load cases in flight occurrence, and secure margin of safety to evaluate structural integrity of KC-100 tail unit. The proprieties of finite element analysis results are compared with the static structure test results. The estimation process of structural integrity for small aircraft tail may help the design.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.264-267
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• 2004

Wall thinning of carbon steel pipe components due to Flow-Accelerated Corrosion (FAC) is one of the most serious threats to the integrity of steam cycle piping systems in Nuclear Power Plants (NPP). Since the mid-1990s, secondary side piping systems in Korean NPPs have experienced wall thinning, leakages and ruptures caused by FAC. Korea Electric power Research Institute (KEPRI) and Korea Hydro & Nuclear Power Co., LTD. (KHNP) have conducted a study to develop the methodology for systematic pipe management and established the Korean Thinned Pipe Management Program (TPMP). To effectively maintain the integrity of piping system, FAC engineer should understand the criterions of the structural integrity evaluation and the safety margin assessment for the thinned pipe component. This paper describes the technical items of TPMP, and shows the example of the integrity evaluation and safety margin assessment for three thinned pipe component of a NPP.

• 한국압력기기공학회 논문집
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• 제11권2호
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• pp.51-60
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• 2015

Local wall thinning and integrity degradation caused by several mechanisms, such as flow accelerated corrosion, cavitation, flashing and/or liquid droplet impingement, is a main concern in secondary steam cycle piping system of nuclear power plants in terms of safety and operability. Thinned pipe management program (TPMP) has being developed and optimized to reduce the possibility of unplanned shutdown and/or power reduction due to pipe failure caused by wall thinning. In this paper, newest technologies, standards and regulations related to the integrity assessment, repair and replacement of thinned pipe component are reviewed. And technical improvement items in TPMP to secure the reliability and effectiveness are also presented.

• Nuclear Engineering and Technology
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• 제32권1호
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• pp.67-76
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• 2000

Significant wall thinning due to flow accelerated corrosion(FAC）was recently reported in main feedwater pipes in 3 Korean pressurized water reactor(PWR) plants. The main feedwater pipes in one plant were repaired using overlay weld method at the outside of pipe, while those in 2 other plants were replaced with new pipes. In this study, the effect of the wall thinning in the main feedwater pipes on piping integrity was evaluated using finite element method. Especially, the effects of both the overlay weld repair and the stress concentration in notch-type thinned area on the piping integrity were investigated. The results are as follows : (1) The piping load carrying capacity may significantly decrease due to FAC. In special, the load carrying capacity of the main feedwater pipe was reduced by about 40% during about 140 months operation in Korean PWR plants. (2) By performing overlay weld repair at the outside of pipe, the piping load carrying capacity can increase and the stress concentration level in the thinned area can be reduced.

• 한국해양공학회지
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• 제24권4호
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• pp.38-46
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• 2010

The wall thinning phenomenon of pipes was simulated as metal loss due to erosion and corrosion. Such wall thinning defects in the pipes of power plants are a very important safety consideration. In this study, we analyzed wall thinning defects that occurred by weld bead of weld zone of boost pump recirculation pipe. From the results of the analysis of pipe failures, numerical analysis was performed by Fluent v6.3.26 using the standard k-$\varepsilon$ model of the weld bead shape, such as an elliptical or a spherical shape, on the inner wall of the pipe. Using the results obtained, we showed the overlap effect by cavitations corrosion and erosion-corrosion at the bottom of the wall-thinning defect.

• Nuclear Engineering and Technology
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• 제26권4호
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• pp.526-535
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• 1994

KMRR(다목적 연구용원자로) 핵연료의 알루미늄 피복재의 부식거동을 평가하기 위해, 부식 예측치와 노내 부식 실측치의 비교를 통해 유도된 열속인자를 도입한 수정된 Griess 경험식을 유도하였다. KMRR 핵연료의 건전성이 유지되는 부식의 설계기준으로써는 산화층의 박리 방지가 보수적으로 설정되었으며, 산화층의 박리는 산화층에서의 온도차이가 114$^{\circ}C$ 이상에서 일어난다고 보수적으로 가정하였다. KMRR 핵연료의 출력이력을 첫 주기부터 평형주기까지 분석하여, 한계출력이력을 결정하였다. 한계출력이력을 가진 KMRR 핵연료의 부식량 예측계산 결과, 최대 산화층의 두께는 50$\mu\textrm{m}$ 이하였으며, 산화층 박리의 설계기준은 2배의 여유도를 가지고 만족하였다. 따라서, KMRR 핵연료는 피복재의 부식으로 인해 손상되지 않을 것으로 판단된다. 그러나, 수정된 Griess 부식경험식의 KMRR에의 적용 타당성은 KMRR 핵연료의 부식 감시를 통해 추가로 검증될 필요성이 있다.