• Proceedings of the KSME Conference
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• 2004.04a
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• pp.268-273
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• 2004

This study is conducted to clarify the effect of internal pressure on the deformation and collapse behaviors of wall thinned elbow under in-plane bending moment. Thus the nonlinear three-dmensional finite element analyses were performed to obtain the moment-rotation curve of elbow contatining various wall thinning defects located at intrados and extrados under in-plane bending (closing and opening modes) with internal pressure of $0{\sim}15MPa.$ From the results of analysis, the effect of internal of collapse moment of elbow on the global deformation behavior of wall thinned elbow was discussed, and the dependence of collapse moment of elbow on the magnitude of internal pressure was investigated under different loading mode, defect location, and defect shape.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2003.05a
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• pp.345-353
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• 2003

탄소강은 가공성과 용접성이 우수하기 때문에 각종 산업설비의 배관재로 많이 사용되고 있으며, 특히 가압중수로형 원전의 1차측 배관과 가압경수로형 원전의 2차측 배관에 주로 사용되고 있다. 그러나 탄소강 배관은 부식에 취약하므로 유동가속부식(FAC, Flow Accelerated Corrosion) 현상에 의한 배관의 두께가 감소하는 감육 손상이 중요하게 대두되고 있는 실정이다. 이러한 감육현상은 다른 어떤 설비보다 안전성의 확보가 강조되고 있는 원전 배관의 경우에 있어서는 특히 중요한 건전성 저해요인으로 인식되고 있다.(중략)

• Journal of the Korean Institute of Gas
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• v.12 no.2
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• pp.57-62
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• 2008

Difference of failure modes was studied by finite element analysis for elbows with local wall thinning area particularly at inner surface of intrados of the elbow. Longitudinal wall thinning length, minimum thickness were kept constant but circumferential wall thinning width was varied to get $90^{\circ}$, $180^{\circ}$ and $360^{\circ}$ thinning width. Elastic-plastic analysis were carried out under the combined loading conditions of internal pressure and in-plane bending moment closing the elbow. Von Mises stress were obtained from the outer surface central surface location in intrados, extrados and crown parts in elbow. The results showed that the plastic deformation and failure started from the crown location when the thinning width small ($90{\sim}180^{\circ}$). However, plastic collapse started from the intrados location when the thinning width is approaching $360^{\circ}C$. This should be reflected to assess structural integrity of elbows after wall thinning measurement is made.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2004.10a
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• pp.52-59
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• 2004

• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.647-657
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• 2012

Although nuclear power plant piping system is designed conforming to design specifications, the piping systems are deteriorated with increase in service life. In this study, monotonic and cyclic loading tests were carried out on TP316 stainless steel pipe specimens, and the effect of local wall thinning and cracking on failure behavior was investigated. In the tests, 0%, 35% and 75% wall thinning and cracking of initial thickness were artificially introduced to inside elbow and straight pipe specimens, and internal pressures of 20MPa were applied to simulate real operation condition. From the test results, the effect of local wall thinning and cracking on failure mode, ultimate load, number of cycle and strain energy was presented, and maximum bending moment was compared with allowable bending moment calculated by ASME code.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.4
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• pp.402-409
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• 2004

The purpose of this study is to investigate the effect of local wall thinning on the collapse of elbow subjected to internal pressure and bending moment. Thus, the nonlinear three-dimensional finite element analyses were performed to obtain the collapse moment of elbow containing various wall thinning defects located at intrados and extrados under two loading modes (closing and opening modes) with internal pressure. From the results of analysis, the effect of wall thinning defect on the global moment-rotation behavior of elbow was discussed, and the dependence of collapse moment of elbow on wall thinning depth, length, and circumferential angle was investigated under different loading mode and defect location.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.622-628
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• 2003

The purpose of this study is to evaluate the effect of local wall thinning on the collapse of elbow subjected to internal pressure and bending moment. Thus, the nonlinear 3D finite element analyses were performed to obtained collapse moment of elbow containing various wall thinning defects under two loading; modes (closing and opening modes) and defect locations (intrados and extrados). From the results of analyses, the influence of wall thinning defect on the global moment-rotation behavior of elbow was discussed, and the dependance of collapse moment of elbow on wall thinning depth, length, and circumferential angle was investigated under different loading mode and defect location.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.12
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• pp.1063-1071
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• 2008

This paper provides a failure pressure evaluation model for local wall-thinned elbows. In this study, parametric finite element analyses are performed on the elbows containing local wall-thinning defect at their intrados and extrados, and the failure pressures are obtained from the analysis results by applying a local failure criterion that was validated by real-scale pipe tests. An evaluation model including the effects of thinning depth, length, circumferential angle, thinning location, and elbow geometries on the failure pressure is derived based on the evaluated failure pressures. The proposed model agrees well with the results of finite element analyses and reasonably estimates the dependence of failure pressure on the wall-thinning dimensions and elbow geometries. Also, the comparison with experimental data demonstrates that the proposed evaluation model can accurately predict the failure pressure of local wall-thinned elbows.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.10a
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• pp.217-218
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• 2006

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.191-198
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• 2008

Flow accelerated corrosion (FAC) phenomenon of low alloy carbon steels in nuclear power plant has been known as one of major degradation mechanisms. It has a potential to cause nuclear pipe rupture accident which may directly impact on the plant reliability and safety. Recently, the equipotential switching direct current potential drop (ES-DCPD) method has been developed, by the present authors, as a method to monitor wall loss in a piping. This method can rapidly monitor the thinning of piping, utilizing either the wide range monitoring (WiRM) or the narrow range monitoring (NaRM) technique. WiRM is a method to monitor wide range of straight piping, whereas NaRM focuses significantly on a narrow range such as an elbow. WiRM and NaRM can improve the reliability of the current FAC screening method that is based on computer modeling on fluid flow conditions. In this paper, the measurements by ES-DCPD are performed with signal sensitivity analyses in the laboratory environment for extended period and showed the viability of ES-DCPD for real plant applications.