• 한국안전학회지
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• 제14권2호
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• pp.32-41
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• 1999

If the Leak-Before-Break (LBB) concept is applicable to the nuclear piping design, it is not necessary to consider the dynamic effect due to pipe rupture. Therefore, the construction cost can be significantly reduced by eliminating unnecessary pipe whip restraints and jet impingement devices. The objective of this paper is to develop the Piping Evaluation Diagram (PED) for efficient application of LBB concept to piping system at an initial piping design stage. For this purpose, the 3-D finite element analyses were performed to evaluate the crack stability. And the stress-strain curve based on the pipe material tests were used to calculate the detectable leakage crack length. Finally, the present PED which was composed as a function of NOP load and allowable SSE load, was developed for an application of LBB concept to the safety injection and shutdown cooling line in Korean Next Generation Reactor (KNGR).

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.80-86
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• 2001

An engineering estimation equation for the crack opening displacement (COD) is proposed for a complex cracked pipe, based on the reference stress approach. To define the reference stress, a simple plastic limit load analysis for the complex cracked pipe subjected to combined bending and tension is performed considering the crack closure effect in the compressive-stressed region. Comparison with ten published test data and the results from existing method shows that the present method not only reduces non-conservatism associated with the existing method, but also provides consistent and overall satisfactory results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.670-677
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• 2003

Although Gas Tungsten Arc Welding (GTAW or TIG welding) is considered as high quality and precision welding process, it also has demerit of low melting rate. Narrow-gap TIG welding which has narrow joint width reduces the groove volume remarkably, so it could be shorten the welding time and decrease the overall shrinkage in heavy wall pipe welding. Generally Narrow-gap TIG welding is used as orbital welding process, it is important to select the optimum conditions for the automatic control welding This paper looks at the application and metallurgical properties on Narrow-gap TIG welding joint of heavy wall large austenitic stainless steel pipe to determine the deposition efficiency, the resultant shrinkage and fracture toughness. The fracture toughness depends slightly on the welding heat input.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.849-855
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• 2000

This study evaluated the effect of restraint of pressure induced bending(PIB) on crack mouth opening displacement(CMOD) for circumferential through-wall crack in pipe by using both elastic and elastic-plastic finite element analyses. The analyses results showed the restraint of PIB was decreased crack opening for a given crack length and tensile stress, and the effect was considerable for large crack and short restraint length. Also, the restraint effect on CMOD was independent on the variation in pipe diameter and decreased with increasing pipe thickness, and it depended on not total restraint length but short restraint length for non-symmetrically restrained. Additionally, the effect of restraint of PIB was more significant in the elastic-plastic analysis results compared with in the elastic analysis results.

• 대한기계학회논문집A
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• 제25권8호
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• pp.1235-1241
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• 2001

An engineering estimation equation for the crack opening displacement(COD) is proposed for a complex cracked pipe, based on the reference stress approach. To define the reference stress, a simple plastic limit load analysis for the complex cracked pipe subjected to combined bending and tension is performed considering the crack closure effect in the compressive-stressed region. Comparison with ten published test data and the results from existing method shows that the present method not only reduces non-conservatism associated with the existing method, but also provides consistent and overall satisfactory results.

• 대한기계학회논문집A
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• 제28권10호
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• pp.1612-1620
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• 2004

This study presents methods to estimate elastic-plastic crack opening displacement (COD) fur circumferential through-wall cracked pipes for the Leak-Before-Break (LBB) analysis of pressurized piping. Proposed methods are based not only on the GE/EPRI approach but also on the reference stress approach. For each approach, two different estimation schemes are given, one for the case when full stress-strain data are available and the other fur the case when only yield and ultimate tensile strengths are available. For the GE/EPRI approach a robust way of determining the Ramberg-Osgood (R-O) parameters is proposed, not only fur the case when detailed information on full stress-strain data is available but also for the case when only yield and ultimate tensile strengths are available. The COD estimates according to the GE/EPRI approach, using the R-O parameters determined from the proposed R-O fitting procedures, generally compare well with the published pipe test data. For the reference stress approach, the COD estimates according to the method based on both full stress-strain data and limited tensile properties are in good agreement with pipe test data. In conclusion, experimental validation given in the present study provides sufficient confidence in the use of the proposed method to practical LBB analyses even though when information on material's tensile properties is limited.

• 대한기계학회논문집A
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• 제40권9호
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• pp.821-826
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• 2016

원자력 배관 설계에는 파단전 누설(leak before break, LBB) 개념이 사용되고 있다. LBB 개념의 적용을 위해서는 관통균열을 통한 누설률을 정확하게 예측할 수 있어야 한다. 단면적이 일정한 관통균열에 대한 누설률 해석은 많이 이루어지고 있으나 실제 관찰되는 관통균열에서는 배관 내면 쪽과 외면 쪽의 단면적이 다른 경우가 많이 발생된다. 따라서 본 논문에서는 유동경로를 따라 선형적으로 변화하는 단면적을 가진 관통균열에 대하여 누설률을 평가하여 단면적의 분포가 누설률에 미치는 영향을 살펴보았다. 또한 클래딩 등에 의하여 두께 방향으로 이중 재료로 된 배관에 존재하는 관통균열에 대해서도 누설률을 평가하여 유동경로를 따라 달라지는 균열면 형태학적 변수가 누설률에 미치는 영향을 살펴보았다.

• 물과 미래
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• 제29권3호
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• pp.197-205
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• 1996

상수도 관망시설에서 각 관로는 시간이 경과함에 따라 각종 부식이 일어나 통수능이 저하된다. 그러므로 적절한 시기에 갱생이나 교체 등의 처리를 해주어야 한다. 본는 연구에서는 각 수요절점에서 요구수량, 요구압력 등 수리학적 조건을 만족시켜주며 동시에 최소의 비용으로 노구된 관로를 처리해주는 의사결정모형을 개발하였다. 교체비용, 관파열보수비용, 양수비용, 관 파열율, 연이율 등은 각 관로의 교체시기를 경제적으로 결정하는데 이용된다. 그리고 배수시설의 수리학적 만족여부는 관망계산 프로그램 KYPIPE에 의해 점검된다. 시스템이 수리학적 조건을 만족지 못할 경우 교체시기는 조건이 만족될 때까지 앞당겨진다. 본 모형은 기존 송배수시설인 수도권 광역상수도 제1단계에 적용되었다. 모형을 이용해 산출한 최적교체시키는 수리학적으로 모의해본 결과 문제가 없으며를 알 수 있었다.

• 대한기계학회논문집A
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• 제25권11호
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• pp.1873-1880
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• 2001

The effects of restraint of pressure induced bending(PIB) on crack opening for circumferential through-wall crack in a pipe were investigated. In this study, the elastic and elastic-plastic finite element analyses were performed to evaluate crack opening displacement(COD) for various restraint conditions and crack size. The results showed the restraint of PIB decreased crack opening for a given crack size and tensile stress, and the decrease in crack opening was considerable for large crack and short restraint length. A1so, the effect was more significant in tole results of elastic-plastic analysis compared with in the elastic analysis results. In the elastic-plastic analysis results, tole restraint effect was increased with increasing applied tensile stress corresponding to internal pressure. Additionally, the restraint effect on COD was independent on the variation in pipe diameter and decreased with increasing pipe thickness, and It depended on not total restraint length but shorter restraint length for non-symmetrically restrained.

• 대한기계학회논문집A
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• 제33권8호
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• pp.826-831
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• 2009

The piping systems in nuclear power plant are composed of various typed pipes such as straight, elbow pipe, branch and reducer etc. The elbow is connected from straight pipe to another pipes in order to establish the complicated piping system. Elbow is one of very important components considering management of wall thinning degradation. It is however applied by various loads such as system pressure, earthquake, postulated break loading and many transient loads, which provoke simply the internal pressure, bending and torsional stress. In this study, firstly pipes in the secondary system of the nuclear power plant are classified as pipe size and type for selecting the investigating range. Next, a large number of finite element analysis considering the all typed dimensions of commercial pipe has been performed to find out the behavior of TES(twice elastic slop) plastic load of elbows, which is based on evaluation of the structural safety factor. Finally performance based structural safety factor was investigated comparing with maximum allowable load by construction code.