• 한국수자원학회논문집
• /
• 제39권2호
• /
• pp.89-98
• /
• 2006

기존의 상수관 파괴로 인한 피해 영역의 산정에서는 파괴된 관만을 피해영역으로 고려하였으나 이는 파괴된 관만이 차폐되었을 경우에만 정확하다 할 수 있다. 차폐에 이용되는 밸브의 배치에 따라 추가로 더 많은 관들이 파괴된 관과 함께 차폐가 될 수 있으며 Walski에 의하여 제안된 segment 개념으로 이러한 추가적인 관의 차폐를 고려할 수 있는 방법이 Jun에 의해서 개발되었다. 그러나, segment 개념으로 찾아질 수 있는 피해영역보다 더 많은 부분이 관 파괴의 영향을 받을 수 있으며, 이는 관들의 연결형상에 의한 차폐와 용수 수요지점에서 적정한 압력수두를 확보하지 못하여 발생하는 추가적인 피해에 기인한다 본 연구에서는 밸브의 위치에 따른 추가적인 피해영역과 함께 관들의 연결형상 그리고 압력수두에 따른 피해를 순차적으로 고려할 수 있는 방법을 제안하여 제안된 방법을 실제 상수관망에 적용하여 적용성을 검토한다 실제 상수관망에 적용한 결과 한 개의 상수관 파괴에 의한 피해 영역이 밸브위치와 용수노선의 설계에 따라 많은 지역에 피해를 발생시킬 수 있음을 보여 주고 있다. 따라서 본 연구에서 제안된 방법을 적용하여 산정된 상수관 파괴에 따른 피해영역이 현실을 정확히 반영함을 알 수 있었다.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제7권4호
• /
• pp.720-738
• /
• 2015

This study examined the dynamic response of a subsea pipeline under an impact load to determine the effect of the seabed soil. A laboratory-scale soil-based pipeline impact test was carried out to investigate the pipeline deformation/strain as well as the interaction with the soil-pipeline. In addition, an impact test was simulated using the finite element technique, and the calculated strain was compared with the experimental results. During the simulation, the pipeline was described based on an elasto-plastic analysis, and the soil was modeled using the Mohr-Coulomb failure criterion. The results obtained were compared with ASME D31.8, and the differences between the analysis results and the rules were specifically investigated. Modified ASME formulae were proposed to calculate the precise structural behavior of a subsea pipeline under an impact load when considering sand- and clay-based seabed soils.

• 상하수도학회지
• /
• 제20권1호
• /
• pp.35-43
• /
• 2006

Concerns related to protecting, identifying, and isolating of subsystems of a water distribution network have led to the realization of the increased importance of valves in the system. The most important purpose of valves in water distribution systems is to isolate a subsystem due to breakage, maintenance activities, or contamination. A subsystem called segment is isolated by the closure of adjacent valves. Minimizing the pipe failure impact, an efficient algorithm is required to identify adjacent valves quickly. In this paper, an algorithm to identify adjacent valves to be closed to isolate a subsystem from the remainder of a network when a pipe failure is presented. The algorithm is operated on a matrix called the valve location matrix containing the information of valve locations. An application to an existing water distribution system demonstrates the developed algorithm efficiently locates the adjacent valves for the isolation of a broken pipe.

• International Journal of Safety
• /
• 제6권2호
• /
• pp.1-7
• /
• 2007

In this study mechanical strength of A53B carbon steel was analyzed using several types of test specimens directly machined from oil recycling pipe experienced a failure due to hydrogen attack in chemical plants. High temperature hydrogen attack (HTHA) is the damage process of grain boundary facets due to a chemical reaction of carbides with hydrogen, thus forming cavities with high pressure methane gas. Driven by the methane gas pressure, the cavities grow on grain boundaries forming intergranular micro cracks. Microscopic optical examination, tensile test, Charpy impact test, hardness measurement, and small punch (SP) test were performed. Carbon content of the hydrogen attacked specimens was dramatically reduced compared with that of standard specification of A53B. Traces of decarburization and micro-cracks were observed by optical and scanning electron microscopy. Charpy impact energy in hydrogen attacked part of the pipe exhibited very low values due to the decarburization and micro fissure formation by HTHA, on the other hand, data tested from the sound part of the pipe showed high and scattered impact energy. Maximum reaction forces and ductility in SP test were decreased at hydrogen attacked part of the pipe compared with sound part of the pipe. Finite element analyses for SP test were performed to estimate tensile properties for untested part of the pipe in tensile test. And fracture toughness was calculated using an equivalent strain concept with SP test and finite element analysis results.

• Journal of Welding and Joining
• /
• 제11권1호
• /
• pp.21-32
• /
• 1993

A cracking failure of a austenitic stainless steel elbow in a naphtha cracking line in a petrochenmical plant occurred, resulting in leakage of organic compound flowing inside the elbow. Due to the failure, emergency shutdown of the plant was enforced to repair the troubled part of the line. The repair cost as well as production loss during the unscheduled plant shutdown has cost the company a great amount of financial loss. In this studies, a failure analysis of the cracked elbow was performed using NDT, chemical analysis, microstructural analysis including optical microscopy as well as scanning electron microscopy with EPMA, mechanical testings such as tensile testing, hardness testing and Charphy impact test fractography. The results indicated that several problems such as a welding defect and presence of a detrimental phase which was found to be relate to improper postforming heat treatment process was identified and the failure was concluded to be due to a low temperature embrittlement of the defect-containing elbows.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.400-405
• /
• 2004

In this study, the optimal welding condition of the input power was selected experimentally through the ERW simulator, which is equal to welding status of ERW part in pipe. This condition is the input power 250kW in the heat treatment of the $900^{\circ}C$ normalizing derived from the nondestructive technique and impact energy. In order to evaluate the variation of the fatigue life in the pipe, fatigue surface crack growth test of base and optimal welded metal were performed statistically. As stress intensity factor range (${\Delta}K_s$) increases, the fatigue crack propagation rate (da/aN) of the base metal is faster than that of the welded joint. The variation of the fatigue life in the ERW pipe was estimated statistically using Monte-Carlo simulation with the standard deviation of material constants (C and m) of the paris law in the specimen.

• Structural Engineering and Mechanics
• /
• 제2권2호
• /
• pp.141-156
• /
• 1994

In this paper, the effect of material elasticity was evaluated through a simple model as proposed by Wang and Yu (1991), for yield mechanisms of a cantilever beam under tip pulse loading. The beam was assumed rigid-perfectly plastic but instead of the usual fully clamped constraints at its root, an elastic-perfectly plastic rotational spring was introduced there so the system had a certain capacity to absorb elastic energy. Compared with a rigid-perfectly plastic beam without a spring root, the present beam-spring model showed differences in the initial plastic hinge position and the minimum magnitude of the dynamic force needed to produce a plastic failure. It was also shown that various failure responses may happen while the hinge travels along the beam segment towards the root, rather than a unique response mode as in a rigid perfectly plastic analysis.

• 한국수자원학회논문집
• /
• 제40권9호
• /
• pp.735-742
• /
• 2007

본 연구에서는 실제 대형 상수관망에서 보다 효율적이면서도 정확한 신뢰도를 추정할 수 있는 segment를 기반으로 한 minimum cutset 방법을 제안하였다. 기존의 상수관망에서 minimum outset을 기반으로 한 모형은 상수관을 minimum outset의 최소단위로 다루어 상수관 파괴에 따른 피해영역을 과소산정할 수 있는 문제점을 가지고 있다. 그러나 제안된 신뢰도 추정 모형은 기존 신뢰도 추정 모형과 달리, 상수관 파괴에 따른 피해영역을 현실적으로 추정하기 위하여 segment와 unintended isolation, 그리고 수리학적 피해인 압력저하영역을 도입하였다. 또한 minimum cutset 방법에서 정의될 수 있는 minimum cutset을 상수관망 내 일부 절점의 비정상 상태를 야기하는 segment 1개로 정의하였으며 정의된 minimum outset의 동시파괴조합의 확률을 고려하기 위하여 success mode approach를 적용하였다. 제안된 모형은 제수밸브의 위치와 수를 고려하여 상수관 파괴에 따른 피해영역을 추정하며, 실제 대형 상수관망인 Chester Water Authority에 적용한 결과, 기존 신뢰도 추정 모형과 비교할 때 보다 실제적인 피해영역의 추정과 이에 따른 신뢰도의 추정이 가능하였다.

• Earthquakes and Structures
• /
• 제26권1호
• /
• pp.77-86
• /
• 2024

To investigate the seismic performance of steel pipe-aeolian sand recycled concrete columns, this study designed and produced five specimens. Low-cycle repeated load tests were conducted while maintaining a constant axial compression ratio. The experiment aimed to examine the impact of different aeolian sand replacement rates on the seismic performance of these columns. The test results revealed that the mechanical failure modes of the steel pipe-recycled concrete column and the steel pipe-aeolian sand recycled concrete column were similar. Plastic hinges formed and developed at the column foot, and severe local buckling occurred at the bottom of the steel pipe. Interestingly, the bulging height of the damaged steel pipe was reduced for the specimen mixed with an appropriate amount of wind-deposited sand under the same lateral displacement. The hysteresis curves of all five specimens tested were relatively full, with no significant pinching phenomenon observed. Moreover, compared to steel tube-recycled concrete columns, the steel tube-aeolian sand recycled concrete columns exhibited improved seismic energy dissipation capacity and ductility. However, it was noted that as the aeolian sand replacement rate increased, the bearing capacity of the specimen increased first and then decreased. The seismic performance of the specimen was relatively optimal when the aeolian sand replacement rate was 30%. Upon analysis and comparison, the damage analysis model based on stiffness and energy consumption showed good agreement with the test results and proved suitable for evaluating the damage degree of steel pipe-wind-sand recycled concrete structures.

• 비파괴검사학회지
• /
• 제29권3호
• /
• pp.219-223
• /
• 2009

This paper prescribed the structural integrity of the API 5L X65 pipeline subjected to tensile pre-strain. The effects of pre-strain on the mechanical properties of API 5L X65 pipe were substantially investigated through a variety of the experimental procedures. Axial tensile pre-strain of 1.5, 5 and 10% was applied to plate-type tensile specimens cut from the pipe body prior to mechanical testing. Tensile test revealed that yield strength and tensile strength were increased with increasing tensile pre-strain. The increasing rate of the yield strength owing to the pre-strain is greater than that of the tensile strength. However, the pre-strain up to 5% had a little effect on the decreasing of the fracture toughness. The structural integrity of the API 5L X65 pipeline subjected to large plastic deformation was evaluated through the fitness-for service code.