• 한국신뢰성학회지:신뢰성응용연구
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• 제15권3호
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• pp.197-206
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• 2015

Failure analysis of pre-insulated pipe (SPPS 380, 400A) transporting high temperature water ($95{\sim}110^{\circ}C$) for a plant was carried out. The damaged area (${\Phi}5mm$) of pre-insulated pipe was found only on welds. The chemical composition of damaged pipe meets specification of carbon steel pipes for pressure service (KS D 3562). As results of microstructure analysis, crack propagated from outer to inside after pitting corrosion occurred on the outside surface. The non-metallic inclusion existed on the end of crack. And the non-metallic inclusion continuously and linearly formed along with the bond line of welds. Based on SEM-EDS analysis, the nonmetallic inclusions have higher Manganese (Mn) and Oxygen (O) content but sulfur (S) was not detected. As results of water quality analysis, hydrogen ion concentration and minerals like Fe, Mg, Si were in low level. But the content of dissolved oxygen (11.2 ppm) was slightly higher than that of standard. It seems that the cause of damaged pipe is grooving corrosion due to MnO inclusion formed on bond line and corrosion took place nearby welds.

• 비파괴검사학회지
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• 제28권4호
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• pp.323-330
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• 2008

소구경 배관 소켓 용접부의 고주기 피로특성윽 평가하고 피로 균열의 발생을 음향방출법을 이용하여 실시간 모니터링 하였다. 스테인리스 316L강 시험편은 가스텅스텐아크용접 공정으로 루트부에 결함이 없는 시험편과 용입불량 결함이 있는 시험편으로 준비하였다. 피로파단은 고응력 일때는 토우부, 상대적으로 저응력일 때는 루트부에서 일어났다. 피로시험동안 음향방출 카운트가 급격히 증가하는 시점을 균열의 발생 싸이클 ($N_i$)로 정의하였고 방사선투과법과 전자현미경을 이용하여 피로균열 생성 싸이클 전과 후에서 균열을 확인하였다. 소켓용접배관의 굽힘피로 손상 진단 및 감시를 위해 균열의 존재와 파괴모드 그리고 균열의 발생 싸이클에 관한 연구를 수행하였다.

• 한국지반공학회논문집
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• 제20권7호
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• pp.107-117
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• 2004

느슨한 모래지반에서 보강재 층수 증가와 보강재의 강성과 형태 변화 그리고 얕은 기초 직하에 매설된 연성관의 깊이 등의 변화가 지지력-침하 곡선에 미치는 영향을 알아보기 위해 일련의 모형실험을 수행하였다. 시험결과, 무보강토 경우는 파괴형태가 국부전단으로 나타났으나 보강재 층수가 2층 이상이 되면 파괴형태는 국부전단에서 전반전단으로 바뀌고, 최적보강재 층수는 2층 이며, 지지력 개선에 있어서는 보강재의 초기강성과 형태가 최대인 장강도보다 중요한 것으로 나타났다. 무보강토에서 기초 직하에 연성관이 매설된 경우, 연성관의 매설 깊이가 기초 폭보다 얕으면 지지력과 극한지지력은 현저하게 감소하고, 보강토의 경우 연성관의 매설 깊이가 기초 폭보다 얕으면 파괴형태는 전반전단에서 국부전단으로 바뀌는 것으로 나타났다.

• 한국가스학회지
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• 제7권2호
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• pp.48-53
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• 2003

에너지 관련 플랜트에 사용되는 배관은 플랜트의 성능이나 안전성유지에 있어서 중요한 설비의 일부이다. 본 연구에서는 고압탄소강 배관의 변형 및 파괴에 대한 음향방출 기초 자료를 얻기 위하여 압력용기용 배관재를 기계가공하여 인장시험편을 만든 후, 인장시험을 실시하여 항복, 소성변형 및 파괴에 이르기까지의 음향방출 신호를 분석하였다. 탄성영역, 최대인장강도 이전의 소성영역 및 최대인장강도 이후의 소성영역에서 검출된 음향방출의 시간-주파수 분석 결과는 탄성영역에서 항복영역까지는 비교적 낮은 저주파수 대역(250${\~}$350kHz)이 나타났으며, 소성영역에서는 저주파수뿐만 아니라 고주파수 대역(500kHz)도 나타났다. 인장시험 후, 이러한 각 영역의 구별이 가능하였던 원인은 항복영역에서의 전위의 이동, 집적에 따른 신호와 최대인장강도 이전의 소성영역에서의 전위들이 개재물이나 결정입계를 통과했을 때 나타나는 신호, 최대인장강도 이후에는 미소공동의 발생, 성장 및 합체에 의하여 나타나는 신호로 분류가 가능하였기 때문인 것으로 판단된다.

• Earthquakes and Structures
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• 제26권4호
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• pp.261-267
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• 2024

With the increase in the exploitation depth of offshore oil and gas, it is possible to control the global buckling of deep-sea pipelines by the snake lay method. Previous studies mainly focused on the analysis of critical buckling force and critical temperature of pipelines under the snake-like laying method, and pipelines often suffer structural failure due to seismic disasters during operation. Therefore, seismic action is a necessary factor in the design and analysis of submarine pipelines. In this paper, the seismic action of steel pipes in the operation stage after global buckling has occurred under the active control method is analyzed. Firstly, we have established a simplified finite element model for the entire process cycle and found that this modeling method is accurate and efficient, solving the problem of difficult convergence of seismic wave and soil coupling in previous solid analysis, and improving the efficiency of calculations. Secondly, through parameter analysis, it was found that under seismic action, the pipe diameter mainly affects the stress amplitude of the pipeline. When the pipe wall thickness increases from 0.05 m to 0.09 m, the critical buckling force increases by 150%, and the maximum axial stress decreases by 56%. In the pipe soil interaction, the greater the soil viscosity, the greater the pipe soil interaction force, the greater the soil constraint on the pipeline, and the safer the pipeline. Finally, the pipeline failure determination formula was obtained through dimensionless analysis and verified, and it was found that the formula was accurate.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2000
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• pp.184-191
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• 2000

In this research, a numerical model is developed for analysis of buried pipelines considering longitudinal permanent ground deformation(PGD) due to liquefaction induced lateral spreading. Buried pipelines and surrounding soil are medeled as continuous pipelines using the beam elements and a series of elasto-plastic springs uniformly distributed along the pipelines, respectively. Idealized various PGD patte군 based on the observation of PGD are used as a loading configuration and the length of the lateral spread zone is considered as a loading parameter. Numerical results are verified with other research results and efficient applicability of developed procedure is shown. Analyses are performed by varying different parameters such as PGD pattern, pipe diameter and pipe thickness. Results show that response of buried pipelines are more affected by pipe thickness than pipe diameter. Finally, the critical length of the lateral spread zone and the critical magnitude of PGD which cause yielding, local buckling or tension failure are proposed for the steel pipe which are normally used in Korea.

• 대한기계학회논문집A
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• 제29권5호
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• pp.734-742
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• 2005

The present study proposes the integrity evaluation model for a straight pipe with local wall thinning defect, which reflects the characteristics of training shape and loading condition in the Piping of nuclear power plant. For this purpose, a series of finite element analyses are performed under various defect geometries and loading conditions, and real pipe experiment data performed previously is employed. The model includes the effect of thinning length as well as thinning depth and width, and also it considers the combined loading effect between internal pressure and bending moment. The proposed model has been validated using the results of finite element analysis and pipe experiment data. The results indicate that the proposed model provides more reliable predictions of pipe failure than the current existing model, in terms of accuracy, consistency, and conservativeness of results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1198-1205
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• 2003

Most domestic fossil power plant have exceeded 100,000 hours of operation with the severe operating condition. Among the critical components of fossil power plant, high temperature steam pipe system have had a many problems and damage from unstable displacement behavior because of frequent start up and shut down. In order to prevent the serious damage and failure of the critical pipe system in fossil power plant, 3-dimensional displacement measurement system were developed for the on-line monitoring system. 3-D Measurement system was developed with using the LVDT type sensor and rotary encoder type sensor, this system was installed and operated on the real power plant successfully. In the future time, network system of on-line diagnosis for critical pipe will be designed.

• 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.

• 대한기계학회논문집A
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• 제25권1호
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• pp.81-88
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• 2001

This study proposed an analytical method to evaluate a local allowable wall thickness (LAWT) for locally thinned pipe subjected to internal pressure and bending moment. In this method, the stresses in the thinned region were calculated by finite element analysis and plastic collapse was applied as a failure criterion of thinned pipe. Using this method, LAWT for a simplified thinned pipe was evaluated with variation in axial extent of thinned area, and it was compared with allowable wall thickness provided by previous pipe wall thickness criteria. The results showed that the LAWT was lower, about 50%, than that calculated by construction code or ASME Code N-597, and it was higher, about 2 times, than that estimated by evaluation model based on pipe experiments. In addition, LAWT was decreased with increasing axial extent of thinned area and saturated with further increase in axial extent. And, the variation in LAWT with axial extent of thinned area depended on type of load, especially a magnitude of bending moment, considering in the evaluation.