• Journal of the Korean Institute of Gas
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• v.14 no.4
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• pp.45-50
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• 2010

The marine pipelines laid in deep waters were evaluated to verify the resistance on the plastic collapse to heavy ambient external pressure due to hydrostatic pressure. In this study, the plastic collapse behavior of the marine pipe subjected to hydrostatic pressure was evaluated with the ovality and ratio of diameter to thickness in FE analyses. A parametric study was shown that the internal pressure increased the plastic collapse depth by increasing of the resistance to the plastic collapse. It was also shown that the collapse depth of the pipeline having a local ovality was deeper than that of the pipeline having a global ovality. Finally, the plastic collapse depth decreased when either the ratio of diameter to thickness or the ovality increased.

• Journal of the Korean Institute of Gas
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• v.14 no.6
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• pp.1-6
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• 2010

River crossing pipelines have been being operated with buried depth of 1.2~4m underneath river bottom to prevent buoyance and external impact. River crossing pipelines have to show resistance to soil load and hydrostatic pressure. In this study, structural integrity of the river crossing pipeline subjected to soil load and hydrostatic pressure was evaluated by using FE analyses. Hoop stress increased with increasing buried depth under identical water height in case of without concrete encasement, however, hoop stress decreased with increasing water height under identical buried depth.

• International Journal of Korean Welding Society
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• v.1 no.2
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• pp.30-35
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• 2001

Nowadays, repair welding on in-service natural gas pipeline is a matter of primary concern of gas company. The main purpose of this study is to investigate the effects of welding conditions on the allowable heat input for crack-free welds and welds without burn-through onto in-service natural gas pipeline. First of all, single pass weld bead on plates of the various thickness was deposited to evaluate the penetration of weld metal, the depth of heat affected zone and the hardness of repair weld under various welding conditions. Also, finite element analysis has been conducted to validate experimental results of bead-on plate welds and to develop appropriate model for repair welding. The welding experiments of bead-on-plate weld confirmed the influence of plate thickness, heat input and welding process on safety. And, the finite element model was demonstrated by comparing experimental results. The agreement between the computed and measured values was shown to be generally good. Therefore, It is possible to predict the safety of repair welding under various welding conditions with experimental results and finite element analysis model.

• Journal of the Korean Institute of Gas
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• v.15 no.5
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• pp.1-6
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• 2011

It is required to construct the pipelines to eliminate pressure drop at the end of transmission line under limitation of maximum operation pressure of 6.86 MPa, however, it highly costs to build the pipelines and takes time-consuming job. Higher operation pressure compared to current operating pressure has been considered to resolve the problem of pressure drop without modification of the existing pipelines and facilities. As a result of the integrity evaluation, the existing pipelines can be operated up to 7.85 MPa in terms of wall thickness and have higher Charpy impact energy than required value in the ASME B31.8. However, Increment of operation pressure gives rise to increase potential impact area if the pipelines burst due to third party damages.

• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.5
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• pp.213-220
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• 2023

Seismic fragility curves play a crucial role in assessing potential seismic losses and predicting structural damage caused by earthquakes. This study compares non-sampling-based methods of seismic fragility curve derivation, particularly the probabilistic seismic demand model (PSDM) and finite element reliability analysis (FERA), both of which require employing sophisticated finite element analysis to evaluate and predict structural damage caused by earthquakes. In this study, a three-dimensional finite element model of API 5L X65, a buried gas pipeline widely used in Korea, is constructed to derive seismic fragility curves. Its seismic vulnerability is assessed using nonlinear time-history analysis. PSDM and a FERA are employed to derive seismic fragility curves for comparison purposes, and the results are verified through a comparison with those from the Monte Carlo Simulation (MCS). It is observed that the fragility curves obtained from PSDM are relatively conservative, which is attributed to the assumption introduced to consider the uncertainty factors. In addition, this study provides a comprehensive comparison of seismic fragility curve derivation methods based on sophisticated finite element analysis, which may contribute to developing more accurate and efficient seismic fragility analysis.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.269-274
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• 2008

For fitness-for-service analyses of underground natural gas pipelines, engineering assessment methods against possible defects need to be developed. The assessment methods for high pressure pipeline of KOGAS, was developed using the full size pipe burst tests and the finite element analysis. It included the defect assessment methods for a single and multi-corrosion, corrosion in girth welding part, corrosion in seam welding part, the mechanical damage defects as dent and gouge, crack and large plastic deformation of API 5L X65 pipe. In addition, we developed method to assess pipeline integrity by internal and external load to buried pipeline. Evaluation results were compared with other methods currently being applied to the gas pipeline. The program of Windows environment is made for easily using assessment methods. It provides a consistent user interface, so non-professional technician can easily and friendly use the FFS program from company intranet. Several evaluation programs is easily installed using one installer. Each program constitutes a common input interface and the output configuration program, and evaluation result store and can be recalled at any time. The FFS program based on independent evaluation method is used to evaluate the integrity and safety of KOGAS pipeline, and greatly contribute to safe and efficient operation of pipeline. This paper presents experimental, analytical and numerical investigations to develop the FFS methods for KOGAS pipeline, used as high pressure natural gas transmission pipeline within KOREA. Also, it includes the description of the integrated program for FFS methods.