• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.9 s.252
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• pp.1086-1093
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• 2006

A local failure criterion for the API X65 steel is applied to predict ductile failure of full-scale API X65 pipes with simulated corrosion and gouge defects under internal pressure. The local failure criterion is the stress-modified fracture strain for the API X65 steel as a function of the stress triaxiality (defined by the ratio of the hydrostatic stress to the effective stress). Based on detailed FE analyses with the proposed local failure criteria, burst pressures of defective pipes are estimated and compared with experimental data. The predicted burst pressures are in good agreement with experimental data. Noting that an assessment equation against the gouge defect is not yet available, parametric study is performed, from which a simple equation is proposed to predict burst pressure fur API X65 pipes with gouge defects.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.12 s.243
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• pp.1621-1628
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• 2005

This paper presents a stress-modified fracture strain for API X65 steel used for gas pipeline, as a function of stress triaxiality. To determine the stress-modified fracture strain, tension test of bars with four different notch radii, made of API X65 steel, is firstly performed, from which true fracture strains are determined as a function of notch radius. Then detailed elastic-plastic, large strain finite element (FE) analyses are performed to estimate variations of stress triaxiality in the notched bars with load. Combining experimental with FE results provides the true fracture strain as a function of stress triaxiality, which is regarded as a criterion of ductile fracture. Application of the developed stress-modified fracture strain to failure prediction of gas pipes made of API X65 steel with various types of defects is discussed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.851-852
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• 2012

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1696-1701
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• 2007

This paper presents a micro-mechanical model of ductile fracture for the API X65 steel using the Gurson-Tvergaard-Needleman (GTN) model. Experimental tests and FE damage simulations using the GTN model are performed for smooth and notched tensile bars, from which the parameters in the GTN model are calibrated. As application, the developed GTN model is applied to simulate small-sized, single-edge-cracked tensile and bend bars, via three-dimensional FE damage analyses. Comparison of FE damage analysis results with experimental test data shows overall good agreements.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.10
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• pp.1483-1491
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• 2004

To assess the integrity of the pipeline is the most important problem to be solved first of all for prevention of any fracture accident of the pipeline. As a result of exerting such efforts, a number of plastic collapse assessment equations have been suggested, however, the scope of using or applying such assessment equations has not been exactly defined. In this study, the case that a surface crack existed in the circumferential direction in the external side of the natural gas pipeline and a bending load was applied to the pipeline was analytically identified as the most critical condition, and a plastic collapse assessment equation fur it was suggested. The flow stress of the API X65 linepipe was defined through the experiment conducted on SENT specimens. Also, a local assessing criterion of a 3-dimensional crack behavior considering not only the crack depth but also the crack length was suggested. Finally, a plastic collapse assessment equation for the API X65 linepipe was developed by performing the 3-dimensional finite element analysis.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.3
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• pp.219-223
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• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.9
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• pp.961-970
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• 2012

The behavior of the load bearing capacity of a pipeline with unequal wall thickness was evaluated using finite element analyses. Pipelines with a wall thickness ratio of 1.22-1.89 were adopted to investigate plastic collapse under tensile, internal pressure, or bending stress. A parametric study showed that the tensile strength and moment of a pipeline with a wall thickness ratio less than 1.5 were not influenced by the wall thickness ratio and taper angle; however, those of a pipeline with a wall thickness ratio more than 1.5 decreased considerably at a low taper angle. The failure pressure of a pipeline with unequal wall thickness was not influenced by the wall thickness ratio and taper angle.

• Journal of the Korean Institute of Gas
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• v.15 no.6
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• pp.14-19
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• 2011

The objective of this study was to investigate the effect of the thickness eccentricity on the collapse pressure of a subsea pipeline subjected to external pressure. The collapse behavior of the subsea pipeline containing initial imperfection was evaluated using elastic-plastic finite element (FE) analyses. API 5L X65 and API 5L X80 Pipelines with the thickness eccentricity values between 4~16% were adopted to investigate the plastic collapse under hydrostatic pressure. A parametric study was shown that the plastic collapse pressure decreased when either the thickness eccentricity or the ratio of diameter to thickness increased.

• Proceedings of the KWS Conference
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• 2000.04a
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• pp.320-322
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• 2000

• Proceedings of the KWS Conference
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• 2000.10a
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• pp.198-200
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• 2000