• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.22 no.4
• /
• pp.363-370
• /
• 2009

We simulated large deformation and inelastic behavior of API-X80 steel linepipes using nonlinear finite element method. Gurson-Tvergaard-Needleman(GTN) model is employed for the development of the constitutive model of the steel. The GTN model is implemented in the form of the user-supplied material subroutine(UMAT) for the commercial software of ABAQUS. To calibrate the model parameters, we simulated the behavior of the uniaxial tension test using ABAQUS equipped with the developed GTN model. Using the set of the model parameters, we were able to capture the characteristics of the plastic buckling of API-X80 steel linepipes.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.36 no.6
• /
• pp.979-990
• /
• 2016

This study presents a nonlinear finite element procedure involving a phenomenological model to validate the tensile strain capacity of the X80 line pipe developed for the strain-based design purpose. The procedure is based on the Gurson-Tvergaard-Needleman (GTN) model, which models nucleation, growth and coalescence of void volume fraction occurred inside a metal. In this study, the user-defined material module (UMAT) is implemented in the commercial finite element platform ABAQUS and is applied to the nonlinear damage analysis of steel specimens. Material parameters for the nonlinear damage analysis of base and weld metals are calibrated from numerical simulations for the tensile tests of round bar and full thickness specimens. They are then employed in the numerical simulations for SENT (Single Edge Notch Tension) test and CWPT (Curved Wide Plate Test) and in the simulations, the tensile strain capacities are naturally evaluated. Comparison of the numerical results with the experimental results and the conventional empirical formulae shows that the proposed numerical procedure can fairly well predict the tensile strain capacity of X80 line pipe. So, it is readily expected to be effectively applied to the strain-based design procedure.

• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.216-221
• /
• 2004

Linepipe steels with a low carbon acicular ferrite microstructure have been recently developed to accommodate the current transportation condition of the gas and oil industry, and they are finally applied to West- East pipeline project in China. By adopting acicular microstructure, both better formability and better toughness could be obtained due to low yield ratio and fine grained microstructure. Mechanical properties of pipe are not greatly different from those of base plates or hot coils with a microstructure of acicular ferrite. Merits of introducing higher strength steels are well known, i.e., reducing the gauge of pipe and the material cost, increasing the welding speed and decreasing construction cost because of reducing the construction period. Threfore, gas and oil industry has required higher strength steel than APIX70 grade steel. Under this background, API-X80 steel has been developed and shall be applied to the several projects. In this paper, developing stage of API-X80 steel is also presented and discussed.

• Proceedings of the KWS Conference
• /
• 2004.05a
• /
• pp.136-137
• /
• 2004

석유나 가스 등의 자원을 안정적으로 수송하기 위하여 사용하는 라인 파이프는 그 사용 환경에 따라서 다양한 소재 특성을 필요로 하며, 한랭지역에서 사용되는 경우에는 낮은 온도에서도 충분한 인성을 유지할 수 있는 높은 인성을 요구하고 있다. (중략)

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2007.04a
• /
• pp.211-216
• /
• 2007

The objective of this paper is to present the results of an experimental and a finite-element investigation into the behavior of X80 grade pipes subjected to bending. For the pipe specimens comprising the test series, different D/t is applied to be representative of those that can be expected in the field. Results from the numerical models are checked against the observations in the testing program and the ability of numerical solutions to predict pipe moment capacity. curvatures. and buckling modes is established. A finite-element model was developed using the finite-element simulator to predict the local buckling behavior of pipes. The comparison between the numerical and the experimental results demonstrates the ability of the analytical model to predict the local buckling behavior of pipes when deformed well into the post-yield range.

• Korean Journal of Metals and Materials
• /
• v.49 no.10
• /
• pp.766-773
• /
• 2011

In this study, three kinds of linepipe steels were processed by changing the amount of Mo and Nb to investigate the effects on microstructures, tensile and Charpy impact properties. All the specimens consisted of acicular ferrite, granular bainite and secondary phases such as martensite and austenite constituents (MA). The increase in Mo raised the volume fractions of the granular bainite and MA, and raised the number of fine precipitates, which increased the yield and tensile strengths and decreased the upper self energy and energy transition temperatures. In the steel having less Mo and more Nb, the volume fractions of the granular bainite and MA decreased, and a finer microstructure was observed. This microstructure suppressed the formation of separation during Charpy impact testing and led to a higher upper shelf energy and lower energy transition temperature, while the yield and tensile strengths were lower than those of the steels with more Mo and less Nb.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1999.08a
• /
• pp.383-389
• /
• 1999

The purpose of this study was to investigate the effects of alloying and rolling condition on the mechanical properties and to develop high strength line pipe steels with good toughness. Tests were carried out by the laboratory experiments followed by mill trials and mass production. It was found that a small addition of microalloying elements, such as Nb, V with Mo or Ti remarkably increased the strength and toughness of hot strips. The optimum condition of thermomechanical rolling on low carbon microalloyed steel improved the toughness through the formation of a fine and uniform microstructure. Based on this mill trials following the fundamental research, the production technology of line pipe steels, grade X70∼X100 with high toughness, has been established. These grade steels exhibit excellent low temperature toughness (vTs= under -80$^{\circ}C$) and sufficient strength in both the base metal and the ERW seam weld position, respectively.

• Korean Journal of Metals and Materials
• /
• v.48 no.1
• /
• pp.8-18
• /
• 2010

This study aimed at investigating quasi-static and dynamic torsional deformation behavior of three API X70 and X80 linepipe steels. Quasi-static and dynamic torsional tests were conducted on these steels. having different grain sizes and volume fractions of acicular ferrite and polygonal ferrite, using a torsional Kolsky bar. The test data were then compared via microstructures and adiabatic shear band formation,. The dynamic torsional test results indicated that the steels rolled in the single phase region had higher maximum shear stress than the steel rolled in the two phase region, because the microstructures of the steel rolled in the single phase region were composed mainly of acicular ferrites. In the X80 steel rolled in the single phase region, the increased dynamic torsional properties could be explained by a decrease in the overall effective grain size due to the presence of acicular ferrite having smaller effective grain size. The possibility of adiabatic shear band formation was analyzed from the energy required for void initiation and variation in effective grain size.

• Korean Journal of Metals and Materials
• /
• v.47 no.3
• /
• pp.155-168
• /
• 2009

In this study, microstructural investigation was conducted on the separation phenomenon occurring during Charpy impact tests of API X80 linepipe steels. Particular emphasis was placed on the role of microstructural phases present in the API X80 steels such as acicular ferrite, bainite, and hard secondary phases. Detailed microstructural analysis of fractured impact specimens showed that highly elongated bainite worked as prior initiation sites for separations, and that the number and length of separations increased with increasing volume fraction of bainite. In the steels having high work hardenability, tearing-shaped separations were found because the hammer-impacted region was seriously hardened during the impact test, which led to the reduction in the impact toughness. As the test temperature decreased, the tendency of separations increased, but separations were not observed when the cleavage fracture prevailed at very low temperatures. Thus, the minimization of the formation of bainite and secondary phases in the steels would be beneficial for preventing or minimizing separations because separations deteriorated low-temperature impact toughness.

• Korean Journal of Metals and Materials
• /
• v.48 no.8
• /
• pp.705-716
• /
• 2010

Effects of specimen thickness and notch shape on fracture mode appearing in drop weight tear test (DWTT) specimens of API X70 and X80 linepipe steels were investigated. Detailed microstructural analysis of fractured DWTT specimens showed that the fractures were initiated in normal cleavage mode near the specimen notch, and that some separations were observed at the center of the fracture surfaces. The Chevron-notch (CN) DWTT specimens had broader normal cleavage surfaces than the pressed-notch (PN) DWTT specimens. Larger inverse fracture surfaces appeared in the PN DWTT specimens because of the higher fracture initiation energy at the notch and the higher strain hardening in the hammer-impacted region. The number and length of separations were larger in the CN DWTT specimens than in the PN DWTT specimens, and increased with increasing specimen thickness due to the plane strain condition effect. As the test temperature decreased, the tendency to separations increased, but separations were not found when the cleavage fracture prevailed at very low temperatures. The DWTT test results, such as upper shelf energy and energy transition temperature, were discussed in relation with microstructures and fracture modes including cleavage fracture, shear fracture, inverse fracture, and separations.