Modeling the Deformation Response of High Strength Steel Pipelines—Part II: Effects of Material Characterization on the Deformation Response of Pipes (original) (raw)
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Journal of Applied Mechanics, 2012
mation response of high strength steel. The response of pipes subjected to frost upheaval at a particular point is studied using an assembly of pipe elements, while buckling of pipes is examined using shell elements. The deformation response is obtained using two different material models. The two different material models used were the isotropic hardening material model and the combined kinematic hardening material model. Two sets of material stress-strain data were used for the isotropic hardening material model; data obtained from the longitudinal direction tests and data obtained from the circumferential direction tests. The combined kinematic hardening material model was calibrated to provide an accurate prediction of the stress-strain behavior in both the longitudinal direction and the circumferential direction. The deformation response of a pipe model using the three different material data sets was studied. The sensitivity of the response of pipelines to the choice of a material model and the material data set is studied for the frost upheaval and local buckling.
European Journal of Mechanics - A/Solids, 2010
Line pipes have anisotropic mechanical properties, such as tensile strength, ductility and toughness. These properties depend on both prestrain during the cold forming process and on the anisotropy of the mother plates. In this study, a phenomenological model combining isotropic and kinematic hardening is developed to represent anisotropic hardening behavior of high strength steel line pipes. The model is adjusted on experiments carried out on smooth and notched axisymmetric bars and plane strain specimens. The model is used to simulate bending tests carried out on large pipes containing a geometric imperfection. Numerical results suggest that prestraining in pipe forming process significantly affects the bending capacity of pipes.
International Journal of Pressure Vessels and Piping, 2012
The stressestrain relationship of contemporary pipeline steels is often approximated by the relatively simple RambergeOsgood equation. However, these steels often show a more complex post-yield behaviour, which can result in significant errors. To address this limitation for cases where an accurate full-range description is needed, the authors developed a new 'UGent' stressestrain model which has two independent strain-hardening exponents. This paper compares the UGent model with the RambergeOsgood model for a wide range of experimental data, by means of least-squares curve fitting. A significant improvement is observed for contemporary pipeline steels with a yield-to-tensile ratio above 0.80. These steels typically exhibit two distinct stages of strain hardening. In contrast to the RambergeOsgood model, both stages are successfully described by the UGent model. A companion paper (Part II) discusses how to find appropriate model parameter values for the UGent model.
Pipeline Engineering [Working Title]
Pipelines are one of the most practical and economically efficient ways to transport dangerous and/or flammable substances, for which road or rail transport is often impossible. The evaluation of the processes that can negatively influence the performance of the pipelines is particularly important for assessing the risk associated with the operation of these technical systems and the potential for technical accidents. The anomalies that can be found on the pipes can be classified into two main categories. Imperfections that do not inadmissibly affect their load-bearing capacity and defects with significant negative influences on the correct operation and load-bearing capacity of the piping, which require supervision and maintenance measures. The influence of these anomalies and the processes that lead to the decrease of the pipeline-bearing capacity constitutes the main objectives of the analysis performed. The local elastic-plastic deformation anomalies are considered, for which th...
Advanced Plasticity Modeling for Ultra-Low-Cycle-Fatigue Simulation of Steel Pipe
Metals, 2017
Pipelines and piping components may be exposed to extreme loading conditions, for instance earthquakes and hurricanes. In such conditions, they undergo severe plastic strains, which may locally reach the fracture limits due to either monotonic loading or ultra-low cycle fatigue (ULCF). Aiming to investigate the failure process and strain evolution of pipes enduring ULCF, a lab-scale ULCF test on an X65 steel pipeline component is simulated with finite element models, and experimental data are used to validate various material modeling assumptions. The paper focuses on plastic material modeling and compares different models for plastic anisotropy in combination with various hardening models, including isotropic, linear kinematic and combined hardening models. Both isotropic and anisotropic assumptions for plastic yielding are considered. As pipes pose difficulty for the measurement of plastic properties in mechanical testing, we calibrate an anisotropic yield locus using advanced multi-scale simulation based on texture measurements. Moreover, the importance of the anisotropy gradient across thickness is studied in detail for this thick-walled pipeline steel. It is found that the usage of a combined hardening model is essential to accurately predict the number of the cycles until failure, as well as the strain evolution during the fatigue test. The advanced hardening modeling featuring kinematic hardening has a substantially higher impact on result accuracy compared to the yield locus assumption for the studied ULCF test. Cyclic tension-compression testing is conducted to calibrate the kinematic hardening models. Additionally, plastic anisotropy and its gradient across the thickness play a notable, yet secondary role. Based on this research, it is advised to focus on improvements in strain hardening characteristics in future developments of pipeline steel with enhanced earthquake resistance.
Interpretation of stress-strain curve in pipeline research
International Journal Sustainable Construction & Design, 2010
For the design of on-shore pipelines installed in areas that are susceptible to ground movements and offshore pipelines, axial stresses above yield must be considered. In such so-called strain-based design,knowledge of the stress-strain behaviour of the pipeline steel and girth welds is highly important. These behaviours are influenced by many factors, including: welding parameters, operation temperature, tensile test specimen geometry and orientation, and microstructure of the steel. This paper focuses on the influence of the tensile test specimen geometry and orientation, for the case of UOE formed pipes. As regards the geometry, it is concluded that the stress-strain diagram is most representative for a flat fullthickness test specimen. As regards the orientation, the yield stress is higher for transversal test specimens, as compared to longitudinally oriented test specimens.
In work with the help of the finite element method (FEM), a numerical solution of stresses and displacements in the form of graphs taking into account different boundary conditions and geometric parameters was obtained. The conducted study showed a significant effect of the accounted effects and boundary conditions on the values of dynamic characteristics and the static stability of pipelines. Introduction Trunk pipelines and pipelines of enterprises in the energy, petrochemical and other industries constitute a fairly large part of their tangible assets. As a rule, pipelines are very highly loaded structures, because even in their design, in order to save metal, the lowest safety factors are actually laid. This requires a very precise justification of the strength and resource for all possible types of loading. Carrying out such an analysis is impossible without the use of modern computer systems. At the same time, the calculator needs to understand the nature of the solution beforehand, and the numerical results should only clarify some of the coefficients. It is important to know the features of the deformation of the structure with its geometrically nonlinear behavior, considering that even for ideally elastic material a slight increase in the load can lead to uncontrolled growth of strains and stresses [1,2,3,4]. Without understanding the specific features of the deformation of various elements achieved through analytical modeling, it is impossible to use the provisions of these standards. To solve the above problem, the finite element method was used [5,6] and computer simulation. Problem formulation methods of solution. The mathematical model of the system is based on the dynamic three-dimensional equations of the linear theory of viscoelasticity according to the rheological Kelvin-Voigt model [6]:
Plastic and damage behaviour of a high strength X100 pipeline steel: Experiments and modelling
International Journal of Pressure Vessels and Piping, 2008
The purpose of this work is to develop a constitutive model integrating anisotropic behaviour and ductile damage for a X100 pipeline steel. The model is based on a set of experiments on various smooth, notched and cracked specimens and on a careful fractographic examination of the damage mechanisms. The model is based on an extension of the Gurson-Tvergaard-Needleman model which includes plastic anisotropy. Provided brittle delamination is not triggered, the developed model can accurately describe the plastic and damage behaviour of the material. The model is then used as a numerical tool to investigate the effect of plastic anisotropy and delamination on ductile crack extension. It is shown in particular that it is not possible to obtain a unified description of rupture properties for notched and cracked specimens tested along different directions without accounting for plastic anisotropy.
Mechanical Behavior of Steel Pipe Bends: An Overview
An overview of the mechanical behavior of steel pipe (elbows) is offered, based on previously reported analytical solutions, numerical results, and experimental data. The behavior of pipe bends is characterized by significant deformations and stresses, quite higher than the ones developed in straight pipes with the same cross section. Under bending loading (in-plane and out-of-plane), the main feature of the response is cross-sectional ovalization, which influences bending capacity and is affected by the level of internal pressure. Bends subjected to cyclic in-plane bending exhibit fatigue damage, leading to base metal cracking at the elbow flank. Using advanced finite-element tools, the response of pipe elbows in buried pipelines subjected to ground-induced actions is also addressed, with emphasis on soil-pipeline interaction. Finally, the efficiency of special-purpose finite elements for modeling pipes and elbows is briefly discussed.