scholarly journals Large Deformation Behavior of Pipe Bends Subjected to In-Plane Bending

1998 ◽  
Author(s):  
Koji Yoshizaki ◽  
Hirokazu Ando ◽  
Noritake Oguchi
Keyword(s):  
Deformation Behavior ◽  
Flexural Rigidity ◽  
Local Buckling ◽  
Ground Displacement ◽  
Straight Pipe ◽  
Shell Elements ◽  
Opening Mode ◽  
Measured Strain ◽  
Central Cross Section ◽  
Plane Bending

Ground liquefaction during earthquakes can produce a significant amount of lateral ground displacement. For buried gas pipelines, deformation and strain are likely to be concentrated on the pipe bends. Closing and opening in-plane bending experiments were conducted for various kinds of pipe bends until the measured strain exceeded 25% using pipe specimens of a diameter from 100 to 300 mm. The deformation behavior was different between the closing mode and the opening one. In the closing mode, an ovalization was observed in the central cross section of the bend, and internal pressure was maintained in all experiments. On the other hand, unique behavior was observed in the opening mode. When the pipe diameter was 300 mm (Do/t=43), local buckling was observed at the center of the bend. However, when Do/t was less than 32 (200 mm in diameter), the flexural rigidity of the bend became much higher than that of a straight pipe, and buckling and rupture were observed in the straight pipe. Finite element analyses were carried out using linear shell elements, and the validity of the numerical modeling technique over 25% of plastic strain was confirmed.

Ultimate Bending Capacity and Buckling of Pressurized 90 deg Steel Elbows

2005 ◽  
Vol 128 (3) ◽  
pp. 348-356 ◽  
Author(s):  
S. A. Karamanos ◽  
D. Tsouvalas ◽  
A. M. Gresnigt
Keyword(s):  
Local Buckling ◽  
Bending Moment ◽  
General Purpose ◽  
Moderate Pressure ◽  
Cross Sectional ◽  
Finite Element Program ◽  
Shell Elements ◽  
Out Of Plane ◽  
Bending Capacity ◽  
Plane Bending

The paper examines the nonlinear elastic-plastic response of internally pressurized 90 deg pipe elbows under in-plane and out-of-plane bending. Nonlinear shell elements from a general-purpose finite element program are employed to model the inelastic response of steel elbows and the adjacent straight parts. The numerical results are successfully compared with real-scale experimental measurements. The paper also presents a parametric study, aimed at investigating the effects of diameter-to-thickness ratio and moderate pressure levels on the ultimate bending capacity of 90 deg elbows, focusing on the failure mode (local buckling or cross-sectional flattening) and the maximum bending moment. Special attention is given to the response of 90 deg elbows under out-of-plane bending moments.

Finite Element Analysis of Elliptical Chord

2013 ◽  
Vol 3 (4) ◽  
pp. 44-61
Author(s):  
K. S. Narayana ◽  
R. T. Naik ◽  
R. C. Mouli ◽  
L. V. V. Gopala Rao ◽  
R. T. Babu Naik
Keyword(s):  
Finite Element ◽  
Natural Frequencies ◽  
Three Dimensional ◽  
Compressive Load ◽  
Dynamic Strength ◽  
Element Analysis ◽  
T Joints ◽  
Shell Elements ◽  
Tubular Joints ◽  
Plane Bending

The work presents the Finite element study of the effect of elliptical chords on the static and dynamic strength of tubular T-joints using ANSYS. Two different geometry configurations of the T-joints have been used, namely Type-1 and Type-2. An elastic analysis has been considered. The Static loading conditions used are: axial load, compressive load, In-plane bending (IPB) and Out-plane bending (OPB). The natural frequencies analysis (dynamic loading condition) has also been carried out. The geometry configurations of the T-joints have been used, vertical tubes are called brace and horizontal tubes are called chords. The joint consists of brace joined perpendicular to the circular chord. In this case the ends of the chord are held fixed. The material used is mild steel. Using ANSYS, finite element modeling and analysis of T-joint has been done under the aforementioned loading cases. It is one of the most powerful methods in use but in many cases it is an expensive analysis especially due to elastic–plastic and creep problems. Usually, three dimensional solid elements or shell elements or the combination of two types of elements are used for generating the tubular joints mesh. In tubular joints, usually the fluid induced vibrations cause the joint to fail under resonance. Therefore the natural frequencies analysis is also an important issue here. Generally the empirical results are required as guide or comparison tool for finite element investigation. It is an effective way to obtain confidence in the results derived. Shell elements have been used to model the assembled geometry. Finite element ANSYS results have been validated with the LUSAS FEA and experimental results, that is within the experimentation error limit of ten percentage.

Nonlinear Response and Failure of Steel Elbows Under In-Plane Bending and Pressure

2003 ◽  
Vol 125 (4) ◽  
pp. 393-402 ◽  
Author(s):  
S. A. Karamanos ◽  
E. Giakoumatos ◽  
A. M. Gresnigt
Keyword(s):  
Finite Element ◽  
Local Buckling ◽  
Shell Element ◽  
General Purpose ◽  
Element Analysis ◽  
Cross Sectional ◽  
Finite Element Program ◽  
Special Cases ◽  
Element Program ◽  
Plane Bending

The paper investigates the response of elbows under in-plane bending and pressure, through nonlinear finite element tools, supported by experimental results from real-scale tests. The finite element analysis is mainly based on a nonlinear three-node “tube element,” capable of describing elbow deformation in a rigorous manner, considering geometric and material nonlinearities. Furthermore, a nonlinear shell element from a general-purpose finite element program is employed in some special cases. Numerical results are compared with experimental data from steel elbow specimens. The comparison allows the investigation of important issues regarding deformation and ultimate capacity of elbows, with emphasis on relatively thin-walled elbows. The results demonstrate the effects of pressure and the influence of straight pipe segments. Finally, using the numerical tools, failure of elbows under bending moments is examined (cross-sectional flattening or local buckling), and reference to experimental observations is made.

Stress Analysis of Mitred Bends by Ring Elements

1984 ◽  
Vol 106 (1) ◽  
pp. 54-62 ◽  
Author(s):  
O. Watanabe ◽  
H. Ohtsubo
Keyword(s):  
Stress Analysis ◽  
Degrees Of Freedom ◽  
Shell Theory ◽  
Trigonometric Functions ◽  
Shape Functions ◽  
Straight Pipe ◽  
Shell Elements ◽  
Hermitian Polynomials ◽  
Ring Elements ◽  
Thin Shell Theory

This paper proposes a ring element for the stress analysis of mitred bends, which is an extension of ring elements for pipe bends proposed by the present authors. Since accurate treatments of continuity conditions on the connecting lines between straight pipe segments are employed and strain-displacement relations derived from the general thin shell theory with shear strains are considered, the present method can be applied to problems of mitred bends of complex configurations under general loading conditions. Shape functions are developed by trigonometric functions and Hermitian polynomials of second order in the circumferential and longitudinal directions, respectively. This finite element method requires fewer number of degrees of freedom for the same accuracy than the conventional shell elements.

Zero Poisson’s Ratio Honeycomb Structures-An FEA Study

2013 ◽  
Vol 446-447 ◽  
pp. 329-334
Author(s):  
Imran Ali ◽  
Jing Jun Yu
Keyword(s):  
Cell Wall ◽  
Elastic Modulus ◽  
Potential Application ◽  
Deformation Behavior ◽  
Lateral Stiffness ◽  
Lateral Direction ◽  
Shell Elements ◽  
Honeycomb Structures ◽  
Fea Analysis ◽  
Poissons Ratio

Conventional honeycomb structures show positive Poissons ratio under in-plane loading while Auxetic honeycombs show negative Poissons ratio. Accordion, Hybrid and Semi re-entrant honeycomb structures show zero Poissons ratio, i.e. they show zero or negligible deformation in lateral direction under longitudinal loadings. In this paper an FEA analysis of these three types of structures is made using commercial software ANSYSR14 using 8 node 281 shell elements. Cell wall thickness and cell angle is varied to analyze their effect on elastic modulus Exand global strains along X direction under X-direction loadings. Eyis also analyzed to measure lateral stiffness and deformation behavior of structure for its potential application as flexures.

Effects of Cross-Section Ovalization of Subsea Thin-Walled Bends Under In-Plane Bending

2010 ◽  
Author(s):  
Ranil Banneyake ◽  
Ayman Eltaher ◽  
Paul Jukes
Keyword(s):  
Cross Section ◽  
Computational Cost ◽  
Straight Pipe ◽  
Limit States ◽  
Element Analysis ◽  
High Tendency ◽  
Thin Walled ◽  
Plane Bending ◽  
The Cross ◽  
The Impact

Ovalization of the cross-section of bends under in-plane bending (a.k.a. Brazier effect) is a known phenomenon caused by the longitudinal stress acting on the cross-section as the pipe bends. Besides its tendency to induce stresses in the bend above what is predicted using simple beam theory, excessive cross-section ovalization is particularly critical to subsea pipes, as it can lead to collapse of the pipe under external pressure. Also, being in a plastic regime may cause the bend material to ratchet and undergo excessive strains under cyclic operational loads, especially under high-pressure high-temperature (HPHT) conditions. Ovalization normally results in local increase of stresses and could lead to failure of the bend before the bend globally reaches its limiting capacity. The offshore industry standards and design codes address the impact of initial ovality in straight pipes, but their applicability to bends is not clear. Therefore, this paper presents an investigation into the increased tendency of thin-walled bends to ovalize, and the effect of bend cross-section ovalization on their stiffness and yielding and collapse limit states, with emphasis on offshore applications. Due to the lack of analytical solutions for the bend response taking into account cross-section ovalization, finite element analysis (FEA) is used in this study. Predictions of the bend models are compared with those of straight pipe models and predictions of models of the bend made of beam elements (with pipe section) are compared with those of models made of brick /shell elements. The increased tendency of thin-walled bends to ovalize compared to straight pipes is investigated (e.g. 100 times in the linear range), and the impact and significance of ovalization in bends are assessed (e.g., stress increase of the order of 35% has been observed in some example situations). Also discussed in the paper is the selection of proper element specifications in order to accurately capture the ovalization response while keeping the computational cost manageable. Recommendations as to how to account for ovalization effects are presented. This paper helps to gain a better understanding of the response of subsea thin-walled bends under in-plane bending and their comparatively high tendency to ovalize compared to straight pipe, and emphasizes the significance of local effects such as cross-section ovalization, the overlooking of which may result in a significant underestimation of involved stresses and strains.

Effect of Geometric and Material Discontinuities on the Reeling of Pipelines

2014 ◽  
Author(s):  
Yafei Liu ◽  
Stelios Kyriakides
Keyword(s):  
Large Scale ◽  
Kinematic Hardening ◽  
Local Buckling ◽  
Nonlinear Finite Element ◽  
Plastic Behavior ◽  
Finite Element Models ◽  
Shell Elements ◽  
Applied Tension ◽  
Material Discontinuities ◽  
Girth Welds

Reeling remains one of the most efficient methods for installing pipelines offshore. The process results in plastic bending, straightening, and reverse bending to strain levels that can be as large as 2–3%. Thus, despite many years of practice, occasional failures during the reeling and unreeling process continue to take place resulting in costly disruptions and repairs. A common cause of such failures is local buckling that can precipitate fracture. This paper presents the results of a study of how discontinuities in geometry and mechanical properties can lead to buckling and failure. Large-scale nonlinear finite element models are used to simulate the reeling/unreeling of pipelines. The pipeline is modeled using shell elements and contact with the hub of the reel is treated appropriately. The elasto-plastic behavior of the steel is modeled using nonlinear kinematic hardening. Typically, a section of pipeline is taken through a winding and unwinding cycle on a reel of a given radius at a constant value of tension. Discontinuities in wall thickness and yield stress such as those that can occur at girth welds are shown to result in sharp local changes in curvature that extend over 3–4 pipe diameters accompanied by severe local straining and ovalization. The combination of these can lead to local buckling. Increase in the applied tension can reduce these at the expense of additional ovalization of the pipeline.

Effects of Stress–Strain Characteristics on Local Buckling of X80 Pipe Subjected to Strike-Slip Fault Movement

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Xiaoben Liu ◽  
Hong Zhang ◽  
Onyekachi Ndubuaku ◽  
Mengying Xia ◽  
J. J. Roger Cheng ◽  
...  
Keyword(s):  
Structural Integrity ◽  
Local Buckling ◽  
Strike Slip ◽  
Strike Slip Fault ◽  
Large Strains ◽  
Fe Model ◽  
Stress Strain ◽  
Shell Elements ◽  
Steel Material ◽  
Buckling Behavior

The structural integrity of underground pipelines are subject to a major threat from permanent ground displacements when they cross active tectonic (e.g., strike-slip) faults, because of large strains potentially induced in pipes, leading to pipe buckling and possible rupture. In this paper, the buckling behavior of X80 pipe is studied numerically with an emphasis on the effects of steel stress–strain characteristics. A rigorous mechanics-based nonlinear finite element (FE) model of a buried X80 pipe crossing a strike-slip fault is developed using shell elements and nonlinear springs for the pipe and soil resistance, respectively. The pipe steel material in the FE model is characterized by a novel and versatile stress–strain relationship, which was established to successfully capture both the round-house (RH) type and the yield-plateau (YP) type stress–strain behaviors. This allows investigating the significant effects of the stress–strain characteristics, as observed in this paper, on the buckling behavior of pressurized and nonpressurized pipes.

Closed-Form Collapse Moment Equations of Throughwall Circumferentially Cracked Elbows Subjected to In-Plane Bending Moment

2004 ◽  
Vol 126 (3) ◽  
pp. 307-317 ◽  
Author(s):  
J. Chattopadhyay ◽  
A. K. S. Tomar ◽  
B. K. Dutta ◽  
H. S. Kushwaha
Keyword(s):  
Closed Form ◽  
Bending Moment ◽  
Moment Equations ◽  
Element Analysis ◽  
Perfectly Plastic ◽  
Circumferential Crack ◽  
Opening Mode ◽  
Plane Bending ◽  
Elastic Perfectly Plastic ◽  
Bending Modes

A large throughwall circumferential crack in an elbow subjected to in-plane bending moment can significantly reduce its collapse load. Therefore, it is very important to know the collapse moment of an elbow in the presence of a throughwall circumferential crack. The existing closed-form collapse moment equations of throughwall circumferentially cracked elbows are either too conservative or inadequate to correctly quantify the weakening effect due to the presence of the crack, especially for opening mode of bending moment. Therefore, the present study has been carried out to investigate through elastic-plastic finite element analysis the effect of a throughwall circumferential crack on the collapse moment of an elbow under in-plane bending moment. A total of 72 cases of elbows with various sizes of circumferential cracks (2θ=0–150 deg), different wall thickness (R/t=5–20), different elbow bend radii Rb/R=2,3 and two different bending modes, namely closing and opening have been considered in the analysis. Elastic-perfectly plastic stress-strain response of material has been assumed. Collapse moments have been evaluated from moment-end rotation curves by twice-elastic slope method. From these results, closed-form expressions have been proposed to evaluate collapse moments of elbows under closing and opening mode of bending moment. The predictions of these proposed equations have been compared with 8 published elbow test data and are found to be within ±11% variation except for one case.

Effects of Crossing Angle on the Behavior of Buried Steel Pipelines Crossing Fault

2013 ◽  
Vol 351-352 ◽  
pp. 630-636
Author(s):  
Nemat Hassani ◽  
Mahdi Shadab Far ◽  
Hadi Kordestani
Keyword(s):  
Parametric Study ◽  
Soil Analysis ◽  
Local Buckling ◽  
Shell Element ◽  
Maximum Strain ◽  
Ground Displacement ◽  
Buried Pipelines ◽  
Steel Pipeline ◽  
Meaningful Relationship ◽  
Pipe Bending

One of the most important factors that may cause a buried steel pipeline to reach the failure limit is the permanent ground displacement. In this paper, assuming SHELL element for pipeline and SOLID element for soil and also considering the interaction of pipe-soil, analysis of buried pipelines crossing fault and parametric study of pipeline behavior were performed. The results of this study show that the behavior of buried pipelines crossing fault is not sensitive to the pipe-fault crossing angle. The main reason for this is the immense strain of the pipe due to the section deformation and local buckling of the pipe body that is caused by the permanent ground displacement. The strain from this phenomenon is so great that the pipe-fault crossing angle cannot have much effect on it. The research also shows that it is better to consider pipe bending than dealing with the pipe-fault crossing angle, because it is a more important parameter in the behavior of buried pipelines crossing faults, and it has a meaningful relationship with the reached maximum strain in the pipeline.

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