scholarly journals Laboratory Study of Local Buckling, Wrinkle Development, and Strains for NPS12 Linepipe

2000 ◽  
Author(s):  
Sreekanta Das ◽  
J. J. Roger Cheng ◽  
David W. Murray ◽  
S. A. Wilkie ◽  
Z. Joe Zhou
Keyword(s):  
Fluid Pressure ◽  
Local Buckling ◽  
Pipe Material ◽  
Axial Loads ◽  
Buried Pipelines ◽  
Test Procedures ◽  
Complex Load ◽  
University Of Alberta ◽  
Full Scale Tests ◽  
Internal Pressures

Buried pipelines are subjected to fluid pressure (oil/gas/water), axial loads, moments, and complex load combination histories. As a result, they may develop large compressive strains and curvatures leading to formation of localized buckles or wrinkles in the pipe shell. Recently, full-scale tests on 12.75″ diameter (NPS12) energy pipes have been carried out at the University of Alberta to study the behavior of wrinkle development and the ultimate limiting strains at the wrinkle locations. Different internal pressures, and axial loads were applied to produce a wrinkle, followed by load variations intended to produce fracture that could develop in buried pipelines in the field. Three different axially loaded tests are reported. Two different internal pressures were applied, namely, (i) 0.8py and (ii) 0.4py, where py is the required internal pressure to cause the yield stress of the pipe material to be developed in the circumferential direction. Also, two different specimen lengths were adopted. They are: (i) 406 mm (16 inch) and (ii) 736 mm (29 inch). All specimens were loaded axially until the wrinkle formed. It was observed that the pipes are highly ductile and very large compressive strains can be developed without fracture or leakage in the pipe wall. Because the pipe specimens of the first two tests did not fail (i.e. fracture) under monotonically increasing displacements and strains, the third wrinkled specimen was subjected to load histories involving strain reversals. This load history resulted in a low cycle failure after a very few cycles. The paper addresses test procedures, buckling and post-buckling behavior of NPS12 energy pipelines and relates them to three different types of strain measures, namely, material strain, wrinkle strain and overall strain as observed from these tests.

Behavior of wrinkled steel pipelines subjected to cyclic axial loadings

2007 ◽  
Vol 34 (5) ◽  
pp. 598-607 ◽  
Author(s):  
Sreekanta Das ◽  
J.J Roger Cheng ◽  
David W Murray
Keyword(s):  
Failure Strain ◽  
Axial Loading ◽  
Cyclic Strain ◽  
Full Scale ◽  
Axial Loads ◽  
Test Procedures ◽  
University Of Alberta ◽  
Ductile Behavior ◽  
Full Scale Tests ◽  
The University

Full-scale laboratory tests were carried out at the University of Alberta to investigate the post-wrinkling ultimate behavior of steel pipelines. The pipe specimens exhibited extreme ductile behavior and did not fail in fracture under monotonically increasing axisymmetric compressive axial loads and displacements. Fractures developed at the wrinkled region, however, when a wrinkled pipe specimen was subjected to cyclic strain reversals due to unloading and loading of primary loads. This paper presents test procedures, complete post-wrinkling behavior, fracture limit strain values, and fracture configurations obtained from full-scale tests on wrinkled pipe specimens under cyclic and monotonic axial loadings. Key words: steel pipeline, laboratory testing, cyclic axial loading, wrinkling, post-wrinkling behavior, accordion failure, strain reversals, fracture.

Fracture in Wrinkled Linepipe Under Monotonic Loading

2002 ◽  
Author(s):  
Sreekanta Das ◽  
J. J. Roger Cheng ◽  
David W. Murray
Keyword(s):  
Boundary Conditions ◽  
Axial Load ◽  
Test Procedure ◽  
Fluid Pressure ◽  
Monotonic Loading ◽  
Load History ◽  
University Of Alberta ◽  
Pipe Segment ◽  
The One ◽  
Full Scale Tests

Buried pipelines may undergo large deformations due to geotechnical movements, temperature effects, and fluid pressure which result in axial loads, shear loads, moments and various complex combinations of these loads and load histories. Consequently, localized buckles and wrinkles may form in the pipe wall and, subsequently, fractures may develop at wrinkle locations. Previous research showed that large deformation due to monotonically applied symmetric loading can produce accordion type wrinkle geometry but fracture is not normally produced unless strain reversals at the wrinkle location occur due to the application of variable loads. Recently, a field fracture that developed in an NPS10 pipe was brought to University of Alberta Structures Laboratory for investigation. From the description of the load history at the failure location, and the inspection of the deformed geometry and fracture surface, it was recognized that no significant strain reversals had occurred in this particular wrinkled pipe segment. Examination implied that the final failure was a “tearing” failure resulting from monotonic application of a longitudinal load not aligned with the axis of the pipe. However, the true load history that caused the pipe to fracture at the wrinkle location was unknown. To verify the nature of the failure mechanism, and determine the characteristics contributing to its formation, it was felt necessary to attempt to reproduce similar failures in a wrinkle by subjecting it simultaneously to monotonically applied axial load and shear. Two full-scale tests applying axial load, and a shear load with different boundary conditions were carried out on NPS12 pipe. The second test produced a deformed geometry and a fracture configuration very similar to the one that developed in the field. This paper describes the test procedure for these two tests and the mechanics of the fracture. It is concluded that, with the appropriate load history and boundary conditions, fractures can be triggered at wrinkle locations by monotonic loading histories.

Full-Scale Tests of Cold Bend Pipes

2004 ◽  
Author(s):  
M. Sen ◽  
J. J. R. Cheng ◽  
D. W. Murray ◽  
J. Zhou ◽  
K. Adams ◽  
...  
Keyword(s):  
Compressive Strain ◽  
Local Buckling ◽  
Full Scale ◽  
Combined Loading ◽  
Experimental Program ◽  
Test Procedures ◽  
Buckling Behavior ◽  
Residual Strains ◽  
Full Scale Tests ◽  
Bend Angles

An experimental program sponsored jointly by SNAM Rete Gas, Tokyo Gas Co., Ltd. and TransCanada Pipelines Ltd. was conducted on cold bend pipes under combined loading. These tests were designed to study the local buckling behavior and to develop the critical compressive strain criteria for cold bend pipes under combined loading. The test program includes eight full-scale specimens of NPS24 and NPS30 pipes with pipe thickness up to 14.3 mm. The test parameters include different D/t ratios (44, 69, and 93), material grades (X60, X65, and X80), bend angles (1.0 to 1.5 degree/diameter), and operation pressures (0%, 40%, 60%, and 80% of SMYS). In addition to full-scale tests, initial imperfections and residual strains due to cold bend processes were also measured. This paper describes the test specimens, test setup, instrumentation, and test procedures used in the program. A brief discussion of the test results is also covered in the paper.

Simulation of the Response of Buried Pipelines to Slope Movement Using 3D Continuum Modeling

2012 ◽  
Author(s):  
Abdelfettah Fredj ◽  
Aaron Dinovitzer
Keyword(s):  
Fluid Pressure ◽  
Slope Movement ◽  
Ground Movement ◽  
Ground Subsidence ◽  
Continuum Modeling ◽  
Buried Pipelines ◽  
Design Standards ◽  
Codes Of Practice ◽  
Modeling Process ◽  
Ongoing Work

Pipeline integrity is affected by the action of external soil loads in addition to internal fluid pressure. External soil loads can be generated by landslides or at sites subject to ground subsidence, heave or seismic effects. Under these varied conditions of ground movement potential pipeline safety involves constraints on design and operations. The design processes includes developing an understanding of strains that could be imposed on the pipe (strain demand) and strain limits that the pipe can withstand without failure. The ability to predict the pipeline load, stress or strains state in the presence of soil restraint and/or soil displacement induced loading is not well described in design standards or codes of practice. This paper describes the ongoing work involved in a study investigating the mechanical behavior of buried pipelines interacting with active landslides. Detailed pipe-soil interaction analyses were completed with a 3D continuum SPH method. This paper describes the LS-DYNA numerical modeling process, previously developed by the authors, which was refined and applied to site-specific conditions. To illustrate the performance of the modeling process to consider a translational slide, additional numerical model validation was completed and is described in this paper. These comparisons illustrate that good agreement was observed between the modeling results and experimental full scale trial results. Sample results of the application of the validated 3D continuum modeling process are presented. These results are being used to develop generalized trends in pipeline response to slope movements. The paper describes both the progress achieved to date and the future potential for simplified engineering design tools to assess the load or deformation capacity requirements of buried pipelines exposed to different types of slope movement.

Modified Equation to Predict Leak/Rupture Criteria for Axially Through-Wall Notched X80 and X100 Linepipes Having Higher Charpy Energy

2004 ◽  
Author(s):  
Shinobu Kawaguchi ◽  
Naoto Hagiwara ◽  
Mitsuru Ohata ◽  
Masao Toyoda
Keyword(s):  
Fracture Toughness ◽  
Flow Stress ◽  
Pipe Material ◽  
Test Results ◽  
Absorbed Energy ◽  
Bending Tests ◽  
Full Scale Tests ◽  
Hoop Stresses ◽  
The Relationship ◽  
Modified Equation

A method of predicting the leak/rupture criteria for API 5L X80 and X100 linepipes was evaluated, based on the results of hydrostatic full-scale tests for X60, X65, X80 and X100 linepipes with an axially through-wall (TW) notch. The TW notch test results clarified the leak/rupture criteria, that is, the relationship between the initial notch lengths and the maximum hoop stresses during the TW notch tests. The obtained leak/rupture criteria were then compared to the prediction of the Charpy V-notch (CVN) absorbed energy-based equation, which has been proposed by Kiefner et al. The comparison revealed that the CVN-based equation was not applicable to the pipes having a CVN energy (Cv) greater than 130 J and flow stress greater than X65. In order to predict the leak/rupture criteria for these linepipes, the static absorbed energy for ductile cracking, (Cvs)i, was introduced as representing the fracture toughness of a pipe material. The (Cvs)i value was determined from the microscopic observation of the cut and buffed Charpy V-notch specimens after static 3-point bending tests. The CVN energy in the original CVN-based equation was replaced by an equivalent CVN energy, (Cv)eq’ which was defined as follows: (Cv)eq = 4.5 (Cvs)i. The leak/rupture criteria for the X80 and X100 linepipes with higher CVN energies were reasonably predicted by the modified equation using the (Cvs)i value.

Pattern Studies of the Strain Distributions for Detecting Pipe Wrinkling

2010 ◽  
Author(s):  
Z. L. Chou ◽  
J. J. R. Cheng ◽  
Joe Zhou
Keyword(s):  
Strain Distribution ◽  
Local Buckling ◽  
Arctic Region ◽  
Distribution Patterns ◽  
Buried Pipelines ◽  
Element Analysis ◽  
Behavioural Characteristics ◽  
Decision Making System ◽  
Parametric Studies ◽  
Buckling Failure

As both the onshore and offshore pipeline constructions push further into higher risk terrains, such as geologically unstable terrain and Arctic region, the risk of local buckling failure (wrinkling) for these buried pipelines has been increasing gradually. However, previous methods used to prevent the buried pipelines from buckling failure are expansive, time consuming, and unreliable. Therefore, to overcome these problems, a reliable method to predict pipeline wrinkling has been proposed. The method can provide active warning for pipeline wrinkling through a decision-making system (DMS). The DMS was designed to identify the strain distribution patterns and their development on the critical pipe segments for early detecting the onset of pipe wrinkling. To conduct the reliable DMS, studies of the strain distribution patterns on the line-pipes during pipe buckling are very important. In this paper, the strain distribution patterns of various line-pipes were presented. These line-pipes have different material and geometric properties, loading conditions, and manufacturing conditions. A total of 32 sets of experimental results and 72 sets of finite element analysis (FEA) along with parametric studies were included in the study. The study concluded significant behavioural characteristics revealed on the strain distribution patterns during pipe buckling and important parameters affecting these strain patterns. For practical application, three thresholds of the strain distribution patterns were proposed. Furthermore, the optimal positions and spacing of the strain measurements for early detecting pipelines wrinkling were discussed as well.

Finite Element Analysis of Cold Bend Pipes Under Bending Loads

2010 ◽  
Author(s):  
Millan Sen ◽  
Roger Cheng
Keyword(s):  
Finite Element ◽  
Local Buckling ◽  
Vertical Direction ◽  
Element Model ◽  
Element Analysis ◽  
Cold Bending ◽  
Bending Process ◽  
Cold Bends ◽  
Full Scale Tests ◽  
The Right

Cold bends are required in pipelines at locations of changes in horizontal or vertical direction in the right of way. Due to this change of direction, pipeline deformations caused by geotechnical or operational loading conditions tend to accumulate at the site of cold bends. These deformations may become sufficient to cause local buckling at the bend. For pipeline design, it is important to understand the level of deformation that a cold bend can accumulate prior to local buckling so that the strain capacity can be compared to the expected pipeline deformations. Evaluating the buckling strain of cold bends is extremely complex due to the residual stresses, ripples, and material transformations cause by the cold bending process. Accordingly a finite element model was developed herein. This model accounted for the cold bend geometry, initial imperfections, and the material transformations caused by the cold bending process. This model was validated against 7 full scale tests of cold bend pipes that were subjected to bend loading and internal pressure. The global and local behavior of this model exhibited reasonable correlation against the tests.

Failure of X52 Wrinkled Pipelines Subjected to Monotonic Axial Deformation

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Y. Zhang ◽  
S. Das
Keyword(s):  
Parametric Study ◽  
Numerical Study ◽  
Numerical Technique ◽  
Small Diameter ◽  
Full Scale ◽  
Thickness Ratio ◽  
Axial Deformation ◽  
Cross Sectional ◽  
Full Scale Tests ◽  
Internal Pressures

This study was undertaken to investigate and understand the behavior of a wrinkled energy pipeline when subjected to sustained monotonic axial compressive deformation. This study involved both experimental and numerical investigations. Two full-scale laboratory tests with moderate and high internal pressures on X52 grade steel pipes with a diameter-to-thickness ratio of 45 show that this pipeline is extremely ductile and did not rupture under axisymmetric compressive axial deformation. However, they fail due to the excessive cross-sectional deformation and the final deformed shape looks like an accordion due to the formation of multiple wrinkles. Subsequently, a detailed parametric study using a numerical technique was undertaken to determine the failure condition and failure mode of this pipeline for various realistic internal pressures and diameter-to-thickness ratios. A nonlinear finite element method was used for the numerical study. The numerical model was validated with the data obtained from the two full-scale tests. The parametric study shows that the X52 linepipe loses its integrity due to the rupture in the pipe wall if the internal pressure is low and/or if the pipe has a small diameter-to-thickness ratio. This paper presents and discusses the results obtained both from the experimental and numerical parametric studies.

scholarly journals Significance of geotechnical loads on local buckling response of buried pipelines with respect to conventional practice

2013 ◽  
Vol 50 (1) ◽  
pp. 68-80 ◽  
Author(s):  
Hiva Mahdavi ◽  
Shawn Kenny ◽  
Ryan Phillips ◽  
Radu Popescu
Keyword(s):  
Load Transfer ◽  
Mechanical Performance ◽  
Three Dimensional ◽  
Local Buckling ◽  
Element Model ◽  
Combined Loading ◽  
Buried Pipelines ◽  
Buried Pipe ◽  
Limit States ◽  
New Criterion

Long-term large deformation geohazards can impose excessive deformation on a buried pipeline. The ground displacement field may initiate pipeline deformation mechanisms that exceed design acceptance criteria with respect to serviceability requirements or ultimate limit states. The conventional engineering approach to define the mechanical performance of pipelines has been based on combined loading events for in-air conditions. This methodology may be conservative, as it ignores the soil effect that imposes geotechnical loads, and also provides restraint, on buried pipelines. The importance of pipeline–soil interaction and load-transfer mechanisms that may affect local buckling of buried pipelines is not well understood. A three-dimensional continuum finite element model, simulating the local buckling response of a buried pipe, using the software package ABAQUS/Standard was developed and calibrated. A comprehensive parametric study was previously conducted to investigate the effect of several parameters on local buckling response of pipelines buried in firm clay. A new strain criterion for local buckling of buried pipelines in firm clay through response surface methodology was developed. In this paper, the new criterion is compared with several existing in-air criteria to study the effect of soil restraint on the local buckling response of buried pipelines. The criterion developed in this study predicts greater characteristic critical strain capacity than in-air based criteria that highlights the influence of soil restraint.

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