Changes in Tensile Properties Due to Cold Bending of Line Pipes

2002 ◽  
Author(s):  
Naoki Fukuda ◽  
Hiroshi Yatabe ◽  
Tomoki Masuda ◽  
Masao Toyoda
Keyword(s):  
Tensile Properties ◽  
Analytical Model ◽  
Bauschinger Effect ◽  
Estimation Method ◽  
Tensile Tests ◽  
Full Scale ◽  
Small Scale ◽  
Cold Bending ◽  
Cold Bends ◽  
Good Agreement

The changes in the tensile properties of line pipes due to cold bending were experimentally and analytically investigated. Full-scale cold bending experiments were performed on API X60 and X80 grade line pipes. The reduction in the yield stress of the cold bends due to the Bauschinger effect was approximately 20% and 35% for X60 and X80, respectively. In order to evaluate the changes in the tensile properties of the pipes quantitatively, finite element (FE) analyses and small-scale experiments were conducted. The FE analytical model for simulating the strain distribution at various bending angles was verified with the results of the full-scale experiments. The tensile properties of the cold bends were in good agreement with those of the small-scale experiments using uni-axially prestrained specimens. Based on the present results, an estimation method was proposed for evaluating the distribution of the tensile properties after cold bending with the analytical model using the results of the tensile tests for prestrained specimens.

Tensile Properties of Cold Bends for Line Pipes

2007 ◽  
Vol 129 (3) ◽  
pp. 229-235 ◽  
Author(s):  
Naoki Fukuda ◽  
Hiroshi Yatabe ◽  
Tomoki Masuda ◽  
Masao Toyoda
Keyword(s):  
Tensile Properties ◽  
Tensile Tests ◽  
Full Scale ◽  
Small Scale ◽  
Fe Model ◽  
Cold Bending ◽  
Bending Process ◽  
Residual Strains ◽  
Cold Bends ◽  
The Relationship

To comprehensively investigate the tensile properties of cold bends, full-scale cold bending experiments, tensile tests using prestrained small-scale specimens, and finite element (FE) analyses of the cold bending processes were conducted on API 5L X60 and X80 grade line pipes. The tensile tests revealed that the tensile properties of the cold bends were comparable to the uniaxially prestrained specimens machined from the straight part of the pipes. A FE model simulating the cold bending process was verified with the full-scale experimental results in terms of the distributions of residual strains. These results supported a procedure for estimating the tensile properties of the cold bends with a combination of the FE model and the tensile tests using the prestrained specimens; the residual strains obtained from the FE model are transformed into the tensile properties based on the relationship between the residual strains and the tensile properties. This study clarified that the tensile properties come close to being uniformly distributed by reducing the distance between the bending locations; the distance between the bending locations has a significant influence on the overlap of adjacent deformed areas, which governs the distribution of the tensile properties of the cold bends.

Experimental and Analytical Study of Cold Bending Process for Pipelines

2003 ◽  
Vol 125 (2) ◽  
pp. 153-157 ◽  
Author(s):  
Naoki Fukuda ◽  
Hiroshi Yatabe ◽  
Shinobu Kawaguchi ◽  
Takahito Watanabe ◽  
Tomoki Masuda
Keyword(s):  
Analytical Study ◽  
Longitudinal Direction ◽  
Tensile Tests ◽  
Full Scale ◽  
Obvious Effect ◽  
Cold Bending ◽  
Bending Process ◽  
Strain Relationship ◽  
Cold Bends ◽  
Good Agreement

The behavior during the cold bending of pipelines was experimentally and analytically investigated. Full-scale cold bending experiments were performed on API X60 and X80 grade line pipes. Finite element (FE) analyses simulated the cold bending process by considering the contact interactions between a pipe and the components of the bending machine. The results of the simulation were in good agreement with the full-scale experiments. The stress-strain relationship and yield to tensile ratio (Y/T) had no obvious effect on the strain distribution after cold bending. The tensile tests quantitatively evaluated the decrease in the yield stress along the longitudinal direction on the cold bends due to the Bauschinger effect.

Effect of Changes in Tensile Properties Due to Cold Bending on Large Deformation Behavior of High-Grade Cold Bend Pipe

2002 ◽  
Author(s):  
Naoki Fukuda ◽  
Hiroshi Yatabe ◽  
Tomoki Masuda ◽  
Masao Toyoda
Keyword(s):  
Tensile Properties ◽  
Large Deformation ◽  
Deformation Behavior ◽  
High Grade ◽  
Bending Angle ◽  
Cold Bending ◽  
Bending Process ◽  
Opening Mode ◽  
Cold Bends ◽  
Good Agreement

The large deformation behavior of cold bend was experimentally and analytically investigated. Full-scale large deformation experiments were conducted on two API X80 grade cold bends with a bending angle of approximately 9 degrees for both closing and opening modes. Finite element (FE) analyses were also conducted to simulate the large deformation behavior by considering the distribution of tensile properties after the cold bending process. The results of the simulation were in good agreement with the large deformation experiments. The deformability of cold bend in the opening mode was greater than that in the closing mode. Changes in the tensile properties due to the cold bending process had a large influence on the deformability of cold bend. In particular, distribution of the part with work hardening after the cold bending process had large effect on the deformability in the closing mode.

Evaluation of Tensile Properties Profile of Weld Zone Using Instrumented Indentation

2010 ◽  
Author(s):  
Seung-Kyun Kang ◽  
Young-Cheon Kim ◽  
Chan-Pyoung Park ◽  
Dongil Kwon
Keyword(s):  
Tensile Properties ◽  
Weld Zone ◽  
Indentation Test ◽  
Tensile Tests ◽  
Structural Safety ◽  
Small Scale ◽  
Stress And Strain ◽  
Instrumented Indentation ◽  
Deformation And Fracture ◽  
Instrumented Indentation Test

Understanding the property distribution in the weld zone is very important for structural safety, since deformation and fracture begin at the weakest point. However, conventional tensile tests can measure only average material properties because they require large specimens. Small-scale tests are being extensively researched to remove this limitation, among such tests, instrumented indentation test (IIT) are of great interest because of their simple procedures. Here we describe the evaluation of tensile properties using IIT and a representative stress-strain approach. The representative stressstrain method, introduced in 2008 in ISO/TR29381, directly correlates the stress and strain under the indenter to the true stress and strain of tensile testing by defining representative functions. Using this technique, we successfully estimate the yield strength and tensile strength of structural metallic materials and also obtain profiles of the weld-zone tensile properties.

Examination of the Transferability of CTOA From Small-Scale DWTT to Full-Scale Pipe Geometries Using a Cohesive Zone Model

2020 ◽  
Author(s):  
Chris Bassindale ◽  
Xin Wang ◽  
William R. Tyson ◽  
Su Xu
Keyword(s):  
Finite Element ◽  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Element Model ◽  
Full Scale ◽  
Opening Angle ◽  
Small Scale ◽  
Zone Model ◽  
Pipe Model ◽  
Good Agreement

Abstract In this work, the cohesive zone model (CZM) was used to examine the transferability of the crack tip opening angle (CTOA) from small-scale to full-scale geometries. The pipe steel STPG370 was modeled. A drop-weight tear test (DWTT) model and pipe model were studied using the finite element code ABAQUS 2017x. The cohesive zone model was used to simulate crack propagation in 3D. The CZM parameters were calibrated based on matching the surface CTOA measured from a DWTT finite element model to the surface CTOA measured from the experimental DWTT specimen. The mid-thickness CTOA of the DWTT model was in good agreement with the experimental value determined from E3039 and the University of Tokyo group’s load-displacement data. The CZM parameters were then applied to the pipe model. The internal pressure distribution and decay during the pipe fracture process was modeled using the experimental data and implemented through a user-subroutine (VDLOAD). The mid-thickness CTOA from the DWTT model was similar to the mid-thickness CTOA from the pipe model. The average surface CTOA of the pipe model was in good agreement with the average experimental value. The results give confidence in the transferability of the CTOA between small-scale specimens and full-scale pipe.

Mechanical Properties of Cold Bend Pipes

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
M. Sen ◽  
J. J. R. Cheng ◽  
D. W. Murray ◽  
J. Zhou
Keyword(s):  
Yield Strength ◽  
Bauschinger Effect ◽  
Strength Reduction ◽  
Moment Capacity ◽  
Initial Imperfections ◽  
Cold Bending ◽  
Pipeline Route ◽  
The Moment ◽  
Cold Bends ◽  
Pipe Joint

Cold bends are frequently required in energy pipelines in order to change the vertical and horizontal orientations of the pipeline route. They are produced by plastically bending a pipe joint in a cold bending machine by creating a series of uniformly spaced incremental bends. This procedure acts to reduce the moment capacity and buckling strain of the pipe, and studying the changes in pipe properties caused by cold bending is valuable in assessing the level of this strength reduction. Accordingly, the initial imperfections and material transformations of five full-scale cold bend pipes were assessed in this research program. The imperfections were measured at several locations around the circumference of the specimens, along the entire bend length. It was determined that the distribution of imperfections was similar in shape to a sine function, and their amplitude ranged from 0.3mmto1.0mm. Tension coupon tests were conducted on the intrados, extrados, and virgin materials of the specimens. It was revealed that the extrados material exhibited an increase in yield strength due to work hardening and that the intrados material demonstrated a reduction in yield strength due to the Bauschinger effect. It was established that the imperfections, and material transformations in the specimens were predominantly unaffected by the incremental-bend magnitude or spacing that was employed during the cold bending procedure.

Mechanical Properties of Cold Bend Pipes

2006 ◽  
Author(s):  
M. Sen ◽  
J. J. R. Cheng ◽  
D. W. Murray ◽  
J. Zhou
Keyword(s):  
Yield Strength ◽  
Bauschinger Effect ◽  
Moment Capacity ◽  
Initial Imperfections ◽  
Horizontal Orientation ◽  
Cold Bending ◽  
Pipeline Route ◽  
The Moment ◽  
Cold Bends ◽  
Pipe Joint

Cold bends are frequently required in energy pipelines in order to change the vertical and horizontal orientation of the pipeline route. They are produced by plastically bending a pipe joint in a cold bending machine, by creating a series of uniformly spaced kinks. This procedure acts to reduce the moment capacity and buckling strain of the pipe, and studying the changes in pipe properties caused by cold bending is valuable in assessing the level of this strength reduction. Accordingly, the initial imperfections and material transformations of five full-scale cold bend pipes were assessed in this research program. The imperfections were measured at several locations around the circumference of the specimens, along the entire bend length. It was determined that the distribution of imperfections was similar in shape to a sine function, and their amplitude ranged from 0.3 to 1.0 mm. Tension coupon tests were conducted on material from the intrados, extrados, and virgin material of the specimens. It was revealed that the extrados material exhibited an increase in yield strength due to work hardening, and that the intrados material demonstrated a reduction in yield strength due to the Bauschinger Effect. It was established that the imperfections, and material transformations in the specimens were predominantly unaffected by the kink magnitude or spacing that was employed during the cold bending procedure.

scholarly journals Conductivity measurement of plaque samples obtained from the insulation of high voltage extruded cables

2017 ◽  
Author(s):  
Hossein Ghorbani ◽  
Andeas Farkas ◽  
Pierre Hulden
Keyword(s):  
Electric Field ◽  
High Voltage ◽  
Thermal History ◽  
High Field ◽  
Conductivity Measurement ◽  
Full Scale ◽  
Small Scale ◽  
Characterization Techniques ◽  
Hv Cable ◽  
Good Agreement

<p>Good understanding of insulation conductivity is of<br />great importance in development and design of high<br />voltage DC cables. Conductivity of polymeric insulation<br />materials is a property which is quite sensitive to many<br />parameters such as temperature, electric field, chemical<br />composition, thermal history, morphology, etc.<br />Therefore, due to different process history, the results<br />obtained from pressed plaques are not necessarily<br />representative of the insulation behavior in an extruded<br />cable. A method was developed to obtain samples from<br />HV cable in form of plaques with a thicknesses up to a<br />few millimeters. Plaque samples were extracted from<br />two cables, their conductivity at high field was<br />measured and compared to those obtained from fullscale<br />tests; the results, confirm a very good agreement<br />between the small scale and full-scale measurements;<br />this hints to a promising prospect for such small scale<br />characterization techniques.</p>

Evaluation of Pressurized Cold Bend Pipe Body Tensile Fractures Under Bending Loads

2014 ◽  
Author(s):  
Celal Cakiroglu ◽  
Muntaseer Kainat ◽  
Samer Adeeb ◽  
J. J. Roger Cheng ◽  
Millan Sen
Keyword(s):  
Experimental Study ◽  
Internal Pressure ◽  
Equivalent Plastic Strain ◽  
Vertical Plane ◽  
Steel Grade ◽  
Full Scale ◽  
Cold Bending ◽  
Steel Grades ◽  
Cold Bends ◽  
Full Scale Tests

Cold bending is applied at locations where the pipeline direction has to be changed in a horizontal or vertical plane. The process of cold bending usually results in residual stresses as well as changes in the material properties at the vicinity of the cold bend location which makes the study of the mechanical behaviour of cold bends indispensable. Due to discontinuous permafrost in arctic regions as well as slope instabilities and earthquakes cold bends within pipelines constructed in such locations can be subjected to significant tensile or compressive forces. Experimental studies were carried out by Sen et al [1][2][3]in order to investigate the buckling behaviour of pressurized cold bends. In these experiments the curvature of the cold bend is increased in the presence of a constant internal pressure. In their experimental study a total of 8 full scale tests were conducted with a variety of pipe diameters, diameter to wall thickness ratio and steel grade. In this set of full scale tests one of the pipes with grade X65 failed due to fracture at the extrados after buckling and formation of wrinkles at the intrados[1]. Our previous work [4], [5] on this subject showed the simulations of this case using finite element analysis. These simulations demonstrated that indeed pipe body tensile side fracture can be observed for this particular pipe specification. Whereby the tension side fractures are expected starting from a specific internal pressure level. The simulation results showed that the equivalent plastic strain values at the cold bend extrados increase dramatically starting from a certain level of applied curvature in load cases with an internal pressure higher than a transition value. In this paper the effect of steel grade on this transition from compressive to tensile failure is investigated. Parametric studies are conducted for the entire range of steel grades tested in the experimental study of Sen et al. It is found that there is a linear proportionality between the steel grade and the transition internal pressure for steel grades between X60 and X80.

scholarly journals Modelling of Clay Behaviour in Pile Loading Test Using One-Gravity Small-Scale Physical Model

2015 ◽  
Vol 773-774 ◽  
pp. 1535-1541 ◽  
Author(s):  
Agus Sulaeman ◽  
Felix N.L. Ling ◽  
Martosuro Sajiharjo
Keyword(s):  
Scaling Factor ◽  
Full Scale ◽  
Small Scale ◽  
Pile Driving ◽  
Loading Test ◽  
Gravity Condition ◽  
Time Scaling ◽  
Set Up ◽  
Reduced Scale ◽  
Good Agreement

The observations and tests under small scale in 1-gravity condition are intended to obtain a comparative behavior of a model and prototype of geotechnical case by imposing the scaling relations. Simulations to represent a related structure, sub-soil and failure mechanism need to be prepared prior to do observations in this modeling. To simulate pile loading test (PLT) on clay, the following models of: clay, pile, driving simulation and procedure of PLT based on ASTM D4410 were set-up. The PLT in reduced scale environment was then followed by performing normal practice of full scale PLT in original clay site. Load settlement curves obtained from both “pile loading test” in small and full scale simulations showed closely good agreement. Further observation and investigation on simulation of pile loading test in clay revealed that modeling the following: clay sub-soil resulted in new properties of clay, em=ep+λLn(N) which reflects stress scaling factor, N, pile size and pile driving hammer need scaling factor n and n3 respectively whereas PLT time needs time scaling factor, tp (n)0.5.

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