Effect of Fracture Speed on Ductile Fracture Resistance: Part 1—Experimental

2010 ◽  
Author(s):  
Do-Jun Shim ◽  
Gery Wilkowski ◽  
Da-Ming Duan ◽  
Joe Zhou
Keyword(s):  
Steady State ◽  
Ductile Fracture ◽  
Fracture Resistance ◽  
State Energy ◽  
Crack Arrest ◽  
Experimental Results ◽  
Displacement Curve ◽  
Charpy Test ◽  
Line Pipe ◽  
Drop Weight Tear Test

The effect of fracture speed on the ductile fracture resistance of line-pipe steels can have an important effect in the basic understanding of the toughness requirements for crack arrest. Over the last few decades, it has become recognized that the drop-weight tear test (DWTT) better represents the ductile fracture resistance than the Charpy test since it utilizes a specimen that has the full thickness of the pipe and has a fracture path long enough to reach steady-state fracture resistance. However, the fracture speed in the DWTT is typically 50 to 60 feet per second (15.2 to 18.3 m/s), whereas the fracture speed in the full-scale pipe test is 300 to 1,000 fps (91.4 to 305 m/s). Recently, the authors have extended the DWTT work and developed a modified back-slot DWTT specimen to obtain higher fracture speeds. One aspect of this modified specimen was to increase the width of DWTT sample from the standard 3-inch (76.2 mm) to 5-inch (127 mm). This was done to increase the ligament length in a relatively deep back-slotted specimen to capture more steady-state data. The initial experimental results demonstrated that this type of specimen can be used to obtain higher fracture speeds. Furthermore, the experimental results clearly showed the effect of fracture speed on the ductile fracture resistance. In this paper, to extend the work on modified back-slot DWTT specimens, the tup was instrumented to measure the load during dynamic impact. From this, the load-displacement curve, steady-state energy (or energy per area) was obtained for the modified back-slot DWTT specimens. These results were compared to those obtained from the standard 3-inch specimens. These results also clearly showed the effect of fracture speed on fracture resistance.

Comparison Between Standard and Modified Back-Slotted DWTT Specimens

2014 ◽  
Author(s):  
Do-Jun Shim ◽  
Mohammed Uddin ◽  
Gery Wilkowski ◽  
Da-Ming Duan ◽  
James Ferguson
Keyword(s):  
Ductile Fracture ◽  
Fracture Resistance ◽  
Cohesive Zone Model ◽  
Crack Arrest ◽  
Zone Model ◽  
Line Pipe ◽  
Static Test ◽  
Drop Weight Tear Test ◽  
Major Factors ◽  
The Impact

The effect of fracture speed on the ductile fracture resistance of line-pipe steels can have an important effect in the basic understanding of the toughness requirements for crack arrest. Recently, the authors have extended the drop-weight tear test (DWTT) work and developed a modified back-slot (MBS) DWTT specimen to obtain higher fracture speeds. The initial experimental observations demonstrated that this type of specimen can be used to obtain higher fracture speeds. Furthermore, the experimental results clearly showed the effect of fracture speed on the ductile fracture resistance. In this paper, an in-depth study was carried out to further investigate why higher fracture speeds are obtained in the MBS-DWTT specimens. For this purpose, quasi-static and dynamic/impact DWTT experiments were conducted for both standard DWTT and MBS-DWTT specimens. In addition, finite element analyses using cohesive zone model were carried out to investigate the fracture behavior in these tests. In summary, the higher fracture speeds in the MBS-DWTT come from two major factors. First, as demonstrated by the quasi-static test results, the natural unloading characteristics of the MBS-DWTT specimen (even under pure displacement-controlled loading) leads to higher fracture speeds. Second, the steep unloading curve of the MBS-DWTT specimen produces a higher possibility of an unstable ductile fracture even during the impact event, which will result in higher fracture speeds.

Effect of Separation on Ductile Crack Propagation Behavior During Drop Weight Tear Test

2010 ◽  
Author(s):  
Takuya Hara ◽  
Taishi Fujishiro
Keyword(s):  
Crack Propagation ◽  
Ductile Fracture ◽  
Fracture Resistance ◽  
High Strength ◽  
Opening Angle ◽  
Ductile Crack ◽  
Line Pipe ◽  
Propagation Behavior ◽  
Drop Weight ◽  
Drop Weight Tear Test

The demand for natural gas using LNG and pipelines to supply the world gas markets is increasing. The use of high-strength line pipe provides a reduction in the cost of gas transmission pipelines by enabling high-pressure transmission of large volumes of gas. Under the large demand of high-strength line pipe, crack arrestability of running ductile fracture behavior is one of the most important properties. The CVN (Charpy V-notched) test and the DWTT (Drop Weight Tear Test) are major test methods to evaluate the crack arrestability of running ductile fractures. Separation, which is defined as a fracture parallel to the rolling plane, can be characteristic of the fracture in both full-scale burst tests and DWTTs. It is reported that separations deteriorate the crack arrestability of running ductile fracture, and also that small amounts of separation do not affect the running ductile fracture resistance. This paper describes the effect of separation on ductile propagation behavior. We utilized a high-speed camera to investigate the CTOA (Crack Tip Opening Angle) during the DWTT. We show that some separations deteriorate ductile crack propagation resistance and that some separations do not affect the running ductile fracture resistance.

Ductile Fracture Resistance Measurements in High Grade Steels

2006 ◽  
Author(s):  
L. N. Pussegoda ◽  
A. Fredj ◽  
A. Fonzo ◽  
G. Demofonti ◽  
G. Mannucci ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Steady State ◽  
Ductile Fracture ◽  
Fracture Resistance ◽  
Process Zone ◽  
Fracture Propagation ◽  
Crack Tip ◽  
Opening Angle ◽  
Displacement Curve ◽  
High Grade

Recent developments in ductile fracture resistance measures in high grade steels in the pipeline industry include the crack tip opening angle (CTOA) and “steady state” fracture propagation energy, using 3-point bend specimens. The CTOA has been found to be a function of specimen ligament size. With the availability of instrumented hammers, it became possible to resolve propagation energy using the load-displacement curve using a single specimen. This paper focuses on refining the steady state fracture propagation energy, using back-slotted Drop Weight Tear Test (DWTT) specimens. The study included numerical simulation of the dynamic response of back-slotted specimens. The significance of the back-slot in altering the stress/strain field ahead of the propagation crack is discussed. The numerical simulation was also used to determine the strain rate in the “process zone” of the crack tip during steady state fracture propagation.

Effects of Soil Cohesiveness and Depth on Dynamic Ductile Fracture Speeds

2008 ◽  
Author(s):  
D. Rudland ◽  
D.-J. Shim ◽  
G. M. Wilkowski ◽  
S. Kawaguchi ◽  
N. Hagiwara ◽  
...  
Keyword(s):  
Ductile Fracture ◽  
Large Scale ◽  
Soil Depth ◽  
Crack Arrest ◽  
Small Scale ◽  
Total Density ◽  
Pipe Material ◽  
Pipe Steels ◽  
Line Pipe ◽  
Fracture Arrest

The ductile fracture resistance of newer line pipe steels is of concern for high grade/strength steels and higher-pressure pipeline designs. Although there have been several attempts to make improved ductile fracture arrest models, the model that is still used most frequently is the Battelle Two-Curve Method (TCM). This analysis incorporates the gas-decompression behavior with the fracture toughness of the pipe material to predict the minimum Charpy energy required for crack arrest. For this analysis, the influence of the backfill is lumped into one empirically developed “soil” coefficient which is not specific to soil type, density or strength. No attempt has been made to quantify the effects of soil depth, type, total density or strength on the fracture speeds of propagating cracks in line pipe steels. In this paper, results from small-scale and large-scale burst tests with well-controlled backfill conditions are presented and analyzed to determine the effects of soil depth and cohesiveness on the fracture speeds. Combining this data with the past full-scale burst data used in generating the original backfill coefficient provides additional insight into the effects of the soil properties on the fracture speeds and the arrest of running ductile fractures in line pipe materials.

Mechanical and Metallurgical Aspects of the Resistance to Ductile Fracture Propagation in the New Generation of Gas Pipelines

2014 ◽  
Author(s):  
Igor Pyshmintsev ◽  
Alexey Gervasyev ◽  
Victor Carretero Olalla ◽  
Roumen Petrov ◽  
Andrey Arabey
Keyword(s):  
Ductile Fracture ◽  
Mechanical Test ◽  
Fracture Propagation ◽  
Rolling Plane ◽  
Full Scale ◽  
Charpy Test ◽  
Line Pipe ◽  
Surface Separation ◽  
Fracture Arrest ◽  
New Generation

The microstructure and fracture behavior of the base metal of different X80 steel line pipe lots from several pipeline projects were analyzed. The resistance of the pipes to ductile fracture propagation was determined by the full-scale burst tests. The high intensity of fracture surface separation (secondary brittle cracks parallel to the rolling plane of the plate) appeared to be the main factor reducing the specific fracture energy of ductile crack propagation. A method for quantitative analysis of microstructure allowing estimation of the steel’s tendency to form separations is proposed. The procedure is based on the EBSD data processing and results in Cleavage Morphology Clustering (CMC) parameter evaluation which correlates with full-scale and laboratory mechanical test results. Two special laboratory mechanical test types utilizing SENT and Charpy test concepts for prediction of ductile fracture arrest/propagation in a pipe were developed and included into Gazprom specifications.

Investigation Into the Use of a Single Specimen for the Determination of Dynamic Steady State Propagation Resistance in High Toughness Line-Pipe Steels

2002 ◽  
Author(s):  
David L. Rudland ◽  
Gery Wilkowski ◽  
Yong-Yi Wang ◽  
David Horsley ◽  
Brian Rothwell ◽  
...  
Keyword(s):  
Steady State ◽  
Fracture Energy ◽  
Ductile Fracture ◽  
Opening Angle ◽  
Single Specimen ◽  
Pipe Steels ◽  
Line Pipe ◽  
Propagation Resistance ◽  
High Toughness ◽  
Dynamic Ductile Fracture

This paper summarizes efforts funded by TransCanada PipeLine Limited on improving the methodology for predicting a true measure of the dynamic steady-state fracture toughness of line-pipe steels using a single mill test specimen. In the past, ductile fracture methodologies generally involved using the Charpy V-notch test to empirically quantify the material dynamic ductile fracture propagation resistance. However, due to its geometry, the use of the Charpy test has proven to be unreliable for high-toughness materials, for materials that have rising-shelf energies, and for higher-grade steels (relative to those for which correlations were originally established). An improved methodology for characterizing the dynamic ductile fracture resistance is to utilize the energy from a full-thickness impact specimen, of which the Drop-Weight Tear Test (DWTT) specimen is the most frequently used type. It has been demonstrated that the total energy from a DWTT-type specimen includes; (1) the energy associated with initiation of the crack (including indentation energy and yielding of the specimen), (2) the energy for transient crack growth from initiation to reaching steady-state fracture, (3) steady-state fracture energy, and (4) a non-steady-state fracture energy region at the end of the test. During the steady-state fracture region it was observed that both the crack velocity and constant crack-tip-opening angle (CTOA) remained constant. This paper presents the results of an investigation aimed at identifying a single specimen that will capture only the steady-state fracture energy present in standard DWTT specimens. Detailed experiments and three-dimensional finite element analyses were used to verify various procedures for eliminating the initiation energy and the residual energy at the end of the tests. A non-instrumented modified specimen, the back-slotted, static-precracked DWTT (BS-SPC-DWTT) specimen, has been developed from the results of these analyses. Energy results from this specimen, for a variety of line-pipe steels, are presented. A correlation between these energies and the propagation energy from standard DWTT specimen is presented. This correlation will aid in the methodology for predicting axial crack arrest in line-pipe steels having higher toughness, a rising upper shelf, or a higher grade.

The Misconception of Employing CVN Toughness as Key-Measure in Ductile Crack Arrest Prediction for Modern Line-Pipe Steels

2014 ◽  
Author(s):  
Alexander Völling ◽  
Christoph Kalwa ◽  
Marion Erdelen-Peppler
Keyword(s):  
Ductile Fracture ◽  
Data Base ◽  
Model Calibration ◽  
Crack Arrest ◽  
Full Scale ◽  
Small Scale ◽  
Material Strength ◽  
Original Material ◽  
Pipe Steels ◽  
Line Pipe

Since the late 1960s’ the Battelle Two-curve (BTC) model is the standard method applied in setting up design requirements with regard to the prevention of long-running ductile fracture in pipelines. It is a straightforward tool employing Charpy-V notch (CVN) toughness as key-measure for material resistance against crack propagation. On basis of pipe dimensions, material strength, and under consideration of decompression behavior of the transferred media, it enables to set up requirements for a minimum CVN toughness level to achieve crack arrest. Overall applicability of the BTC model is based on calibration of the underlying equations to a sound data-base, including both full-scale burst test results and small-scale laboratory testing data involving typical line-pipe grades at that period, i.e. up to grade X70 steels with below 100 J upper-shelf CVN toughness. Now over the last decades, mechanical behavior of line-pipe steels was improved significantly. Responding to market demands, higher grades were designed and also toughness levels were raised as outcome of R&D efforts within the steel industry. Unfortunately, stepping outside the original material data-base from BTC model calibration, this method did forfeit its reliability. At the beginning, mispredictions were mainly related to higher grade steels and elevated operating pressures. But more recent full-scale tests did reveal discrepancies in application of the BTC model also for so-called new vintage steels, i.e. grades actually being inside the original data base for model calibration but from current production routes. With regard to applicability/reliability of BTC model based predictions for crack arrest, the origin of uncertainty has particularly been traced back to the involved material toughness measure. Nowadays, it is common sense that the CVN upper-shelf toughness value inadequately describes the resistance against running ductile fracture. More recent thoughts coherently argue towards closer involving stress-strain response and plastic deformation capacities of the material. On basis of results for grades X65, X80 and X100, the general relation between ductility and toughness is discussed. Finally, an elastic-plastic fracture mechanics related analytical approach is introduced which enables to quantify the resistance against ductile fracture propagation. The objective is to provide a reliable procedure for crack arrest prediction in line-pipe steels.

Ductile Fracture Resistance Modeling Approach in Two High Grade Steels

2006 ◽  
Author(s):  
L. N. Pussegoda ◽  
A. Fredj ◽  
A. Dinovitzer ◽  
D. Horsley ◽  
D. Carlson
Keyword(s):  
Steady State ◽  
Crack Propagation ◽  
Ductile Fracture ◽  
Fracture Resistance ◽  
Fracture Propagation ◽  
Tension Test ◽  
Model Parameters ◽  
High Grade ◽  
Damage Mechanisms ◽  
Point Bend

Recent developments in ductile fracture resistance measures in high grade steels in the pipeline industry include the crack tip opening angle (CTOA) and “steady state” fracture propagation energy, using 3-point bend specimens. The CTOA has been found to be a function of specimen ligament size. Alternatives would be “steady state” fracture propagation energy, critical fracture strain and adoption of damage mechanisms. This paper focuses on modeling approaches for crack propagation using damage mechanisms. The tension test is used to “calibrate” the damage model parameters and applied to the crack propagation in a 3-point bend specimen in candidate high grade steels. The effects of using parameters developed from tension test and extending to a 3-point bend crack propagation scenario is discussed.

Determination of the Region of Steady-State Crack Growth From Impact Tests

2002 ◽  
Author(s):  
Gery M. Wilkowski ◽  
David L. Rudland ◽  
Yong-Yi Wang ◽  
David Horsley ◽  
Alan Glover ◽  
...  
Keyword(s):  
Steady State ◽  
Ductile Fracture ◽  
Crack Growth ◽  
Fracture Resistance ◽  
Crack Tip ◽  
Opening Angle ◽  
Test Results ◽  
Crack Tip Opening Angle ◽  
Linepipe Steels ◽  
Crack Tip Opening

Large-diameter gas pipelines typically have a design requirement to ensure that the toughness is sufficient to avoid brittle or ductile fractures from occurring. New pipeline design requirements with richer gases, higher-grade steels, higher operating pressures, and in some cases lower operating temperatures require considerable extrapolation of the current ductile fracture design equations. To obtain a better understanding of ductile fracture arrest toughness, TCPL has funded efforts to assess the steady-state fracture toughness from specimens that can be used in mill applications. This paper reviews past efforts to assess the regions of steady-state ductile crack growth in test specimens, as well as current test results from numerous highly instrumented impact specimens. The new test results were for X52, X70, and X80 linepipe steels, whereas the past efforts were from linepipe steels, aerospace materials, as well as ferritic and austenitic nuclear piping steels. All of these results show that there is a limited region over which the steady-state fracture resistance can be determined. The fracture energy associated with steady-state fracture is the total energy minus; (1) the energy associated with initiation of the crack (including indentation energy and global yielding of the specimen), (2) the transient crack growth from initiation to reaching steady-state fracture, and (3) a non-steady-state fracture region at the end of the test record. Instrumented load versus load-line displacement data were linked to high-speed digital video data of the crack growth, crack-tip-opening angle (within 2 mm of the crack tip), and crack-mouth-opening displacement. These data allowed for comparison of J-R curves and crack-tip-opening angle values during crack growth to help determine the regions of steady-state crack growth. The results from these efforts are an important consideration in the development of a single test specimen method that can be used for determining the ductile fracture resistance of high-strength and high-toughness linepipe steels.

Holdup and holdup profiles in the reciprocating plate extractor VPE

1990 ◽  
Vol 55 (11) ◽  
pp. 2648-2661 ◽  
Author(s):  
Helena Sovová ◽  
Vladislav Bízek ◽  
Jaroslav Procházka
Keyword(s):  
Steady State ◽  
Experimental Results ◽  
Model Parameters ◽  
Dispersed Phase ◽  
Pulse Form ◽  
Sieve Plates

In this work measurements of mean holdup of dispersed phase, of axial holdup profiles and of flooding points in a reciprocating plate contactor with both the VPE-type plates and the sieve plates were carried out. The experimental results were compared with a monodisperse model of steady-state column hydrodynamics and the model parameters were evaluated. Important differences in the behaviour of the two plate types could be identified. Comparison was also made between two reciprocating drives of different pulse form.

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