Brittle Fracture Arrest in High Charpy Energy Steels: Comparisons With Some Existing Data

2014 ◽  
Author(s):  
G. Wilkowski ◽  
D-J. Shim ◽  
Y. Hioe ◽  
S. Kalyanam ◽  
M. Uddin
Keyword(s):  
Brittle Fracture ◽  
Pipe Steels ◽  
Shelf Energy ◽  
Line Pipe ◽  
Pipe Burst ◽  
Sensitivity Studies ◽  
Shear Area ◽  
Fracture Arrest ◽  
Pipeline Design ◽  
Very High

Current line-pipe steels have significantly higher Charpy upper-shelf energy than older steels. Many newer line-pipe steels have Charpy upper-shelf energy in the 300 to 500J range, while older line-pipe steels (pre-1970) had values between 30 and 60J. With this increased Charpy energy comes two different and important aspects of how to predict the brittle fracture arrestability for these new line-pipe steels. The first aspect of concern is that the very high Charpy energy in modern line-pipe steels frequently produces invalid results in the standard pressed-notch DWTT specimen. Various modified DWTT specimens have been used in an attempt to address the deficiencies seen in the PN-DWTT procedure. In examining fracture surfaces of various modified DWTT samples, it has been found that using the steady-state fracture regions with similitude to pipe burst test (regions with constant shear lips) rather than the entire API fracture area, results collapse to one shear area versus temperature curve for all the various DWTT specimens tested. Results for several different materials will be shown. The difficulty with this fracture surface evaluation is that frequently the standard pressed-notch DWTT only gives valid transitional fracture data up to about 20-percent shear area, and then suddenly goes to 100-percent shear area. The second aspect is that with the much higher Charpy energy, the pipe does not need as much shear area to arrest a brittle fracture. Some analyses of past pipe burst tests have been recently shown and some additional cases will be presented. This new brittle fracture arrest criterion means that one does not necessarily have to specify 85-percent shear area in the DWTT all the time, but the shear area needed for brittle fracture arrest depends on the pipeline design conditions (diameter, hoop stress) and the Charpy upper-shelf energy of the steel. Sensitivity studies and examples will be shown.

Determination of Brittle-to-Ductile Transition Temperatures of Large-Diameter TMCP Linepipe Steel With High Charpy Energy by Use of Modified West Jefferson Testing

2016 ◽  
Author(s):  
Y. Hioe ◽  
G. Wilkowski ◽  
M. Fishman ◽  
M. Myers
Keyword(s):  
Transition Temperature ◽  
Brittle Fracture ◽  
Large Diameter ◽  
Pipe Steels ◽  
Line Pipe ◽  
Brittle To Ductile Transition ◽  
Pipe Burst ◽  
Drop Weight Tear Test ◽  
Fracture Appearance ◽  
Shear Area

In this paper the results will be presented for burst tests from a Joint Industry Project (JIP) on “Validation of Drop Weight Tear Test (DWTT) Methods for Brittle Fracture Control in Modern Line-Pipe Steels by Burst Testing”. The JIP members for this project were: JFE Steel as founding member, ArcelorMittal, CNPC, Dillinger, NSSMC, POSCO, Tenaris, and Tokyo Gas. Two modified West Jefferson (partial gas) pipe burst tests were conducted to assess the brittle-to-ductile transition temperature and brittle fracture arrestability of two 48-inch diameter by 24.6-mm thick X65 TMCP line-pipe steels. These steels had very high Charpy energy (350J and 400J) which is typical of many modern line-pipe steels. In standard pressed-notch DWTT specimen tests, these materials exhibited abnormal fracture appearance (ductile fracture from the pressed notch prior to brittle fracture starting) that occurs with many high Charpy energy steels. Such behavior makes the transition temperature difficult to determine. The shear area values versus temperature results for these two burst tests compared to various modified DWTT specimens are shown. Different rating methodologies; DNV, API, and a Best-Estimate of steady-state fracture propagation appearance were evaluated.

Modified West Jefferson Burst Test for Assessment of Brittle Fracture Arrest in Thick-Wall TMCP Line-Pipe Steel With High Charpy Energy

2016 ◽  
Author(s):  
S. Igi ◽  
T. Sakimoto ◽  
J. Kondo ◽  
Y. Hioe ◽  
G. Wilkowski
Keyword(s):  
Transition Temperature ◽  
Brittle Fracture ◽  
Ductile Fracture ◽  
Base Metal ◽  
The Other ◽  
Line Pipe ◽  
Burst Test ◽  
Seam Weld ◽  
Shear Area ◽  
Fracture Arrest

Three partial gas pipe burst tests were conducted to assess the brittle-to-ductile transition temperature and brittle fracture arrestability of a heavy-walled TMCP line-pipe steel. This steel had a very high Charpy energy (400 J) which is typical of many modern line-pipe steels. In standard pressed-notch DWTT specimen tests this material exhibited abnormal fracture appearance (ductile fracture from the pressed notch prior to brittle fracture starting) that occurs with many high Charpy energy steels. Such behavior gives an invalid test by API RP 5L3, which makes the transition temperature difficult to determine. The first burst test was conducted in a manner that is typical of a traditional West Jefferson (partial gas vessel) burst tests. The crack was initiated in the center of the cooled vessel (with a partial air gap), but an unusual result occurred. In this test a ductile fracture just barely started from each crack tip, but one of the endcaps blew off. The pipe rocketed into the wall of a containment building. The opposite endcap impacted the wall of the building and brittle fractures started there with one coming back to the center of the vessel. The implication from this test was that perhaps initiation of the brittle fracture in the base metal gives different results than if the initial crack came from a brittle location. The second burst test used a modified West-Jefferson Burst Test procedure. The modification involved cutting a short length of pipe at the center of the vessel and rotating the seam weld to the line of crack propagation. The HAZ of the axial seam weld had a higher dynamic transition temperature. The initiation flaw was across one of the center girth welds so that one side of the initial through-wall crack had the crack tip in the base metal while the other side initiated in the seam weld HAZ. On the base metal side, the crack had about 220 mm of crack growth before reaching steady-state shear area, i.e., the shear area gradually decreased as the fracture speed was increasing. On the other side, a brittle fracture was started in the HAZ as expected, and once it crossed the other central girth weld into the base metal, the fracture immediately transformed to a lower shear area percent. These results along with those from the first burst test suggest that the DWTT specimen should have a brittle weld metal in the starter notch region to ensure the arrestability of the material. The final burst test was at a warmer temperature. There was a short length of crack propagation with higher shear area percent, which quickly turned to ductile fracture and arrested. In addition various modified DWTTs were conducted and results were analyzed using an alternative brittle fracture arrest criterion to predict pipe brittle fracture arrestability.

Fracture Behavior in West Jefferson Test Under Low-Temperature Condition for X65 Steel Pipe With High Charpy Energy: Current Activities in HLP Committee, Japan, Report 1

2016 ◽  
Author(s):  
Toshihiko Amano ◽  
Satoshi Igi ◽  
Takahiro Sakimoto ◽  
Takehiro Inoue ◽  
Shuji Aihara
Keyword(s):  
Transition Temperature ◽  
Low Temperature ◽  
Brittle Fracture ◽  
Pressure Vessel ◽  
Fracture Behavior ◽  
Line Pipe ◽  
Burst Test ◽  
Pipe Burst ◽  
Test Vessel ◽  
Fracture Appearance

This paper describes the results of pressure vessel fracture test which called West Jefferson and/or partial gas burst testing using Grade API X65 linepipe steel with high Charpy energy that exhibits inverse facture in the Drop Weight Tear Test (DWTT). A series of pressure vessel fracture tests which is as part of an ongoing effort by the High-strength Line Pipe committee (HLP) of the Iron and Steel Institute of Japan (ISIJ) was carried out at low temperature in order to investigate brittle-to-ductile transition behavior and to compare to DWTT fracture behavior. Two different materials on Fracture Appearance Transition Temperature (FATT) property were used in these tests. One is −60 degree C and the other is −25 to −30 degree C which is defined as 85 % shear area fraction (SA) in the standard pressed notch DWTT (PN-DWTT). The dimensions of the test pipes were 24inches (609.6 mm) in outside diameter (OD), 19.1 mm in wall thickness (WT). In each test, the test pipe is cooled by using liquid nitrogen in the cooling baths. Two cooling baths are set up separately on the two sides of the test vessel, making it possible to obtain fracture behaviors under two different test temperatures in one burst test. The test vessel was also instrumented with pressure transducers, thermocouples and timing wires to obtain the pressure at the fracture onset, temperature and crack propagation velocity, respectively. Some informative observations to discuss appropriate evaluation method for material resistance to brittle facture propagation for high toughness linepipe materials are obtained in the test. When the pipe burst test temperatures are higher than the PN-DWTT transition temperature, ductile cracks were initiated from the initial notch and propagated with short distance in ductile manner. When the pipe burst test temperatures were lower than the PN-DWTT transition temperature, brittle cracks were initiated from the initial notch and propagated through cooling bath. However, the initiated ductile crack at lower than the transition temperature was not changed to brittle manner. This means inverse facture occurred in the PN-DWTT is a particular problem caused by the API DWTT testing method. Furthermore, results for the pipes tested indicated that inverse facture occurred in PN-DWTT at the temperature above the 85 % FATT may not affect the arrestability against the brittle fracture propagation and it is closely related with the location of brittle fracture initiation origin in the fracture appearance of PN-DWTT.

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.

Fracture Control for the Alliance Pipeline

2000 ◽  
Author(s):  
Bob Eiber ◽  
Lorne Carlson ◽  
Brian Leis
Keyword(s):  
Natural Gas ◽  
New Technology ◽  
Fracture Initiation ◽  
Line Pipe ◽  
Control Plan ◽  
High Toughness ◽  
Pipe Burst ◽  
Fracture Control ◽  
Pipe Fittings ◽  
Fracture Arrest

This paper reviews the fracture control plan for the Alliance Pipeline, which is planned for operation in 2000. This natural-gas pipeline is 2627 km (1858 miles) long, running from British Columbia, Canada to Illinois, USA. Interest in the fracture control for this pipeline results from its design, which is based on transporting a rich natural gas (up to 15% ethane, 3% propane) at a relatively high pressure 12,000 kPa (1740 psi). This break from traditional pressures and lean gases, which frequently are constrained by incremental expansion, is more efficient and more economical than previous natural gas pipelines. Use of higher pressures and rich gas requires adequate fracture control for the line pipe, fittings, and valves. This fracture control has been achieved for the Alliance Pipeline by specifying high-toughness steels, in terms of both fracture-initiation and fracture-propagation resistance for the line pipe, fittings and heavy wall components. While beneficial from an economics viewpoint, the need for higher toughnesses raised concern over the validity of the fracture control plan, which was based on existing and new technology. The concern focused on fracture arrest using high toughness steels. The concern was associated with characterizing fracture arrest resistance using Charpy V-notch impact toughness, the most commonly used method to measure fracture arrest resistance. Developments were undertaken to address problems associated with the use of higher-toughness steel and these were validated with full-scale pipe burst tests to demonstrate the viability of the fracture control plan. The solution involved extending existing methods to address much higher toughness steels, which provided a significantly improved correlation between fracture arrest predictions and experimental results. In the burst tests, data was collected to validate the Alliance design and also to extend the database of fracture arrest data to assist future pipelines. Data such as the pressure between the pipe and soil as the gas escapes from the pipe, the sound levels in the atmosphere, the movement and strains in the pipe ahead of the running fracture were instrumented in the test and the available results are presented.

Control of %age Shear Area in DWTT at Low Temperature in Niobium Microalloyed Line Pipe Steel

2018 ◽  
Author(s):  
Sundaresa Subramanian ◽  
Xiaoping Ma ◽  
Xuelin Wang ◽  
Chengjia Shang ◽  
Xiaobing Zhang ◽  
...  
Keyword(s):  
Low Temperature ◽  
Brittle Fracture ◽  
Cube Texture ◽  
High Angle ◽  
Austenite Grain Size ◽  
Line Pipe ◽  
Nano Scale ◽  
Austenite Grain ◽  
The Matrix ◽  
Shear Area

Microstructural engineering to obtain 100% shear area in DWTT at low temperature requires target parameters to suppress brittle fracture. In-depth characterization of benchmarked steels has confirmed that %age shear area is decreased by high number density of ultra-fine precipitates (<10nm) that contribute to precipitation strengthening, high intensity of rotated cube texture and coarse brittle constituents like M/A or carbides. The control of these parameters by nano-scale precipitate engineering of TiN-NbC was covered in a previous presentation in IPC 2016 [1]. The present paper focuses on crystallographic variants selection that controls the density and dispersion of high angle boundaries, which arrest microcracks to suppress brittle fracture, thereby increasing %age shear area in DWTT at low temperature. Studies on crystallographic variants selection in single undeformed austenite grain have clarified crystallographic variants configuration which gives rise to high angle boundaries is influenced by hardenability parameters, i.e., alloying, cooling rate and austenite grain size. The profound effect of carbon and solute niobium on density and dispersion of high angle boundaries in CGHAZ is demonstrated by analyzing EBSD data to reconstruct the shear transformation of undeformed austenite using K-S relationship. Moreover, pancaking of austenite influences crystallographic variants through Sv factor and dislocation density. Experimental results on nano-scale TiN-NbC composite precipitate engineered steel confirm that adequate solute niobium (>0.03wt%) is retained in the matrix, which is aided by the suppression of delayed strain induced precipitation of ultra-fine precipitates of NbC. The hardenability from solute niobium is found to be adequate to give high density of high angle boundaries to give about 95% shear area in DWTT at −40°C in 32 mm gage K-60 plate and 100% shear area in 16.3 mm X-90 strip. Both steels were processed by nano-scale precipitate engineering of TiN-NbC composite to control size and uniformity of distribution of austenite grains before pancaking.

How New Vintage Line-Pipe Steel Fracture Properties Differ From Old Vintage Line-Pipe Steels

2012 ◽  
Author(s):  
G. Wilkowski ◽  
D.-J. Shim ◽  
Y. Hioe ◽  
S. Kalyanam ◽  
F. Brust
Keyword(s):  
Brittle Fracture ◽  
Fracture Behavior ◽  
Pipe Steel ◽  
Full Scale ◽  
Actual Behavior ◽  
Correction Factors ◽  
Pipe Steels ◽  
Line Pipe ◽  
Line Pipe Steel ◽  
Fracture Control

Newer vintage line-pipe steels, even for lower grades (i.e., X60 to X70) have much different fracture behavior than older line-pipe steels. These differences significantly affect the fracture control aspects for both brittle fracture and ductile fracture of new pipelines. Perhaps one of the most significant effects is with brittle fracture control for new line-pipe steels. From past work brittle fracture control was achieved through the specification of the drop-weight-tear test (DWTT) in API 5L3. With the very high Charpy energy materials that are being made today, brittle fracture will not easily initiate from the pressed notch of the standard DWTT specimen, whereas for older line-pipe steels that was the normal behavior. This behavior is now referred to as “Abnormal Fracture Appearance” (AFA). More recent work shows a more disturbing trend that one can get 100-percent shear area in the standard pressed-notch DWTT specimen, but the material is really susceptible to brittle fracture. This is a related phenomenon due to the high fracture initiation energy in the standard DWTT specimen that we call “Abnormal Fracture Behavior” (AFB). This paper discusses modified DWTT procedures and some full-scale results. The differences in the actual behavior versus the standard DWTT can be significant. Modifications to the API 5L3 test procedure are needed. The second aspect deals with empirical fracture control for unstable ductile fractures based on older line-pipe steel tests initially from tests 30-years ago. As higher-grade line-pipe steels have been developed, a few additional full-scale burst tests have shown that correction factors on the Charpy energy values are needed as the grade increases. Those correction factors from the newer burst tests were subsequently found to be related to relationship of the Charpy energy values to the DWTT energy values, where the DWTT has better similitude than the Charpy test for fracture behavior (other than the transition temperature issue noted above). Once on the upper-shelf, recent data suggest that what was once thought to be a grade correction factor may really be due to steel manufacturing process changes with time that affect even new low-grade steels. Correction factors comparable to that for X100 steels have been indicated to be needed for even X65 grade steels. Hence the past empirical equations in Codes and Standards like B31.8 will significantly under-predict the actual values needed for most new line-pipe steels.

The Effects of Soil Properties on the Fracture Speeds of Propagating Axial Cracks in Line Pipe Steels

2006 ◽  
Author(s):  
D. Rudland ◽  
G. Wilkowski ◽  
B. Rothwell
Keyword(s):  
Moisture Content ◽  
Ductile Fracture ◽  
Soil Type ◽  
Small Diameter ◽  
Valuable Insight ◽  
Total Density ◽  
Pipe Material ◽  
Pipe Steels ◽  
Line Pipe ◽  
Fracture Arrest

The ductile fracture resistance of newer line pipe steels is of concern for higher 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 Ductile Fracture Arrest Model, which 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 model, the effect of backfill on the propagating crack fracture speeds is lumped into one empirically based “backfill coefficient,” which does not distinguish different soil types or strengths. Some modifications to this backfill coefficient have been proposed for frozen soil as a function of moisture content, and for water backfill for offshore applications, but no attempt has been made to quantify the effects of soil type, total density or strength on the fracture speeds of propagating cracks in line pipe steels. This paper presents the results from a series of small diameter pipe burst tests that were conducted with different soil backfills. The soils’ moisture content, density, and strength were fully characterized in situ and in the laboratory. In addition, fracture speed data in both unbackfilled and backfilled conditions were recorded. The comparison of the change in fracture speed as a function of soil type, moisture and strength gives valuable insight into the effects of soil on the arrest of running ductile fractures in line pipe materials.

Design and Processing of Niobium Microalloyed Cost Effective Line Pipe Steel With Enhanced Strength and Fracture Toughness

2013 ◽  
Author(s):  
S. V. Subramanian ◽  
J. M. Gray
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Brittle Fracture ◽  
Heat Input ◽  
Large Strain ◽  
Cost Effective ◽  
Accelerated Cooling ◽  
Pipe Steels ◽  
High Angle ◽  
Line Pipe

The functional role of niobium in the original HTP X-80 design of high niobium (0.1wt%), low interstitial ( C 0.03 to 0.04, N<0.005wt%) cost-effective base chemistry is (i) to use Zener drag from strain induced precipitation of NbC during thermo-mechanical rolling and solute drag from solute niobium to retard static recrystallization, (ii) to impart adequate rolling reduction below temperature of no recrystallization to promote large strain accumulation in pancaked austenite, and (iii) to promote fine ferrite grain size by strain induced phase transformation under accelerated cooling conditions, thereby obtain high strength and fracture toughness at low temperature through grain size effect. Residual niobium in austenite is used to impart additional strength through transformation hardening, dislocation hardening from accelerated cooling and precipitation strengthening of ferrite through accelerated cooling and interrupted cooling at coiling temperature. Recent research has confirmed the importance of control of density and dispersion of crystallographic high angle boundaries which are superimposed on the morphological microstructure in order to prevent the initiation of brittle fracture. Extensive research has been carried out in HTP base chemistry to determine the processing options to control the density and dispersion of high angle boundaries to produce higher grade (>X-80) line pipe steels with enhanced fracture toughness. Whereas the resistance to ductile fracture is measured by Charpy toughness, the resistance to brittle fracture is inferred from ductile to brittle transition temperature and percentage shear in DWTT. The research has underscored the importance of austenite grain refinement in upstream processing of HTP before pancaking in finish rolling to control density and dispersion of high angle boundaries in order to prevent brittle fracture initiation. Experimental results are presented which demonstrate that HTP base chemistry is a cost effective design to produce higher grade line pipe steels, not only to achieve high resistance to ductile and brittle fracture in the base plate, but also in HAZ regions associated with relatively high heat input welding in weld fabrication of pipes from plates, and Girth field welding of pipes involving low heat input multi-pass welding.

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