Mechanical Properties and Microstructure of Weld Metal and HAZ Regions in X100 Single and Dual Torch Girth Welds

2010 ◽  
Author(s):  
James Gianetto ◽  
William Tyson ◽  
Yong-Yi Wang ◽  
John Bowker ◽  
Dong-Yeob Park ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Tensile Strength ◽  
Weld Metal ◽  
Welding Process ◽  
T Test ◽  
Fusion Line ◽  
Small Scale ◽  
Single Edge ◽  
Testing Procedures ◽  
Girth Welds

The main objectives of the current study were to further develop tensile and toughness testing protocols and to provide a better understanding of the factors that control both weld metal and HAZ microstructure and properties in pipeline girth welds. In this investigation, two series of rolled (1G) girth welds were made in X100 pipe of 36 in. diameter and 0.750 in. wall thickness using two pulsed-gas metal arc welding process variants: single and dual torch. The small-scale testing program included evaluations of all-weld-metal tensile strength, Charpy impact and standard fracture toughness measured by single-edge bend SE(B) tests, along with preliminary fracture toughness results using a single-edge tension SE(T) test developed at CANMET. Additional information was obtained from detailed microstructural characterizations of weld metal and HAZ regions along with microhardness testing. All-weld-metal tensile tests using round and strip tensile specimens showed variations with through-thickness location and in some case with clock position. Full stress-strain curves were generated, and 0.2% offset yield strength, flow stress, ultimate tensile strength, and uniform strain were measured and compared with pipe properties using calculated weld strength mismatch factors based on these properties. Charpy V-notch transition curves were generated for both weld metal and HAZ (notched within 0.5 mm of the fusion line). Fracture toughness of both weld metal and HAZ regions of single torch welds was assessed using standard SE(B) testing procedures with Bx2B preferred specimens notched through–thickness at the weld centerline and in the HAZ (within 0.5 mm of the fusion line). Full J-resistance curves were measured using SE(T) tests of surface-notched WM and HAZ specimens; the SE(T) test was designed to match the constraint of full-size pipeline girth welds.

Fracture Toughness Estimation for Pipeline Girth Welds

2002 ◽  
Author(s):  
Henryk G. Pisarski ◽  
Colin M. Wignall
Keyword(s):  
Fracture Toughness ◽  
Weld Metal ◽  
Specimen Geometry ◽  
Single Edge ◽  
Single Edge Notch ◽  
Edge Notch ◽  
Loading Modes ◽  
Girth Welds ◽  
The Relationship ◽  
Single Edge Notch Bend

The relationship between fracture toughness estimated using standard single edge notch bend (SENB), single edge notch tension (SENT) test specimens and fracture toughness associated with a circumferential flaw in a pipe girth weld is explored in terms of constraint using the Q parameter. It is shown that in the elastic-plastic regime, use of standard deeply notched SENB specimens provides a conservative assessment of fracture toughness, for both weld metal and HAZ, because of the high constraint associated with this specimen geometry. Use of specimen geometries and loading modes associated with lower constraint (e.g. SENT and shallowed notched SENB specimens), allow for improved estimates of fracture toughness to be made that are appropriate for the assessment of circumferential flaws in pipe girth welds. Recommendations are given on the specimen designs and notch orientations to be employed when evaluating weld metal and HAZ fracture toughness.

Evaluation of Weld Metal Strength Mismatch in X100 Pipeline Girth Welds

2004 ◽  
Author(s):  
Henryk G. Pisarski ◽  
Yuri Tkach ◽  
Marie Quintana
Keyword(s):  
Fracture Toughness ◽  
Adverse Effects ◽  
Weld Metal ◽  
Axial Stress ◽  
Limit Load ◽  
Allowable Stress ◽  
Simple Method ◽  
Weld Width ◽  
Girth Welds ◽  
Assessment Procedures

A relatively simple method based on standard fracture mechanics flaw assessment procedures, such as BS 7910, but modified using published mismatch limit load solutions is described. It is used to illustrate the effects of weld width and strength mismatch on CTOD requirements for girth welds in Grade X100 strength pipeline material subjected to axial stress. It is shown that fracture toughness requirements based on standard analyses not allowing for mismatch effects can be unnecessarily conservative when either undermatched or overmatched welds are present. Adverse effects of undermatching, in reducing the allowable stress, can be mitigated by reducing weld width. It is shown that even small amounts of overmatching (e.g. 10%) can be beneficial by allowing axial stress to exceed the SMYS of the parent pipe and reducing CTOD requirements.

Tensile and Toughness Properties of Pipeline Girth Welds

2006 ◽  
Author(s):  
J. A. Gianetto ◽  
J. T. Bowker ◽  
R. Bouchard ◽  
D. V. Dorling ◽  
D. Horsley
Keyword(s):  
Weld Metal ◽  
Welding Process ◽  
Strain Curve ◽  
High Strength ◽  
Primary Objective ◽  
Stress Strain ◽  
Line Pipe ◽  
Arc Welding Process ◽  
Girth Welds ◽  
Metal Microstructure

The primary objective of this study was to develop a better understanding of all-weld-metal tensile testing using both round and strip tensile specimens in order to establish the variation of weld metal strength with respect to test specimen through-thickness position as well as the location around the circumference of a given girth weld. Results from a series of high strength pipeline girth welds have shown that there can be considerable differences in measured engineering 0.2% offset and 0.5% extension yield strengths using round and strip tensile specimens. To determine whether or not the specimen type influenced the observed stress-strain behaviour a series of tests were conducted on high strength X70, X80 and X100 line pipe steels and two double joint welds produced in X70 linepipe using a double-submerged-arc welding process. These results confirmed that the same form of stress-strain curve is obtained with both round and strip tensile specimens, although with the narrowest strip specimen slightly higher strengths were observed for the X70 and X100 linepipe steels. For the double joint welds the discontinuous stress-strain curves were observed for both the round and modified strip specimens. Tests conducted on the rolled X100 mechanized girth welds established that the round bar tensile specimens exhibited higher strength than the strip specimens. In addition, the trends for the split-strip specimens, which consistently exhibit lower strength for the specimen towards the OD and higher for the mid-thickness positioned specimen has also been confirmed. This further substantiates the through-thickness strength variation that has been observed in other X100 narrow gap welds. A second objective of this study was to provide an evaluation of the weld metal toughness and to characterize the weld metal microstructure for the series of mechanized girth welds examined.

Variables Affecting Fracture Toughness of Welds in T-K-Y Connections

2014 ◽  
Author(s):  
Radhika Panday ◽  
Shenjia Zhang ◽  
Jon Ogborn ◽  
Badri K. Narayanan
Keyword(s):  
Heat Treatment ◽  
Fracture Toughness ◽  
Transition Temperature ◽  
Weld Metal ◽  
Welding Process ◽  
Post Weld Heat Treatment ◽  
Factors Affecting ◽  
Brittle Transition ◽  
Brittle Transition Temperature ◽  
Ductile To Brittle Transition

Fracture toughness of tubular welded joints is one of the critical factors affecting the structural integrity and reliability of offshore structures, such as platforms and subsea pipelines. The factors affecting the design fracture toughness of these structures are related to, both, the welding process as well as the chemical composition of the weld metal. The welding process in this application typically comprises of depositing weld metal in the tubular joints of varying thicknesses through series of weld passes. The number of weld passes required for welding these joints subjects the weld metal to repetitive cycles of heating and cooling. The effect of the thermal cycling introduces significant heterogeneity in the microstructure. This is further exacerbated by the presence of micro-alloying elements such as Niobium (Nb) and Vanadium (V) that form complex carbides, nitrides and carbo-nitrides during post weld heat treatment (PWHT). The focus of this work is to evaluate the effect of micro-alloying elements on the ductile to brittle transition temperature and the mode of fracture at temperatures relevant to offshore applications. A threshold Nb and V level has been determined for achieving acceptable weld metal toughness. The improvement in the fracture toughness using this approach has been quantified by Charpy V-Notch (CVN) and Crack Tip Opening Displacement (CTOD) measurements. The Ductile to Brittle Transition Temperature (DBTT) has been shown to be shifted to lower temperatures by 25 °C after post weld heat treatment in the welds where the total amount of Nb and V are controlled to less than 40 ppm. A wet precipitate extraction technique was used to extract precipitates from the welds to establish the presence of fine Nb rich precipitates in the welds with the higher DBTT. The weld deposited with controlled levels of Nb and V was further tested in different joint configurations and base plate thickness. The fracture toughness was evaluated by CTOD testing of the weld in two different thicknesses (50 mm and 70 mm). Increased specimen thickness resulted in lower CTOD values.

Girth Weld Qualification for High Strain Pipeline Applications

2005 ◽  
Author(s):  
Martin W. Hukle ◽  
Agnes M. Horn ◽  
Douglas S. Hoyt ◽  
James B. LeBleu
Keyword(s):  
Plastic Strain ◽  
Weld Metal ◽  
Heat Affected Zone ◽  
High Strain ◽  
Flaw Size ◽  
Small Scale ◽  
Plastic Strains ◽  
Strain Capacity ◽  
Metal Properties ◽  
Girth Welds

Pipeline applications that are subject to global plastic strains require specific testing and qualification programs intended to verify the strain capacity of the girth welds. Such strain demands are generally beyond the limits of standard ECA applicability which normally cover demands up to 0.5% strain. Therefore, qualification of welding procedures for high strain environments require significantly more testing than weld procedures intended for stress-based designs. The plastic strain capacity of girth welds is a function of the pipe and weld metal properties, as well as the maximum flaw size allowable in the girth weld. Specific weld metal/heat affected zone properties, based on small scale testing, should be combined with full scale curved wide plate testing of girth welds that include artificial flaws.

Prediction of Initiation Toughness Under Small Scale Yielding (SSY) and J0.2BL vs. Q Fracture Locus Using Local Approach Methodologies in 304SS

2012 ◽  
Author(s):  
A. Wasylyk ◽  
A. H. Sherry ◽  
J. K. Sharples
Keyword(s):  
Fracture Toughness ◽  
Small Scale ◽  
Initiation Toughness ◽  
Single Edge ◽  
Small Scale Yielding ◽  
Local Approach ◽  
Three Point Bending ◽  
Fracture Locus ◽  
Scale Yielding ◽  
Cracked Specimens

Structural integrity assessments of structures containing defects require valid fracture toughness properties as defined in national and international test standards. However, for some materials and component geometries, the development of valid toughness values — particularly for ductile fracture — is difficult since sufficiently large specimens cannot be machined. As a consequence, the validity of fracture toughness properties is limited by the development of plasticity ahead of the crack tip and the deviation of crack tip conditions at failure from small scale yielding. This paper described the use of local approach models, calibrated against invalid test data, to define initiation toughness in 304 stainless steel pipe material. Three fracture toughness geometries were tested, shallow cracked single edge cracked specimens tested under three point bending, deep cracked single edge cracked specimens tested under three point bending, and deep cracked single edge cracked specimen tested under tension. Initiation toughness and J-Resistance curves were defined for each specimen using the multi-specimen technique. All initiation toughness values measured were above the specimen validity limits. The fracture conditions at initiation were analysed using three local approach models: the Generalised Rice & Tracey, High Constraint Rice & Tracey and the Work of Fracture. The adequacy of local approaches to define the fracture conditions under large strains in 304 stainless steels was demonstrated. A modified boundary layer analysis combined with the local approach models was used to predict the “valid” initiation toughness under small scale yielding condition in this material by defining a J-Q fracture locus. The analytically derived fracture locus was compared to the J-Q values obtained experimentally and shown to be consistent.

Fracture Toughness of X70 Pipe Girth Welds Using Clamped SE(T) and SE(B) Single-Specimens

2014 ◽  
Author(s):  
Dong-Yeob Park ◽  
Jean-Philippe Gravel ◽  
C. Hari Manoj Simha ◽  
Jie Liang ◽  
Da-Ming Duan
Keyword(s):  
Fracture Toughness ◽  
Heat Affected Zone ◽  
Peak Load ◽  
Single Specimen ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Resistance Curves ◽  
Girth Welds ◽  
Crack Tip Opening

Shallow-notched single edge-notched tension (SE(T) or SENT) and deep- and shallow-notched single edge-notched bend (SE(B) or SENB) specimens with notches positioned in the weld and the heat-affected zone were tested. Crack-tip opening displacement (CTOD) versus resistance curves were obtained using both a single and double clip gauge consolidated in a SE(T) single-specimen. Up until the peak load the resistance curves from both gauging methods yield approximately the same results; thereafter the curves deviate. Interrupted testing showed that the crack had initiated below 50% of the peak load, and in some cases had propagated significantly prior to reaching the peak load.

Reversing the Chell Model to Predict Using Monte Carlo Simulations the Original Fracture Toughness of Ferritic Steels

2018 ◽  
Author(s):  
Derreck Van Gelderen ◽  
Julian Booker
Keyword(s):  
Fracture Toughness ◽  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Compact Tension ◽  
Load Cycle ◽  
Small Scale ◽  
Ferritic Steels ◽  
Single Edge ◽  
Edge Notch ◽  
Single Edge Notch Bend

Warm pre-stress (WPS) is the process of subjecting a pre-cracked component to a load cycle at a temperature higher than subsequent operating temperatures. This process is widely acknowledged as being able to enhance the load to fracture, especially in ferritic steels which exhibit lower shelf cleavage fracture. Various models exist to predict this type of enhancement, with the Chell model being one of the most widely used within industry. Previous research conducted by Van Gelderen et al. have reformulated the Chell model to create a method of undertaking Monte Carlo Simulations (MCS) to study the effect of WPS on brittle fracture. Following on from this research, the Chell model could effectively be reversed providing a means of predicting the underlying fracture toughness from experimental WPS data. It also offers the possibility of assessing whether or not a specific specimen has indeed seen an enhancement, solely based on its experimental apparent toughness post WPS. The reverse Chell model was applied to different experimental data and provided reasonable estimates of the original fracture toughness. In the same way that the traditional Chell model offers conservative estimates, the reverse Chell model also provides “reverse conservative” estimates of the original fracture toughness. It was also used to provide confidence that a typical fatigue pre-cracking procedure performed according to ASTM standard E399 would not be sufficient to induce a WPS benefit on the specimens. This type of check can be of particularly interest when manufacturing small scale specimens (small scale Single Edge Notch Bend (SENB) or miniature sized Compact Tension C(T) specimens); a practice often favoured by industry to maximise the number of tests possible.

scholarly journals Fracture Toughness Characteristics of High-Manganese Austenitic Steel Plate for Application in a Liquefied Natural Gas Carrier

Metals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 2047
Author(s):  
Gyubaek An ◽  
Jeongung Park ◽  
Hongkyu Park ◽  
Ilwook Han
Keyword(s):  
Fracture Toughness ◽  
Brittle Fracture ◽  
Weld Metal ◽  
Ductile Fracture ◽  
Austenitic Steel ◽  
Fusion Line ◽  
High Fracture Toughness ◽  
High Manganese ◽  
High Fracture ◽  
High Manganese Austenitic Steel

High-manganese austenitic steel was developed to improve the fracture toughness and safety of steel under cryogenic temperatures, and its austenite structure was formed by increasing the Mn content. The developed high-manganese austenitic steel was alloyed with austenite-stabilizing elements (e.g., C, Mn, and Ni) to increase cryogenic toughness. It was demonstrated that 30 mm thickness high-manganese austenitic steel, as well as joints welded with this steel, had a sufficiently higher fracture toughness than the required toughness values evaluated under the postulated stress conditions. High-manganese austenitic steel can be applied to large offshore and onshore LNG storage and fuel tanks located in areas experiencing cryogenic conditions. Generally, fracture toughness decreases at lower temperatures; therefore, cryogenic steel requires high fracture toughness to prevent unstable fractures. Brittle fracture initiation and arrest tests were performed using 30 mm thickness high-manganese austenitic steel and SAW joints. The ductile fracture resistance of the weld joints (weld metal, fusion line, fusion line + 2 mm) was investigated using the R-curve because a crack in the weld joint tends to deviate into the weld metal in the case of undermatched joints. The developed high-manganese austenitic steel showed little possibility of brittle fracture and a remarkably unstable ductile fracture toughness.

Characterization of Weld Metal Deposited With a Self Shielded Flux Cored Electrode for Pipeline Girth Welds and Offshore Structures

2010 ◽  
Author(s):  
Badri K. Narayanan ◽  
Lisa McFadden ◽  
M. J. Mills ◽  
Marie A. Quintana
Keyword(s):  
Electron Microscopy ◽  
Weld Metal ◽  
Carbon Content ◽  
Orientation Imaging Microscopy ◽  
Welding Process ◽  
Offshore Structures ◽  
Precipitation Process ◽  
Girth Welds ◽  
Precipitate Evolution

Pipeline girth welds deposited with a self-shielded flux cored electrode process (FCAW-S) have been characterized to assess the effect of micro-alloying elements on microstructure and precipitate evolution and correlate it to strength and toughness. A 2.0 mm diameter electrode was used to deposit weld metal in a 12.7 mm thick API grade X-70 pipe joint. The weld metal properties were characterized and shown to overmatch the pipe. The DBTT of the weld metal has been determined through Charpy V-Notch toughness measurements. The effect of heat input and welding procedure has been assessed over a range of heat inputs (1–1.5 kJ/mm.). The effect of dilution from the base plate on toughness has been assessed by measuring the sensitivity of weld metal toughness to changes in carbon content. The as-welded region of the weld has been characterized using different characterization techniques. Ferritic weld metal deposited with a self-shielded arc welding process has intentional additions of aluminum, magnesium, titanium and zirconium. This results in a complex precipitation process that has been characterized with a combination of electron microscopy techniques. The effect of micro-alloying additions on the variant selection during the austenite to ferrite transformation and microstructure evolution has been studied with electron back scattered diffraction (EBSD) in conjunction with orientation imaging microscopy (OIM). Transmission electron microscopy (TEM) was used to characterize the precipitate evolution in these welds. The evidence shows that the formation of a spinel oxide is critical for the nucleation of nitrides of zirconium and titanium and prevents the agglomeration of aluminum rich oxides and the formation of large aluminum nitrides. The evolution of precipitate formation is critical to limit large inclusions and improve weld metal toughness. The presence of titanium and zirconium increases the fraction of high angle grain boundaries within the microstructure resulting in increased resistance to crack propagation. The characterization of the microstructures at two different carbon contents indicates the greater propensity to form twin related variants with increase in carbon content. This suggests a lower transformation temperature of austenite and may be the reason for poor toughness.

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