Methodology for Assessment of Surface Defects in Undermatched Pipeline Girth Welds

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Aurélien Pépin ◽  
Tomasz Tkaczyk ◽  
Noel O'Dowd ◽  
Kamran Nikbin
Keyword(s):  
Weld Metal ◽  
Surface Defects ◽  
Analytical Formula ◽  
Strain Curve ◽  
High Strength ◽  
Cost Effective ◽  
Medium Size ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Girth Welds

The demand for subsea transport of highly corrosive constituents has noticeably increased in recent years. This has driven the requirement for high strength pipelines with enhanced corrosion resistance such as chromium stainless steel or bimetal pipes. The latter are carbon steel pipes with a corrosion resistant alloy lining. Reeling is a cost effective installation method for small to medium size subsea pipelines, up to 457.2 mm (18 in.) in diameter. However, plastic straining associated with reeling has an effect on weld defect acceptance criteria. The maximum acceptable defect sizes are typically developed using engineering critical assessment (ECA), based on the reference stress method, which requires that the weld metal is equal to or stronger than the parent metal in terms of the stress–strain curve. However, evenmatch/overmatch cannot always be achieved in the case of subsea stainless or bimetal pipelines. In this work, a parametric finite-element (FE) study was performed to assess the effect of weld metal undermatch on the crack driving force, expressed in terms of the crack tip opening displacement (CTOD). Subsequently, the fracture assessment methodology for reeled pipes was proposed, where the ECA as per BS7910 is first carried out. These acceptable defect sizes are then reduced, using an analytical formula developed in this work, to account for weld undermatch.

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.

Experimental Study on Fracture Toughness of Q460C the High-Strength Construction Steel at Low Temperature

2011 ◽  
Vol 71-78 ◽  
pp. 890-897 ◽  
Author(s):  
Yuan Qing Wang ◽  
Yun Lin ◽  
Yan Nian Zhang ◽  
Yong Jiu Shi
Keyword(s):  
Low Temperature ◽  
High Strength ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Three Point Bending ◽  
Function Fitting ◽  
Ductile Brittle Transition Temperature ◽  
Boltzmann Function ◽  
Fracture Appearance ◽  
Crack Tip Opening

Three point bending tests were carried out on 14mm-thick Q460C the high-strength structural steel at low temperature, and scanning electronic microscope of the fracture appearance was analyzed. The results showed that the obvious feature of brittle mechanism was shown on the three point bending specimen fracture whose testing took place at -40°C. And the crack tip opening displacement value of Q460C steel, which was less than that of Q235 steel, Q345 steel and Q390 steel at low temperature, tended to decrease with respect to the temperature reduction. Moreover, a Boltzmann function fitting analysis was applied to the experimental data, and the ductile-brittle transition temperature and the changing regularity were obtained.

Evaluation of FCAW Consumables for Offshore and Arctic Structure Fabrication

1993 ◽  
Vol 115 (1) ◽  
pp. 76-82 ◽  
Author(s):  
S. R. Bala ◽  
L. Malik ◽  
J. E. M. Braid
Keyword(s):  
Weld Metal ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Inclusion Content ◽  
Ambient Temperatures ◽  
Weld Metals ◽  
Arctic Regions ◽  
Flux Cored Arc Welding ◽  
Crack Tip Opening ◽  
Cored Wires

A primary consideration in the welding of structures for service in Canadian offshore and arctic regions is the toughness of weld metals required at very low ambient temperatures (−30°C to −60°C). To assess the suitability of cored wires for applications in these environments, some currently available commercial consumables for the flux-cored arc welding (FCAW) process were evaluated. Cored wires belonging to four different categories: basic, rutile, metal-cored and innershield, were used to prepare welds with similar welding procedures. Weld metal Charpy V-notch (CVN) and crack tip opening displacement (CTOD) tests were carried out and the effect of weld metal composition, microstructure and inclusion content in the weld metal toughness was examined. The Charpy transition temperatures and the CTOD toughness results indicated that, of the 16 wires tested, there were only seven that would be suitable for critical applications.

Applying Gurson Type of Damage Models to Low Constraint Tests of High Strength Steels and Welds

2006 ◽  
Author(s):  
Ming Liu ◽  
Yong-Yi Wang
Keyword(s):  
Damage Mechanics ◽  
Ductile Failure ◽  
High Strength Steels ◽  
High Strength ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Critical Crack ◽  
Gtn Model ◽  
Strain Capacity ◽  
Low Constraint

Pipelines experiencing displacement-controlled loading need to have adequate strain capacity. Large tensile strain capacity can only be achieved when the failure processes are ductile. In ductile failure analyses, the strain capacity may be determined by two approaches. The first approach uses the conventional fracture mechanics criteria, such as the attainment of the critical crack tip opening displacement, to assess the onset of the crack propagation. The other approach uses damage mechanics models in which the onset and propagation of cracks are controlled by the nucleation, growth, and coalescence of voids in the material. The damage mechanics models can provide some insights of the ductile failure processes as they have more physical mechanisms built in the constitutive model. In this paper, the Gurson-Tvergaard-Needleman (GTN) model is applied to two types of low-constraint tests: curved wide plates and back-bend specimens. The wide plate test is considered more representatives of full-scale pipes than the conventional laboratory-sized specimens, but requires large-capacity machines. The back-bend test is a newly developed low-constraint laboratory-sized test specimen. A relatively simple approach to determine the damage parameters of the GTN model is discussed and the transferability of damage parameters between those two test types is also analyzed.

An Innovative ECA Approach For Reeled CRA Welds And Its Validation Programme

2021 ◽  
Author(s):  
Richard Jones ◽  
Dr Thurairajah Sriskandarajah ◽  
Dr Daowu Zhou ◽  
James Hymers ◽  
Kieran Munro ◽  
...  
Keyword(s):  
High Stress ◽  
Crack Tip ◽  
Test String ◽  
Test Rig ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Defect Growth ◽  
Girth Welds ◽  
Stress Fatigue ◽  
Crack Tip Opening

Abstract This paper presents an innovative defect growth ECA methodology for pipeline girth welds and its validation programme, applied specifically to reeling ECA of pipelines with under-matched strength welds. The ECA method is a tear-fatigue approach that accounts for the blunting limit in JR curves during pipe spooling and reel-lay. Fatigue crack growth may occur by low cycle high stress fatigue and by tearing, but the latter only if the crack tip opening displacement exceeds the blunting limit. Conventional ECA with BS7910 is limited because the weld's strength needs to be over-matched. Alternative industry methods for the application of FEA to under-matched strength welds are computationally more intensive than the presented innovative approach. Fatigue crack growth for low cycle high stress fatigue is calculated using Paris’ Law in the approach but, if the crack tip opening due to the tearing mechanism is less than the blunting limit then tearing growth is zero. With the innovative method, if the crack tip opening displacement exceeds the blunting limit then the tearing defect growth is included. Hence, the method is a combined tear-fatigue approach. Welded pipe strings were fabricated from pups composed of clad material; i.e. carbon backing steel pipe with a 3 mm layer of corrosion resistant alloy (CRA) on the inner circumference. Each test string was approximately 10.5m long and fabrication was from a mix of six 0.5m length pups in the central zone of each string and two longer end pups. Three girth welds included EDM notches for test purposes which simulated planar flaws. The notches were on the extreme tension fibre, as the test string gets pulled to the reel former in a reeling test rig. Full scale reeling simulations involved pulling the test strings up to 6 times to the reel former in a reeling test rig. Measurement of defect growth associated with the EDM notches was by scanning electron microscope (SEM), from specimen segments extracted from the test strings. Predictions of defect growth were by finite element models in combination with pipe-specific data that was the outcome of an associated small-scale test programme. Validation of the ECA-by-FEA approach is by a predictive best estimate study, for which there is excellent agreement between the measured values and the calculated defect growths. The ECA-by-FEA approach is conservative for project work, as shown by a high estimate study and an offset blunting limit study. Early development of the ECA approach was for small diameter CRA pipelines during the execution of the Guara-Lula project (Sriskandarajah et al, 2015). The presented full-scale tests, innovative defect growth measurement by scanning electron microscope and the FEA and defect growth calculations were full validation of the approach, with pipe strings that had outer diameter of 323.9mm.

scholarly journals Guide for Recommended Practices to Perform Crack Tip Opening Displacement Tests in High Strength Low Alloy Steels

2016 ◽  
Vol 21 (3) ◽  
pp. 290-302 ◽  
Author(s):  
Julián A. Ávila ◽  
Vinicius Lima ◽  
Cassius O. F. T. Ruchert ◽  
Paulo Roberto Mei ◽  
Antonio J. Ramirez
Keyword(s):  
Crack Tip ◽  
High Strength ◽  
Low Alloy Steels ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Alloy Steels ◽  
Recommended Practices ◽  
Crack Tip Opening

Weld Metal Hydrogen Cracking in Transmission Pipelines Construction

2010 ◽  
Author(s):  
Sheida Sarrafan ◽  
Farshid Malek Ghaini ◽  
Esmaeel Rahimi
Keyword(s):  
Weld Metal ◽  
Construction Projects ◽  
High Strength Steels ◽  
High Strength ◽  
Carbon Equivalent ◽  
Transverse Cracks ◽  
Diffusible Hydrogen ◽  
Hydrogen Cracking ◽  
Girth Welds ◽  
Welding Position

Developments of high strength steels for natural gas pipelines have been in the forefront of steelmaking and rolling technology in the past decades. However, parallel to such developments in steel industry, the welding technology especially with regards to SMAW process which is still widely used in many projects has not evolved accordingly. Decreasing carbon equivalent has shifted the tendency of hydrogen cracking from the HAZ to the weld metal. Hydrogen cracking due to its complex mechanism is affected by a range of interactive parameters. Experience and data gained from field welding of pipeline construction projects indicated that weld metal hydrogen cracking is related to welding position as it occurs more in the 6 o’clock position of pipeline girth welds. In this research an attempt is made to open up the above observation in order to investigate the contributory factors such as welding position and welding progression in terms of diffusible hydrogen and possibly residual stress considerations. It was observed that transverse cracks produced in laboratory condition may not be detected by radiography. But, the higher tendency for cracking at 6 o’clock position was confirmed through bend test. It is shown that more hydrogen can be absorbed by the weld metal in the overhead position. It is shown that welding progression may also have a significant effect on cracking susceptibility and it is proposed that to be due to the way that weld residual stresses are developed. The observations can have an important impact on planning for welding procedure approval regarding prevention of transverse cracking in pipeline girth welds.

Welding of High Strength Pipelines

2004 ◽  
Author(s):  
Bill Bruce ◽  
Jose Ramirez ◽  
Matt Johnson ◽  
Robin Gordon
Keyword(s):  
Weld Metal ◽  
Charpy Impact ◽  
High Strength ◽  
Shielding Gas ◽  
Hydrogen Cracking ◽  
Mechanized Welding ◽  
Margin Of Safety ◽  
Girth Welds ◽  
Welding Consumables

This paper presents the results of a project jointly funded by PRCI and EWI to evaluate the welding of X100 pipe grades using commercially available welding consumables. The welding trials included manual, semi-automatic and mechanized welding procedures. It was found that the combination of Pulsed GMAW and ER100S-1 (using a mixed shielding gas) produced both excellent Charpy impact and CTOD performance, but could result in undermatched girth welds if the pipe significantly exceeds minimum strength requirements. Although ER120 S-1 provides an additional margin of safety in strength, which should accommodate variations in X-100 pipe properties, the toughness results were marginal at −10°C. The risk of weld metal hydrogen cracking in X100 girth welds was also investigated.

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.

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