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.

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.

Analysis of Porosity Characteristics in Weld Metal of High Strength Aluminum Alloy and the Effect of Mixed Shielding Gas

2005 ◽  
pp. 309-312
Author(s):  
Xiao Mu Zhang ◽  
Zhi Yong Zhang ◽  
Yun Peng ◽  
Zhi Ling Tian ◽  
Chang Hong He ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
Weld Metal ◽  
High Strength ◽  
Shielding Gas ◽  
High Strength Aluminum Alloy

Evaluation of Hydrogen Cracking Susceptibility in X120 Girth Welds

2004 ◽  
Author(s):  
M. L. Macia ◽  
D. P. Fairchild ◽  
J. Y. Koo ◽  
N. V. Bangaru
Keyword(s):  
Laboratory Tests ◽  
High Strength ◽  
Test Method ◽  
Laboratory Studies ◽  
Long Distance ◽  
Hydrogen Cracking ◽  
Girth Welding ◽  
Groove Test ◽  
Girth Welds ◽  
The Cost

To reduce the cost of long distance gas transmission, high strength pipeline steels are being developed. Implementation of high strength pipeline materials requires the avoidance of hydrogen cracking during field girth welding. A study of hydrogen cracking in X120 girth welds has been conducted. Cracking resistance of both the weld metal and heat affected zone (HAZ) were investigated. The laboratory tests included the controlled thermal severity (CTS) test, the WIC test and the Y-groove test. In addition, multi-pass plate welds and full pipe welds were completed and examined for the presence of hydrogen cracks. The suitability of each test method for predicting cracking in X120 girth welds is determined. The morphology of hydrogen cracks in X120 girth welds is described, and the conditions necessary to prevent hydrogen cracking are identified. Following the laboratory studies, construction of X120 pipelines without cracking was demonstrated through a 1.6 km field trial.

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.

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.

A New Method for Reducing Diffusible Hydrogen in Weld Metal

2012 ◽  
Author(s):  
Susan Fiore ◽  
Steve Barhorst ◽  
Mario Amata ◽  
Joe Bundy
Keyword(s):  
Weld Metal ◽  
Raw Materials ◽  
Shielding Gas ◽  
Feeding Problems ◽  
Diffusible Hydrogen ◽  
Flux Cored Arc Welding ◽  
Hydrogen Assisted Cracking ◽  
Wire Feeding ◽  
Metal Properties ◽  
Welding Consumables

The effect of hydrogen on weld metal and weld heat-affected zones (HAZ) has been well established over many years. The potential for hydrogen-assisted cracking increases as the strength of the steel increases. High fuel costs have driven the need for lower weights in the transportation and shipbuilding industries, and increased regulations have driven the need for higher safety factors in the pipeline industry. As a result, many industries are requiring higher and higher base metal strengths. The push for higher strength steels has resulted in an increased demand for ultra-low hydrogen welding consumables and processes. Manufacturers of flux-cored arc welding (FCAW) electrodes have generally attacked the problem of weld metal hydrogen through the use of raw materials that react with hydrogen to take it out of solution, by baking the wires in-process, and by using special drawing techniques and lubricants to minimize hydrogen pick-up. Unfortunately, many of the potential solutions result in electrodes that have poor operability, wire feeding problems, and/or increased welding fume. Hobart Brothers has recently developed a method of producing very low-hydrogen weld deposits, which utilizes fluorine-containing gas compounds in the weld shielding gas. The modified shielding gas has no effect on the weld metal properties or the operation of the welding electrodes. This paper provides details of the method, along with test results that have been achieved using a number of flux- and metal-cored electrodes representing a variety of American Welding Society (AWS) classifications.

Analysis of Porosity Characteristics in Weld Metal of High Strength Aluminum Alloy and the Effect of Mixed Shielding Gas

2005 ◽  
Vol 475-479 ◽  
pp. 309-312 ◽  
Author(s):  
Xiao Mu Zhang ◽  
Zhi Yong Zhang ◽  
Yun Peng ◽  
Zhi Ling Tian ◽  
Chang Hong He ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
Weld Metal ◽  
Welded Joint ◽  
High Strength ◽  
Mig Welding ◽  
Shielding Gas ◽  
Mixed Gas ◽  
Porosity Formation ◽  
High Strength Aluminum Alloy ◽  
Softened Zone

Aluminum alloy has being widely used in modern automobile and aeronautic industry. However, the welding of aluminum alloy, especially high strength aluminum alloy，is difficult. Porosities are usually brought in the weld metal. In this paper, MIG welding using mixed gas shielding is carried out. The characteristic shapes of porosity in weld metal are described, the mechanism of porosity formation is analyzed, and the factors that influence the tendency of porosity formation are studied. Experiment results indicate that by the use of mixed shielding gas of 38%He+62%Ar, the number of porosity is reduced, the width of HAZ and softened zone is decreased, and the mechanical properties of welded joint is increased.

Development of Optimized Weld Metal Chemistries for Pipeline Girth Welding of High Strength Line Pipe

2008 ◽  
Author(s):  
Susan R. Fiore ◽  
James A. Gianetto ◽  
Mark G. Hudson ◽  
Suhas Vaze ◽  
Shuchi Khurana ◽  
...  
Keyword(s):  
Mechanical Property ◽  
Yield Strength ◽  
Weld Metal ◽  
High Strength ◽  
Process Variations ◽  
Line Pipe ◽  
Girth Welding ◽  
Dimensional Finite Element ◽  
Initial Work ◽  
Girth Welds

The primary objectives of this program were to provide a better understanding of the factors that control strength and toughness in high strength steel girth welds and to develop optimized welding consumables and welding procedures for high strength pipelines. The initial work on the program involved developing cooling rate models so that optimized weld metal compositions for high-strength pipelines could be developed, ensuring that the ideal balance of strength and ductility, together with tolerance to process variations and resistance to hydrogen cracking is achieved. The model, which was developed under a companion program, uses a two-dimensional finite element approach. Complete details can be found in Reference [1]. The model predicts the cooling rates during various weld passes in narrow groove welding of X80 and X100 pipes. Using this model, along with experimental datasets, a neural network model was developed which has been used to predict weld metal properties for various weld metal compositions. Based on the predictions, eight target compositions were selected and were manufactured by one of the team partners. The results of mechanical property testing showed that it was possible to develop weld metal compositions which exceeded the target yield strength of 820 MPa and also provided excellent toughness (>50J at −60°C). It was also found that the weld metal yield strength measured close to the ID of the pipe was significantly higher than that which was measured closer to the OD of the pipe. Complete mechanical property results, including results for round-bar and strip tensiles, CVN impact toughness, microhardness and more, are presented.

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