LOW STRAIN CAPACITY GIRTH WELDS OF NEWLY CONSTRUCTED PIPELINES AND MITIGATIVE APPROACHES

2020 ◽  
pp. 269-278
Author(s):  
Yong-Yi Wang ◽  
Dan Jia ◽  
Steve Rapp ◽  
David Johnson
Keyword(s):  
Strain Capacity ◽  
Girth Welds

Estimation of Tensile Strain Capacity of Vintage Girth Welds

2021 ◽  
Author(s):  
Banglin Liu ◽  
Bo Wang ◽  
Yong-Yi Wang ◽  
Otto Jan Huising
Keyword(s):  
Tensile Strain ◽  
Strain Capacity ◽  
Girth Welds ◽  
Tensile Strain Capacity

Pressure Correction Factor for Strain Capacity Predictions Based on Curved Wide Plate Testing

2012 ◽  
Author(s):  
Matthias Verstraete ◽  
Wim De Waele ◽  
Rudi Denys ◽  
Stijn Hertelé
Keyword(s):  
Correction Factor ◽  
Large Scale ◽  
Strain Capacity ◽  
Defect Assessment ◽  
Ductile Crack Growth ◽  
Large Scale Testing ◽  
Weld Defect ◽  
Girth Welds ◽  
Assessment Procedures ◽  
Tensile Strain Capacity

Strain-based girth weld defect assessment procedures are essentially based on large scale testing. Ever since the 1980’s curved wide plate testing has been widely applied to determine the tensile strain capacity of flawed girth welds. However, the effect of internal pressure is not captured in curved wide plate testing. Accordingly, unconservative predictions of strain capacity occur when straightforwardly transferred to pressurized pipes. To address this anomaly, this paper presents results of finite element simulations incorporating ductile crack growth. Simulations on homogeneous and girth welded specimens indicate that a correction factor of 0.5 allows to conservatively predict the strain capacity of a pressurized pipe through wide plate testing under the considered conditions.

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.

Effects of Biaxial Loading on the Tensile Strain Capacity of Girth Welds With Weld Strength Undermatching and HAZ Softening

2020 ◽  
Author(s):  
Banglin Liu ◽  
Yong-Yi Wang ◽  
Xiaotong Chen ◽  
David Warman
Keyword(s):  
Internal Pressure ◽  
Tensile Strain ◽  
Biaxial Loading ◽  
Reduction Factor ◽  
Pressure Level ◽  
Weld Strength ◽  
Strain Capacity ◽  
Weld Region ◽  
Girth Welds ◽  
Tensile Strain Capacity

Abstract The ability to accurately estimate the tensile strain capacity (TSC) of a girth weld is critical to performing strain-based assessment (SBA). A wide range of geometry, material, and loading factors can affect the TSC of a girth weld. Among the influencing factors, an increase in the internal pressure level has been shown to have a detrimental effect on the TSC. The overall influence of internal pressure is usually quantified by a TSC reduction factor, defined as the ratio of the TSC at zero pressure to the lowest TSC typically attained at pressure factors around 0.5–0.6. Here the pressure factor is defined as the ratio of the nominal hoop stress induced by pressure to the yield strength (YS) of the pipe material. A number of numeric and experiment studies have reported a TSC reduction factor of 1.5–2.5. These studies generally focused on strain-based designed pipelines with evenmatching or overmatching welds, minimum heat affected zone (HAZ) softening, and a surface breaking flaw at the weld centerline or the fusion boundary. This paper examines the effects of pipe internal pressure on the TSC of girth welds under the premise of weld strength undermatching and HAZ softening. The interaction of biaxial loading and the local stress concentration at the girth weld region was quantified using full-pipe finite element analysis (FEA). The relationship between TSC and the internal pressure level was obtained under several combinations of weld strength mismatch and HAZ softening. Results from the FEA show that the effects of the internal pressure on the TSC are highly sensitive to the material attributes in the girth weld region. Under less favorable weld strength undermatching and HAZ softening conditions, the traditionally assumed reduction factor or 1.5–2.5 may not be applicable. Further, the location of tensile failure is found to depend on both the weld material attributes and the internal pressure. It is possible for the failure location to shift from pipe body at zero internal pressure to the girth weld at elevated internal pressure levels. The implications of the results for both girth weld qualification and integrity assessment are discussed.

Framework for Key Influences on Tensile Strain Capacity of Flawed Girth Welds

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Stijn Hertelé ◽  
Rudi Denys ◽  
Anthony Horn ◽  
Koen Van Minnebruggen ◽  
Wim De Waele
Keyword(s):  
Tensile Strain ◽  
Influence Factor ◽  
Weld Strength ◽  
Strain Capacity ◽  
Strain Behavior ◽  
Weld Geometry ◽  
Girth Welds ◽  
Tearing Resistance ◽  
Tensile Strain Capacity ◽  
Element Study

A key influence factor in the strain-based assessment of pipeline girth weld flaws is weld strength mismatch. Recent research has led to a framework for tensile strain capacity as a function of weld flow stress (FS) overmatch. This framework is built around three parameters: the strain capacity of an evenmatching weldment, the sensitivity of strain capacity to weld FS overmatch, and the strain capacity at gross section collapse (GSC). A parametric finite element study of curved wide plate (CWP) tests has been performed to identify the influence of various characteristics on each of these three parameters. This paper focuses on flaw depth, tearing resistance of the weld, stress–strain behavior of the base metal, and weld geometry. Influences of these characteristics are mostly found to be limited to one or two of the three framework parameters. A preliminary structure is proposed for equations that further develop the strain capacity framework.

Weld Strength Mismatch in Strain Based Flaw Assessment: Which Definition to Use?

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Stijn Hertelé ◽  
Wim De Waele ◽  
Rudi Denys ◽  
Matthias Verstraete ◽  
Koen Van Minnebruggen ◽  
...  
Keyword(s):  
Tensile Strength ◽  
Ultimate Tensile Strength ◽  
Driving Force ◽  
Experimental Validation ◽  
Weld Strength ◽  
Crack Driving Force ◽  
Strain Capacity ◽  
Strength Based ◽  
Key Factor ◽  
Girth Welds

Weld strength mismatch is a key factor in the strain based assessment of flawed girth welds under tension. A strength overmatching weld shields potential flaws within the weld itself from remotely applied deformations and consequently reduces crack driving force. Although this effect has been recognized for decades, different weld strength overmatch definitions exist, and it is not yet fully established which of those is most relevant to a strain based flaw assessment. In an effort to clarify this unsolved question, the authors have performed a large series of parametric finite element analyses of curved wide plate tests. This paper provides an experimental validation of the model and subsequently discusses representative results. It is found that crack driving force is influenced by the shape of the pipe metals' stress–strain curves, which influences the representativeness of two common mismatch definitions (based on yield strength and on ultimate tensile strength). Effects of strength mismatch on strain capacity of a flawed girth weld are best described on the basis of a flow stress, defined as the average of yield and ultimate tensile strength. Based on the observations, a framework for a new strain capacity equation is proposed.

Effect of Girth Welding on Strain Capacity of X80 SAW Pipes

2014 ◽  
Author(s):  
Hidenori Shitamoto ◽  
Eiji Tsuru ◽  
Hiroyuki Nagayama ◽  
Nobuaki Takahashi ◽  
Yuki Nishi
Keyword(s):  
Matching Condition ◽  
Construction Cost ◽  
Bending Test ◽  
Long Distance ◽  
Strain Capacity ◽  
Girth Welding ◽  
Girth Welds ◽  
Welded Pipe ◽  
Submerged Arc ◽  
Pipe Bending

Application of API X80 grade line pipes has been promoted to reduce a construction cost of the pipeline. Assessment of the strain capacity of X80 submerged arc welded (SAW) pipe is required for strain-based design (SBD). Long distance gas pipelines are usually constructed using girth welded line pipes. In the assessment of the strain capacity, it is important to keep over-matching at girth welds. However, since strength variation exists in base metal and girth weld metal, the value of the matching ratio also changes. In this study, X80 SAW pipes produced by the UOE process were welded under slightly over-matching condition and full-scale pipe bending test of the girth welded pipe was performed to evaluate the effect of the matching ratio on the strain capacity.

Enhancing Tensile Strain Capacity Through the Optimization of Weld Profiles

2014 ◽  
Author(s):  
Yong-Yi Wang ◽  
Yaoshan Chen ◽  
Mamdouh Salama
Keyword(s):  
Tensile Strain ◽  
High Strength Steels ◽  
High Strength ◽  
Recent Analysis ◽  
Strain Concentration ◽  
Strain Capacity ◽  
Weld Defects ◽  
Weld Region ◽  
Girth Welds ◽  
Tensile Strain Capacity

In order to optimize cost and performance of high pressure gas pipelines by reducing the wall thickness, pipeline companies are considering the use of higher grade (X70 or above) steels or a composite pipe of thin steel liner and fiber wrap. The use of high strength steels and thinner pipes can result in challenges when the pipe is installed in areas imposing high strain demand such as discontinuous permafrost regions. For high strength steels, the difficulty of ensuring the strength overmatching of the weld metal and the potential softening of the heat affected zone (HAZ) can result in gross strain concentration in the weld region and thus reduce the strain capacity of the pipeline in the presence of weld defects. Also, a thinner pipe has lower strain capacity than a thicker pipe for the weld defect of the same dimensions. One of the economical and effective ways of mitigating the possibility of gross strain concentration and increasing the strain capacity of a weld region containing weld defects is through the use of appropriate weld profiles. For instance, adding a smooth and wide layer of weld reinforcement (termed weld overbuild) can increase the effective strength of the weld. The effectiveness of the weld overbuild in improving the tensile strain capacity of girth welds is evaluated using the Level 4a approach of the PRCI-CRES tensile strain models. The crack-driving force is obtained through finite element analysis (FEA) of welds with planar weld and HAZ flaws of various sizes. It was demonstrated that weld overbuild with appropriate dimensions is an effective method to increase the tensile strain capacity (TSC) of girth welds which may have limited TSC without the overbuild. The role of weld profiles in girth weld integrity is discussed from the perspectives of historical evidence and more recent analysis and experimental tests.

Attributes of Modern Linepipes and Their Implications on Girth Weld Strain Capacity

2018 ◽  
Author(s):  
Yong-Yi Wang ◽  
Steve Rapp ◽  
David Horsley ◽  
David Warman ◽  
Jim Gianetto
Keyword(s):  
Tensile Properties ◽  
Weld Strength ◽  
Potential Contribution ◽  
Contributing Factors ◽  
Strain Capacity ◽  
Strain Tolerance ◽  
Industry Standards ◽  
Girth Welding ◽  
Girth Welds ◽  
Welding Procedure

There has been a number of unexpected girth weld failures in newly constructed pipelines. Girth weld failures have also been observed in pre-service hydrostatic testing. Post-incident investigations indicated that the pipes met the requirements of industry standards, such as API 5L. The welds were qualified per accepted industry standards, such as API 1104. The field girth welding was performed, inspected, and accepted per industry standards, such as API 1104. Some of the traditional causes of girth weld failures, such as hydrogen cracks and high-low misalignment, were not a factor in these incidents. This paper starts with a review of the recent girth weld incidents. A few key features of a failed weld and their implications are examined. The characteristics of the recent failures is summarized, and the major contributing factors known to date are given. Some of the options to prevent future failures include (1) changes to the tensile properties of the pipes and enhanced hardenability, (2) welding options aimed at increasing the weld strength and minimizing heat-affected zone (HAZ) softening, and (3) reduction of stresses on girth welds. This paper focuses on the first two options. The trends of chemical composition and tensile properties of linepipe are reviewed. The potential contribution of these trends to the girth weld incidents is examined. Possible changes to the linepipe properties and necessary updates in the testing and qualification requirements of the linepipes are provided. Welding options beneficial to enhanced girth weld strain capacity are discussed. Possible revisions to welding procedure qualification requirements, aimed at achieving a minimum level of strain tolerance/capacity, are proposed. The application of previously developed tools in estimating the propensity of HAZ softening is reviewed.

Weld Strength Mismatch in Strain Based Flaw Assessment: Which Definition to Use?

2012 ◽  
Author(s):  
Stijn Hertelé ◽  
Wim De Waele ◽  
Rudi Denys ◽  
Matthias Verstraete ◽  
Koen Van Minnebruggen ◽  
...  
Keyword(s):  
Tensile Strength ◽  
Ultimate Tensile Strength ◽  
Driving Force ◽  
Experimental Validation ◽  
Weld Strength ◽  
Crack Driving Force ◽  
Strain Capacity ◽  
Strength Based ◽  
Key Factor ◽  
Girth Welds

Weld strength mismatch is a key factor in the strain based assessment of flawed girth welds under tension. A strength overmatching weld shields potential flaws within the weld itself from remotely applied deformations and consequently reduces crack driving force. Although this effect has been recognized for decades, different weld strength overmatch definitions exist and it is not yet fully established which of those is most relevant to a strain based flaw assessment. In an effort to clarify this unsolved question, the authors have performed a large series of parametric finite element analyses of curved wide plate tests. This paper provides an experimental validation of the model and subsequently discusses representative results. It is found that crack driving force is influenced by the shape of the pipe metals’ stress-strain curves, which influences the representativeness of two common mismatch definitions (based on yield strength and on ultimate tensile strength). It can be concluded from further observations that effects of strength mismatch on strain capacity of a flawed girth weld are best described on the basis of a flow stress, defined as the average of yield and ultimate tensile strength. Based on the observations, a framework for a new strain capacity equation is proposed.

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