Estimation of Tensile Strain Capacity of Vintage Girth Welds

2020 ◽  
Author(s):  
Bo Wang ◽  
Banglin Liu ◽  
Yong-Yi Wang ◽  
Otto Jan Huising
Keyword(s):  
Driving Force ◽  
Tensile Strain ◽  
Software Tool ◽  
Ground Movement ◽  
Small Scale ◽  
Crack Driving Force ◽  
Strain Capacity ◽  
Girth Welds ◽  
The Impact ◽  
Tensile Strain Capacity

Abstract Being able to estimate the tensile strain capacity (TSC) of vintage girth welds is sometimes necessary for the integrity management of vintage pipelines. Assessing girth weld integrity could be a top priority after a confirmed ground movement event. Decisions may also be needed about the disposition of a girth weld when weld anomalies are found. Typical fitness-for-service (FFS) procedures, such as API 1104 Annex A and API 579/ASME FFS-1, generally target materials under nominally elastic conditions and strain demands less than 0.2%. These procedures may produce overly conservative results when the strain demand exceeds 0.2%. This paper summarizes the development and validation of a TSC estimation tool for vintage girth welds under PRCI funding. The work consisted of three components: the development of a TSC model for vintage girth welds, the implementation of the model into a software tool, and the experimental validation of the performance of the tool using curved wide plate (CWP) tests. The TSC model was developed following the procedures established through a previous PRCI-PHMSA cofounded work. Finite element analyses (FEA) were performed to obtain a crack-driving force database while considering the salient features of vintage girth welds, such as larger weld caps and weld strength mismatch levels. The TSC model was then derived from the crack-driving force database using apparent toughness values representative of vintage girth welds. A graphical user interface (GUI) and a user manual were developed to facilitate the application of the TSC model. The software tool produces TSC estimates based on geometry, material, loading, and flaw characteristics of a girth weld. For inputs that might not have readily available values, recommended values are provided. The tool allows the evaluation of the impact of various input parameters on TSC. The performance of the TSC estimation tool was evaluated against eight purposely designed CWP tests. Accompanying small-scale material characterization tests, including chemical composition, round bar tensile, microhardness, and Charpy impact tests, were performed to provide additional inputs for the evaluation of the tool. The tool is shown to provide reasonably conservative estimates for TSC. An example problem is presented to demonstrate the application of the tool. Gaps and future work to improve the tool are highlighted at the end of the paper.

Multi-Tier Tensile Strain Models for Strain-Based Design: Part 2 — Development and Formulation of Tensile Strain Capacity Models

2012 ◽  
Author(s):  
Ming Liu ◽  
Yong-Yi Wang ◽  
Yaxin Song ◽  
David Horsley ◽  
Steve Nanney
Keyword(s):  
Driving Force ◽  
Tensile Strain ◽  
Weld Strength ◽  
Experiment Data ◽  
Pipe Wall Thickness ◽  
Crack Driving Force ◽  
Strain Capacity ◽  
Welding Processes ◽  
Tensile Strain Capacity

This is the second paper in a three-paper series related to the development of tensile strain models. The fundamental basis of the models [1] and evaluation of the models against experiment data [2] are presented in two companion papers. This paper presents the structure and formulation of the models. The philosophy and development of the multi-tier tensile strain models are described. The tensile strain models are applicable for linepipe grades from X65 to X100 and two welding processes, i.e., mechanized GMAW and FCAW/SMAW. The tensile strain capacity (TSC) is given as a function of key material properties and weld and flaw geometric parameters, including pipe wall thickness, girth weld high-low misalignment, pipe strain hardening (Y/T ratio), weld strength mismatch, girth weld flaw size, toughness, and internal pressure. Two essential parts of the tensile strain models are the crack driving force and material’s toughness. This paper covers principally the crack driving force. The significance and determination of material’s toughness are covered in the companion papers [1,2].

Tensile Strain Capacity of X80 Pipeline Under Tensile Loading With Internal Pressure

2010 ◽  
Author(s):  
Satoshi Igi ◽  
Takahiro Sakimoto ◽  
Nobuhisa Suzuki ◽  
Ryuji Muraoka ◽  
Takekazu Arakawa
Keyword(s):  
Internal Pressure ◽  
Driving Force ◽  
Tensile Strain ◽  
Surface Defects ◽  
Axial Loading ◽  
Element Analysis ◽  
Crack Driving Force ◽  
Strain Capacity ◽  
High Internal Pressure ◽  
Tensile Strain Capacity

This paper presents the results of experimental and finite element analysis (FEA) studies focused on the tensile strain capacity of X80 pipelines under large axial loading with high internal pressure. Full-pipe tensile test of girth welded joint was performed using high-strain X80 linepipes. Curved wide plate (CWP) tests were also conducted to verify the strain capacity under a condition of no internal pressure. The influence of internal pressure was clearly observed in the strain capacity. Critical tensile strain is reduced drastically due to the increased crack driving force under high internal pressure. In addition, SENT tests with shallow notch specimens were conducted in order to obtain a tearing resistance curve for the simulated HAZ of X80 material. Crack driving force curves were obtained by a series of FEA, and the critical global strain of pressurized pipes was predicted to verify the strain capacity of X80 welded linepipes with surface defects. Predicted strain showed good agreement with the experimental results.

scholarly journals The influence of material anisotropy and spiral welding on tensile strain capacity of spiral welded pipes

2015 ◽  
Vol 6 (3) ◽  
pp. 9
Author(s):  
Michiel De Backer ◽  
Koen Van Minnebruggen ◽  
Wim De Waele
Keyword(s):  
Driving Force ◽  
Tensile Strain ◽  
Pipeline Steel ◽  
Experimental Testing ◽  
Outcome Analysis ◽  
Mode Iii ◽  
Plane Shear ◽  
Crack Driving Force ◽  
Strain Capacity ◽  
Tensile Strain Capacity

The longitudinal strain capacity of spiral welded pipelines displays to some extents unexplained behaviour. Therefore, they are not (yet) used extensively in offshore applications and harsh conditions, demanding a strain based design. An important factor that influences the tensile strain capacity is the quantity of anisotropy in terms of strength and toughness. Starting from an anisotropic hot rolled highstrength steel skelp, the process of helical forming and post-treating of the pipe adds heterogeneity and changes the level of anisotropy of the product. A parameter that should be examined with respect to anisotropy is the crack driving force, a measure for the toughness of the pipeline steel. Additional to the mode I loading (opening of the crack), the mode III component drives the in-plane shear motion of a crack in the spiral weld when the pipe is subjected to longitudinal deformation. This action, not present inlongitudinal welded pipes, shows a decreasing contribution with increasing plasticity. FE simulations have demonstrated a rise of crack driving force in anisotropic cases with respect to an isotropic reference. However, exact data and variation of various parameters, along with experimental testing need to be conducted. The outcome analysis of such simulations and tests can validate existing models, or help create a better understanding of anisotropic and heterogenic influences on the tensile strain capacity of spiral welded pipes.

Tensile Strain Capacity of X80 Girth Welded Linepipes and Crack Growth Analysis

2012 ◽  
Author(s):  
Satoshi Igi ◽  
Takahiro Sakimoto ◽  
Shigeru Endo ◽  
Ryuji Muraoka ◽  
Takekazu Arakawa
Keyword(s):  
Internal Pressure ◽  
Driving Force ◽  
Tensile Strain ◽  
Axial Loading ◽  
Crack Driving Force ◽  
Strain Capacity ◽  
Strain Behavior ◽  
Welded Pipe ◽  
High Internal Pressure ◽  
Tensile Strain Capacity

This paper examines the tensile strain capacity of girth welded pipelines. A pressurized and no pressurized full-pipe tension tests were conducted together with FE analyses in order to investigate the strain behavior of pipe under large axial loading with high internal pressure. The critical tensile strain drastically decreased under a high internal pressure condition. Single edge notch tension (SENT) tests with shallow notched specimens were also performed to obtain the material resistance curve (R-curve), and a series of FE analyses was conducted to obtain the crack driving force for ductile crack propagation. The R-curve and crack driving force curve were used in predicting the tensile strain limit of X80 girth welded pipe with a surface defect in the HAZ. The predicted critical tensile strain showed good agreement with that obtained in the pressurized and no pressurized full-pipe tension test.

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

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.

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.

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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