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

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.

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

Journal of Pressure Vessel Technology ◽

10.1115/1.4029589 ◽

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.

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Enhancing Tensile Strain Capacity Through the Optimization of Weld Profiles

Volume 4: Production Pipelines and Flowlines; Project Management; Facilities Integrity Management; Operations and Maintenance; Pipelining in Northern and Offshore Environments; Strain-Based Design; Standards and Regulations ◽

10.1115/ipc2014-33589 ◽

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.

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

Volume 6B: Materials and Fabrication ◽

10.1115/pvp2013-97201 ◽

2013 ◽

Cited By ~ 3

Author(s):

Stijn Hertelé ◽

Rudi Denys ◽

Anthony Horn ◽

Koen Van Minnebruggen ◽

Wim De Waele

Keyword(s):

Flow Stress ◽

Tensile Strain ◽

Influence Factor ◽

Weld Strength ◽

Strain Capacity ◽

Weld Geometry ◽

Strain Behaviour ◽

Girth Welds ◽

Tearing Resistance ◽

Tensile Strain Capacity

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 overmatch. This framework is built around three parameters: the strain capacity of an evenmatching weldment, the sensitivity of strain capacity to weld flow stress overmatch and the strain capacity at gross section collapse. A parametric finite element study of curved wide plate 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 behaviour 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.

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

Volume 4: Pipelining in Northern and Offshore Environments; Strain-Based Design; Risk and Reliability; Standards and Regulations ◽

10.1115/ipc2012-90659 ◽

2012 ◽

Cited By ~ 4

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].

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Estimation of Tensile Strain Capacity of Vintage Girth Welds

10.1115/1.0003507v ◽

2021 ◽

Author(s):

Banglin Liu ◽

Bo Wang ◽

Yong-Yi Wang ◽

Otto Jan Huising

Keyword(s):

Tensile Strain ◽

Strain Capacity ◽

Girth Welds ◽

Tensile Strain Capacity

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Design of the Full Scale Experiments for the Testing of the Tensile Strain Capacity of X52 Pipes With Girth Weld Flaws Under Internal Pressure and Tensile Displacement

10.1115/ipc2014-33225 ◽

2014 ◽

Cited By ~ 1

Author(s):

Celal Cakiroglu ◽

Samer Adeeb ◽

J. J. Roger Cheng ◽

Millan Sen

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Internal Pressure ◽

Tensile Strain ◽

Oil And Gas ◽

Full Scale ◽

Element Analysis ◽

Simultaneous Application ◽

Strain Capacity ◽

Tensile Strain Capacity

Pipelines can be subjected to significant amounts of tensile forces due to geotechnical movements like slope instabilities and seismic activities as well as due to frost heave and thaw cycles in arctic regions. The tensile strain capacity εtcrit of pipelines is crucial in the prediction of rupture and loss of containment capability in these load cases. Currently the Oil and Gas Pipeline Systems code CSA Z662-11 0 contains equations for the prediction of εtcrit as a function of geometry and material properties of the pipeline. These equations resulted from extensive experimental and numerical studies carried out by Wang et al [2]–[6] using curved wide plate tests on pipes having grades X65 and higher. Verstraete et al 0 conducted curved wide plate tests at the University of Ghent which also resulted in tensile strain capacity prediction methods and girth weld flaw acceptability criteria. These criteria are included in the European Pipeline Research Group (EPRG) Tier 2 guidelines. Furthermore Verstrate et al 0 introduced a pressure correction factor of 0.5 in order to include the effect of internal pressure in the tensile strain capacity predictions in a conservative way. Further research by Wang et al with full scale pipes having an internal pressure factor of 0.72 also showed that εtcrit decreases in the presence of internal pressure [10]–[15]. In their work, Wang et al presented a clear methodology for the design of full scale experiments and numerical simulations to study the effect of internal pressure on the tensile strain capacity of pipes with girth weld flaws [10]–[15]. However, there has been limited testing to enable a precise understanding of the tensile strain capacity of pipes with grades less than X65 as a function of girth weld flaw sizes and the internal pressure. In this paper the experimental setup for the testing of grade X52 full scale specimens with 12″ diameter and ¼″ wall thickness is demonstrated. In the scope of this research 8 full scale specimens will be tested and the results will be used to formulate the tensile strain capacity of X52 pipes under internal pressure. The specimens are designed for the simultaneous application of displacement controlled tensile loading and the internal pressure. Finite element analysis is applied in the optimization process for the sizes of end plates and connection elements. Also the lengths of the full scale specimens are determined based on the results from finite element analysis. The appropriate lengths are chosen in such a way that between the location of the girth weld flaw and the end plates uniform strain zones could be obtained. The internal pressure in these experiments is ranging between pressure values causing 80% SMYS and 30% SMYS hoop stress. The end plates and connection elements of the specimens are designed in such a way that the tensile displacement load is applied with an eccentricity of 10% of the pipe diameter with the purpose of increasing the magnitude of tensile strains at the girth weld flaw location. The results of two full scale experiments of this research program are presented. The structural response from the experiments is compared to the finite element simulation. The remote strain values of the experiment are found to be higher than the εtcrit values predicted by the equations in 0.

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

2010 8th International Pipeline Conference, Volume 4 ◽

10.1115/ipc2010-31281 ◽

2010 ◽

Cited By ~ 1

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.

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Influence of Girth Weld Flaw and Pipe Parameters on the Critical Longitudinal Strain of Steel Pipes

Volume 3: Materials and Joining ◽

10.1115/ipc2012-90736 ◽

2012 ◽

Author(s):

Celal Cakiroglu ◽

Kajsa Duke ◽

Marwan El-Rich ◽

Samer Adeeb ◽

J. J. Roger Cheng ◽

...

Keyword(s):

Internal Pressure ◽

Wall Thickness ◽

Tensile Strain ◽

Critical Strain ◽

Pipe Wall ◽

Pipe Wall Thickness ◽

Strain Capacity ◽

Steel Pipes ◽

Tensile Strain Capacity ◽

Maximum Minimum

The design of steel pipelines against longitudinal loading induced by soil movement and temperature requires an understanding of the strain demand induced by the environment in comparison with the strain resistance of the pipes. Girth weld flaws have been identified as the potential location of failure under longitudinal tensile strains due to being the least ductile. Strain based design for the prediction of the longitudinal tensile strain capacity of steel pipes have been extensively studied by Wang, et al and included in the Canadian standards association code of practice CSA Z662.11 [1]. The extensive track record of tests have culminated into two sets of equations for the critical strain in girth welded pipes with surface breaking and buried defects as functions of the different pipe and flaw parameters. The CSA Z662.11 strain capacity equations were developed using wide plate tests with the obvious limitation of the inability to consider the effect of the internal pressure of the pipe. However, recent studies by Wang et al led to the development of a new set of equations that predict the tensile strain capacity for pipes with an internal pressure factor of 0.72. This paper analyses the two critical strain equations in CSA Z662-11 to understand the effect of different girth weld flaw and pipe parameters on the expected behavior of pipes. Also the critical strain equations developed in [2]have been analysed and compared to the equations in CSA Z662-11. Using the equations in CSA Z662-11, a 34 and 36 full factorial experimental design was conducted for the planar surface-breaking defect and the planar buried defect respectively. For the case of surface breaking defects the dependence of the tensile strain capacity (εtcrit) on apparent CTOD toughness (δ), ratio of defect height to pipe wall thickness (η), ratio of yield strength to tensile strength (λ) and the ratio of defect length to pipe wall thickness (ξ) has been studied. εtcrit has been evaluated at the maximum, minimum and intermediate values of each parameter according to the allowable ranges given in the code which resulted in the evaluation of εtcrit for 81 different combinations of the parameters. The average value of εtcrit at the maximum, minimum and middle value of each parameter has been calculated. The visualization of the results showed that η, δ and ξ have the most significant effect on εtcrit among the four parameters for the case of surface breaking defect. Similarly for buried defects the dependence of εtcrit on δ, η, λ, ξ, and the pipe wall thickness (t) has been studied. The evaluation of εtcrit for all possible combinations of the maximum, intermediate and minimum values of the 6 parameters resulted in εtcrit values for 729 different combinations. The variation of the average εtcrit over the maximum, intermediate and minimum values of the parameters showed that δ, ψ, ξ and η are the parameters having the greatest effect on εtcrit for the case of a buried defect. Further investigations could be carried out to determine suitable upper and lower bounds for the parameters for which no bounded range is defined in the CSA Z662-11 code.

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Development of a Tensile Strain Capacity Predictive Model for American Petroleum Institute 5L X42 Welded Vintage Pipelines

Journal of Pressure Vessel Technology ◽

10.1115/1.4047561 ◽

2020 ◽

Vol 142 (6) ◽

Author(s):

Sylvester Agbo ◽

Ali Imanpour ◽

Yong Li ◽

Muntaseer Kainat ◽

Nader Yoosef-Ghodsi ◽

...

Keyword(s):

Regression Analysis ◽

Predictive Model ◽

Nonlinear Regression ◽

Tensile Strain ◽

Biaxial Loading ◽

American Petroleum Institute ◽

Nonlinear Regression Analysis ◽

Strain Capacity ◽

Integrity Assessment ◽

Tensile Strain Capacity

Abstract Pipelines can be exposed to a wide variety of loads, depending on the environments and the area of application. These loads may impose large longitudinal plastic strain on pipelines, which could constitute a significant threat to the structural capacity of the pipeline. Reliable calibration of the strain capacity of pipelines plays an important role in the strain-based design (SBD) method. In this paper, a tensile strain capacity (TSC) predictive model (an equation) for welded X42 vintage pipes has been developed by conducting nonlinear parametric analysis followed by nonlinear regression analysis. First, our previously validated extended finite element method (XFEM) model was used to demonstrate the applicability of the XFEM in simulating full-scale ductile fracture response of pipelines subjected to biaxial loading, using pressurized American Petroleum Institute (API) 5L X42 vintage pipes subjected to four-point bending. Second, a parametric study investigating the effects of pipe and defect geometries as well as loading on the pipe TSC is presented. The nonlinear parameterization using XFEM was conducted in abaqus/standard. The TSC trends obtained for the various parameters considered were examined to derive appropriate individual variable functions for each parameter while taking any significant interactions between the parameters into consideration. Also, a nonlinear regression analysis is employed to develop a nonlinear semi-empirical model for predicting the TSC. The results obtained from the developed TSC predictive model (TSCvin.) was compared with those evaluated using the validated XFEM models. The results showed good agreement. Finally, statistical analysis was conducted to ensure the model is unbiased and predicts conservative TSCs by modifying the model using probabilistic error analysis. The modified model is capable of increasing the confidence level in the predicted TSC hence becoming a practical tool for reliable prediction of TSC of X42 vintage pipes needed for conducting pipeline integrity assessment. This modified predictive model is useful in practical applications because it provides a quantifiable degree of conservatism and reliability to the predicted TSCs.

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