Effects of High-Low Misalignment on Girth Weld Integrity

2014 ◽  
Author(s):  
Yong-Yi Wang ◽  
Kunal Kotian ◽  
Steve Rapp
Keyword(s):  
Load Capacity ◽  
Weld Strength ◽  
Contributing Factors ◽  
Element Analysis ◽  
Absolute Level ◽  
Service Failures ◽  
Weld Profile ◽  
Circumferential Extent ◽  
Girth Welds ◽  
The Impact

High levels of high-low misalignment in pipeline girth welds have been identified as one of the possible contributing factors to some of the recent pre-service hydrostatic test failures or subsequent service failures. However, pipeline service experience indicates that nominally defect-free girth welds with high levels of misalignment and proper weld profiles can provide satisfactory long-term service. In this paper, recent analytical and experimental work aimed at understanding the impact of high-low misalignment in girth welds is described. In nominally defect-free welds, the performance of the welds is found to be predominantly determined by the misalignment ratio, weld strength mismatch ratio, and the weld profile. Iso-load-capacity relations are developed through finite element analysis (FEA) to capture the interdependence of those key parameters. The analysis procedure is validated by cross-weld tensile testing of girth welds with various levels of misalignment and weld strength mismatch. The effects of the circumferential extent of misalignment, alternatively termed local misalignment, are also analyzed. The effects of misalignment in girth weld with planar flaws are examined in the context of the tensile strain capacity. The analytical and experimental evidence indicate that the absolute level of misalignment is not a sole indicator of girth weld performance. Weld transition profile, pipe wall thickness, and weld strength mismatch all play an important role. With proper weld profiles, minimal or small reduction of load capacity is observed even at very high levels of misalignment. Work is continuing to further examine the effects of high-low misalignment with a goal of making practical recommendations to be included in codes and standards.

Comparison of Plastic Collapse Solutions for Surface Breaking Flaws in Standard Assessment Procedures With FEA

2013 ◽  
Author(s):  
Rajil Saraswat ◽  
Ali Mirzaee-Sisan
Keyword(s):  
High Fracture Toughness ◽  
Plastic Collapse ◽  
High Fracture ◽  
Element Analysis ◽  
Integrity Assessment ◽  
Standard Assessment ◽  
Definition Of ◽  
Girth Welds ◽  
Assessment Procedures ◽  
The Impact

Engineering Critical Assessment (ECA) procedures generally use the Failure Assessment Diagram (FAD) concept for integrity assessment of components containing flaws. An FAD assessment is described by Kr and Lr values, where Kr reflects the toughness of the material while Lr measures the proximity to plastic collapse. Nowadays pipeline girth welds generally have high fracture toughness (Kmat) and it can be argued that plastic collapse is the governing failure mode. The definition of plastic collapse can affect the determination of the Lr parameter and should be carefully chosen. In the present work finite element analysis has been carried out to evaluate the collapse load under local collapse and global collapse conditions. These have been compared with the solutions available in the BS7910 and R6 procedures and the differences have been highlighted. The impact of the choice of plastic collapse solution on the crack driving force has been analysed.

Improved Linepipe Specifications and Welding Practice for Resilient Pipelines

2020 ◽  
Author(s):  
Yong-Yi Wang ◽  
Dan Jia ◽  
Dave Warman ◽  
David L. Johnson ◽  
Steve Rapp
Keyword(s):  
Construction Projects ◽  
Tensile Tests ◽  
Weld Strength ◽  
Contributing Factors ◽  
The North ◽  
Pipe Replacement ◽  
Girth Welds ◽  
Welding Procedure ◽  
Internal Procedures ◽  
Welding Processes

Abstract At least 10 girth weld incidents in newly constructed pipelines are known to have occurred in North America. More than 30 girth weld incidents in newly constructed pipes have been identified worldwide. A review of the North American incidents identified a few main contributing factors: (1) weld strength undermatching, (2) heat-affected zone (HAZ) softening, and (3) elevated stresses/strains from normal settlement and other loads. Weld bevel geometries of manual welding processes that favor plastic straining along the softened HAZ and low strength root passes were also compounding contributing factors. Prior publications focused on the industry practices that led to the formation of those contributing factors. This paper covers the enhanced linepipe specifications and improved welding practice that aim to reduce the risk of similar girth weld incidents, thus leading to more resilient pipelines. The enhanced linepipe specifications include interim recommendations that aim to limit the upper-bound longitudinal strength for a given pipe grade and reduce the linepipe steels’ susceptibility to HAZ softening. The implementation of the interim recommendations is assisted by allowing alternative hoop tensile tests. The improved welding practice includes (1) the selection of welding procedures, including consumables, that minimizes the likelihood of weld strength undermatching and reduces the propensity for HAZ softening and (2) welding procedure qualification tests and requirements for the production of strain-resistant girth welds. The recommendations covered in this paper principally target new pipeline construction projects but are also applicable to pipe replacement projects. It is expected that pipeline operators would incorporate the recommendations in their internal procedures and work with welding contractors to execute the recommendations. The improved linepipe specifications and welding practice are expected to increase the resilience of pipelines subjected to realistic construction and in-service loads. The implementation of the recommendations requires changes to some long-standing industry practices and can only occur with collaborative efforts from all stakeholders.

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.

Significance of HAZ Softening on Strain Concentration and Crack Driving Force in Pipeline Girth Welds

2005 ◽  
Author(s):  
Ming Liu ◽  
Yong-Yi Wang ◽  
David Horsley
Keyword(s):  
Driving Force ◽  
Crack Tip ◽  
Functionally Graded ◽  
Weld Strength ◽  
Heat Affect Zone ◽  
Crack Driving Force ◽  
Strain Concentration ◽  
Symmetric Deformation ◽  
Girth Welds ◽  
The Impact

Modern micro-alloyed, control-rolled TMCP steels generally have good strength, high toughness, and good weldability. However, these valuable properties come along with certain undesirable features, such as low strain hardening (high yield to tensile ratio), low ductility as measured by uniform elongation (elongation at ultimate tensile strength), and possible heat-affect-zone (HAZ) softening due to reduced hardenability. These undesirable features are particularly detrimental in strain-based design of pipelines. Although the phenomenon of HAZ softening has been known for a long time, the impact of the HAZ softening on the integrity of pipeline girth welds was not well understood. The objective of this work was to understand the impact of HAZ softening on girth weld integrity. Finite element analysis was conducted to investigate the effects of HAZ softening on crack driving force and strain concentration in girth welds under longitudinal tensile loading. The material properties of WM and BM were obtained from an X100 girth weld. The HAZ was modeled as a functionally graded material based on its measured hardness. The models contained surface-breaking defects located at the fusion boundary simulating lack-of-sidewall fusion defects. The analysis results showed that increased CTOD driving force can be expected due to HAZ softening. The extent of increase is positively related to the width and degree of softening of the HAZ. On the other hand, weld strength overmatch reduces the total CTOD driving force. The strain concentration in the softened HAZ circumferentially remote from a surface-breaking defect was small. However, high strain concentration existed over the circumference covering the length of the defect. This concentration was primarily attributable to the existence of the defect and secondarily to the HAZ softening. One significant result from this work was that the relative increase in CTOD driving force and strain concentration due to HAZ softening was independent of defect size. In other words, on a relative basis, HAZ softening was no worse on large defects than on smaller defects. This result should be helpful in rationalizing the effects of HAZ softening for defects of various sizes that exist in field applications. Non-symmetrical crack-tip deformation occurred with softened HAZ. A large proportion of the crack-tip deformation was located in the HAZ. The magnitude of non-symmetric deformation increased with the increase of HAZ width and degree of softening. Even higher degree of non-symmetric deformation occurred with the increase of weld overmatching level. The structural significance of reduced total CTOD driving force and increased un-symmetric deformation at the crack tip due to weld strength overmatch warrants further study. The reduction in total CTOD driving force alone does not necessarily results in a higher level of weld integrity if the “intrinsic” toughness of the HAZ is substantially lower than the weld metal.

Integrity Assessment of Interaction of Dents With Residual Stresses of Welds Using Probabilistic Design Analysis

2012 ◽  
Author(s):  
Husain Mohammed Al-Muslim ◽  
A. F. M. Arif
Keyword(s):  
Residual Stresses ◽  
Weld Line ◽  
Design Analysis ◽  
Probabilistic Design ◽  
Stress Range ◽  
Element Analysis ◽  
Integrity Assessment ◽  
Girth Welds ◽  
Longitudinal Welds ◽  
The Impact

The interaction of dent with the weld has always been considered a threat to the pipeline. Therefore, Codes and procedure impose more stringent rules than normally applied to plain dents. For example, ASME B31.8 considers dents deeper than 2% and interacting with welds to be injurious and requires an engineering assessment if they are to be left without repair. The objective of this paper is to present a new method of assessment that utilizes finite element analysis couples with probabilistic design analysis. In this paper, the impact of interaction of dent with longitudinal welds and girth welds will be under static and cyclic pressure conditions will be evaluated. The combined effects are included in a single FEA model and the welds will be simulated by imposing initial residual stresses along the weld line. The first part of the paper uses deterministic analysis to present strain and stress contours at the end of indentation stage as well as the stress range and fatigue cycles at the end of pressure cycle stage for a longitudinal weld case as well as girth weld case. The second part uses probabilistic design analysis with variable geometry, material and pressure in addition to the weld location and residual stress value to determine the sensitivity of the strain, stress, and stress range to the input. Two probabilistic design analyses are conducted: one for the interaction of dent with longitudinal welds, the other for the interaction of dent with girth welds.

Finite Element Analysis and Calculation of Load Capacity on Aerostatic Thrust Bearing

2011 ◽  
Vol 188 ◽  
pp. 566-571
Author(s):  
P.C. Shu ◽  
S.H. Xiao ◽  
H. Wu
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
High Speed ◽  
Thrust Bearing ◽  
Load Capacity ◽  
Hydrodynamic Effect ◽  
Element Analysis ◽  
Ultra High Speed ◽  
The Impact ◽  
Aerostatic Spindle

For the design and application of ultra-high speed aerostatic spindle, it is often difficult to determine the load capacity of bearing gas film because of nonlinear problem, especially when the gas film is very thin. As ultra-high speed aerostatic spindle is working, rotational velocity of spindle ranges up to 300,000 rpm, while Reynolds number of air flow also increases in aerostatic bearing, so we need to consider the impact of gas inertia on the load capacity. In order to improve design accuracy of ultra-high speed aerostatic spindle, it is vitally necessary to consider hydrodynamic effect of aerostatic bearings. By using finite element analysis software ANSYS software as analysis platform, through finite element the analysis of the internal flow field of aerostatic thrust bearing, this paper obtains the relationship of rotation speed and load capacity of aerostatic thrust bearing.

Efficacy of Crisis Intervention

Crisis ◽  
1999 ◽  
Vol 20 (2) ◽  
pp. 78-85 ◽  
Author(s):  
Thomas Reisch ◽  
Petra Schlatter ◽  
Wolfgang Tschacher
Keyword(s):  
Crisis Intervention ◽  
Intervention Program ◽  
Suicide Ideation ◽  
Indirect Evidence ◽  
Well Being ◽  
Term Therapy ◽  
Contributing Factors ◽  
Step Therapy ◽  
Long Term Therapy ◽  
The Impact

This study assesses the efficacy of the treatment approach implemented in the Bern Crisis Intervention Program, where particular emphasis is placed on the remediation of suicide ideation and suicidal behavior, and depression, fear, and phobia are generally considered to be contributing factors. Four questionnaires addressing psychopathology, emotional well-being, social anxiety, and personality were administered prior to and after the treatment of 51 patients over a period of 2 to 3 weeks. The reduction of symptoms contributing to suicidal ideation and behavior was interpreted as indirect evidence of an antisuicidal effect of the program. Significant improvements were found in the psychopathology ratings, with depression and anxiety showing the largest reductions. The impact on personality and social phobia, however, was only moderate, and on average patients still exhibited symptoms after attending the program. This residual symptomatology points to the necessity of introducing a two-step therapy approach of intensive intervention targeted at the precipitating causes of the crisis, augmented by long-term therapy to treat underlying problems.

scholarly journals Potential and limitations of finite element modelling in assessing structural integrity of coralline algae under future global change

2015 ◽  
Vol 12 (19) ◽  
pp. 5871-5883 ◽  
Author(s):  
L. A. Melbourne ◽  
J. Griffin ◽  
D. N. Schmidt ◽  
E. J. Rayfield
Keyword(s):  
Climate Change ◽  
Finite Element ◽  
Structural Integrity ◽  
Geometric Model ◽  
Algal Growth ◽  
Coralline Algae ◽  
Rocky Shores ◽  
Element Analysis ◽  
Scan Data ◽  
The Impact

Abstract. Coralline algae are important habitat formers found on all rocky shores. While the impact of future ocean acidification on the physiological performance of the species has been well studied, little research has focused on potential changes in structural integrity in response to climate change. A previous study using 2-D Finite Element Analysis (FEA) suggested increased vulnerability to fracture (by wave action or boring) in algae grown under high CO2 conditions. To assess how realistically 2-D simplified models represent structural performance, a series of increasingly biologically accurate 3-D FE models that represent different aspects of coralline algal growth were developed. Simplified geometric 3-D models of the genus Lithothamnion were compared to models created from computed tomography (CT) scan data of the same genus. The biologically accurate model and the simplified geometric model representing individual cells had similar average stresses and stress distributions, emphasising the importance of the cell walls in dissipating the stress throughout the structure. In contrast models without the accurate representation of the cell geometry resulted in larger stress and strain results. Our more complex 3-D model reiterated the potential of climate change to diminish the structural integrity of the organism. This suggests that under future environmental conditions the weakening of the coralline algal skeleton along with increased external pressures (wave and bioerosion) may negatively influence the ability for coralline algae to maintain a habitat able to sustain high levels of biodiversity.

Impact Load Buffering Method Based on Stress Wave Attenuation Principle

2019 ◽  
Vol 11 (02) ◽  
pp. 1950019 ◽  
Author(s):  
Lin Gan ◽  
He Zhang ◽  
Cheng Zhou ◽  
Lin Liu
Keyword(s):  
Stress Wave ◽  
Wave Attenuation ◽  
Impact Load ◽  
Dynamics Simulation ◽  
Scanning System ◽  
Isolation Method ◽  
Element Analysis ◽  
System A ◽  
High Emission ◽  
The Impact

Rotating scanning motor is the important component of synchronous scanning laser fuze. High emission overload environment in the conventional ammunition has a serious impact on the reliability of the motor. Based on the theory that the buffer pad can attenuate the impact stress wave, a new motor buffering Isolation Method is proposed. The dynamical model of the new buffering isolation structure is established by ANSYS infinite element analysis software to do the nonlinear impact dynamics simulation of rotating scanning motor. The effectiveness of Buffering Isolation using different materials is comparatively analyzed. Finally, the Macht hammer impact experiment is done, the results show that in the experience of the 70,000[Formula: see text]g impact acceleration, the new buffering Isolation method can reduce the impact load about 15 times, which can effectively alleviate the plastic deformation of rotational scanning motor and improve the reliability of synchronization scanning system. A new method and theoretical basis of anti-high overload research for Laser Fuze is presented.

scholarly journals Experimental studies on the possibility of using a pulsed laser for spot welding of thin metallic foils

2020 ◽  
Vol 10 (1) ◽  
pp. 674-680
Author(s):  
Piotr Sęk
Keyword(s):  
Experimental Studies ◽  
Pulsed Laser ◽  
Welding Process ◽  
Pulse Mode ◽  
Weld Strength ◽  
Spot Welds ◽  
Butt Welding ◽  
Strength Tests ◽  
Metallic Foils ◽  
The Impact

AbstractThe purpose of the experiment was to study the influence of the laser beam in pulse mode on metallic foils in order to obtain a spot weld. The welding process was carried out using the overlap weld method, using spot welds in various quantities. The Nd - YAG BLS 720 pulsed laser was used to conduct the experiment. The impact of the number of spot welds on the value of force needed to break the sample was examined. A number of measurements were carried out to determine the best process parameters. Butt welding and overlap welding were also performed using a continuous weld consisting of spot welds. Weld strength tests were performed to select the most appropriate parameters for the process under consideration.

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