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.

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.

Dissimilar Girth Joints Under Combined Cyclic Thermal and Mechanical Loading: Experimental and Numerical Investigations

2004 ◽  
Author(s):  
Ralf Mohrmann ◽  
Vale´rie Denner ◽  
Thomas Hollstein
Keyword(s):  
Finite Element ◽  
Mechanical Loading ◽  
Low Cycle Fatigue ◽  
Material Model ◽  
Tensile Tests ◽  
Base Metals ◽  
Creep Tests ◽  
Numerical Investigations ◽  
Girth Welds ◽  
Welding Processes

Experimental and numerical investigations were conducted to qualify dissimilar girth welds in tubes fabricated in 9% Chromium steels T91 and E911 and the austenitic steel X3 CrNiMoN 17-13 for service temperatures up to 625°C [1]. Girth welds were produced on tubes by different welding processes such as automatic and manual TIG welding as well as friction welding. Ni-based consumables (NiCr20Nb) were used in the arc welding processes and NiCr15Fe transition rings in case of friction welded joints. The girth welds were investigated in the annealed as well as in the quenched and tempered post weld condition. The tubes were tested under combined cyclic thermal and mechanical loading [1]. A full material characterization (tensile tests at different strain rates, creep tests, low cycle fatigue tests at temperatures up to 650°C) for base metals and weld metals as well as weld thermal simulated heat affected zones were performed. This data was used to apply a non-isothermal viscoplastic Chaboche-type material model. This model describes primary, secondary and tertiary creep as well as the softening and hardening during cyclic loading. The viscoplastic model was implemented in the finite element code ABAQUS. Each material zone (base metals, three different heat affected zone materials, weld metal) was treated separately. Various finite element simulations were performed to analyze and predict the in-service behavior of the welded tubes. The comparison of long term laboratory tests with these predictions are promising.

Study on the Mismatched Girth Welds of X80 Line Pipes

2006 ◽  
Author(s):  
Chuanjing Zhuang ◽  
Yaorong Feng ◽  
Chunyong Huo
Keyword(s):  
Fracture Resistance ◽  
Weld Seam ◽  
Limit Load ◽  
Defect Size ◽  
Weld Strength ◽  
High Grade ◽  
Critical Defect ◽  
Critical Defect Size ◽  
Girth Welds ◽  
Welding Procedure

X80 linepipes are going to be widely used for gas transmission pipelines in China. The welding procedure for girth weld is very critical to the safety of the X80 pipeline. In this paper, different welding procedures are employed to obtain three different mismatched girth welds, with which tests were carried out to analyze effect of mismatch on the properties of girth welds. Plastic deformation and critical defect size (δc) is calculated and discussed for the different mismatched girth welds utilizing both FAD and FEM methods. Overmatched or evenmatched girth weld is recommended for high grade linepipes because overmatched weld has the advantages of improving limit load and enhencing fracture resistance of pipe girth welds. But the increase of weld strength may reduce the resistance of the weld to HIC and SCC, as well as make the field weld operation more difficult. The level of mismatch shouldn’t be too high because too much weld seam strength will not only be a way of waste, but also decrease weld resistance to HIC cracks.

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].

Integrity Management of Ground Movement Hazards

2016 ◽  
Author(s):  
Yong-Yi Wang ◽  
Don West ◽  
Douglas Dewar ◽  
Alex McKenzie-Johnson ◽  
Millan Sen
Keyword(s):  
Management Program ◽  
Ground Movement ◽  
Tensile Failure ◽  
Weld Strength ◽  
Factors Affecting ◽  
Ground Movements ◽  
Decision Points ◽  
Starting Point ◽  
Integrity Management ◽  
Girth Welds

Ground movements, such as landslides and subsidence/settlement, can pose serious threats to pipeline integrity. The consequence of these incidents can be severe. In the absence of systematic integrity management, preventing and predicting incidents related to ground movements can be difficult. A ground movement management program can reduce the potential of those incidents. Some basic concepts and terms relevant to the management of ground movement hazards are introduced first. A ground movement management program may involve a long segment of a pipeline that may have a threat of failure in unknown locations. Identifying such locations and understanding the potential magnitude of the ground movement is often the starting point of a management program. In other cases, management activities may start after an event is known to have occurred. A sample response process is shown to illustrate key considerations and decision points after the evidence of an event is discovered. Such a process can involve fitness-for-service (FFS) assessment when appropriate information is available. The framework and key elements of FFS assessment are explained, including safety factors on strain capacity. The use of FFS assessment is illustrated through the assessment of tensile failure mode. Assessment models are introduced, including key factors affecting the outcome of an assessment. The unique features of girth welds in vintage pipelines are highlighted because the management of such pipelines is a high priority in North America and perhaps in other parts of the worlds. Common practice and appropriate considerations in a pipeline replacement program in areas of potential ground movement are highlighted. It is advisable to replace pipes with pipes of similar strength and stiffness so the strains can be distributed as broadly as possible. The chemical composition of pipe steels and the mechanical properties of the pipes should be such that the possibility of HAZ softening and weld strength undermatching is minimized. In addition, the benefits and cost of using the workmanship flaw acceptance criteria of API 1104 or equivalent standards in making repair and cutout decisions of vintage pipelines should be evaluated against the possible use of FFS assessment procedures. FFS assessment provides a quantifiable performance target which is not available through the workmanship criteria. However, necessary inputs to perform FFS assessment may not be readily available. Ongoing work intended to address some of the gaps is briefly described.

Effects of Weld Strength Heterogeneity on Crack Driving Force in Stress and Strain Based Design Scenarios

2014 ◽  
Author(s):  
Stijn Hertelé ◽  
Noel O’Dowd ◽  
Matthias Verstraete ◽  
Koen Van Minnebruggen ◽  
Wim De Waele
Keyword(s):  
Driving Force ◽  
Large Scale ◽  
Limit State ◽  
Weld Strength ◽  
Force Response ◽  
Crack Driving Force ◽  
Key Factor ◽  
Weld Properties ◽  
Girth Welds ◽  
Strain Hardening Behavior

Weld strength mismatch is a key factor with respect to the assessment of a flawed girth weld. However, it is challenging to assign a single strength mismatch value to girth welds, which are generally heterogeneous in terms of constitutive behavior. The authors have recently developed a method (‘homogenization’) to account for weld strength property variations in the estimation of crack driving force response and the corresponding tensile limit state. This paper separately validates the approach for stress based and strain based assessments. Whereas homogenization is reliably applicable for stress based assessments, the strain based crack driving force response is highly sensitive to effects of actual heterogeneous weld properties. The sensitivity increases with increased weld width and decreased strain hardening behavior. For strain based design, a more accurate methodology is desirable, and large scale testing and/or advanced numerical modeling remain essential.

On the Mechanics of Residual Stresses in Girth Welds

2006 ◽  
Vol 129 (3) ◽  
pp. 345-354 ◽  
Author(s):  
P. Dong
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Relative Importance ◽  
Stress Distributions ◽  
Unified Framework ◽  
Joint Geometry ◽  
Weld Residual Stress ◽  
Girth Welds ◽  
Welding Procedure

In this paper, some of the important controlling parameters governing weld residual stress distributions are presented for girth welds in pipe and vessel components, based on a large number of residual stress solutions available to date. The focus is placed upon the understanding of some of the overall characteristics in through-wall residual stress distributions and their generalization for vessel and pipe girth welds. In doing so, a unified framework for prescribing residual stress distributions is outlined for fitness-for-service assessment of vessel and pipe girth welds. The effects of various joint geometry and welding procedure parameters on through thickness residual stress distributions are also demonstrated in the order of their relative importance.

scholarly journals Prediction of Residual Stresses in a Multipass Pipe Weld by a Novel 3D Finite Element Approach

2018 ◽  
Author(s):  
Hui Huang ◽  
Jian Chen ◽  
Blair Carlson ◽  
Hui-Ping Wang ◽  
Paul Crooker ◽  
...  
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
High Performance ◽  
Large Scale ◽  
Graphics Processing Unit ◽  
Computational Cost ◽  
Three Dimensional ◽  
Processing Unit ◽  
Girth Welds ◽  
Welding Processes

Due to enormous computation cost, current residual stress simulation of multipass girth welds are mostly performed using two-dimensional (2D) axisymmetric models. The 2D model can only provide limited estimation on the residual stresses by assuming its axisymmetric distribution. In this study, a highly efficient thermal-mechanical finite element code for three dimensional (3D) model has been developed based on high performance Graphics Processing Unit (GPU) computers. Our code is further accelerated by considering the unique physics associated with welding processes that are characterized by steep temperature gradient and a moving arc heat source. It is capable of modeling large-scale welding problems that cannot be easily handled by the existing commercial simulation tools. To demonstrate the accuracy and efficiency, our code was compared with a commercial software by simulating a 3D multi-pass girth weld model with over 1 million elements. Our code achieved comparable solution accuracy with respect to the commercial one but with over 100 times saving on computational cost. Moreover, the three-dimensional analysis demonstrated more realistic stress distribution that is not axisymmetric in hoop direction.

Development of Defect Interaction Criteria for Pipeline Girth Welds Subjected to Plastic Collapse Conditions

2006 ◽  
Author(s):  
Wim De Waele ◽  
Rudi Denys ◽  
Antoon Lefevre
Keyword(s):  
Large Scale ◽  
Specific Interaction ◽  
Ductile Failure ◽  
Elastic Interaction ◽  
Tensile Tests ◽  
Ductile Material ◽  
Plastic Collapse ◽  
Material Behaviour ◽  
Defect Interaction ◽  
Girth Welds

Multiple defects in welds, when detected, have to be assessed for interaction. Current defect interaction rules are largely based on linear elastic fracture mechanics principles (brittle material behaviour). Pipeline welding codes, however, specify toughness requirements to ensure ductile failure by plastic collapse. Therefore, the use of current (elastic) interaction rules for ductile girth welds can lead to unnecessary and possibly harmful weld repairs or cutouts. This paper reports on an assessment of the engineering significance of existing pipeline specific interaction criteria and on the development of new criteria. Rules for the interaction of coplanar surface breaking defects and ductile material behaviour have been developed on the basis of the performance requirement of remote yielding. The results of large-scale tensile tests illustrate that current interaction rules have a high degree of conservatism for plastic collapse conditions. The test data have been used to demonstrate that the developed procedure can be safely used for ductile girth welds.

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