Development of a FAD-Based Girth Weld ECA Procedure: Part I — Theoretical Framework

2002 ◽  
Author(s):  
Yong-Yi Wang ◽  
David Rudland ◽  
David Horsley
Keyword(s):  
Limit Load ◽  
Weld Strength ◽  
Plastic Collapse ◽  
Mismatch Correction ◽  
Load Limit ◽  
Failure Assessment ◽  
Scale Test ◽  
Girth Welds ◽  
Extensive Experimental Data ◽  
Experimental Data Analysis

Beginning in the late 1970’s and early 1980’s, “alternative defect acceptance criteria” were adopted in various codes and standards in the pipeline industry. These criteria relate the tolerable defect sizes with the magnitude of loads and materials’ resistance to failure. They allow engineers to assess the suitability of the pipes containing defects for intended service conditions, or fitness-for-service. Assessments based on the fitness-for-service principles are often referred to as Engineering Critical Assessment, or ECA. Although most of these codes are based on fracture mechanics principles, the defect tolerance levels vary significantly from code to code. This paper describes a two-year effort funded by PRCI (Pipeline Research Council International) to develop an ECA procedure specifically tailored to pipeline girth welds. The newly developed procedure is in FAD (failure assessment diagram) format. The key features of this procedure are provided in this paper. Based on prior research and extensive experimental data analysis, a modified Miller plastic collapse solution was selected for its rigorous formulation and good agreement with full-scale test results. The effects of weld strength mismatch on plastic collapse load (limit load) were examined and validated through finite element (FE) analysis. Parametric formulae of mismatch correction factors to the plastic collapse solution were adopted. The stress intensity factor solutions of finite-length surface-breaking defects in girth welds were developed and validated. Failure assessment curves (FACs) for girth weld defects were generated. These curves incorporated the effects of material’s strain hardening rate and defect size. They are more accurate than some of the generic material and defect independent FACs, yet easy to use.

Limit Plastic Collapse on Remaining Ligament of Flawed Welds for ECA Application

2014 ◽  
Author(s):  
Antonio Carlucci ◽  
Kamel Mcirdi
Keyword(s):  
Fracture Toughness ◽  
Brittle Fracture ◽  
Mechanical Strain ◽  
Plastic Collapse ◽  
Fracture Toughness Test ◽  
Element Analysis ◽  
Critical Fracture ◽  
Failure Assessment ◽  
The One ◽  
Girth Welds

Engineering Critical Assessments (ECAs) are routinely used to provide defect acceptance criteria for pipelines girth welds. The Failure Assessment Diagram (FAD) concept is the most widely used methodology for elastic-plastic fracture mechanics analysis of structural components and adopted by standards/documents including BS7910 [1], API579-1/ASME FFS-1 [2], R6 [3]. It is defined by two criterion Kr and Lr which describe the interaction between brittle fracture and fully ductile rupture: Kr measures the proximity to brittle fracture whereas Lr reflects the closeness to plastic collapse. The BS7910 FAD level 2B is the most employed for assessment of flaws under mechanical strain lower than 0.4%, the FAD associated is material-specific and it based on single toughness value obtained from CTOD test, the latter-on gives no information about the tearing initiation. The objective of this paper is to propose an approach for determination of the critical fracture toughness (associated to zero-tearing: JΔa=0). This approach is based on the comparison between the load-CMOD curve provided from a fracture toughness test to the one obtained by Finite Element Analysis (FEA). The goals is to propose a conservative guidance on how to identify a remote strain level below which it may be considered guaranteed the integrity of the remaining ligament.

Limit Load and Reference Stress for Curved Wide Plates

2010 ◽  
Author(s):  
Stijn Hertele´ ◽  
Wim De Waele ◽  
Rudi Denys ◽  
Jeroen Van Wittenberghe ◽  
Matthias Verstraete
Keyword(s):  
Experimental Validation ◽  
Limit Load ◽  
Plastic Collapse ◽  
Test Results ◽  
Finite Element Analyses ◽  
Flat Plates ◽  
Stress Equation ◽  
Reference Stress ◽  
Plate Curvature ◽  
Girth Welds

Curved wide plates are a valuable tool in the assessment of defective pipeline girth welds under tension. Throughout the years, Laboratory Soete collected an extensive database of curved wide plate test results. In an effort to investigate these results through FAD analysis, the authors recently developed a reference stress equation for curved plates. The approach followed is similar to the development of the Goodall and Webster equation for flat plates. This paper elaborates finite element analyses of the equation’s capability to predict plastic collapse. It is found that, although overestimated, the influence of plate curvature is correctly predicted in a qualitative way. For all simulations, the curved plate reference stress equation produced conservative estimations. This indicates that the proposed equation is suited to safely predict the plastic collapse of defective pipeline girth welds. An experimental validation is underway.

Application of Limit Load Solutions for Engineering Critical Assessment of Embedded Flaws in Evenmatch Pipeline Girth Welds

2020 ◽  
Author(s):  
Aurélien Pépin ◽  
Tomasz Tkaczyk ◽  
Noel O’Dowd ◽  
Kamran Nikbin ◽  
Suresh V. Chettiar
Keyword(s):  
High Strain ◽  
Closed Form Solution ◽  
Limit Load ◽  
Form Solution ◽  
Embedment Depth ◽  
Plastic Collapse ◽  
J Integral ◽  
Crack Driving Force ◽  
Fracture Assessment ◽  
Girth Welds

Abstract Engineering Critical Assessment (ECA) is commonly undertaken to derive the acceptance criteria for girth weld flaws in rigid pipelines deployed subsea by low-strain installation methods, such as S-Lay or J-Lay, or high-strain installation methods, such as Reel-Lay. The ECA generally considers the whole load history seen by the pipeline from fabrication to the end of service, and involves fracture and fatigue assessments. Fracture, which is the main focus of this paper, is deemed to have initiated when either (i) the crack driving force, expressed in terms of the J-integral or the Crack Tip Opening Displacement (CTOD), δ, is greater than the materials resistance, or (ii) the applied load exceeds the bearing capacity of the ligament of a cracked structure, also referred to as the plastic collapse or limit load. The robustness of the ECA procedure relies on the accuracy of the assessment solutions. Most flaws in pipeline girth welds are embedded. Unlike surface breaking flaws, embedded flaws are typically not directly assessed in a high-strain fracture ECA because the available assessment solutions are too conservative. A work-around approach is often followed, where the maximum acceptable surface breaking flaw sizes are also considered acceptable below the surface if the embedment depth is equal to or greater than half of the flaw height. Otherwise, an embedded flaw must be reclassified as a surface breaking flaw with a height equal to the sum of the embedded flaw height and embedment depth. To enable the direct fracture assessment of embedded flaws, the authors undertook in a previous work a parametric finite-element (FE) study on the effect of the embedment depth, the crack height and the crack length on the plastic collapse load of the shorter ligament of embedded flaws. Subsequently, a new limit load solution was proposed for the fracture assessment of embedded flaws in evenmatch pipeline girth welds subjected to tension and/or bending. This closed-form solution was shown to be significantly more accurate for estimating the crack driving force and the ligament plastic collapse load than other solutions available in the literature. For some geometries, however, the predicted limit load still needs to be significantly adjusted (increased) to correctly evaluate the J-integral, in a combined tearing and collapse assessment. This suggests that further enhancement of the solution is possible. This paper describes small-scale fracture tests which were undertaken to determine the load required to collapse a smaller ligament of embedded flaws in a modified middle crack tension (MMCT) specimen. A closed-form solution, which can also be used as a flaw reclassification criterion, is fitted to the test results and then compared to the FE-based solution. Finally, recommendations are made for the direct fracture assessment of embedded flaws in evenmatch pipeline girth welds subjected to load or displacement-controlled conditions.

Girth Weld ECA From the Perspective of Code Revisions in North America

2002 ◽  
Author(s):  
Yong-Yi Wang ◽  
Jim F. Swatzel ◽  
David Horsley ◽  
Alan Glover
Keyword(s):  
North America ◽  
Fracture Criterion ◽  
Safety Margin ◽  
Cost Savings ◽  
Step Function ◽  
Weld Strength ◽  
Plastic Collapse ◽  
Defect Assessment ◽  
Girth Welds ◽  
Continuous Relation

In North America there are two primary girth weld ECA (Engineering Critical Assessment) codes: API 1104 Appendix A and CSA Z662 Appendix K. Both codes were developed in the early-to mid-1980’s and thus represent the technology of that time. Significant progress has been made since then in understanding the structural behavior of girth welds containing welding defects. This paper describes an effort funded by the PRCI (Pipeline Research Council International) to establish the technical basis for the revisions of these codes using the knowledge generated since the inception of the codes. The CSA Z662 Appendix K sets defect tolerance using separate fracture and plastic collapse criteria, while API 1104 Appendix A has only a fracture criterion. The worldwide trend in defect assessment is moving towards FAD (Failure Assessment Diagram) based approach, by which both fracture and plastic collapse can be assessed in one consistent format. An FAD-based ECA procedure specifically tailored to girth welds has been developed in a separate PRCI-funded project. This procedure incorporates refined fracture and plastic collapse solutions and the effects of weld strength mismatch. The experimental verification has shown that the procedure is accurate and can become the basis for future code revisions. As an interim step towards the eventual adoption of a fully FAD-based approach, a number of revisions may be made to the API 1104 Appendix A, including (1) adding a plastic collapse criterion; (2) lowering the minimum CTOD requirement of using Appendix A to 0.003 inch (0.076 mm) from the current minimum of 0.005 inch (0.127 mm); (3) setting the allowable defect length as a continuous function of defect depth (height for buried defects); (4) allowing the use of any valid CTOD toughness greater than a set minimum value; (5) revising the notching procedure for HAZ CTOD testing. These recommendations are interdependent. Selectively adopting any of those recommendations may result in undesirable consequences. For instance, lowering minimum CTOD requirements necessitates the revision of allowable defect height. Adding the plastic collapse criterion would almost certainly require the change of defect length allowance of the fracture criterion from the current step function to a continuous relation. It should be made absolutely clear that lowering the minimum CTOD requirements for using Appendix A does not mean inferior weld quality control. It merely allows the assessment of significance of weld defects using the fracture mechanics methodology that has been proven effective. The interim step for the CSA Z662 Appendix K is revising the plastic collapse criterion. These revisions, when implemented, should result in more consistent degree of conservatism than the current codes. In certain cases, the size of the allowable defects is less restrictive than the current codes while maintaining consistent and adequate safety margin. This should translate to cost savings in both new construction and the maintenance of existing pipelines without sacrificing the safety and integrity of the pipelines.

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.

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.

Evaluation of Weld Metal Strength Mismatch in X100 Pipeline Girth Welds

2004 ◽  
Author(s):  
Henryk G. Pisarski ◽  
Yuri Tkach ◽  
Marie Quintana
Keyword(s):  
Fracture Toughness ◽  
Adverse Effects ◽  
Weld Metal ◽  
Axial Stress ◽  
Limit Load ◽  
Allowable Stress ◽  
Simple Method ◽  
Weld Width ◽  
Girth Welds ◽  
Assessment Procedures

A relatively simple method based on standard fracture mechanics flaw assessment procedures, such as BS 7910, but modified using published mismatch limit load solutions is described. It is used to illustrate the effects of weld width and strength mismatch on CTOD requirements for girth welds in Grade X100 strength pipeline material subjected to axial stress. It is shown that fracture toughness requirements based on standard analyses not allowing for mismatch effects can be unnecessarily conservative when either undermatched or overmatched welds are present. Adverse effects of undermatching, in reducing the allowable stress, can be mitigated by reducing weld width. It is shown that even small amounts of overmatching (e.g. 10%) can be beneficial by allowing axial stress to exceed the SMYS of the parent pipe and reducing CTOD requirements.

scholarly journals Development of Flaw Acceptance Criteria for Aging Management of Spent Nuclear Fuel Multiple-Purpose Canisters

2015 ◽  
Author(s):  
Poh-Sang Lam ◽  
Robert L. Sindelar
Keyword(s):  
Residual Stress ◽  
Nuclear Fuel ◽  
Spent Nuclear Fuel ◽  
Storage Period ◽  
Limit Load ◽  
American Petroleum Institute ◽  
Acceptance Criteria ◽  
Long Term Storage ◽  
Flaw Tolerance ◽  
Failure Assessment

A typical multipurpose canister (MPC) is made of austenitic stainless steel and is loaded with spent nuclear fuel assemblies. The canister may be subject to service-induced degradation when it is exposed to aggressive atmospheric environments during a possibly long-term storage period if the permanent repository is yet to be identified and readied. Because heat treatment for stress relief is not required for the construction of an MPC, stress corrosion cracking may be initiated on the canister surface in the welds or in the heat affected zone. An acceptance criteria methodology is being developed for flaw disposition should the crack-like defects be detected by periodic Inservice Inspection. The first-order instability flaw sizes has been determined with bounding flaw configurations, that is, through-wall axial or circumferential cracks, and part-through-wall long axial flaw or 360° circumferential crack. The procedure recommended by the American Petroleum Institute (API) 579 Fitness-for-Service code (Second Edition) is used to estimate the instability crack length or depth by implementing the failure assessment diagram (FAD) methodology. The welding residual stresses are mostly unknown and are therefore estimated with the API 579 procedure. It is demonstrated in this paper that the residual stress has significant impact on the instability length or depth of the crack. The findings will limit the applicability of the flaw tolerance obtained from limit load approach where residual stress is ignored and only ligament yielding is considered.

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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