Reliability-Based Assessment of Safe Excavation Pressure for Dented Pipelines

2020 ◽  
Author(s):  
Chike Okoloekwe ◽  
Matthew Fowler ◽  
Amandeep Virk ◽  
Nader Yoosef-Ghodsi ◽  
Muntaseer Kainat
Keyword(s):  
Numerical Models ◽  
Mechanical Damage ◽  
Structural Response ◽  
Assessment Method ◽  
Full Scale ◽  
Burst Pressure ◽  
Operating Pressure ◽  
Element Analysis ◽  
Fea Model ◽  
Full Scale Tests

Abstract Dents in a pipe result in alteration of its structural response when subjected to internal pressure. Excavation activities further lead to change in load and boundary conditions of the pipe segment which may exacerbate the stress state within the dented region. Depending on the severity of a dent, excavation under full operating pressure may lead to failure, injuries or fatalities. Although uncommon, an incident has been reported on a gas pipeline where a mechanical damage failed during investigation leading to one death and one injury [10]. While current pipeline regulations require that operators must depressurize a line to ensure safe working conditions during repair activities, there are no detailed provisions available in the codes or standards on how an operator should determine such a safe excavation pressure (SEP). As a result, the safe excavation process of dents has received attention in the industry in recent years. A detailed review of the recent research on dent SEP showed that the current recommendations are primarily dependent on one of two aspects: careful assessment of inline inspection (ILI) data, or a fitness for service (FFS) assessment of the dent feature leveraging numerical models. Enbridge Liquid Pipelines had previously demonstrated a feature specific assessment approach which incorporated both ILI data and finite element analysis (FEA) to determine the SEP. This assessment also accounted for uncertainties associated with material properties and ILI tool measurement. In the previous publication, the authors demonstrated a methodology for assessing the SEP of dents at a conceptual level from both deterministic and reliability-based standpoints. In this paper, a validation study has been performed to compare the results of fracture mechanics based FEA models against ten full scale burst tests available in literature. The study showed good agreement of the burst pressure of dent-crack defects predicted by FEA models with those observed in the full-scale tests. The assessment method is further streamlined by incorporating the API 579 [14] Failure Assessment Diagram (FAD) method on an uncracked FEA model as opposed to explicitly incorporating the crack geometry in the FEA model. The results of FEA in conjunction with FAD are compared with the full-scale tests to ensure accuracy and conservatism of burst pressure prediction. A reliability-based approach is then designed which accounts for the uncertainties associated with the analysis. A case study is presented where the reliability-based SEP assessment method has been implemented and feature specific SEP has been recommended to ensure target reliability during excavation.

Integrity Assessment of API 5L X65 and X70 Pipelines With Mechanical Damages

2012 ◽  
Author(s):  
Kyu Jung Yeom ◽  
Yong Kwang Lee ◽  
Kyu Hwan Oh ◽  
Cheol Man Kim ◽  
Woo Sik Kim
Keyword(s):  
Finite Element ◽  
Structural Integrity ◽  
Mechanical Damage ◽  
Local Stress ◽  
Assessment Method ◽  
Full Scale ◽  
Burst Pressure ◽  
Element Analysis ◽  
Integrity Assessment ◽  
Failure Pressure

Gas pipelines with mechanical damages could affect the structural integrity and causes local stress and strain concentration. Failures in gas pipeline as leakages that could affect the supply of gas, loss of production, and environmental pollution. It is important to determine if pipelines are fitness-for-service. ASME B31G code is still widely used criterion although the assessment method is the conservative method. Further examinations are needed on the effects of material grade and pipeline shape on the burst pressure of damaged pipelines. The goal of this paper is to predict the failure pressure of mechanical damaged made of API X65 and X70 pipelines, by conducting full scale burst tests and finite element analysis (FEA). Different pipeline grades, effects of gouges, and dent depths were considered for an integrity assessment. The full scale burst tests were performed for pipelines with artificial mechanical damage. The gouge defect was made in a V-notch shape and the dented pipeline was generated using a ball shaped indenter that was pressed into the pipe. A three dimensional FEA was performed to obtain the burst pressure of a pipe with gouge and dent defects as a function of defect depth and length. A FEA was used to simulate the and externally damaged pipes under internal pressure. Failure pressure was predicted with stress based and strain based assessments by the finite element method (FEM).

Strain Capacity Prediction of Strain-Based Pipelines

2014 ◽  
Author(s):  
Huang Tang ◽  
Doug Fairchild ◽  
Michele Panico ◽  
Justin Crapps ◽  
Wentao Cheng
Keyword(s):  
Damage Mechanics ◽  
Critical Role ◽  
Active Regions ◽  
Full Scale ◽  
Element Analysis ◽  
Strain Capacity ◽  
Fea Model ◽  
Full Scale Tests ◽  
Numerical Program ◽  
Allowable Stress Design

Strain-based design (SBD) is used to complement conventional allowable stress design for pipelines operated in environments with potentially large ground movements such as those found in permafrost and seismically active regions. Reliable and accurate prediction of tensile strain capacity (TSC) plays a critical role in strain-based design. As reported previously over the past 6+ years, a comprehensive experimental and numerical program was undertaken to characterize the TSC of welded pipelines, develop a finite element analysis (FEA) approach and equations capable of predicting TSC, and establish a strain-based engineering critical assessment (SBECA) methodology. The previous FEA model and TSC equations were validated against about 50 full-scale pipe strain capacity tests and are accurate within the validated variable ranges. In the current paper, enhancements of the previous model and equations are described. The enhancements include incorporation of advanced damage mechanics modeling into TSC prediction, development of a new TSC equation, expansion of variable ranges and functionality upgrades. The new model and equation are applicable over larger ranges of material properties and flaw sizes. The new FEA model is also used to establish surface flaw interaction rules for SBD. The new FEA model is validated against more than 40 full-scale non-pressurized and pressurized tests and underpins the development of the new TSC equation. The equation is validated against a total of 93 full-scale tests (FST). In addition to the enhancements, sample applications of the TSC model and equation are presented in the paper, for example, an investigation of the effects on strain capacity of Lüders strain and ductile tearing. Challenges in predicting TSC are also addressed.

Full scale test of a PC bridge to calibrate assessment methods

2021 ◽  
Author(s):  
Niklas Bagge ◽  
Jonny Nilimaa ◽  
Silvia Sarmiento ◽  
Arto Puurula ◽  
Jaime Gonzalez-Libreros ◽  
...  
Keyword(s):  
Prestressed Concrete ◽  
Structural Response ◽  
Sensitivity Study ◽  
Assessment Method ◽  
Full Scale ◽  
Concrete Bridges ◽  
Fractional Factorial ◽  
Fe Model ◽  
Load Carrying ◽  
Existing Bridges

<p>In this paper, experiences on the development of an assessment method for existing bridges are presented. The method is calibrated using the results of full-scale testing to failure of a prestressed bridge in Sweden. To evaluate the key parameters for the structural response, measured by deflections, strains in tendons and stirrups and crack openings, a sensitivity study based on the concept of fractional factorial design is incorporated to the assessment. Results showed that the most significant parameters are related to the tensile properties of the concrete (tensile strength and fracture energy) and the boundary conditions. A finite element (FE) model in which the results of the sensitivity analysis were applied, was able to predict accurately the load-carrying capacity of the bridge and its failure mode. Two additional existing prestressed concrete bridges, that will be used to improve further the method, are also described, and discussed.</p>

The Story of the Dent-Gouge Fracture Model

2020 ◽  
Author(s):  
Andrew Cosham ◽  
Phil Hopkins
Keyword(s):  
Empirical Model ◽  
Factor Of Safety ◽  
Original Model ◽  
Full Scale ◽  
Fracture Model ◽  
Burst Pressure ◽  
Two Dimensional ◽  
Dimensional Representation ◽  
Full Scale Tests ◽  
Semi Empirical

Abstract Once upon a time the dent-gouge fracture model was developed by the then British Gas Corporation to estimate the burst pressure of a dent and gouge subject to internal pressure. The dent-gouge fracture model is based on a two-dimensional representation of a dent and gouge; it assumes an infinitely long, longitudinally-orientated gouge (a crack) at the base of infinitely long, longitudinally-orientated dent. The model was calibrated using the results of 109 ring tests and 23 vessel tests conducted by the British Gas Corporation; a dent was introduced and then a slot was machined in the base of the dent (all at zero pressure). It is a semi-empirical model. Part 12 of API 579-1/ASME FFS-1 2016 quotes the original dent-gouge fracture model. A number of variations on the theme of the original dent-gouge fracture model have been developed. The variants have not significantly improved the accuracy of the original model, as is demonstrated by comparing the variants against the results of burst tests on rings and vessels containing a dent and gouge (or notch) reported in the published literature. The dent-gouge fracture model is deconstructed in order to illustrate its component parts. The deconstruction clearly identifies the parts of the model that could be improved. It also highlights where semi-empiricism is embedded in the model. The effect of changes to the original model is illustrated using the results of the full-scale tests. The difficulties introduced by the scatter in the full-scale tests are discussed, noting that a number of different methods have been used to introduce the dent and gouge (or notch) into the ring or vessel. A factor of safety is proposed. Pointers are given to how the dent-gouge fracture model might be improved or replaced. The need for a dent-gouge model is also considered, in the context of the guidance given in API Recommended Practice 1160 and ASME B31.8S.

Effect of Thickness Measurement Procedure on Stress Analysis of Pipes With Local Metal Loss

2013 ◽  
Author(s):  
Nobuyuki Yoshida ◽  
Atsushi Yamaguchi
Keyword(s):  
Decision Making ◽  
Measurement Procedure ◽  
Thickness Measurement ◽  
Burst Pressure ◽  
Metal Loss ◽  
Element Analysis ◽  
Fea Model ◽  
Laser Displacement Meter ◽  
The Difference ◽  
Corrosion Under Insulation

Fitness-For-Service (FFS) assessment using Finite Element Analysis (FEA) has been a problem in deciding yes-no which vary from evaluator to evaluator. The difference in decision making is caused by the degree of freedom in modeling a FEA model. In this study, burst pressures of pipes with local metal loss were calculated by using FEA in order to investigate the influence of thickness measurement intervals on FFS assessment. The analyzed pressures by FEA were verified by burst tests. A pipe specimen, which was thinned by corrosion under insulation in the actual plant, was used for the burst tests. Shape of the pipe specimen was measured by laser displacement meter and extracted at several types of interval. It is concluded that the analyzed pressures in various measurement intervals showed almost no difference, but were higher than the actual burst pressure of the specimen.

Validation of Sleeve Weld Integrity and Workmanship Level Development

2006 ◽  
Author(s):  
Robert Lazor ◽  
Brock Bolton ◽  
Aaron Dinovitzer
Keyword(s):  
Finite Element ◽  
Numerical Models ◽  
Full Scale ◽  
Loading Conditions ◽  
Element Analysis ◽  
Service Failures ◽  
Applied Loading ◽  
Fea Modeling ◽  
Field And Laboratory Conditions ◽  
Scale Data

Full encirclement repair sleeves with fillet-welded ends are often used as permanent repairs on pipelines to reinforce areas with defects, such as cracks or corrosion. In-service failures have occurred at reinforcing sleeves as a result of defects associated with the sleeve welds, such as hydrogen-induced cracks and undercut at the fillet welds, inadequate weld size, and sleeve longitudinal seam ruptures. This work was undertaken to support the development of tools for sleeve design and for conducting an engineering assessment to determine the tolerable dimensions of flaw indications at full encirclement repair sleeves. In particular, the project was intended to validate the stresses estimated using finite element analysis (FEA) models against actual in-service loading conditions experienced at reinforcing sleeves. The experimental work focused on the collection of full-scale experimental data describing pipe and sleeve strains for the following field and laboratory conditions: • Strains induced by sleeve welding, • Strains induced by pressurization of the sleeved pipe, • Strains induced by pressurization of the sleeved pipe and the annulus between the pipe and sleeve. Finite element models of the field and laboratory sleeved pipe segments were developed and subjected to the same applied loading conditions as the full-scale sleeved pipe segments. Comparisons of the measured strains against those estimated using FEA were completed to determine the ability of the models to predict the behaviour of the sleeved pipe segments. Comparisons were made to illustrate the relative strain levels and deformation trends, the accuracies of the strain predictions and trends in changes with pressure, the differences in behaviours between tight and loose fitting sleeves, and the effects of pressurizing the annulus between the pipe wall and sleeve. The analysis of the field data and FEA modeling predictions led to several conclusions regarding to use of numerical models for predicting sleeved pipe behaviour and weld flaw acceptance: • FEA results demonstrated behaviours that were consistent with full scale data, • Trends in the FEA predicted strains agreed with the full-scale data, • FEA models describing the effects of gaps between the pipe and sleeve and annulus pressurization agreed with field experience and engineering judgment, • Evaluation of the significance of root and toe flaws can be completed by extending the models validated in this work.

Experimental and Analytical Leak Characterization for Axial Through-Wall Cracks in a Liquids Pipeline

2014 ◽  
Author(s):  
Mohamed R. Chebaro ◽  
Nader Yoosef-Ghodsi ◽  
David M. Norfleet ◽  
Jason H. Bergman ◽  
Aaron C. Sutton
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Internal Pressure ◽  
Crack Opening ◽  
Full Scale ◽  
Leak Rate ◽  
Propagation Mechanism ◽  
Element Analysis ◽  
Fea Model ◽  
Experimental Findings

Three pipeline sections containing defects of interest were non-destructively tested in the field, cut out and shipped to a structural laboratory to undergo full-scale testing. The common objectives of the experiments were to determine (1) the leak initiation pressure and (2) the leak rate at various specified internal pressures. While two spools (Specimens A and B) contained through-wall cracks, the third (Specimen C) had a partial through-wall crack with similar characteristics. The capacity of through-wall defects to withstand a level of internal pressure without leaking is due to the resultant local, compressive hoop residual stresses. Specimen C underwent full-scale pressure cycling to further comprehend the crack propagation mechanism in order to correlate it to field operation and analytical fatigue life predictions. To enhance the understanding of the physical crack behaviour as a function of internal pressure, a comprehensive finite element analysis (FEA) model was built using SIMULIA’s Abaqus software. The model inputs incorporated results from the above-mentioned laboratory tests, in addition to extensive radial, circumferential and axial residual stress measurements using the X-ray diffraction (XRD) technique, obtained on three pipe spools cut out from the same line. The resulting crack opening parameters from FEA were input into a closed-form fluid mechanics (FM) model, which was calibrated against a computational fluid dynamics (CFD) model, to determine the corresponding leak initiation pressures and leak rates. These outcomes were then compared to experimental findings. The FEA and FM models were subsequently employed to carry out a parametric study for plausible combinations of feature geometries, material properties, operational pressures and residual stresses to replicate field conditions. The key outcome from this study is the experimental and analytical demonstration that, for given fluid properties and pressures, the leak threshold and leak rate for through-wall cracks are primarily dependent upon the crack geometry and local residual stress distributions.

scholarly journals Modeling Material Failure During Cab Car End Frame Impact

2009 ◽  
Author(s):  
Richard Stringfellow ◽  
Christopher Paetsch
Keyword(s):  
Static Loading ◽  
Full Scale ◽  
Test Material ◽  
Material Strength ◽  
Model Parameters ◽  
Material Failure ◽  
Failure Model ◽  
Shell Elements ◽  
Fea Model ◽  
Full Scale Tests

New standards have been proposed to increase the strength requirements for cab car end structures and impose further requirements on their ability to absorb energy during a grade-crossing collision [1, 2]. To aid in the development of these new standards, the Federal Railroad Administration (FRA) and the Volpe Center recently completed a set of full-scale tests aimed at assessing the quasi-static and dynamic crush behavior of these end structures. In support of this testing program, end frames designed to meet the new standards were fabricated and retrofitted onto the forward end of an existing cab car. A series of large-deformation quasi-static and explicit dynamic finite element analyses (FEAs) were performed to evaluate the performance of the design. Based on the results of a 2002 full-scale test in which a heavy steel coil impacted the corner post of an end frame built to these new standards, some fracture was expected in certain key end frame components during the tests. For this reason, a material failure model, based on the Bao-Wierzbicki fracture criterion [3], was implemented in the FEA model of the cab car end frame using ABAQUS/Explicit. The FEA model with material failure was used to assess the effect of fracture on the deformation behavior of cab car end structures during quasi-static loading and dynamic impact and, in particular, the ability of such structures to absorb energy. The failure model was implemented in ABAQUS/Explicit for use with shell elements. A series of preliminary calculations were first conducted to assess the effects of element type and mesh refinement on the deformation and fracture behavior of structures similar to those found on cab car end frames, and to demonstrate that the Bao-Wierzbicki failure model can be effectively applied using shell elements. Model parameters were validated through comparison to the results of the 2002 test. Material strength and failure parameters were derived from test data for A710 steel. The model was then used to simulate the three full-scale tests that were conducted during 2008 as part of the FRA program: a collision post impact, and quasi-static loading of both a collision post and a corner post. Analysis of the results of the two collision post tests revealed the need for revisions to both the design of some key end frame components and to key material failure parameters. Using the revised model, pre-test predictions for the outcome of the corner post test were found to be in very good agreement with test results.

Fatigue Resistant Threaded and Coupled Connectors for Deepwater Riser Systems: Design and Performance Evaluation by Analysis and Full Scale Tests

2008 ◽  
Author(s):  
Celine Sches ◽  
Emmanuel Desdoit ◽  
Jacky Massaglia
Keyword(s):  
Performance Evaluation ◽  
Fatigue Cracks ◽  
Systems Design ◽  
High Strength Steels ◽  
Full Scale ◽  
Post Treatment ◽  
Mechanism Analysis ◽  
Element Analysis ◽  
And Performance ◽  
Full Scale Tests

Threaded and Coupled (T&C) riser connectors with High Strength Steels have been developed for deepwater top tensioned riser (TTR) applications up to 10,000ft Water Depth. These developments have been ongoing for a decade, and the resulting solutions are now becoming the standard in the industry. Due to the stringent fatigue requirements involved, new design and performance evaluation methods were needed and have been built over time. In this article, we will demonstrate how these methods were implemented into the standard development process of T&C connectors, with a focus on finite element analysis (FEA) techniques. This process includes full scale tests programs on resonant fatigue frames, statistical post treatment of the resulting data, and fatigue cracks expertise for failure mechanism analysis. These elements are a key for the evaluation of T&C connectors’ fatigue performance and for the determination of influencing parameters, leading to the proper design optimization possibilities. The application of these methods will be illustrated with actual examples on T&C connectors’ recent developments. Namely, we will describe FEA methodologies, testing methods and results post-treatment techniques. We will show how the connectors’ performance is eventually derived after such analysis and test data accumulation. The reader will see that innovative and effective fatigue enhancement techniques have resulted, along with premium fatigue compliant sealing devices. The experience and expertise gained, together with a continuous improvement process of our methods have made T&C riser connectors a viable solution to meet emerging needs within deepwater industry, including xHP-HT, SCR and flow lines.

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