An Overview of Strain-Based Fracture Assessment of Pipelines

2018 ◽  
Author(s):  
Guiyi Wu ◽  
Longjie Wang
Keyword(s):  
Plastic Deformation ◽  
Fracture Mechanics ◽  
Test Data ◽  
Oil And Gas ◽  
Full Scale ◽  
Plastic Strains ◽  
Offshore Pipelines ◽  
Pipeline Networks ◽  
Fracture Assessment ◽  
Girth Welds

Development of remote energy requires large pipeline networks to be placed in more challenging environments such as offshore in deeper waters or on land in Arctic or near-Arctic locations. Pipeline installed and operated in such regions may be subjected to large plastic strains. Engineering critical assessments (ECA) are commonly carried out during design, installation and operation of offshore pipelines to determine acceptable flaw sizes in pipeline girth welds. A number of fracture mechanics-based procedures are available for ECA of pipeline girth welds. Most of these methods are primarily stress-based assessments and are therefore not directly applicable to cases where the displacement-/strain-controlled loading generates large amounts of plastic deformation. For such cases, strain-based fracture assessment for pipeline/girth welds should be carried out instead. However, limited guidance on strain-based assessment is available in the current codes and standards used primarily by the oil and gas industries. This paper reviews the existing strain-based fracture assessment methods, and reports the results of preliminary studies performed to compare the methods reviewed with the available full-scale pipe test data.

Research on Full-Scale Hydrostatic Burst Testing of Different Pipeline Girth Weld Defects

2016 ◽  
Vol 853 ◽  
pp. 351-355
Author(s):  
Wen Bo Xuan ◽  
Fu Xiang Wang ◽  
Li Jian Zhou ◽  
Ting Wang ◽  
Jian Chen ◽  
...  
Keyword(s):  
Bearing Capacity ◽  
Oil And Gas ◽  
Full Scale ◽  
Experimental Results ◽  
Fitness For Purpose ◽  
Technical Challenge ◽  
Weld Defects ◽  
Oil And Gas Pipelines ◽  
Girth Welds ◽  
Pipeline Safety

Recently incidents related to cracking of girth welds in oil and gas pipelines occurred frequently. With highly concentrated stresses, girth weld defects may significantly reduce bearing capacity of pipelines. Many girth weld defects were detected in the in-line inspection and excavated verification. How to assess the severity of these defects to avoid the excessive and unnecessary repair was a technical challenge. Four different kinds of girth weld defects were manufactured in the 32-inch pipeline and full-scale hydrostatic burst testing were carried out to assess the pressure performance of these defects. Many fitness-for-purpose assessment methods were applied to verify the accuracy of experimental results. After the testing, pipelines with failure defects were cut out to carry out the microanalysis. The research results make us understanding the severity of these defects and avoid the excessive and unnecessary repair of these defects to ensure the pipeline safety.

Ductile Damage Study of Defective Girth Welds for Oil and Gas Pipeline: A Tailored Numerical and Finite Element Method Calibration From SENT Fracture Mechanics Test

2017 ◽  
Author(s):  
Roberto Bruschi ◽  
Marco Rossi ◽  
Alex Di Michele ◽  
Daniele Scarsciafratte ◽  
Enrico Torselletti
Keyword(s):  
Finite Element ◽  
Oil And Gas ◽  
Calibration Procedure ◽  
Ductile Damage ◽  
Element Analysis ◽  
Gurson Model ◽  
Offshore Pipelines ◽  
Crack Driving Force ◽  
Girth Welds ◽  
Model Preparation

In this paper, the evolution of ductile damage in pipe girth welds for offshore pipelines application is studied with the use of Finite Element Analysis. To this purpose, the Gurson-Tvergaard-Needlmen (GTN) model is calibrated and applied to different finite element simulations. Saipem internally developed software, written in Matlab® environment, is used to automatically calibrate the Gurson model from experimental data and run several Finite Element Models of the pipe with different flaws in the girth weld. The objective of this paper is to present and discuss this numerical tool, developed by Saipem coupling a Matlab® GUI and the ABAQUS FE solver. The tool allows speeding up and automatizing the calibration procedure of the Gurson model and making a rapid evaluation in terms of the Crack Driving Force (CDF) for defective girth weld. The tool allows also a quick and efficient model preparation, full FE analysis and post-processing, with saving of engineering hours.

Fatigue Design Data Derived From Full Scale Tests on 6”OD Pipe Girth Welds

2007 ◽  
Author(s):  
Per J. Haagensen ◽  
Hans Olav Knagenhjelm ◽  
Oddvin O̸rjasæter
Keyword(s):  
Fatigue Test ◽  
Test Data ◽  
Local Stress ◽  
Fracture Initiation ◽  
Full Scale ◽  
Published Data ◽  
High Quality ◽  
Design Data ◽  
Failure Initiation ◽  
Girth Welds

A literature survey of high quality girth welds intended for pipelines risers was carried out and the results are compared with full scale resonance fatigue test data on 6” pipes. The samples were made from 168.3×9.9mm (OD×WT) seamless pipes, each having two welds. Axial misalignments (hi-lo’s) and lack of penetration (LOP) defects were introduced in the test pipes to study the effects on the mean minus 2 stand, deviation design S-N curve that was calculated. Post failure examination of the welds was performed to determine the type and size of defects in the failure initiation area. Fracture mechanics calculations were carried out to determine the effect of defects on fatigue life. The test results were compared with published data on 6” pipes with high quality welds. The scatter in the fatigue test data was reduced when comparisons were based on the local stress at the point of fracture initiation. The implications for design rules of the findings in this work are discussed.

Application of SEM-EBSD for Measurement of Plastic Strain Fields Associated With Weld Metal Hydrogen Assisted Cold Cracking

2012 ◽  
Author(s):  
I. H. Brown ◽  
W. L. Costin ◽  
F. Barbaro ◽  
R. Ghomashchi
Keyword(s):  
Plastic Deformation ◽  
Plastic Strain ◽  
Weld Metal ◽  
Cold Cracking ◽  
Low Alloy Steels ◽  
Plastic Strains ◽  
Shielded Metal Arc Welding ◽  
Electron Backscattered Diffraction ◽  
Construction Time ◽  
Girth Welds

The requirement for more efficient use of materials for pipelines has lead to the application of high strength low alloy steels such as X70 and X80 in pipelines. As the strength of these alloys has increased so has the risk of hydrogen assisted cold cracking (HACC). In Australia to minimize construction time, the root runs of girth welds are produced by shielded metal arc welding using cellulosic electrodes without either pre or post heating. Well defined welding criteria have been developed and are incorporated into the weld procedures for the elimination of HACC in the heat affected zone but the risk of cracking to the weld metal is still of concern. It has been reported that plastic deformation occurs prior to the formation of hydrogen cracks in weld metal. Therefore the evaluation of plastic strains at the micro- and nano-scale and their relationship to the weld metal microstructure could be of great significance in assessing the susceptibility of welds to weld metal hydrogen assisted cold cracking (WMHACC). A method for analysing plastic strains on the micro- and nano-scales using electron backscattered diffraction (EBSD) has been developed. This technique is based on the degradation and rotation of diffraction patterns as a result of crystallographic lattice distortion resulting from plastic deformation. The analysis can be automated to produce an Image Quality (IQ) map in order to relate the spatial distribution of plastic deformation to microstructural features e.g. grains or cracks. The development and assessment of techniques using Scanning Electron Microscopy (SEM) and EBSD for the determination of local plastic strain distribution in E8010 weld metal used for the root pass of X70 pipeline girth welds is discussed.

Full Scale Fatigue Performance of Pre-Strained SCR Girth Welds: Comparison of Different Reeling Frames

2010 ◽  
Author(s):  
Philippe P. Darcis ◽  
Israel Marines-Garcia ◽  
Eduardo A. Ruiz ◽  
Elsa C. Marques ◽  
Mariano Armengol ◽  
...  
Keyword(s):  
Arc Welding ◽  
Oil And Gas ◽  
Gas Metal Arc Welding ◽  
Welding Process ◽  
Full Scale ◽  
Strain History ◽  
Oil And Gas Development ◽  
Arc Welding Process ◽  
Girth Welds ◽  
Welding Procedure

The current work aims to point out the influence of plastic strain history, due to reel-lay installation, on the fatigue resistance of welded SMLS (seamless) steel pipes used for fabrication of Steel Catenary Risers (SCRs) for oil and gas development. A C-Mn steel X65 pipe 10.75″ (273.1 mm) outside diameter (OD) and 25.4 mm wall thickness (WT) was chosen for this program. The Welding Procedure designed for girth welds manufacturing involved the use of Lincoln STT-GMAW™ (Surface Tension Transfer–Gas Metal Arc Welding) process for the root pass and SAW (Submerged Arc Welding) process with twin wire configuration for the fill and cap passes. This welding procedure presents a special post-weld finishing treatment, which consists in flapping the inner and outer weld overfills to produce a flush profile between weld metal and outer/inner pipe surfaces. The experimental approach was focused on quantifying the effect of accumulated plastic deformation using two different reeling frames simulating the same laying vessel: the Technip’s Apache. In this program, two reeling trials were performed at Heriot Watt University, Edinburgh, U.K., and two other trials at Stress Engineering Services, Houston, U.S.A. Then, the strained specimens were full scale fatigue tested at TenarisTamsa R&D facilities. Those results have been compared with fatigue results obtained on unstrained specimens. Post-tests fractographic investigations were systematically performed on all samples to identify the causes for fatigue initiation. The results were statistically analyzed to determine which standard fatigue design curves best represent the measured S-N fatigue endurance. Finally, the results were also compared with the available literature.

Undermatching and Low Strain In-Service Failures in X70 Line Pipe: Contributions From Standards, Specifications and Coating

2020 ◽  
Author(s):  
Frank Barbaro ◽  
Leigh Fletcher
Keyword(s):  
North America ◽  
Best Practice ◽  
Test Methods ◽  
Full Scale ◽  
Line Pipe ◽  
Service Failures ◽  
Pipeline Networks ◽  
Before And After ◽  
Pipeline Failure ◽  
Girth Welds

Abstract Some 10 incidents of low strain in-service and pre-service hydrotest failures in girth welds have been reported in North America since the Enterprise Products ethane pipeline failure in 2015. No such failures have been reported in Australia, despite the similarities in Standards, the line pipe data, and the use of manual SMAW using fully cellulosic procedures. There are however significant differences that warrant further investigation and adoption in terms of best practice to ensure the security and safety of our pipeline networks. Some unique differences and observations in terms of pipe properties, weld qualification procedures, test methods and even full scale pressure burst tests before and after coating are described to highlight subtle differences in the standards that may provide clarity in explaining pipeline girth weld failures and it is anticipated may also provide guidance for the future.

Analysis and Testing of a 13Cr Pipeline to Demonstrate “Leak Before Break”

2012 ◽  
Author(s):  
Robert M. Andrews ◽  
Neil Millwood ◽  
Sanjay Tiku ◽  
Nick Pussegoda ◽  
Menno Hoekstra ◽  
...  
Keyword(s):  
Fracture Mechanics ◽  
Weld Metal ◽  
Limit Load ◽  
Parent Material ◽  
Full Scale ◽  
Small Scale ◽  
Element Analysis ◽  
Girth Welds ◽  
Full Scale Tests ◽  
Leak Before Break

As part of a safety case for a subsea 13Cr pipeline, the operator wished to demonstrate that if a circumferential through wall crack developed, the crack would remain stable as a leak rather than growing to a full bore rupture. An initial fracture mechanics analysis had suggested that the margins on crack length were too small to make such a “leak before break” argument. This paper reports an integrated programme of small scale testing, numerical modelling and full scale testing which showed that a leak before break case could be made. 13Cr martensitic steel generally shows excellent toughness at the service temperature, as does the super duplex weld metal that was used for the girth welds. However, as the pipeline had been installed by reeling, there was some concern that the toughness may have been reduced. Hence a programme of fracture toughness testing was designed to generate tearing resistance curves for both as-received and pre-strained parent material and weld metal. Deep and shallow through thickness notched specimen geometries were tested to explore the effect of constraint on the toughness. Finite element analysis was used to predict the stress intensity for a range of crack lengths, including the effects of misalignment. Non-linear analyses were used to estimate the limit load for the cracked pipe. The test results were used as input to tearing analyses to Level 3 of BS 7910. These showed that the tolerable length of a through wall crack exceeded the length of anticipated defects by a factor of at least two. To confirm the fracture mechanics predictions, two full scale tests were carried out. These used pressure cycling to grow a through wall crack by fatigue. These cracks were stable under an internal pressure equal to the pipeline design pressure. The cracked specimens were then axially loaded to failure. Extensive tearing occurred before final failure at loads above those predicted by the fracture analysis, confirming the conservatism of the predictions.

Multi-Tier Tensile Strain Models for Strain-Based Design: Part 3 — Model Evaluation Against Experimental Data

2012 ◽  
Author(s):  
Ming Liu ◽  
Yong-Yi Wang ◽  
David Horsley ◽  
Steve Nanney
Keyword(s):  
Experimental Data ◽  
Test Data ◽  
Wall Thickness ◽  
Model Evaluation ◽  
Tensile Strain ◽  
Full Scale ◽  
Weld Strength ◽  
Model Predictions ◽  
Girth Welds ◽  
Level 2

This is the third paper in a three-paper series related to the development of tensile strain models. The fundamental basis [1] and formulation [2] of the models are presented in two companion papers. This paper covers the evaluation of the models against large-scale experimental data which include a total of 24 full-scale pipe tests with and without internal pressure [3,4] and 30 curved wide plate (CWP) tests [5,6]. The 24 full-scale pipe specimens are nominally X65 grade (12.75″ OD and 12.7-mm wall thickness) and made by two manufacturers. The actual yield strength of the two pipes differs by approximately 14 ksi. The girth welds are made with three welding procedures, creating three weld strength levels. The full-scale test program are designed to evaluate the effects of internal pressure, weld strength mismatch, pipe strength, pipe Y/T ratio, flaw location, flaw size, and toughness. The 30 CWP specimens are from 36″ OD and 19.1 mm wall thickness X100 pipes. The girth welds are made with two welding procedures, creating two slightly different weld strength mismatch levels. The CWP test specimens expand the range of material grade and wall thickness for the model evaluation. The model evaluation demonstrates that the overall correlations between the experimental test data and model predations are similar when the model predictions are made with Level 2 and 3 procedures and various toughness options. The Level 2 procedure with Charpy energy option and Level 3b provide the best overall one-to-one correlation between the test data and model prediction. The Level 3b shows greater scatter than Level 2 with the Charpy energy option. The most significant contributor to the TSC variations and the difference between the measured and predicted TSCs is the strength variation in the pipes. A small variation in the strength can lead to a large variation of the measured remote strain even when the flaw behavior is essentially the same. For the 24 full-scale pipe tests, a strength variation of 1 ksi in the pipes would explain the large variations of the measured TSC in comparison to the model predictions. The TSC models produce consistent results that capture the overall trend of the test data.

Fracture Control in Pipelines Under High Plastic Strains: A Critique of DNV-RP-F108

2008 ◽  
Author(s):  
Andrew Cosham ◽  
Kenneth A. Macdonald
Keyword(s):  
Fatigue Loading ◽  
Practical Experience ◽  
Ground Movement ◽  
Plastic Strains ◽  
Offshore Pipelines ◽  
Fracture Control ◽  
Offshore Industry ◽  
Girth Welds ◽  
Pipeline Design ◽  
High Plastic

Offshore pipelines experience strains greater than yield during pipelay and in service. Installation by reeling introduces high levels of plastic strain, typically on the order of 2 percent for a 12 in. flowline. Controlled lateral buckling in offshore pipelines, due to high operating pressures and/or temperatures, may also give rise to high strains and large cyclic loads. Similarly, frost heave or ground movement in onshore pipelines can cause high strains. To date, most of the cases involving high strains are to be found in offshore pipelines, in terms of both design and the assessment of accidental states. However, some of the experiences in the offshore industry have relevance to onshore pipelines. Fracture control in this context is designing pipelines to address the implications of these high static and cyclic strains during installation/construction and operation. Pipeline design codes such as DNV-OS-F101 and DNV-RP-F108 give guidance. Two issues to consider are: the degradation of the material properties, and the failure of the girth welds. High strains may cause failure or the growth — by stable ductile tearing — of preexisting flaws in the weld. Subsequent fatigue loading may cause pre-existing flaws to grow to failure. Engineering critical assessments (ECAs) are conducted during pipeline design to determine tolerable sizes for weld flaws. Standards such as BS 7910 and API 579 are primarily stress-based and it is not straightforward to apply them to strain-based situations. DNV-RP-F108 addresses this gap by providing additional guidance derived from UK and Norwegian research programmes. Assessing flaws subject to high strains is at the ‘cutting-edge’ of applied fracture mechanics. ECAs often have a reputation of being ‘over-conservative’. ECAs of pipelines subject to high strains may indicate that only very small flaws would be acceptable, whereas practical experience has shown that the girth welds are highly tolerant to the presence of flaws. It is therefore instructive to consider under what situations might ECAs be too conservative, and when they may be non-conservative. The available guidance for ensuring fracture control in pipelines under high plastic strains is discussed in this paper, and the wider issues are addressed.

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