Fracture Control — Offshore Pipelines: Probabilistic Fracture Assessment of Surface Cracked Ductile Pipelines Using Analytical Equations

2005 ◽  
Author(s):  
Andreas Sandvik ◽  
Erling O̸stby ◽  
Arvid Naess ◽  
Gudfinnur Sigurdsson ◽  
Christian Thaulow
Keyword(s):  
Fracture Behaviour ◽  
Crack Growth Resistance ◽  
Bending Moments ◽  
Line Pipe ◽  
Offshore Pipelines ◽  
Crack Driving Force ◽  
Ductile Tearing ◽  
Fracture Assessment ◽  
Fracture Control ◽  
Probability Of Fracture

Since modern pipelines usually display ductile fracture behaviour, fracture assessments accounting for ductile tearing should be used. In this work we use a simplified strain-based fracture mechanics equation in the probabilistic fracture assessments. Furthermore, we use the traditional tangency criterion between the crack driving force and the crack growth resistance, in calculation of the onset of critical ductile tearing. Additionally, two types of external load on the line-pipe are considered, namely strains due to external bending moments and internal pressure. We establish the probability of fracture for line-pipes with relevant diameter to thickness ratios, and thicknesses, for J-laid or S-laid offshore pipelines. The distinction between system effects, in which all defects are likely to be subject to the same loading, and cases where only a small part of the pipeline will experience high loading, is also discussed.

Fracture Control — Offshore Pipelines: Current Status of Fracture Assessment for Pipelines, Limitations and the Need for Development

2005 ◽  
Author(s):  
Roberto Bruschi ◽  
Enrico Torselletti ◽  
Luigino Vitali ◽  
Mons Hauge ◽  
Erik Levold
Keyword(s):  
Failure Modes ◽  
Design Guidelines ◽  
Assessment Methods ◽  
Current Status ◽  
Design Criteria ◽  
Safety Factors ◽  
Design Guideline ◽  
Offshore Pipelines ◽  
Fracture Assessment ◽  
Fracture Control

Recent development plans envisage the exploitation of very deep offshore reservoirs as well as transport of hydrocarbons at temperature and pressure conditions far more severe than in past projects. Technical feasibility of such projects requires higher material utilisation, and the design guidelines need to be improved to allow for the new design conditions. Fracture assessment methods have been used in the evaluation of pipeline integrity for several years. In particular, the verification of acceptable defect sizes for installation and operational loads are now widely used and assessment methods are referenced in pipeline standards and guidelines. However, design guidelines are still missing the calibrated safety factors and stringent design format required to let the fracture failure mode be consistent with the other failure modes in the pipeline design such as bursting, local buckling and fatigue. The Fracture Control Offshore Pipelines Project is a Joint Industry Research and Development Project, whose objective is to study the behaviour of defected girth welds in pipelines subject to construction and operational loads ever experienced before. Due to the envisaged high loading condition and the high costs of recent offshore pipeline projects it is important, with an accurate defect assessment analysis, to avoid delays caused by unnecessary repairs or failures because of flaws that should have been detected and repaired. The final objective is the development of specific design criteria in the form of a design guideline to be used in the verification and design of offshore pipelines against the fracture/plastic collapse failure of a defected girth weld. The design criteria are based on the application of reliability methods to calibrate the partial safety factors in compliance with the safety philosophy established by DNV OS-F101 and will include the rational application of new NDT techniques. The JI Project is carried over 5 years and has started in 2002. The JI project is sponsored by the industry (BP, ENI Norge, Hydro and Statoil) and by the Norwegian Research Council. This paper describes the current status of existing fracture assessment procedures for pipelines with particular attention to their limitations and the needs for development and a brief overview of the results obtained in the project so far as well as the challenges to be solved in the project.

Fracture Control — Offshore Pipelines: Experimental Studies on the Effect of Crack Depth and Asymmetric Geometries on the Ductile Tearing Resistance

2005 ◽  
Author(s):  
Ba˚rd Nyhus ◽  
Erling O̸stby ◽  
Hans Olav Knagenhjelm ◽  
Scott Black ◽  
Per Arne Ro̸stadsand
Keyword(s):  
Fracture Toughness ◽  
Crack Depth ◽  
Experimental Studies ◽  
Single Edge ◽  
Offshore Pipelines ◽  
Ductile Tearing ◽  
Single Edge Notch ◽  
Edge Notch ◽  
Fracture Control ◽  
Tearing Resistance

Engineering critical assessment of offshore pipelines is usually very conservative if standardized single edge notch bend (SENB) specimens are used for the fracture mechanics testing. It is commonly accepted that the fracture toughness is dependent on the geometry constraint at the crack tip. The standardized SENB specimens have a high geometry constraint, and give lower bound fracture toughness for all geometries. For circumferential flaws in pipes the single edge notch tension (SENT) specimens is taken more into use, to establish more correct fracture toughness for the pipe in question. In this paper the effect of crack depth, misalignment and different wall thicknesses in SENT specimens have been studied. In addition the effect of crack depth and internal pressure in pipes have been studied with FE simulations.

Fracture Control Offshore Pipelines: Advantages of Using Direct Calculations in Fracture Assessments of Pipelines

2005 ◽  
Author(s):  
Christian Thaulow ◽  
Bjo̸rn Skallerud ◽  
K. R. Jayadevan ◽  
Espen Berg
Keyword(s):  
Internal Pressure ◽  
Biaxial Loading ◽  
Crack Depth ◽  
Deformation Capacity ◽  
Surface Cracks ◽  
Simple Method ◽  
Offshore Pipelines ◽  
Ductile Tearing ◽  
Fracture Control ◽  
Direct Calculations

Surface cracks pose major challenges for the structural integrity of pipelines. In fracture assessment programs the use of constraint parameters, such as the T-stress, along with K, J or CTOD are important to account for the limitations of single-parameter fracture mechanics. However, the three-dimensional nature of surface cracks precludes detailed 3-D finite element modeling for routine calculations. Here line-spring/shell-element models are demonstrated to be an efficient and reasonably accurate tool for constraint estimation even under large deformation levels when general yielding prevails in the pipe. Envisaging the potential use of this procedure in fracture analysis of pipelines, a new software, LINKpipe, has been developed. The program has been developed as a part of the Joint Industry project Fracture Control Offshore Pipelines. The objective of this project is to study the behaviour of defected girth welds in pipelines subject to construction and operational loads ever experienced before. The calculations have been performed in close cooperation with the project participants; see presentations of project-colleagues at OMAE 2005: Bruschi et al (2005), O̸stby (2005), Nyhus et al (2005) and Sandvik et al (2005). In this paper the line-spring calculations are compared with 3-D FE calculations and computations according to BS 7910. A pipe geometry, with OD = 400mm, was selected for the comparisons. The line-spring calculations were close to the 3-D calculations, while BS7910 was very conservative for long cracks and unconservative for short cracks. In highly ductile materials, such as pipeline steels, considerably amount of stable crack growth can be tolerated prior to the final failure of the structure. A simple method for simulating ductile tearing in surface cracked pipes with the line-spring model has been developed. A detailed parametric study has been performed to examine the effect of ductile tearing for pipes loaded in tensile, bending and with internal pressure. A significant reduction in deformation capacity from the stationary case is noticed. As the crack depth increases, the effect of ductile tearing becomes more important. And under biaxial loading a significant reduction of the deformation capacity is found as the internal pressure is increased. The development of the line-spring methodology paves the way for a transition from to-days rule-based design to direct calculations.

Failure assessment diagrams. II. The use of single failure assessment lines

1994 ◽  
Vol 444 (1922) ◽  
pp. 483-496 ◽  
Keyword(s):  
Crack Growth ◽  
Deformation Theory ◽  
Curve Analysis ◽  
Alternative Proof ◽  
Crack Driving Force ◽  
Ductile Tearing ◽  
Natural Mapping ◽  
Tearing Instability ◽  
Failure Assessment ◽  
Level 3

In a previous paper a natural mapping was noted from the ( a, J ep ) diagram of R-curve analysis into the ( L r , K r ) failure assessment diagram (FAD) of the R6-revision 3 procedure. Assuming that J ep is obtained by a deformation theory of plasticity, the analytical expression for this mapping is given and used to derive the images in the FAD of the applied J ep curves and of the R-curve. If this mapping is sufficiently smooth, it may be used to provide an alternative proof that the critical R6-revision 3 load locus touches the R-curve image (RCI) when the crack extension and the load are the same as those predicted by R-curve analysis. The natural mapping may not always be 1:1 and this is illustrated by considering the example of a family of linear R-curves. The relations between the various other functions used in the FAD and R-curve analysis are studied analytically. In particular it is shown how to derive from any single failure assessment line (FAL) on which the assessment point is assumed to move during crack growth, either the implied R-curve (IRC) or, alternatively, the implied applied J ep curve (IAJC). Further comments are made on the internal consistency or conservatism of analyses of ductile tearing instability which use a single FAL on which the assessment point is assumed to move during crack growth, such as those characteristic of level 3 of PD6493 and options 1 and 2 of R6-revision 3. The method for testing the consistency or conservatism of an FAD with a single FAL which involves the calculation of the IAJC requires that the function J ep = j ep ( a, L ) of the structure be known for a specific restricted range of a and L only. In contrast, the deduction of the IRC requires a knowledge of the j ep ( a, L ) over a wider domain. It is emphasized that the assessment of conservatism throughout is not absolute but only relative to the predictions of R-curve analysis. As in the previous paper, the discussion is given in terms of the J based parameters. But the conclusions hold equally well for an FAD based on any other parameters describing crack driving force and crack resistance.

scholarly journals Crohn Disease and Fracture Risk Assessment With FRAX

2019 ◽  
Vol 1 (2) ◽  
Author(s):  
Grethe B Jonasson ◽  
Jack Hilon ◽  
Bengt Hasseus ◽  
Torgny Alstad ◽  
Hossein Kashani
Keyword(s):  
Risk Assessment ◽  
Risk Factor ◽  
Fracture Risk ◽  
Crohn Disease ◽  
Assessment Tool ◽  
Fracture Risk Assessment ◽  
Health Questionnaire ◽  
Fracture Assessment ◽  
Probability Of Fracture ◽  
Frax Score

Abstract Background Studies are inconsistent whether people with Crohn disease (CD) have an increased fracture risk. This study showed that patients with Crohn’s disease (CD) had a higher ten year probability of fracture, assessed by the fracture assessment tool FRAX, and more fractures, but the proportion of CD patients with a fracture was not significantly higher than that of controls. Methods Forty-nine CD and 49 controls participated. All 98 completed a health questionnaire. A score with the fracture assessment tool FRAX > 15% was considered risk factor for fracture. Results Mean FRAX score for 49 CD was 10.1 ± 10.3% and for 49 controls 5.0 ± 3.9% (P = 0.002). The variables correlated with fracture were being female (P = 0.04) and having a fractured mother (P = 0.002). Conclusion The CD group had significantly higher FRAX scores and more fractures, but the proportion of CD subjects with a fracture was not significantly higher than that of controls.

Recent Studies Towards Updating the BS7910 Flaw Interaction Rule

2018 ◽  
Author(s):  
Bostjan Bezensek ◽  
Harry E. Coules
Keyword(s):  
Aspect Ratio ◽  
Rule Based ◽  
Crack Driving Force ◽  
Reference Stress ◽  
Surface Flaws ◽  
Close Proximity ◽  
Fracture Assessment ◽  
Assessment Procedures ◽  
Work Done ◽  
Interaction Rule

Fitness for service assessment procedures rely on flaw interaction rules for assessment of multiple flaws in close proximity. Such rules are aimed at avoiding excessive amplification of the crack driving force that may result in a non-conservative fracture assessment. In BS7910, the 2013 edition [1] introduced a new flaw interaction rule for the co-planar flaws where the proximity of adjacent flaws is judged based on flaw height (i.e. s = 0.5*max(a1,a2) for surface flaws). The rule was introduced for flaws with aspect ratio of a/c < 1 for both flaws, while for other flaw shapes and combinations the earlier rule from the predecessor document PD6493:1993 [2] was retained. This paper summarises the recent work done by the authors and work from literature to examine the applicability of the s = 0.5*max(a1,a2) rule to flaws with aspect ratio a/c ≥ 1 and dissimilar flaw combinations. It is shown that the current BS7910 rule based on s = 0.5*max(a1,a2) produces a conservative flaw assessment with the use of BS7910 solutions for stress intensity factor and reference stress. An exception are cases of two deep surface flaws where the rule is proposed to change to: s ≤ max(a1, a2) for two surface flaws with a1/t & a2/t > 0.5

The Specifications Dilemma Posed by Ultra High Toughness Line Pipe Steels

2016 ◽  
Author(s):  
B. N. Leis ◽  
J. M. Gray ◽  
F. J. Barbaro
Keyword(s):  
Critical Element ◽  
Line Pipe ◽  
Control Plan ◽  
Full Size ◽  
Manufacturing Procedure ◽  
High Vapor ◽  
Qualification Testing ◽  
Fracture Control ◽  
Shear Failures ◽  
Propagating Shear

Pipelines transporting compressible hydrocarbons like methane or high-vapor-pressure liquids under supercritical conditions are uniquely susceptible to long-propagating failures in the event that initiation triggers this process. The unplanned release of hydrocarbons from such pipelines poses the risk for significant pollution and/or the horrific potential of explosion and a very large fire, depending on the transported product. Accordingly, the manufacturing procedure specification (MPS) developed to ensure the design requirements are met by the steel and pipe-making process is a critical element of the fracture control plan, whose broad purpose is to protect the environment and ensure public safety, and preserve the operator’s investment in the asset. This paper considers steel specification to avoid long-propagating shear failures in advanced-design larger-diameter higher-pressure pipelines made of thinner-wall higher-grade steels. Assuming that the arrest requirements can be reliably predicted it remains to specify the steel design, and ensure fracture control can be affected through the MPS and manufacturing procedure qualification testing (MPQT). While standards exist for use in MPQTs to establish that the MPS requirements have been met, very often CVN specimens remain unbroken, while DWTT specimens exhibit features that are inconsistent with the historic response and assumptions that underlie many standards. In addition, sub-width specimens are often used, whereas there is no standardized means to scale those results consistent with the full-width response required by some standards. Finally, empirical models such as the Battelle two curve model (BTCM) widely used to predict required arrest resistance have their roots in sub-width specimens, yet their outcome is widely expressed in a full-size context. This paper reviews results for sub-width specimens developed for steels in the era that the BTCM was calibrated to establish scaling rules to facilitate prediction in a full-size setting. Thereafter, issues associated with the use of sub-width specimens are reviewed and criteria are developed to scale results from such testing for use in the MPS, and MPQT, which is presented as a function of toughness. Finally, issues associated with the acceptance of data from unbroken CVN specimens are reviewed, as are known issues in the interpretation of DWTT fracture surfaces.

Fracture Control for the Alliance Pipeline

2000 ◽  
Author(s):  
Bob Eiber ◽  
Lorne Carlson ◽  
Brian Leis
Keyword(s):  
Natural Gas ◽  
New Technology ◽  
Fracture Initiation ◽  
Line Pipe ◽  
Control Plan ◽  
High Toughness ◽  
Pipe Burst ◽  
Fracture Control ◽  
Pipe Fittings ◽  
Fracture Arrest

This paper reviews the fracture control plan for the Alliance Pipeline, which is planned for operation in 2000. This natural-gas pipeline is 2627 km (1858 miles) long, running from British Columbia, Canada to Illinois, USA. Interest in the fracture control for this pipeline results from its design, which is based on transporting a rich natural gas (up to 15% ethane, 3% propane) at a relatively high pressure 12,000 kPa (1740 psi). This break from traditional pressures and lean gases, which frequently are constrained by incremental expansion, is more efficient and more economical than previous natural gas pipelines. Use of higher pressures and rich gas requires adequate fracture control for the line pipe, fittings, and valves. This fracture control has been achieved for the Alliance Pipeline by specifying high-toughness steels, in terms of both fracture-initiation and fracture-propagation resistance for the line pipe, fittings and heavy wall components. While beneficial from an economics viewpoint, the need for higher toughnesses raised concern over the validity of the fracture control plan, which was based on existing and new technology. The concern focused on fracture arrest using high toughness steels. The concern was associated with characterizing fracture arrest resistance using Charpy V-notch impact toughness, the most commonly used method to measure fracture arrest resistance. Developments were undertaken to address problems associated with the use of higher-toughness steel and these were validated with full-scale pipe burst tests to demonstrate the viability of the fracture control plan. The solution involved extending existing methods to address much higher toughness steels, which provided a significantly improved correlation between fracture arrest predictions and experimental results. In the burst tests, data was collected to validate the Alliance design and also to extend the database of fracture arrest data to assist future pipelines. Data such as the pressure between the pipe and soil as the gas escapes from the pipe, the sound levels in the atmosphere, the movement and strains in the pipe ahead of the running fracture were instrumented in the test and the available results are presented.

Fracture Toughness in the Transition Temperature Region

2018 ◽  
Vol 1146 ◽  
pp. 92-97
Author(s):  
Emina Džindo ◽  
Zoran Radaković ◽  
Blagoj Petrovski ◽  
Srdjan Tadić ◽  
Sanja Petronić ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Transition Temperature ◽  
Temperature Region ◽  
Upper Bound ◽  
Low Temperatures ◽  
Fracture Behaviour ◽  
Base Material ◽  
Statistical Analyses ◽  
The Other ◽  
Fracture Assessment

The steels fracture toughness was measured at two different temperature T= - 60°C and T = -90°C, at v=0.02 mm/min and v=0.5mm/min. The following steels: CrMoV, 20MnMoNi55, A533B and A508 were tested with three different sizes of CT specimens 50 and 100 and 200. Those steels are weldable, although the authors investigated the fracture behaviour of base material. In order to satisfy statistical analyses, a large number of specimens were tested. Fracture behaviour has turned out to be typical, S-shaped curve for transitional fracture at low temperatures. Apart from the other variables, specimen’s width significantly affects measured toughness. Smaller specimens, CT50, might be considered of upper bound reliability while the CT200 specimens were shown to be the most conservative. In this way it has been shown that wider specimens are more reliable in a fracture assessment of the examined steels. In this paper, the fracture probabilities of specimens in function of fracture toughness were determined as well, and it could be concluded that the widest specimens are the most likely to be broken for the same values of the fracture toughness.

scholarly journals Design, Development and Confirmation of a High Toughness Gas Line Pipe for Alliance Pipeline at Camrose Pipe Company

2000 ◽  
Author(s):  
Alex J. Afaganis ◽  
James R. Mitchell ◽  
Lorne Carlson ◽  
Alan Gilroy-Scott
Keyword(s):  
Design Development ◽  
Line Pipe ◽  
High Toughness ◽  
Assessment Tests ◽  
Chevron Notch ◽  
Energy Measure ◽  
Drop Weight Tear Test ◽  
Fracture Assessment ◽  
Fracture Arrest ◽  
Pipe Manufacturing

Through 1999, Camrose Pipe Company manufactured ∼152 km (∼45 000 tonnes) of 1067 × 11.4mm pipe for Alliance Pipeline Partnership Ltd. This section of Alliance’s pipeline was manufactured to a design whose pipe fracture toughness requirements was significantly beyond those historically manufactured in Canada and initiated a major leap in plate/pipe manufacturing toughness capability. The development of line pipe toughness in Canada culminating in this order will be profiled. Further, this high toughness design is at the far reaches of the traditional fracture arrest models. Besides the traditional Charpy energy measure, and to confirm Alliance’s confidence in their fracture arrest design, another two sets of fracture assessment tests were used on a trial and production basis: the API chevron notch drop weight tear test (CN DWTT) energy and the energy of a similar test using an Alliance notch modification. The results of these tests will be reviewed and compared.

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