The Practical Application of Fracture Control to Natural Gas Pipelines

2008 ◽  
Author(s):  
K. A. Widenmaier ◽  
A. B. Rothwell
Keyword(s):  
Natural Gas ◽  
Large Scale ◽  
High Strength ◽  
Fracture Initiation ◽  
Opening Angle ◽  
Pipe Material ◽  
Design Factor ◽  
Line Pipe ◽  
Natural Gas Pipelines ◽  
Crack Tip Opening

The use of high strength, high design-factor pipe to transport natural gas requires the careful design and selection of pipeline materials. A primary material concern is the characterization and control of ductile fracture initiation and arrest. Impact toughness in the form of Charpy V-notch energies or drop-weight tear tests is usually specified in the design and purchase of line pipe in order to prevent large-scale fracture. While minimum values are prescribed in various codes, they may not offer sufficient protection in pipelines with high pressure, cold temperature, rich gas designs. The implications of the crack driving force arising from the gas decompression versus the resisting force of the pipe material and backfill are examined. The use and limitations of the Battelle two-curve method as the standard model are compared with new developments utilizing crack-tip opening angle and other techniques. The methodology and reasoning used to specify the material properties for line pipe are described and the inherent limits and risks are discussed. The applicability of Charpy energy to predict ductile arrest in high strength pipes (X80 and above) is examined.

scholarly journals Evaluation and instrumentation of the drop weight tear test

2012 ◽  
Vol 3 (1) ◽  
pp. 52-58
Author(s):  
S. Vervaet ◽  
W. De Waele
Keyword(s):  
High Strength ◽  
Test Method ◽  
Opening Angle ◽  
Safety Issues ◽  
Natural Gas Pipelines ◽  
Drop Weight Tear Test ◽  
Fracture Appearance ◽  
Oil And Natural Gas ◽  
Linepipe Steels ◽  
Crack Tip Opening

With the use of high strength and high toughness steels in the pipeline industry it has become necessary tobetter understand the factors which influence the reliability and integrity of oil and natural gas pipelines. TheDrop-Weight Tear Test (DWTT) is a common test method to determine the fracture appearance andfracture ductility of steel. Its fundamental purpose is to determine the appearance of propagating fracturesin steels over the temperature range where the fracture mode changes from brittle to ductile. But there arestill many subjects of discussion concerning which results must be obtained, in which manner they shouldbe obtained and how they should be interpreted. Is it still possible to deduce a shear appearance fromsamples which have such an abnormal fracture that they used to be discarded as invalid ? Could resultsfrom the DWTT be correlated with the Crack Tip Opening Angle (CTOA), which is particularly important forfinite element modelling ? What to think about methods such as the two specimen CTOA and the simplifiedsingle specimen method ? How severe is the effect of tunnelling in contemporary linepipe steels and howcan this be dealt with ? Many questions still remain and many aspects are still vague despite the correlatingecological, economical and safety issues. Therefore, there is a major necessity for further investigations.

Validation of EMAT ILI for Management of Stress Corrosion Cracking in Natural Gas Pipelines

2014 ◽  
Author(s):  
Toby Fore ◽  
Stefan Klein ◽  
Chris Yoxall ◽  
Stan Cone
Keyword(s):  
High Resolution ◽  
Natural Gas ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Probability Of Detection ◽  
Gas Pipelines ◽  
Line Pipe ◽  
Natural Gas Pipelines ◽  
Electro Magnetic

Managing the threat of Stress Corrosion Cracking (SCC) in natural gas pipelines continues to be an area of focus for many operating companies with potentially susceptible pipelines. This paper describes the validation process of the high-resolution Electro-Magnetic Acoustical Transducer (EMAT) In-Line Inspection (ILI) technology for detection of SCC prior to scheduled pressure tests of inspected line pipe valve sections. The validation of the EMAT technology covered the application of high-resolution EMAT ILI and determining the Probability Of Detection (POD) and Identification (POI). The ILI verification process is in accordance to a API 1163 Level 3 validation. It is described in detail for 30″ and 36″ pipeline segments. Both segments are known to have an SCC history. Correlation of EMAT ILI calls to manual non-destructive measurements and destructively tested SCC samples lead to a comprehensive understanding of the capabilities of the EMAT technology and the associated process for managing the SCC threat. Based on the data gathered, the dimensional tool tolerances in terms of length and depth are derived.

Development of X90 and X100 Steel Grades for Seamless Linepipe Products

2014 ◽  
Author(s):  
Diana Toma ◽  
Silke Harksen ◽  
Dorothee Niklasch ◽  
Denise Mahn ◽  
Ashraf Koka
Keyword(s):  
Wall Thickness ◽  
Deep Water ◽  
High Strength ◽  
Oil And Gas Industry ◽  
Pipe Material ◽  
Line Pipe ◽  
Materials Development ◽  
Additional Tool ◽  
Technical Requirements ◽  
Steel Grades

The general trend in oil and gas industry gives a clear direction towards the need for high strength grades up to X100. The exploration in extreme regions and under severe conditions, e.g. in ultra deep water regions also considering High Temperature/High Pressure Fields or arctic areas, becomes more and more important with respect to the still growing demand of the world for natural resources. Further, the application of high strength materials enables the possibility of structure weight reduction which benefits to materials and cost reduction and increase of efficiency in the pipe line installation process. To address these topics, the development of such high strength steel grades with optimum combination of high tensile properties, excellent toughness properties and sour service resistivity for seamless quenched and tempered pipes are in the focus of the materials development and improvement of Vallourec. This paper will present the efforts put into the materials development for line pipe applications up to grade X100 for seamless pipes manufactured by Pilger Mill. The steel concept developed by Vallourec over the last years [1,2] was modified and adapted according to the technical requirements of the Pilger rolling process. Pipes with OD≥20″ and wall thickness up to 30 mm were rolled and subsequent quenched and tempered. The supportive application of thermodynamic and kinetic simulation techniques as additional tool for the material development was used. Results of mechanical characterization by tensile and toughness testing, as well as microstructure examination by light-optical microscopy will be shown. Advanced investigation techniques as scanning electron microcopy and electron backscatter diffraction are applied to characterize the pipe material up to the crystallographic level. The presented results will demonstrate not only the effect of a well-balanced alloying concept appointing micro-alloying, but also the high sophisticated and precise thermal treatment of these pipe products. The presented alloying concept enables the production grade X90 to X100 with wall thickness up to 30 mm and is further extending the product portfolio of Vallourec for riser systems for deepwater and ultra-deep water application [1, 3, 4].

Effects of Soil Cohesiveness and Depth on Dynamic Ductile Fracture Speeds

2008 ◽  
Author(s):  
D. Rudland ◽  
D.-J. Shim ◽  
G. M. Wilkowski ◽  
S. Kawaguchi ◽  
N. Hagiwara ◽  
...  
Keyword(s):  
Ductile Fracture ◽  
Large Scale ◽  
Soil Depth ◽  
Crack Arrest ◽  
Small Scale ◽  
Total Density ◽  
Pipe Material ◽  
Pipe Steels ◽  
Line Pipe ◽  
Fracture Arrest

The ductile fracture resistance of newer line pipe steels is of concern for high grade/strength steels and higher-pressure pipeline designs. Although there have been several attempts to make improved ductile fracture arrest models, the model that is still used most frequently is the Battelle Two-Curve Method (TCM). This analysis incorporates the gas-decompression behavior with the fracture toughness of the pipe material to predict the minimum Charpy energy required for crack arrest. For this analysis, the influence of the backfill is lumped into one empirically developed “soil” coefficient which is not specific to soil type, density or strength. No attempt has been made to quantify the effects of soil depth, type, total density or strength on the fracture speeds of propagating cracks in line pipe steels. In this paper, results from small-scale and large-scale burst tests with well-controlled backfill conditions are presented and analyzed to determine the effects of soil depth and cohesiveness on the fracture speeds. Combining this data with the past full-scale burst data used in generating the original backfill coefficient provides additional insight into the effects of the soil properties on the fracture speeds and the arrest of running ductile fractures in line pipe materials.

Crack Tip Opening Angle: Measurement and Modeling of Fracture Resistance in Low and High Strength Pipeline Steels

2006 ◽  
Author(s):  
Ph. P. Darcis ◽  
G. Kohn ◽  
A. Bussiba ◽  
J. D. McColskey ◽  
C. N. McCowan ◽  
...  
Keyword(s):  
Steady State ◽  
Fracture Resistance ◽  
Fracture Process ◽  
Pipeline Steel ◽  
Crack Tip ◽  
High Strength ◽  
Opening Angle ◽  
Test Technique ◽  
Crack Tip Opening Angle ◽  
Crack Tip Opening

Crack tip opening angle (CTOA) is becoming one of the more widely accepted properties for characterizing fully plastic fracture. In fact, it has been recognized as a measure of the resistance of a material to fracture, in cases where there is a large degree of stable-tearing crack extension during the fracture process. This type of steady-state fracture resistance takes place when the CTOA in a material reaches a critical value, as typically occurs in low-constraint configurations. Our current research has applied the CTOA concept as an alternative or an addition to the Charpy V-notch and the drop weight tear test (DWTT) fracture energy in pipeline characterization. A test technique for direct measurement of CTOA was developed, using a modified double cantilever beam (MDCB) specimen. A digital camera and image analysis software are used to record the progression of the crack tip and to estimate CTOA using the crack edges adjacent to the crack tip. A steady-state CTOA has been successfully measured on five different strength grades of gas pipeline steel (four low strength grades and one high strength grade: X100). In addition, two-dimensional finite element models (2D FEMs) are used to demonstrate the sequence of the fracture process and the deformation mechanisms involved. The CTOA measurements and models are correlated and agree well.

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.

Alloying Concept for High-Strength Seamless Heavy-Wall Line Pipe Suitable for Sour Service Applications

2004 ◽  
Author(s):  
K. Biermann ◽  
C. Kaucke ◽  
M. Probst-Hein ◽  
B. Koschlig
Keyword(s):  
Heat Treatment ◽  
Wall Thickness ◽  
Oil And Gas ◽  
High Strength ◽  
Gas Production ◽  
Pipe Material ◽  
Low Carbon ◽  
Line Pipe ◽  
Oil And Gas Production ◽  
Sour Service

Offshore oil and gas production worldwide is conducted in increasingly deep waters, leading to more and more stringent demands on line pipes. Higher grades and heavier wall thicknesses in combination with deep temperature toughness properties, good weldability and suitability for sour service applications are among the characteristics called for. It is necessary that pipe manufacturers develop materials to meet these at times conflicting requirements. An alloying concept based on steel with very low carbon content is presented. This type of material provides excellent toughness properties at deep temperatures in line pipe with a wall thickness of up to 70 mm, produced by hot rolling followed by QT heat treatment. Pipes from industrial production of identical chemical composition and heat treatment achieved grades X65 to X80, depending on wall thickness. The properties of the steel used in pipes are presented. The resistance of the pipe material to the influence of sour gas was assessed by standard tests. To demonstrate weldability, test welds were performed and examined.

Evaluation of Ductile Cracking Criterion for Grade X100 Linepipe and Relationship to Large Scale Fracture Behavior

2003 ◽  
Author(s):  
Nobuyuki Ishikawa ◽  
Shigeru Endo ◽  
Alan Glover ◽  
David Horsley ◽  
Masao Toyoda
Keyword(s):  
Plastic Strain ◽  
Ductile Fracture ◽  
Fracture Behavior ◽  
Large Scale ◽  
Notch Root ◽  
Equivalent Plastic Strain ◽  
High Strength ◽  
Fracture Initiation ◽  
Linepipe Steels ◽  
Ductile Fracture Initiation

Recent developments in the manufacturing process of steel plate for high strength linepipe have enabled superior toughness to prevent brittle fracture of the pipe body. Techniques for non-destructive inspection have also improved, and large flaws that could lead to brittle fracture are highly unlikely in recent high strength pipelines. However, large amounts of plastic deformation can be expected in seismic or permafrost regions. Prevention of ductile fracture of the pipe body or weldment therefore becomes a key issue in defining the tensile strain limit. Ductile fracture is considered to occur by growth and coalescence of voids, and is affected by stress triaxiality and plastic straining at the cracked region. Although many studies have been carried out to evaluate ductile cracking criteria, its transferability to large-scale fracture behavior has not been thoroughly investigated. In this study, ductile cracking of high strength linepipe steels, Grade X80 and X100, was investigated. Notched round bar specimens with different notch root radii were tested to determine the precise conditions for initiation of ductile fracture. Stress and strain conditions at the notch regions were evaluated by FE analysis, and the “critical equivalent plastic strain” was defined at conditions corresponding to ductile fracture initiation in the experimental small specimen tests. Ductile crack initiation behavior was also determined for wide plate test specimens by making close observations of the notch root area. 3-D FE analysis of the wide plate tensile test showed that the equivalent plastic strain at the point of ductile fracture initiation was in close agreement with that in the notched round bas specimen. Thus, the “critical equivalent plastic strain,” determined by small notched round bar specimens, can be considered as a transferable criterion to predict large-scale fracture behavior in wide plate tests. Concepts of strain based design in terms of preventing ductile failure from a surface flaw by applying critical strain to cracking were also discussed in this paper. Results were compared to conventional grade linepipe steels and structural steels, showing that recent high strength linepipe steels have higher resistance to ductile cracking than conventional structural steels. In addition, 3-D FE analyses were used in a parametric study to determine the effects of Y/T and uniform strain on the onset of ductile cracking behaviour. The results of these analyses show the relative importance of materials properties on the resistance to ductile cracking.

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