Assessing Low-Constraint Fracture Toughness Test Methods Using Clamped SENT Specimens

2019 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Tom McGaughy
Keyword(s):  
Fracture Toughness ◽  
Oil And Gas ◽  
Oil And Gas Industry ◽  
Test Methods ◽  
Fracture Toughness Test ◽  
Single Edge ◽  
Gas Industry ◽  
End Conditions ◽  
The Difference ◽  
Low Constraint

Abstract The low-constraint fracture toughness can be measured using a single edge-notched tension (SENT) specimen in the clamped-end conditions. The SENT specimen has been used in the oil and gas industry in the strain-based design and the crack assessment for transmission pipelines. Since 2006 when DNV published the first SENT test practice, many investigations have been done, and various SENT test methods were developed, including CANMET and ExxonMobil methods in terms of the J-integral and CTOD. The effort led to the first SENT test standard BS 8571 being published in 2014. However, the experimental evaluation methods remain in developing, and different methods may determine inconsistent results. For this reason, the present paper gives a brief review on SENT fracture testing and assesses the available test methods, including progresses on study of stress intensity factor, geometric eta factors, elastic compliance equation, and constraint m factor as well. The difference between J-converted CTOD and double clip gage measured CTOD is also discussed. On those bases, agreements and challenges in SENT testing are identified. The results provide a direction for further investigation to improve the current SENT test methods.

A Wide Range Stress Intensity Factor Solution for Single Edge Notched Tension Specimen With Clamped Ends

2016 ◽  
Author(s):  
Xian-Kui Zhu
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Oil And Gas ◽  
Test Procedure ◽  
Oil And Gas Industry ◽  
Test Methods ◽  
Single Edge ◽  
Wide Range ◽  
Low Constraint

Single edge notched tension (SENT) specimen with clamped ends has been accepted in the oil and gas industry as a low-constraint fracture test specimen to directly determine fracture toughness or resistances in low constraint conditions. Different SENT test methods have been developed, including DNV-RP-F108 test practice, CANMET J-resistance curve test procedure, ExxonMobil CTOD test procedure, and others. Based on these methods, a SENT test standard BS 8571 was developed and published in December of 2014. However, the stress intensity factor K used in BS 8571 was a very complicated function and difficult to use. Moreover, the present author found that this complicated K solution is correct only for a/W≤0.6, but incorrect for deep cracks of a/W>0.6. In order to obtain a simple and accurate K solution for the clamped SENT specimen, this paper revisits this topic. Using the crack compliance method, the desired K solution is obtained. Results show that the proposed K solution and its curve fit are very accurate over a wide range of crack sizes, and validated by existing finite element results of K for the SENT specimens.

When Metals and Microbes Meet: Preventing Microbial Corrosion in Crude Oil Transmission Pipelines

2020 ◽  
Author(s):  
Lisa M. Gieg ◽  
Mohita Sharma ◽  
Trevor Place ◽  
Jennifer Sargent ◽  
Yin Shen
Keyword(s):  
Crude Oil ◽  
Oil And Gas ◽  
Combined Treatment ◽  
Oil And Gas Industry ◽  
Test Methods ◽  
Microbial Corrosion ◽  
Gas Industry ◽  
Chemical Treatments ◽  
Transmission Pipeline ◽  
Transmission Pipelines

Abstract Corrosion of carbon steel infrastructure in the oil and gas industry can occur via a variety of chemical, physical, and/or microbiological mechanisms. Although microbial corrosion is known to lead to infrastructure failure in many upstream and downstream operations, predicting when and how microorganisms attack metal surfaces remains a challenge. In crude oil transmission pipelines, a kind of aggressive corrosion known as under deposit corrosion (UDC) can occur, wherein mixtures of solids (sands, clays, inorganic minerals), water, oily hydrocarbons, and microorganisms form discreet, (bio)corrosive sludges on the metal surface. To prevent UDC, operators will use physical cleaning methods (e.g., pigging) combined with chemical treatments such as biocides, corrosion inhibitors, and/or biodispersants. As such, it necessary to evaluate the efficacy of these treatments in preventing UDC by monitoring the sludge characteristics and the microorganisms that are potentially involved in the corrosion process. The efficacies of a biocide, corrosion inhibitor, and biodispersant being used to prevent microbial corrosion in a crude oil transmission pipeline were evaluated. A combination of various microbiological analyses and corrosivity tests were performed using sludge samples collected during pigging operations. The results indicated that the combined treatment using inhibitor, biocide 1 and biodispersant was the most effective in preventing metal damage, and both growth-based and Next-Generation Sequencing approaches provided value towards understanding the effects of the chemical treatments. The efficacy of a different biocide (#2) could be discriminated using these test methods. The results of this study demonstrate the importance of considering and monitoring for microbial corrosion of crucial metal infrastructure in the oil and gas industry, and the value of combining multiple lines of evidence to evaluate the performance of different chemical treatment scenarios.

Methods to Determine Low-Constraint Fracture Toughness: Review and Progress

2016 ◽  
Author(s):  
Xian-Kui Zhu
Keyword(s):  
Fracture Toughness ◽  
Test Methods ◽  
Standard Test ◽  
Initiation Toughness ◽  
Fracture Toughness Test ◽  
Crack Tip Opening Displacement ◽  
Test Procedures ◽  
Opening Displacement ◽  
Resistance Curves ◽  
Low Constraint

Fracture toughness is often described by the J-integral or crack-tip opening displacement (CTOD) for ductile materials. ASTM, BSI and ISO have developed their own standard test methods for measuring fracture initiation toughness and resistance curves in terms of the J and CTOD using bending dominant specimens in high constraint conditions. However, most actual cracks are in low constraint conditions, and the standard resistance curves may be overly conservative. To obtain more realistic fracture toughness for actual cracks in low-constraint conditions, different fracture test methods have been developed in the past decades. To facilitate understanding and use the test standards, this paper presents a critical review on commonly used fracture toughness test methods using standard and non-standard specimens in reference to the fracture parameters J and CTOD, including (1) ASTM, BSI and ISO standard test methods, (2) constraint correction methods for formulating a constraint-dependent resistance curve, and (3) direct test methods using the single edge-notched tension (SENT) specimen. This review discusses basic concepts, basic methods, estimation equations, test procedures, historical efforts and recent progresses.

Fractography and Fracture Toughness Measurement

2009 ◽  
Vol 409 ◽  
pp. 17-27 ◽  
Author(s):  
Roger Morrell
Keyword(s):  
Fracture Toughness ◽  
Surface Crack ◽  
Ceramic Materials ◽  
Test Methods ◽  
Fracture Toughness Test ◽  
Single Edge ◽  
Fracture Toughness Measurement ◽  
Beam Method ◽  
Toughness Measurement ◽  
Good Agreement

Using a variety of advanced ceramic materials, a comparison has been conducted of fracture toughness test methods using the single edge vee-notch beam method and the surface crack in flexure method, the latter restricted to optical fractography. Good agreement has been found between the two methods on materials which were amenable to the SCF method. It has further been shown that the SEVNB method can produce reliable results on materials to which the SCF method is not readily applicable.

Comparison between fresh and exposed swelling elastomer

2012 ◽  
Vol 44 (3) ◽  
pp. 237-250 ◽  
Author(s):  
T. Pervez ◽  
S. Z. Qamar ◽  
Mark van de Velden
Keyword(s):  
Oil And Gas ◽  
Nonlinear Behavior ◽  
Oil And Gas Industry ◽  
Test Methods ◽  
Test Duration ◽  
Gas Industry ◽  
Compression Set ◽  
Highly Nonlinear ◽  
Different Temperatures ◽  
Water Swelling

Last decade has seen growing use of swelling elastomers in various applications by the oil and gas industry. Elastomers with special properties have been developed to sustain the specific downhole conditions of temperature, pressure, and chemical environment in different wells. Apart from targeted short-term tests conducted by rubber developers and drilling application companies, little is known about material characterization of such elastomers. Even these test results are not generally available in the public domain due to proprietary rights. In particular, an important factor that has not been previously explored is the effect of exposure on material response of swelling elastomers. Zonal isolation packers and other forms of elastomer-mounted tubulars are often stacked in open yards for a long time before their deployment in wells. Properties of elastomers may significantly change due to their exposure to air, sunlight, and humidity. Some results from a comparative study of the behavior of fresh and exposed samples of an ethylene propylene diene monomer (EPDM)-type water-swelling elastomers are reported here. Methodology of the swelling test was developed in consultation with petroleum engineers and rubber manufacturers. Other experiments were designed and performed in line with standard ASTM test methods. Properties of elastomers that are investigated are hardness, compression set, tensile set, tensile properties, and swelling behavior. Elastomer samples were allowed to swell for a total test duration of 1000 h. Two specimen geometries were tested for swelling: unconfined disc samples to study the behavior of free elastomer and plate samples (elastomer vulcanized on steel plate) to emulate the actual seal performance. Swelling was carried out in salt solutions of different concentrations and at different temperatures. Hardness of exposed elastomer samples (EPDM1) was generally higher than that of fresh samples (EPDM2). Similarly, exposed elastomer showed significantly higher amount of compression set when compared with fresh elastomer. Short-duration tensile set values (10 min test) were almost the same for both sample types. However, tensile set results for the longer-duration tests (10 h and 20 h) were higher for exposed samples. Surprisingly, stress–strain graphs for both fresh and exposed elastomers were almost linear, while rubber-type materials typically show a highly nonlinear behavior. Values of modulus of elasticity and stress at fracture were considerably higher for exposed samples. In contrast, percentage elongation results were higher for fresh samples. Amount of swelling against swelling time showed an up-and-down trend for both the sample types. At the same temperature and under brine solution of the same concentration, fresh elastomer generally swelled far more than the exposed one. The overall observation from the variety of experimental results is that exposure to sun and moisture for extended periods of time reduces the flexibility and swelling capacity of these elastomers.

IEC 61511—functional safety in the process industry: the prominence of validation and verification in the lifecycle of a safety instrumented system

2015 ◽  
Vol 55 (1) ◽  
pp. 379
Author(s):  
Andrew Derbyshire
Keyword(s):  
Oil And Gas ◽  
Oil And Gas Industry ◽  
Process Industry ◽  
Functional Safety ◽  
Validation And Verification ◽  
Gas Industry ◽  
Cherry Picking ◽  
The Difference ◽  
Correct Understanding ◽  
Verification Strategy

As the concept of risk management has gathered momentum in the oil and gas industry during the past decade, so to has the adoption of IEC 61511, the internationally recognised standard for functional safety in the process industry. IEC 61511 is a risk-based standard that uses the concept of an electrical/electronic/programmable electronic based control system to implement autonomous means of risk reduction against a pre-defined unwanted hazardous deviation in a process. While IEC 61511 has been in existence for more than a decade, the correct understanding and implementation of the standard to derive an effective demonstrate of compliance is still debatable. The standard follows a cradle-to-grave approach to the lifecycle of any safety instrumented system and, unlike other standards where cherry-picking of the requirements may be carried out, IEC 61511 necessitates a demonstration of compliance to all lifecycle phases and their associated requirements. The author of this peer-reviewed paper is fully aware of how difficult-to-digest the subject is; therefore, this paper on the prominence of validation and verification is presented in a pictorial, unambiguous and easy-to-digest manner while paying particular attention to the requirements defined for validation and verification in the standard. The topic of validation and verification in the overall lifecycle of IEC 61511 will be covered by the following questions: What is the difference between validation and verification in the context of IEC 61511? What is the difference between verification against IEC 61511 and IEC 61508? When should planning for validation and verification happen? When should validation and verification be carried out? What are the implications of not carrying out validation and verification? How does validation and verification fit into the wider context of the IEC 61511 lifecycle? What level of independence is required for validation and verification? The paper will also attempt to provide a practical example of how to implement an effective validation and verification strategy into an overall Functional Safety Plan to give the reader a clearer understanding of the obligations toward demonstrating compliance.

Explosion risk on offshore and onshore facilities—is there an explosion risk problem or an explosion modelling problem?

2015 ◽  
Vol 55 (1) ◽  
pp. 337
Author(s):  
Ingar Fossan ◽  
Sverre Nodland
Keyword(s):  
Gas Turbines ◽  
Oil And Gas ◽  
Oil And Gas Industry ◽  
Control Measures ◽  
Risk Level ◽  
Gas Industry ◽  
Industry Practice ◽  
Ultimate Outcome ◽  
The Difference ◽  
Explosion Risk

Management of the risk related to the loss of containment of flammable fluid is paramount to ensure safe operations at facilities processing or storing flammable fluids. According to best industry practice, an extensive set of safety functions—including measures that reduce the frequency of initiating events (e.g. leaks) and measures that mitigate consequences in case of ignition—are implemented in design to control the risk. Adopting the risk-based design principles that are commonly enforced in the oil and gas industry, the performance of implemented safety barriers are assessed both qualitatively and quantitatively using different methodologies such as hazard and operability analysis (HAZOP), failure mode and effects analysis (FMEA), and quantitative risk analysis (QRA). The ultimate outcome from the QRA methodology is used to assess the overall risk level as well as to assess dimensioning accidental loads (DALs) for equipment and structures that will ensure a design that is within the tolerable risk level set for the facility. An accurate assessment of DALs resulting from fires and explosion is crucial to manage both the risk and corresponding cost driving factors. The most critical safety barrier in this regard is to minimise leaks and thereafter to prevent ignition of the dispersed flammable fluid. A fundamental safety design principle is to find ways to avoid the occurrence of incidents rather than implement measures that mitigate consequences. This peer-reviewed paper demonstrates the significance of modelling the safety functions that are in place to ensure that the initial leak does not ignite by presenting a case example for different layouts of a conventional jacket installation with gas turbines. It is concluded that the difference between various available ignition models can be more prominent than the uncertainty related to any other model element in the QRA. To uncover potential hazards not reflected by the model and identify optimal control measures, the effect of the ignition model applied should be investigated in detail for installations where the QRA displays a prominent fire and explosion frequency.

Practical Application of Low Constraint SENT Fracture Toughness Testing for Pipeline Girth Welds

2014 ◽  
Author(s):  
Peter B. Schamuhn Kirk ◽  
Victoria Chum
Keyword(s):  
Fracture Toughness ◽  
Temperature Shift ◽  
Test Methods ◽  
Fracture Toughness Test ◽  
Brittle Behavior ◽  
Temperature Regimes ◽  
Adjustment Factors ◽  
Toughness Testing ◽  
Low Constraint ◽  
Girth Welds

Fracture mechanics methods for engineering assessment of acceptable flaw sizes in pipeline girth welds have been widely and successfully embraced by the pipeline industry. Advancements driven by strain-based design have identified elevated conservatism in assessment of material toughness by standardized high constraint fracture toughness test methods. Methods of reducing conservatism include the use of constraint adjustment factors or constraint-matched test specimens. Variants of the single edge-notched tensile (SENT) specimen have been widely reported as appropriate constraint-matched laboratory-scale specimens. This paper presents the results of SENT and SENB toughness testing of pipeline girth welds in both ductile and brittle/transitional temperature regimes. Testing of 19.2mm weldments was conducted at room temperature (RT) and −5°C, with the intent of assessing the practicality of the single-specimen SENT methodology for low constraint fracture toughness assessment of typical high toughness production welds. Typical SENT specimens exhibited up to 50% higher upper shelf toughness results compared to SENB specimens. The majority of specimens failed E1820 crack straightness validity criteria, while the majority of specimens met E2818 (ISO 15653) criteria. Testing of 10.4mm weldments was conducted on pipe known to exhibit low HAZ toughness (brittle pop-ins) at −5°C in the SENB configuration. SENT testing was conducted over temperatures spanning typical operating, design, and winter construction lowering-in temperatures (i.e. RT to −35°C), with the intent of investigating material sensitivity to brittle response under constraint-matched conditions. Brittle responses were observed in SENT specimens at both −20°C and −35°C, and ductile (upper shelf) behavior at −5°C and warmer; SENB specimens exhibited consistently brittle behavior at RT and −5°C, suggesting a HAZ transition temperature shift of at least −30°C for the constraint-matched test geometry.

Test Protocol Definition to Measure Fracture Toughness J-Parameter Using Non-Standard Four-Point Bending Specimens

2020 ◽  
Author(s):  
Denis Alves Ferreira ◽  
Vagner Pascualinotto Junior ◽  
Diego F. B. Sarzosa
Keyword(s):  
Fracture Toughness ◽  
Oil And Gas ◽  
Oil And Gas Industry ◽  
Deformation Energy ◽  
Test Protocol ◽  
Gas Industry ◽  
Four Point Bending ◽  
Test Methodology ◽  
Crack Tip Constraint ◽  
The Impact

Abstract This work proposes a new test methodology to characterize the fracture toughness values for either brittle or ductile materials, such as steels of risers and pipelines used in the oil and gas industry by using non-standard four-point bending specimens. Four-point bending (4PB) specimens show to be reliable configuration to characterize fracture toughness values. The methodology involves obtaining compliance equations, stress intensity factors, the proportionality factors between the deformation energy and J-integral, known as η-factor. This study evidences the impact of geometry variation on the crack-tip constraint. Laboratory tests were performed with four-point bending specimens. These experiments were compared with experimental data of standardized geometries SE(B) and SE(T). The results from the preliminary experimental campaign validated the numerical analysis. Thus, the proposed equations can be used to obtain the fracture toughness values using four-point bending specimens.

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