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.

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.

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.

Low-Constraint Testing of Pipeline Girth Welds

2006 ◽  
Author(s):  
D. Rudland ◽  
Y. Wang
Keyword(s):  
Fracture Toughness ◽  
Transition Curve ◽  
Fracture Toughness Test ◽  
Test Configuration ◽  
Notched Specimens ◽  
High Crack ◽  
Low Constraint ◽  
Girth Welds ◽  
Crack Tip Constraint ◽  
Linepipe Steel

Conventional fracture toughness test specimens have high crack-tip constraint. Defects in pipelines are typically under low constraint conditions. Assessment of the pipeline defects using the fracture toughness of the conventional test specimens can be overly conservative. This paper presents a novel low-constraint test configuration termed back-bend test to measure the toughness of pipeline girth welds. Full transition curve tests were conducted with both weld centerline and HAZ notched specimens. The test setup, instrumentation, and data analysis are described in the paper. The crack initiation transition temperature results for an X70 and X100 linepipe steel girth weld and heat affected zone are presented and discussed.

Single Edge Precrack V-Notched Beam (SEPVNB) Fracture Toughness Testing on Silicon Nitride

2019 ◽  
Vol 962 ◽  
pp. 205-209
Author(s):  
Tjokorda Gde Tirta Nindhia ◽  
Tanja Lube
Keyword(s):  
Fracture Toughness ◽  
Silicon Nitride ◽  
Crack Size ◽  
Fracture Toughness Test ◽  
Single Edge ◽  
Razor Blade ◽  
Sintered Ceramic ◽  
Toughness Test ◽  
Toughness Testing ◽  
Diamond Paste

The previous Measurement of fracture toughness test by using bright indentation for precracked beam method (ASTM C1421) was found difficult to be carried out due to difficulty in precrack generation and measurement of the crack size. In this research single edge precrack V-notch beam (SEPVNB) is introduced as an alternative to solve the problem from previous standardized method. A real crack that can created with referred size is recognized as the best condition for fracture toughness test. The material prepared for this purpose was silicon nitride (Si3N4) produced by CeramTec (Plochingen, Germany) under the name SL200 B. It is a gas pressure sintered ceramic containing 3 wt.% Al2O3 and 3 wt.% Y2O3. The V Notch was prepared by using razor blade with diamond paste following ISO/FDIS 23146 standard preparation with more addition on precrack introduction. The precrack was introduced by so called opposite roller loading. The fracture toughness test was carried out by following procedure in ISO/FDIS 23146 . The result then was compared for validation with both single edge V-notch beam standard (ISO/FDIS 23146 ) and Surface crack in Flexure SCF (ASTM C 1421). The result of fracture toughness by using method that is introduce in this research is found 5.8270.275 MPa1/2 which is close to the result of SCF (5.335 0.222 MPa1/2). Meanwhile the value of fracture toughness by using V-notch beam is 4.9130.098 MPa1/2

Limit Plastic Collapse on Remaining Ligament of Flawed Welds for ECA Application

2014 ◽  
Author(s):  
Antonio Carlucci ◽  
Kamel Mcirdi
Keyword(s):  
Fracture Toughness ◽  
Brittle Fracture ◽  
Mechanical Strain ◽  
Plastic Collapse ◽  
Fracture Toughness Test ◽  
Element Analysis ◽  
Critical Fracture ◽  
Failure Assessment ◽  
The One ◽  
Girth Welds

Engineering Critical Assessments (ECAs) are routinely used to provide defect acceptance criteria for pipelines girth welds. The Failure Assessment Diagram (FAD) concept is the most widely used methodology for elastic-plastic fracture mechanics analysis of structural components and adopted by standards/documents including BS7910 [1], API579-1/ASME FFS-1 [2], R6 [3]. It is defined by two criterion Kr and Lr which describe the interaction between brittle fracture and fully ductile rupture: Kr measures the proximity to brittle fracture whereas Lr reflects the closeness to plastic collapse. The BS7910 FAD level 2B is the most employed for assessment of flaws under mechanical strain lower than 0.4%, the FAD associated is material-specific and it based on single toughness value obtained from CTOD test, the latter-on gives no information about the tearing initiation. The objective of this paper is to propose an approach for determination of the critical fracture toughness (associated to zero-tearing: JΔa=0). This approach is based on the comparison between the load-CMOD curve provided from a fracture toughness test to the one obtained by Finite Element Analysis (FEA). The goals is to propose a conservative guidance on how to identify a remote strain level below which it may be considered guaranteed the integrity of the remaining ligament.

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.

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