Low-Constraint Toughness Testing of Two SE(T) Methods in a Single Specimen

2014 ◽  
Author(s):  
Dong-Yeob Park ◽  
Jean-Philippe Gravel ◽  
C. Hari Manoj Simha ◽  
Jie Liang ◽  
Da-Ming Duan
Keyword(s):  
Crack Tip ◽  
Crack Size ◽  
Size Estimation ◽  
Single Specimen ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Line Pipe ◽  
Low Constraint ◽  
Girth Welds ◽  
Crack Tip Constraint

Single-edge notched tension (SE(T) or SENT) specimens has been increasingly proposed as a low-constraint toughness test to measure toughness of line pipe materials, as the crack tip constraint approximates a circumferential surface flaw in a pipe under loading. The clamped SE(T) single-specimen procedures recently developed by Shen and Tyson [1, 2] and Tang et al. [3] have in common the use of a clamped single-specimen of similar geometry and rely on unloading compliance technique for crack size estimation. In the former case, a single clip gauge is attached to the integral knife edge and the crack-tip opening displacement (CTOD) is estimated by means of a J-integral-to-CTOD conversion, similar to the procedure of ASTM E1820. The latter uses a pair of clip gauges mounted to an attachable raised set of knife edges to estimate CTOD at the original crack tip position by a triangulation rule. Consolidating these two sets of clip gauges in a specimen makes direct comparisons of two SE(T) methods on identical test conditions: material, specimen geometry, equipment, test temperature and operator [4]. In this study, SE(T) testing employing these two SE(T) methods on a single specimen was conducted on BxB shallow-cracked (a/W∼0.35) specimens of two x70 pipeline girth welds. This paper discusses the details of two SE(T) methods and techniques on the same specimen.

Low-Constraint Toughness Testing of Two Single-Edge Notched Tension Methods in a Single Specimen

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Dong-Yeob Park ◽  
Jean-Philippe Gravel ◽  
C. Hari Manoj Simha ◽  
Jie Liang ◽  
Da-Ming Duan
Keyword(s):  
Fracture Toughness ◽  
Crack Tip ◽  
Size Estimation ◽  
Single Specimen ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Line Pipe ◽  
Toughness Testing ◽  
Low Constraint

Single-edge notched tension (SE(T) or SENT) specimens have been increasingly proposed as a low-constraint toughness test to measure toughness of line pipe materials, as the crack tip constraint approximates a circumferential surface flaw in a pipe under loading. The clamped SE(T) single-specimen procedures recently developed by Shen and Tyson (2008, “Fracture Toughness Evaluation of High Strength Steel Pipe,” ASME Paper No. PVP2008-61100; 2008, “Development of Procedure for Low-Constraint Toughness Testing Using a Single-Specimen Technique,” CANMET Materials Technology Laboratory, Technical Report No. 2008-18 (TR)) and Tang et al. (2010, “Development of the SENT Test of Strain-Based Design of Welded Pipelines,” 8th International Pipeline Conference, IPC 2010, Calgary, AB, Canada) have both used in common the use of a clamped single-specimen of similar geometry and relied on the unloading compliance technique for crack size estimation. In the former case, a single clip gauge is attached to the integral knife edge and the crack-tip opening displacement (CTOD) is estimated by means of a J-integral-to-CTOD conversion, similar to the procedure of ASTM E1820-11. The latter uses a pair of clip gauges mounted on an attachable raised set of knife edges to estimate CTOD at the original crack tip position by a triangulation rule. Consolidating these two sets of clip gauges in a specimen makes direct comparisons of two SE(T) methods under identical test conditions: material, specimen geometry, equipment, test temperature, and operator (Weeks et al., 2013, “Fracture Toughness Instrumentation Techniques for Single-Specimen Clamped SE(T) Tests on X100 Linepipe Steel: Experimental Setup,” 6th Pipeline Technology Conference, Ostend, Belgium). In this study, SE(T) testing employing these two SE(T) methods on a single specimen was conducted on B × B shallow-cracked (a/W ∼ 0.35) specimens of two X70 pipeline girth welds. This paper discusses details of the two SE(T) methods and techniques on the same specimen.

Evaluation of Two Low-Constraint Toughness Test Methods in a Single Specimen

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Dong-Yeob Park ◽  
Jean-Philippe Gravel ◽  
Muhammad Arafin ◽  
Jie Liang ◽  
C. Hari Manoj Simha
Keyword(s):  
Crack Size ◽  
Test Methods ◽  
Single Specimen ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Resistance Curves ◽  
Unloading Compliance ◽  
The Difference ◽  
Low Constraint ◽  
Identical Test

In previous studies, the single- and double-clip gauge methods were successfully consolidated in a single-edge notched tension (SE(T)) single specimen so that crack tip opening displacement (CTOD) values obtained from both SE(T) methods could be compared under identical test conditions. The current study investigated the effect of unloading compliance crack size equations on resistance curves obtained from both gauging methods combined in a single specimen. It was found that the unloading compliance crack size equations of Cravero and Ruggieri and the single clip gauge method predict crack sizes well within approximately 2% error in average. Two CTOD-resistance curves obtained from both gauging methods produce approximately the same results until peak loads, and thereafter the curves deviate. The results obtained from the double clip gauge method are consistently higher than those from the single clip gauge, although the difference between two resistance curves is reduced when the same unloading compliance crack size prediction procedure is used. This observation is very important within the framework of engineering critical assessment (ECA) and defect assessment procedures. An “apparent” higher resistance curve will generate larger tolerable defects thereby reducing the conservatism of an ECA analysis.

Review of Low-Constraint Fracture Resistance Testing With SENT Specimens

2014 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Tom McGaughy ◽  
Fabian Orth ◽  
Jon Jennings
Keyword(s):  
Fracture Resistance ◽  
Crack Tip ◽  
Test Methods ◽  
Resistance Testing ◽  
Resistance Curve ◽  
Single Specimen ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Resistance Curves ◽  
Low Constraint

Fracture resistance is an important material property and characterized by a J-integral resistance curve (J-R curve) or a crack-tip opening displacement (CTOD) resistance curve. ASTM standard specimens with deep cracks are subject to bending dominant forces, leading to high crack-tip constraint conditions and conservative fracture resistance curves. Actual cracks occurring in line pipes and welds are often shallow ones dominated by tensile forces, resulting in low constraint conditions. Shallow cracks have been shown to generate elevated fracture resistance curves in comparison to standard deep-crack results. To reduce the over-conservatism of standard resistance curves and to produce more realistic toughness properties to meet the needs of strain-based design approaches for pipelines, different procedures and technologies have been developed over the years to determine the low-constraint fracture resistance curves by use of the single edge-notched tension (SENT) specimens. This includes the multiple specimen method developed and standardized by DNV for J-R curve testing, the single specimen method developed by CanMet for J-R and CTOD-R curve testing, and the single-specimen method developed by ExxonMobil for CTOD-R curve testing. This paper delivers a technical review of existing fracture test methods using SENT specimens, and discusses the advantages and limitations of each method.

An Innovative ECA Approach For Reeled CRA Welds And Its Validation Programme

2021 ◽  
Author(s):  
Richard Jones ◽  
Dr Thurairajah Sriskandarajah ◽  
Dr Daowu Zhou ◽  
James Hymers ◽  
Kieran Munro ◽  
...  
Keyword(s):  
High Stress ◽  
Crack Tip ◽  
Test String ◽  
Test Rig ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Defect Growth ◽  
Girth Welds ◽  
Stress Fatigue ◽  
Crack Tip Opening

Abstract This paper presents an innovative defect growth ECA methodology for pipeline girth welds and its validation programme, applied specifically to reeling ECA of pipelines with under-matched strength welds. The ECA method is a tear-fatigue approach that accounts for the blunting limit in JR curves during pipe spooling and reel-lay. Fatigue crack growth may occur by low cycle high stress fatigue and by tearing, but the latter only if the crack tip opening displacement exceeds the blunting limit. Conventional ECA with BS7910 is limited because the weld's strength needs to be over-matched. Alternative industry methods for the application of FEA to under-matched strength welds are computationally more intensive than the presented innovative approach. Fatigue crack growth for low cycle high stress fatigue is calculated using Paris’ Law in the approach but, if the crack tip opening due to the tearing mechanism is less than the blunting limit then tearing growth is zero. With the innovative method, if the crack tip opening displacement exceeds the blunting limit then the tearing defect growth is included. Hence, the method is a combined tear-fatigue approach. Welded pipe strings were fabricated from pups composed of clad material; i.e. carbon backing steel pipe with a 3 mm layer of corrosion resistant alloy (CRA) on the inner circumference. Each test string was approximately 10.5m long and fabrication was from a mix of six 0.5m length pups in the central zone of each string and two longer end pups. Three girth welds included EDM notches for test purposes which simulated planar flaws. The notches were on the extreme tension fibre, as the test string gets pulled to the reel former in a reeling test rig. Full scale reeling simulations involved pulling the test strings up to 6 times to the reel former in a reeling test rig. Measurement of defect growth associated with the EDM notches was by scanning electron microscope (SEM), from specimen segments extracted from the test strings. Predictions of defect growth were by finite element models in combination with pipe-specific data that was the outcome of an associated small-scale test programme. Validation of the ECA-by-FEA approach is by a predictive best estimate study, for which there is excellent agreement between the measured values and the calculated defect growths. The ECA-by-FEA approach is conservative for project work, as shown by a high estimate study and an offset blunting limit study. Early development of the ECA approach was for small diameter CRA pipelines during the execution of the Guara-Lula project (Sriskandarajah et al, 2015). The presented full-scale tests, innovative defect growth measurement by scanning electron microscope and the FEA and defect growth calculations were full validation of the approach, with pipe strings that had outer diameter of 323.9mm.

Fracture Toughness of X70 Pipe Girth Welds Using Clamped SE(T) and SE(B) Single-Specimens

2014 ◽  
Author(s):  
Dong-Yeob Park ◽  
Jean-Philippe Gravel ◽  
C. Hari Manoj Simha ◽  
Jie Liang ◽  
Da-Ming Duan
Keyword(s):  
Fracture Toughness ◽  
Heat Affected Zone ◽  
Peak Load ◽  
Single Specimen ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Resistance Curves ◽  
Girth Welds ◽  
Crack Tip Opening

Shallow-notched single edge-notched tension (SE(T) or SENT) and deep- and shallow-notched single edge-notched bend (SE(B) or SENB) specimens with notches positioned in the weld and the heat-affected zone were tested. Crack-tip opening displacement (CTOD) versus resistance curves were obtained using both a single and double clip gauge consolidated in a SE(T) single-specimen. Up until the peak load the resistance curves from both gauging methods yield approximately the same results; thereafter the curves deviate. Interrupted testing showed that the crack had initiated below 50% of the peak load, and in some cases had propagated significantly prior to reaching the peak load.

Direct Comparison of Single-Specimen Clamped SE(T) Test Methods on X100 Line Pipe Steel

2014 ◽  
Author(s):  
Timothy S. Weeks ◽  
Enrico Lucon
Keyword(s):  
Crack Growth ◽  
Mouth Opening ◽  
Closed Form Solution ◽  
Test Methods ◽  
J Integral ◽  
Single Specimen ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Line Pipe ◽  
Resistance Curves

The clamped single edge-notched tension (SE(T)) specimen has been widely used in a single-specimen testing scheme to generate fracture resistance curves for high strength line-pipe steels. The SE(T) specimen with appropriate notch geometry is a low-constraint specimen designed to reduce conservatism in the measurement of fracture toughness. The crack driving force is taken as either the J-integral or crack tip opening displacement (CTOD); it is generally accepted that the two parameters are interchangeable and equivalent using a simple closed form solution. However, the assumption that they are interchangeable, and to what extent, hasn’t been previously investigated experimentally on the same SE(T) specimen. This paper presents multiple test methods that were simultaneously employed on the same SE(T) specimens. The instrumentation includes: clip-gauges to measure surface crack mouth opening displacements (CMOD) and CTOD by the double-clip-gauge method; strain-gage arrays for direct J-integral measurements; and direct-current potential-drop (DCPD) instrumentation for supplementary crack size measurement. A direct comparison of ductile crack-growth resistance curves generated using J-integral and CTOD is presented here where each represents a different experimental and analytical approach. The two methods are in reasonable agreement over a narrow range of crack growth, differing slightly at initiation and diverging with increasing crack growth. Analysis of the supplementary instrumentation (i.e., strain gages, extensometers and DCPD) will be provided in a future publication.

Development of a Low-Constraint SE(T) Toughness Test

2011 ◽  
Vol 488-489 ◽  
pp. 126-129 ◽  
Author(s):  
W. R. Tyson ◽  
G. Shen ◽  
J. A. Gianetto ◽  
D.Y. Park
Keyword(s):  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
J Integral ◽  
Single Edge ◽  
Opening Displacement ◽  
Bending Loads ◽  
Low Constraint ◽  
Girth Welds ◽  
Crack Tip Constraint ◽  
Tension Loading

CANMET-MTL has developed a low-constraint test designed to reduce unnecessary conservatism in the measurement of toughness for use in the assessment of flaws in pipeline girth welds. The design is based on tension loading using fixed (clamped) grips of a single-edge-notched BxB SE(T) specimen, side-grooved to promote plane-strain conditions. Equations have been developed to derive J-integral, CTOD and crack growth from measurement of load and crack-mouth opening displacement. Loading conditions (essentially distance between the grips) have been chosen to reproduce the crack-tip constraint of a circumferential surface flaw in a pipe in service under tensile or bending loads. In this paper, the development of the test and the principal findings from its use will be described.

A Review of Fracture Toughness Testing and Evaluation Using SENT Specimens

2014 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Tom McGaughy
Keyword(s):  
Fracture Toughness ◽  
Test Procedure ◽  
Crack Tip ◽  
Test Methods ◽  
Fracture Toughness Test ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Test Standards ◽  
Resistance Curves ◽  
Crack Tip Constraint

Fracture toughness is an important material property in describing material resistance against fracture with a point value or in the format of a resistance curve. For ductile materials, the commonly used fracture parameters are the J-integral and the crack-tip opening displacement (CTOD, or δ). ASTM E1820 provides standard procedures for determining the JIc, δIc, J-R curve and δ-R curve using bending specimens with deep cracks. This usually leads to high crack-tip constraint conditions and conservative fracture resistance curves. Actual cracks found in pipelines and welds are often shallow and dominated by tensile forces, resulting in low constraint conditions and elevated resistance curves. Thus the standard resistance curves can be overly conservative for a shallow crack. To obtain realistic fracture toughness values to meet the practical needs for pipelines, different test methods have been developed using a single edge-notched tension (SENT) specimen. This includes the multiple specimen method, the single specimen method, the J-R curve test procedure, and the δ-R curve test procedure. This paper presents a critical technical review of existing fracture toughness test methods and procedures using SENT specimens, with discussions on the toughness estimation equation, key parameter calibration, rotation correction, and test procedure limitation. Historical efforts related to the SENT testing and applications of ASTM fracture test standards to the SENT specimens are also reviewed briefly.

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