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.

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.

Why Conduct SEN(T) Tests and Considerations in Conducting/Analyzing SEN(T) Testing

2010 ◽  
Author(s):  
S. Kalyanam ◽  
G. M. Wilkowski ◽  
D.-J. Shim ◽  
F. W. Brust ◽  
Y. Hioe ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Traditional Approach ◽  
Crack Tip ◽  
Maximum Load ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Growing Crack ◽  
Crack Tip Opening

This paper outlines a methodology used to conduct a SEN(T) fracture test and discusses the analysis procedure used to obtain J-R and CTOD-R resistance curves from the experimental data. The CTOD-R curve depicts the change in toughness with crack growth, in a manner similar to the J-R curve methodology. Significant crack growth can arise from the start of ductile tearing to maximum load in the case of surface-cracked pipes with heavier-wall piping used in recent designs of natural gas pipelines that are required to handle greater pressures and much lower temperatures. CTOD-R curves provide toughness values that are a factor of 2 to 3 times higher at maximum load when compared to the toughness at crack initiation. The impacts of this on stress and strain-based design of pipelines are highlighted. Further, the differences between the traditional approach that uses the crack-tip-opening-displacement at the initial crack tip (CTOD′) versus the more recent developments that employ the crack-tip-opening-displacement at the growing crack tip (CTOD) are examined. The CTOD-R curve for the growing crack tip is more consistent with J-R curve analyses. Single-edge-notched bend [SEN(B)] or popularly called bend-bar specimens are used for crack-tip-opening-displacement (CTOD) as well as J-integral toughness testing. This paper discusses the advantages of using the fracture toughness data determined from a single-edge-notched tension [SEN(T)] specimen from considerations of the constraints faced by surface cracks in pipelines and the differences in fracture toughness values seen between the SEN(T) and SEN(B) specimens in the transition temperature region.

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.

Analysis on Critical CTOD of Long-Term Used Penstock

2017 ◽  
Vol 741 ◽  
pp. 57-62
Author(s):  
Fumito Kawamura ◽  
Masazumi Miura ◽  
Ryuichiro Ebara ◽  
Keiji Yanase
Keyword(s):  
Fracture Toughness ◽  
Structural Integrity ◽  
Steel Structures ◽  
Chemical Compositions ◽  
Structural Components ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Critical Crack ◽  
Crack Tip Opening

Many studies have been conducted to characterize the fracture toughness of structural steels and their welded joints. However, most studies focus on newly developed steels, and the number of studies on the fracture toughness of long-term used steels in structural components is rather limited. Furthermore, a lack of data on the fracture toughness causes difficulties in evaluating the structural integrity of existing steel structures. In this study, CTOD tests were performed to characterize the fracture toughness of penstock that has been in service for 50 years. By measuring the critical crack tip opening displacement in conjunction with analysis for chemical compositions, the characteristics of fracture toughness were investigated.

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.

Experimental Study on CTOD Fracture Toughness of Welded Joints of Low Temperature Steel

2011 ◽  
Vol 328-330 ◽  
pp. 1272-1276 ◽  
Author(s):  
Zong Tao Fang ◽  
Bo Sun ◽  
Chun Run Li
Keyword(s):  
Fracture Toughness ◽  
Low Temperature ◽  
Welded Joints ◽  
Welding Process ◽  
Offshore Platform ◽  
Fracture Toughness Test ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Welding Procedure ◽  
Crack Tip Opening

According to BS7448 fracture toughness test standard, crack tip opening displacement (CTOD) for ASTM A333 Gr.6 low temperature steel which is used in offshore platform were carried out in low temperature (0°C, -29°C). Three point bending tests were conducted on the specimens, the dimension of which is B×2B (B is the thickness) and notch direction is NP. The final value of CTOD was calculated by P-V curves of both the welds and HAZ (heat affected zone). And the experimental results were analyzed and discussed in the paper. The low temperature steel welded joints show good low temperature toughness, the selected welding procedure is applied to construction of pipelines.The CTOD value of HAZ is larger than weld metal and weld is the weakest position in the whole structure. The experiment results provide an important basis for the choice of welding method and welding process parameters, ECA assessment and construction of offshore platform.

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