Numerical Analysis of the Crack Driving Force of Mismatched Girth Welded Pipes Subject to Large Plastic Deformations

2021 ◽  
Author(s):  
Kai Wu ◽  
Hong Zhang ◽  
Yue Yang ◽  
Xiaoben Liu
Keyword(s):  
Crack Length ◽  
Driving Force ◽  
Crack Depth ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Plastic Deformations ◽  
Crack Driving Force ◽  
Ground Deformations ◽  
Global Strain ◽  
Large Plastic Deformations

Abstract Strength mismatched pipes with part-through cracks can suffer large plastic deformation from permanent ground deformations caused by geohazards. Thus, the crack driving force involved in engineering critical assessments plays an important role in guaranteeing pipeline integrity when pipes are subjected to complex loads induced by a hostile environment. In this paper, Python scripts are developed to generate up to 200 finite element models of strength mismatched pipes with various crack sizes under large plastic deformations based on the commercial software ABAQUS. The effects of crack length, crack depth, and strength mismatch factors on the evolution of crack tip opening displacement (CTOD) and global strain were investigated. An approximately linear relationship was observed in all cases tested with global strain values varying from 0.5% to 3%. Meanwhile, the value of the CTOD increased with the increase of crack length and crack depth, and decreased with increasing mismatch factor from the undermatch to the overmatch conditions. The effect of the crack depth on the CTOD is comparatively larger than the crack length, which presented an obvious change of the CTOD for deep cracks coupled with undermatched conditions. Overmatched welding only affected the value of CTOD slightly, while a drastic increase of CTOD value was observed for the undermatched welding conditions, especially for deep and long cracks.

Modeling and CMOD Mapping of Surface-Cracked Wide Plates

2008 ◽  
Author(s):  
Da-Ming Duan ◽  
Yong-Yi Wang ◽  
Yaoshan Chen ◽  
Joe Zhou
Keyword(s):  
Test Data ◽  
Driving Force ◽  
Mouth Opening ◽  
Quality Data ◽  
Crack Mouth Opening Displacement ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Crack Driving Force ◽  
Strain Capacity ◽  
Test Conditions

Curved wide plate (CWP) tests are frequently used to measure the tensile stress and strain capacity of pipeline girth welds. The parameters affecting the CWP measurement include specimen geometry and cooling setups. High-quality data is obtained when valid test conditions are confirmed. Crack mouth opening displacement (CMOD) is often measured in CWP tests. CMOD is a direct indicator of the amount of deformation at the cracked plane. It is an indirect indicator of the crack driving force (CDF) imparted on the crack. For a given test geometry and material, certain relationships can be derived between the measured CMOD and the more conventional representation of crack driving force, such as CTOD (crack tip opening displacement) and J-integral. Such relationships are a key element in fracture toughness testing standards. This kind of relationship is also particularly useful in strain-based design where CWP specimens are used for strain capacity and flaw growth prediction. In this paper finite element (FE) analysis is first used in modeling CWP testing conditions for X100 specimens with girth weld flaws to validate the test conditions. A novel approach called CMOD mapping is then developed to characterize the flaw behavior which, by making a direct use of CMOD test data from the CWP tests, is used to estimate the crack growth in the CWP. Finally analysis of strain limits using crack driving force (CDF) for the CWP specimens is also given by comparing experimental test data and FE estimation.

Significance of Biaxial Stress on the Strain Concentration and Crack Driving Force in Pipeline Girth Welds With Softened HAZ

2007 ◽  
Author(s):  
Ming Liu ◽  
Yong-Yi Wang
Keyword(s):  
Driving Force ◽  
Hoop Stress ◽  
Surface Strain ◽  
Biaxial Stress ◽  
Material Anisotropy ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Crack Driving Force ◽  
Loading Sequence ◽  
Longitudinal Strains

The effect of the biaxial stress and HAZ softening on the crack driving force of girth weld defects was investigated using finite element analyses (FEA). The defects were of elliptic shape and located on the inner surface of the pipe. The crack driving force is represented by the crack tip opening displacement (CTOD) normal to the cracked plane (Mode I). The effect of hoop stress on a homogeneous pipe was revisited at first. It was found that the application of hoop stress tends to increase the crack driving force. However, in the practical range of longitudinal strains (≤4.0%), the effects of hoop stress is not monotonic. For example, at a constant longitudinal strain, as the pre-existing hoop stress increases, the driving force may firstly increase then decrease. The combined effect of HAZ softening and biaxial stress was then studied. With the application of hoop stress, the increase of the crack drive force due to HAZ softening was amplified. It was found that the crack driving force can be closely correlated with the surface strain measured over a structurally significant scale right above the defect. In addition, the effects of loading sequence and material anisotropy on the crack driving force were also briefly examined. The increase of the crack driving force from the hoop stress is more pronounced when it is applied prior to the application of longitudinal strains than the reverse loading sequence. The material anisotropy was found to further increase the crack driving force and therefore representative material models are necessary to analyze the anisotropy effects.

Fracture Behaviour of Thin Sheet Stainless Steel

2012 ◽  
Vol 525-526 ◽  
pp. 549-552
Author(s):  
Nenad Gubeljak ◽  
Darko Jagarinec ◽  
Jožef Predan ◽  
John Landes
Keyword(s):  
Fracture Toughness ◽  
Stainless Steel ◽  
Crack Initiation ◽  
Driving Force ◽  
Crack Tip ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Crack Driving Force ◽  
Integrity Assessment ◽  
Crack Tip Opening

The differences in fracture behavior between the compact tension C(T) and the middle tensile M(T) specimens make structure integrity assessment uncertain. Two different types of specimens C(T) and M(T) specimens made from stainless steel have been used for fracture toughness testing at the room temperature by the principles of the ASTM 1820-05 standard procedure. Stable crack initiation and crack propagation occurred for the C(T) specimens at lower values of crack driving force than for the M(T) specimens. Crack tip opening displacement-CTOD has been directly measured on the surface of specimens by using a stereo-optical grading method. The critical crack tip opening displacement at crack initiation CTODi has been measured as a plastic Stretch Zone Width (SZW) during a post test fractographic inspection. Comparison between the CTOD-R curves of both types of specimens shows some difference between the C(T) and the M(T) specimens, but a more significant difference appeared in the crack driving force, as consequence of different constraint (triaxiality) of the C(T) versus the M(T) specimens. Therefore, the result obtained by test on laboratory C(T) specimens cannot be directly used as fracture toughness material properties in a structure integrity assessment, except as a conservative lower bound estimate.

Role of Constraint in Specimen Geometries When Evaluating Fracture Toughness/Material Fracture Resistance for a Surface-Flawed Elbow

2019 ◽  
Author(s):  
S. Kalyanam ◽  
G. Wilkowski ◽  
F. W. Brust ◽  
Y. Hioe ◽  
E. Punch
Keyword(s):  
Surface Crack ◽  
State Of The Art ◽  
Crack Depth ◽  
Bending Moment ◽  
Compact Tension ◽  
Fe Analysis ◽  
Significant Finding ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Variable Surface

Abstract The fracture behavior of a circumferential surface crack in an elbow was evaluated using past data from the International Piping Integrity Research Group (IPIRG-2) Experiment 2-4. The elbow tested was nominal 16-inch diameter Schedule 100 TP304 material, which was solution-annealed after final fabrication. The elbow was loaded with an in-plane-closing bending moment and internal pressure of 15.51 MPa (2,250 psig) at 288 C (550 F). The surface crack was 180-degrees on the ID surface and centered on the extrados, but after fatigue precracking the depth was variable and the greatest was at about 45-degrees from the extrados. FE analysis of the IPIRG-2 elbow test was conducted with a state-of-the-art and precise 3D FE mesh (including variable surface crack depth, variable thickness, and initial elbow ovalization). The flaw depth for the single-edge notch tension (SENT) tests was selected to be equivalent to the deepest point in the elbow specimen crack front that provided the largest J-value in the elbow experiment, i.e., ao/W = 0.68. Comparison of the J-value for initiation (Ji) and crack-tip-opening displacement (CTODi) at crack initiation suggested that there was a slight difference in constraint between an identical depth SENT specimen (a/W = 0.68 with the same L-R orientation as the surface crack in the pipe) and an elbow with a circumferential surface crack (a/t = 0.68) [Ji was 0.368 MN/m, (2.1 ksi-inch) in the SENT tests, while it was 0.490 MN-m (2.8 ksi-inch) in the elbow test]. The more significant finding in this work was that the compact tension (C(T)) test Ji-value was much higher at 1.086 MN/m (6.2 ksi-inch) or ∼3 times higher. The elbow to SENT to C(T) specimen comparison illustrates very large differences in constraint between these geometries. From past work by several researchers it was determined that the constraint in C(T) specimens gives Ji-values that agree well with a circumferential through-wall crack in a straight pipe, but this difference with surface-cracked elbow or pipe is envisaged to be new information to the international research community. Additionally, from state-of-the-art FE analysis of the 180-degree surface-cracked elbow test it was found that the maximum J-value occurs at a position that was about 45-degree away from the extrados location. This trend showed that caution should be exercised when selecting the crack locations for elbow integrity evaluation, since for shorter flaw lengths it may be more critical to consider a crack that is closer to the 45-degrees from the extrados, which could be true for fracture as well as stress corrosion cracking (SCC) elbow evaluations.

CTOD Fracture Toughness Assessment Under Different Notch Type (Fatigue Pre-Cracking and EDM)

2019 ◽  
Author(s):  
Israel Marines-Garcia ◽  
Aaron Aguilar ◽  
Kristian Carreon ◽  
Philippe Darcis
Keyword(s):  
Fracture Toughness ◽  
Crack Length ◽  
Heat Affected Zone ◽  
Crack Tip ◽  
Fusion Line ◽  
Testing Time ◽  
Pipe Material ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Electro Discharge Machining

Abstract The standardization of any mechanical material characterization is aiming to get homogenization on the testing physical execution by independent laboratories and to drive for accurate material evaluation between different entities. However, from time to time, standard tests may be reconsidered in order to improve their efficacy, execution time and incorporate new testing techniques or technologies without compromising the testing results and consistency. In the present work, fracture toughness crack tip opening displacement (CTOD) testing is addressed and particularly the need to perform fatigue pre-cracking prior monotonic testing. Without the fatigue pre-cracking, CTOD testing time can be significantly reduced during the preparation of specimens, meaning that specimens can be tested as soon as they are machined. Wire electro-discharge machining (EDM) technique allows generating sharp tip notches, and presents a good alternative to the standards specified fatigue pre-cracking [1–2]. In addition, this machining technology reduces the risk of rejecting the specimen testing, particularly when targeting weld heat affected zone/fusion line (HAZ/FL) microstructure on specimens with surface notch DNV-ST-F101 Figure B-9 [3], where it is specified that the crack tip shall be within a narrow distance (0.5 mm) from the fusion line (FL) or assess grain coarsened heat affected zone (GCHAZ) microstructure as indicated in DNV-ST-F101 section B.2.8.7 [3]. Herein, it is presented an assessment carried out in order to identify the notch type effect over the fracture toughness (CTOD) considering notches conditions as standard fatigue pre-crack and wire electro-discharge machining (EDM). Fifteen (15) CTOD specimens were manufactured from plain pipe material (same pipe), 251.3 mm OD × 20.9 mm WT, SMLS 450PD and tested according to ISO 12135 recommendations [1], they were distributed as follow; five (5) specimens according to standard recommendations with fatigue pre-cracking length ≥ 1.3 mm or 2.5%W (whichever is bigger), five (5) specimens with a fatigue pre-cracking length < 1.3 mm (between 0.5 mm to 1 mm), and five (5) specimens without fatigue pre-cracking (EDM notch), additionally, results from five (5) specimens previously tested in a round robin (RR) testing performed internally by Tenaris using the same LP material and standard fatigue pre-crack length. The crack length target (a/W) was kept 0.5 for all cases. Even if the sampling population is relatively small considering the three notch conditions, it seems that EDM might be an alternative to the standard specified fatigue pre-cracking. Thus, this experimental assessment aims to open the discussion on the use of EDM notch as alternative.

Comparison of Flaw Driving Force Estimates in Simulated Weld Residual Stress Fields

2013 ◽  
Author(s):  
David J. Dewees ◽  
Robert H. Dodds
Keyword(s):  
Residual Stress ◽  
Driving Force ◽  
Three Dimensional ◽  
Crack Size ◽  
J Integral ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Weld Residual Stress ◽  
Future Work ◽  
Crack Tip Opening

Previous work has focused on the methods and results for calculating flaw driving force in simulated three-dimensional (3D) weld residual stress (WRS) fields using contour (J) integral techniques. This paper extends that work to look at explicit modeling of the crack tip opening displacement (CTOD) in these same WRS fields, and for the same range of semi-elliptical flaws. Comparison is made between the predicted trends of driving force with crack size for the calculated driving force (J-integral) versus the “measured” value (CTOD). Implications for fracture assessments are given, and recommendations for future work are made.

Fracture Control — Offshore Pipelines: New Strain-Based Fracture Mechanics Equations Including the Effects of Biaxial Loading, Mismatch, and Misalignment

2005 ◽  
Author(s):  
Erling O̸stby
Keyword(s):  
Fracture Mechanics ◽  
Wall Thickness ◽  
Driving Force ◽  
Biaxial Loading ◽  
Crack Depth ◽  
Offshore Pipelines ◽  
Crack Driving Force ◽  
Fe Simulations ◽  
Definition Of ◽  
2D And 3D

In this paper a framework for a strain-based fracture mechanics crack driving force methodology for pipes with surface cracks, are presented. The model addresses the effects of crack depth, crack length, pipe diameter, wall thickness and yield to tensile ratio. Based on FE simulations, an equation to calculate the applied crack driving force, either through CTOD or J, has been derived. The equation is intended for use in cases where global plastic deformation occurs. A general approach to introduce the effects of biaxial loading, yield stress mismatch, and misalignment on the driving force, through definition of an effective wall thickness and an effective crack ligament height, is outlined. Models to quantify the effects of the different parameters are also derived. Finally, results are presented from comparison between 2D and 3D FE simulations and the predictions made by the proposed driving force equations.

Estimates of Crack-Driving Force in Surface-Cracked Elbows

2000 ◽  
Vol 123 (1) ◽  
pp. 32-40 ◽  
Author(s):  
Gery M. Wilkowski ◽  
Raj Mohan ◽  
Thomas J. Kilinski
Keyword(s):  
Crack Length ◽  
Driving Force ◽  
Stress Index ◽  
Simple Relationship ◽  
Surface Cracks ◽  
Straight Pipe ◽  
Crack Driving Force ◽  
Large Matrix ◽  
Simplified Procedure ◽  
J Estimation

The objective of this effort was to assess whether a simple relationship could be developed between the behavior of surface cracks in straight pipe and in elbows. If such a geometric relationship could be developed, then a simple multiplier could be applied to the current straight-pipe solutions that are already used in codes and standards such as the ASME or other codes. In order to accomplish this objective, solutions from elbow and straight-pipe elastic-plastic fracture mechanics (EPFM) analyses were used along with experimental data. The elbow EPFM solution came from a J-estimation scheme developed during the IPIRG-2 program. These solutions were for an elbow with a pressure at the design stress limits of Section III of the ASME Code for typical nuclear piping steels. Significant efforts were undertaken in that program to develop J-estimation schemes for axial (along the side of the elbow) and circumferential surface cracks (centered on the extrados) in elbows under constant pressure and in-plane bending. These analyses were developed using the GE/EPRI methodology of determining an elastic and plastic contribution to J, and developing the appropriate functions through a matrix of EPFM finite element analyses. Even with this large matrix of FEM analyses, only one circumferential crack length and one axial crack length were investigated. Hence, it was desirable to develop a method to extend the analysis capabilities to other crack geometry, as well as developing a simplified procedure. A comparison of the elbow to straight-pipe moment versus crack-driving force curves showed that there is a simple multiplier linearly related to the ASME B2 stress index for elbows of different R/t ratios. Hence, a simplified procedure was determined where the straight-pipe solution could be multiplied by a function of the elbow stress indices to give the maximum load prediction of the surface-cracked elbow. Comparisons were made to circumferential surface-cracked elbow data from the IPIRG-2 program, and an axial surface-cracked elbow test conducted by EDF. The comparisons showed the simplified methods to be quite promising.

Probabilistic Failure Assessment of a Complex Nozzle Structure With Flaw Defect Based on FITNET Procedure

2016 ◽  
Author(s):  
Yan Wang ◽  
Yan-Wei Wang ◽  
Hanxin Chen ◽  
Linwei Ma
Keyword(s):  
Crack Growth ◽  
Failure Probability ◽  
Driving Force ◽  
Complex Geometry ◽  
Crack Depth ◽  
Initial Crack ◽  
Structural Safety ◽  
Crack Driving Force ◽  
Failure Assessment ◽  
Nozzle Structure

A probabilistic failure assessment based on the fracture and fatigue modules of European FITNET procedure is presented in this work. Analysis of the leak probability of a complex nozzle structure with postulated flaw defect under thermal mechanical loading is performed. Crack growth is calculated using FITNET fatigue module, in which the crack driving force ΔKeq considering mixed-mode load is applied. For the structural safety evaluation, the failure assessment diagram (FAD) within the frame of FITNET fracture module is utilized with the parameter Keff combing KI and KII. The fracture mechanical parameters are calculated using finite element (FE) method because of the complex geometry and load conditions. To meet the needs of probabilistic analyses, formulas calculating crack driving force are developed specific for this nozzle structure through nonlinear regression based on the FE results. With an initial crack depth of 5 mm, the nozzle failure probability in form of leak comes to 1.84×10−4 in next fifty years. The good agreement of the results of Monte Carlo simulation and stratified sampling technique confirms that the crack growth parameter C and the initial crack shape ratio c/a have considerable effect on the structural failure probability.

Development of the SENT Test for Strain-Based Design of Welded Pipelines

2010 ◽  
Author(s):  
Huang Tang ◽  
Mario Macia ◽  
Karel Minnaar ◽  
Paulo Gioielli ◽  
Sandeep Kibey ◽  
...  
Keyword(s):  
Ductile Fracture ◽  
Fracture Resistance ◽  
Crack Depth ◽  
Crack Tip ◽  
Specimen Geometry ◽  
Outer Diameter ◽  
Specimen Thickness ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Specimen Width

Strain-based design (SBD) pipelines are being considered to develop hydrocarbon resources in severe environments. As part of a research program to develop a SBD methodology, work was conducted to develop a suitable fracture mechanics test that can be used as part of a strain capacity prediction technique. The single edge notched tensile (SENT) specimen geometry has been chosen due to the similarity in crack-tip constraint conditions with that of defects in pipeline girth welds. This paper describes a single-specimen compliance method suitable for measuring ductile fracture resistance in terms of crack tip opening displacement resistance (CTOD-R) curves. The development work included investigation of the following items: specimen geometry, crack geometry and orientation (including crack depth effects), direct measurement of CTOD. The results demonstrate that toughness measurements obtained using a B = W configuration (B = specimen thickness, W = specimen width) with side grooves are similar to those using a B = 2W configuration without side grooves; however, specimens with side grooves and B = W geometry facilitates even crack growth. Studies of crack depth have shown that ductile fracture resistance decreases with increasing ratio of the initial crack depth to specimen width, a0/W. Studies of notch location and orientation (outer diameter (OD) and inner diameter (ID) surface notches and through-thickness notches) have shown an effect of this variable on the CTOD-R curves. This has been partly attributed to crack progression (tearing direction) with respect to weld geometry and this effect is consistent with damage modeling predictions. However the experimentally observed difference of CTOD-R curves between ID and OD notches is believed to be primarily due to the material variability through the pipe thickness.

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