Crack Growth During Full Scale Reeling Simulation of Pipes With Girth Welds

2004 ◽  
Author(s):  
Oddvin O¨rjasaeter ◽  
Olav Jan Hauge ◽  
Guy Ba¨rs ◽  
Per Egil Kvaale
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
High Strain ◽  
High Stress ◽  
Strain Range ◽  
Full Scale ◽  
Small Scale ◽  
Final Fracture ◽  
Lack Of Fusion ◽  
Girth Welds

Installation of pipelines by reeling has proved to be an effective method. However, the pipe bending results in very high stress and strain and cannot be handled by conventional design rules, as stated in design codes, e.g. [2]: High strain crack growth must be assessed according to specific case-by-case selected criterions. In the present work the performance of 10” and 12 3/4” pipes with typical weld defects is studied — from initiation of cracks at notches to final fracture. Information was obtained from several sources: full scale cyclic bending of pipes, FE simulations, and small-scale tests. The plasticity during reeling operations results in substantial non-linear behavior due to varying cross section properties, cyclic creep, and different material response at tensile and compression side of the pipe. Hence, a full scale reeling simulation must be carefully planned and include sufficient tolerances. Critical cracks in pipe girth welds initiate mainly from the surface (undercuts, lack of penetration, or lack of fusion), but potentially also internally (lack of fusion or large pores). Various configurations of these parameters were investigated in full scale pipe tests. It was possible to verify both crack propagation during the reeling cycles, and the point of final fracture (for ECA verifications). In pipe design on must assure safe conditions for both reeling operations and for later in-service loading. Proper design tools must be available. Several methods for high strain crack growth analysis were considered and also compared to small-scale specimen data. Conventional strain-life methodology failed to predict the crack propagation accurately. A new approach including a tensile strain range parameter offered promising results.

Development of Fatigue Design Data for the Ormen Lange Offshore Project: An Overview

2006 ◽  
Author(s):  
Hans Olav Knagenhjelm ◽  
Oddvin O̸rjasæter ◽  
Per J. Haagensen
Keyword(s):  
Crack Growth ◽  
Full Scale ◽  
Small Scale ◽  
Formation Water ◽  
Worst Case ◽  
Vortex Induced Vibrations ◽  
Welding Defects ◽  
Condensed Water ◽  
Full Scale Tests ◽  
Full Scale Testing

The Ormen Lange offshore pipelines from shore to the field go through very difficult terrain creating freespans in the range 40–80m for the 30” lines. For the 6” lines long freespans will be present prior to burial and vortex induced vibrations (VIV) will give a contribution during laying due to strong currents. Using existing codes for fatigue calculation was giving too conservative results compared to the welding technology used and experience from SCR work showed that better S-N data should be expected. A dedicated program was started as part of the Ormen Lange (OL) technology verification program overseen by Norwegian Authorities. An overview of the results is presented here. A full evaluation of the data is not yet complete. Papers will be published later presenting the full technical details and dataprocessing. Fatigue test results from the OL pipeline fatigue verification are presented focusing on the following topics: • Defect sizes in pipeline production welds; • Contractor-A: 5G welding position; • Contractor-B: 2G welding position; • 6” pipe full scale testing; • 30” pipe full scale testing; • Residual stresses; • Crack growth tests and sector specimen fatigue tests in production environments. The following are a summary of the main test variables in the program: • Mapping of actual welding defects compared to AUT results. • Welds with varying misalignment (high/low) and lack of penetration (LOP) from installation contractors tested in air. • Welds with natural welding defects in internal environment (Condensed water and formation water). • Welds with notches made by electrical discharge machining (EDM) (2×65mm and 2×15mm) in internal environment (condensed water and formation water). • Crack growth tests using large compact tension (CT) specimens in air, seawater and internal product environments (condensed water and formation water). • Full scale tests including worst case high/low, LOPs, and tests with normal welds including repair welds. The following main conclusions can be drawn from the work: • Small scale testing with representative worst case defects predicts well large scale testing results with the same features when the small scale specimen stresses are corrected for bending moments etc. arising from the cutout of the pipe. • Full scale testing of 30”×35.5mm wall thickness 2G pipes welded continuously (without start/stop) with worst case defects and high/low exceeds the D curve. • Full-scale tests of 30”×35.5mm wall thickness 5G non continuous welds with worst case defects and high/low exceeds the E curve. • Pipe welds showed low or even compressive residual stresses in the root. For continuously welded pipes the stress levels were low but more varying, also on the cap side. This partly explains the good results. • It is verified that the fatigue loads during operation are below the threshold of crack growth, and thus fatigue will not be a probable failure mechanism. This is under the condition that the measurements of vortex induced vibrations (VIV) during operation confirm the engineering calculations.

Full Size Fatigue Crack-Growth Testing for Girth Welds

2004 ◽  
Author(s):  
Paulo Gioielli ◽  
Jaime Buitrago
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Production Quality ◽  
Small Scale ◽  
Loading Frequency ◽  
Growth Data ◽  
Girth Welds ◽  
Crack Growth Modeling ◽  
Fatigue Crack Growth Testing

Fatigue crack-growth modeling has a significant impact in establishing defect acceptance criteria for the inspection of fracture-critical, girth-welded components, such as risers and tendons. ExxonMobil has developed an experimental technique to generate crack-growth data, in actual welded tubulars, that account for the particular material properties, geometry, and residual stresses. The technique is fully compatible with conventional fracture mechanics models. It uses a series of pre-designed notches made around the welds on a production quality, full-scale specimen that is tested efficiently in a resonant fatigue setup. The crack development from notches is monitored during testing and evaluated post-mortem. Given its simplicity and high loading frequency, the technique provides growth data germane to the component at hand at a lower cost and faster than standard, small-scale tests.

Slow Crack Growth in Dental Composites

1985 ◽  
Vol 55 ◽  
Author(s):  
G. M. Montes-G. ◽  
R. A. Draughn ◽  
T. H. Simpson
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
High Stress ◽  
Torsion Test ◽  
Stable Crack Growth ◽  
Test Method ◽  
Volume Percent ◽  
Stick Slip ◽  
Model Composite

ABSTRACTThe fracture properties of selected commercial composite dental restorative materials and a model composite system were studied to determine the influences of the reinforcing phase, exposure to water, and particle/polymer adhesion on crack propagation. The content of inorganic fillers ranged from 36 to 62 volume percent. In the model system the polymer phase approximated that of the commercial products, a constant size distribution of quartz fillers was used, and polymer/particle adhesion was varied. The double torsion test method was employed to measure relationships between applied stress intensity factor and velocity of crack propagation during stable crack growth. In all systems, cracks propagated through regions of high stress concentration at the low end of the velocity range studied (10−7 m/sec to 10−3 m/sec). Wet materials fractured at lower stress intensities than dry materials at all velocities. At high velocities unstable (stick-slip) growth occurred in dry materials with strong filler/matrix interfaces and in wet specimens with initially strong interfaces and less than 41 volume percent filler. In wet conditions, materials with poorly bonded fillers fractured by slow crack growth at stress intensities 10% to 30% below the levels of composites with strong interfaces.

On the Influence of the Corner Singularity on Kinking Mixed-Mode Crack Propagation

2007 ◽  
Vol 348-349 ◽  
pp. 585-588
Author(s):  
Henning Schütte ◽  
Kianoush Molla-Abbasi
Keyword(s):  
Stress Intensity ◽  
Crack Propagation ◽  
Crack Growth ◽  
Stress Intensity Factors ◽  
Mixed Mode ◽  
Small Scale ◽  
Intensity Factors ◽  
Plastic Energy ◽  
Mixed Mode Crack ◽  
The Impact

The aim of the presentation is to highlight the influence of the kink, developing at the beginning of mixed-mode crack growth, on the propagation behavior of the crack. Le et al. [1] have shown that the variational principle of a body containing a crack results in the principle of maximum energy release rate incorporating the stress intensity factors of the kinked crack. Here the influence of the kink and the kinking angle, resulting in a singular field around the corner, on the crack growth is analyzed. The generalized stress intensity factors at the kinks corner are computed with the help of a FEM strategy. The influence of these on the T-stresses and the plastic energy dissipated at the kink is determined using a small scale yielding approach. The impact of these results on mixed-mode crack propagation is discussed.

Crack Growth in Pipes Under Service Contortions

2009 ◽  
Author(s):  
Oddvin O¨rjasaeter ◽  
Richard Verley ◽  
Per Egil Kvaale ◽  
Tor Gunnar Eggen
Keyword(s):  
Crack Growth ◽  
Cathodic Protection ◽  
Growth Rates ◽  
Fatigue Cracks ◽  
High Growth ◽  
Potential Drop ◽  
Fatigue Tests ◽  
Full Scale ◽  
Small Scale ◽  
Loading Frequency

At the A˚sgard field a leak on a 10″, 13Cr production pipeline was discovered in December 2000 during pressure testing. The cause was a crack at an anode pad fillet weld (pads are connectors for the cathodic protection system). Later, a similar leak occurred on another A˚sgard flowline. During pigging inspection (AUT) several smaller crack indications were found at similar locations. Propagation of such cracks will depend on loading and environmental conditions. To investigate this further, a test programme was carried out using 13Cr pipe materials. Both small scale tests and full scale pipes were used. Specimens were prepared with small initial fatigue cracks at the pad weld. The propagation of the cracks was then recorded under various environmental and loading conditions. The loading was selected to cover a crack growth rate range of ∼10−6 to 10−3 mm/cycle for various crack depths and for two loading frequencies. Tests were conducted under cathodic protection (hydrogen in the material measured) and for temperatures up to 140°C and pressures up to 30bar. The crack growth was recorded by the potential drop method (ACPD). For the full scale pipe tests, specially developed equipment was used for simultaneous measuring at up to 24 individual locations. The results showed that low loading frequency (0.1 Hz) enhances the growth rates; elevated temperature gave equal or lower propagation rates than at 25°C and a pressure of 30bar did not influence the results. A few cracks were also initiated during the corrosion fatigue tests and exhibited high growth rates; possibly due to the so-called “small crack” effect and possibly in synergy with the influence of hydrogen.

Girth Weld Qualification for High Strain Pipeline Applications

2005 ◽  
Author(s):  
Martin W. Hukle ◽  
Agnes M. Horn ◽  
Douglas S. Hoyt ◽  
James B. LeBleu
Keyword(s):  
Plastic Strain ◽  
Weld Metal ◽  
Heat Affected Zone ◽  
High Strain ◽  
Flaw Size ◽  
Small Scale ◽  
Plastic Strains ◽  
Strain Capacity ◽  
Metal Properties ◽  
Girth Welds

Pipeline applications that are subject to global plastic strains require specific testing and qualification programs intended to verify the strain capacity of the girth welds. Such strain demands are generally beyond the limits of standard ECA applicability which normally cover demands up to 0.5% strain. Therefore, qualification of welding procedures for high strain environments require significantly more testing than weld procedures intended for stress-based designs. The plastic strain capacity of girth welds is a function of the pipe and weld metal properties, as well as the maximum flaw size allowable in the girth weld. Specific weld metal/heat affected zone properties, based on small scale testing, should be combined with full scale curved wide plate testing of girth welds that include artificial flaws.

Effect fracture resistance on retardation of crack growth

2015 ◽  
Vol 6 (4) ◽  
pp. 510-521
Author(s):  
Jirí Behal ◽  
Petr Homola ◽  
Roman Ružek
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Aluminium Alloy ◽  
Crack Growth ◽  
Stress Intensity Factors ◽  
High Stress ◽  
Intensity Factors ◽  
Content Type

Purpose – The prediction of fatigue crack growth behaviour is an important part of damage tolerance analyses. Recently, the author’s work has focused on evaluating the FASTRAN retardation model. This model is implemented in the AFGROW code, which allows different retardation models to be compared. The primary advantage of the model is that all input parameters, including those for an initial plane-strain state and its transition to a plane-stress-state, are objectively measured using standard middle-crack-tension M(T) specimens. The purpose of this paper is to evaluate the ability of the FASTRAN model to predict correct retardation effects due to high loading peaks that occur during variable amplitude loading in sequences representative of an aircraft service. Design/methodology/approach – This paper addresses pre-setting of the fracture toughness K R (based on J-integral J Q according to ASTM1820) in the FASTRAN retardation model. A set of experiments were performed using specimens made from a 7475-T7351 aluminium alloy plate. Loading sequences with peaks ordered in ascending-descending blocks were used. The effect of truncating and clipping selected load levels on crack propagation behaviour was evaluated using both experimental data and numerical analyses. The findings were supported by the results of a fractographic analysis. Findings – Fatigue crack propagation data defined using M(T) specimens made from Al 7475-T7351 alloy indicate the difficulty of evaluating the following two events simultaneously: fatigue crack increments after application of loads with maximum amplitudes that exceeded J Q and subcritical crack increments caused by loads at high stress intensity factors. An effect of overloading peaks with a maximum that exceeds J Q should be assessed using a special analysis beyond the scope of the FASTRAN retardation model. Originality/value – Measurements of fatigue crack growth on specimens made from 7475 T7351 aluminium alloy were carried out. The results indicated that simultaneously evaluating fatigue crack increments after application of the load amplitude above J Q and subcritical increments caused by the loads at high stress intensity factors is difficult. Experiments demonstrated that if the fatigue crack reaches a specific length, the maximal amplitude load induces considerable crack growth retardation.

Crack Propagation in a Strain-Crystallizing Elastomer

1962 ◽  
Vol 35 (1) ◽  
pp. 210-223 ◽  
Author(s):  
E. H. Andrews
Keyword(s):  
Stress Distribution ◽  
Crack Propagation ◽  
Natural Rubber ◽  
Crack Growth ◽  
Cyclic Deformation ◽  
Maximum Stress ◽  
Applied Strain ◽  
Small Scale ◽  
Mechanical Hysteresis ◽  
Axis Of Symmetry

Abstract The dependence of small-scale crack propagation in a strain-crystallizing elastomer (natural rubber) upon the applied strain has been studied under conditions of cyclic deformation over a range of frequencies. During each cycle the crack propagates along a well-defined path, different from the axis of symmetry, which is identified as the locus of maximum stress in a stationary stress distribution (i.e., one which does not move with small advances of the crack). The stationary stress hypothesis also accounts for the quantitative dependence of crack growth upon the external constraint. It is shown that a stationary stress distribution could arise as a result of the severe mechanical hysteresis displayed by strain-crystallizing rubbers.

Full Scale Sour Fatigue Testing With Dense Phase Gases

2012 ◽  
Author(s):  
Pedro M. Vargas ◽  
Ben Crowder ◽  
Weiwei Yu ◽  
Sam Mishael ◽  
Keith Armstrong
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Research Work ◽  
Full Scale ◽  
Acceleration Factor ◽  
Fatigue Performance ◽  
Small Scale ◽  
Dense Phase ◽  
Sour Service

The petrochemical industry is very interested in the sour service fatigue performance of girth welded steel pipes. As a result several papers are published every year addressing this issue, and several Joint Industry Projects (JIP) are currently underway addressing different aspects of sour service performance of steel pipelines. To date research work has focused on quantifying the fatigue performance via small scale specimens due to the difficult and danger in dealing with H2S. Currently a JIP is underway that promises to provide full scale fatigue performance of pipeline welds under sour service. This paper documents the knockdown-factor-on-life (KD) determination for full scale sour service testing. In an industry first, a very difficult full scale sour service test was performed: 1) High Pressure, 2) High content of H2S, 3) Dense phase gases with ultra low water content (less than 400 ppm), and 4) Loading rate of 0.01 Hz. The loading was applied in full longitudinal tension. The full scale sour tests are compared with full scale in-air tests to obtain the knockdown factor. Resource constraint limited the number of full scale tests to 3. The main objective of the tests for the practical application was to ensure that the usage of crack growth based knock-down factors, i.e. the use of Fatigue-Crack-Growth-Acceleration-Factor (FCGAR) from small scale fracture mechanics specimens, was reasonable and conservative. Some additional comparisons are done with crack-growth based knockdown factors that may help explain the effect of the ultra-low water concentration. Knockdown factors from small scale crack growth specimens, Fatigue-Crack-Growth-Acceleration-Factor = 60 (FCGAR), are significantly higher than the full scale results, KD = 7. The ultra-low-water dense phase gases do not pit the surface, thus leaving the initiation life relatively intact. The knockdown factor for the full scale test is then mostly the result of the accelerated crack growth that occurs once a macro-crack nucleates.

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