The Significance of Low Toughness Areas in the Seam Weld of Linepipe

2004 ◽  
Author(s):  
Robert M. Andrews ◽  
Glyn C. Morgan ◽  
W. Jack Beattie
Keyword(s):  
Fracture Mechanics ◽  
Charpy Impact ◽  
Coarse Grained ◽  
Plastic Collapse ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Seam Weld ◽  
Weld Defect ◽  
T Stress ◽  
Crack Tip Opening

There are concerns that there may be areas of low toughness in the seam welds of submerged are welded linepipe. These areas are typically associated with the Coarse Grained Heat Affected Zone and manifest themselves through low values obtained in Charpy impact and crack tip opening displacement (CTOD) tests. Although it is possible to locate areas of low toughness in linepipe seam welds, it is not clear if these are structurally significant. If it can be shown that low toughness areas in the seam weld HAZ do not affect the fitness for service of the pipe as a structure, these could be accepted for use. Under funding from PRCI, a study has been carried out to investigate this problem quantitatively. Experience in the offshore structural field, where the similar problem of local brittle zones in weld HAZs has received considerable attention, was reviewed. A constraint based fracture mechanics analysis was developed using the T-stress approach. Cracked body finite element analyses were used to obtain the T-stress for a range of surface breaking and buried defects in typical linepipe geometries. The results from these models were used to develop a constraint modified Failure Assessment Diagram for a fracture analysis. Fracture analyses showed that the structural constraint is low and failure will occur by plastic collapse for practical seam weld defect sizes. This shows that even when the seam weld toughness is very low, the dominant failure mode for the structure will be plastic collapse. Hence the low toughness values obtained in fracture mechanics tests are not structurally significant for practical defect sizes likely to occur in linepipe.

The Inelastic Line-Spring: Estimates of Elastic-Plastic Fracture Mechanics Parameters for Surface-Cracked Plates and Shells

1981 ◽  
Vol 103 (3) ◽  
pp. 246-254 ◽  
Author(s):  
D. M. Parks
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Computing Time ◽  
Crack Tip ◽  
J Integral ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Elastic Plastic ◽  
Plates And Shells ◽  
Crack Tip Opening

Recent studies of the mechanics of elastic-plastic and fully plastic crack growth suggest that such parameters as the J-integral and the crack tip opening displacement can, under certain conditions, be used to correlate the initiation and early increments of the ductile tearing mode of crack growth. To date, elastic-plastic fracture mechanics has been applied mainly to test specimen geometries, but there is a clear need for developing practical analysis capabilities in structures. In principle, three-dimensional elastic-plastic finite element analysis could be performed, but, in fact, such analyses would be prohibitively expensive for routine application. In the present work, the line-spring model of Rice and Levy [1-3] is extended to estimate the J-integral and crack tip opening displacement for some surface crack geometries in plates and shells. Good agreement with related solutions is obtained while using orders of magnitude less computing time.

Improvement on Mechanical Properties of Cu-Containing Low Alloy Steel of Long Part Forging for Offshore Applications by Manufacturing Process

2017 ◽  
Author(s):  
Yuta Honma ◽  
Gen Sasaki ◽  
Kunihiko Hashi
Keyword(s):  
Mechanical Properties ◽  
Alloy Steel ◽  
Charpy Impact ◽  
Low Alloy Steel ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Weight Test ◽  
Effective Grain Size ◽  
Drop Weight Test ◽  
Crack Tip Opening

Effects by intercritical quenching, which is quenching from dual-phase of ferrite (α) and austenite (γ) region from 953 to 1068 K, on mechanical properties and microstructures of Cu-containing low alloy steel based on ASTM A707 5L grade (hereafter called A707 modified steel) were investigated using 50 kg test ingots. The mechanical properties of the A707 modified steel, i.e. strength at room temperature and fracture toughness at low temperature, were significantly improved by intercritical quenching. This is probably because its effective grain size decreased by intercritical quenching. Then, the optimum temperature of intercritical quenching for A707 modified steel was 1068 K near the AC3 point. Based on the experimental results of the test ingot, we applied intercritical quenching to a trial full-size forging production of about 20,000 mm in length, and researched the tensile, Charpy impact, crack tip opening displacement (CTOD) and drop weight test (DWT) properties across whole length of the trial production. It was found that the trial production has good mechanical properties across whole length. From the present work, an appropriate intercritical quenching is considered to apply for improvement method of the mechanical properties in A707 modified steel forgings.

Fracture Mechanics

2012 ◽  
pp. 101-145
Keyword(s):  
Fracture Mechanics ◽  
Strain Energy ◽  
Subsequent Development ◽  
Strain Energy Release ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Linear Elastic ◽  
Energy Release Rates ◽  
Cracked Structures ◽  
Crack Tip Opening

Abstract Fracture mechanics is the science of predicting the load-carrying capabilities of cracked structures based on a mathematical description of the stress field surrounding the crack. The fundamental ideas stem from the work of Griffith, who demonstrated that the strain energy released upon crack extension is the driving force for fracture in a cracked material under load. This chapter provides a summary of Griffith’s work and the subsequent development of linear elastic and elastic-plastic fracture mechanics. It includes detailed illustrations and examples, familiarizing readers with the steps involved in determining strain energy release rates, stress intensity factors, J-integrals, R-curves, and crack tip opening displacement parameters. It also covers fracture toughness testing methods and the effect of measurement variables.

scholarly journals DAMAGE AND FRACTURE MECHANICS CONCEPTS IN CALCULATING CYCLICALLY LOADED PRESSURE EQUIPMENT

2016 ◽  
Vol 19 (2) ◽  
Author(s):  
VALI-IFIGENIA IORDĂCHESCU (NICOLOF) ◽  
TEODOR SIMA
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Damage And Fracture ◽  
History Of ◽  
Mechanics Concepts ◽  
Crack Tip Opening ◽  
Weld Seams

<p>In the history of technology there occurred many accidents caused by the presence and propagation of cracks in a mechanical structure, especially cracks in weld seams or already existing in the material. The paper evaluates the damage caused by cracks, the superposition of effects by using fracture mechanics concepts (the stress intensity factor, the contour integral and the crack tip opening displacement), while in the case of superposition fracture modes I and II , the relation was checked against the experimental literature data.</p>

scholarly journals A Probabilistic Approach to the Modeling of Coarse Grain Heat Affected Zone Fracture in A707 Steel Welds

2000 ◽  
Author(s):  
J. Zhou ◽  
W. O. Soboyejo
Keyword(s):  
Weak Link ◽  
Probabilistic Approach ◽  
Crack Tip ◽  
Coarse Grained ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Temperature Regimes ◽  
Physically Based ◽  
Steel Welds ◽  
Crack Tip Opening

Abstract A probabilistic framework is presented for the modeling of the variability in crack-tip opening displacement (fracture toughness) during the fracture of coarse grained heat affected zones in A707 steel welds. The variability in inclusion distribution and fracture conditions is modeled using weak link statistics in physically-based fracture mechanics models that describe the fracture behavior in the lower-shelf and transition-temperature regimes. The models are used to explain the measured trends in experiments designed to explore the effects of heat input on crack-tip opening displacement. The implications of the results are also analyzed for the design of welded structures.

CTOD Application to Elastic-Plastic Fracture Mechanics Using Cyclic Ramberg-Osgood Law and HRR Solution

2012 ◽  
Author(s):  
Piotr Bednarz ◽  
Ilya Fedorov ◽  
Jaroslaw Szwedowicz
Keyword(s):  
Cyclic Loading ◽  
Fracture Mechanics ◽  
Crack Closure ◽  
Crack Tip ◽  
Compact Tension ◽  
Loading Conditions ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Crack Tip Opening ◽  
Closure Effect

Very often in the open literature the crack propagation simulation is based on the linear elastic fracture mechanics. This article describes a novel application of the cyclic crack tip opening displacement (ΔCTOD) method for evaluation of the cyclic nonlinear energy release rate under large plasticity and cyclic loading conditions. In order to consider the cyclic loading in the Hutchinson-Rice-Rosengren (HRR) solution, the monotonic plastic deformation of the material behaviour needs to be replaced by its cyclic counterpart. During cyclic loading conditions, a reverse plasticity occurs and leads to a crack closure effect via blunting of the crack tip. As a result, crack flanks are in contact during compression. This effect is determined from the effective difference between the maximum and minimum crack deformation. Then, the cyclic crack tip opening displacement is evaluated by applying the Shih rule. The proposed extension of the HRR solution in application to cyclic loading conditions via stress and strain transformation as well as accounting for the crack closure effect is validated in a good agreement with Dowling and Begley Compact Tension (CT) experiment. Potential crack closure due to crack surface roughness is neglected in current modeling. The proposed methodology extends the existing HRR solution for the reliable lifetime prediction.

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