Evaluation of Ductile Cracking Criterion for Grade X100 Linepipe and Relationship to Large Scale Fracture Behavior
Bibliographic record
Abstract
Recent developments in the manufacturing process of steel plate for high strength linepipe have enabled superior toughness to prevent brittle fracture of the pipe body. Techniques for non-destructive inspection have also improved, and large flaws that could lead to brittle fracture are highly unlikely in recent high strength pipelines. However, large amounts of plastic deformation can be expected in seismic or permafrost regions. Prevention of ductile fracture of the pipe body or weldment therefore becomes a key issue in defining the tensile strain limit. Ductile fracture is considered to occur by growth and coalescence of voids, and is affected by stress triaxiality and plastic straining at the cracked region. Although many studies have been carried out to evaluate ductile cracking criteria, its transferability to large-scale fracture behavior has not been thoroughly investigated. In this study, ductile cracking of high strength linepipe steels, Grade X80 and X100, was investigated. Notched round bar specimens with different notch root radii were tested to determine the precise conditions for initiation of ductile fracture. Stress and strain conditions at the notch regions were evaluated by FE analysis, and the “critical equivalent plastic strain” was defined at conditions corresponding to ductile fracture initiation in the experimental small specimen tests. Ductile crack initiation behavior was also determined for wide plate test specimens by making close observations of the notch root area. 3-D FE analysis of the wide plate tensile test showed that the equivalent plastic strain at the point of ductile fracture initiation was in close agreement with that in the notched round bas specimen. Thus, the “critical equivalent plastic strain,” determined by small notched round bar specimens, can be considered as a transferable criterion to predict large-scale fracture behavior in wide plate tests. Concepts of strain based design in terms of preventing ductile failure from a surface flaw by applying critical strain to cracking were also discussed in this paper. Results were compared to conventional grade linepipe steels and structural steels, showing that recent high strength linepipe steels have higher resistance to ductile cracking than conventional structural steels. In addition, 3-D FE analyses were used in a parametric study to determine the effects of Y/T and uniform strain on the onset of ductile cracking behaviour. The results of these analyses show the relative importance of materials properties on the resistance to ductile cracking.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".