The Role of Residual Stress in Circumferential Stress Corrosion Cracking – An Initial Study
Bibliographic record
Abstract
Abstract In the past decade, several near-neutral pH external circumferential stress corrosion cracking (C-SCC) were found in various pipelines, and some features have led to in-service or hydrostatic test leaks. Previous studies have emphasized the significant role of stress in the integrity management of C-SCC, primarily in two aspects: i) the initiation and propagation of C-SCC, and ii) the burst and fitness for service (FFS) assessment of known C-SCC features. Earlier research revealed that most C-SCC colonies were located near the top or bottom of the pipe, often associated with vertical field bends or local deformation at the bottom of the pipe, and often they are found on slopes. The mechanisms of stress corrosion cracking suggest that axial stress must surpass hoop stress for cracks to align in the circumferential direction. Historically, the sources of axial stress were identified as geohazard-induced axial stress, pressure-induced axial tension, or cross-sectional or local deformation. However, stress analysis on several recently discovered C-SCCs in operational natural gas pipelines revealed low global axial stress at these locations. This finding, confirmed by the observation of minimal or no movement during cut-out, necessitates a better understanding of additional axial stress sources, such as surficial residual stress at these locations. In this study, detailed electron microscopy characterization was carried out on pipeline sections containing developed C-SCC. Advanced microscopy using focused ion beam (FIB) and S/TEM (scanning transmission electron microscopy) revealed that the formation of SCC is closely related to development of cracking/corrosion on cementite precipitates at the grain boundaries. Through thickness residual stress measurement and mapping were performed using high energy Synchrotron x-ray diffraction on both cracked and non-cracked pipe sections cut from in-service natural gas pipelines. The test results suggest high residual stress with substantial amplitude variation existed in the pipeline that had C-SCCs formation.
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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 | 0.000 |
| 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 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".