The role of pressure in carburisation: Crack dynamics in Type 316H austenitic stainless steel under CO2 environments
Bibliographic record
Abstract
The oxidation and carburisation of steel in advanced gas-cooled nuclear reactors limit the life of key components during plant operation. To achieve a mechanistic understanding of the origin of carburisation phenomena, simulation or replication of service exposure conditions is needed. Laboratory tests are usually performed to accelerate processes such as crack initiation and growth in the material, and to simulate plant conditions as precisely as possible. This paper describes the results of carburisation data analysis of AISI Type 316H stainless steel under several CO 2 gas exposure conditions. The behaviour of ex-service welded pipe components from advanced gas-cooled reactors at service temperature and pressure is compared to a range of specimens loaded and cracked in air and under surrogate/simulated CO 2 conditions. Both atmospheric pressure and pressurised CO 2 gas (4.14 MPa) conditions were studied. Microstructural characterisation of the crack tip region and the bulk/matrix of the specimens was performed using advanced electron microscopy techniques. The regions ahead of the crack tips were systematically analysed as they have a potential to significantly influence crack propagation behaviour. This study shows a significant effect of carburisation at the crack tip compared to the bulk of the material, but only for pressurised CO 2 conditions, whereas atmospheric pressure CO 2 conditions more closely resembled the specimen exposed in air. Importantly, this study reveals that in simulated experiments, pressurised CO 2 environments are essential to replicate the carburisation behaviour observed in ex-service conditions. • Both ex-service 316H austenitic steel and 316H specimens exposed to pressurised CO 2 show carburisation ahead of crack tips. • Air and atmospheric pressure CO 2 tests fail to replicate this carburisation behaviour. • The proposed mechanism reflects the role of pressurised CO 2 environment on carburisation of 316H steel.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 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) | 0.000 | 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 teacher head, 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".