Comprehensive analysis of alloy 800 corrosion using Thermo-Kinetic diagrams
Bibliographic record
Abstract
Alloy 800 has been used as the tubing material in CANDU® steam generators for over 30 years because of its excellent corrosion resistance. However, recent studies and operational findings have raised critical concerns about its long-term performance, highlighting the urgent need for a deeper understanding of its corrosion mechanisms. This study provides a comprehensive understanding of the corrosion behavior of Alloy 800 under varying pH levels and temperatures by constructing Thermo-Kinetic (TK) diagrams for the alloy and its key elements. The alloy is essentially immune to corrosion at 25 ℃ but becomes susceptible in highly acidic environments at 85 ℃. Immersion tests confirmed these predictions, revealing significant dissolution of the alloying elements at pH 1 and 85 ℃, while the alloy had a corrosion rate of less than 1 µm/year at higher pH levels. SEM analysis identified pitting corrosion at pH 1 and 85 ℃, with the TiN inclusions/matrix interface found to be the primary site for pitting nucleation. Notably, no significant dealloying was observed across the entire pH range at both 25 and 85 ℃. XPS analysis revealed that the corrosion observed at pH 1 and 85 ℃ is due to the instability of the Cr 2 O 3 passive layer. Alloy 800 undergoes pitting corrosion in 0.1 M NaAc solution at pH= 1 and 85 ℃ due to instability of the Cr 2 O 3 passive layer. The TiN inclusions/matrix interface is the primary site for pit initiation. • Thermo-Kinetic diagrams were constructed for alloy 800, nickel, iron, and chromium at 25 and 85 ℃. • Thermo-Kinetic diagrams were used to predict the conditions of susceptibility to corrosion. • Immersion experiments proved that TK diagrams accurately predict corrosion mechanisms under complex conditions. • A mechanistic insight for pitting corrosion of Alloy 800 in acidic pHs is provided.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.006 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| 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 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".