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 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 | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".