Thermodynamics of the Corrosion of Alloy 625 Supercritical Water Oxidation Reactor Tubing in Ammoniacal Sulfate Solution
Bibliographic record
Abstract
During the process of supercritical water oxidation (SCWO), organic chemical streams are oxidized at temperatures and pressures in excess of 647 K and 221 bar. Due to high operating temperatures and pressures, severely corrosive environments often ensue and eventually lead to SCWO reactor tube failures. This case study looked at one such failure of Alloy 625 (61Ni-21.5Cr-9Mo [UNS N06625]) tubing, which occurred at the UBC SCWO pilot plant while treating a feed of waste-water containing ~0.1 m 2,4 dinitrophenolate (C6H4N2O5), ~0.25 m ammonium sulfate ([NH4]2SO4), and ~1.3 m free ammonia (NH3). The feed pH was approximately 10 and therefore not expected to be corrosive; in fact, the tube failed when exposed to this feed (with oxygen) for a period of about 1 h at two sections subjected to temperatures in the 650 K to 655 K range. Through a detailed thermodynamic examination of the Ni-H2O-NH3 system at 373, 473, 573, and 653 K, as well as scanning electron microscopy (SEM) and energy-dispersive x-ray (EDX) analysis of the ruptured portions of tubing, it was found that the addition of ammonia and sulfate lead to solution acidification and NiO instability, which resulted in little protection for the alloy when subjected to the oxidative high-temperature medium. The alloy ultimately failed by transpassive dissolution.
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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 | 0.000 | 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) | 0.001 | 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".