Corrosion Behaviour of High-Carbon High-Molybdenum Stellite Alloys in Amine Environment
Bibliographic record
Abstract
Stellite alloys are cobalt-based alloys which display exceptional mechanical properties, wear and corrosion resistance owing to its unique chemical compositions. Stellite 6 is the most popular Stellite alloy employed in various applications, one of which is the hardfacing of valve trim components within control valves in boiler feedwater treatment systems where hydrazine and/or amine derivatives are used. Erosion-corrosion caused failure of Stellite 6 hardfacing has been reported from industry in such applications. To find a better replacement of Stellite 6 for improved corrosion resistance in amine environment, 700 series Stellite alloys, including Stellite 706, Stellite 712 and Stellite 720, are proposed, which are high-carbon high-molybdenum Stellite alloys. The corrosion performance of these alloys in morpholine solution with pH 9.5, which simulates the corrosive environment of boiler feedwater service, is evaluated using a series of electrochemical tests such as electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and potentiostatic polarization. Both regular polarization tests (potential up to 1.2 V) and failure polarization tests (potential up to 12 V) are conducted on the alloys. The former identifies general and localized corrosion behaviour, while the latter intends to fail the alloy surface to analyze their limitations. Two different surface conditions (intact and damaged) and two different temperature variables (25C and 50C) are also studied to simulate erosion-corrosion behaviour. Stellite 6 alloy is also tested under the same condition for comparison. It is shown that these 700 series Stellite alloys are comparably better than Stellite 6 with respect to oxide film stability, all exhibiting excellent corrosion resistance in morpholine solution with pH 9.5. The protective chromium oxide film on their surfaces is retained well for both regular and failure tests. These alloys behave similarly, however, Stellite 720 containing the highest carbon and molybdenum contents performed better at room temperature and Stellite 706 with the least carbon and molybdenum iii contents performed better at the elevated temperature. Although wear changes the surface condition, the corrosion resistance of the worn alloys is similar to that of intact alloys in the tested solution. The outcomes of this research suggest that 700 series Stellite alloys are good candidates for replacing Stellite 6, where Stellite 720 displayed the best performance under the conditions tested.
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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) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 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 | 0.001 | 0.001 |
| 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".