Elimination of Corrosion and Stress Corrosion Cracking Risks in a Carbon Steel and in a Stainless Steel Digester
Bibliographic record
Abstract
Abstract Digester corrosion has become a major topic for the pulp and paper industry in that it brought about the need for high expenditures with repairs, replacement of components and upgrade of materials, as well as losses in connection with unplanned outages. Risks to life and property are also significant, as catastrophic failure of pressurized equipment may result. From the eighties to present day, corrosion problems in many pulp and paper mills around the world have been intensifying, for reasons ranging from materials and design aspects of the digesters themselves, to process modifications introduced ever since. The present work has the main objective to study the corrosive behavior of continuous digesters with modified processes. Actual corrosion cases in two digesters are presented: (i) carbon steel and (ii) stainless steel clad (316L) digester. Electrochemical testing, metallurgical analyses, corrosion testing and field inspections were used to support the discussions and conclusions. In one field case, a carbon steel digester experienced rapid thinning on its top sections with wall loss of 5 mm over 30 months, after a process change. In the second case, also following a process change, a type 316L stainless-clad continuous digester, the only one in such material known in the Kraft pulping, presented an altered electrochemical profile indicating prospective stress corrosion cracking risk. This prompted the execution of studies and protective measures that are unique for stainless cooking vessels. The risks to carbon or austenitic stainless steel digesters running on modern cooking processes are demonstrated to be significant. The effectiveness of the protective technologies, as well as their compatibility, was proved. The need to consider these technologies upon cooking retrofit projects was established.
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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 | 0.001 | 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 | 0.000 |
| 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".