Water transport through epoxy-based powder pipeline coatings
Bibliographic record
Abstract
Hydration of epoxy coatings reduces adhesion performance and causes degradation of the material, such as microstructural failures. Quantification of water vapor transport at elevated temperatures is fundamental to understanding polymer coating performance, especially when the coating is exposed to extreme operating conditions. As the water activity increases, the permeability/selectivity of polymers against other permeants changes. In this study, we examined the water permeation kinetics of two common epoxy-based powder coating systems for pipelines (fusion-bonded epoxy, FBE, and high-performance powder coating, HPPC) across a range of industrially-relevant temperatures (from room temperature to 80°C). Specifically, we utilized vapor permeation features of FBE and HPPC films with quantification of equilibrium flux as a function of temperature and pressure. In addition, we analyzed the nonlinear dependency of water transport on the vapor concentration at 65°C. The vapor transport analysis demonstrated that although data for FBE were indicative of a decrease in permeability around 65°C, perhaps due to self-association of water molecules, the coating was likely to experience a plasticization pressure around this temperature. We also examined microstructural changes of the epoxy network due to water transport. Our results revealed evidence of irreversible damage to epoxy coatings under wet-state conditions above 65°C. It appears that the combination of thermal exposure and internal stresses in the glassy epoxy lead to a phase separation of filler particles from the epoxy matrix, as well as to a distinctive cavity formation in the coating membrane. Yet, despite formation of percolating paths for water transport, our results indicate that vapor permeation is primarily restrained due to self-association of water molecules. The vapor transport flux and its permeance are lowered by one order of magnitude in the multilayered HPPC thanks to the moisture-resistant polyethylene topcoat, thus reducing the extent of damage to the underlying substrate. Since barrier protection against gas phase diffusion is controlled by the FBE primer, however, consequences of coating hydration are more pronounced in the overall selectivity toward gaseous transport. Hydrothermal exposure is likely to increase aggregate porosity of the coating and a conservative implementation of standard coating requirements is therefore reasonable to avoid early degradation issues.
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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 | 0.000 | 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".