Water transport through epoxy-based powder pipeline coatings
Water can change the molecular structure of polymeric coatings over time and affect the mass transport of other permeants. Hydration of the epoxy network at elevated temperatures increases the aggregate porosity within the coating.
Scientists have examined the water permeation kinetics of two common epoxy-based powder coating systems for pipelines across a range of industrially-relevant temperatures (from room temperature to 80 °C). They exclusively analysed the nonlinear dependency of water transport on the vapor concentration at 65 °C. The vapor transport analysis of epoxy coatings demonstrated a turning point around this temperature, perhaps due to clustering of water molecules. At higher temperatures, break-up of water clusters and plasticisation of the polymer expedited the transport.
Increased aggregate porosity of the coating
The researchers also examined microstructural changes of the epoxy network due to water transport and found evidence for irreversible damage to epoxy coatings under hydrothermal exposures. It appears that the combination of thermal exposure and internal stresses in the glassy epoxy leads to a phase separation of filler particles from the epoxy matrix, as well as to a distinctive cavity formation in the coating membrane. The results indicate that hydrothermal exposure is likely to increase aggregate porosity of the coating and a conservative implementation of standard coating procedures is therefore reasonable to avoid early degradation issues. Analysis of wet-state permeation is not only crucial for protection of transport pipelines, but it also is of high relevance to process equipment and underground storage tanks.
The study has been published in Progress in Organic Coatings, Volume 168, July 2022.
