Chemical and Biomolecular Engineering - Theses
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ItemRetrofitting pipelines by in situ coating( 2024-01)Global energy demand is on the rise, urging a shift toward sustainable solutions. Hydrogen stands out as a clean, efficient energy source that could significantly reduce emissions. However, challenges persist in its storage and transportation. Using current natural gas pipelines for hydrogen transport is cost-effective but raises concerns about potential steel degradation due to hydrogen's ability to permeate steel. Hydrogen embrittlement threatens the safety and reliability of these pipelines. Addressing hydrogen embrittlement effects on steel infrastructure is crucial to maintain the safety and reliability of hydrogen transportation via pipelines. Internal coatings on pipelines can hinder the contact between hydrogen gas and the pipeline steels, thus preventing embrittlement. Nonetheless, the limitations of buried pipelines pose constraints on coating selection. Space restrictions and extensive pipeline distances limit the use of thermal or chemical treatments. Optimal coating materials need to be liquid or solution-based and not reliant on expensive materials to enable widespread usage. Considering these limitations, utilizing polymers for internal steel pipe coatings emerges as a promising solution. Polymer materials are cost-effective and easy to process, showing effectiveness in gas barriers and pipeline coatings. This thesis focuses on developing internal polymeric coatings for existing pipelines to prevent hydrogen embrittlement during transportation. Numerous commercially available pipeline coating materials have been studied for their gas permeability, particularly concerning oxygen. However, none of these studies have documented the permeability of hydrogen thus far. The thesis examined the hydrogen permeability of various coating materials, including poly (vinyl chloride), poly (vinyl alcohol) (PVA), crosslinked PVA and bisphenol A diglycidyl ether (DGEBA)/polyetheramine (D-400) films, and twelve commercial coatings. Notably, among these materials, two commercial two-part epoxy coatings exhibited promising results with hydrogen permeability of 0.40 and 0.35 Barrer respectively which are still too high for adequate protection, necessitating further enhancements. Glutaraldehyde crosslinked PVA exhibited the lowest permeability at 0.0084 Barrer, indicating strong potential as a coating. The level of hydrogen concentration within steel that can trigger embrittlement, however, remains unclear. Therefore, this thesis developed a mathematical model to evaluate unsteady state hydrogen diffusion through coated steel. The results suggested that a 2 mm thick crosslinked PVA film could extend the time to reach diffusion equilibrium from eight days to seven years, with a 44% decrease in final hydrogen concentration on the steel surface. Besides low hydrogen permeability, the material needs to be shear-thinning to be applied in situ onto underground pipelines. The thesis demonstrated the development of poly (ethylene glycol) diglycidyl ether (PEGDGE) and PVA crosslinked polymer coatings with ultralow hydrogen permeability and appropriate shear-thinning properties for on-site application. The material reached a hydrogen permeability of 0.01 Barrer, which is two magnitudes lower than most commercial coatings. The work found that alkali catalyst (KOH) concentration variations do not affect film permeability but promote the shear-thinning behaviour with shorter reaction times. Higher PVA to PEGDGE ratios enhance polymer crystallinity, reducing permeability but have a negative impact on the rheology. The molecular weight of reactants was also investigated. PVA with higher molecular weight reduces permeability and promotes shear-thinning. PEGDGE with higher molecular weight increases permeability but enhances shear-thinning properties with quicker reaction times. During hydrogen embrittlement processes, hydrogen molecules first dissociate into hydrogen radicals and then penetrate steel. Hence, in addition to barrier coatings for hydrogen embrittlement protection, this thesis also investigated a novel approach in hydrogen radical scavenging coatings. Polydopamine (PDA) was chosen here as the scavenging material. PDA films were fabricated on cellophane supporting films by dopamine self-polymerization. A microwave-assisted plasma chemical vapor deposition system generated hydrogen radicals which reacted with the PDA films. X-ray photoelectron spectroscopy analyzed the change in the composition and chemical structure of PDA and indicated its reactions with hydrogen radicals occur mainly within catechol and quinone groups in the PDA structure, reducing oxygen atoms and altering group proportions. Molecular dynamic simulations affirmed experimental findings, confirming that the hydrogen radicals indeed react with the quinone and catechol moieties present in PDA. The study in this thesis underscores the potential of PDA as a coating for scavenging hydrogen radicals on steel piping, thereby mitigating the risk of hydrogen embrittlement. In summary, this thesis delves into the hydrogen barrier properties of various coatings, employing mathematical models to assess their effectiveness. Additionally, it investigates novel coating materials, focusing on their hydrogen permeability and rheological properties. A novel insight into hydrogen radical scavenging materials for hydrogen embrittlement protection and the scavenging mechanisms, are also presented through both experiments and molecular dynamic simulation.