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Investigation and Optimization of Corrosion-resistant Electroless Ni-P Coating in Steam-assisted Gravity Drainage System
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- Author / Creator
- Li, Jiankuan
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The boosting energy demand has propelled the increasing utilization of oil and gas resources, but severe corrosion occurs on traditional carbon steel materials. Driven by the harsh service conditions in steam-assisted gravity drainage system (SAGD) operations, a promising corrosion-resistant coating, electroless Ni-P coating, has attracted growing attentions due to its good balance between satisfactory performance and reasonable cost. Therefore, in this thesis, the corrosion behavior and mechanism of Ni-P coating in SAGD-related environments were elucidated, and further coating optimization approaches were made to meet diverse requirements under service conditions.
First, the electrochemical corrosion behavior of Ni-P coating in CO2/H2S/Cl- brine was investigated. The added H2S enhances the corrosion of Ni-P coating by affecting both anodic and cathodic processes. The well-accepted H2PO2- adsorbed layer only exists in the early stage of corrosion and barely improves the anti-corrosion performance. The formation of NiO and Ni3S2 renders temporary protection during immersion, but the addition of H2S accelerates the diffusion process at the electrolyte/coating interface and promotes the electrolyte penetration through the coating, causing severe localized corrosion and coating disbondment. A corrosion model was proposed to illustrate the corrosion and degradation process of Ni-P coated steel in the CO2/H2S/Cl- environment.
Secondly, the effects of Ca2+ on the corrosion behavior and film characteristics of N80 carbon steel and electroless Ni-P coating at high temperature and high pressure were studied. The corrosion of N80 steel is significantly influenced by Ca2+ concentrations, which not only alters the corrosion film microstructure, but also changes the water chemistry of the aqueous phase. Meanwhile, Ni-P coating exhibits exceptional corrosion resistance regardless of Ca2+ concentration, owing to the protection of the formed NiO/Ni(OH)2 film and the absence of scale formation.
The optimization methods of Ni-P coating were then developed to acquire better anti-corrosion properties. The electroless Ni-Mo-P/Ni-P composite coating was successfully applied on N80 carbon steel, and the effects of Mo addition and heat treatment on the corrosion resistance enhancement in CO2/H2S/Cl- brine were studied. The Mo addition in the as-deposited Ni-P coating causes the microstructural transformation from amorphous to crystalline due to the reduced P content, thereby suffering severe corrosion. Nonetheless, the heat-treated Ni-Mo-P/Ni-P coating exhibits desirable corrosion resistance. Heat treatment facilitates the formation of Ni4Mo phase and the growth of an oxide film consisting of nickel and molybdenum oxides with better passivation properties, which accounts for the remarkable corrosion resistance improvement.
In addition, a smart electroless Ni-P composite coating incorporated with pH-responsive benzotriazole-loaded nanocapsules was successfully fabricated and applied on N80 carbon steel, and the improved corrosion resistance was evaluated. The coating incorporated with the functionalized nanocapsules exhibits excellent anti-corrosion performance. It is primarily originated from the filling of nanocapsules into intrinsic micropores of the coating that impairs the electrolyte penetration, and the release of BTA when triggered by the local acidification of the micropores due to penetration of aggressive medium. The incorporated nanocapsules endow the smart coating with good anti-corrosion stability, showing a maximum inhibition efficiency of nearly 80%, as well as a well-protected coating surface with much less corrosion pits and the absence of lateral coating disbondment at the coating/substrate interface. -
- Graduation date
- Fall 2020
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.