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Degradation of OCTG Steel in SAGD Application
- Author / Creator
- Aghaie, Ermia
The present research was conducted with the intent of evaluating the degradation of OCTG (Oil Country Tubular Goods) steel used in SAGD (Steam Assisted Gravity Drainage) applications, and developing a promising surface modification method and a novel composite coating using a technique that will have a high possibility of commercialization to improve the corrosion resistance of the OCTG steel in SAGD applications. The corrosion mechanism of OCTG steel in the sour environment consisting of H2S and CO2 was fully understood but the performance of the coated (Ni-P coating) and uncoated OCTG steel in a real SAGD operation was not evaluated till now. So in this study, at the first, the coated (electroless Ni-P coating) and uncoated slotted liner used in a real SAGD operation for three months were evaluated by X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and optical stereoscopic microscope (OSM) from cross section and surface of the samples. Elemental mapping analysis of the corrosion scale formed on the samples was done from the cross section in order to have a better perspective on performance of the coated and uncoated slotted liner in SAGD operation. Results revealed that applying the Ni-P coating considerably decreased the thickness of the corrosion scale formed on the samples. Also a condensed layer of nickel sulfide formed on the coated samples which can function as a barrier against the diffusion of the corrosive ions from the environment to the substrate. However, the corrosion product formed on the uncoated sample was very porous.
Alloy carbon steel is of great interest in oil sands industry due to its desired strength, flexibility, and low cost. However, the corrosion of this widely used steel in corrosive environments is a great concern. Indeed, finding and applying a promising coating on carbon steel which is used in sour environment (including H2S and CO2) have always attracted a significant attention of oil sands industry specifically SAGD industry. The sour environments consisting of H2S and CO2 accelerate the corrosion process and degradation of the carbon steel, resulting in replacement of the OCTG in oil sands industry.
As a matter of fact, nitrogen has a substantial effect on the corrosion behavior of steels. In part two of this study, gas nitriding at 850 °C and 950 °C was applied to the carbon steel. The corrosion resistance behavior of the modified samples was investigated by the electrochemical impedance spectroscopy and potentiodynamic polarization tests at the simulated sour environment. After the corrosion test, optical microscope and scanning electron microscopy were employed to evaluate the surface morphology of the samples modified by gas nitriding technique. The results of the polarization testes revealed that the localized corrosion of the carbon steel specimens modified by nitrogen decreased significantly. In addition, the polarization resistance of the carbon steel samples increased considerably after applying the gas nitriding process. However, due to the lack feasibility of using this technique for the industry, I shifted from the gas nitriding to a more applicable technique - electroless plating technique. With this in mind, Ni-P-GO (graphene oxide) composite coating was applied on carbon steel by using electroless plating technique. The electrochemical behavior of the Ni-P-GO was evaluated by potentiodynamic polarization test and EIS in a simulated sour environment saturated by H2S and CO2. Morphology, microstructure, elemental analysis, and phase analysis of the coating are investigated by OSM, FESEM equipped with EDS, and X-ray diffraction technique. Microscopic images taken from the Ni-P-GO composite coating revealed that GO nanosheets distributed uniformly through the coating. Electrochemical tests showed that adding graphene oxide nanosheets significantly improved the corrosion resistance of electroless Ni-P coating in the sour environment. Also, results of the EIS test revealed that adding GO nanosheets increased the coating resistance of the electroless Ni-P coating from 1 KΩ.cm2 to around 12.3 KΩ.cm2.
- Graduation date
- Fall 2017
- Type of Item
- Master of Science
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