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Electrochemical frequency modulation (EFM), which has been widely used in the research field of semiconductors, was used to study CO2 corrosion on carbon steel under film forming and non-film forming conditions. In the EFM technique two sinusoidal voltage signals of different frequencies are applied to the system and the response current is measured at zero, harmonic and intermodulation frequencies from which the corrosion rate is calculated. The corrosion rate calculation depends upon whether the system is under activation, diffusion or passivation control. In this research rotating cylindrical electrodes made of AISI carbon steel 1018 were immersed in 3% (w/w) NaCl solution saturated with carbon dioxide. The experiment was done at 5 rpm, 24 rpm and 100 rpm simulating laminar, transient and turbulent flow regions respectively. The exposure time was varied from 1 hour to 24 hours and the results were compared with other electrochemical methods such as linear polarization (LP) and electrochemical impedance spectroscopy (EIS). It was found that it was crucial to select the correct EFM model to ensure accurate corrosion rate measurement. A very good agreement in the polarization resistance was obtained between EIS and EFM indicating that EFM can be used as an effective tool in corrosion studies providing that the corrosion mechanism is known.

Mineral scale formation is important to many areas of science and engineering, from drinking water treatment to oceanography to oil and gas production. In some cases mineral deposition is beneficial, as in water treatment for heavy metal or arsenic removal, and sometimes it is deleterious, as occurs in oil and gas production due to co-produced water. In either case, understanding the mechanisms of precipitation and inhibition is critical. Work in this thesis has focused on the impact of metal ions on mineral scale formation, and control. The results reveal that the addition of metal ions in the pill solution significantly improved the retention of scale inhibitors. Both BHPMP and DTPMP returns were significantly extended by the addition of Ca 2+ and Fe 2+ Also trace levels of Zn 2+ significantly enhanced the performance and retention of both BHPMP and DTPMP. The enhanced scale inhibition may be caused by a complex of metal ions with amine group of polyamino- polyphosphonates. It is known that the effectiveness of inhibitors varies upon the type of scale formed where it has been mentioned in the literature that common calcium carbonate inhibitors are not effective for preventing iron carbonate. Therefore, this work was also intended to investigate the impact of calcium and iron ions in the co-precipitation of iron-calcium carbonate solid solutions (Fe x Ca 1-x CO 3 ). Three different experimental methods were applied to investigate and predict the precipitation of Fe x Ca 1-x CO 3 : Free drift, continuous feeding, and constant composition experiments. The results from all methods showed that calcium carbonate was kinetically favored to precipitate rather than iron carbonate when the solution is supersaturated with respect to calcium carbonate and iron carbonate. In the constant composition experiments a series of solid solutions of iron-calcium carbonate ranging from calcium-rich to iron-rich was precipitated. Based upon the experimental results and the theoretical derivation, a new model in a form of logistic function was developed to predict the stoichiometry of Fe x Ca 1-x CO 3 as a function of the aqueous solution composition. The model showed an excellent representation for the experimental results with R 2 greater than 0.97 and 0.88 for Fe x Ca 1-x CO 3 and Ba x Ca 1-x CO 3 , respectively. The experimental equipment and procedures described in this work provide an effective means of producing and handling oxygen sensitive solid solutions. The precipitation kinetics of a number of solid solutions in aquatic systems could be studied by adapting the experimental design developed herein.

Electrochemical frequency modulation (EFM), which has been widely used in the research field of semiconductors, was used to study CO2 corrosion on carbon steel under film forming and non-film forming conditions. In the EFM technique two sinusoidal voltage signals of different frequencies are applied to the system and the response current is measured at zero, harmonic and intermodulation frequencies from which the corrosion rate is calculated. The corrosion rate calculation depends upon whether the system is under activation, diffusion or passivation control. In this research rotating cylindrical electrodes made of AISI carbon steel 1018 were immersed in 3% (w/w) NaCl solution saturated with carbon dioxide. The experiment was done at 5 rpm, 24 rpm and 100 rpm simulating laminar, transient and turbulent flow regions respectively. The exposure time was varied from 1 hour to 24 hours and the results were compared with other electrochemical methods such as linear polarization (LP) and electrochemical impedance spectroscopy (EIS). It was found that it was crucial to select the correct EFM model to ensure accurate corrosion rate measurement. A very good agreement in the polarization resistance was obtained between EIS and EFM indicating that EFM can be used as an effective tool in corrosion studies providing that the corrosion mechanism is known.

[pt] A seleção de materiais para o transporte de óleo e gás não é feita pela sua resistência à corrosão, mas sim pelas suas boas propriedades mecânicas, facilidade de fabricação e baixos custos. Devido às taxas de perda de material, causado pela corrosão interna, existe necessidade em se conhecer o comportamento dos aços de mais alta resistência, utilizados especialmente em gasodutos e oleodutos tais como API 5L X70 e API 5L X80. Um dos elementos responsáveis pela corrosão interna é o dióxido de carbono (CO2). O principal produto de corrosão da reação deste gás com o aço é um precipitado de carbonato de ferro que em determinada temperatura se acredita poder retardar o processo de corrosão, agindo como uma barreira à difusão das espécies. Neste trabalho foi estudado o comportamento destes aços numa solução de 1% NaCl contendo CO2, e a estabilidade do filme formado (FeCO3) à diferentes temperaturas. Técnicas de análise eletroquímicas como: curvas de polarização, resistência à polarização linear e de impedância eletroquímica foram usadas para estudar a formação do filme de carbonato de ferro sobre a superfície dos aços. O filme também foi observado e caracterizado por microscópio eletrônico de varredura (MEV) e difração de raios-X. / [en] The selection of materials for the transport of oil and gas, is not always made sufficiently emphasizing corrosion resistance, but rather good mechanical properties, ease of fabrication and low cost. Due to the material loss rates resulting from internal corrosion, it becomes necessary to thoroughly characterize the behaviour of the high strength steels which are used for oil and gas pipelines, such as API 5L X70 and API 5L X80. One the contributing factors responsible for internal corrosion is carbon dioxide (CO2). The main corrosion product resulting from the action of this gas, in solution, on the steel is an iron carbonate precipitate which is believed to retard further corrosion at some temperatures, acting as a diffusion barrier to the chemical species involved. The current work studies the behaviour of the above steels in a 1% NaCl solution containing CO2, and the stability of the FeCO3 film formed at different temperatures. Electrochemical analysis techniques, such as polarization curves, linear polarization resistance and impedance measurements were used to study the formation of the iron carbonate film on the surface of the steels. The film was also observed and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

abstract: This study explores the possibility of two matrices containing metallic particulates to act as smart materials by sensing of strain due to the presence of the conducting particles in the matrix. The first matrix is a regular Portland cement-based one while the second is a novel iron-based, carbonated binder developed at ASU. Four different iron replacement percentages by volume (10%, 20%, 30% and 40%) in a Portland cement matrix were selected, whereas the best performing iron carbonate matrix developed was used. Electrical impedance spectroscopy was used to obtain the characteristic Nyquist plot before and after application of flexural load. Electrical circuit models were used to extract the changes in electrical properties under application of load. Strain sensing behavior was evaluated with respect to application of different stress levels and varying replacement levels of the inclusion. A similar approach was used to study the strain sensing capabilities of novel iron carbonate binder. It was observed that the strain sensing efficiency increased with increasing iron percentage and the resistivity increased with increase in load (or applied stress) for both the matrices. It is also found that the iron carbonate binder is more efficient in strain sensing as it had a higher gage factor when compared to the OPC matrix containing metallic inclusions. Analytical equations (Maxwell) were used to extract frequency dependent electrical conductivity and permittivity of the cement paste (or the host matrix), interface, inclusion (iron) and voids to develop a generic electro-mechanical coupling model to for the strain sensing behavior. COMSOL Multiphysics 5.2a was used as finite element analysis software to develop the model. A MATLAB formulation was used to generate the microstructure with different volume fractions of inclusions. Material properties were assigned (the frequency dependent electrical parameters) and the coupled structural and electrical physics interface in COMSOL was used to model the strain sensing response. The experimental change in resistance matched well with the simulated values, indicating the applicability of the model to predict the strain sensing response of particulate composite systems. / Dissertation/Thesis / Masters Thesis Civil and Environmental Engineering 2017

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