http://hdl.handle.net/11422/92 2026-04-19T06:23:54Z http://hdl.handle.net/11422/28417 Title: CO2 corrosion of high strength steel wires in the annulus of flexible pipes Author(s)/Inventor(s): Campos, Tatiane Seixas Advisor: Gomes, José Antônio da Cunha Ponciano Abstract: Corrosion of carbon steel may occur at near neutral pH in deoxygenated solutions with high bicarbonate concentration when the corrosion reaction produces elemental hydrogen. Such conditions are encountered in the annulus of flexible pipes when it contains water with dissolved CO2, which produces high concentration of ferrous ion (Fe2+) and bicarbonate (HCO3-). The objective of the present study was to investigate if high levels of Fe2+ and HCO3- can persist for the time required to induce SCC in armor wire steels. It implies that the nucleation and growth of siderite (FeCO3) is so slow that the solution remains supersaturated for several days. The role of surface finishing and cathodic areas composed of cementite were also evaluated, as well as the salinity, temperature, and pCO2. The results show that, at temperatures lower than 40 °C and CO2 partial pressure of 5 to 10 kPa, the saturation ratio (SR) of siderite can persist at values much higher than 1 and maintain a near neutral pH for several hundred hours. The uniform corrosion rate of armor wire steel is low if pH soon achieves near neutral range. The siderite forms a layer on the steel surface and the cathodic reaction becomes limited by diffusion through it. The corrosion rate increases with increasing salt content and exposed cementite, being even more pronounced at 25 °C. In such cases, siderite could not completely inhibit localized corrosion, which may be a great site for SCC cracks to start. That is related with a join action of the higher solubility of siderite and the effect of ion chloride. At 25°C and brine, the pCO2 is the main parameter to concern in active surfaces of armor steels. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação 2022-05-01T00:00:00Z http://hdl.handle.net/11422/28416 Title: Caracterização de frações segregadas de catalisadores de equilíbrio de FCC por microscopia eletrônica de varredura e transmissão Author(s)/Inventor(s): Carvalho, Paulo Sergio da Silva Advisor: Jardim, Paula Mendes Abstract: In the present study, two FCC equilibrium catalysts (e-cat) were fractionated by density, each generating 4 fractions that represent increasing levels of particles density and contamination. The eight samples were characterized by X-Ray Fluorescence Spectroscopy (XRF), Nitrogen Physisorption, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) combined with Energy Dispersive X-Ray Spectroscopy (XEDS) and Transmission Electron Microscopy (TEM) combined with XEDS and Electron Diffraction. An image analysis methodology was developed and allowed the realization of a quantitative visual characterization of the elements of interest based on the SEM/XEDS mappings. The XRF, XRD and textural analyses indicated that the density separation was successful and that the contaminating metals are more concentrated in the denser fractions, which also presented greater deterioration of zeolites crystal structure. The SEM/XEDS analyses revealed the existence of particles populations with different compositions regarding the Si/Al ratio, making it possible to relate the type of catalyst with its level of contamination by Ni. A strong interaction between Ni and Al was observed by STEM/EDS and electron diffraction analyses, possibly due formation of a nickel aluminate. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação 2022-01-01T00:00:00Z http://hdl.handle.net/11422/28411 Title: Investigação de gradiente de propriedades ao longo da espessura em amostras de PVDF exposto a fluido nitrogenado Author(s)/Inventor(s): Souza, Josefa Nágila Cabral de Advisor: Costa, Marysilvia Ferreira da Abstract: In this work, PVDF samples were aged in nitrogen fluid at 93°C and 120°C, for up to 100 days, to investigate the effect of aging on the mechanical, thermal and microstructure properties of the polymer along its thickness. The samples were divided into three groups and were subjected to different aging conditions: samples completely exposed to the fluid, samples partially exposed to the fluid, control group, which consisted of samples exposed to air at high temperature, for evaluation only of the thermal effect over the polymer. After aging, the samples were sectioned into three regions of their thickness, each of which was characterized by TGA, DSC and instrumented microindentation analysis. With the results obtained, it was verified that only the temperature did not impose great changes in the thermal and mechanical behavior of the PVDF, the contact with the fluid induced a high mass gain and promoted changes both in the mechanical properties, EIT and HIT, as in the crystallinity, microstructure and melting temperature, originally presented by the polymer. The second heating in the DSC showed that these changes were permanent. A property gradient was also identified along the thickness of the samples partially in contact with the fluid, evidencing how the presence of the fluid is a key factor for the reordering of the crystalline structure and for the changes in the material properties, which occur gradually and heterogeneously in the different regions of the thickness of the samples, as the diffusion of the fluid from the surface to the interior of the polymer progresses. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação 2022-06-01T00:00:00Z http://hdl.handle.net/11422/27555 Title: Effect of flow on the corrosion behaviour of API 5L X80 steel in supercritical CO2 systems Author(s)/Inventor(s): Sá, Jonas da Silva de Advisor: Gomes, José Antônio da Cunha Ponciano Abstract: In this work,the effect of water-saturated supercritical CO2 and CO2-saturated water flow rate on the corrosion behaviour of API 5L X80 steel at a temperature of 35°C and pressure of 80 bar was investigated. Tests were carried out with the samples attached to a rotating shaft inside an autoclave. Results indicate that increasing the CO2-saturated water flow rate increased the corrosion rate in the absence of a corrosion product film, but later favoured the precipitation of a dense and more protective crystalline carbonate layer. Besides that, the presence of Ca2+ in the brine favoured the precipitation of a mixed iron-calcium carbonate (FexCa1˘xCO3) film with increasingly calcium molar mass that offered better protectiveness to the carbon steel when compared to the pure iron carbonate (FeCO3). On the other hand, in water-saturated supercritical carbon dioxide systems, increasing the flow rate had no significant influence on the general/localized corrosion rate under the various dynamic conditions considered, because the size of the condensed water droplets, were much smaller than the calculated critical droplet size needed to be displaced by the supercritical CO2 flow. Publisher: Universidade Federal do Rio de Janeiro Type: Tese 2022-03-01T00:00:00Z