Resumo em Inglês:

Saturation of acidic gases in seawater, resulting from deepwater activities in the oil and gas industry, can promote detrimental effects on the internal metallic sheath of pipelines due to an eventual failure of the outer sheath. Failures in the tensile armor typically occur in a confined space due to the low volume of electrolyte, i.e. seawater, in comparison to the exposed surface area of the steel. This condition promotes the supersaturation of several species in this environment. This study was conducted to investigate the complex chemistry and electrochemical mechanism involved in CO2 corrosion in confined spaces. The aim is to elucidate the impact of low CO2 partial pressures, either 1 or 3 bar, on the supersaturation of species as well as the formation of a solid FeCO3 film onto the alloy surface and evaluate its protectiveness degree. The data obtained suggests the presence of a more protective layer associated with a pressure of 3 bar, represented by a continuous and compact FeCO3 film approximately 26.54 µm thick. Despite the faster growth of FeCO3 films at 1 bar, they appear to exhibit non-protective properties, as observed through SEM analyses, with a discontinuous layer measuring about 20.86 µm in thickness.

Resumo em Inglês:

Durability and corrosion resistance are essential requirements in the development of aerospace components, and the optimization of anodizing processes stands out as an effective strategy to enhance the corrosion performance of aluminum alloys used in this sector. In this context, the present study provides new insights into the effect of the presence of different carboxylic acids (oxalic, citric, and succinic) in a sulfuric acid-based anodizing electrolyte on the corrosion resistance of the AA2024-T3 aluminum alloy. The anodic oxide films were characterized using microscopy and electrochemical analyses to assess their morphological and corrosion-resistant behavior. The results indicated the formation of oxide films with different surface morphologies, uniform thickness ranging from 16.7 to 23.8 µm, and satisfactory protection against corrosion in NaCl media (0.1 mol.L-1), especially with regard to treatment with oxalic acid (OSA), which, compared to other treatments with carboxylic acids (citric – CSA, and succinic – SSA) and the standard treatment (sulfuric acid – SA), maintained the highest protective performance of the coating over 21 days of immersion.

Resumo em Inglês:

Zirconium-based conversion coatings provide an environmentally friendly, chromate-free alternative to traditional phosphating and chromating processes for enhancing the corrosion protection of metal substrates. This study investigates the formation and characterization of zirconium-based conversion coatings (Zr-CC) on AA3105-H16. The coatings were produced by immersion in an hexafuorozirconic acid (H2ZrF6) solution and characterized using SEM-FEG, SEM/EDS, and Raman spectroscopy. Considering that the incorporation of organic and/or inorganic additives can enhance the anticorrosive performance of Zr-CCs, electrochemical techniques were employed to assess the influence of Cu2+ ions on corrosion resistance in a sodium chloride medium. The results indicate that, under the tested conditions, Cu2+ ions act as precursors for film formation, increasing the open-circuit potential and decreasing the coating formation time. However, coatings formed in the presence of Cu2+ ions exhibited lower corrosion resistance, revealing a detrimental effect on anticorrosive performance.

Resumo em Inglês:

The formation of scale deposits in pipelines within the oil and gas sector is a recurring challenge that impacts operational efficiency and incurs various associated costs. Understanding the processes of mineral formation and dissolution that contribute to these deposits is essential for the implementation of effective control and mitigation strategies. This study used thermodynamic simulations to predict mineral species present in inorganic scale deposits in saline water systems within the oil and gas industry in order to provide background knowledge for future scale inhibition studies. To this end, the software The Geochemist’s Workbench was employed to construct stability diagrams, taking into account thermodynamic parameters such as pH, temperature, and pressure, through focusing on a high-bicarbonate, low-sulfate formation water, a common but challenging scenario where carbonate scaling dominates. Through the thermodynamic simulations, the software suggested the precipitation of Witherite (BaCO3), Strontianite (SrCO3), and Dolomite (CaMg(CO3)2), which were not expected for the present scenario, due to the low concentrations of Ba, Mg and Sr. Thus it was suggested that such results did not take into consideration the precipitation kinetics and the amount of crystalized material. In addition to the simulations, the systems were analyzed through static tests, and the resulting precipitates were characterized using optical microscopy, X-ray diffraction, and thermal analysis. The thermodynamic simulation results were compared with the experimental data, enabling an assessment of the consistency between the theoretical models and the observed results.

Resumo em Inglês:

The operational conditions for oil and gas production frequently change. Consequently, equipment and pipes originally specified for milder conditions may no longer meet the standards requirements. This study addresses the safety of maintaining AISI304 and 316L flexible pipe carcasses in sour service with high chloride content. A rigorous laboratory testing program was carried out with specimens machined from field-removed carcass sections, designed to reproduce a more aggressive scenario than current operational conditions. The methodology employed the U-bend technique to apply stress in the plastic regime, combined with crevice formers, and included welded samples to study the effect of sensitization. The results confirmed that sensitization and cold work influences corrosion susceptibility of both steels. Similar performance was observed to AISI304 and AISI316L in high chloride and H2S environments. This good field performance is attributed to the influence of H2S, in concentrations above 100ppm. The formation of a dense sulfide layer is favored, constraining pit development. A new unified operational limit was established for AISI304 and AISI316L carcass: high chloride environment, 60oC and 1≤[H2S]≤5% in gas mixture. The experimental data provides essential criteria for life extension and reuse of flexible assets under conditions not specified on current standards.

Resumo em Inglês:

To address the critical challenges of melt impurities and coarse microstructures in Al-Cu-Mg alloys, this study presents a novel approach combining ultra-low Ti-Zr microalloying with a proprietary composite refining process. While conventional refiners often fall short in simultaneously achieving melt purification and grain refinement, the integration of Ti-Zr additions addresses this gap by promoting the in-situ precipitation of nanoscale heterogeneous nucleation cores. The microstructural evolution, defect reduction, and mechanical enhancements of the alloy were systematically investigated using comprehensive experimental characterizations. Results demonstrate that the self-developed refining agent substantially outperforms commercial counterparts in optimizing the alloy's overall performance, yielding an average yield strength of 200.1 ± 10.2 MPa and a significantly improved average elongation of 26.7 ± 0.31%. Furthermore, first-principles calculations of the Al(001) || Al3Zr(001) interface were conducted to seamlessly link theoretical interfacial thermodynamics with experimental findings. The calculations reveal that the Al3Zr non-Zr end bridge stacking configuration exhibits the strongest interfacial bonding, with a minimum interface equilibrium distance of 2.0 Å and a maximum adhesion work of 6.0 J/m2. These theoretical insights perfectly corroborate the experimental observations of enhanced nucleation and microstructural refinement facilitated by the Ti-Zr microalloying process.

Resumo em Inglês:

This study examines the use of sigma phase formation to enhance the high-temperature abrasive wear performance of SAF 2507 super duplex stainless steel. We investigated two states: as-received and a pre-heat-treated condition (850 °C for 30 min, air-cooled). Wear tests were conducted at 400 °C and 800 °C to evaluate the combined influence of prior thermal treatment and operating temperature on the material's tribological behavior. Microstructural analysis revealed the pre-heat-treated condition developed a fine, homogeneous sigma phase. At 800 °C, both conditions underwent in-situ sigma phase formation, leading to increases in hardness, reduced friction, and lower wear rates associated with both microstructural strengthening and oxidation-assisted mechanisms. The findings suggest two approaches for enhancing wear resistance. For service below 800 °C, a pre-service heat treatment is effective. For service near the sigma transformation temperature (around 850 °C), the operating conditions can act as an in-situ heat treatment, producing similar strengthening effects without prior processing. By strategically using the sigma phase as a controllable strengthening constituent, this study presents an approach for designing super duplex stainless steels for extreme environments, demonstrating that microstructural conditioning and high-temperature surface interactions enhance hardness and wear resistance at high temperatures.

Resumo em Inglês:

This work investigates the surface integrity of AISI 316L produced by additive manufacturing (AM) and subsequently machined, with an emphasis on residual stresses. A full factorial design was applied to evaluate the influence of laser power from AM and milling parameters, including cutting speed, cutting depth, feed rate, and cutting fluid. Eight samples were selected for Vickers microhardness characterization. Machined surfaces were examined by scanning electron microscopy. Microhardness results showed higher values at top surfaces, reaching increases of up to 22.7%. Variations in machining parameters significantly affected residual stresses, with changes of up to 500 MPa; all measured values were tensile. Surface roughness Rt ranged from 1.59 to 4.34 µm. The best surface integrity was achieved using 160 W laser power, 170 m/min cutting speed, 0.1 mm/tooth feed rate, 0.35 mm cutting depth, and cutting fluid. ANOVA identified feed rate as the most influential factor, followed by laser power and cutting depth. Machine learning models were developed for residual stress prediction, with PCA-RBFN showing superior performance for parallel residual stress (R2 = 94,53%) and SVM for perpendicular residual stress (R2 = 89.85%). The hybrid approach enabled isolation of individual parameter effects while minimizing interactions between AM and machining.