RESUMO O presente trabalho teve como objetivo desenvolver e caracterizar revestimentos nanocompósitos de Ni e Ni-Grafeno aplicados em superfície de aço API 5L X80, utilizando o processo de eletrodeposição, para obter melhores propriedades anticorrosivas. Corpos de prova de dimensões de 20x20x3 mm foram submetidos à limpeza e preparação metalográfica, para posterior deposição dos revestimentos. Para o processo de eletrodeposição foi utilizado um banho à base de níquel contendo dodecil sulfato de sódio (SDS) como surfactante. Para obtenção dos revestimentos Ni-Grafeno, foram adicionadas partículas de grafeno (0,2g/L) ao banho eletrolítico. Os eletrodepósitos obtidos foram caracterizados por Difração de Raios-X (DRX) e Microscopia Eletrônica de Varredura (MEV). A resistência à corrosão dos revestimentos foi avaliada por meio de ensaios de Polarização Linear (PL) e Espectroscopia de Impedância Eletroquímica (EIE). A inserção de grafeno ao revestimento promoveu a formação de depósitos com grãos mais refinados, e com a direção de crescimento de cristais bem definida. Foram observados depósitos com estruturas lamelares sobrepostas, associadas ao grafeno incorporado à matriz de Ni. A deposição de grafeno influenciou na orientação preferencial dos grãos durante o processo de eletrodeposição, sendo o plano (200) idenfiticado como a orientação preferencial para o nanocompósito Ni-Grafeno. O revestimento Ni-Grafeno obteve melhor desempenho anticorrosivo em comparação ao revestimento de Ni puro e ao metal base, apresentando valor de potencial de corrosão (Ecorr) mais elevado, menor valor de densidade de corrente de corrosão (icorr) e módulo de impedância (|Z|) superior.

ABSTRACT The aim of the present work was to develop and characterize nanocomposite coatings of Ni and Ni-Graphene applied on API 5L X80 steel surface, using the electrodeposition process, to obtain better anticorrosive properties. Test specimens of dimensions of 20x20x3 mm were submitted to metallographic cleaning and preparation, for later deposition of the coatings. For the electrodeposition process, a nickel-based bath containing sodium dodecyl sulfate (SDS) was used as the surfactant. To obtain the Ni-Graphene coatings, graphene particles (0.2 g/L) were added to the electrolytic bath. The electrodeposits obtained were characterized by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The insertion of graphene to the coating promoted the formation of deposits with more refined grains, and with a well-defined crystal growth direction. Deposits with overlapping lamellar structures were observed and associated to the graphene incorporated into the Ni matrix. The deposition of graphene influenced the preferential orientation of the grains during the electrodeposition process, with the plane (200) being identified as the preferred orientation for the Ni-Graphene nanocomposite. The Ni-Graphene coating obtained better corrosion performance in comparing to the coating of pure Ni and the base metal, presenting a higher corrosion potential value (Ecorr), lower corrosion current density (icorr) value and higher impedance modulus (|Z|).

Corrosion of pipelines can be significantly affected by the activity of microorganisms present in the environment. The objective of this work was to investigate the influence microbial in the corrosion behavior of API 5L X80 steel in produced water by open circuit potential, polarization curves and electrochemical impedance spectroscopy measurements. Physical-chemical and microbiological analyzes were performed in the produced water and the tests were conducted in biotic and abiotic systems. The films and corrosion morphology developed in the steel over time were characterized by scanning electron microscopy. The results confirm that the activity of the consortium of microorganisms in the formed biofilm accelerated the dissolution of the iron, causing pitting corrosion in the steel exposed to the biotic system. Through the adjustment of the equivalent electrochemical circuit, the impedance results allowed to interpret the interactions between electrode, film and electrolyte.

The mechanical behavior of the API 5L X80 steel exposed to the produced water by the petroleum industry, besides being dependent on the intrinsic properties of the steel, is influenced by the corrosivity characteristics of the electrolyte that may be associated with the presence of microorganisms. The objective of this work was to investigate the plastic deformation of API 5L X80 steel exposed to produced water. The tests were conducted in static systems (abiotic and biotic) containing produced water after 360 days. The process of corrosion of the coupons were evaluated by topographic 3D analysis and roughness, and the mechanical behavior by tensile test and fracture analysis by scanning electron microscopy. Surface topography and roughness were modified by the interaction of the consortium of microorganisms with the substrate associated with the corrosion process. The results indicate that microorganisms induced the formation of pits which caused the coupons to lose plasticity.

High-strength low-alloy steel is used in pipelines, which transport oil/gas and also produced water in the process of the secondary recovery of oil. This paper investigates the corrosion of X80 steel after immersion in static systems (biotic and abiotic). The corrosion rate, the corrosion morphology and the hardness of the coupons were investigated. The corrosion products were determined by SEM/EDS and XRD. The corrosion rates of the coupons in the biotic system were moderate and had an agressive pit morphology, while those of the coupons in the abiotic system were low with less aggressive pit. The hardness of the coupons after exposure to the systems of produced water was not changed compared with that of the control coupons. The corrosion products formed in the biotic system were Fe(OH)3, Fe(OH)2, FeOOH, Fe3O4, FeS2, FeCl3, and in the abiotic system, NaCl, CaCl2 and SrSO4. BaSO4 and CaCO3 were identified in both systems.

Co-Ni/SiC nanocomposite coatings were obtained by codeposition of SiC nanoparticles in a bath with nickel and cobalt, using API 5L X80 as the substrate. The influence of cathodic current density on deposit properties was investigated. Measurements of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PP) were performed in 3.5 wt% NaCl solution to investigate a corrosion performance. The morphology and chemical analysis of the surfaces were analyzed by scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) and related with micro-hardness and X-ray diffraction (XRD). The results indicate which composite coatings have acicular morphology, with higher micro-hardness values than those found for the carbon steel substrate. The Co-Ni/SiC coating increased the corrosion potential and the resistance to polarization, which resulted in lower corrosion rates than those obtained without uncoated steel.

Galvanized steel has been widely applied in different applications and the industry significantly increased its production in recent years. Some galvanized structures can be completely or partially buried, such as transmission tower footings. The corrosion of these metallic structures is related to the soil chemical and physicochemical properties, which define the aggressiveness of the environment. To assess the effect of the soil moisture on galvanized steel corrosion, a comparative study was carried out. Carbon steel coupons, with or without galvanization, were buried in clay soil collected from an industrial region in the northeast of Brazil. The chemical, physicochemical and microbiological characteristics of the soil were determined. The thickness of the galvanized coating was measured by scanning electron microscopy (SEM). Corrosion tests were conducted in different soil moisture conditions using the following techniques: potentiodynamic polarization curves and gravimetric tests. The results showed the influence of soil moisture on corrosion rates. The electroplating decreased corrosion rates, especially when the coupons were exposed to low moisture soil.