Adriana da Cunha Rocha

Duplex Al-based thermal spray coatings for corrosion protection in high temperature refinery applications

The application of thermal spray coatings has been effective in preventing corrosion of steel and iron products. It has been used in a wide range of applications spreading from the petroleum to the food industry. In this work, the performance and effectiveness of a two-layered aluminum-based thermal spray coating applied to an ASTM A387 G11 steel was evaluated. The coating structure was comprised of an inner Al-Fe-Cr layer and an outer layer of aluminum. Coated samples were tested in the reactor zone of a fluid catalytic cracking unit (FCCU) of a petrochemical plant for 2.5 years. The reactor zone temperature was about 793 K (520 °C) and the environment was a mixed gas containing sulfur, oxygen and carbon. Laboratory-scale tests were also conducted on the coated samples in order to gain a better understanding of the corrosive effect of the gaseous species present in the FCCU atmosphere. Porosity present in the thermal spray coatings allowed the penetration of the atmosphere corrodents, which instigated intergranular corrosion of the steel substrate. The presence of an inner Al-Fe-Cr layer did not prevent coating spallation, which further contributed to the internal corrosion process.

Stress and integrity analysis of steam superheater tubes of a high pressure boiler

Sources that can lead to deterioration of steam superheater tubes of a high pressure boiler were studied by a stress analysis, focused on internal pressure and temperature experienced by the material at real operating conditions. Loss of flame control, internal deposits and unexpected peak charge are factors that generate loads above the design limit of tube materials, which can be subjected to strain, buckling, cracks and finally rupture in service. To evaluate integrity and dependability of these components, the microstructure of selected samples along the superheater was studied by optical microscopy. Associated with this analysis, dimensional inspection, nondestructive testing, hardness measurement and deposit examination were made to determine the resultant material condition after twenty three years of operation.

Microstructural Evaluation of a Lean Duplex UNS S32304‐X‐Ray Diffraction and Scanning Electron Microscopy Techniques Correlated with Eddy Current Testing

A UNS S32304 Lean Duplex Steel was subjected to a series of controlled heat treatments to promote the formation of deleterious phases. All treatments were performed at 800°C in different ageing times. The choice for such temperature was due to the formation of detrimental phases in that steel when subjected to welding processes. The goal of this study was to determine the real correlation between the deleterious phases over the NDE signal. The steel was subjected to an extensive microstructural characterization by SEM and X-Ray Diffraction. Eddy Current Testing was carried out and compared to phase analysis by x-ray diffraction.

High Temperature In-Situ X-Ray Analysis of a Lean Duplex Stainless Steel

Duplex Steels have been used for different applications in the oil and gas industry due to their high strength and corrosion resistance. In this work, a Lean Duplex Steel (UNS S32304) has been investigated by High Temperature In-Situ X-Ray Diffraction, in order to address phases transformations occurring during high-temperature real time exposure and the formation of deleterious phases such as sigma phase. Samples were subjected to a temperature of 800 °C for different time intervals (30 and 60 min) inside a high temperature furnace attached to an x-ray diffractometer. Formation of sigma phase was observed, both in the ferrite grain boundaries and in the ferrite/austenite interface. The volume of sigma phase was measured by quantitative phase analysis using the Rietveld method and results varied from 2.80 to 15.92% in volume.

Kinetic Behavior of Self-Reducing Pellets Containing Coal of Elephant Grass

Aiming to reducing the gas emissions in the steel mill, in the present study the kinetic behavior of self-reducing pellets containing elephant grass coal and iron ore was investigated through kinetic isotherms for different temperatures. The pellets were isothermally treated in different time intervals for X-Ray diffraction and SEM analyzes. The results obtained by XRD showed that the higher mass of iron in the sample was achieved until the first 24 min. The SEM analysis allowed visualizing the presence of a metallic porous structure closer to edge and whiskers in the center of sample.

ANÁLISE DE TEXTURA CRISTALOGRÁFICA POR DIFRAÇÃO DE RAIOS X EM AÇOS IF COM DIFERENTES ADIÇÕES DE TITÂNIO, NIÓBIO E FÓSFORO

Os acos IF (do ingles “interstitial free”) encontram ampla aplicacao na industria automobilistica devido a sua superior estampabilidade. A textura cristalografica desenvolvida durante a laminacao de acos IF tem um papel fundamental na conformabilidade das chapas laminadas, sendo desejavel o desenvolvimento de uma forte fibra gama e fraca fibra alfa. Neste trabalho, tres tipos de acos IF, com diferentes adicoes de titânio, niobio e fosforo, foram submetidos a analise de textura cristalografica por difracao de raios X, de modo a avaliar o impacto dos tratamentos termomecânicos realizados e da variacao de composicao quimica nas orientacoes cristalograficas formadas. As texturas foram analisadas utilizando-se funcoes de distribuicao de orientacao (ODF). Os resultados das secoes de ODF foram comparados a valores anteriormente obtidos para os coeficientes de anisotropia normal e planar destes mesmos acos. A textura nas amostras laminadas de fato apresentou fibra gama intensificada e fibra alfa parcial. O aco IF-TiNbP foi o que apresentou melhor textura para estampagem profunda. No entanto, foi observada componente Goss na superficie do mesmo.

Microstructural Characterization of New Super-Ferritic-Martensitic Stainless Steel

The demand for high strength materials with improved corrosion resistance boosted the development of supermartensitic steels from conventional martensitic stainless steels The first alloys were designed with 11-13%Cr, extra-low carbon and nickel addition. More recently, experimental alloys with higher Cr (15-17%) and other ferritizing elements (Mo, W, Nb,…) were developed with the aim of obtain higher corrosion resistance in high chloride environments. In this work, the microstructure features of a new 17%Cr stainless steel were investigated.

Abrasive blasting contamination in Super Duplex and carbon steels - a quantification approach by rietveld analysis

A methodology for quantifying the contamination after abrasive blasting by Aluminum Oxide and Martensitic Carbon Steel particles in Super Duplex and Carbon Steel substrates has been developed. The method consisted of performing x-ray diffraction in the blasted steel substrates and calculating the particle contamination using Rietveld Quantitative Method. In this way, it is possible to evaluate the substrate volume in which the abrasive particles have been trapped (taking into account the surface roughness) rather than solely performing visual examination, as indicated by standards documents. Equations describing the intensity model of the diffracted peaks as well as those describing the quantitative measurements are presented. Correction functions are also employed to compensate the effect of the surface roughness generated on the metallic substrates after blasting. Alumina and martensitic steel abrasives contaminations were detected and quantified in both steel substrates. Results showed that Super Duplex Steel substrates revealed a higher degree of contamination when compared to the Carbon Steel substrates, both for alumina abrasives as for martensitic abrasives. Also, the abrasive that generated the lower degree of contamination was the Martensitic Carbon Steel, for both substrates.