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No description available.

The influence of impurities in magnesium chloride upon the rate of attack of stress corrosion cracking in AISI 304 stainless steel has been investigated. Previous investigations in this laboratory indicated that different batches of technical grade magnesium chloride produced poor reproducibility of results. These inconsistencies were attributed to the presence of varying amounts of impurities which are commonly found in technical grade magnesium chloride. In this investigation, certified grade magnesium chloride was used with impurities intentionally added in order to determine how each affected the constants M and C in the following equation, which relates the maximum crack depth D, to the time of exposure to the corrosive medium, t: log t • D/M + log C The constant C represents the time of exposure to the corrosive media to nucleate cracking, and M is a function of the rate at which cracks propagate. It was determined that the impurity ions most commonly found in magnesium chloride were nitrate, sulfate, and calcium. A significant difference in the constants V and M was found to exist with the presence of each impurity. It was not determined, however, if a change in pH resulted from the addition of the impurity compounds. Hence, a further study is required in order to determine the pH of the corrosive media and the effects of its changes. / Master of Science

Corrosion of reinforcing steel in concrete exposed to chloride-laden environments is a well-known and documented phenomenon. The need for cost effective systems for protection against corrosion has become increasingly clear since the first observations of severe corrosion damage to interstate bridges in the 1960's. As one potential solution to the mounting problem of corrosion deterioration of structures, corrosion-inhibiting admixtures have been researched and introduced into service. This report conveys the results of a three-part laboratory study of corrosion inhibiting admixtures in concrete. The commercial corrosion inhibiting admixtures for concrete have been analyzed by three evaluation methods, including: • Conventional concrete corrosion cell prisms under ponding, • Black steel reinforcing bars immersed in simulated concrete pore solutions, • Electrochemical screening tests of special carbon steel specimens in electrochemical corrosion cells containing filtered cement slurry solution. The purposes of the study include: • Determining the influence of a series of commercially available corrosion inhibiting admixtures on general concrete handling, performance and durability properties not related to corrosion. • Determining the effectiveness of corrosion inhibiting admixtures for reduction or prevention of corrosion of reinforcing steel in concrete, relative to untreated systems, under laboratory conditions. • Conducting a short-term pore solution immersion test for inhibitor performance and relating the results to those of the more conventional long-term corrosion monitoring techniques that employ admixtures in reinforced concrete prisms. • Determining whether instantaneous electrochemical techniques can be applied in screening potential inhibitor admixtures. Concrete properties under test included air content, slump, heat of hydration, compressive strength, and electrical indication of chloride permeability. Monitoring of concrete prism specimens included macro-cell corrosion current, mixed-cell corrosion activity as indicated by linear polarization, and ancillary temperature, relative humidity, and chloride concentration documentation. Simulated pore solution specimens were analyzed on the basis of weight loss and surface area corroded as a function of chloride exposure. Electrochemical screening involved polarization resistance of steel in solution. Results include corrosion potential, polarization resistance and corrosion current density. / Master of Science

M.S.

O aço inoxidável super duplex é um material muito utilizado na indútria de óleo e gás e o mandrilamento interno é um dos processos de manufatura utilizado para fabricação de componentes para esta indútria. O acabamento gerado pelo processo de mandrilamento interno é muito importante, pois estes componetes sofrem grandes ataques corrosivos por estarem em contato com petróleo e gás acidos e, também, por serem utilizados em grandes profundidades e altas pressões, no fundo do mar. A necessidade de utilização de barras de mandrilar com sistemas antivibratórios se dá quando seu comprimento é quatro vezes maior que o diâmetro usinado. Para análise da influência do mandrilamento foi utilizada uma barra de mandrilar com sistema antivibratório, tendo seu comprimento oito vezes seu diâmetro. O material utilizado para este estudo é o aço inox superduplex SAF2507. As variáveis de entrada foram velocidade de corte, avanço, raio de ponta da ferramenta de corte e pressão de refrigeração. Para análise da intregridade no material foi medido a rugosidade superficial utilizando os parâmetros Sq, Ssk, Sku, Str, Sal, Sk, Sk, SvK, a tensão residual, dureza e a temperatura de usinagem dissipada na região da peça. Os resultados mostraram a presença de tensão residual de tração com aumento da dureza com rugosidade Sq acima de 2 μm. Para rugosidade Sq abaixo de 2 μm ocorreu tensão residual de baixa tração ou tensão residual de compressão. A temperatura média no material usinado foi de 33,6 oC, sendo medida temperatura na região peça-cavaco-ferramenta de 350oC. A melhor combinação das condições de corte encontrada para obter os menores valores de rugosidade e de tensão residual de compressão, no acabamento, para profundidade de corte de 0,4 mm, foi a maior velocidade de corte (140 m/min), o menor avanço (0,1mm/rot), menor raio (0,4 mm) e a menor pressão de refrigeração (15bar). / Super duplex stainless steel is a material widely used in oil and gas industry and boring is one of the manufacturing processes used to manufacture components for this industry. The finishing surface generated by boring process is very important once these parts are exposed to great corrosive attacks by being in contact with oil and gas acids and, also, because they are used at big depths and high pressures in the seabed. The need of using dampened boring bars occurs when the length is four times greater than the machined diameter. It was used one of these dampened boring bars to analyze its influence on a boring processes, with its length eight times its diameter. The material used for this study is the super duplex stainless steel SAF2507. Input variables for analysis were cutting speed, feed, nose radius of the cutting tool and coolant pressure. For analysis of the material integrity it was measured the surface roughness using Sq, Ssk, Sku, Str, Sal, Sk, Sk, SvK parameters, residual stress, hardness and machining temperature dissipated in part region. The results have shown the presence of residual tensile stress with increasing hardness when Sk roughness is up to 2 μm and Sk roughness below 2 μm showed low residual tensile or residual tensile compression. The average temperature dissipated in the proof body was 33.6 °C, and the temperature in the region play-chip-tool was 350 oC. The best combination of cutting conditions found for the lowest roughness values and residual compressive stress were, finishing, cutting depth of 0.4 mm was the highest cutting speed (140 m / min), the lowest forward (0.1 mm / rev), smaller radius (0.4 mm) and the lower pressure coolant (15bar).

Orientador: Rodnei Bertazzoli / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-20T09:33:23Z (GMT). No. of bitstreams: 1 Costa_RytneySantos_D.pdf: 3018655 bytes, checksum: 4c710836a20f71e366fa51b7e28fddfe (MD5) Previous issue date: 2012 / Resumo: O Brasil, em busca de combustíveis alternativos, menos poluentes e com sustentabilidade econômica eficiente, apresentou uma solução para suas necessidades, acrescentando na sua matriz energética o etanol combustível e com isto, submeteu materiais metálicos dos sistemas veiculares e tanques de armazenamento de combustível a processos corrosivos. Aços inoxidáveis têm se mostrado uma alternativa viável, no entanto é necessário estudos para obter dados que permitam averiguar a suscetibilidade desse material a processos corrosivos neste novo meio. O enfoque deste trabalho é analisar os efeitos da corrosão do álcool etílico hidratado combustível (AEHC) sobre o aço inox AISI 304 nas condições de sobtensão e sem tensão, fundamentando-se na possível influência da corrosão nas propriedades mecânicas da liga. Foram realizados ensaios de imersão em longo prazo para avaliação de perda de massa e observação por microscopia eletrônica de varredura (MEV). Paralelamente, amostras na forma de corpos de prova para ensaios de tração e fadiga, foram imersos no meio (AEHC) para avaliação dessas propriedades. Os resultados acusaram, a partir de 3456 horas de imersão, ganho de massa nas condições tensionadas e não tensionadas, sugerindo a ocorrência de passivação do metal. Imagens obtidas por MEV mostraram a formação de pites, cujo tamanho evoluiu em função do tempo de imersão. O ensaio eletroquímico com utilização arranjos de microeletrodos de diâmetros de 10, 20, 30, 100, 200 e 500 ?m acusou baixa corrente de corrosão. As propriedades mecânicas de resistência à tração, limite de escoamento e deformação específica não se mostraram influenciáveis aos efeitos corrosivos do meio sobre a liga. O ensaio de fadiga, usando os parâmetros da distribuição de probabilidade de Weibull e a durabilidade característica (?), mostrou redução da resistência à fadiga da liga quando imersa em AEHC, evidenciando que o meio corrosivo, contendo cloreto, inicializou a nucleação de pites e potencializou a formação de trincas durante os ensaios de fadiga, favorecendo a redução do limite de resistência à fadiga do aço inox AISI 304 / Abstract: The Brazil, in search of alternative fuels, cleaner and with economic efficiency, presented a solution to their needs, adding its energy in the fuel ethanol and with that submitted materials of metal vehicle systems and storage tanks of fuel processes corrosive. Stainless steels have proven a viable alternative; however it is necessary studies to obtain data to determine the susceptibility of this material to corrosive processes in this new medium. The focus of this paper is to analyze the effects of corrosion of hydrous ethanol (AEHC) on AISI 304 stainless steel under conditions of tension and without tension, the ground of the possible influence of corrosion on the mechanical properties of the alloy. Immersion tests were conducted to evaluate long-term weight loss and observation by scanning electron microscopy (SEM). In parallel, samples as specimens for tensile and fatigue, were immersed in the medium (AEHC) for evaluation of these properties. The results showed, as of 3456 hours of immersion, the weight gain of not tensioned and stressed conditions, suggesting the occurrence of passivation of the metal. Images obtained by SEM showed the formation of pits whose size has evolved as a function of immersion time. The electrochemical assay using microelectrode arrays of diameters 10, 20, 30, 100, 200 and 500 ?m charged low-current corrosion. The mechanical properties of tensile strength, yield strength and strain specific were not influenced to the corrosive effects of the medium on the league. The fatigue test, using the parameters of the Weibull probability distribution and durability characteristic (?), showed a reduction in fatigue resistance of the alloy when immersed in AEHC, indicating that the corrosive medium, containing chloride, initiated the nucleation of pits and potentiated the formation of cracks during the fatigue tests, favoring the reduction of the fatigue endurance limit of stainless steel AISI 304 / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

The objectives of this research were to investigate the sensitivity of two-prong and fourprong resistivity measurements to certain operator-controlled variables and to conduct a direct comparison of the sensitivity of two-prong and four-prong resistivity measurements to certain concrete material variables. Four full-factorial experiments were designed for this research. In the experimentation on operator-controlled variables with two-prong resistivity testing, main effects that are both statistically significant and practically important include hole depth and surface water. In the experimentation on operator-controlled variables with four-prong resistivity testing, probe position, surface water, and prong spacing are all neither statistically significant nor practically important. This high degree of unexplained variation may be of concern to practitioners. In the experimentation on concrete material variables with two-prong and four-prong resistivity testing, main effects that are both statistically significant and practically important include chloride concentration and temperature, both of which exhibit inverse relationships with resistivity. These research findings support several important recommendations for resistivity testing. Operators of the two-prong resistivity device should use an accurately positioned drill stop to ensure that the prepared holes are consistently the correct depth, and they should expect to obtain different values depending on the presence of surface water on the deck surface. Operators considering use of the four-prong resistivity device should not expect the measurements to be sensitive to probe position with respect to rebar, presence of surface water, or prong spacing for conditions similar to those investigated in this research. Operators interested in monitoring resistivity values over time to ascertain material changes in a bridge deck should develop protocols for measuring concrete temperature in the field and subsequently normalizing resistivity measurements to a standard temperature.

No description available.

Aluminium smelting is a high temperature electrometallurgical process, which suffers considerable inefficiencies in power utilization and equipment maintenance. Aluminium smelting cell works in the extreme environments that contain extraordinarily aggressive gases, such as HF, CO and SO2. Mild steel used as a structural material in the aluminium industry, can be catastrophically corroded or oxidized in these conditions. This project was mainly concerned with extending the lifetime of metal structures installed immediately above the aluminium smelting cells. An aluminium-rich coating was developed on low carbon steel A06 using pack cementation technique. Yttria (Y2O3) was also used to improve the corrosion resistance of coating. Kinetics of the coating formation were studied. XRD, FESEM and FIB were employed to investigate the phase constitution and the surface morphology. Together with other potentially competitive materials, aluminium-rich coating was evaluated in simulated plant environments. Results from the long time (up to 2500h) isothermal oxidation of materials at high temperature (800??C) in air showed that the oxidation resistance of coated A06 is close to that of stainless steel 304 and even better than SS304 in cyclic oxidation tests. Coated A06 was also found to have the best sulfidation resistance among the materials tested in the gas mixture contains SO2 at 800??C. Related kinetics and mechanisms were also studied. The superior corrosion resistance of the coated A06 is attributed to the slow growing alpha-Al2O3 formed. Low temperature corrosion tests were undertaken in the gas mixtures containing air, H2O, HCl and SO2 at 400??C. Together with SS304 and 253MA, coated A06 showed excellent corrosion resistance in all the conditions. The ranking of the top three materials for corrosion resistance is: 253MA, coated A06 and SS304. It is believed that aluminised A06 is an ideal and economical replacement material in the severe corrosive aluminium smelting cell environment.