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Flexible pipes are complex structures made of different layers and different materials. They are used in the oil and gas production in the off-shore platforms to conduct the oil or gas between different units, such as platforms, Christma's tree and transportation ships. The internal carcass of flexible pipes is made of duplex stainless steels type 2205 (UNS S32205 or S31803). In the production line, sheets of 1.8 mm thickness of this material are submitted to uncoiling and cold bending operations to form “S” profiles which are assembled to form the internal carcass. The end of one coil is welded to the begin of another, to make the process continuous. The welding process is autogenous automatic gas tungsten arc (GTAW). This work analyses the microstructure and corrosion resistance of the weld metal and compares to the base metal. Besides, non-destructive tests and electrical resistance measurements were conducted in the welded joint and base metal. The samples analyzed were from a flexible pipe manufacturer. It was concluded that the joints of this producer were not heat treated, which results in inadequate microstructure and lower corrosion resistance in the weld metal.

Total hip arthroplasty or total hip replacement (THR) is a surgical procedure for inserting an implant, which aims to restore the functionality of movements lost due to fractures, joint wear, bone loss and other problems. Although the THR procedure is consolidated in medicine, failures in THR implants associated with different problems are frequently reported in the literature. The aim of the present study was to identify and evaluate the reasons that led a THR implant to fail prematurely after 2 years of use in a 65-year-old female patient. In order to identify the reason of the failure, the following techniques were used: optical microscopy, scanning electron microscopy, chemical analysis by energy-dispersive spectroscopy, Vickers microhardness measurements, digital image processing technique and a mathematical method of finite element analysis. It was concluded that the fractured implant presented a fatigue mechanism, due to existence of pits on the surface.

Industrial equipment is usually high in cost. Design engineering needs to specify fuses that have the role of protecting the main parts of the equipment. The aim of this work is to identify the reason that led to a high number of fractures in mechanical fuses of a rolling mill and suggest improvements to fix the problem. Two components were analyzed: one that failed and one that was used inside the equipment but did not fail. According to their datasheet, the components are made of quenched and tempered type 4140 (UNS G41400) steel. Chemical analysis of the fuse was performed using x-ray fluorescence. Microstructural and fractographic aspects were investigated by optical and scanning electron microscopy. The existence of surface cracks is investigated by liquid penetrant test. Tensile analyses in the component are made using analytical and numerical methods. Numeric analyses are performed by the finite element method. The chemical analysis is in agreement with that expected for type 4140. The fractographic analysis shows intergranular brittle fracture. No surface cracks are found by the liquid penetrant, and no evidence of fatigue mechanism fracture is found the fractographic analysis. All results indicate that the component fractured due to the action of overload. By comparing the numerical and analytical methods, it is possible to identify that the stress concentration in the fuse analyzed results has a value of 9.44% lower when the analytical method is used. It is possible to conclude that the analytical method causes an error in the design, which was not covered by the safety factor because mechanical fuses did not use a safety factor in their projects. Increasing the radius of stress concentration can compensate the error, without requiring dimensional changes in the component. A new component is manufactured according to this concept, which is in operation without any issues.

RESUMO Este trabalho teve como objetivo quantificar e avaliar através de técnicas de análise e processamento digital de imagens (PDI) defeitos formados em revestimentos metálicos à base de ligas ferro-cromo e ferro-cobalto, obtidas por aspersão térmica à arco elétrico (AT). Imagens obtidas por microscopia óptica (MO) foram processadas e analisadas utilizando-se o software FIJI (Image J) para quantificação de poros, redes de óxidos e trincas. Também foram feitas medidas de microdureza Vickers (HV) e testes de corrosão segundo a norma ASTM-G48. Foram realizados dois testes de corrosão em meio de cloreto férrico: um expondo-se apenas o revestimento, onde a resistência a corrosão foi avaliada qualitativamente através de imagens de MO e a possível presença de pites de corrosão e outro expondo-se o conjunto revestimento e substrato, neste caso, a resistência a corrosão foi avaliada quantitativamente através de medidas na espessura da camada de revestimento antes e depois da exposição. Foi realizada uma avaliação microestrutural por MO e microscopia eletrônica de varredura (MEV). Os resultados obtidos por MO, MEV e microdureza indicaram uniformidade nas camadas depositadas e porcentagem de defeitos variando entre 3,7% e 4,3% para os revestimentos estudados. Todos mostraram possuir excelente resistência à corrosão em meio de cloreto férrico, que é considerado agressivo aos aços inoxidáveis, exceto para a liga de revestimento à base de ferro-cobalto quando encontrou-se combinada ao cobre e com o substrato também exposto ao meio corrosivo

This work aimed to analyze the causes of premature failure by fracture of a tie rod of a large rotary forklift or Stacker Reclaimer. A methodology that included visual inspection techniques, macrographic analysis, optical microscopy (OM), Vickers microhardness (HV) measurements, scanning electron microscopy (SEM), semi-quantitative chemical scattering spectroscopy (EDS) and quantitative chemical analysis by optical emission spectrometry and combustion was employed. It could be concluded that the chemical composition of the material and / or the manufacturing process were outside the specification of the material due to the unexpected presence of magnesium and carbon graphite nodules, the latter considered to cause fragility that may have led the material to fracture by fatigue.

In the present work we have studied the effects of nitrogen addition on the equilibrium of the volume fraction ratio austenite/ferrite and on the structural properties of weldments produced by gas tungsten arc welding (GTAW). The welded joints in tubes UNS S32707 of hyper-duplex steel were produced using argon and nitrogen gas welding, with nitrogen added in ratios of 1.5, 2.5, 3.5, 4.5, and 5.5%. Microstructural characterization of this material under the different processing condition was conducted by means of optical microscopy, scanning electron microscopy, local chemical analysis by X-ray energy dispersive spectroscopy, electron backscatter diffraction Vickers microhardness test, and digital image processing. All welding conditions resulted in welded joints with equiaxial grains microstructure containing austenite both at the boundaries and in the ferrite matrix. Microhardness measurements did not show significant variation in relation to the base metal. The use of welding gases with higher percentages of nitrogen resulted in increases in the austenite volume fraction in the order of 39 to 57% when considering the nitrogen content ranging from 1.5 to 5.5%.

In this paper, a European black Japanned piece of furniture (dated to approximately 1860) was analyzed by XRF, Raman spectroscopy and FT-IR techniques. The analyses detected pigments such as vermilion/cinnabar [HgS], Massicot [PbO], lamp black [C] and green earth [K[(Al,FeIII),(FeII,Mg)](AlSi3,Si4)O10(OH)2], which were possibly dissolved in gum arabic. The analyses also determined that the metallic ornaments consist of a brass alloy with traces of gold and that gold was also used in some golden regions of the polychrome. The results obtained assisted restorers in choosing suitable intervening procedures and contributed to a better understanding of the cupboard manufacturing process.

Foram obtidos os aspectos micrográficos das zonas de fusão e das zonas termicamente afetadas de juntas soldadas pelo método comumente utilizado por protéticos de uma liga Ni-Cr usada para a confecção de próteses dentárias conhecidas como pontes-fixas. O método consiste em soldagem por maçarico com gás liquefeito de petróleo (GLP) e oxigênio, metal de adição e fluxo, para soldas de liga à base de níquel comercialmente conhecida como FIT. Corpos de prova soldados da liga FITCAST- SB (261MPa, Ni 61% – Cr 25% – Mo10,5% – Si 1,5% – Ti

This work aimed to identify and evaluate the reasons that led to a compression spring to fail. The compression spring was operating in a wagon torpedo, a vehicle that transported pig iron in a liquid state from the blast furnace to the steel mill. For this purpose, optical microscopy (OM), scanning electron microscopy (SEM), quantitative chemical analysis by combustion and x-ray fluorescence, Vickers microhardness test (HV), Rockwell superficial hardness with N scale (HRN), and residual stress analysis by x-ray diffraction were used. The industrial quenching, tempering heat treatment, and shot peening process, were also redone for the spring under analysis, all in order to simulate the treatments that were supposedly done on the original spring. It can be concluded that the process that led to spring fracture was a mechanism of fatigue failure that originated from a defect in the spring surface. Although residual stresses on the spring surface were expected to prevent fatigue failures from surface defects, the hardness in this region of the material was lower than specified due to a decarburizing process.

This work aimed to analyze a failure that occurred prematurely in an ASTM SS Grade 70 steel tube in the cooling system of a reheating furnace. The following techniques were used: visual inspection, optical microscopy (OM), scanning electron microscopy (SEM), chemical analysis by energy dispersive spectroscopy (EDS), Vickers microhardness (HV) and measurements and chemical analysis by optical emission spectrometry (OES). It was concluded that the failure was caused by a drastic corrosion process, due to microstructural changes resulting from the loss of the refractory coating.

Statement of the problem Fixed prosthesis and partial dental prosthesis frameworks are usually made from welded Ni-Cr-based alloys. These structures can corrode in saliva and have to be investigated to establish their safety. Purpose The purpose of this study was to evaluate the corrosion behavior of joints joined by tungsten inert gas (TIG) welding and conventional brazing in specimens made of commercial Ni-Cr alloy in Fusayama artificial saliva at 37°C (pH 2.5 and 5.5). Material and methods Eighteen Ni-Cr base metal specimens were cast and welded by brazing or tungsten inert gas methods. The specimens were divided into 3 groups (base metal, 2 welded specimens), and the composition and microstructure were qualitatively evaluated. The results of potential corrosion and corrosion current density were analyzed with a 1-way analysis of variance and the Tukey test for pairwise comparisons (α=.05). Results Base metal and tungsten inert gas welded material showed equivalent results in electrochemical corrosion tests, while the air-torched specimens exhibited low corrosion resistance. The performance was worst at pH 2.5. Conclusions These results suggest that tungsten inert gas is a suitable welding process for use in dentistry, because the final microstructure does not reduce the corrosion resistance in artificial saliva at 37°C, even in a corrosion-testing medium that facilitates galvanic corrosion processes. Moreover, the corrosion current density of brazed Ni-Cr alloy joints was significantly higher ( P

The superduplex stainless steels (SDSS) are widely used in chemical, oil and gas industries, to pipelines and storage material facilities. In welding process or working in temperature elevated, secondary phases may appear in the form of precipitates, as the sigma phase (σ) which is an intermetallic compound. This compound is harmful to the properties of steel, deteriorating its mechanical properties, such as decreasing corrosion resistance and toughness. In this paper it is analyzed the formation, kinetics and microstructural evolution of sigma phase in SDSS UNS S32750 after isothermal aging at 700ºC, 750ºC and 800ºC. In this work sigma phase kinetics is studied by JMAK theory and by two microstructural path descriptors, SV, interfacial area per unit of volume between sigma phase and austenite, and , mean chord length of sigma, both in function of the VV, volumetric fraction of sigma, known in the literature as microstructural partial path (MP). The MP formulation is common in recrystallization studies, but so far has not been used in the sigma phase precipitation studies, being applied here for the first time. The results indicated that the sigma phase nucleates by site saturation with anisotropic linear impingement. This means that sigma phase nucleates on edges.

Esforcos constantes de pesquisa tem sido conduzidos na selecao de materiais, combinando propriedades de interesse (mecânicas, quimicas, eletricas ou termicas), versatilidade de uso, tempo de vida util elevado e baixo custo de producao. A busca por materiais de elevado desempenho mecânico despertou grande interesse na pesquisa e desenvolvimento dos cerâmicos avancados com aplicacoes estruturais e funcionais, como o carbeto de silicio (SiC). Entretanto, a porosidade ainda e vista como fator limitador do alto desempenho destes materiais visto que, acima de determinada porcentagem, reduz largamente sua resistencia mecânica. Seu controle atualmente e realizado atraves de tecnicas de alto custo, com a utilizacao de tomografos. Este trabalho quantificou a porosidade atraves de analise e processamento digital de imagens (PDI), obtidas por microscopia otica com controle dos parâmetros de lixamento e polimento ao longo de diversas profundidades da cerâmica avancada. A metodologia foi comparada ao metodo de Arquimedes, mais tradicionalmente utilizado. Os resultados mostraram que a tecnica de PDI para o tipo e distribuicao de poros existentes foi bem sucedida pra um material de dificil caracterizacao.