This study is focused on the performance evaluation of flash-butt-welded rail joints concerning their mechanical strength and fatigue life. Residual stresses created in the heat-affected zone were measured and the effects of the welding process and notch sensitivity on the fatigue behavior in the weld region were experimentally assessed. Aiming at clarifying the physical phenomenon behind the flash-butt welding, nonlinear transient thermomechanical finite-element analyses were performed to reconstitute the welding process and to simulate the subsequent formation of residual stresses. A new hypothesis for explaining higher temperatures in the rail web than in the rail foot and head was suggested and numerically verified. Experimental fatigue results showed high notch sensitivity and highlighted the effects of microstructure variations on the fatigue life. In general, a good agreement was achieved between numerical and experimental measurements of residual stresses, which was essential for understanding the fatigue phenomenon and the formation of residual stresses in flash-butt-welded rail joints. A relevant outcome is the simulation of the hot burrs from the welding process as prescribed heat inputs on a convenient part of the rail surface. This simulation strategy has shown adequate to explain the non-uniform temperature changes and the corresponding originated residual stresses. flashbuttwelded flash butt welded life heataffected affected assessed flashbutt finiteelement finite element verified general surface nonuniform non uniform

ABSTRACT Duplex stainless steel UNS S31803 exhibits high mechanical strength with high corrosion properties, due to its microstructure composed of ferrite and austenite phases, in equal proportion. When the UNS S31803 steel is submitted to high temperatures, some precipitations can occur, such as nitrites, carbides, and third phases (e.g. sigma phase -σ, and alpha prime - α'). These phases are deleterious in relation to the mechanical properties and corrosion resistance, and their effects are analyzed regarding the properties of the steel. In order to evaluate the precipitation of this deleterious phase, isothermal treatment was done at 500°C for 144 hours (α' phase) and at 850ºC for 80 minutes (σ phase). The results were obtained through the microstructural analysis and tensile tests. The presence of sigma phase was verified in the grain boundary, an increase in the mechanical resistance with a loss of toughness. There was as well as an increase in mechanical resistance with the precipitation of α', with less loss of ductility than that observed in the experiments involving the presence of sigma phase.

Seamless steel pipes for application in the oil and gas industries are manufactured from quenched and tempered steel. Aiming to meet the required characteristics, it is necessary that the microstructure and the mechanical properties are homogeneous along the wall thickness of the pipes, which is even more critical for thick wall pipes. Considering the seamless steel pipe manufacturing process, any chemical segregation along the thickness could affect the phase transformation kinetics during heat treatments and, consequently, microstructure and mechanical properties. In this context, this pioneer work when evaluating the effect of the chemical homogeneity of a seamless pipe on the mechanical properties and phase transformations. The studied pipe was manufactured by a C-Mn steel designed for oil and gas industry applications. Two regions of the pipe wall were analyzed - a region close to the inner surface and another near the outer surface. The steel was subjected to quenching and tempering heat treatments. Scanning electron and optical microscopy techniques were used to characterize the resultant microstructures. Microhardness and Charpy impact tests were performed aiming to analyze the pipe mechanical behavior in the studied regions. In addition, dilatometric tests were performed in order to determine the continuous cooling transformation diagrams of these regions.

Abstract The corrosion of C-Mn steels in the presence of hydrogen sulfide (H2S) represents a significant challenge to oil production and natural gas treatment facilities. The failure mechanism induced by hydrogen-induced cracking (HIC) in a Inconel 625 coating / C-Mn steel has not been extensively investigated in the past. In the present work, an API 5CT steel was coated with In625 alloy using laser cladding and the HIC resistance of different regions, such as the coating surface, the substrate and HAZ, were evaluated. SEM observations illustrated that all HIC cracks were formed at the hard HAZ after 96h of exposure. No HIC cracks were observed in the substrate and the In625 coating after the same exposure duration. Pitting was recorded in the substrate caused by non-metallic inclusion dissolving.

Resumo Características microestruturais e mecânicas foram avaliadas ao longo da seção transversal de juntas obtidas por soldagem (GMAW), de tubos sem costura de aço API 5L X65Q. Dois tipos de juntas foram obtidas a partir da confecção de chanfro V e ½ V. Dividindo-se as chapas soldadas em 8 camadas espaçadas de 3mm, no sentido transversal, corpos de prova foram confeccionados para ensaios de tração, microdureza Vickers e análise química. Foi realizada ainda caracterização metalográfica no metal base e nas juntas soldadas. Observou-se pequena alteração na composição química do metal de solda entre as camadas da junta V e junta ½ V. A maior taxa de resfriamento promoveu maior fração de ferrita acicular no chanfro ½ V. Alguns corpos de prova de tamanho reduzido não atenderam aos limites mínimos de escoamento e de resistência especificados na Norma API 5L, resultado atribuído à presença de descontinuidades em algumas regiões da solda. A maior microdureza Vickers da junta ½ V foi atribuída à maior presença de ferrita acicular. A adoção de chanfro estreito para aumento de produtividade na soldagem do aço em estudo não impactou negativamente as propriedades da junta, entretanto, aumentou a ocorrência de falta de fusão na face do bisel.

Abstract Microstructural and mechanical characteristics were evaluated along the cross section of joints obtained by (GMAW) of seamless API 5L X65Q steel pipes. Two types of joints were obtained from the bevel V and ½ V. By the division of the welded plates into 8 layers spaced 3 mm in the transverse direction, specimens were prepared for tensile tests, Vickers microhardness and chemical analysis. In addition, metallographic characterization was performed on the base metal samples and welded joints. It was observed a small change in the chemical composition of the weld metal between the 1st and 8th layer of the V joint and ½ V joint. The higher cooling rate of the ½ V bevel promoted higher acicular ferrite content. Some specimens of reduced size did not meet the minimum tensile properties limits specified in API 5L, a result attributed to the presence of discontinuities in some regions of the weld. The highest Vickers microhardness of the ½ V joint was attributed to the greater presence of the acicular ferrite. The adoption of narrow groove to improve the welding productivity did not negatively impact the properties of the joint, however, increased the occurrence of lack of fusion in the bevel face.

Resumo Trilhos com perfil TR-57 do tipo intermediário foram soldados por centelhamento em um estaleiro brasileiro e passaram por detalhada caracterização mecânica e metalográfica. Os dados quantitativos da caracterização metalográfica e dos ensaios mecânicos foram submetidos a análises de variância (ANOVA). Na metalografia confirmou-se a presença majoritária de perlita, porém há também ferrita proeutetóide na linha central da solda e globulização parcial da cementita em regiões da Zona Termicamente Afetada (ZTA), sobretudo na zona de transformação parcial. O tamanho das colônias perlíticas e o espaçamento interlamelar foram correlacionados à microdureza Vickers em toda a extensão da junta. Ensaios de tração revelaram que o metal base atendeu às especificações da Norma AREMA, no entanto, as juntas soldadas não atenderam e a fratura dos corpos de prova ocorreu na região de menor dureza da ZTA. Os resultados permitem compreender, em detalhes, as consequências do processo de soldagem sobre a estrutura do aço e as variações de propriedades em diversas regiões da junta, com destaque às alterações morfológicas da perlita. Relações com modos de falha anteriormente relatados na literatura científica também são apresentadas.

Abstract TR-57 intermediate steel rails were welded in a Brazilian flash butt welding plant and the joints were subjected to a detailed mechanical and structural characterization. Quantitative data were subjected to ANOVA analysis. The metallography has confirmed the majority presence of pearlite, but pro-eutectoid ferrite was also verified in the weld centerline. Globulized cementite appeared in some regions of the Heat Affected Zone (HAZ), particularly in the partial transformation zone. The pearlite colony size and pearlite interlamellar spacing were related to Vickers microhardness over the full joint length. The base metal met the minimum specified tensile properties in the AREMA standard. However, the weld joints did not meet the minimum tensile strength and all samples fractured in the partial transformation zone, which has lower hardness. The results help to deep understand the structure-properties relationships over the full joint, highlighting the relations between the welding process and the resultant pearlite morphology. Considerations about the component failure modes previously related in scientific literature are also presented.

Threaded and coupled connections generally present a non-uniform stress distribution, which is related to the higher stiffness of the box when compared to the pin. The non-uniform stress distribution can contribute to fatigue cracks and other failure modes in high pressure oil wells. An API 5CT P110 steel obtained from a seamless pipe was mechanically characterized. FEA models were carried out to investigate and compare two API casing connections under make-up torque and tensile efforts. A parametric study was performed using numerical models to determine the influence of some geometric features on the behavior of the API Buttress threaded connection. The API Buttress connection supported higher tensile loads than the API Short Round, however both standard connections showed high stress concentration in the last engaged thread and a non-uniform stress distribution. The manufacturing of grooves at the first and the last engaged threads proved to be an efficient way to reduce the stress concentration of Buttress casing connection and could be an alternative to the development of new products.

Resumo Neste trabalho, investigaram-se efeitos do fenômeno de envelhecimento por deformação em juntas obtidas por soldagem a arco elétrico com proteção gasosa (GMAW), de tubos sem costura de aço API5L X65Q. Corpos de prova (CPs) obtidos a partir das juntas soldadas foram submetidos à uma deformação plástica a frio de 3% e posteriormente envelhecidas por 1h a 250°C, de forma a se induzir envelhecimento estático. Buscando avaliar o envelhecimento dinâmico, os CPs foram deformados até 3% e o carregamento foi mantido durante 1h a 250°C. Os CPs envelhecidos foram submetidos a ensaios de tração e amostras representativas foram analisadas ao microscópio óptico e microscópio eletrônico de varredura. Observou-se que o fenômeno modificou a fração volumétrica de constituintes secundários no metal de solda e na ZTA, com aumento na proporção de agregados ferrita-carbonetos. Com relação às propriedades mecânicas, constatou-se que o fenômeno reduziu a razão elástica das juntas soldadas devido a um aumento no limite de resistência, além de aumentar o alongamento total, não prejudicando, portanto, as propriedades mecânicas em tração das juntas soldadas. Ao se comparar o envelhecimento estático com o envelhecimento dinâmico, observou-se que o aumento na capacidade de deformação plástica das juntas soldadas foi maior após envelhecimento estático por deformação.

Abstract In this work was investigated the influence of the strain ageing on joints obtained by gas-metal arc welding (GMAW) of API 5L X65Q seamless pipes. Specimens were machined from the welded joints, plastically strained to 3% and aged at 250°C for 1h posteriorly, in order to characterize effects of static strain ageing. For the dynamic strain ageing characterization, the specimens were simultaneously strained and aged. Then, the aged specimens were submitted to tensile tests and representative samples were analyzed at a light optical microscope and a scanning electron microscope (SEM). From the results, it was observed that the strain ageing phenomenon changed the volumetric fraction of secondary constituents in the weld metal and in the heat-affected zone, increasing the proportion of ferrite-carbide aggregates. Regarding the mechanical properties, it was noticed that the phenomenon led to higher tensile mechanical properties such as ultimate tensile strength and total elongation and lower elastic ratio, and, therefore, not impaired the mechanical properties under tensile of the welded joints. Comparing the static strain ageing with dynamic strain ageing it was observed that the effect on the plastic straining ability of welds was higher after static strain ageing.

ResumoAços que atendem à norma API 5L são aplicados na construção de dutos e há grande interesse naqueles de maior resistência, como o grau API 5L X70Q. Ainda são escassos os estudos relacionados a tubos sem costura. Durante a montagem, os tubos podem ser soldados por eletrodos revestidos (SMAW) e eventualmente sofrer aquecimento indutivo para adequação à topografia do terreno, processos que podem alterar a microestrutura das juntas. Neste trabalho foram obtidas juntas soldadas pelo processo SMAW, a partir de tubo sem costura grau API 5L X70Q. As juntas foram submetidas a tratamentos térmicos pós-soldagem nas temperaturas 920 °C e 600 °C. Foram realizados ensaios de tração, impacto Charpy e microdureza, além de caracterização metalográfica nas amostras de metal base e nas juntas como soldadas e após os tratamentos térmicos. O tratamento térmico a 920 °C promoveu a formação de estrutura ferrita/perlita, com consequente redução na resistência mecânica das juntas a valores inferiores aos especificados para o grau X70Q. Porém, o tratamento térmico a 600 °C mostrou-se benéfico devido à redução da fração volumétrica dos constituintes martensita/austenita e martensita-austenita-bainita, sem reduzir de forma significativa a resistência mecânica e com relativo ganho na tenacidade ao impacto na ZTA e na ZF.

AbstractPipelines for oil and gas conduction are manufactured of steel tubes that meet the API 5L requirements. Currently, much of the research related to the materials used in this industry is target to steels with higher tensile strength such as API 5L X70Q. But studies related to seamless pipes remains rare. During the manufacture of the pipelines, the pipes are usually welded by the SMAW process and may be heated by the inducted bending process to fit the topography of the land, processes that can change the proportion or morphology of the constituents in the heat affected zone (HAZ) and in the fused metal. The present study used an API 5L X70Q seamless steel manufactured by the Mannesmann Process to produce weld joints by the SMAW process. The joints were subjected to post weld heat treatments in the temperatures of 920 °C and 600 °C. Mechanical tests which included tensile test, Charpy impact and microhardness were applied, in addition to microstructure evaluation in the joints as welded and after heat treatments. The results showed that the first heat treatment (920 °C) promoted the formation of structure ferrite/pearlite, which reduced the mechanical properties to values under the specified for materials API grade X70Q. The second heat treatment (600 °C) was feasible in reducing the volume fraction of the Martensite-Austenite and Martensite-Austenite-Bainite constituents, without significant reduction in mechanical strength of the welded joints and with significant gain in impact toughness in the HAZ and in the weld metal.

This research compares the mechanical behavior of two API steels (X60 and X70) used in the longest pipeline in the world for the conveyance of iron ore. Tensile tests, Charpy impact tests, CTOD tests and fatigue crack growth tests are performed at ambient temperature. Metallographic examination showed a banded microstructure consisting of polygonal ferrite and pearlite in both steels, with smaller grain size and the presence of a small quantity of bainite in the X70 steel. All the mechanical tests revealed a ductile behavior for the two steels. The X70 steel is preferable for the pipeline project, due its better mechanical resistance, with no significant loss of fracture toughness and fatigue resistance. Its performance could be even better, if an appropriate combination of thermomechanical processing parameters were able to produce a microstructure with minor amount of pearlite, where acicular ferrite/bainite are present.

A arte da Cantaria usando o quartzito foi utilizada na construção dos monumentos históricos de Ouro Preto/MG. Após mais de 300 anos de existência, parte de algum desses monumentos encontra-se em avançado estágio de deterioração. Na restauração desses monumentos, alguns restauradores empregam a resina poliéster ortoftálica. Nesse trabalho, o quartzito itacolomi não colado e colado com diversas resinas foi submetido a ensaio de resistência em flexão e constatou-se que a resina suportou carga maior que o quartzito. Todos os corpos-de-prova romperam fora da região da aplicação da resina, confirmando a eficácia das resinas para colar a rocha.

The art of carving stone using itacolomi quartzite was employed in the monuments of Ouro Preto city in Minas Gerais. More than 350 years after being built, some of these monuments are in an advanced stage of deterioration. In the restoration of these buildings, some restaurateurs employ orthophthalic polyester resin. In the present study, both non-glued and glued (using different types of resins) itacolomi quartzite were submitted to a flexion strength test. After some trials, it was verified that the resins supported greater loads than the quartzite. All specimens broke outside the resin's application area, thus confirming the effectiveness of resin adherence to rock.

Esse trabalho procurou diagnosticar os fenômenos patológicos apresentados pela "Ponte da Barra" (ponte metálica restaurada e reforçada para implantação da Ferrovia Turística Cultural entre Ouro Preto e Mariana/MG) e apresentar soluções para o combate a tais fenômenos. Para o cadastro da ponte, foram identificadas, por inspeção visual e registros fotográficos, as patologias presentes. Também foi realizada a modelagem numérica através de elementos finitos (elemento de barra com seis graus de liberdade por nó), visando a analisar o comportamento estrutural da ponte antes e após reforço estrutural. Dessa maneira foi possível fazer a avaliação da estabilidade da mesma e, também, a avaliação da eficiência do reforço estrutural proposto. A análise numérica foi viabilizada através de parâmetros levantados in loco, como geometria, propriedades mecânicas e fatores patológicos. Os estudos laboratoriais, como caracterização química, ensaio de tração, análise metalográfica e dos produtos de corrosão, foram determinadas através de amostras do aço de elementos estruturais da própria ponte. Observou-se que o sistema de curva tensionada utilizado para reforço estrutural agravou, sistematicamente, a estabilidade global da ponte, introduzindo acréscimo de carga aos elementos estruturais mais críticos.

This work sought to diagnose and propose solutions for the pathological phenomena occurring on the bridge "Ponte da Barra" (a metallic bridge that was restored and reinforced for use by the Tourist-Culture Railroad between Ouro Preto and Mariana/MG). To obtain the bridge profile, a visual inspection and photographic registers were performed to evaluate existing pathologies. Numerical modeling was also performed, using finite elements (bar elements with six degrees of freedom per node), aiming to analyze the bridge's structural behavior before and after reinforcement. This permitted evaluation of the bridge's stability as well as the efficiency of the structural reinforcement proposed. The numerical analysis proved feasible when parameters measured in situ, such as geometry, mechanical properties and pathological factors were implemented. The laboratory studies, such as: chemical characterization, stress tests, metalographic analysis, and corrosion, were performed using steel samples from the bridge's structural elements. The conclusion reached was that the Rigid Tension Curve System used for structural reinforcement systematically diminished the overall stability of the bridge, introducing a load increase on the most critical structural elements.

Sabe-se que a degradação que ocorre em estruturas de pontes metálicas é um problema mundial. Isto ocorre por diversas razões, como envelhecimento da ponte, aumento da carga de tráfego, ataque ambiental e, algumas vezes, devido a projetos, detalhamento e construção da estrutura inadequados. Para resolver esses problemas, procedimentos diferentes de inspeção de pontes têm sido aplicados em diferentes países. No Brasil, no entanto, parece não haver preocupação em preservar a integridade das estruturas, não sendo comum a realização de inspeções e/ou manutenções, o que pode afetar a segurança estrutural, levando à necessidade de reparos mais severos e mais caros. Esse trabalho procurou diagnosticar e propor soluções visando à minimização da corrosão desenvolvida na Ponte Marechal Hermes (rio São Francisco). Para isso, foram feitas visitas in locu e, através de inspeção visual, filmagem e registros fotográficos, coletaram-se os dados necessários para análises. Também foram coletadas amostras e, então, realizadas caracterizações química, mecânica e metalográfica do aço empregado na ponte. Fez-se modelagem através de elementos finitos, visando a analisar o comportamento estrutural da ponte com e sem danos por corrosão, o que possibilitou a verificação dos elementos estruturais mais solicitados e a influência da corrosão nessas regiões. Foram realizados ensaios com névoa salina em diferentes sistemas de pintura, visando a identificar o melhor procedimento de revestimento para proteção da ponte. Verificou-se que o emprego do sistema de pintura constituído de etil silicato de zinco, com primer epóxi-amida, rico em zinco e esmalte poliuretano alifático, foi o que apresentou melhor desempenho.

It's known that the degradation, which occurs in steel bridge structures, is a worldwide problem. This happens for several reasons such as the bridge's advanced age, the increase of the traffic weight, environmental attacks and, sometimes, because of designs, inadequate detailment and construction of structures. In order to solve these problems, different procedures in inspection of bridges have been used in different countries. In Brazil, however, it seems there is not any concern about keeping the integrity of the structures, not being commonly used proper procedures such as inspections and maintenance of the structures that can affect its safety, causing the need of more severe and expensive repairs. This research intends to make a diagnosis and propose solutions, which aim for the least occurrence of the corrosion developed by Marechal Hermes Bridge (São Francisco River). Therefore visits were made in locus, in which visual inspection, screen and photo registers, the information necessary for the analysis, were collected. Some samples were also collected and than, chemical, mechanical and metalographic characterizations were made on the steel used on the bridge, besides the analysis of the corrosion. The numerical modeling was made by using the finite element method, which aimed to analyze the structural behavior of the bridge with or without damages made by corrosion in these areas. There were made tests with salt spray in different systems of painting which aims to identify the best procedure of covering in order to protect the bridge. It was verified that the use of etil silicate of zinc, with primer epoxy-amide, rich in zinc and aliphatic varnish polyurethane was the one which presented the best performance.

O presente trabalho avaliou a tenacidade à fratura e a resistência à propagação de trinca de fadiga de dois aços bifásicos, um deles com teor significativo de cromo e o outro com teor significativo de silício. Com relação à tenacidade, observou-se uma ligeira superioridade (maiores valores) do aço ao silício em relação ao aço ao cromo. Verificou-se, também, o efeito deletério do aumento da profundidade do entalhe lateral dos corpos-de-prova sobre a tenacidade. Não foi encontrado efeito significativo de anisotropia. Com relação à fadiga, os resultados mostraram que os dois aços apresentam um comportamento semelhante com inexistência de anisotropia. A elevação na razão R entre tensões provocou um aumento na taxa de propagação de trinca e um decréscimo no valor de deltaKth dos materiais.

Fracture toughness J Q and fatigue crack growth da/dN x deltaK have been studied in two dual-phase steels used in the automotive industry, with 8.8% to 12.5% of martensite volumetric fraction. The main difference between the steels is the chemical composition: one of the steels had chromium additions while the other had silicon as an alloy element. Silicon steel presents higher fracture toughness than chromium steel. It was not noticed significant effect of anisotropy in both steels, while an increase of side grooves decreased the value of J Q of the materials. The two steels present a similar behavior in fatigue crack growth resistance with no significant effect of anisotropy. An increase of R ratio increased the crack growth rates and decreased the value of deltaKth of the materials.

Esse trabalho apresenta o estudo do comportamento de juntas soldadas de um aço estrutural, do tipo SAC 50, sob fadiga. O material foi soldado através do emprego do processo ao arco elétrico com eletrodo revestido. Além dos ensaios mecânicos tradicionais, aplicaram-se metodologias da Mecânica de Fratura, através de ensaios de tenacidade à fratura (COD), e ensaios de propagação de trincas por fadiga. Avaliaram-se as características comportamentais das três regiões do material: zona fundida, zona termicamente afetada e metal base. Verificou-se, em termos de tenacidade, que as três regiões do material, pelo efeito da soldagem, apresentaram comportamento semelhante. Correlacionaram-se os valores obtidos nos ensaios de tenacidade com ensaios de impacto Charpy. A zona fundida apresentou valor de COD, deltam, maior que a zona termicamente afetada e que o metal-base, o que significa maior resistência à propagação de trincas. O efeito do fator R não influenciou significativamente o posicionamento das curvas de propagação de trinca por fadiga. No entanto, para R = 0,7, o valor-limiar (threshold), deltaKth, sofreu alteração, diminuindo para o caso do metal-base. Pôde-se verificar, também, que, para o ensaio de propagação de trinca por fadiga, o valor-limiar, para o metal- base foi inferior às outras regiões do CP, caracterizando um pior desempenho.

This study observes the behavior of welded joints of structural steel type "SAC 50" under fatigue. The material was welded by use the electric arc with coated electrodes process. Besides using the traditional mechanical tests, Fractural Mechanical Methods were applied while performing tests on fracture resistance (COD) and crack propagation caused by fatigue. The behavioral features for the material's three areas (cast zone, thermally affected zone and base metal) were determined. In terms of resistance, the conclusions were that the material's three areas presented similar behavior considering the welding effect. The values obtained after the resistance tests coincide with those related to the Charpy impact tests. The cast zone presented a higher COD value than the base metal i.e. higher resistance to crack propagation. The effect of the R factor did not present a strong influence in the position of the curves of crack propagation caused by fatigue. However, for R = 0.7, the threshold value (deltaKth), was altered, being reduced in the case of the base metal. For the crack propagation test caused by fatigue, the threshold value for the base metal was lower than that in other areas of the specimens, indicating a poorer performance.