Evaluation of standard API casing connections and parametric API buttress improvement by finite element analysis.

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

Evaluation of hydrogen-Induced cracking resistance of the In625 laser coating system on a C-Mn steel substrate.

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

Laser cladding and thermal spray coatings on steel pipe serving the oil and gas industry.

Different coating systems were characterized using a commercial API 5CT steel grade L80 type 1, which is commonly used in the oil and gas industry. Two Ni-based alloys and one Co-based alloy were deposited by laser cladding. Two coatings were deposited (Ni-based alloy and a composite W-C/Co-base) by means of thermal spray process. It has been shown the presence of a hard heat affected zone (HAZ) in the substrate for the as-laser deposited coating. The main explanation for this HAZ is devoted to the heat gradient causing a gradient on the prior austenite grain size and consequently different martensite hardness along the HAZ. For the thermal sprayed coatings, no HAZ was formed due to low heat input process. All the studied coating systems seem to be very interesting for different technically demanding applications, such as, stress sulfide corrosion and wear resistance

Evaluation of the structural integrity of Itacolomi quartzite employed in historical monuments of Ouro Preto/MG that was either non-glued or glued using different types of resins.

A arte da Cantaria usando o quartzito foi utilizada na constru??o dos monumentos hist?ricos de Ouro Preto/MG. Ap?s mais de 300 anos de exist?ncia, parte de algum desses monumentos encontra-se em avan?ado est?gio de deteriora??o. Na restaura??o desses monumentos, alguns restauradores empregam a resina poli?ster ortoft?lica. Nesse trabalho, o quartzito itacolomi n?o colado e colado com diversas resinas foi submetido a ensaio de resist?ncia em flex?o e constatou-se que a resina suportou carga maior que o quartzito. Todos os corpos-de-prova romperam fora da regi?o da aplica??o da resina, confirmando a efic?cia 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

Failure analysis of recurrent cases of fatigue fracture in flash butt welded rails.

Medium carbon steel rails are commonly jointed by flash butt welding procedures. To ensure an adequate service life for the structural component, commonly subjected to fatigue loading, a rigorous quality control should be performed, both in welding parameters and in the surface quality of the welded joint. This work investigated the causes of recurrent failures in railroads, with cracking always initiated in the rail in the region of the welded joint. Two case studies are presented. Aiming to execute the failure analysis, all standard procedures were applied, with a careful assessment of the material characteristics and the fractured surface. It was concluded that, for both cases, fatigue cracks initiated near the weld bead and spread in a brittle mode, leading to premature fracture of the material. An in-depth analysis of the rails showed that the surface finishing of the weld bead was not appropriate, generating undesirable stress concentration. Some undesirable microstructural characteristics were also found in the weld region. A recommendation to control welding parameters and to change the procedure of surface finishing of welded joints was held, aiming to decrease the number of accidents on the railroads

Fatigue failure of a welded automotive component.

Automotive components are commonly tested in fatigue before the final assembly of the vehicle, to ensure the accomplishment of technical specifications of the customer, and to avoid premature failure and accidents with autos. This work investigated the cause of failure of a control arm (component of the automobile movement system), made of high strength and low alloy steel, stamped and welded by robot procedure. The fatigue cracking of the component occurred during the application of standardized blocks of fatigue loading. All standard procedures of failure analysis were applied, with a careful assessment of the material characteristics and the cracked surface. It was concluded that fatigue cracks initiated near the weld bead, at the beginning of the welding procedure. An in-depth analysis of this region showed that there was presence of stress concentration, and the microstructure of the steel has been completely changed, due to an excessive amount of heat at the beginning of the welding. A recommendation to change the welding procedure was performed, ensuring the lifetime specified for the component in the fatigue test

Failure analysis of a sleeper anchor model used in railroads.

The sleeper anchors are important elements in railroads. They are introduced into the ballast, and, as the name suggest, they have an anchor function, increasing the railway stiffness. Many rail companies have used a double fixing sleeper anchor model for many years. However, with the increasing of the transported load last decades, this model has failed in service, allowing the undesired ballast movement and creating a dangerous situation, with imminent risk of accidents. In this context, this work presents a complete failure analysis of this sleeper anchor model. Chemical, macro and microstructural analysis were done, and mechanical tests were performed. An alternative European model was also characterized, aiming to compare their metallurgical characteristics. The obtained results showed that the recurrent failures are associated to an overload applied to the studied device. This overload promotes an undesirable plastic strain and the anchor is removed from the ballast. It was possible to conclude that the mechanical properties of this double fixation anchor do not meet the specifications for the actual load demand in railways. The European model presented best characteristics for this application

Effect of the chemical homogeneity of a quenched and tempered C-Mn steel pipe on the mechanical 3 properties and phase transformations.

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

Microestrutura e propriedades mec?nicas de um a?o para trilhos ferrovi?rios soldado por centelhamento.

Trilhos com perfil TR-57 do tipo intermedi?rio foram soldados por centelhamento em um estaleiro brasileiro e passaram por detalhada caracteriza??o mec?nica e metalogr?fica. Os dados quantitativos da caracteriza??o metalogr?fica e dos ensaios mec?nicos foram submetidos a an?lises de vari?ncia (ANOVA). Na metalografia confirmou-se a presen?a majorit?ria de perlita, por?m h? tamb?m ferrita proeutet?ide na linha central da solda e globuliza??o parcial da cementita em regi?es da Zona Termicamente Afetada (ZTA), sobretudo na zona de transforma??o parcial. O tamanho das col?nias perl?ticas e o espa?amento interlamelar foram correlacionados ? microdureza Vickers em toda a extens?o da junta. Ensaios de tra??o revelaram que o metal base atendeu ?s especifica??es da Norma AREMA, no entanto, as juntas soldadas n?o atenderam e a fratura dos corpos de prova ocorreu na regi?o de menor dureza da ZTA. Os resultados permitem compreender, em detalhes, as consequ?ncias do processo de soldagem sobre a estrutura do a?o e as varia??es de propriedades em diversas regi?es da junta, com destaque ?s altera??es morfol?gicas da perlita. Rela??es com modos de falha anteriormente relatados na literatura cient?fica tamb?m s?o apresentadas.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

Strain ageing in welded joints of API5L X65Q seamless pipes.

In this work, we investigated the effects of the phenomenon of strain ageing in joints obtained by gas-shielded arc welding (gas metal arc welding, GMAW), of seamless pipes of API5L X65Q steel. Test specimens obtained from the welded joints were submitted to cold plastic strain of 3% and then aged for 1 h at 250 ?C, so as to induce static ageing. For evaluating dynamic ageing, the test specimens were strained to 3% and loading was maintained for 1 h at 250 ?C. The aged specimens were submitted to tensile testing and representative samples were examined in the light microscope and the scanning electron microscope. It was observed that the phenomenon altered the volume fraction of secondary constituents in the weld metal and in the HAZ, with increase in the proportion of ferrite?carbide aggregates. Regarding the mechanical properties, it was found that the phenomenon reduced the elastic ratio of the welded joints due to an increase in the ultimate strength, besides increasing the total elongation, but without impairing the tensile properties of the welded joints. On comparing static ageing with dynamic ageing, it was observed that the increase in the capacity for plastic strain of the welded joints was greater after static strain ageing