Theophilo Moura Maciel

Estudo do comportamento do aço API 5L X80 quando submetido à soldagem por processo automatizado

The welding of pipes has been largely manual in Brazil, however, the use of automated welding processes have greatly increased in recent years, contributing to greater control of welding parameters, and consequently, the possibility of obtaining welded joints with better mechanical properties. The welding of pipes of API 5L X80 steel has been evaluated in Brazil considering to best practices, parameters and welding processes; the implementation of automated processes in the specific field conditions is relevant project and innovative design in this area. Therefore, the objective is to evaluate the behavior in the HAZ of the API 5L X80 steel used for transporting oil and gas when subjected to automated welding processes; the results indicated besides the reduction of HAZ extent grain size the preservation of bainitic structure in this region for robotic welding process.

Deposition of thin film of titanium on ceramic substrate using the discharge for hollow cathode for Al2O3/Al2O3 indirect brazing

Thin films of titanium were deposited onto Al2O3 substrate by hollow cathode discharge method for the formation of a ceramic-ceramic joint using indirect brazing method. An advantage of using this technique is that a relatively small amount of titanium is required for the metallization of the ceramic surface when compared with other conventional methods. Rapidly solidified brazing filler of Cu49Ag45Ce6 in the form of ribbons was used. The thickness of deposited titanium layer and the brazing temperature/time were varied. The quality of the brazed joint was evaluated through the three point bending flexural tests. The brazed joints presented high flexural resistance values up to 176 MPa showing the efficiency of the technique.

Development of methodology for measurements of residual stresses in welded joint based on displacement of points in a coordinated table

Residual stresses in a welded joint of ASTM A131 grade AH32 steel was measured either by the X-ray diffraction or by displacements of referenced points measured on a coordinate measuring machine before and after heat treatment. For all tests, the welding was performed with Shielded Metal Arc Welding, vertical-up position, by a certified welder. After welding, some specimens were subjected to marking, made through small holes evenly spaced and mapped on a coordinate measuring machine. After labeling, the samples were subjected to heat treatment at temperatures nearby recrystallization. After heat treatment, the samples were subjected to new measurements by coordinate measuring machine to evaluate the displacements of the points produced by the recrystallization. In parallel, residual stress measurements were made by XRD for validation of this new methodology. The results obtained either by X-ray or by coordinate measuring machine showed a good correlation between the two measurement methodologies employed.

Numerical evaluation of multipass welding temperature field in API 5L X80 steel welded joints

Many are the metallurgical changes suffered by materials when subjected to welding thermal cycle, promoting a considerable influence on the welded structures thermo mechanical properties. In project phase, one alternative for evaluating the welding cycle variable, would be the employment of computational methods through simulation. So, this paper presents an evaluation of the temperature field in a multipass welding of API 5L X80 steel used for oil and gas transportation, using the ABAQUS ® software, based on Finite Elements Method (FEM). During the simulation complex phenomena are considerable including: Variation in physical and mechanical properties of materials as a function of temperature, welding speed and the different mechanisms of heat exchange with the environment (convection and radiation) were used. These considerations allow a more robust mathematical modeling for the welding process. An analytical heat source proposed by Goldak, to model the heat input in order to characterize the multipass welding through the GTAW (Gas Tungsten Arc Welding) process on root and the SMAW (Shielded Metal Arc Welding) process for the filling passes were used. So, it was possible to evaluate the effect of each welding pass on the welded joint temperature field, through the temperature peaks and cooling rates values during the welding process.

Evaluation of the diffusivity and susceptibility to hydrogen embrittlement of API 5L X80 steel welded joints

This paper presents a study of susceptibility to hydrogen embrittlement of API 5L X80 steel welded joints by SMAW and GTAW processes. By varying the consumables used and the use of the same interpass temperature three different welded joints were obtained. Tests of hydrogen embrittlement susceptibility were performed according to ASTM G129-2006 with an aqueous solution (Solution A - TM0177/2005 NACE) sodium thiosulfate (Na 2 S 2 O 3 ) replacing the bubbling of H 2 S. From the elongation values was observed that the joint obtained in all welding conditions showed susceptibility to hydrogen embrittlement, which was determined by the elongation ratio. The joints that showed higher levels of hardness showed higher susceptibility to hydrogen embrittlement. The joints obtained with higher welding speeds for the same amount of heat input presented a reduction in the rate of hydrogen embrittlement. All joints tested in solution showed fracture surfaces with quasi cleavage zones.

Estudo das tensões residuais de juntas soldadas de aço API 5L X80

This study aimed to determine the levels of residual stresses due to welding processes in welded joints of API 5L X80 steel. Initially were executed the welded joint using the Shielded Metal Arc Welding (SMAW) and Gas Tungsten Arc Welding (GTAW) processes, with different consumables and employing an interpass temperature of 175oC. Three different welded joints were obtained. The residual stress measurements were carried out by x-ray diffraction using a portable diffractometer and software for analyzing the results. In the upper region, it was observed that to higher heat inputs the residual stresses levels were more compressive and more displaced were the tensile stresses peaks. In the lower region of the welded joints, it was found that for higher heat input, were higher levels of tensile residual stresses in the region of the Weld Metal (WM) and the lower the level of tensile residual stresses in the Heat Affected Zone (HAZ).

Avaliação da microestrutura e propriedades mecânicas de metais de solda obtidos por processos de soldagem manual e automatizado utilizado na soldagem de aço API 5L X80

The objective of this work was to evaluate the heat affected zone characteristics and weld metals microstructure and mechanical properties of API 5L X80 steel welded joints, obtained for four different welding procedures using manual and automated processes. For this, plates of this steel were welded by manual Shielded Metal Arc Welding (SMAW) process with interpasses temperatures of 473 e 673 K, and using AWS E8010-G electrode as filler metals; robotized Flux Cored Arc Welding (FCAW) process, using AWS E71T-1C wire and Ar25%CO2 as consumable and mechanized Gas Tungsten Arc Welding (GTAW) process, for the root pass using AWS ER70S-3 and Ar as consumable .The microstructural analysis was related with the weld metals Charpy impact test results and with the welded joint Vickers microhardness profiles. The results indicated that weld metals obtained by automatized welding process presented a shorter and more refined heat affected zone and a weld metal with greatest Acicular Ferrite percentiles which promoted the best results of the impact test.

Brazing of Al2O3 with Rapidly Solidified Melt Spun Ni-Cr-P Alloy Ribbons

Melt spun Ni-Cr-P alloy ribbons were used as filler metal to join Al2O3 substrates together using a vacuum brazing process. The influence of the brazing load, brazing temperature and holding time on the shear resistance of brazed joints was evaluated. The experimental results showed that the holding time was the most important parameter. At a brazing temperature of 1060°C, the shear resistance value increased from 6.17 to 93.7 MPa with increasing brazing time from 20 to 100 min, respectively.

Optimization of submerged arc welding process parameters for overlay welding

Abstract In this work, we evaluated the influence of welding variables on weld beads applied by the submerged arc process (SAW) with conventional current, aiming future application in overlays against corrosion. Segments of steel API 5L Gr B pipe as substrate, a 1.13 mm-diameter electrode wire of nickel alloy, classification AWS ERNiCrMo-4 (Hastelloy C-276) as filler metal, and a flux neutral, basic and crowded were used. The variables voltage, wire feed speed and contact tip to work distance (CTWD) were analysed, with the remaining parameters constant by an experimental design with full factorial design in two-level and central points. Statistically significant and predictor mathematical models for response dilution and average current were obtained. However, for the response reinforcement/width, the model was characterized as statistically significant, but not predictive, and containing a lack of fit. The CTWD was the most significant variable reducing the dilution.

Influência da geometria do pino da ferramenta de soldagem nas propriedades mecânicas e tensões residuais de juntas soldadas de ligas de alumínio 5052-O pelo processo FSW

Ligas de aluminio possuem excelentes caracteristicas e propriedades mecânicas. No entanto, a soldagem desses materiais atraves de processos convencionais ao arco eletrico resulta em uma degradacao excessiva destas propriedades, afetando diretamente sua vida util. Neste contexto, os processos de soldagem por friccao tem recebido atencao nos ultimos anos, principalmente devido a minimizacao do aporte de calor fornecido durante o processo, nao atingindo o ponto de fusao do material. Este trabalho tem por objetivo analisar diferentes perfis de pino da ferramenta de soldagem por FSW e sua influencia nas propriedades mecânicas das juntas soldadas. Para tanto, 12 geometrias de ferramentas foram projetadas, fabricadas e testadas. Ensaios mecânicos de dobramento de raiz a 60°, tracao uniaxial, determinacao do perfil de dureza e de tensoes residuais das juntas soldadas foram empregados para caracterizacao eanalise das propriedades. Observou-se uniformidade tanto nos perfis de dureza como nos de tensoes residuais. Os ensaios de tracao uniaxial e dobramento de raiz indicaram que a ferramenta 1, com pino em formato de tronco de cone e com rosca, obteve valores de resistencia mecânica inferiores as demais, sendo as ferramentas 4 e 9, cilindricas com e sem rosca, respectivamente, as que proporcionaram as melhores propriedades mecânicas.