Abstract Welding operations are one of the most important operations during pipeline construction and most are still carried out manually with SMAW. The challenges associated with the automation of orbital welding are related to several variables, including the weld pool behavior in vertical and overhead positions, monitoring of parameters and metal transfer, bevel preparation and orbital welding head control. In order to achieve a 360º orbital root pass with GTAW process, this study was focused on evaluating the influence of the arc voltage control (AVC) system for pulsed current process, the bevel geometry and filler wire insertion technique on the welding process and weld bead. Experiments were carried out using 16” ASTM A36 pipes with ½” wall thickness and an automated orbital welding head. The results show that the AVC control must be appropriate for the current mode applied (pulsed or constant) in order to avoid arc length oscillation. Also, the counterboring operation during the bevel preparation increases the amount of material of the groove land and promotes less penetration. Regarding the metal transfer, the continuous bridge transfer mode is recommended for automated orbital GTAW welding and this is achieved with an appropriate AVC control method and filler wire positioning.

ABSTRACT The Oil and gas exploration is one of the most strategic industrial sectors in the Brazilian economy. The discovery of deep water reserves adds more difficulty to the already problematic use of materials in equipment in extremely corrosive environments. With the objective of increasing the service life of the equipment, and consequently reducing the cost of maintenance and preventing against environmental catastrophes, it is common to use CRA claddings via welding processes, in which the nickel superalloy coatings stand out via the PTA welding process. In this context, the operation of internal cladding of risers becomes extremely complex due to the operational and metallurgical requirements imposed by the application. The present work aims at the development and empirical evaluation of the internal cladding procedure of risers with Nickel-based superalloy 625 via PTA welding process. From tests of cladding on plate, satisfactory preliminary parameters were reached for the performance of internal cladding tests on risers. From the adaptation of the welding parameters, comparative analyzes of three different procedures were carried out, with different weaving amplitude. Visual analysis and inspections were carried out via penetrating liquid and radiography, confirming the welding quality of all procedures performed. Still, proving the metallurgical quality of the developed procedures, analysis of chemical composition was carried out via EDX, presenting satisfactory results. Finally, a financial comparison of the process was elaborated, showing comparatively the consumption of powder and gas, and the time needed for internal cladding.

Abstract Numerous GMAW processes have appeared for one-pass welding of medium to high thickness. This concept originated in the 1980s with the T.I.M.E. technique and the 1990s and 2000s saw the emergence of Rapid Arc, Rapid Melt and Buried Arc techniques. These processes did not include any special control features, but rather parameter combinations to improve bead geometry. A new interpretation of the factors that are critical to achieving high performance GMAW (penetration) is presented herein. Tests with a voltage controlled power source with inductance control and the Rapid Arc process were conducted on bead-on-plate for high speed videography. Later, validation tests were conducted on butt joints, with the technique developed, with and without groove on AISI 1020, 3/8” thick steel plates. The power source may be of voltage control but has to provide a dynamic response able to sustain a metastable equilibrium of the molten pool applying the semi-keyhole technique. The technique developed was able to weld, in a single pass, 3/8” thick butt joint steel plates. The results showed that a power source, to achieve the GMAW buried arc condition, only needs to provide dynamic characteristics able to maintain the molten pool in a metastable equilibrium.

This study analyzed the average temperature value of the metallic droplets and weldpool of the Pulsed GMAW welding process using 309L-Si electrode as the addition metal. The study was based on the formulation and evaluation of pulsed waves, starting from the equation of energy constant (or detachment constant), and waveforms from two commercial welding sources, that were evaluated and reproduced. The technique of filming by high speed infrared radiation was used for evaluation. The results point to a higher droplet temperature for a lower intensity of pulse current, due to longer dwell time at this level, and also revealing that a longer time in the base phase may be responsible for a further heating of the fusion pool.

Abstract: Recent profusion of advanced GMAW process variants impairs understanding of the nature of each one, with the arc rotation technique among them. This paper’s objective is investigating influences of wire-electrode rotation over metal transfer mode and melting rate. A bead on plate experimental matrix was performed and electrical signals acquired in synchronicity with high speed videography. Impacts of electrode rotation were observed on welding voltage and current, whereby rotation speed exerts marked influence. Droplet short-circuiting frequency was affected, culminating in free-flight transfer mode for higher rotation speeds. Increase of melting rate was observed for lower electrical power, indicating efficiency enhancement of the process. Moreover, arc rotation proved to expand controllability of the thermal development of the workpiece. Results are supported by videothermography.

Resumo Inserido no cenário de inovações e tendências tecnológicas da Industria 4.0, esse trabalho visa obter conhecimento detalhado da influência do intervalo de tempo entre a deposição de camadas como técnica de controle térmico do processo Wire Arc Additive Manufacturing (WAAM) com duas variantes do processo GMAW de alta controlabilidade (CMT e CMT Pulse). A problemática foca na deposição de paredes espessas, buscando emular os desafios da fabricação de peças grande e com média complexidade geométrica, como hélices e fusos, as quais usualmente apresentam secções com esta característica. Embora trabalhos na área de manufatura aditiva apontem o uso do tempo entre camadas como uma ferramenta de estabilização do gradiente térmico, informações detalhadas sobre o comportamento térmico acabam sendo omitidas. Além disso, por questões de produtividade, maior entendimento sobre os fenômenos térmicos envolvidos são necessários, como subsídio para racionalização do ciclo de trabalho (redução de tempos de espera). As duas versões do processo utilizadas possuem alta estabilidade na transferência metálica e alta controlabilidade do aporte térmico se comparado ao GMAW convencional, sendo diferenciais positivos para o WAAM. Os experimentos envolveram a construção de paredes com oito camadas de aço ER309LSi, nas quais variou-se o tempo entre camadas de 0 a 300 s. Pode-se concluir que o ambos os processos são aptos ao WAAM, e, que embora o CMT Pulse tenha aporte energético superior, o controle de temperatura por tempo de espera entre camadas foi capaz de controlar o acúmulo térmico na peça para ambos os processos.

Abstract: Inserted in the scenario of innovations and technological trends of Industry 4.0, this work aims to obtain detailed knowledge on the influence of idle time between layers as thermal control technique for the Wire Arc Additive Manufacturing (WAAM) with two GMAW process variants of high controllability (CMT and CMT Pulse). The problem focuses on the deposition of thick walls, seeking to emulate the challenges of manufacturing big parts with medium geometric complexity, such as propellers and screws, which usually have sections of this thickness. Although works in the area of additive manufacturing point out the use of idle time as a feature to stabilize the thermal gradient, detailed information about the thermal behavior ends up being omitted. Both processes variants used presented high metallic transference stability and low thermal input when compared to the conventional GMAW, being positive differentials for WAAM. In the tests, walls with eight layers were built with ER309LSi steel in which the interlayer idle time varied from 0 to 300 s. It can be concluded that both processes are WAAM compliant, and that although the CMT Pulse has a higher energy input, the temperature control by idle time was able to control the thermal accumulation in the part for both processes.

Resumo Atualmente, no cenário brasileiro de óleo e gás a execução dos processos de soldagem para aços inoxidáveis consiste em sua grande maioria de aplicações manuais, dificultando qualquer aumento de produtividade e repetibilidade dos processos. Portanto, a automação desta etapa permite grandes avanços com resultados mais confiáveis, menores custos relacionados à mão-de-obra e condições de saúde mais favoráveis para os soldadores. Com o objetivo de automatizar a soldagem GTAW em aplicações orbitais, testes experimentais foram realizados em tubos de aço inoxidável 304 L, posicionados na posição 5G de soldagem. As amostras foram soldadas pelo processo GTAW com alimentação dinâmica de arame, utilizando um manipulador robótico em 2 etapas de 180º na progressão vertical descendente. Os parâmetros de soldagem e a condição estável de soldagem obtidos foram discutidos e o comportamento da poça durante a soldagem do passe de raiz foi monitorado por videografia em HDR. Foi possível se alcançar alta velocidade de soldagem no passe de raiz, 50 cm/min com o modo keyhole. O movimento dinâmico do arame contribuiu para alcançar-se grande estabilidade do processo e robustez na soldagem de todos os passes, da raiz ao acabamento. As macrografias e ensaios de raio-x realizados na junta não indicaram a presença de descontinuidades como poros e falta de fusão.

Abstract Currently, in the Brazilian Oil and Gas scenario the execution of welding processes for stainless steel consists mostly of manual applications, rendering hard any increase in productivity and repeatability. Therefore, the automation of this step allows several advances such as more reliable results, lower costs and healthier condition for welders. With the aim of developing automation for GTAW welding of these applications, experimental tests were carried out in a 304L stainless steel pipe laid out at 5G position. The samples were orbitally welded by GTAW with dynamic wire feeding process, using a robotic manipulator in two steps of 180º in vertical down progression. The welding parameters and the stable condition obtained are discussed and the weld pool behavior during the root pass was online monitored by HDR (High Dynamic Range) videography. It was possible to reach high welding speed in the root pass, 50 cm/min in a keyhole mode. The wire dynamic movement contributed to reach great process stability and robustness for all joint passes, from root to finishing. The macrographs and x-ray analysis did not indicate discontinuities as porosity nor lack of fusion.

Abstract: The GTAW process is recognized as a process of high metallurgical quality, being widely used in the pipelines welding, mainly in the root pass. The relative independence between the heat delivered to the melting pool and the amount of material added helps to control the melting of the material and to avoid the appearance of welding discontinuities such as lack of fusion and lack ok penetration. When orbital welding is carried out, mainly in the overhead position, there is a tendency of electrode contamination by the melted wire, reducing process productivity and quality. In this scenario, there are some strands of the GTAW process that aim for increased productivity, reconciled with the already present high metallurgical quality. These includes low and high frequency dynamic wire feeding, preheating wire and tangential wire insertion. The present work deals with the contribution of the high frequency dynamic wire feeding for the increase of robustness in the GTAW process, evidencing through voltage monitoring and high speed filming the formation of regular and uniform drops for the process stability.

Resumo O presente trabalho visa obter o conhecimento detalhado de diferentes versões do processo MIG/MAG por transferência em curto-circuito com controle de corrente e sua aplicabilidade na soldagem de raiz em chanfro V sem a utilização de anteparo da poça (backing). Embora muitos trabalhos na área de soldagem de tubos descrevam realizar o procedimento inteiramente mecanizado através de sistemas orbitais, informações mais detalhadas sobre como este foi realizado acabam não sendo divulgadas. Além disso, diferentes condições de aplicação impõem conhecimento mais aprofundado, para devida adaptação / parametrização específica. Nesse contexto, a soldagem de raiz com manipulador orbital mecanizado foi realizada em tubos utilizados na indústria do petróleo e gás, verificando as condições de operação de três versões comerciais do processo MIG/MAG em curto-circuito com controle de corrente, sendo duas com controle eletrônico e uma com controle eletromecânico da transferência metálica. As três versões possuem níveis controlados de energia, bom controle de estabilidade na transferência metálica e baixo índice de respingos, diferenciais na aplicação de raiz. Nos ensaios, feitos em tubos da classe API 5L grau B, foi possível a realização da soldagem orbital em situações nas quais a junta dos tubos apresentava geometria favorável, sem a presença de desnivelamento (high-low) e em condições estreitas dos valores de tolerância para abertura de raiz (gap). Quanto ao perfil geométrico de fusão no chanfro, os ensaios com as versões eletrônicas apresentaram bons resultados sem defeitos que pudessem comprometer a integridade da junta. No entanto, dentro das faixas abordadas, com a utilização da versão eletromecânica, verificou-se a presença de defeitos de falta de fusão, o que gerou hipóteses quanto a diferentes faixas de parâmetros para esta versão na aplicação de raiz em tubos com chanfro V.

Abstract The present work aims to obtain the detailed knowledge of different versions of the MIG/MAG process by short-circuit transfer with current control and its applicability in V-groove root welding without the use of backing. Although many pipe welding researches describe performing the fully machined procedure through orbital systems, more detailed information on how this was accomplished ends up not being disclosed. In addition, different application conditions require in-depth knowledge for proper adaptation/specific parameterization. In this context, root welding with a mechanized orbital manipulator was performed in tubes used in the oil and gas industry, by verifying the operating conditions of three commercial versions of the MIG/MAG process in short circuit with current control, two of which with electronic control and one with electromechanical control of metal transfer. The three versions have controlled levels of energy, good stability control on the metal transfer and low spatter index, differentials in root application. In the tests, which were carried out on API 5L grade B pipes, it was possible to perform orbital welding in situations in which the pipe joint presented favorable geometry, without the presence of unevenness (high-low) and narrow conditions of tolerance values for gap opening. As for the geometric profile of fusion on the groove, the tests with the electronic versions presented good results without defects that could compromise the integrity of the joint. However, within the ranges covered, with the use of the electromechanical version, it was verified the presence of lack of fusion defects, which generated hypotheses regarding different parameter ranges for this version in the root application in V-groove tubes.

Resumo A medição da geometria da junta é tarefa fundamental para a automação da soldagem. Dentre os sensores utilizados para tal finalidade, os Sensores de Triangulação Laser para soldagem (STL) estão entre as tecnologias que melhor caracterizam a geometria da junta durante a soldagem. A medição da abertura de raiz (gap) é especialmente importante para o sucesso na deposição automatizada do passe de raiz, com benefícios de produtividade e qualidade em diferentes aplicações, como a construção de dutos para o setor de Petróleo e Gás. A medição desta característica é sensível aos ruídos gerados pela soldagem e à reflexividade da superfície da junta. Os algoritmos de processamento de imagem para medição do gap apresentados na literatura não têm as características desejadas de erro de medição e flexibilidade para medição em chanfros de diferentes dimensões. Este artigo apresenta um novo algoritmo para a medição do gap em juntas de chanfro “V” empregando a técnica de ajuste linear. O algoritmo de medição desenvolvido foi avaliado a partir dos erros de medição do gap encontrados em imagens capturadas antes e durante o procedimento de soldagem de raiz de um corpo de prova padrão. As mesmas imagens foram processadas com os algoritmos de correlação de padrões e algoritmo de derivadas, ambos apresentados por trabalhos acadêmicos. O algoritmo proposto apresentou os melhores resultados de erro de medição, robustez e flexibilidade.

Abstract Joint geometry measurement is a key task for welding automation. Among the sensors used for this purpose, the Laser Triangulation Sensors for welding (LTS) are the ones that best characterize the joint geometry. Root gap measurement is especially important for success in the automated root pass deposition, with production and quality benefits in different applications, such as pipeline construction for the Oil & Gas industry. The measurement of this feature is sensitive to noises generated by welding and joint surface reflexivity. The image processing algorithms for gap measurement available in literature do not have the desired characteristics of measurement error and flexibility for dimensional variability of welding joints. This paper presents a new algorithm for root gap measurement of “V” type joints using a linear adjustment technique. This developed algorithm was evaluated from measurement errors found in images captured before and during orbital welding procedure of a standard test piece. The same images were processed with pattern correlation algorithm and derivative algorithm, both presented in academic papers. The proposed algorithm presented the best results of measurement error, robustness and flexibility.

Abstract: When they are damaged by cavitation, hydroelectric power plant turbine blades must be repaired using operations that could benefit from developments in welding technologies. In light of this, the LABSOLDA welding laboratory at the Federal University of Santa Catarina is making efforts to enhance the flexibility and robustness of the powder-fed plasma transferred arc (PTA-P) process so that it can be used in any welding position and with different powders. The use of consumables in powder form in PTA-P welding allows experiments to be carried out to develop an alloy with special properties suitable for use in generator repairs. To this end, the RV-F PF powder feeder, which can operate with consumables with non-standard morphologies and particle sizes, was developed. The feeder was required to provide a regular flow of consumable material in out-of-position welding operations without the need for high gas flow rates and regardless of the morphology or particle size of the consumables. The RV-F PF is shown to operate efficiently with materials whose properties differ greatly from those of standard consumables. It is also suitable for overhead PTA-P welding and provides a constant supply of filler material efficiently with normal gas flow rates. The welding tests carried out involved deposition of a mixture of two alloys and were followed by cavitation testing of the resulting coating.

Resumo Os sistemas comerciais destinados à automação da soldagem orbital enfrentam desafios perante o controle da trajetória e a parametrização do processo. Os tubos e dutos do setor de Petróleo e Gás apresentam descontinuidades, advindas de sua fabricação, críticas para o processo de soldagem. Para superar isto, o presente trabalho investiga a utilização de sensores para correção em tempo real da soldagem orbital. Um robô antropomórfico atua na condução da tocha. Um sensor a arco para seguimento de junta e um sensor baseado no contato elétrico para procura da junta foram empregados. Um programa em forma de algoritmos para geração de uma trajetória orbital automática e alocação dos parâmetros de soldagem foi desenvolvido. A validação da estratégia proposta e do controle da tocha pelo sensor a arco foi realizada com depósitos em corpos de prova de tubos. A soldagem do passe de raiz com um processo MIG/MAG com controle de corrente no curto-circuito também foi executada em conjunto com o sensor a arco.

Abstract The commercial welding systems for orbital welding automation face challenges regarding the robot path control and the process parameters. Pipes from oil and gas companies present discontinuities caused by the manufacturing stage that are critical for the welding process. To overcome this, the present paper investigates the use of sensors for real time correction in orbital welding. An anthropomorphous robot guides the torch. A through-arc sensor for seam tracking and an electrical contact sensor for seam finding were employed. A program for automatic path planning and welding parameters allocation was developed. The proposed strategy and the arc sensor torch control were validated based on weld deposits on pipe. The root pass welding was next performed using a short-circuit control GMAW process with the arc sensor.

Resumo A característica mais marcante da soldagem TIG Orbital é a constante alteração na posição de soldagem enquanto a tocha acompanha o perfil geométrico dos tubos. No contexto da soldagem TIG orbital de tubos de grande diâmetro e paredes espessas, é investigada a relação entre a posição de soldagem, uso de corrente constante ou pulsada e ainda valor da corrente média nas características geométricas dos cordões obtidos. Foram realizadas soldas de deposição em tubos de aço carbono SAE 1020, bem como macrografias das seções transversais dos cordões via microscopia óptica. Filmagens em alta definição contribuíram para a compreensão do comportamento da poça de fusão nas diferentes posições de soldagem. As características geométricas foram quantificadas através das macrografias com o uso de um software e foi traçada a relação destas com as variáveis citadas. Além disso, foi feita uma análise microestrutural das amostras, correlacionando com a microdureza Vickers. Concluiu-se que cordões soldados com corrente pulsada apresentam maiores reforço e largura, bem como maior dureza e microestrutura mais refinada. A posição vertical ascendente resulta em cordões com menor fator de forma e maior penetração, e a posição sobre cabeça resulta em cordões de baixo fator de forma.

Abstract The most important characteristic of TIG Orbital welding is the constant change in weld position while the torch follows the geometric profile of the pipes. In this context, large diameter and thick wall pipes orbital TIG welds were investigated, by studying the relation between the welding position, use of constant or pulsed current and magnitude of welding current and the resulting geometric characteristics. Weld beads were made on SAE 1020 carbon steel pipes, as well as transversal section macrographs via optical micrograph. High definition filming contributed to comprehension of the weld pool trend on different welding positions. Geometric characteristics were quantified through the macrographs by using software, and its relations with the cited variables were made. Besides that, a microstructural analysis was made, comparing it to Vickers micro hardness. One could conclude that beads made with pulsed current had higher reinforcement and width, as well as higher hardness and a finer microstructure. The ascendant vertical position resulted in low reinforcement form factor and higher penetration, and the overhead position results in low reinforcement form factor beads.

This work presents the first results of the plasma nitriding study performed in pure niobium in order to increase its cavitation erosion resistance. Samples were prepared from 98.9% purity and 90% reduction cold-rolled niobium bars. Annealing treatment of the cold-worked niobium samples was carried out in vacuum furnace at 1.33 Pa pressure, in the temperature of 1000 °C, for a time of 60 min. Annealed samples showing hardness of 80 HV were cut to dimensions of 20 × 30 × 4 mm3. Nitriding treatment was conducted at 1080 °C, gas mixture of 90% N2 + 10% H2, flow rate of 5 × 10–6 Nm3s–1, and pressure of 1200 Pa (9 Torr), for a total time of 4 h comprised by two treatment steps of 2 h each. For comparison purpose, results for nitrided and non-nitrided niobium are confronted. Samples were characterized by XRD, nanoindentation, microhardness, SEM, and 2D surface topography and 3D interferometry profile analysis techniques. Cavitation testing was conducted according to ASTM G32-09. Comparatively, promising results based on the formation of niobium nitride phases in treated surfaces are presented and discussed in the present work.