Underwater Remote Welding Technology for Offshore Structures

The construction of offshore structures, equipment and devices requires a high level of mechanical reliability in terms of strength, toughness and ductility. One major site for mechanical failure, the weld joint region, needs particularly careful examination, and weld joint quality has become a major focus of research in recent times. Underwater welding carried out offshore faces specific challenges affecting the mechanical reliability of constructions completed underwater. The focus of this thesis is on improvement of weld quality of underwater welding using control theory. This research work identifies ways of optimizing the welding process parameters of flux cored arc welding (FCAW) during underwater welding so as to achieve desired weld bead geometry when welding in a water environment. The weld bead geometry has no known linear relationship with the welding process parameters, which makes it difficult to determine a satisfactory weld quality. However, good weld bead geometry is achievable by controlling the welding process parameters. The doctoral dissertation comprises two sections. The first part introduces the topic of the research, discusses the mechanisms of underwater welding and examines the effect of the water environment on the weld quality of wet welding. The second part comprises four research papers examining different aspects of underwater wet welding and its control and optimization. Issues considered include the effects of welding process parameters on weld bead geometry, optimization of FCAW process parameters, and design of a control system for the purpose of achieving a desired bead geometry that can ensure a high level of mechanical reliability in welded joints of offshore structures. Artificial neural network systems and a fuzzy logic controller, which are incorporated in the control system design, and a hybrid of fuzzy and PID controllers are the major control dynamics used. This study contributes to knowledge of possible solutions for achieving similar high weld quality in underwater wet welding as found with welding in air. The study shows that carefully selected steels with very low carbon equivalent and proper control of the welding process parameters are essential in achieving good weld quality. The study provides a platform for further research in underwater welding. It promotes increased awareness of the need to improve the quality of underwater welding for offshore industries and thus minimize the risk of structural defects resulting from poor weld quality.

Relacao entre o angulo da ponta do eletrodo e a geometria do cordao de solda no processo de soldagem tig

No processo de soldagem TIG (Tungstênio Inerte Gás), um dos fatores que influenciam o formato do cordão de solda é o ângulo da extremidade do eletrodo. Para estudar o comportamento do arco elétrico em função da geometria de ponta do eletrodo e suas conseqüências nos cordões de solda, efetuaram-se soldagens sobre corpos de prova sem deposição de material (bead-on-plate) através de parâmetros controlados e a mecanização do processo. Parâmetros tais como vazão do gás, velocidade de avanço da tocha e comprimento do arco foram testados para verificar a atuação em conjunto com o ângulo do eletrodo. Pela análise metalográfica (macrografia) estudaram-se os perfis dos cordões de solda, verificando-se que o ângulo exerce uma influência significativa na característica do arco tensão-corrente, na largura e profundidade de penetração da solda. Para maiores ângulos de extremidade do eletrodo obteve-se aumento na penetração, diminuição da tensão e largura do cordão de solda para uma mesma intensidade de corrente.

Introducao ao estudo de fluxos para arco submerso

O maior objetivo deste trabalho foi estudar os efeitos da composição dos fluxos para arco submerso sobre algumas importantes características de um metal de solda ferrítico, como composição química, microestrutura, propriedades mecânicas e geometria do cordão. Para realizar tal pesquisa, vinte oito fluxos aglomerados foram elaborados de compostos de pureza comercial e utilizados em soldagens ao aorco submerso, mantendo constante todas as demais condições de soldagem. Houve uma notável influência da composição química e do índice de basicidade dos fluxos sobre os níveis de oxig~enio, silício e manganês do metal de solda. Um modelo termodinâmico, baseado no conceito de potencial de oxigênio, foi proposto para explicar as reações gás-meta-escória ocorrendo durante a soldagem. Este modelo mostrou-se usável para as reações entre silício, oxigênio e carbono, permitindo um melhor entendimento das mesmas. A composição química do metal de solda pôde ser relacionada a sua microestrutura, através de metalografia quantitativa. Foi observado que oxigênio, silício, manganês e titânio têm grande influência sobre ela. A fase mais tenaz encontrada foi a ferrita acicular. A respeito da geometria do cordão, a sílica mostrou o efeito mais forte, com os outros compostos influenciando somente o acabamento do cordão soldado.

Influência da corrente de pulso, do tempo de pulso e diâmetro de gota sobre a estabilidade da transferência metálica no processo MIG-P

To obtain a process stability and a quality weld bead it is necessary an adequate parameters set: base current and time, pulse current and pulse time, because these influence the mode of metal transfer and the weld quality in the MIG-P, sometimes requiring special sources with synergistic modes with external control for this stability. This work aims to analyze and compare the effects of pulse parameters and droplet size in arc stability in MIG-P, four packets of pulse parameters were analysed: Ip = 160 A, tp = 5.7 ms; Ip = 300 A and tp = 2 ms, Ip = 350 A, tp = 1.2 ms and Ip = 350 A, tp = 0.8 ms. Each was analyzed with three different drop diameters: drop with the same diameter of the wire electrode; droplet diameter larger drop smaller than the diameter of the wire electrode. For purposes of comparison the same was determined relation between the average current and welding speed was determined generating a constant (Im / Vs = K) for all parameters. Welding in flat plate by simple deposition for the MIG-P with a distance beak contact number (DBCP) constant was perfomed subsequently making up welding in flat plate by simple deposition with an inclination of 10 degrees to vary the DBCP, where by assessment on how the MIG-P behaved in such a situation was possible, in addition to evaluating the MIG-P with adaptive control, in order to maintain a constant arc stability. Also high speed recording synchronized with acquiring current x voltage (oscillogram) was executed for better interpretation of the transfer mechanism and better evaluation in regard to the study of the stability of the process. It is concluded that parameters 3 and 4 exhibited greater versatility; diameters drop equal to or slightly less than the diameter of the wire exhibited better stability due to their higher frequency of detachment, and the detachment of the drop base does not harm the maintenance the height of the arc

Influência do tipo de chanfro, tecimento e sentido de laminação na distorção angular em soldagem GMAW-P robotizada de alumínio

The industry's interest in having a greater control of the deformations caused by welding is due to the geometric and dimensional tolerances been more and more precise in the project specifications, motivating the manufacturing engineering to develop stable processes and to ensure routine production. Aiming at it, the main goal of this present work is to analyze how much routine situations used in automatic aluminum welding can influence on the angular deformations of this material. Using the alloy AA 5052 H34, and the automatic welding in pulsed GMAW process, three types of weaving were applied throughout the length of the weld, in butt joints assembled without groove and with 60 degrees single-V-groove, arranged transversely as well as longitudinally to the rolling direction of the plate. The measurement of the deformations was made by a three-dimensional equipment, before and after the welding, in three distinct regions in the specimens. The profile of the weld bead was the main factor for the different types of deformations found, as revealed by macrographical analysis. The 60 degrees single-V-groove had higher amplitudes of deformations as the joint without groove. The torch oscillation wasn't a variable of statistically significant influence on this amplitudes.

Repair Welding Effects on the Bending Fatigue Strength of AISI 4130 Aeronautical Steel used in a Critical to the Flight-Safety Structure

The aim of this study was to analyze the effect of successive TIG (tungsten inert gas) welding repairs on the reverse bending fatigue strength of AISI 4130 steel, which is widely used in components critical to the flight-safety. In order to simulate the abrupt maneuvers, wind bursts, motor vibration and helixes efforts, which generate cyclic bending loadings at the welded joints of a specific aircraft component called motor cradle, experimental reverse bending fatigue tests were carried out on specimens made from hot-rolled steel plate, 1.10 mm (0.043 in) thick, by mean of a SCHENK PWS equipment, with load ratio R = -1, under constant amplitude, at 30 Hz frequency and room temperature. It was observed that the bending fatigue strength decreases after the TIG (Tungsten Inert Gas) welding process application on AISI 4130 steel, with subsequent decrease due to re-welding sequence as well. Microstructural analyses and microhardness measurements on the base material, heat-affected zone (HAZ) and weld metal, as well as the effects of the weld bead geometry on the obtained results, have complemented this study.

Estudo Comparativo de Juntas Soldadas a TIG e Laser Empregando-se Ti com Pureza Comercial Utilizado em Prótese sobre Implantes

Welding in the dentistry has been used for great part of the specialized dentist-surgeons in the implants area to solve prosthesis supported by implant adaptation problems. The development of new equipments Laser and TIG allowed a larger use of these processes in the prosthesis production. In this work, it was studied welded joints made by Laser and TIG, using commercial purity titanium, cpTi, applied in prosthesis supported by implants. The weld characterizations were carried out by light microscopy, EDS_elementary mapping, microhardness and tensile test. Through metallographic characterization, the weld bead presented a martensitic microstructure in the Laser welding process, originated from shear provoked by deformations in the lattice. This caused structural changes of the transformed area, which determines a fine plate-like morphology. In the weld bead from TIG, besides presenting higher hardness, was observed formation of Widmansttaten structure, which is characteristic of a geometric model, resulted of new phase formation along of the crystallographic plans. The martensitic structure is more refined than Widmansttaten structure, due to the high-speed cooling (10(3)degrees C/s) imposed by the Laser process.

Investigation of the metal/porcelain interface in LASER-welded Ni-Cr-Mo alloy

The interface formed between the metal and the porcelain of laser-welded Ni-Cr-Mo alloy was studied on a metallurgical basis. The characterization was carried out by using optical microscope, electron scan microscopy and X-ray dispersive spectroscopy techniques and mechanical three-point flexion tests, in the laser-welded region, with and without porcelain. The union of the porcelain with the alloy is possible only after the oxidation of the metallic surface and the subsequent application of a bonding agent known as opaque. The porcelain applied to the base metal and weld bead showed different behaviours - after the flexion test, the base metal showed cracks, while that in the weld bead broke away completely. It was noted that the region subjected to laser welding had lower adherence to the porcelain than the base metal region, due to microstructural refinement of the weld bead. These results can be shown by the X-ray dispersive spectroscopy carried out on the regions studied. The flexion tests demonstrated that the Ni-Cr-Mo alloy subject to laser welding had significant alterations in its mechanical properties after application of the porcelain.

Caracterização microestrutural do metal de solda depositado por arco submerso em chapas de aço-carbono estrutural

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Soldagem GMAW-P robotizada de alumínio: influência do tipo de chanfro, tecimento e sentido de laminação na distorção

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Desenvolvimento de uma EPS especificação de procedimento de soldagem para união de chapas de aço ASTM A131 com processo FCAW

In any welding process is of utmost importance by welders and responsible qualities of the area understand the process and the variables involved in it, in order to have maximum efficiency in welding both in terms of quality as the final cost , never forgetting, of course, the process conditions which the welder or welding operator shall be submitted. Therefore, we sought to understand the variables relevant to the welding process and develop an EPS (Welding Procedure Specification) as ASME IX for cored wire welding process (FCAW Specification AWS) with shielding gas and automated process for base material ASTM a 131, with 5/16 thick, using a single pass weld, for conditions with pre-and post-heating and the destructive testing for verification and analysis of the resulting weld bead

Caracterização microestrutural de uma estrutura tubular aeronáutica submetida a sucessivos reparos de solda TIG

This work examines the possible effects of successive repair procedures on the microstructure of welded steel SAE 4130 by TIG welding process. Discussions and results were made about the metallographic analysis , non-metallic inclusions and microhardness tests , which were conducted on samples taken from the cradle engine component after the end of its life , a model airplane T-27 Tucano , made by EMBRAER and belonging were performed FAB . The choice of such component is due to the fact that this is critical to flight safety since it provides support for the aircraft engine . Thus regions of the weld metal , base metal and heat affected , with samples of the original weld bead , free of weld bead and also with four rework procedures for TIG welding zone were analyzed . It was found that after the fourth rework there is an increase in the amount of martensite , which may weaken the material with respect to resistance to fatigue. It was also found that the regions of the heat affected zone and weld metal have higher microhardness values when compared to those found in the base metal due to favoring the formation of ferritic and tempered martensite microstructures . Moreover, a welding process promotes a region with less non-metallic inclusions than metal base , which also explains the difference in the results obtained

Análise metalográfica do titânio puro submetido à soldagem laser Nd: YAG e TIG

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Influência do desbalanceamento da onda retangular na liga de alumínio 6063-T6 soldada pelo processo TIG-CA

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Desarrollo, análisis y caracterización de procesos de soldeo térmico de espumas de aluminio

Uno de los retos actuales aún pendiente de lograr trabajando con espumas de aluminio, es el desarrollo de métodos de unión fácilmente reproducibles a nivel industrial que permitan la unión de espumas de aluminio entre sí o con otros componentes tipo pletinas, para así poder fabricar piezas de mayor tamaño o con formas complejas, a la vez que se conserven las propiedades y características principales de las espumas de aluminio, tanto en la zona principal de unión o cordón, como en la interfase y zona afectada térmicamente, que se encuentran anexa. Los actuales procesos de unión más utilizados con espumas de aluminio, se basan principalmente en adhesivos y uniones mecánicas. Estas soluciones a priori válidas, añaden problemas técnicos a determinadas aplicaciones de las espumas que frenan la completa integración de estos materiales en un entorno de fabricación flexible y global. Por esta razón, los actuales procesos de producción de las espumas de aluminio se restringen a determinadas ofertas hechas a la medida del cliente, no pudiendo atender por falta de soluciones, a una gran parte del potencial mercado de estos materiales. En el presente trabajo de investigación se han desarrollado y caracterizado diferentes métodos de unión de espumas de aluminio, en configuración a tope y de espumas de aluminio con pletinas en configuración a solape, basados en procesos por soldeo térmico. One of the current challenges even pending of being achieved working with aluminium foams, is the development of easily reproducible methods at industrial level that allow the joint of aluminium foams between them or with other elements as for example aluminium plates for making bigger pieces or with more complex forms, remaining simultaneously in the weld bead the properties and main characteristics of aluminium foam, so much in the joint area or interface, since in the affected closer thermal zone. Currently, the most used joint processes for applying to aluminium foams are based mainly on adhesives and mechanical joins. These solutions initially valid, add technical problems to certain aluminium foams applications, which stop the complete integration of these materials in a more flexible and global manufacture environment. For this reason, current aluminium foam manufacturing processes are restricted to certain offers done to a specific customer requirement, not being able to attend for lack of available solutions, to a great potential market of these materials. In the present work, different joint methods between aluminium foams and between aluminium foams and plates for butt and lap configurations have been developed and characterized based on thermal welding processes.