Ricardo Reppold Marinho

Microstructure evaluation of UNS S32205 duplex stainless steel friction stir welds

UNS S32205 duplex stainless steel welds were performed by friction stir welding (FSW). Advancing and retreating sides showed distinct characteristics in the welded joint. The advancing side shows the strongest grain refinement which is corroborated by microhardness measurements. The microstructure characterization was carried out by optical, scanning and transmission electron microscopy. The thermomechanically affected zone displays austenite islands deformed in a ferrite matrix. The stir zone (SZ) showed a fine recrystallized microstructure providing an outstanding increase of hardness associated with better corrosion performance. Transmission electron microscopy and corrosion tests have corroborated the absence of intermetallic phases on welded joints.

Influência do molibdênio em propriedades do metal de solda na soldagem molhada com eletrodos óxi-rutílicos

A tecnica de soldagem subaquatica molhada com eletrodos revestidos apresenta um crescente potencial de aplicacao para reparos submarinos em elementos estruturais de unidades flutuantes de producao de petroleo (profundidade ate 20 m). Porem, ela apresenta problemas tais como o maior risco de fissuracao a frio e de formacao acentuada de porosidade. O presente trabalho tem como objetivo melhorar a resistencia mecânica do metal de solda de um eletrodo experimental do tipo oxi-rutilico. Foram estudadas as influencias de adicoes de Mo (ate 0,4% no metal de solda) na microestrutura e em propriedades mecânicas. As soldas foram realizadas em simulador de soldagem subaquatica em profundidade equivalente de 10m utilizando um sistema de soldagem por gravidade. As analises das micrografias mostrou que o aumento do teor de Mo no metal de solda diminui significantemente o tamanho medio de grao da regiao reaquecida de graos finos. O aumento do teor de Mo no metal de solda resultou, ainda, em aumento do limite de resistencia a tracao sem perdas de tenacidade e ductilidade ate aproximadamente 0,25%Mo.

Evaluation and Development of Electrodes for Wet Welding of Structural Ship Steels

To better understand the behavior of some commercial wet welding electrodes down to 20 m equivalent water depth as well as to develop a new electrode, a research program was initiated in 2007. This depth is considered the maximum expected in the in situ repair of structural parts of floating production units. The weld metal evaluation was done by microstructural characterization, Vickers hardness, Charpy and tensile tests, chemical analysis, and diffusible hydrogen measurement. The influences of pressure on the mechanical properties of the weld metal are presented and discussed on the basis of chemical composition, microstructure and porosity. The electrode under development showed promising results concerning the possibility to broaden the range of qualified welding procedures. This expectation is based on the good results of diffusible hydrogen, porosity, impact toughness and ductility down to 20 m equivalent water depth. The susceptibility of hydrogen cracking in weld metal and in heat affected zone was estimated comparatively. The presence of hydrogen cracks is discussed as an important limiting factor for the qualification of welding procedures in the class A of the AWS D3.6M:1999 specification.© 2010 ASME

Rotation Control Performance of a Friction Welding Repair System Using a Neural Network

This paper presents the rotation control performance of a friction welding repair system. The control parameters are adjusted by a neural network (NN). This control is capable of supporting the wide variations in torque that occur in this type of repair process. The rotation system consists of a hydraulic motor whose speed is controlled by a proportional directional valve. For this, a NN was developed with various structures composed of one, three, four and six neurons having activation functions of the following type: linear, quadratic, sigmoid and step. A theoretical plant was developed that simulates the behavior of the rotation system of a friction drive unity. This plant was used in the adjustment of the weights of the NNs by means of a genetic algorithm (GA). This plant was also used to evaluate the performance of NNs in the rotation control after their adjustment. The choice of the most suitable NN was made taking into consideration not only their control performance, but also the number of parameters to be adjusted, because the higher the number of these parameters, the greater the difficulty faced by the GA in the adjustment. Having selected the NN, its performance was compared to that of a PID controller. It was observed that the NN that reached the best performance was of one neuron with a linear activation function and its performance was higher than that of the PID controller.

Friction stir welding of steels for the oil and gas industry

Friction stir welding (FSW) has become a viable and important manufacturing alternative in several industries. This solid-state welding process offers considerable improvements in the mechanical properties of the joint. At the beginning it was developed as a joining alternative for light Al and Mg alloys and it eventually evolved to higher melting temperature alloys, such as steels, stainless steels, titanium alloys and Ni-based alloys. Most of these alloy systems are widely used in the oil and gas industry, where dissimilar joining among them is not uncommon. Conventional arc welding processes and more recently hybrid combinations with laser welding are widespread or under development to be used in these industries. However, metallurgical issues associated with the solidification process and hydrogen embrittlement impair the weldability of most of these high melting temperature alloys. Therefore, FSW is an interesting alternative to overcome some of the challenges associated with the similar and dissimilar joining of structural steels, stainless steels, and Ni-based alloys, especially for circumferential joining of pipelines. Recent developments on weldability studies of pipeline steels seeking the technology deployment will be presented ranging from parameters development, microstructural characterization, and fracture toughness to process robustness evaluation.

Wet Welding Field Trials in Shallow Waters for Structural Repairs in Floating Oil Production Units

Saving costs is a major attraction of wet welding application in structural repairs of offshore installations. Nevertheless, improve the quality of wet welding to get it as close as possible to plain structural steel quality and also qualify welding procedures in AWS D3.6 class ‘A’ have been challenges not consistently overcome. This paper describes wet welding trials in shallow waters (5m and 10m) with a rutile and an oxy-rutile type, both commercial electrodes. Two different base metal compositions were employed in the preparation of butt and fillet joints. The main objective is to amend new results of wet weds properties to those already published aiming the application of this welding technique under more reliable conditions and the qualification of welding procedures. The weldments were tested by Vickers hardness, Charpy V notch, tensile, shear strength, bending and fillet weld break tests, chemical and macrographic analysis. Some of these properties and diffusible hydrogen, obtained in laboratory with a mechanized gravity system, will also be presented in order to complement or explain the field testes results obtained. Both electrodes produced class AWS E 70XX weld metals and overall results according class “B” requirements of the AWS D3.6M:2010 code. Some good elongation results obtained encourage future trials to achieve class “A”. Barriers to the class “A” qualification of welding procedures in shallow waters are also discussed.Copyright