Marcelo Ferreira Motta

Aspectos metalúrgicos de revestimentos dissimilares com a superliga à base de níquel inconel 625

To extend the life and reliability of pipes and equipment in oil & gas production and processing settings is a continuous demand. These aspects are essentially dependent on corrosion resistant alloys used. In this context, the weld overlay with Ni-based superalloys is a great interesting alternative, since improve the corrosion resistance without increase the cost of manufacture when compared to massive equipment. Thus, the objective of this study was to evaluate the metallurgical aspects of Inconel 625 weld overlays deposited by GTAW cold wire feed process. The welds were performed using a robotic workbench, an electronic power supply and a data acquisition system. The microstructural characterization was carried out using scanning electron microscopy (SEM), transmission electron microscopy (MET), electron dispersive spectroscopy (EDS) and X-ray diffraction. The results shown that the microstructure of overlays was formed by a gamma matrix and secondary phases rich in Nb. These precipitates were identified as Nb-rich Laves phase and a complex TiN/NbC.

A Study on out-of-phase current pulses of the double wire MIG/MAG process with insulated potentials on coating applications: part II

The part 1 of this work presents a study about the use of the out-of-phase current pulses technology applied to the Double Wire MIG/MAG welding process with Insulated Potentials on welded coating. High-speed digital back-lighted images were recorded to evaluate the influence of the levels of out-of-phase current pulses on the behavior of both metallic transfer modes and voltaic arcs configurations. The results showed that, with the electrodes positioned side by side and the mean currents below the transition current, the out-of-phasing parameter setting reduces the deviations of the arcs and changes the paths of the droplets. However, no significant effect was noticed on bead finishing or arc stability.

Avaliação do Uso do Tecimento sobre o Nível de Diluição e Geometria do Cordão de Solda na Soldagem TIG com Alimentação Automática de Arame Frio

This work aims to study the influence of arc waving in GTAW process with cold wire feeding deposited in single pass in order to use nickel-based alloys as coating to of petroleum and natural gas industries, where low dilution is needed to avoid reduction in corrosion resistance of the coatings. The welds were made using an robot workbench and a cold wire feeder system. The alloy used as filler metal was AWS ER NiCrMo-3 (Inconel 625) and the substrate was ASTM A516 Gr 60 steel plates. Welds were carried out with automatic cold wire feeding varying without arc waving and with triangular type arc waving. In addition the heat input was changed at three levels. The results showed that the use of arc waving has considerably influence on the geometry of the weld bead and the level of dilution. With use of arc waving the weld bead reinforcement was reduced and the width were increased, providing a better distribution of material on the workpiece surface, thereby reducing the reinforcement/width (R/W) ratio. This parameter indicates the degree of convexity of the weld bead. A high R/W ratio indicates that the degree of convexity may be excessive; thereby hampering an adequate overlap between the passes aiming to produce weld overlay without voids between them. Penetration and dilution showed similar behaviors, with significantly reduction under conditions where the arc waving was applied. These results show that the use of arc waving ensures a combination of low R/W ratio with low dilution, condition that is desirable to weld coatings.

Minimização de defeitos em revestimentos de superligas de níquel depositada pelo processo TIG com alimentação de arame frio

The objective of the present work was to evaluate the influence of the welding parameters in the formation of defects in weld overlays with nickel-based alloys, and its possible elimination through the correct adjustment of the welding parameters. Coatings were deposited with the nickel-based alloys type Inconel 625, Hastelloy C276 and Inconel 686, on C-Mn steel plates, using GTAW cold wire feed process. The planning of the experiments was accomplished being applied the Taguchi method. The control factors evaluated were the Energy Technique (ET), the welding heat input (E), the type of alloy (L), the shielding gas (G) and the type of arc oscillation (T). Other parameters were maintained constant, having previously been investigated. The results showed that the arc oscillation type in spiral, although it contributes significantly to reduce the dilution level, it cause a strong instability to the process, resulting in most of the cases in surface defects or defects among passes. The optimum condition to avoid defects among passes was identified by the Taguchi method, which was constituted by the following combination of control factors: 2-2-2-3-3, or be: I energy technique (TE-I); medium heat input level (Emedium); Hastelloy C276 alloy; Shielding gas Ar+He; Double-8 arc oscillation. The optimum condition for the welding without defects results in high dilution level not being indicated for the welding of resistant coverings to the corrosion.

Dilution Control of Weld Overlay Superalloys Using Taguchi Method

The objective of this work was to optimize the operational conditions aiming to deposit weld overlays with a minimal dilution and iron content as low as possible, and a thickness of weld higher than 3 mm just in a single layer. The alloys studied were Inconel 625, Hastelloy C276 and Inconel 686. The ASTM A516 Gr 60 steel was used as substrate. The welds were performed by GTAW cold wire feed process. The Taguchi method was applied to design the experiments and to evaluate the influence of the variables. The results showed that the arc oscillation (weaving) has a strong effect on the penetration and dilution of welds. The confirmation test for the optimal settings indicated that the additive model of the Taguchi method was not only confirmed the excellent reproducibility, but also provides sufficient confidence in the factorial effects.Copyright

Effect of square-wave AC GMAW on weld beam geometry

Aluminium welds are found in all fields relating to structures, especially those that need to balance mechanical resistance with light weight, durability, and corrosion resistance. Many features make the aluminium weld different from low carbon steel. When exposed to air, aluminium forms a film of tough and reflective oxide that must be removed before or during welding, which complicates the establishment and maintenance of an electric arc. Aluminium does not change colour when heated in a weld, which makes it difficult to identify the fusion point. As well as these factors, the electrode wire of aluminium is malleable, which makes supplying it with power more complex. Among the various processes used for welding aluminium, GMAW stands out for its high productivity, weld quality, and ease of automation. In all cases, the GMAW process depends directly on the type of metallic transfer and requires a careful adjustment to parameters to obtain suitable characteristics for the weld Traditionally, GMAW welding is carried out with direct current with a positive polarity electrode (DC+), which is known to give high weld penetration. However, aluminium welding, particularly with fine plates, requires special care to ensure that perforation and high levels of distortion do not occur in the welded part, along with other problems. To resolve these problems, alternating current (AC) welding can be used. A square wave alternating current may be a good solution, since it offers the ability to control the thermal input of the part, not just by a simple pulsed current, but also by control of the duration of each polarity. The square wave alternating current weld balances the advantages of CC+ with those of direct current with a negative polarity electrode (CC–). In CC–, most of the heat is concentrated on the point of the electrode wire, causing a higher rate of fusion and lower weld penetration. When CC + is used, most of the heat is concentrated in the part, resulting in a higher penetration of the weld. CC + is also characterised by good arc stability, as well as ease of obtaining stable metallic transfers in short-circuit and spray welding modes. In CC–, there is less arc stability, compared with CC +, and the predominant metallic transfer is globular, which is characterised by beads larger than the diameter of the electrode at low frequencies. In alternating current welding, this type of transfer may be avoided, limiting the life of the voltaic arc in the negative polarity, and so the adjustments allow metallic transfer only in a state of positive polarity. We can cite three general advantages of the GWAC process with rectangular wave alternating current in comparison with GWAC using CC+, which are: ease of welding fine plates, less distortion, and higher rate of deposition. This is due to the percentage of the current in the negative polarity of the AC, which increases the rate of fusion in the wire electrode, lowering the heating of the plate and reducing weld penetration. Despite these advantages, the use of alternating current in the GWAC process is still in its early stages, principally due to the inadequate technology of old welding sources, in respect to controlling the wave forms of the current, and, because of this, there have not been any exploratory studies covering this type of process. In this way, this work is proposed with the intention of exploring AC GWAC welding. The basic objective is to study the effect of welding with alternating current on the geometry and aspect of welds, using three percentages of negative polarity (10%, 20% and 30%), three wave forms and two levels of current to weld fine aluminium plates. This will be done with a basic comparative study between alternating current welding and conventional and pulsed direct current welding.

Estudo de Procedimentos de Soldagem MIG/MAG para Aplicação de Revestimentos de Liga de Níquel Inconel 625 em Aço Estrutural ASTM A387 Gr.11

O presente trabalho objetiva o estudo de tecnicas de soldagem aplicadas a reparo de componentes fabricados em aco ASTM A387 Gr.11, largamente utilizado em aplicacoes da industria do petroleo e gas. Devido ao regime de trabalho e necessidade de utilizacao de materiais com boa resistencia mecânica e a corrosao, utilizou-se como metal de adicao a liga UNS N06625 (Inconel 625). O processo de soldagem utilizado foi o MIG/MAG e a tecnica de soldagem aplicada foi a dupla camada. A metodologia do presente trabalho foi dividida em etapas, sendo a primeira a realizacao de ensaios exploratorios para definir a relevância dos fatores de controle estudados. A segunda etapa consistiu na aplicacao do criterio de dureza e de microestrutura para definir as melhores relacoes de energia para aplicacao da tecnica da dupla camada. A tecnica da dupla camada se mostrou eficaz na melhora das propriedades da microestrutura da ZAC-GG dos revestimentos, verificou-se intenso refinamento de grao. Houve tambem reducao nas medidas de dureza e microdureza. Para ambos os gases de protecao utilizados (Ar+25%He e Ar+4%CO2) foi possivel obter relacoes de energia com afastamentos positivos. Em todas essas relacoes a energia da segunda camada foi maior que a energia da primeira camada.

Evaluation of the Corrosion Resistant Weld Cladding Deposited by the TIG Cold Wire Feed Process

The aim of this study is to evaluate the microstructure and properties, resulting from the dissimilar welding of Ni-based alloys like Hastelloy C276 and Inconel 625 with ASTM A516 Gr 60 steel, through the deposition of overlays by the TIG welding process with cold wire feed. The results showed that it is feasible to produce coatings with low dilution levels in a single layer. Regarding the microstructure, there was a strong segregation of alloying elements during solidification. The phenomenon of microsegregation is directly or indirectly associated with the mechanism of corrosion attack. The shear resistance tests showed that coalescence between coating and substrate, provided a high shear strength, even with the possible presence of defects and high hardness martensitic zones. The immersion test in FeCl3 showed that the alloy 625 had lower CPT when compared to alloy C276. However, in the CPT temperature for the alloy C276, the intensity of the attack for the alloy 625 was lower than the alloy C276.

Evaluation of the effect of heat input in superduplex stainless steel deposition by the plasma powder process

Abstract Plasma powder surfacing is one of the latest processes for application of coatings, with control of dilution as its main feature. Surfacing with superduplex stainless steels is an interesting option for the construction and repair of equipment for applications in a highly corrosive environment, allowing the desired characteristics to be achieved: corrosion resistance and good mechanical properties. The aim of this work is to assess the ferrite content in the weld metal and the mechanical characteristics via microhardness profiles in surfacing of C-Mn steel pipes with deposition of UNS S32760 by plasma powder surfacing. Welding operations were carried out on pipes with deposition of SDSS, employing three welding heat input levels, varying the welding speed or the welding current. Then the geometry was analysed, the ferrite content in the weld metal was quantified and the microhardness profile was recorded. Variation in welding heat input caused changes in weld bead geometry, with variation in the welding current producing the most significant changes. Increase in heat input caused decrease in ferrite content of the weld metal. Regarding microhardness, only the condition with a higher level of welding current gave sufficiently high levels of microhardness in the weld metal.

A Study on the Effect of the Interpass Temperatures in Properties and Microstructures of the Alloy 625 Dissimilar Fusion Zone

The purpose of this study is to evaluate the effectiveness in the contribution of the interpass welding in the microstructures and properties of the dissimilar fusion zones produced with an alloy 625 and API 5L X65 steel pipes. Three multipass welded joints with v-groove, were made under the same welding parameters, therefore, changing only the interpass temperatures at: 150°C, 250°C and 450°C. The microstructural characterization was performed using the light microscopy and the scanning electron microscopy (SEM). The hardness test, charpy-V impact test and the transverse tensile test were conducted according to specific standards. The results have shown that all ruptures in the tensile tests occurred in the base metal. Both yield strengths and ultimate tensile strengths, have dropped to the 450°C interpass temperature. It was also observed a slight drop in the hardness with increasing interpass temperature. The Charpy-V impact test results showed no significant differences among the interpass temperatures. These said results indicated that the maximum interpass temperature for the alloy 625/X65 steel dissimilar welding is limited by the steel properties.