Hélio Cordeiro de Miranda

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.

Naphthenic corrosion resistance, mechanical properties and microstructure evolution of experimental Cr-Mo steels with high Mo content

One method to face the effects of naphthenic acid corrosion in petroleun refining plants is to use alloys with good resistance to this kind of corrosion. For this purpose, molybdenum additions to chromium containing steels are specially recommended. In this work, experimental Fe-9Cr-xMo (x = 5, 7 and 9 wt. (%)) ingots were cast, forged and hot rolled before being tested in a naphthenic acid environment. Evolution of the mechanical properties with composition is presented. The precipitation and dissolution of phases were investigated with the help of Thermocalc and electron backscattered diffraction (EBSD).

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

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.

Avaliação das tensões residuais em tubos de pequeno diâmetro soldados pelo processo TIG orbital

This work aims in evaluate the effect of orbital TIG welding on the joints residual stress level, the final microstructure and the superficial aspect of the weld filet, observing the welding energy, number of passes and the type of pulsation effects in small diameter pipes. The test specimens were welded with different energy, pulsation and number of passes levels and after that it were submitted to residual stress measurement in a X-Ray diffractometer, samples were extracted from the test specimens and it were submitted to metallographic analysis. The ending of this work is that: residual stress in the pipes outer surface are compressive, residual stress level in pipes goes down with increasing welding energy, it is smaller for pipes welded with pulsation and in this work it were not effectively influenced by number of passes. Metallographic analyses have shown expected microstructures for the employed material.

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.

Effect of Multipass Welding Using a Low Transformation Temperature Filler Metal on Residual Stress and Toughness

Residual stresses in welded components are consequence of stress and/or thermal gradients and influenced by factors such as joint geometry, variation in strength of the material, preheat temperature, heat input, post-weld heat treatment and phase transformation strains. During the 70’s, it was observed that the level of residual stress accumulated in a constrained sample during cooling from austenite could be reduced after transformation to martensite or bainite. Some works have evaluated effect of welding using a low transformation temperature martensitic filler metal on the level of residual stress in single pass joints. According to these studies, martensite start temperature in the range 200–250°C can be extremely effective for mitigation of tensile residual stresses. The outcome of most of these works was on one hand increase of fatigue life due to the mitigation of tensile residual stresses via transformation strains, on the other a significant reduction of the fracture toughness.In the present study, sections of API 5L class B steel tubes were multipass welded using a 12Cr-5Ni low transformation temperature filler metal in addition to a conventional filler metal. Residual stresses in the inner and outer surfaces were measured by X-ray diffraction. Aspects related to the improvement of toughness in the weld metal due to the tempering of one pass by the subsequent were also discussed.