Resumo

Concern for the environment has motivated several studies on the use of new materials to extend the life of equipment operating in harsh environments in the oil sector. One alternative that has been used is the application of coatings with high corrosion resistance welding process materials. The objective of this study was to evaluate the effects of different welding parameters on the geometric characteristics, dilution, microhardness, microstructure and corrosion resistance of the coatings with Inconel 625 alloy deposited on the API 5L X70 steel used in oil pipelines to transport plate. The parameters were optimized using the factorial statistical experimental design for analysis of process parameters, and the results analyzed by Response Surface Methodology (RSM). Three deposits were carried out ½ overwrite process GMAW (Gas Metal Arc Welding), followed by cross-sectional analysis of samples for the geometrical and metallographic characteristics. For the analysis corrosion, the coating surface being machined to have a height of 3 mm according to Standard N-1707 Petrobrás coating. The electrochemical behavior of the coating surface (Inconel 625) was investigated at room temperature in NaCl solution using the technique of linear potentiodynamic polarization and electrochemical impedance spectroscopy. To reveal the corrosion resistance of the coatings, featuring some important parameters were considered, such as: the polarization resistance (Rp) and the corrosion potential (Ecorr). The results showed dilution values D (%) ranging from 12.77% to 24.88% in the maximum levels (18.99 KJ/cm) and minimum (8.34 KJ/cm) welding power, and the amounts the most important of 12.77%. As to the corrosion resistance, the results were more satisfactory for the highest level of welding power.Keywords: GMAW; Coating; Corrosion. RESUMOA preocupação com o meio ambiente vem motivando diversas pesquisas sobre o uso de novos materiais para prolongar a vida útil de equipamentos que operam em ambientes agressivos no setor de petróleo. Uma das alternativas que vem sendo utilizada é a aplicação de revestimentos com materiais de alta resistência à corrosão por processo de soldagem. Objetivou-se neste estudo avaliar os efeitos dos diferentes parâmetros de soldagem sobre as características geométricas, diluição, microdureza, microestrutura e resistência à corrosão dos revestimentos com liga Inconel 625 depositados sobre chapa do aço API 5L X70 utilizado em dutos para transporte de petróleo. Os parâmetros foram otimizados utilizando o planejamento experimental fatorial completo para analise dos parâmetros de processo, sendo os resultados analisados pela Metodologia de Superfície de Resposta (MSR). Foram realizados três depósitos com sobreposição de ½ por processo de soldagem GMAW (Gas metal arc welding), seguido de corte transversal das amostras para a analise das caraterísticas geométricas e metalograficas. Para as analises de corrosão, as superfície do revestimento foram usinadas ficando com uma altura de 3 mm de acordo com a norma N...

Metallic materials undergo many metallurgical changes when subjected to welding thermal cycles, and these changes have a considerable influence on the thermo-mechanical properties of welded structures. One method for evaluating the welding thermal cycle variables, while still in the project phase, would be simulation using computational methods. This paper presents an evaluation of the temperature field and residual stresses in a multipass weld of API 5L X80 steel, which is extensively used in oil and gas industry, using the Finite Element Method (FEM). In the simulation, the following complex phenomena were considered: the variation in physical and mechanical properties of the material as a function of the temperature, welding speed and convection and radiation mechanisms. Additionally, in order to characterize a multipass weld using the Gas Tungsten Arc Welding process for the root pass and the Shielded Metal Arc Welding process for the filling passes, the analytical heat source proposed by Goldak and Chakravarti was used. In addition, we were able to analyze the influence of the mesh refinement in the simulation results. The findings indicated a significant variation of about 50% in the peak temperature values. Furthermore, changes were observed in terms of the level and profile of the welded joint residual stresses when more than one welding pass was considered.

Resumo IntroduçãoAtualmente no Brasil a demanda energética apresenta uma projeção crescente o que faz com que se intensifiquem os investimentos no setor de petróleo e gás, este fato justifica a procura por técnicas de menor custo para montagem de dutos. Na linha de redução de custos uma iniciativa é a utilização de tubos com menor espessura de parede e processos de soldagem com maior produtividade.A característica citada para os tubos conduz à utilização de aços de alta resistência e baixa liga que possuem alta resistência a esforços, boa tenacidade e boa soldabilidade, função de uma combinação de baixo teor de Carbono e processos termomecânicos de fabricação.Uma classificação de aços indicados para o transporte de petróleo e gás é especificada na API 5L [1], sendo o aço em estudo classificado como API 5L X80, vários trabalhos reportam a boa soldabilidade deste aço [2,3,4,5].Durante a soldagem destes aços, se a taxa de resfriamento é alta, a austenita enriquecida de carbono transforma-se parcialmente em martensita e a austenita restante fica retida à temperatura ambiente formando o microconstituinte AM, que pode resultar em zonas de fragilização localizada que degradam a tenacidade na região de grãos grosseiros da zona termicamente afetada -ZTA GG [6]; logo, para que ocorra boa tenacidade na zona termicamente afetada -ZTA é importante observar a quantidade, tipo e distribuição do constituinte A-M ai presente [7]; Davis e King [8] enfatizam que a presença do constituinte A-M não é necessariamente nociva, depende da sua fração volumétrica, morfologia e dureza, fato também observado por

Residual stresses in a welded joint of ASTM A131 grade AH32 steel was measured either by the X-ray diffraction or by displacements of referenced points measured on a coordinate measuring machine before and after heat treatment. For all tests, the welding was performed with Shielded Metal Arc Welding, vertical-up position, by a certified welder. After welding, some specimens were subjected to marking, made through small holes evenly spaced and mapped on a coordinate measuring machine. After labeling, the samples were subjected to heat treatment at temperatures nearby recrystallization. After heat treatment, the samples were subjected to new measurements by coordinate measuring machine to evaluate the displacements of the points produced by the recrystallization. In parallel, residual stress measurements were made by XRD for validation of this new methodology. The results obtained either by X-ray or by coordinate measuring machine showed a good correlation between the two measurement methodologies employed.