Abstract Welded joints for subsea systems are usually buttered with a nickel alloy, heat-treated and then joined together. Although the majority of these joints have been successful throughout their service, some have suffered catastrophic failure, leading to investigations into the possible causes. The use of heat treatment has been considered the primary cause for failure in this type of joint. The main objective of this article is, with background on the methodology used on Double-Layer Controlled Deposition Technique – DL-CDT, along with the LPTS decision diagrams, to determine the relations between the buttering parameters that allow the welding of subaquatic joints, and the low need for heat treatment. MIG single-bead-on-plate welding was executed on samples of AISI 8630M steel. The welded samples were submitted to metallographic analyses of their geometric and microstructural characteristics and the confection of decision diagrams. Among the 200 possible relationships between the buttering parameters, only one presented positive gaps over all criteria. Grain refinements were observed in the HAZ of joints buttered for the parameters approved by the decision diagrams, while for the joints submitted to the Post Welding Heat Treatment (PWHT) peaks of microhardness on the buttering interface were found, which may result in fragilization of that region.

Resumo O presente trabalho objetiva o estudo de técnicas de soldagem aplicadas a reparo de componentes fabricados em aço ASTM A387 Gr.11, largamente utilizado em aplicações da indústria do petróleo e gás. Devido ao regime de trabalho e necessidade de utilização de materiais com boa resistência mecânica e à corrosão, utilizou-se como metal de adição a liga UNS N06625 (Inconel 625). O processo de soldagem utilizado foi o MIG/MAG e a técnica de soldagem aplicada foi a dupla camada. A metodologia do presente trabalho foi dividida em etapas, sendo a primeira a realização de ensaios exploratórios para definir a relevância dos fatores de controle estudados. A segunda etapa consistiu na aplicação do critério de dureza e de microestrutura para definir as melhores relações de energia para aplicação da técnica da dupla camada. A técnica da dupla camada se mostrou eficaz na melhora das propriedades da microestrutura da ZAC-GG dos revestimentos, verificou-se intenso refinamento de grão. Houve também redução nas medidas de dureza e microdureza. Para ambos os gases de proteção utilizados (Ar+25%He e Ar+4%CO2) foi possível obter relações de energia com afastamentos positivos. Em todas essas relações a energia da segunda camada foi maior que a energia da primeira camada.

Abstract This work aims to study welding techniques applied to repair of components made of ASTM A387 Gr.11 steel, widely used in the oil and gas industry. Due to the working conditions it is needed use materials having good strength and corrosion resistance. UNS N06625 Ni-based alloy (Inconel 625) was used as the filler metal. MIG / MAG welding process was used to apply the temper bead welding technique with two layers. The methodology of this study was divided in stages, in the first one, exploratory trials were carried out to define the relevance of the studied control factors. In the second step, hardness and microstructure criteria were applied for defining the best heat input relations for the application of the double layer technique. The double layer technique was effective in improving the properties of the microstructure in heat affect zone coatings, it was found intense grain refinement. There was also a reduction in microhardness and hardness measurements. For both used shielding gases (Ar + 25% He and Ar + 4% CO2) have been achieved heat input relations with positive deviations. In all these relations the heat input of the second layer is greater than the heat input of the first layer.