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Avanços tecnológicos do processo TIG: técnicas inovadoras de alimentação de arame e procedimentos automatizados como contribuição para a união de tubos internamente cladeados

  • Riffel, Kauê Correa
Publication Date
Sep 22, 2018
Repositório Institucional da UFSC
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Abstract : The discovery of large oil reservoirs, under a geological salt layer called pre-salt, raised Brazil in oil overseas oil market. The exploration of these reservoirs becomes very attractive from the financial perspective, but the wells are found about 7 km deep, which create great challenges in oil extraction and transportation. Due to greater loads and hostile environments high performance materials are necessary. In this context, the application of clad pipes made of high mechanical strength steels, internally cladded with high corrosion resistant alloys, as Inconel 625, has been used as solution. In the traditional joining weld method of clad pipes, the joint is totally filled with Inconel 625 and depending on steel substrate can result in undermatching condition, since strength requirements are not achieved. In this way, the alternative is a bilateral pipe welding method, allowing the use of steel welding consumables in joint fulfillment passes, which meet the substrate strength properties. With this technique, the Inconel is circumferentially deposited in the pipe internal wall, just with aim of ensure the corrosion resistance. Therefore, the aim of this work is the study and application of TIG welding techniques to accomplish an internal circumferential welding with Inconel 625. The work also compares the use of different wire feed methods as dynamic and continuous wire feed, aiming to verify the effects over the weld pool and the development of a robustness welding process. Thus, the welding tests were divided in two steps. Firstly the welds were carried out in carbon steel plates with and without cladding. These ones were positioned at manly welding positions, which are encountered in an orbital process (flat, vertical and overhead). During the welding were carried out tracking filming by high speed camera and thermography. In the second step, the bests results reached in first one were reproduced in internally cladded steel pipes. Then, it was realized a weld beads visual inspection by videoscopy, in addition to macrography of the welds transversal section. As results, it is emphasized that dynamic wire feed improves the metallic transfer characteristics, avoiding electrode contamination susceptibility in difficult welding positions and, due to differentiated heat behavior in the weld pool and wire, provide weld beads with good surface appearance and homogeneity, enabling the pipes circumferential welding in 360º with higher robustness and repeatability (in process and weld bead geometry) than continuous wire feed.

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