The objective of the present research work is focused on evaluating the fatigue performance of different prefabrication welding procedures and determining the best compromise between manufacturing specifications, productivity and fatigue strength. Therefore, a large full scale fatigue campaign was launched at Tenaris to comply with this objective. SMLS SCR pipe (grade X65, outer diameter 10 3/4″, wall thickness 25.4 mm) was selected and manufactured according with the current most challenging offshore specifications and girth joints representative of prefabrication welding were manufactured in 1G position. Two different bevel geometries, two different welding techniques for the root pass and two different welding techniques for fill and cap passes were studied and compared. Finally, a post weld finishing technique has been implemented, aiming to improve the fatigue strength by removal of the weld root and cap reinforcements. Misalignment measurements, with stress concentration factor calculations, and post-tests fractographic investigations have been systematically performed on all the samples after testing. This activity was of paramount importance in determining the causes for fatigue initiation. The tests results demonstrated the important role played by the girth weld root internal geometry on the fatigue strength, the influence of the High-Low, the preferential fatigue initiation sites and the fatigue strength improvement by removal of weld reinforcements.

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Abstract. Welding is the most common process to join two types of metal. Capacitive welding is used in small alloys, jewelry and temperature sensors. A good quality welding is composed by a homogeneous distribution and uniformity of the material at welding point and a mass conservation, keeping the metal crystalline proprieties. Capacitive welding consists in submitting a metal to an electric arc, storing energy in capacitors, when released will melt alloy and creates a union. In an inertial chamber the atmosphere is controlled, and Argon is injected by a solenoid valve, responsible to control Argon from a cylinder. Argon is a shielding gas responsible for the non-inclusion of external elements in the weld. This study develops equipment able to make capacitive welding using the principles mass and energy conservation in alloys and gauges pre-established, of different types of metals in an inertial environment, with the objective of create a good quality and efficient weld with low cost equipment with easy manipulation.

ResumoEste trabalho analisa a tenacidade e dureza do metal de solda e ZAC da solda circunferencial de tubos X65, X70 e X80 para serviço ácido. Os tubos de elevada resistência, fabricados para serviço ácido, apresentam grande desafio para a soldagem. Os consumíveis e processos devem ser capazes de produzir uma junta soldada de alta resistência, baixa dureza e elevada tenacidade. O objetivo deste estudo foi identificar problemas de amolecimento ou fragilização da ZAC e verificar se a elevada resistência não prejudica a tenacidade e dureza do metal de solda. A metodologia incluiu a soldagem circunferencial e ensaios de dureza e CTOD. Os resultados mostraram que o metal de solda e a ZAC do X65 e X70, são adequadas para o emprego em dutos terrestres. Observou-se um amolecimento na ZAC do X70 e X80 que, de acordo com a literatura, não é crítico para projetos baseados em tensão. Para o X80, o CTOD da ZAC ficou abaixo do valor mínimo desejado, indicando que pode ter ocorrido a formação de zonas frágeis localizadas e resultando na necessidade de estudos complementares para ajustar os parâmetros de soldagem. Os resultados deste estudo servem como base para uma futura aplicação destes materiais em campo. Palavras-chave: Soldagem circunferencial; X70; X80; Serviço ácido. EFFECT OF GIRTH WELDING AT THE WELD METAL AND HAZ OF X65MS, X70MS AND X80MS PIPES AbstractThis paper analyses the HAZ and weld metal toughness and hardness of sour service X65, X70 and X80 girth welds. The high strength steel pipes produced for sour service introduce a big challenge for welding. The process and consumables applied should be able to produce a high strength, high toughness and low hardness welded joint. The purpose of this study was identify HAZ softening and embrittlement and whether the high strength does not affect the weld metal hardness and toughness. The methodology includes pipe girth welding, CTOD and hardness tests. Results showed that HAZ and weld metal of X65 and X70 pipes are suitable for pipelines. The X70 and X80 HAZ presented softening that, according to the literature, is not a critical point for stress based design. The X80 HAZ presented CTOD below the desired value. It indicates that local brittles zones could be present and new tests should be done in order to define better welding parameters.