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Abstract
Welding is the principal process of manufacture used in the fitting and repair of tube sections. However, there is a lack of information about the alterations mechanically/metallurgically caused by the welding heat cycle, especially about the behaviour of the residual stresses. The objective of the first part of this work was to evaluate the welding residual stress in small diameter pipes used in oil refineries. Two-inch diameter pipes were welded using the manual GTAW process. AWS ER 70 S3 filler rods with diameters of 2.5 and 3.25 mm were employed. An electronic power supply was used, together with data acquisition systems to control the welding parameters. Stress measurements were carried out with an X-ray mini diffractometer. The axial residual stress profiles determined in the outer surface of the pipes were formed by compressive stresses in the weld region (the fusion zone and heat affected zone) and for tension stresses in the areas more distant from the weld bead. The evidence suggested that on the inner surface of the pipes, the stress profile is the opposite from that observed for the outer surface, with tension stress in the welding zone and compressive stress in the region further from the weld bead.
Acknowledgements
The authors would like to thank Professor Joaquim Teixeira de Assis and Professor Vladimir Monin of the IPRJ–UERJ (Nova Friburgo) for the laboratory support, ANP–PRH31 for providing the grant, the staff of PETROBRAS/LUBNOR/MI, especially Eng. Danúbio I. S. de Souza, Eng. Gerardo J. A. Pérez and maintenance technician João César Matias da Silva, the technical team of the PETROBRAS/CENPES Research Centre and the FINEP and CNPq investment bodies for their financial support.