Methodology for Measurement of Residual Stress in Welded Joints by the Technique of Pulse-Echo Ultrasound
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Methodology for Measurement of Residual Stress in Welded Joints by the Technique of Pulse-Echo Ultrasound A. Ballesteros-Hinojosa, J.J. Ruíz- Mondragón, J. Acevedo-Dávila and F. Macias-Lopez. Corporación Mexicana de Investigación en Materiales (COMIMSA). Calle Ciencia y Tecnología No 790 Fraccionamiento Saltillo 400, Saltillo, Coahuila, México, C.P. 25290. Email: [email protected] ABSTRACT Recently they have discovered a large number of oil wells, however these are found in deeper waters. So it is necessary to develop a repair's methodology and inspection for this type of system to prove its operation. This research was focused to establish a methodology for evaluating residual stress generated from the application of solder in a subsea environment, in order to establish whether there is a relationship between residual stress and the depth of the sea. For this purpose was used underwater electrodes (UW -CS- 1) and an API 5L X65 steel to the development of underwater welds, which was welded at 10 and 15 meters depth by a diver welder on site. The measurement of residual stress is developed using non-destructive techniques, the first one was ultrasound technique (UT) which was the technique proposed by viability to being applied in site and as a second option, was applied X-ray diffraction (XRD), with the objective to validate the results obtained by ultrasound technician. The results showed a similar behavior between both non-destructive techniques. In this study was observed the tendency to increase the level of residual stress with increasing the work depth. Keywords: welding, x-ray diffraction, thermal stresses, phase transformation, microstructure. INTRODUCTION With the consumption of oil reserves in the world, the need arises to look, operate and manage this resource to greater depths under the sea. Leading to use of appropriate technologies to ensure the extraction and the transportation of the oil. Several factors have effect under the weld quality, one of them is the hydrostatic pressure, however it is not known the extent that it affects for generation of residual stresses. The manual metal arc welding acts directly in contact with the water environment without any physical barrier to prevent direct contact of the arc [1-2], affecting mainly in the solidification time of the wet welds at difference with the dry welds [3, 4, 5]. In wet welding, heat generated by the welding arc is lost in greater proportion due the diffusion with water from the environment and an amount for the base metal conduction, anything contrary to what happens in the dry welds. Deriving from these changes, a further deterioration of the mechanical properties and susceptibility to the joint failure [1, 2, 5, 6, 7]. these are the main reasons why this type of welding is provisionally applied during the repair work and the materials applied has an equivalent carbon content less than 0.4%[5, 7]. Most research in underwater welding has been focused on improving the mechanical properties based primarily on the filler metal used for th
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