Superduplex stainless steels (SDSS) are materials that have high mechanical strength and corrosion resistance and, for this reason, they are widely used in components for the offshore industry. Despite this, there are great challenges in the welding process of this material in relation to productivity and costs whilst maintaining the high quality of the weld produced. In reality, during the pre-assembly and assembly of SDSS pipelines at offshore platforms, backing gas protection of the root is executed until the last pass of the welding procedure. The most common gases used are helium, argon and nitrogen, or a mixture of these. Up to 3% of nitrogen is typically added to the mix to promote the stabilization of austenitic phase at the welding root surface. Due to the high cost of the protection gas, there is a market need to determine the pass or layer in which the root backing gas protection is effective, in terms of the mechanical properties and the corrosion resistance, because the region will be in constant contact with the fluid during the component service life. This work presents the results of the influence of the utilization of backing gas on the root of welded joints of superduplex stainless steel (SDSS) UNS S32750 piping, with a thickness of 9mm, welded by the gas tungsten arc welding (GTAW) process. The thermal cycle, nitrogen content and the toughness of the welding root were evaluated in function of the heat input for various samples with different levels of backing gas protection on the root. The primary objectives of this work are; the reduction of costs of the welding process of pipes and to show which layer requires backing gas protection on the root in function of the heat input.
Superduplex Stainless Steel; Welding, GTAW; Backing Gas; Heat Input
