Performing higher speeds with dynamic feeding gas tungsten arc welding (GTAW) for pipeline applications

Most of pipeline welding still applies manual procedures, which increase production time and is stressful to the welding operator. This happens mainly due to the accurate melt pool control that hand operation enables. It yields high flexibility between material addition and heat source and is therefore adaptable to the welding condition and situation of each moment. This feature is not fully found when mechanized welding with automatic feeding is performed, despite every benefit of welding automation. This renders an optimized parameterization of a complex task. Automatic orbital welding is already a reality, though only applied in large scale in developed countries and/or by few expert companies from developed countries, due to such controllability, repeatability, and robustness difficulties. In this paper, a concept for dynamic wire feeding and respective implementation and analysis are presented. It consists of a low-frequency wire speed oscillation, aiming to decouple wire speed and arc power to a larger extent, which approaches to manual procedure as it guarantees user flexibility, but still keeping the benefits of welding automation. ASTM 139 Grade D tubes were welded under stable processing conditions. The macrographs did not indicate discontinuities such as porosity or lack of fusion, resulting in complete joint penetration. The average welding speed reached was 27.8 cm/min (10.9 in/min), much higher than that found by other authors.