Autogenous welding of copper pipe using orbital TIG welding technique for application as high vacuum boundary parts of nuclear fusion devices

Abstract

This research work describes the development of autogenous orbital gas tungsten arc welding for oxygen-free copper pipe. Neutral beam system for fusion devices consists of the different water-cooled component, which is designed and fabricated from pure copper to have the excellent thermal and electrical conductivity from the functionality point of view. Due to their application in a high vacuum along with the nuclear environment, a weld joint of full penetration configuration with a 100% volumetric examination is a mandatory requirement. Welding of pure copper has always been a challenging task because of its high conductivity and reflectivity, even with the use of high energy beam welding techniques (e.g., Electron beam welding and laser beam welding). Further, to compensate the heat dissipation, if the higher arc energy is provided to the base material, it results in the loss of strength, and therefore the selection of welding process and determining the parameters plays a crucial role for pressure withstanding welded connections. Though electron beam welding is a conventionally practiced process for welding of pure copper, the need for massive infrastructure limits its applicability to the large components. The present aim to have an understanding of the applicability of pulsed TIG process, in an autogenous mode for welding of pure copper material is presented. During this research work range of process parameters were used to assess the quality and strength of the joint. The range of process parameters was used to retain the mechanical properties of base material to the extent possible level. While doing, so weldability assessment was made for the shielding gas, welding program (pulse current, background current, and their duty cycles), joint geometry, arc length, and heat inputs. The mechanical and microstructural properties have been evaluated for the range of these parameters. The results have also been compared with the properties achieved by the electron beam welding process to understand what best researchers can achieve with the conventional welding process compared to high energy beam welding.