Advancements of testing activities for development of in-bore welding tool for large feeding pipes of in-vessel components

This work presents the results of welding tests made on large pipes (DN200) in austenitic stainless steel AISI316L to be used in the nuclear fusion DEMOnstration power plant, DEMO. Samples were designed and manufactured to physically simulate the coupling and the alignment of the two pipes and their joining by an in-bore welding system. The trajectories describing the movement of the TIG torch during the operation were selected for the specific geometric configuration where the multi-pass operation has to start from the outer diameter of the pipe and to proceed inwards. The temperature in the material close to the welding zone was monitored before and after each welding pass. The shielding gas (argon) was used on the top of the weld seam and, in a specific ad-hoc set of tests, also on the back side (back shielding) in order to check the need to protect the rear (external) part of the weld seam during the first passes. Destructive tests were then carried out to preliminarily assess the quality of the joint. Several pieces of information were collected including suitable process parameters, the time required to complete the individual joint and wear of the tungsten electrode.