Historical overview on Vacuum suitable Welding and fatigue resistance in Research Devices

New inventions change the approach of vacuum suitable welding for research purpose. With orbital welding, laser welding and robot welding the possibilities increase to fabricate larger vessels more accurately. Despite this development there is still no perfect understanding on how to avoid virtual leaks and how to make such joints suitable for dynamic stress. By recalling its historical development, it is apparent how welding mistakes began occurring systematically and how to avoid them. With ASDEX-Upgrade as an example, it is shown how the attempt to conduct vacuum suitable welding has decreased the fatigue strength. ITER could repeat the mistakes of ASDEX-Upgrade even for unwanted welding (accidental fusing of joints).