Reduced pressure electron beam welding in the power generation industry

Electron beam welding offers many advantages when considered alongside more conventional multi-pass arc welding processes for the fabrication of heavy section structures and components, particularly in high value materials for strategic applications. The ability to complete a weld in a single pass, without filler, almost irrespective of material thickness leads to huge productivity potential and avoids many of the problems associated with the multi-pass, arc welding processes. Traditionally, however, to apply EB welding successfully it has been necessary to envelop the components to be joined entirely in a vacuum chamber which has to be pumped to a pressure of the order of 10-3 mbar, Fig.2. This requirement has, to a large extent, inhibited the application of the process in the fabrication of large structures. However, EBW process benefits are potentially greatest forthe thick materials often employed in large structures. The prohibitive capital investment necessary for the construction of large vacuum chambers and the attendant cost of pumps has limited the use of the process. In addition, the high vacuum EB process is intolerant to poor surface condition and it is not always practical or economic to accurately machine joint details on large parts. (Example: fabrication and sealing of high level nuclear waste containers, C-Mn steel, Alloy 22.)