Demagnetisation of Thick-Section Ferritic Steel Components for Electron Beam Fabrication
Status: Completed
Date Announced: February, 2012
Project reference: 21993
There is a resurgence of interest in welding thick section steels within the renewable energy, nuclear and fossil fuelled power industries. Although Electron Beam (EB) and narrow gap (NG) arc welding processes provide a cost effective and high integrity joining solution, the presence of residual magnetism in the materials can impede the effective application of these processes. This project will investigate how such fields arise and what practical steps can be taken to eliminate their effect during fabrication of heavy section low alloy steels. Experience with these materials is that they are easily magnetised and difficult to fully demagnetise. This is problematic in EB welding as the process is less tolerant to residual magnetism than conventional arc welding processes, and as section thicknesses increase the possibility of the occurrence of lack of fusion flaws, due to deflection of the beam resulting in a missed joint, is increased. In addition it has been noted that some arc welding processes, particularly in thick steel with NG joint details, are also sensitive to residual magnetism. As a consequence, there is a need to measure and mitigate residual magnetic fields in ferromagnetic materials. The project will examine the origins of residual magnetic fields in large structures, and will develop techniques for demagnetising of large components using numerical and experimental methods. The work will provide a framework for a European standard on assessment of residual magnetism and guidelines for demagnetisation for welding requirements.