Evaluation of the Influence of Residual Magnetism on GTAW Welding of Parts Inspected by the Magnetic Particle Method

Abstract

Non-destructive magnetic particle testing is a technique widely used in industry to identify surface and subsurface discontinuities in ferromagnetic materials, both in the manufacturing stages (semi-finished parts) and in service conditions. The parts need to be subjected to a magnetic field, which allows magnetic particles to move and accumulate in areas with discontinuities. However, residual magnetism can cause problems in processing stages such as welding and machining. With this in mind, this study set out to investigate the behavior of parts subjected to magnetic inspection and the possible consequences of residual magnetism. Parts of different chemical compositions were subjected to the test and had the magnetic field strength values measured and underwent welding steps (GTAW). It was possible to identify the low-intensity occurrence of the phenomenon of magnetic blowing during welding. As it does not represent a high risk to the result of the weld, it can be concluded that, for this specific case and under the conditions established for the experiments, demagnetization after the test is optional. Demagnetization after the welding processes can be explained by the increase in temperature above the Curie point.

Key-words:
Non-destructive testing; Magnetic particles; Residual magnetism; Demagnetization; Welding