Demagnetization of thick section steels for electron beam welding

Demagnetization of thick section steels for electron beam welding
Colin Ribton


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High power electron beam welding can be applied to structures such as pressure vessels with wall thicknesses of up to 200 mm. Such applications often make use of steels that exhibit ferromagnetic properties. If the work pieces acquire a magnetic field, on assembly it has been found that reasonably strong external fields can be measured. Such fields do not need to be greater than 0.2 mT to cause an electron beam to be deflected, and such deflection can lead to missed joint defects at the cap or root of the weld. Correction of these weld defects in thick sections is costly.

This paper examines in detail the magnetic behavior of a steel frequently selected for nuclear plant – A508 grade 3. It has frequently been observed that this grade of steel can be more problematic to demagnetize, and beam deflection has been observed if no counter measures are taken. Special equipment has been designed to carry out the demagnetization of large segments, 200 mm thick and some 900 mm in length. A new approach has been taken to monitoring the magnetic field during the demagnetization cycle, which allows the effectiveness of the process to be assessed. Within this paper, magnetic modelling results, the demagnetization equipment, instrumentation and results are presented.

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Ribton C. Demagnetization of thick section steels for electron beam welding. Electrotechnica & Electronica (Е+Е), Vol. 57 (5-8), 2022, pp.56-61, ISSN: 0861-4717 (Print), 2603-5421 (Online)