Comparative Study of Typical Electromagnetic Heating Methods in Welded Pipe: Induction Heating Versus Contact Heating

Typical electromagnetic heating techniques include induction heating (IH) and contact heating (CH). The study of these techniques in welding has always been a controversial topic owing to the lack of straightforward quantitative analysis of heat transfer characteristics. Therefore, to explore the comparative nature of heat transfer in CH and IH, high-frequency welding of ferromagnetic materials was studied. Our results revealed quantitative differences between the two heating methods in terms of heating rate and intercritical heat-affected zone (ICHAZ). Compared with IH, CH resulted in a higher active current accumulating at the V-shaped angle of a welded pipe and a greater heating rate for a thick-walled pipe, because of variable magnetic flux leakage in IH. Given identical electrical input, the area of the heat-affected zone (HAZ) in the case of CH was found to be