The main process for which induction welding is used is longitudinal seam welding in tube production from metal strip. In a continuous process, the strip material is unrolled and the strip edges are moulded via a set of rollers to form a tube which is nearly closed except for a V-shaped gap. Here is where a ring-shaped inductor is situated. This induces a circulating current which also flows some way along both edges of the gap, heating these to melting temperature. With the help of squeeze rolls to compress the gap, the tube can thus be joined without any filler metal.
The weld seam is a weak point in the tube and must therefore be subjected to inductive stress-relief annealing after welding.