ERW (electric resistance welding) steel tube is one of the most commonly found types of tube in the market. The manufacturing process consists of roll-forming a strip of steel into a tubular section and then subsequently welding the edges together using electric resistance to first heat up the edges and then subsequently forging them together.
The current is typically induced into the edges by high frequency magnetic induction. A coil around the tube, through which a high alternating current flows, generates an oscillating magnetic field which in turn induce the current in the edges of the strip. Forging the hot edges together between a set of weld-rolls then does the rest.
The advantages of using this form of welding are: