An experimental test of the new welding system, High Frequency Preheating plus Plasma (High Plasma), was carried out in the commercial line to make SUS304 welded tube of 60, 5 mm outside diameter, 3 mm wall thichness. A high frequency induction coil and an impeder assembly were set up in the preceding position of a plasma torch which is located between pairs of squeeze roll. An available speed of the High Plasma could be at least doubled by preheating at the temperature of 723 to 773 K (450 to 500°C), and also accompanied the satisfactory weld quality as well as small electric power consumption of High Frequency preheating.
