Plasma arc seam welding process with preheating for welded stainless steel pipe

To improve the productivity of welded stainless steel pipe, new plasma are welding with preheating has been developed. The critical welding rate of plasma seam welding is restricted by the amount of molten metal that is generated in welding, and the separate bead that breaks out by the small amount of molten metal in high speed welding must be prevented. The preheating by high frequency current is efficient to increase this molten metal, and optimum preheating temperature for high speed welding is about 300 degrees C. This new welding process has twice productivity as high as conventional plasma are welding, and enables to manufacture the pipe of 3mm in thickness at a rate of 2.5m/min. At the preheating temperature over 300 degrees C, critical welding rate is decreased caused by the lack of plasma heat transmission to base metal with the surface oxide layer generated in preheating.