The high frequency welding is based on the principle of electromagnetic induction and exchange charge in the conductor skin effect, proximity effect and eddy current heating effect, so that the weld steel edge of the local heating to the molten state by extrusion of the wheel, so that the butt welds to achieve crystal indirect together to achieve the purpose of the weld. High-frequency welding is an induction welding (or pressure contact welding), it is no need to weld filler, weld spatter, weld forming beautiful narrow heat-affected zone, welding welding good mechanical properties, etc. Therefore, in the production of steel pipes by wide range of applications. 
 The high-frequency welding of steel pipe is the use of AC skin effect and proximity effect, steel (strip) after roll forming, forming a cross-section circular tube disconnected, near the induction coil near the center of rotation in the tube a thermal effects of an electromagnetic induction loop or a group of impedance (magnetic bar), the impedance device with the tube openings in the role of the skin effect and proximity effect, the edge of the tube openings have a strong, centralized weld edge rapidly heated to the welding required temperature to achieve crystal indirect co-extruded by the pressure roller, the molten metal, formed by cooling a solid butt weld