It can be traced back to the high frequency welding of 1950 s. It is a new welding process that uses the skin effect and proximity effect generated by high frequency current to realize the docking of steel with other metal materials. The emergence and maturity of high-frequency welding technology has directly promoted the development of the straight welded pipe industry, and is the key to the production process of ERW Steel Pipe. The quality of high frequency welding directly affects the overall strength quality level and production speed of welded pipe products ,. Basic principle of high frequency welding so- Known as high frequency, compared to the frequency of 50hz AC, it generally refers to the high frequency current of 50khz to 400 KHZ. When the high-frequency current passes through the metal conductor, there are two peculiar effects: skin effect and proximity effect. High-frequency welding is to use these two effects to weld the steel pipe. Then, these two effects are actually skin effects, referring to a certain frequency of alternating current density that is not evenly distributed across all crosses when passing through a conductor The section of the conductor, which is mainly concentrated on the surface of the conductor, the current density on the surface of the conductor is large, and the inside of the conductor is small, so we call it vividly: \"Skin Effect \". It must be noted that although steel is a conductor, its penetration rate will decrease with the increase of temperature, that is, when the temperature of the steel plate rises, the penetration rate will decrease and the effect of the skin will decrease. Proximity effect means that when the high frequency current flows back through the two adjacent conductors, the current flows centrally to the edges of the two conductors, even if there is a short edge in the two conductors, the current also does not flow along a shorter path, which we call a \"proximity effect \". These two effects are the basis for achieving high-frequency metal welding. And use the skin effect to concentrate the energy of high-frequency current on the surface of the workpiece; The proximity effect is used to control the position and range of the high-frequency current flow. The current speed is fast, can heat and melt the adjacent edge of the plate in a very short time, and finally realize docking by extrusion.