ERW steel pipe is fed into the machine, change the formation of a cylindrical tube through an induction loop or contact fillet, induction loop induced magnetic field near the edge of the current through the strip, the strip edge due to its resistance generated thermal resistance is heated, the heated extruded strip edges of the roll formed by extrusion welds. 

Defects in ERW Piping are: ① inclusions (black burnt oxide); ② Pre-arc (white burnt oxide); ③ fusion inadequate (slit); ④ edge fusion deficiency (edge waves); ⑤ Central fusion inadequate (Central cold welding); ⑥ stick welding (cold welding); ⑦ cast welding (brittle weld); ⑧ hole (pinhole); ⑨ jump welding. 

There are reasons other than the weld zone to produce welding defects, such as cold welding may occur due to the cooling pump cavitation (evacuated) phenomenon, can not make sufficiently cooled magnet, magnetic moment becomes hot, making concentrated in the V-shaped mouth of the current weakened, the current conduction along the back pipe, V-mouth lower heat, cold welding phenomenon occurs. All cooling pump does not work, before the complete failure of the magnet, increasing welding heat input can prevent cold welding defects.