The cross-sectional area of the impeder should be 70%-75% of the pipe inner diameter cross-sectional. If lower than 70%, efficiency will obviously reduce. The impeder used in H.F pipe welding has high initial permeability. UA ≥ 800 saturation flux density Bs value greater than 3000GS, the Curie temperature as high as possible and low loss as high as possible. In operation, impeder cooling should be adequate to prevent broken magnet or ineffective when temperature exceeds the Curie point.
The length and position of the impeder both have the effect on welding efficiency. The impeder total cross-sectional area and length should adjust to the welding pipe diameter. Usually, when welding large diameter pipe, the impeder length should be less. But the VEE shaping side should exceed the squeezing roll central line.
