ERW tubes and pipes are cold formed from a strip of steel (skelp) pulled through a series of forming horizontal and vertical rollers positioned to gradually form the flat strip into a tube, which is then allowed to pass through the welding process. In most mills, the position of the weld seam is the 12 o'clock position (top). High-frequency welders also require the use of an inside impeder, a cylindrical fer-rite cylinder used to concentrate the induction current (heat) from the weld process on the skelp edges, especially on the inside circumference.
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