Deperming technology in large ferromagnetic pipes

This report describes a deperming technique for reducing the arc blow effect in DC welding of ferromagnetic pipelines. The technique is based on compensation of the axial field in the welding gap by a re-magnetization of the pipe near the joint. The re-magnetization is produced with a coil set driven with a bipolar impulse. We examined an axisymmetrical model of the pipes with commercial finite element software (ANSYS). The model has plane symmetry in the middle of the welding gap. Initial magnetization levels in the model were determined from a preliminary experimental investigation of an oil pipeline in Ukraine. A prototype of the deperming device was fabricated, including a coil set, an impulse power supply and a magnetometer. A magnetic measuring procedure was also developed to optimize the transient current in the coils. Our experimental results have confirmed the efficacy of this deperming technique, which provides an acceptable level of the magnetic field in the welding gap.