Method of non-contact detection of defect in coated cylinder

The method of non-contact detection of defects in a ferromagnetic cylinder is proposed. This method is designed to test of corrosion or mechanical damages of underground and underwater pipelines metal. This can be used to find defects in long cylindrical objects such as bars, wires, tires under insulation and process pipes under coatings. The results of calculations of the effect of a steel pipe defect on the distribution of the magnetic field are presented. The procedure for excitation of a rotating magnetic field, its reception and visualization of field anomalies to detect cylinder defects is described.