Inspection Method of Outer Side Defect in Ferromagnetic Steel Tube by Insertion-Type Electromagnetic Sensor Using Square Wave Alternating Magnetic Field With DC Bias

The ferromagnetic steel tubes are used for heat transfer tubes of heat exchangers in power plants or oil plants. The outside defect in the ferromagnetic steel tube is generated by friction with the supporting steel plate (baffle). In this research, in order to detect the outer side defect in the ferromagnetic steel tubes, the electromagnetic inspection sensor probe of the type inserted in the ferromagnetic steel tubes using square wave alternating magnetic field with dc bias is proposed. The flux density and eddy current in the ferromagnetic steel tubes are estimated by the 3-D nonlinear finite-element method (FEM) taking account of minor loop curve using the play hysterons model method. The usefulness of this proposal inspection method is shown also from comparison with an experimental verification.