Study on the Effect of Steel Support Plate during Electromagnetic Detection for In-Service Ferromagnetic Nuclear Pipe

Based on the electromagnetic detection technology inside of the ferromagnetic nuclear pipe, this paper theoretically analyzed the change of the magnetization state of pipe wall caused by steel support plate and studied the redistribution mechanism of the MFL (magnetic flux leakage) of defect that lies underneath the support plate. ANSYS modeling and simulation were used to analyze the MFL distribution characteristics of different located transverse defects which lay outside surface of the pipe and also underneath the support plate. Furthermore, verification experiments were finished with MFL inner detector which was realized by permanent magnet magnetization in consideration of the specificity of nuclear pipe with small diameter and thin wall. Simulation and experimental results show that the leakage magnetic field signal of defect is greatly reduced dues to the existence of support plate, besides, as the distance between the center of defect and support plate increases, the defect signal increases gradually.