REMOTE FIELD EDDY CURRENT TESTING OF FERROMAGNETIC DOUBLE WALL TUBE

Abstract Ferromagnetic double wall tube has been under development to ensure the high reliability of the steam generator in fast breeder reactor. The airgap between the tube two walls should prevent the conventional nondestructive test methods from detecting defects especially in the outer tube wall. Thus the development of the in-service inspection technique of the double wall tube has become a necessity in the field. The authors have investigated the feasibility of applying the remote field eddy current technique (RFECT)to the in-service inspection of the ferromagnetic double wall tube. The energy flow and the distribution of low frequency electromagnetic field in the RFECf have been derived through finite element analysis. It has been shown that defects in both inner and outer tube walls can be detected with almost the same defect indication by RFECT if the air gap between the ube walls is as small as 0.04 mm.