Efficient Design of Remote Field Eddy Current Array Probe for Imaging of Defects in Small Diameter Ferromagnetic Tube

Array probe design is challenging in remote field eddy current (RFEC) technique due to the exciter and receiver separation. This paper presents the design of a multi-element RFECarray probe for imaging of defects in ferromagnetic steam generator tubes. Systematic investigations of the axial and radial magnetic field distribution at the remote zone are performed to understand their detection sensitivity. The radial magnetic field, showed higher perturbation near defect and hence higher sensitivity. Hence, receiver coiloriented in the radial direction is chosen for the array probe. Further optimization of the number of radial type receiver coils,diameter, height, and angular distance between the coils are carried out after systematic investigations with experimental studies and verified with model results. An array probe with eightnumbers of 4 mm x 4 mm (diameter and height) radial receiver coils placed at 45 degrees apart in the circumferential direction is found to be optimum to detect a1.2 mm diameter through hole. The performance of the radial receiver coil is encouraging for enhanced detection of defects and design of array probe.