Design, Fabrication, and Characterization of Staggered Array Radial Coil RFEC Probe for Small Diameter Ferritic Steel Tube

This article deals with a first of its kind design and fabrication of an arrayed multicoil probe for detection and characterization of defects in steam generator (SG) (9 Cr-1 Mo) tube used in fast breeder reactor (FBR) by remote field eddy current (RFEC) testing. Preliminary studies on the choice of detector orientation and the optimization of the detector size, shape, and angular position are carried out using finite element (FE) model and verified experimentally. Equal sensitivity, good spatial resolution, absence of dead zone, and defect characterization are the main requirements of a good array probe. With a multicoil arrangement, the array probe exhibits high detection sensitivity and high speed for defect detection around the whole tube without a need for probe rotation. The detailed knowledge of the number of defects and their axial and circumferential positions provided by an array probe helps in enhanced defect characterization. Furthermore, a methodology to create uniform thresholding to separate the defect and defect free regions is also presented. Experimental results show that the developed probe provides high detectability and is capable of reconstructing smaller defects.