Window multi-frequency ECT for multi-coils in a RFEC system for FBR SG tubes

摘要

The paper presents the application of window multi-frequency (WMF) algorithms using eddy currents (EC) to the in-service inspection of fast breeder reactor (FBR) steam generator (SG) tubes in the presence or absence of sodium. Detection of defects filled with sodium were investigated based on three dimensional finite element simulations, using an in-house developed code, of remote field eddy current (RFEC) multi-coil sensors system. WMF algorithms, previously confirmed using 3D FEM simulations, are validated for the first time in the paper for multi-coil RFEC systems with either experimental measurements or mixed simulations-measurements from defects near tube support plate (SP) of FBR before and after sodium draining. The efficient suppression of combined sodium and SP signal is acquired through the use of WMF to enhance the signal/noise ratio (between 6 and 9) for detection of partial (up to 30% depth from tube wall thickness) or full circumferential (20% depth) outer tube defects.