Magnetic Sensor for the Defect Detection of Steam Generator Tube With Outside Ferrite Sludge

Steam generator tube in nuclear power plant is a boundary between primary side and secondary side. Nondestructive test for the steam generator tube, eddy current testing (ECT) method has been carried out. In case of bobbin-type ECT probe, transverse defect, defect with ferro-phase, outside of tube having ferrite sludge were very difficult to detect. To overcome these problems, a motorized rotating probe coil (MRPC) probe was developed but scan speed is slow and not effective method in time. In this work we have developed a new sensor having U-shape of yoke to measure permeability variation of test specimen, which can detect ferro-phase generated as well as normal defects in the tube material of Inconel 6oo. Electronics for signal processing, 2-phase lock-in amplifier per sensor, ADC, and embedded controller were employed in one probe and measured digital data were transmitted to the PC data acquisition software using RS232C interface. Using the developed sensors we have applied to detect defects in the tube outside with ferrite sludge which is very difficult to detect conventional bobbin-type ECT probe. Developed sensor could measure defect size of 0.2 mm times 10 mm times 0.44 mm (width times length times depth) for the normal defect and defect outside of tube having ferrite sludge. We expect the developed sensor could detect defects like as MRPC probe and scan sensor speed like as bobbin-type ECT probe.