Qualification of the LF-eddy current technique for the inspection of stainless steel cladding and applications on the reactor pressure vessel

As part of the re-inspection of the reactor pressure vessel of the nuclear power plant. the low-frequency-eddy current technique was implemented durin g the 1995 outage. Since then, this inspection technique and the testing eq uipment have seen steady further development. Therefore, optimization of th e entire testing system, including qualification based on the 1995 results, was conducted. The eddy current testing system was designed as a ten-chann el test system with sensors having separate transmitter and receiver coils. The first qualification of the testing technique and sensors was performed using a single-channel system; a second qualification was then carried out using the new testing electronics. The sensor design allows far a simultan eous detection of surface and subsurface flaws. This assumes that testing i s performed simultaneously using four frequencies. Data analysis and evalua tion are performed using a digital multi-frequency regression analysis tech nique The detection limits determined using this technique led to the defin ition of the following recording limits for testing in which the required s ignal-to-noise ratio of 6 dB was reliably observed. . Detection of surface connected longitudinal and transverse flaws: . notch, 3 mm deep and 10 mm long, for weave bead cladding; . notch, 2 mm deep and 20 mm long, for strip weld cladding. . Detection of embedded planar longitudinal and transverse flaws: . ligament of 7 mm for 8 mm clad thickness and 3 mm; 3 . ligament for 4 mm clad thickness, notch starting at the carbon steel base material with a length of 20 mm. . Detection of embedded volumetric longitudinal and transverse flaws: . 3 mm diameter side-drilled hole (SDH) for 8 mm clad thickness; ligament, 4 mm. For 4 mm clad thickness: diameter, 2 mm SDH; ligament, 2 mm. All SDHs are 55 mm deep. (C) 2001 Elsevier Science B.V. All rights reserved.