Crack indications in pulsed eddy current testing: Behaviour of the signals and problems related to spatial resolution of probe coils

Detecting of cracks formed by thermal shock loads within the cladding for a nuclear pressure vessel nozzle is given as an example, on which problems related to the spatial resolution of probe coil systems are discussed. Investigations about the behaviour of the signals received from coil systems especially constructed for crack detection led to a numerical simulation of crack field indications. Matching those synthetical curves with curves obtained from real test conditions will provide the possibility of analysing cluster of cracks, which are normally not resolved by the applied coil systems. For reasonable time duration of computation, the knowledge of the local position of the single cracks had to be required. For this purpose, a novel, very small sized probe coil for the use with pulsed eddy current testing had been developed. (orig.)