Testing heat exchanger tubes using eddy current techniques with computerised signal analysis

Eddy-current testing is subject to interference problems when conventional rotating probes are used to test certain shaped tubes. Also random, irregular metallic deposits and oxide sludges, which may contain ferrous and non-ferrous particles, can cause random effects in the eddy-currents. A technique which can process, typify and classify defects has been developed. The development steps are discussed. The technique enables checks to be made on the complete straight part of a heat exchanger tube including the critical area associated with the header plate. For high test speeds a combination of transit coil and rotating head probe or a twin frequency technique can be used. On-line monitoring followed by off-line evaluation is possible. (U.K.)