Field experiences with multifrequency-multiparameter eddy-current technology

A multifrequency/multiparameter eddy current system was assembled for the inservice inspection of pressurized water reactor steam generator tubing. Five steam generators were inspected for a total data base of approximately 11,000 tubes. Based on a comparison with conventional single frequency inspection methods, multifrequency/multiparameter eddy current technology offers significant improvements. Multifrequency eddy current, with its multiple frequency coil excitation, can offer benefits in reducing in containment data acquisition time by the performance of parallel tube tests; in addition the resulting broad spectrum data base is useful for the analysis of complex or nonunique signals which can arise during a steam generator inspection. Multiparameter eddy current offers an approach for the real time suppression of extraneous variables such as support plates/tube sheet, ID noise and denting. With appropriate mixing/basis frequency combinations, tube degradation in the presence of the extraneous variables can be more reliably detected and characterized.