Computer-aided Analysis of Eddy Current Rotating Probe Data*

Eddy current (EC) estimate of flaw size obtained from inservice inspection is often the primary means of assessing the structural integrity of steam generator tubes. Reliable prediction of failure pressure and leak rate in tubes with complex cracking requires more detailed information about the geometry and extent of degradation than is generally available from conventional bobbin coil examinations. High-resolution inspections with EC rotating probes are thus carried out on selected regions of tubing to provide the more extensive nondestructive evaluation (NDE) information that is needed to better assess flaw size and distribution. Interpretation of signals from complex cracking that are often distorted by coherent and incoherent noise can be a challenging NDE task. Studies at Argonne National Laboratory have demonstrated that computer-aided data analysis can be used for more accurate and efficient processing of the large amounts of data collected by such probes. The basic structure of a rule-based multiparameter data analysis algorithm is described in this paper. Multiple-frequency inspection data from a standard rotating pancake coil were used for the analyses. The codes were implemented as MATLAB scripts and provide, as the final outcome, profiles of flaw depth in a section of tube. Graphical user interface tools were devised to read the information needed to carry out various stages of data processing. These interactive tools allow conversion, calibration, analysis, and display of data in various formats. Representative cases of estimated flaw profiles are shown for tube specimens with laboratory-grown cracks (with and without simulated artifacts) that were used to assess sizing accuracy. The statistical analyses used to determine NDE performance are also discussed briefly. Results of investigations to date suggest that improved resolution and sizing accuracy can be obtained in a fraction of the time required for manual analysis. Argonne National Laboratory Energy Technology Division 9700 South Cass Avenue Argonne, Illinois 60439 E-mail: [email protected] COMPUTER-AIDED ANALYSIS OF EDDY CURRENT ROTATING PROBE DATA S. Bakhtiari, J. Y. Park, D. S. Kupperman, and W. J. Shack