Eddy-current inspection for steam-generator tubing program. Quarterly progress report for period ending September 30, 1978

Eddy-current methods provide the best in-service inspection of steam generator tubing, but present techniques can produce ambiguity because many independent variables affect the sig nals.The current development program will use mathematical models and develop or modify computer programs to design optimum probes, instrumentation, and techniques for multifrequency, multiproperty examinations.Interactive calculations and exper imental measurements are made with the use of modular eddycurrent instrumentation and a minicomputer.These establish the coefficients for the complex equations that define the values of the desired properties (and the attainable accuracy), despite changes in other significant variables.The final eddycurrent instruments will contain on-board microcomputers for real-time data processing and interpretation.The computer programs for calculating the accuracy with which various prop erties can be measured indicate that the tubing wall thickness and the defect size can be measured much more accurately than is currently required, even when other properties are varying.A prototype model of the modular three-frequency eddy-current instrument with its own internal microcomputer has been completed and tested.Alloy 600 tubing standards have been machined, with variations in diameter wall thickness, and defect size and location; tube support plates with various inner diameters have also been machined.