Utilization of a Fisher linear discriminant function in IGSCC detection

The authors report the use of a Fisher linear discriminant function to separate geometric indications from IGSCC (intergranular stress corrosion cracking) indications in 304 stainless steel piping during an ultrasonic examination. A transducer selection criterion is outlined which enables the reflectors to be located efficiently. Dual element angle beam transducers are used for thick pipes and single element angle beam transducers for thin pipes. An algorithm selection criterion is then established as a function of both pipe diameter and thickness. Algorithms are all Fisher Linear Discriminant functions that make use of features like rise time of the RF waveform, envelope, pulse duration, fall time, partial powers for different frequency ranges. The authors explain the excellent performance of the dual angle beam transducers. Results are presented for a variety of test specimens