Intergranular stress-corrosion cracking (IGSCC), which has occurred in nuclear power plant piping systems, is detected ultrasonically. The principal problem is discrimination between the few acoustic reflections from flaws and the large number from geometry of the weld root and counterbore. This paper discusses two areas of recent work on the IGSCC problem: the development, fabrication, and initial testing of a miniature automated ultrasonic search head, and the detection and characterization of IGSCC using an imaging technique.
The search head contains a toroidal-axicon-lens system with folded acoustic optics. The resulting beam is remotely controlled to produce a small-diameter beam that is near parallel or defocused 2.5° or 5°. The transducer's linear and two angular motions and nearly all field operation steps are automated. This allows certified Level II inspectors, who are in short supply because of radiation “burnout,” to operate primarily from the radiationfree computer console area.
The imaging technique consists of comparing multiple images that present amplitude, position, and reflector “texture” information. The surface of IGSCC has small and highly irregular facets which scatter strongly in all azimuths at high frequencies. Other classes of targets have similarly distinctive characteristics.