An EMAT System for Detecting Flaws in Steam Generator Tubes

The detection of flaws in steam generator tubing is often made difficult by environmental considerations. The small diameter, 7/8 inch (2.2 cm), long, 70 feet (21.3m), tubes occur in large bundles with access only being possible from the inside of the end of each tube. Furthermore, inspection must be fully automatic when the steam generator is part of a nuclear power plant because of radiation exposure limits. Consequently, a couplant free probe which can be operated remotely at the end of an automatic probe puller is needed. This paper SUillllarizes the development of an EMAT systan for this application. The device uses periodic permanent magnet probes to excite the fundamental torsional mode traveling along the axis of the tube. Included is a discussion of data obtained during a recently completed feasibility study and a description of a prototype system presently under construction.