Improvement of detection of small defects located near or far from welds of magnetic steam generator tubes using remote field eddy current

Mihalache, O. ; Yamaguchi, Toshihiko ; Date, Koji*; Ueda, Masashi ; Yamashita, Takuya

Using numerical software optimization, new remote field eddy current systems based on small multiple vertical and horizontal coils were build in laboratory to investigate smaller outer tube defect detection in ferromagnetic steam generator tubes of nuclear power plants. Small defects located on the outer tube surface as pinholes axial and circumferential notches are better visualized using the C-scan experimental data, even when these defects are located near weld zones and the inspection is done from the inside of the tube. Comparing with the classical system, based on Bobbin coils, the new system shows an improved detection and a better coping with the electromagnetic signal noise in the data arising from unknowns in the: weld structure (from electromagnetic point of view), probe wobbling during inspection, variation in the inner tube surface.