The conducted experiments showed that such defects are detected well enough by an eddy-current method.

The eddy-current set was designed to test zirconium alloy tubes under production conditions. An electronic eddy-current instrument has two channels. One channel is more sensitive to tube outer surface defects, the other - to inner surface defects. The specially designed encircling three-coil probe (one excitation winding, two differentially connected sensing windings), having an extremely local electro-magnetic field, and a signal filtering system permitted the sensitivity and output signal-to-noise ratios to be essentially improved. The eddy- current instrument is equipped with a logic tube rejection system. The equipment sensitivity is adjusted using a standard test specimen with a through wall hole of 0.1 mm diameter. The eddy-current method is included into the standard specification for zirconium alloy fuel cladding tubes.