INSPECTION OF PIPE MATERIAL BY MULTIFREQUENCY EDDY CURRENT FLAW DETECTION

PURPOSE:To facilitate the inspection of defects in work by indicating a defect detection pattern with a phase detection of individual frequencies employing frequency thoroughly penetrating into work in eddy current and frequency developing near the surface thereof as test frequency. CONSTITUTION:From work 3 in which a defect 1 exists on the surface thereof while a corrosion 2 as factor of blocking detection exists in an area equivalent to 1/2 or less of the thickness on the back thereof, the surface defect 1 alone is detected with a coil 4 arranged on the back side. Test frequencies herein used are a frequency fL penetrating into the work 3 in eddy current at a level of more than thickness of the work in terms of depth and a frequency fH adapted to only receive changes in the impedance in a corrosion area 2 as noise factor. Eddy current detection are performed simultaneously using these two frequencies and phase detection outputs obtained from respective frequencies are indicated as a pattern on the X-Y coordinate using complex number. Even when the corrosion components are removed completely, a comparison is made with the pattern of the pre-corrosion state to facilitate devision on the quality of the work.