Clear Flaw Image Construction in Eddy Current Nondestructive Testing Using CT Technique

Flaw images have recently been utilized in eddy current nondestructive testing in order to improve the evaluation accuracy of the surface flaw depth in the test material. The conventional eddy current testing can provide only blurred flaw images because of the expansion of the eddy current induced in the test material depending on the diameter of the circular test coil. As a result, eddy current testing has mainly been applied only to detect flaws and not to evaluate flaws in nondestructive testing.The authors have applied CT inversion technique to the flaw signal by a thin tangential test coil in eddy current nondestructive testing in order to obtain clear flaw images. Since the flaw signals obtained by eddy current testing are totally different from those from X-ray projection, the authors have converted the eddy current testing signals into those analogous to Radon transform and applied CT inversion technique to the resulting signals. The experimental results have indicated that the CT inversion technique provides far clearer flaw images and higher possibility of quantitative flaw evaluation than the conventional method.