Abstract
This paper describes a new eddy-current inspection method that enables noncontact detection of the corrosion wastage of a pipe and the flaw/defect on a back of thick-walled magnetic and non-magnetic metal specimens. This paper proposes a method for detecting the faint signal component from the eddy current induced on the back surface of the specimen, by offsetting the strong signal from the surface eddy current with the external sinusoidal signal which amplitude and phase are equal to the detection signal of the sensor. Using this method, it is possible to detect the flaw/defect of the inner surface of a thick-walled pipe from the outer surface and to detect the corrosion wastage from the outer surface of a pipe with lift-off height of tens mm, and to detect the internal crack on the weld zone of a seam weld pipe from the outer surface of the pipe.
