EDDY CURRENT FLAW DETECTOR

An eddy current flaw detector particularly for use inside a steel pipeline, comprising an alternating or pulsating current drive coil having its axis essentially perpendicular to the pipe wall or other workpiece and surrounding at least one eddy current sensor. The sensor is formed by a C or E shaped core, which may be either ferrite or other ferromagnetic material such as laminated iron, having the free ends of the two or three legs thereof adjacent the workpiece, with a pair of sense coils wound approximately symmetrically on the core and connected, preferably in series reinforcement, to give a null signal in the absence of flaw. Where an array of sensors is used within a single drive coil to increase coverage, these are preferably arranged in a chevron or herringbone pattern with chevron axes oriented in the direction of scan in order to decrease directional sensitivity. Signal processing circuitry is provided which typically includes a narrow band pass synchronous amplifier tuned or gated by reference to the same signal that is used to drive the drive coil.