Investigations on a pulsed eddy current system for flaw detection using an encircling coil on a steel pipe

Conventional eddy current techniques have been used to a great extent for the detection of surface-breaking defects in conductive materials. However, the detection of subsurface defects is limited due to skin effect phenomena and material properties. Pulsed eddy current (PEG) techniques excite the probe's driving coil with a repetitive broadband pulse, usually a square wave. The resulting transient current through the coil induces transient eddy currents in the test-piece; these pulses consist of a broad frequency spectrutn and the reflected signal contains important depth information. Extensive research has been carried out on surface-type pulsed eddy current probes, with a gap in investigations for encircling type probes. The work in this paper employs COMSOL Multiphysics, the finite element (FE) modelling software, to investigate the behaviour of a new encircling probe design. This involves modelling of an encircling coil around a steel pipe with high lift-off to simulate non-conductive insulation. The 3D modelling of the coil wrapped around a steel pipe was employed and surface-breaking discontinuities were modelled. The simulation of these scenarios provided essential information about the behaviour of this probe design.