Design of a Pulsed Eddy Current Sensor for Characterization of Sub-surface Defects in Ferromagnetic Steels

Ferromagnetic pipelines provide a major means for transportation of natural gas and oil. These structuresare usually buried underground which can be subject to deformation and corrosion. Therefore, there is a need forreliable techniques for evaluating the structural integrity of pipelines. This paper presents the development of a pulsededdy current sensor to detect and characterize sub-surface pitting defects on a steel specimen. The sensor comprises anexcitation coil excited with pulsed signal, a receiver coil internal to the excitation coil, and a ferrite core. Theoptimization of sensor dimensions, coil parameters, and testing parameters have been carried out by developing amodel and solving it using a finite element modeling software COMSOL. Moreover, to minimize the effects of the highmagnetic permeability of steel material and improve the detection sensitivity of pulsed eddy current sensor, the use ofmagnetization will be considered. Following the FEM simulations, pulsed eddy current tests are performed on a steelsample containing machined pitting defects at the laboratory facilities. The experimental results have shown that theproposed sensor has the potential to detect sub-surface defects in carbon steel specimens with thickness of 10mm.

Keywords:

Characterization of sub-surface defects , Pulsed eddy current , Magnetization