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 structures are usually buried underground which can be subject to deformation and corrosion. Therefore, there is a need for reliable techniques for evaluating the structural integrity of pipelines. This paper presents the development of a pulsed eddy current sensor to detect and characterize sub-surface pitting defects on a steel specimen. The sensor comprises an excitation coil excited with pulsed signal, a receiver coil internal to the excitation coil, and a ferrite core. The optimization of sensor dimensions, coil parameters, and testing parameters have been carried out by developing a model and solving it using a finite element modeling software COMSOL. Moreover, to minimize the effects of the high magnetic permeability of steel material and improve the detection sensitivity of pulsed eddy current sensor, the use of magnetization will be considered. Following the FEM simulations, pulsed eddy current tests are performed on a steel sample containing machined pitting defects at the laboratory facilities. The experimental results have shown that the proposed sensor has the potential to detect sub-surface defects in carbon steel specimens with thickness of 10mm.