Design of an FPGA-based eddy current instrument for the detection of corrosion pits

This paper presents a method for pitting corrosion detection using a custom developed instrument based on the eddy current testing principle. Previously, eddy current testing has been used in NDT applications where large features such as cracks are detected. However, for pitting corrosion of a size of the order of 0.1mm remains a challenge. In this paper we discuss the development of a highly integrated, Field Programmable Gate Array (FPGA)-based digital single-frequency eddy current instrument, which has high sensitivity and is capable of detecting corrosion pits in metallic plates. Pits with controlled size were created by a micro-capillary technique operating under galvanostatic control. Experimental results show that pits created with sizes of order of 100-450 μm depth can be reliably detected and there is a good correlation between the size of the pit and the amplitude of the signal from the instrument.