Stainless steel plate thickness detection using transient eddy current oscillations method

Abstract

The stainless steel structures such as the pipelines in the large industries like thermal power, nuclear power, oil natural gas and petro chemical industries play a crucial role to transport the steam, chemicals and hazardous gases. As the pipelines are operated in harsh operating conditions which lead the erosion from the inside of the pipe and the corrosion from the outside. This results in local wall thinning in pipelines; this causes unwanted leakages and pipeline unexpected failures. Therefore the local-wall thickness change in pipelines is a crucial factor to be measured in order to avoid the accidents. In the present work, a Transient Eddy Current Oscillation (TECO) system is developed in the laboratory to detect the stainless steel material thickness. The reliability of the method is tested using a SS304 steel test specimen having different thicknesses. A TECO probe has been fabricated consisting of capacitor to discharging through the inductor coil which results a decay of oscillations of current and hence oscillatory magnetic field by the probe. The magnetic field is detected in the presence of test specimen beneath the probe using a Hall-effect magnetic field sensor. The sensor is placed in the excitation-induction coil. The results are analyzed by difference signal obtained by reference subtraction method. The envelope of the difference signal is used to interpret the obtained results with the actual thickness of the test specimen. The experimental results conclude that, proposed method can be a potential NDT tool to detect corrosion and wall thickness in industrial structures.