Development of signal processing method to measure wall thickness of corrosion specimens by electromagnetic acoustic resonance method

Abstract

Electromagnetic acoustic resonance method (EMAR) is promising for online monitoring of pipes wall thinning with corrosion during operation. However, the improvement of measurement accuracy is one of issues to be solved, although some signal processing methods such as superposition of nth compression method (SNC) have been proposed in order to improve the accuracy of wall thickness estimation. In this study, for the purpose of highly accurate evaluation of the wall thickness, the thickness of 51 corrosion specimens was measured and compared with the true thickness obtained by 3D laser scanner. The fundamental resonance frequency of EMAR signal spectrum was evaluated by discrete Fourier transform method (DFT) and SNC method, and the wall thickness was calculated. As a result, evaluated thickness by EMAR almost corresponded to the average of true thickness. The accuracy of the evaluated thickness by the SNC method depends on the method to set the postulated thickness for determining the number of compressions. It was found that using the evaluated thickness by the DFT method for determining the number of compressions improved the estimation accuracy of the evaluated thickness by the SNC method. In addition, it was confirmed the estimation accuracy of this evaluated thickness was higher than that of the evaluated thickness by the DFT method.

Keywords

• emat
• emar
• pipe wall thinning
• thickness mesurement
• signal processing