Application of Microwave for Remote NDT and Distinction of Biofouling and Wall Thinning Defects Inside a Metal Pipe

Abstract

Wall-thinning and biofouling/biofilm defects inside metal pipes are frequently reported, and each occurrence will cause a discontinuity along the metal pipe, which can be taken as a circular waveguide of microwave. If their existence and detailed distribution are unknown in advance, evaluated results may become confusing due to their possible coexistence and then complicate the correct interpretation of signals. To solve this problem, both S11 and S21 parameters are measured using a vector network analyzer and two newly designed probes. This experimental approach is based on the fact that similar reflections of different kinds of defects would have different wavelength changes and/or energy attenuation. Characteristic signals of these two kinds of defects are comparatively studied to distinguish them and generalize the remote microwave NDE application.