Localizing, identification and sizing of inner surface pipe wall thinning by means of domain transformation and spectral analysis

Abstract

In microwave inspection of inner surface pipe wall thinning (PWT), the signals measured by a vector network analyzer (VNA) are usually single side-banded, complex-valued S-parameters in the frequency domain, whereas what we seek for, the location and dimension of a PWT, are real-valued quantities in spatial domain. In order to realize a more intuitive and direct detection and localization and avoid the intensive work of dispersion compensation, which is required in dealing with dispersive medium, we firstly transformed the S-parameters in the frequency domain into the wavenumber domain, and then to the spatial domain as a distance trace. A discontinuity along the pipe wall showed up as a distinct impulse in the distance trace, from which the location could be read out directly. Moreover, we applied gating to concerned responses and performed spectral analysis to reveal respectively spectral characteristics of flanged connection, pipe-end and PWT. We were thus able to classify PWT from other discontinuities. Spectral analysis of a PWT’s gated responses also revealed that the spectrum’s lob width is correlated to PWT length, whereas the lob’s peak value is a measure of PWT thickness. We also investigated the utmost length of a pipe that can be explored by means of the proposed technology. The experimental results showed the feasibility of the proposed method and procedures for microwave pipeline inspection and monitoring.