Patent ID: 7880484
Filing Date: 2011-02-01
Classification: G01N

Abstract:
1. A method for estimating a condition of a coating on an underground metal structure using bulk structure-to-soil spectroscopy, comprising: providing an AC voltage between a ground-return electrode and an injection end point of the structure via a feed line at a plurality of test frequencies; positioning a reference electrode proximate said structure; positioning a magnetometer adjacent to the feed line to sense all currents being provided to the structure; receiving a first voltage potential representing a difference between the voltage at the injection end point and the reference electrode; receiving a second voltage potential representing a difference between a voltage at the injection end point and the ground-return electrode; and computing, from the first voltage potential and the magnetometer-measured currents, a first net impedance between the structure and soil at the plurality of frequencies, thereby defining a first impedance spectrum; computing, from the second voltage potential and magnetometer measured currents, a second net impedance between the structure and the ground-return electrode at the plurality of frequencies, thereby defining a second impedance spectrum; determining the difference between the first and second net impedances and/or determining the difference between the first and second impedance spectra, said differences providing indicia of the earthing resistance of the ground-return electrode; and analyzing the first, second or both impedance spectra to assess the general or bulk condition of the coating on the structure under test.