Patent ID: 8310251

Claim:
A method for assessment of an external condition of buried pipe, the method comprising: disposing a multi-electrode probe having structure for sensing potential comprising at least a first electrode and a second electrode spaced apart from one another in a medium proximate to a section of a pipe to be analyzed, said pipe section having a coating disposed on at least a portion of its length; measuring a difference in potential (V 1 ) between said first and second electrodes, and using V 1 together with a value for soil resistivity proximate to said pipe section to determine a local current density; forcing an alternating current into a circuit comprising said pipe and a bias electrode selected from said first and second electrodes at a plurality of different frequencies and measuring a resulting potential difference (V 2 ) between said pipe and said electrode other than said bias electrode; determining a local impedance at said plurality of frequencies from said V 2 and said local current density, and evaluating a condition of said coating in said section based on said local impedance, or a parameter derived therefrom.