Method and apparatus for estimating the condition of a coating on an underground pipeline
First Claim
1. A method for estimating a condition of a coating on a portion of a coated pipeline buried in soil using a magnetometer, comprising:
- conducting a magnetically-detected electrochemical impedance spectroscopy (MEIS) test at a location over a selected segment of the buried pipeline;
compensating for undesirable interfering and/or stray current signals flowing through the test location by generating at least one sinusoidal signal having a predominant amplitude and frequency and adding said sinusoidal signal to an output signal from the magnetometer; and
switching between operation modes of a dual-mode potentiostat for performing a calibration step and performing the MEIS test;
wherein the potentiostat includes a galvanostat and calibration mode of operation includes generating a complex calibration factor for each frequency by injecting a constant current from the galvanostat down the pipeline segment and measuring a resultant magnetometer output, and wherein during the MEIS mode of operation the calibration factor is used to compute actual on-pipe current at the location.
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Abstract
Methods are provided for reducing interference from stray currents in buried pipelines/metal structures during MEIS testing or other current-sensing applications in the pipeline. Methods are also provided for measuring bulk complex electrical impedance between a buried pipe and the soil, thereby rendering an indication of the quality of the anti-corrosive coating. Methods are also provided for measuring the complex propagation constant of AC voltages propagating along an attenuative pipeline. This information is useful for assessing the general condition of the anti-corrosive coating involved, or to enhance MEIS inspection of the pipeline. Methods are also provided for enhancements to MEIS testing, including (a) canceling magnetometer offset effects associated with the Earth'"'"'s magnetic field after the magnetometer is positioned for measurement, (b) implementing a separate sensing connection to the pipe so as to avoid interference from voltage loss in the pipe feed-line connection, (c) providing a power amplifier to excite the pipe with large-amplitude signals.
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Citations
22 Claims
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1. A method for estimating a condition of a coating on a portion of a coated pipeline buried in soil using a magnetometer, comprising:
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conducting a magnetically-detected electrochemical impedance spectroscopy (MEIS) test at a location over a selected segment of the buried pipeline; compensating for undesirable interfering and/or stray current signals flowing through the test location by generating at least one sinusoidal signal having a predominant amplitude and frequency and adding said sinusoidal signal to an output signal from the magnetometer; and switching between operation modes of a dual-mode potentiostat for performing a calibration step and performing the MEIS test; wherein the potentiostat includes a galvanostat and calibration mode of operation includes generating a complex calibration factor for each frequency by injecting a constant current from the galvanostat down the pipeline segment and measuring a resultant magnetometer output, and wherein during the MEIS mode of operation the calibration factor is used to compute actual on-pipe current at the location. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. An apparatus for estimating a condition of a coating on a portion of a coated pipeline buried in soil using a magnetometer, comprising:
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means for conducting a magnetically-detected electrochemical impedance spectroscopy (MEIS) test at a location over a selected segment of the buried pipeline; means for compensating for undesirable interfering and/or stray current signals flowing through the test location by generating at least one sinusoidal signal having a predominant amplitude and frequency and adding said sinusoidal signal to an output signal from the magnetometer; and means for switching between operation modes of a dual-mode potentiostat for performing a calibration step and performing the MEIS test; wherein the potentiostat includes a galvanostat and calibration mode of operation includes generating a complex calibration factor for each frequency by injecting a constant current from the galvanostat down the pipeline segment and measuring a resultant magnetometer output, and wherein during the MEIS mode of operation the calibration factor is used to compute actual on-pipe current at the location. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
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21. A method for estimating a condition of a coating of a pipeline buried in the soil using a coated pipeline test sample containing synthetic disbonds, the pipeline test sample comprising an elongated section of pipe having a predetermined diameter and length, an end cap disposed over each end of the pipe section, a low dielectric material wrapped around the pipe section between the end caps, the low dielectric material having characteristics that simulate disbonds, and a sealing tape wrapped over the low dielectric material, the balance of the pipe, and end caps, the method comprising the steps of:
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burying the pipe section having the low dielectric material wrapped around the pipe section with the simulated disbonds in the soil at a predetermined depth; applying current at varying frequencies between each end of the pipe section; and measuring input and output currents from the sample pipe having said low dielectric material that simulates disbonds. - View Dependent Claims (22)
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Specification