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Title:
A METHOD FOR MEASURING CATHODIC PROTECTION CURRENT
Document Type and Number:
WIPO Patent Application WO/2019/156584
Kind Code:
A1
Abstract:
A method of noncontact measurement of Cathodic Protection Current (CPC) is disclosed. The method includes inline measurement of a magnetic field induced by the CPC. To induce a non-zero magnetic field, an inline magnet is placed next to a wall in a way to produce axially asymmetric magnetic saturation inside a metal. Further, a value of the CPC is determined by using the measured magnetic field.

Inventors:
BONDARENKO, Alexey Vladimirovich (ul. Demakova, 18 kv.20, Novosibirsk 7, 630117, RU)
VELKER, Nikolay Nikolaevich (ul. Zelenaya Gorka, 10 kv.1, Novosibirsk 0, 630060, RU)
DASHEVSKY, Yuliy Aleksandrovich (ul. Vyazemskaya, 2 kv.1, Novosibirsk 8, 630128, RU)
EDWARDS, Carl M. (23303 Millcross Lane, Katy, Texas, 77494, US)
DUTTA, Sushant Madhukul (1511 Meadowsweet Drive, Sugar Land, Texas, 77479, US)
Application Number:
RU2018/000076
Publication Date:
August 15, 2019
Filing Date:
February 07, 2018
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
BAKER HUGHES, A GE COMPANY, LLC (17021 Aldine Westfield, Houston, TX, 77073, US)
BONDARENKO, Alexey Vladimirovich (ul. Demakova, 18 kv.20, Novosibirsk 7, 630117, RU)
VELKER, Nikolay Nikolaevich (ul. Zelenaya Gorka, 10 kv.1, Novosibirsk 0, 630060, RU)
DASHEVSKY, Yuliy Aleksandrovich (ul. Vyazemskaya, 2 kv.1, Novosibirsk 8, 630128, RU)
EDWARDS, Carl M. (23303 Millcross Lane, Katy, Texas, 77494, US)
DUTTA, Sushant Madhukul (1511 Meadowsweet Drive, Sugar Land, Texas, 77479, US)
International Classes:
C23F13/02; F16L58/00; G01N27/72
Domestic Patent References:
WO2008074161A12008-06-26
Foreign References:
US4134059A1979-01-09
GB1586581A1981-03-18
EP0905497A11999-03-31
EP0825435A11998-02-25
US20060220640A12006-10-05
Other References:
None
Attorney, Agent or Firm:
VESELITSKIY, Maxim Borisovich et al. (Spartakovskiy pereulok, 2 build. 1, section 1, 3d floo, Moscow 2, 105082, RU)
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Claims:
CLAIMS

1. A method for estimating cathodic protection current (CPC) in a pipeline having a longitudinal axis, comprising:

- disturbing a symmetry of a magnetic permeability of the pipeline using a magnet positioned at at least one selected location in the pipeline;

- measuring a value of a magnetic field induced by CPC in the pipeline at the at least one selected location using a magnetic field sensor; and

- estimating the CPC using the measured magnetic field.

2. The method of claim 1 , further comprising using a flux concentrator to amplify the induced magnetic field.

3. The method of claim 2, wherein the flux concentrator is one of: (i) a flux tube, and (ii) a magnetic core.

4. The method of claim 2, wherein the flux concentrator is perpendicular to the longitudinal axis of the pipeline.

5. The method of claim 2, wherein opposing ends of the flux concentrator are separated by a gap from a wall of the pipeline.

6. The method of claim 2, wherein the magnetic field sensor is positioned at a center of the flux concentrator to measure the magnetic field.

7. The method of claim 1 , wherein poles of the magnet are separated by a gap from the wall of the pipeline.

8. The method of claim 1 , further comprising normalizing the measured magnetic field.

9. The method of claim 1, further comprising determining a B-H curve for the pipeline at the at least one selected location.

10. The method of claim 1 , wherein the at least one selected location comprises a plurality of selected locations, and wherein the disturbing, measuring, and estimating steps are performed at each of the plurality of selected locations.

1 1. The method of claim 1 , further comprising:

positioning the magnet in a pipeline investigation tool; and

conveying the pipeline investigation tool along a bore of the pipeline.

12. An apparatus for estimating cathodic protection current (CPC) in a pipeline having a longitudinal axis, comprising:

- an enclosure configured to be conveyed through the pipeline;

- a magnet carried by the enclosure, the magnet being configured to disturb a symmetry of a magnetic permeability of the pipeline; and

- a magnetic field sensor carried by the enclosure and configured to measure the induced magnetic field.

13. The apparatus of claim 12, further comprising a flux concentrator carried by the enclosure, the flux concentrator being configured to concentrate the magnetic field induced by CPC.

14. The apparatus of claim 1 1, wherein opposing ends of the flux concentrator are separated by a gap from an immediately adjacent wall of the pipeline.

15. The apparatus of claim 1 1, wherein poles of the magnet are separated by a gap from an immediately adjacent wall of the pipeline.

Description:
A METHOD FOR MEASURING CATHODIC PROTECTION CURRENT

FIELD OF THE DISCLOSURE

The present disclosure relates to cathodic protection systems for corrosion protection of metal objects that are buried in soil or located underwater. In aspects, the present disclosure relates to a system and method for measuring the electric current in a pipeline imposed by a cathodic protection system using inline non-contact measurement.

BACKGROUND

Metal structures, such as pipelines, are expensive investments. To prevent pipeline external corrosion, a cathodic protection (CP) system may be implemented. CP is a method of combating corrosion of metals that come in contact with potentially corrosive mediums. The purpose of cathodic protection is to reduce or eliminate corrosion of steel or other metals in a given environment. The corrosion of metal in an electrolyte at ambient temperature is an electrochemical process involving the flow of electrons in metals and ions in electrolytes. This corrosion can be controlled by the application of currents from an external source such as a generator or rectifier, or from a galvanic sacrificial anode, which supplies all of the current for the

electrochemical reduction of the corrodant by a source other than the corroding steel.

Currently, Cathodic Protection Current (CPC) is managed based on detection of a magnitude of the CPC. A pipeline inspection tool is used for measuring the CPC. Typically, the pipeline inspection tool moves along a bore of the pipeline and detects the CPC by measuring potential difference between electrodes being in contact with walls of the pipeline. However, such techniques require a quality contact between the sensing instrument and a wall of the pipeline, which may not be present or may cause undesirable noise that affects the inspection activity. The present disclosure addresses these and other drawbacks of the prior art.

SUMMARY

In aspects, the present disclosure provides a method for estimating cathodic protection current (CPC) in a pipeline having a longitudinal axis. The method may include the steps of disturbing a symmetry of a magnetic permeability of the pipeline using a magnet positioned at at least one selected location in the pipeline; measuring a value of a magnetic field induced by CPC in the pipeline at the at least one selected location; and estimating the CPC using the measured magnetic field.

In aspects, the present disclosure provides an apparatus for estimating cathodic protection current (CPC) in a pipeline having a longitudinal axis. The apparatus may include an enclosure configured to be conveyed through a pipeline; a magnet carried by the enclosure, the magnet being configured to disturb a symmetry of a magnetic permeability of the pipeline; and a magnetic field sensor configured to measure the induced magnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS

For detailed understanding of the present disclosure, references should be made to the following detailed description of the preferred embodiment, taken in

conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein:

FIG. 1 illustrates one method of estimating cathodic protection current in accordance with the present disclosure;

FIG. 2A depicts an end view of a pipeline inspection tool for noncontact measurement of cathodic protection current, according to an embodiment;

FIG. 2B depicts a side view of the pipeline inspection tool for the noncontact measurement of the cathodic protection current, according to an embodiment;

FIGS. 2C-D depicts side views of flux concentrator configurations that may be used in conjunction with a pipeline inspection tool according to embodiments;

FIG. 3 depicts the B-H curves of several metals;

FIG. 4 depicts an illustrative cathodic protection system for a pipeline;

FIG. 5 is a graphical depiction of a current to normalized B y curve;

FIG. 6 illustrates one method of estimating CPC using a normalized B y curve in accordance with the present disclosure;

FIG. 7 illustrates one non-limiting embodiment of a pipeline investigation device in accordance with the present disclosure;

FIG. 8 depicts an illustrative graph plotted between recorded values of magnetic flux density (B) and magnetic field strength (H) or BH-curve for a particular pipeline metal;

FIGS. 9A-B depicts an illustrative space distribution of absolute values of induced magnetic field (B) in the wall of a pipeline; and FIG. 10 depicts an illustrative graph of a logarithm plot of induced magnetic field (B y ) shown against logarithmic values of Cathodic Protection Current (CPC) density.

DETAILED DESCRIPTION

In aspects, the present disclosure relates to methods and associated devices for non-contact measurement of Cathodic Protection Current (CPC). In one case, the non- contact measurement of CPC may be performed for a pipeline. Referring to FIG. 1 , one non-limiting method for estimating CPC in a pipeline may include a step 10 of disturbing a symmetry of a magnetic permeability of the pipeline using a magnet at a selected location, a step 20 of measuring a value of a magnetic field induced in the pipeline at the selected location, and a step 30 of estimating the CPC using the measured induced magnetic field.

Generally, the FIG. 1 method may be implemented using a pipeline investigation tool, sometimes referred to as a "pig," that travels through a pipeline. At selected locations, the pig may disturb the symmetry of magnetic permeability of the pipeline by placing a magnet next to a wall of the pipeline. The magnet does not directly physically contact a wall of the pipeline. The magnet is oriented to produce axially asymmetric magnetic saturation inside the metal of the pipeline. The value(s) of the CPC may be estimated by measuring the value(s) of the magnetic field using a magnetic field sensor, which also does not directly physically contact the pipeline. Illustrative embodiments for performing the FIG. 1 method are described below.

FIGS. 2 A and 2B depict an end view and a side view of one non-limiting embodiment of a pipeline inspection tool 102, respectively, for non-contact

measurement of the CPC. In one arrangement, the pipeline inspection tool 102 may include a magnet 108 and a magnetic field sensor assembly 1 10.

The magnet 108 may be used to disturb the symmetry of a magnetic permeability in the pipeline 104. As best seen in FIG. 2B, the magnet 108 may be placed along a longitudinal axis 120 of the pipeline 104 to axially asymmetrically saturate the pipeline 104 with a magnetic field. The longitudinal axis 120 is generally the axis along which fluid flows through the pipeline 104. By“asymmetric saturation,” it is meant that the magnetic saturation is localized along a circumference of a cross- section of the pipeline 104. This is done by axially aligning the poles 1 12 with the longitudinal axis 120; i.e. , a North pole and a South pole of the magnet 108 are arranged to be parallel with the longitudinal axis 120. The poles 1 12 are immediately adjacent to the walls 106 of the pipeline 104. By "immediately adjacent," it is meant the wall 106 closest to the poles 1 12. However, it should be noted that the terminal faces 122 of the magnet 108 do not directly contact the pipeline 104. By "not directly contact," it is meant that a gap 124 separates the terminal face 122 from the pipeline 104 while operating.

The magnetic field sensor assembly 1 10 measures a value of a magnetic field associated with the CPC while the wall 106 of the pipeline 104 is asymmetrically magnetically saturated. In one arrangement, the magnetic field assembly 1 10 includes a flux concentrator 1 14 and a magnetic field sensor 1 16 that measures a magnetic field within the flux concentrator 1 14. The flux concentrator 1 14 is a member shaped to concentrate magnetic flux, i.e. , act as an amplifier. Generally, the flux concentrator 1 14 may be elongated along a longitudinal axis 1 18 that is perpendicular to the longitudinal axis 120 of the pipeline 104.

The flux concentrator 1 14 may be a magnetic core shaped like a rod or cylinder as shown provided with a suitable air gap. However, such a geometry is not required. Other cross-sections may also be used. For example, FIG. 2C illustrates a flux concentrator 144a shaped as a tube having different cross-sectional thicknesses and a hollow core. FIG. 2D illustrates a flux concentrator 1 l4b having a frusto-conical shape. Thus, flux concentrator 1 14 is not limited to any particular shape or

configuration. The magnetic field sensor 1 16 may be placed in a center of the flux concentrator 1 14 to measure a magnetic field in an air gap in the flux concentrator 1 14 that is induced by CPC. Like the magnet 108, a gap 126 prevents direct contact between the terminal faces 128 of the flux concentrator 1 14 and the pipeline line 104. The magnet 108 and the flux concentrator 1 14 are considered perpendicular to one another because the poles of the magnet 108 are lie along a line that is perpendicular to the line along which the flux concentrator 1 14 is elongated.

In other embodiments, a flux concentrator 1 14 may be omitted. That is, a flux concentrator 1 14 may be desirable to enhance sensitivity of a magnetic field sensor. But there may be situations for which a magnetic field sensor may have adequate sensitivity without the flux concentrator 1 14.

In arrangements using a magnetic core for a flux concentrator 1 14, the magnetic field sensor 1 16 is configured to measure the magnetic field in an air gap formed within the magnetic core. In other embodiments, the magnetic field sensor 1 16 may be a flux-gate magnetometer incorporated into the flux concentrator 1 14, thus not requiring an air gap. However, any other type of magnetic field sensor may be used.

Step 30 of the FIG. 1 method, which is estimating the CPC based on the measured magnetic field, may be performed using a variety of methodologies. Two illustrative and non-limiting methods are described below.

One method for estimating CPC may utilize a B-H curve for the pipeline 104. Since conventional pipelines are made of carbon steel, the nonlinearity of the relationship between magnetic flux density (B) and magnetic field strength (H) (B-H curve) will result in decreasing of the pipeline's walls’ magnetic permeability in the vicinity of the magnet’s poles. Thus, one method of transforming the magnetic flux density into an estimate of cathodic current requires determining a B-H curve of the pipeline 104, either in situ or a priori. When the symmetry of a magnetic permeability is disturbed, a CPC-induced magnetic field directed perpendicular to the pipeline’s axis 120 will appear inside the pipeline 104. Measuring this magnetic field enables a measurement of CPC.

FIG. 3 illustrates for four different B-H curves 40, 42, 44, 46. It should be noted that the current is linear as a function of magnetic flux density. Depending on the B-H curve, the magnetic flux density at the center of the flux tube can be more or less sensitive to the cathodic current.

In some embodiments, the B-H curve may be known through prior

measurements or historical data. The B-H curve may also be determined using known material properties of the pipeline 104. In other embodiments, the B-H tool may be measured in situ using a suitable measurement device.

Another method of transforming magnetic flux density into an estimate of cathodic current involves normalizing the measured magnetic flux. Referring to FIG.

4, there is schematically illustrated a pipeline 104 with a cathodic protection system 140. The system may include a wire circuit 142, sacrificial anodes 144, and a power supply such as a rectifier 146. The rectifier 146 is attached to the pipeline 104 via the wire circuit 142 and supplies the sacrificial anodes 144 with a total amount of current, which then flows into the pipeline 104 to complete the electrical circuit. Over time, the sacrificial anodes 144 corrode and are replaced periodically. The current 150 on the "left-hand" side 152 of the rectifier 146 is positive and the current 154 on the "right-hand" side 156 is negative. The sum 160 of the currents is the total output of the rectifier 146 and it is known or can be measured using known instruments. The estimate of cathodic current takes advantage of how the cathodic current is applied to the pipeline 104.

The magnetic flux density at the center of the flux concentrator, B y , is linear in the cathodic current density and therefore the current for a pipeline with a constant cross-section. Thus

l(z) = KB t (z), (1 )

where / is the current at a particular location in the pipe, z, and k is the constant of proportionality. Assuming without loss of generality that the rectifier is located at z = 0, then

where the ± signs represent the location on the left-hand and right-hand sides of the rectifier. The total current that the rectifier supplies is I T - Thus,

The constant of proportionality can be estimated from

and the estimate of cathodic current at any location in the pipeline 104 can be made using equation (4) as shown in FIG. 5. In FIG. 5, there is shown a line 170 that demonstrates the linear relationship between the normalized B y and current (I). Thus, B y may be used to estimate CPC current.

Referring to FIG. 6, there is shown an illustrative method 180 that utilizes the above-described methodology for using a normalized magnetic flux measurement to estimate CPC. The method may include a step 182 for estimating a total current at a power source, such as a rectifier 106. The current may be measured or determined at the rectifier 106. The next step 184 is estimating a magnetic flux inside the pipeline 104 associated with the positive current and the negative current proximate to the rectifier 106. This step may be performed using the FIG. 2A-B tool 102. If the positive and negative currents are known to be identical, then doubling one of the measured magnetic fluxes may be adequate. In other instances, it may be desirable to measure both magnetic fluxes and sum the values to account for variances. At step 186, the coefficient of proportionality may be determined using the measured current, the measured magnetic fluxes, and equation 4 above.

At step 188, the CPC is estimated at one or more points by measuring magnetic flux using the tool 100 of FIGS. 2A-B and using the determined coefficient of proportionality. The CPC system 140 may include a plurality of axially spaced apart rectifiers 106. Therefore, the magnetic flux density to current transform can be reestablished as successive rectifiers are encountered along a pipeline 104.

Referring to FIG. 7, there is shown one non-limiting embodiment of a pipeline investigation tool ("pig") 200 in accordance with the present disclosure. The pig 200 may include a CPC estimating tool 210, a processor 220, a power module 230, and a propulsion system 240. The pig may include a suitable enclosure 202 in which these components are housed or carried. The CPC estimating tool 210 may include the magnet 108 and the magnetic field sensor assembly 1 10 as described in FIGS. 2A,B. The processor 220 may include micro-processing circuitry, memory modules programmed with algorithms, and other known components of information processing devices. The power module 230 may be a battery or other suitable source for supplying electrical power. The propulsion system 240 may use self-propulsion and / or an external motive power. A self-propulsion system can, for example, include a tractor-type device. External motive power may be provided by pressurized fluid, which is used to create a pressure differential that propels the pig 200. Additionally, in embodiments, a communication system 250 may be included to provide either uni- directional and/or bidirectional signal communication between the pig 200 and an remote unit (not shown). The general components of pigs are well known in the art and will not be discussed in further detail. Additionally, it is emphasized that the teachings of the present disclosure are not limited to any particular configuration of a pipeline investigation device.

In one illustrative mode of operation, the pig 200 may move inside the pipeline 104 in such a way that the magnet 108 produces a magnetic field intense enough to saturate the metal of the walls 106, and thereby creating axial asymmetric saturation of the pipeline 104. Such axial asymmetric saturation of the pipeline 104 results in asymmetry of magnetic permeability of the walls 106, which generates a CPC-induced magnetic field. The CPC-induced magnetic field is perpendicular to the longitudinal axis of the pipeline 104 and detected by the magnetic field sensor assembly 1 10. The measurements may be taken while the pig 200 is stationary or in motion. Information from the magnetic field sensor assembly 100 is received in the processor, which writes the information to the memory module and / or transmits the information to a remote unit (not shown).

When a normalization technique is used, the FIG. 5 method may be periodically used to generate the coefficient of proportionality as rectifiers or other power sources associated with a CPC are encountered. When a B-H curve is used, a suitable B-H curve generating tool 280 may be used to generate a B-H curve for each location at which magnetic field measurements are taken. Alternatively, the B-H curve may be established beforehand. The measurement information may be written to the memory module and stored. Alternatively or additionally, the measurement information may partially or completely processed; e.g., compressed or processed to obtain CPC values.

To verify validity of the measurement method, a numerical simulation was carried out using commercially available software packages such as COMSOL

MULTIPHYSICS and CST EM STUDIO. Referring to FIGS. 2A-B, the simulation used a model based on a pipeline radius of 0.5m, pipe’s wall thickness of 0.0 lm, a gap between the poles 1 12 of the magnet 108 and the walls 106 of the pipeline 104 being 0.0 lm, and a gap between ends of the measuring flux concentrator 1 10 and the walls 106 of the pipeline 104 being 0.0 lm.

FIG. 8 depicts an illustrative graph 200 plotted between recorded values of magnetic flux density (B) and magnetic field strength (H). The graph 200 shows a B- H curve corresponding to carbon steel (for example, carbon steel AISI 4130). In the graph 200, the magnetic flux density (B) is shown along y-axis and the magnetic field strength (H) is shown along x-axis. The graph 200 shows a nonlinearity of

relationship between the magnetic flux density (B) and the magnetic field strength (H) (i.e., a B-H curve) and changing magnetic permeability of the walls 106 in the vicinity of the poles 1 12 of the magnet 108.

Referring to FIGS. 9A-B, there is shown a space distribution 300 of absolute values of induced magnetic field (B y ) along the walls 106 of the pipeline 104 (FIG. 2A). The space distribution 300 was determined using COMSOL MULTIPHYSICS as a tool. To determine the space distribution 300, a casing of cylindrical shape filled with ferromagnetic material was used as a model of the flux concentrator 1 16.

Further, values of relative magnetic permeability (m) = 4000 and diameter (d) = 0.1 m were used for the flux concentrator 1 16.

FIG. 10 depicts an illustrative graph 400 of a logarithm plot of the induced magnetic field (B y ) shown against logarithmic values of the CPC. Calculations of the induced magnetic field (B y ) were performed using COMSOL MULTIPHYSICS and CST EM Studio 404. In the graph 400, each current value ( 1 <I< 10 A) corresponds to measured values of the induced magnetic field (B y ). The graph 400 further shows a match between values of the induced magnetic field (B y ) determined by use of different software packages. Further, the graph 400 shows that value of the magnetic field in the measuring flux concentrator for a CPC of 10A is about 35mT, which may be detected using conventional magnetic field sensors.

For example, a Hall effect based sensor MAG31 10 may be used for recording values of the induced magnetic field (B y ). Other sensors, such as a flux-gate magnetometer, may also be used. It should be noted that the Hall effect based sensor MAG31 10 could operate over an extended temperature range of -40°C to +85°C. Further, features of the magnetic field sensor may include full-scale range of ±1000 mT, sensitivity of 0.10 mT, and noise down to 0.25 mT rms. It should be understood that the above simulation is merely to demonstrate the efficacy of the present teachings and is not intended to limit the present teachings in any way.

In an embodiment, further analysis of the method for inline noncontact measurement of the CPC may include electromagnetic modeling that may account for saturation history, coercive force (H c ), and residual saturation (B r ).