JP2011191288A - Method and device for estimating current density of damaged coating portion of underground pipe, and method and device for controlling electric protection - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the need for access to the area around a damaged coating portion of an underground pipe and to evaluate alternating-current corrosion risks. <P>SOLUTION: When a current of the damaged coating portion 2 of the underground pipe 1 is estimated, a potential difference between a first reference electrode 14a on the ground surface directly above the damaged coating portion 2 of the underground pipe 1 at a predetermined distance d or on the ground surface at an optional distance from directly above it, and a second reference electrode 14b apart from the first reference electrode 14a by an optional distance g is measured by a direct-current and alternating-current voltmeter 13, respectively; a direct-current current I<SB>DC</SB>and an alternating-current current I<SB>AC</SB>are derived respectively from the potential difference using predetermined formulas (7), (8) or (7'), (8'); and a direct-current density and an alternating-current density of the damaged coating portion 2 are derived by dividing the currents by a predefined area S of the damaged coating portion. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a current density estimation method, device, and anticorrosion management method and device for a coating damage part of an underground pipe, and particularly, access to the periphery of the coating damage part of an underground pipe is unnecessary. In addition, the present invention relates to a method and an apparatus for estimating a current density of a coating-damaged portion of a buried underground pipe capable of evaluating an AC corrosion risk, and an anticorrosion management method and apparatus using the same.

As a method for evaluating the anticorrosion effect of underground pipes, Patent Document 1 discloses the coating damage portion 2 of the coated steel pipe 1 as shown in FIG. 1 (corresponding to FIG. 1 of Patent Document 1). Measure the potential difference (tube-to-ground potential) between the proximity terminal (conducting wire connected to the buried pipe) 5 and the two reference electrodes 4a and 4b inserted into the ground with the multi-channel digital voltmeter 3, respectively. 2 (corresponding to FIG. 5 of Patent Document 1) is plotted on a graph showing the change in DC potential, and from the slope, the DC current density (corrosion protection current density) i _DC necessary for evaluating the corrosion protection effect is calculated. The calculation method is described.

  Further, as a related technique, Patent Document 2 discloses an AC potential distribution generated around a coating damage portion when an alternating current of a specific frequency is passed through the underground buried pipe. A technique for measuring the area of a coating damage portion of an underground pipe by detecting and analyzing with a plurality of reference electrodes inserted into the ground is described. Non-patent document 1 also describes coating by potential distribution analysis. Describes the corrosion protection evaluation technique for buried steel pipes with damaged parts.

JP-A-4-95868 (FIGS. 1 and 5) Japanese Patent Laid-Open No. 4-95867

Adachi et al. "Evaluation of cathodic protection of buried steel pipes with coating defects by potential distribution analysis" Corrosion and Corrosion Association Materials and Environment, Vol. 40, pp. 19-25 (1991)

  Conventionally, however, it is necessary to make contact with the buried pipe metal part near the damaged part to be diagnosed or a terminal, and when there is no terminal near the damaged part of the coating, it takes time to prepare. However, there was a problem that the evaluation of AC current, that is, AC corrosion risk, was not possible.

  The present invention has been made to solve the above-mentioned conventional problems, and does not require access to the area around the coating damage (including defects) of underground pipes, and can evaluate the risk of AC corrosion. The task is to do.

  In order to carry out the present invention in the field, the rough position of the coating damage portion of the underground buried pipe is known by the conventional technique such as the needle electrode method or the Pearson method, It is assumed that the area and depth position are known, and that the earth (soil) resistivity is known.

  In the present invention, when estimating the current density of the coating damage portion of the underground buried pipe, the first reference electrode on the surface directly above the coating damage portion of the underground buried pipe at a predetermined depth, A potential difference between second verification electrodes separated by an arbitrary distance from one verification electrode is measured with a direct current and an alternating current voltmeter, and a direct current and an alternating current are respectively derived from the potential difference by a predetermined formula. The problem is solved by deriving the DC current density and the AC current density of the damaged coating portion by dividing the area of the damaged coating portion obtained.

Here, the depth of the underground pipe is d, the distance between the reference electrodes is g, the earth (soil) resistivity is ρ, the measured ground potential difference of the direct current is ΔV _DC , and the desired ground surface potential difference of the alternating current the measured values as ΔV _AC, the following equation
The DC current density and the AC current density are estimated by deriving the DC current I _DC and the AC current I _AC flowing into the coating damage part and dividing them by the coating damage part area S obtained in advance. it can.

  In addition, a first reference electrode on the ground surface at an arbitrary distance from directly above the coating damage portion of the underground buried pipe at a predetermined depth, and a first reference electrode separated from the first reference electrode by an arbitrary distance. The potential difference between the two reference electrodes is measured with a direct current and alternating current voltmeter, and the direct current and alternating current are derived from the potential difference by a predetermined formula, and divided by the coating damage area obtained in advance. Thus, the direct current density and the alternating current density of the coating damage portion can be derived.

Here, the depth of the underground buried pipe is d, the interval between the reference electrodes is g, the distance from just above the coating damage part of the underground buried pipe to one of the reference electrodes is G, and the ground (soil) the resistivity [rho, [Delta] V _DC and ground surface potential measured value of the direct current, the earth surface potential measurements of the earth surface potential of the alternating current of interest as [Delta] V _AC, the following equation
The DC current density and the AC current density can be estimated by deriving the DC current I _DC and the AC current I _AC flowing into the coating damage part and dividing by the previously obtained coating damage area. .

  In addition, a potential difference (voltage) between the underground tube and each reference electrode is measured, a voltage between the first reference electrode and the underground tube, and the second reference electrode The potential difference (ΔV) between the first verification electrode and the second verification electrode can also be obtained from the difference from the voltage with the underground pipe.

  The present invention also provides an anticorrosion management method characterized in that the anticorrosion state of a coating damage part is evaluated using the current density estimated by the above method.

  A first verification electrode on the surface directly above the coating damage portion of the underground buried pipe at a predetermined depth; a second verification electrode separated by an arbitrary distance from the first verification electrode; A voltmeter that measures the potential difference between the reference electrodes in a direct current and an alternating current, respectively, and a direct current and an alternating current are derived from the potential difference by a predetermined formula, and divided by the area of the coating damage portion obtained in advance. And a means for deriving the direct current density and the alternating current density of the coating damage part, and providing a current density estimation device for the coating damage part of the underground buried pipe. is there.

  Further, the first reference electrode on the ground surface at an arbitrary distance from directly above the coating damage portion of the underground buried pipe at a predetermined depth, and the first reference electrode separated from the first reference electrode by an arbitrary distance. 2 and the voltmeter for measuring the potential difference between the reference electrode in direct current and alternating current, respectively, the direct current and the alternating current are derived from the potential difference by a predetermined formula, and the coating previously obtained Means for deriving the direct current density and the alternating current density of the coating damage part by dividing by the area of the damage part, and estimating the current density of the coating damage part of the underground buried pipe A device is provided.

  Here, the verification electrode can be formed of conductive wheels, and the verification electrode and the voltmeter can be mounted on a vehicle capable of traveling.

  The present invention also provides an anti-corrosion management device characterized by evaluating the anti-corrosion state of a coating damage portion using the current density estimated by the above-described device.

  According to the present invention, the damaged portion current can be estimated from the ground surface potential difference measurement value that does not require access to the underground buried pipe around the coating-covered damaged portion. In addition to DC current (corrosion protection current) estimation, the AC corrosion risk can be evaluated by measuring the AC ground surface potential difference and estimating the damaged portion AC current.

  In particular, when the verification electrode is composed of conductive wheels and the apparatus is mounted on a vehicle capable of traveling, movement to the site is extremely easy.

The figure which shows schematic structure of the apparatus which implements the conventional cathodic protection effect evaluation method described in patent document 1 Graph showing change in DC potential used in the evaluation method The figure which shows 1st Embodiment of this invention The figure which shows an example of the cathodic protection management standard used in order to guess the effect of cathodic protection in the said embodiment. The figure which shows the water tank experiment circuit when applying a direct current and alternating current to a probe in an example. The figure which shows the actual measurement value and calculation value of the probe direct current The figure which shows the actual measurement value and calculation value of the probe alternating current The figure which shows the actual measurement value and calculation value of the probe direct current density The figure which shows the actual measurement value and calculation value of the probe alternating current density similarly The figure which shows the example plotted to an example of the cathodic protection management standard by the probe current The figure which shows 2nd Embodiment of this invention. Diagram showing a variation of potential difference measurement

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The first embodiment of the present invention uses the coating damage search apparatus 10 shown in FIG. 3 to directly above the coating damage portion 2 of the underground pipe (for example, steel pipe) 1 at a predetermined depth d. The potential difference between the first collation electrode 14a on the surface and the second collation electrode 14b that is separated from the first collation electrode 14a by an arbitrary distance g is measured by the DC and AC voltmeters 13, respectively. The DC current and the AC current are derived from the following formulas (7) and (8), respectively, and the damaged part DC current density and the AC current density are divided by the coating damaged part area obtained in advance by the prior art. It is derived.

  Hereinafter, the principle of the present invention will be described.

When the depth from the ground surface to the coating damage part 2 is d, the potential V (x, y) appearing on the ground surface is based on a certain point on the ground surface, the tube axis direction is x, and the horizontal direction is When the direction perpendicular to the tube axis direction is y, the depth direction is z, the current flowing through the coating damage part 2 is I, and the earth (soil) resistivity is ρ, the anode (anode) is sufficiently away from the cathode (cathode). If it is installed at a distant position, it is expressed by the following equation from the relative potential based on infinity.

  The coating damage survey apparatus 10 shown in FIG. 3 includes a power source (not shown) that applies, for example, an AC signal voltage of commercial frequency between the underground tube 1 and the ground electrodes (14a, 14b), and a coating. It has the direct current and alternating current voltmeter 13 which measures the electrical potential difference formed with the electric current which flows into the damage part 2 using an electrical potential difference method.

When the coating damage exploration device 10 is directly above the underground pipe 1 as in the first embodiment, since y = 0, the expression (1) is given by the following expression.

Here, when the first verification electrode 14a is located immediately above the coating damage part 2, the ground surface potential detected by the first verification electrode 14a is given by the following equation.

The ground surface potential detected by the second verification electrode 14b at this time is given by the following equation where the verification electrode interval is g.

Therefore, the difference ΔV (= V (0) −V (g)) between the ground surface potentials detected by the first and second verification electrodes 14a and 14b is given by the following equation.

Since ΔV can be measured by the coating damage survey apparatus 10, if the ground (soil) resistivity ρ is known, the current I flowing through the coating damage portion 2 can be calculated by the following equation.

When the measured value of the _DC ground surface potential difference is expressed as ΔV _DC , the direct current I _DC flowing into the coating damage part 2 is expressed by the following expression from the expression (6).

On the other hand, the alternating current flowing into and out of the underground buried pipe 1 is usually a commercial frequency (50 Hz or 60 Hz). Therefore, when the ground surface potential difference measurement value at the commercial frequency is expressed as ΔV _AC , the AC current I _AC flowing into and out of the coating damage part 2 is expressed by the following equation from Equation (6).

(7) is divided by the coating-covering lesion area S of the direct current I _DC obtained in the prior art obtained by the expression, lesion direct current density is obtained. Similarly, the damaged portion alternating current density is obtained from the equation (8) and the coating damaged portion area S obtained by the conventional technique. These are shown in Fig. 4 (Cross-corrosion association materials and environment, Volume 51, No. 5, pp. 221-226 (2002)), the effect of cathodic protection can be estimated. In addition, the effect of cathodic protection is also within the scope of the cathodic protection control standard set forth in German Industrial Standard DIN 50 925: Nachweis der Wirksamkeit des kathodishen Korrosionsschutzes erdverlegter Anlagen.p.5 (1992). It can be evaluated by whether there is a current density and damaged portion alternating current density evaluation. However, an ideal model is assumed for the calculation of contact resistance and potential. Actually, the correlation between the obtained formula and the actually measured value (see FIGS. 6, 7, 8, and 9 shown below). Etc.) and the correction needs to be considered. Correction factors obtained in experiments using a water bath were 1.1 to 1.2. Although not shown, the correction coefficient was 0.6 to 1.8 for various measurements.

  As described above, values obtained by non-excavation, such as the coating damage portion depth d, the collation electrode interval g, the ground (soil) resistivity ρ, and the ground surface potential difference ΔV detected by the front and rear collation electrodes 14a and 14b. Therefore, the current density flowing into the coating damage part 2 can be obtained by calculation.

In the above calculation, the coating damage part 2 is assumed to be a hemisphere (originally assumed to be a disk is closer to the actual situation, but the hemisphere is easier to integrate). In this case, the contact resistance R of the anode Is as follows.
Here, r is the radius of the hemisphere.

  In this case, the current I calculated from the potential difference is expressed by the above equation (6).

On the other hand, assuming that the damage is a disk, the contact resistance R of the anode is expressed by the following equation.
Here, r ′ is the radius of the disk.

In this case, the current I calculated from the potential difference ΔV is expressed by the following equation.

Furthermore, the contact resistance R of the anode can also be expressed by the following formula where the surface area of the anode is S ′.

In this case, the current I calculated from the potential difference ΔV is expressed by the following equation.

  For this reason, even if the calculation method of the ground resistance of a coating damage part changes, an electric current can be calculated.

[Example]
A simulation test using a water tank was conducted to evaluate the coating damage area and the coating damage current density by measuring the ground surface potential.

(1) DC / AC probe current estimation Using the experimental circuit shown in FIG. 5, the DC current and the AC current generated by the oscillator (OSC) 25 are applied to the probe (made by SS400) 22 submerged in the water tank 20. The DC / AC water surface potential difference ΔV (E) between the verification electrodes 28a and 28b when applied through the potentio galvanostat 26 as a transmitter is measured with a DC and AC voltmeter 29, and the equations (7) and (8) The probe direct current I _DC and the probe alternating current I _AC were calculated from the equations. In the figure, 30 is a counter electrode (made of SUS).

FIG. 6 and FIG. 7 show calculated values for the measured values of the probe direct current I _DC and the probe alternating current I _AC , respectively.

(2) DC / AC probe current density estimation Probe DC / AC current I _DC and I _AC obtained in the previous section (1) are divided by the probe area S obtained in advance to obtain probe DC current density and probe AC current density. Asked.

  FIG. 8 and FIG. 9 show the calculated values for the actual measurement values of the probe direct current and the alternating current density, respectively.

  FIG. 10 shows a plot of the calculated values plotted on the anticorrosion management standard based on the probe current shown in FIG. In this experimental example, the DC current density is in the anticorrosion region, but there is a probe in which the AC current density deviates from the control reference value.

  In many cases, it is a commercial frequency that causes a problem with corrosion, but AC is not limited to the commercial frequency.

  Next, a second embodiment of the present invention will be described with reference to FIG.

  The coating damage exploration device 20 of the present embodiment is configured by a two-wheeled vehicle that can travel on the ground by itself, and is, for example, a commercial one between the underground tube 1 and the ground electrode (front wheel electrode 24a, rear wheel electrode 24b). In-vehicle DC and AC voltmeters (not shown) that measure the potential difference formed by the current flowing in the coating damage part 2 using the potential difference method, applying an AC signal voltage other than the frequency. Have The wheel electrodes 24a and 24b used in the coating damage search apparatus 20 are made of conductive rubber, and the potential difference between the front and rear wheel electrodes 24a and 24b can be measured.

  When the coating damage exploration device 20 is traveling immediately above the underground buried pipe 1, y = 0 as in the first embodiment, so the above expression (1) is the above expression (2). It is represented by

  Here, when the front wheel electrode 24a, which is the first reference electrode, is located immediately above the coating damage part 2, the ground surface potential detected by the front wheel electrode 24a is given by the above equation (3).

  The ground surface potential detected by the rear wheel electrode 24b, which is the second reference electrode at this time, is given by the above equation (4), where g is the wheel electrode interval.

  Therefore, the potential difference ΔV between the front and rear wheel electrodes 24a and 24b is given by the above equation (5).

  Since ΔV can be measured by the coating damage survey apparatus 20, if the ground (soil) resistivity ρ is known, the current I flowing through the coating damage portion 2 can be calculated by the above equation (6).

Here, the above equation (3) assumes that the front wheel electrode 24a is located immediately above the coating damage part 2, but the reference electrode is not directly above the coating damage part 2, The current can be calculated if the distance from directly above the coating damage part 2 is known. That is, when the front wheel electrode 24a is separated from the coating damage part 2 by G, the expression (3) becomes the following expression.

The ground surface potential detected by the rear wheel electrode 24b at this time is expressed by the following equation when the wheel electrode interval is g.

Therefore, the potential difference ΔV between the front and rear wheel electrodes 24a and 24b is given by the following equation.

Since ΔV can be measured by the coating damage search apparatus 20, the current I flowing through the coating damage portion 2 can be calculated by the following equation.

Since the relationship between the current and the potential is established for both direct current and alternating current, the direct current I _DC can be estimated from the direct current potential difference ΔV _DC and the alternating current I _AC can be estimated from the alternating current potential difference Δ _AC using the following equations.

  In the present embodiment, the coating damage inspection device 20 is integrated with the two-wheeled vehicle and is capable of self-propelling, so that it is very easy to move to the site. It should be noted that instead of the two-wheeled vehicle, it can be integrated with a three-wheeled vehicle or a four-wheeled vehicle, or can be a portable type or a stationary type separate from the traveling means.

  In addition, as shown in FIG. 12, when there is a terminal 30 that can be electrically connected to the pipe, the potential difference (voltage) between the underground buried pipe 1 and the verification electrodes 24a and 24b. From the difference between the voltage between the first verification electrode 24a and the underground tube 1 and the voltage between the second verification electrode 24b and the underground tube 1. The potential difference between 24a and the second verification electrode 24b can also be obtained.

  In any of the above embodiments, the present invention is applied to a steel pipe, but the application target of the present invention is not limited to this and can be applied to a metal pipe in general. Damage also includes defects.

DESCRIPTION OF SYMBOLS 1 ... Underground pipe 2 ... Coating damage part 10, 20 ... Coating damage search apparatus 13 ... DC and AC voltmeter 14a, 14b ... Collation electrode 24a ... Front wheel electrode (1st collation electrode)
24b ... Rear wheel electrode (second reference electrode)

Claims (10)

Potential difference between the first reference electrode on the ground surface immediately above the coating damage portion of the underground buried pipe at a predetermined depth and the second reference electrode separated by an arbitrary distance from the first reference electrode Are measured with a DC and AC voltmeter,
A direct current and an alternating current are respectively derived from the potential difference by a predetermined formula,
The current density of the coating damage part of the underground pipe, wherein the DC current density and the AC current density of the coating damage part are derived by dividing by the area of the coating damage part obtained in advance. Estimation method. The depth of the underground pipe is d, the distance between the reference electrodes is g, the earth (soil) resistivity is ρ, the measured ground potential difference of the direct current is ΔV _DC , and the measured ground potential difference of the target alternating current is as ΔV _AC, the following equation
The underground pipe according to claim 1, wherein the direct current I _DC and the alternating current I _AC flowing into the coating damage part are derived by the above and divided by the coating damage part area obtained in advance. Of estimating the current density of the damaged part of the coating. A first reference electrode on the ground surface at an arbitrary distance from directly above the coating damage portion of the underground buried pipe at a predetermined depth, and a second reference electrode separated from the first reference electrode by an arbitrary distance Measure the potential difference between the reference electrodes with a DC and AC voltmeter,
A direct current and an alternating current are respectively derived from the potential difference by a predetermined formula,
The current density of the coating damage part of the underground pipe, wherein the DC current density and the AC current density of the coating damage part are derived by dividing by the area of the coating damage part obtained in advance. Estimation method. The depth of the underground pipe is d, the distance between the reference electrodes is g, the distance from just above the coating damage portion of the underground pipe to one reference electrode is G, and the earth (soil) resistivity is ρ, DC ground surface potential difference measurement value is ΔV _DC , and the target AC ground surface potential measurement value is ΔV _AC.
The underground pipe according to claim 3, wherein the direct current I _DC and the alternating current I _AC flowing into the coating damaged part are derived by the above and divided by the coating damaged part area obtained in advance. Of estimating the current density of the damaged part of the coating.   The potential difference (voltage) between the underground buried tube and each verification electrode is measured, the voltage between the first verification electrode and the underground buried tube, the second verification electrode, and the underground 5. The underground embedment according to claim 1, wherein a potential difference (ΔV) between the first verification electrode and the second verification electrode is obtained from a difference with a voltage between the embedded tube and the first verification electrode. A method for estimating the current density of a damaged portion of a pipe coating.   6. An anticorrosion management method for evaluating an anticorrosion state of a coating damage portion using the current density estimated by the method according to any one of claims 1 to 5. A first reference electrode on the surface immediately above the coating damage portion of the underground buried pipe at a predetermined depth;
A second verification electrode separated from the first verification electrode by an arbitrary distance;
A voltmeter for measuring a potential difference between the reference electrodes with each of direct current and alternating current;
Means for deriving a direct current and an alternating current from the potential difference from a predetermined formula, respectively, and dividing by a previously obtained coating damage portion area to derive a direct current density and an alternating current density of the coating damage portion When,
An apparatus for estimating the current density of a coating-damaged portion of a buried underground pipe. A first reference electrode on the ground surface at an arbitrary distance from directly above the coating damage portion of the underground buried pipe at a predetermined depth;
A second verification electrode separated from the first verification electrode by an arbitrary distance;
A voltmeter for measuring a potential difference between the reference electrodes with each of direct current and alternating current;
Means for deriving a direct current and an alternating current from the potential difference from a predetermined formula, respectively, and dividing by a previously obtained coating damage portion area to derive a direct current density and an alternating current density of the coating damage portion When,
An apparatus for estimating the current density of a coating-damaged portion of a buried underground pipe.   The coating electrode damage part of the underground pipe according to claim 7 or 8, wherein the verification electrode is made of a conductive wheel, and the verification electrode and the voltmeter are mounted on a vehicle capable of traveling. Current density estimation device.   10. An anti-corrosion management apparatus for evaluating an anti-corrosion state of a coating damage part using the current density estimated by the apparatus according to claim 7.