JP2007271541A - Corrosion diagnosis device of underground embedded structure, and corrosion diagnostic method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize the corrosion diagnosis of an underground embedded structure with high precision. <P>SOLUTION: The corrosion diagnosis device for diagnosing corrosion of the underground embedded structure has an underground embedded structure made of steel, of which the outer surface is coated with a predetermined material, a coupon made of the same material as that of the underground embedded structure, electrically connected to the underground embedded structure and embedded in the vicinity of the underground embedded structure in a non-coated state, the grounding electrode embedded at a position separated from the underground embedded structure, a measuring means for measuring the electrochemical impedance between the underground embedded structure and the grounding electrode and a control means for diagnosing the corrosion of the underground embedded structure from the electrochemical impedance between the underground embedded structure and the grounding electrode obtained by the measuring means and the electrochemical impedance between the underground embedded structure, in a state where the coupon is electrically connected and the grounding electrode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an underground buried structure corrosion diagnostic apparatus and corrosion diagnostic method, and more particularly to an underground underground structure corrosion diagnostic apparatus and corrosion diagnostic method for realizing highly accurate corrosion diagnosis of steel underground buried structures. About.

  For example, underground buried structures consisting of tanks and pipes for storing fuel oil such as gasoline, kerosene, light oil, heavy oil (including pipes connected to the tank), or both, Installed in factories, offices, buildings, etc. with heavy oil / light oil boilers. In addition, the outside of the underground tank, which is an underground structure, is covered with asphalt, tar epoxy, FRP (Fiber Reinforced Plastics) or the like so as not to be corroded by soil. Furthermore, since the inside of the underground tank does not corrode the steel plate, which is a normal tank material, in the case of fuel oil or the like, the steel plate is in a bare state without special anticorrosion measures.

Conventionally, the above-described underground tank corrosion deterioration diagnosis method has been developed in the United States and the like (for example, see Non-Patent Document 1). This method includes underground tank data (capacity, years elapsed since burial, etc.), equipment corrosion environment data (stray current, soil resistivity, ground potential, etc.), soil chemistry data (chloride concentration, sulfide) Concentration, pH, etc.) and the amount of corrosion progress in the underground tank are measured, and the relationship between each data and the amount of corrosion progress in the underground tank is statistically analyzed. It is a technique to do. By using the prediction program developed by this method, the underground tank data of the diagnosis target underground tank, the corrosion environment data of the equipment, and the chemical property data of the soil are collected and applied to the prediction program. It is a technique.
ASTM standard G158-98, method A

  The problems of the above-described method are as follows. That is, the on-site data facilities to be collected are corrosive environment data and soil chemistry data, which are data on whether the environment in which the underground tank is buried is corrosive. However, even if the buried environment is corrosive, the underground tank will not corrode if the underground tank coating is sound. That is, it cannot be determined whether corrosion occurs in the underground tank to be diagnosed only from the corrosive environment data and the chemical property data of the soil. Therefore, it is considered that the diagnostic method based only on the corrosion environment data and the soil chemical property data has a low accuracy of prediction.

  The present invention has been made in view of the above problems, and provides a corrosion diagnosis apparatus and a corrosion diagnosis method for an underground buried structure for realizing a highly accurate corrosion diagnosis of a steel underground buried structure. For the purpose.

  In order to solve the above problems, the present invention employs means for solving the problems having the following characteristics.

  The invention described in claim 1 is a corrosion diagnostic apparatus for diagnosing the corrosion of underground structures, and is the same kind as an underground structure made of steel whose outer surface is coated with a predetermined material. A coupon that is electrically connected to the underground buried structure and is not covered in the vicinity of the underground buried structure, and buried at a position away from the underground buried structure. A grounding electrode, a measuring means for measuring an electrochemical impedance between the underground buried structure and the ground electrode, and an electrochemical impedance between the underground buried structure and the ground electrode obtained by the measuring means And a control means for diagnosing corrosion of the underground buried structure from the electrochemical impedance between the underground buried structure and the ground electrode in a state where the coupon is electrically connected Characterized in that it has and.

  According to the first aspect of the present invention, the corrosion diagnosis of the steel underground buried structure can be easily realized with the electrochemical impedance.

  The invention described in claim 2 is a corrosion diagnostic apparatus for diagnosing the corrosion of an underground buried structure, wherein the steel underground buried structure whose outer surface is coated with a predetermined material, and the same kind of the underground buried structure A plurality of coupons which are electrically connected to the underground buried structure and are not covered in the vicinity of the underground buried structure, and positions away from the underground buried structure A ground electrode embedded in the ground, a measuring means for measuring an electrochemical impedance between the underground buried structure and the ground electrode, and an electric power between the underground buried structure and the ground electrode obtained by the measuring means From the chemical impedance and the electrochemical impedance between the ground buried electrode and the ground electrode in a state where at least one of the plurality of coupons is electrically connected, the underground buried structure And having a control means for the diagnosis of corrosion of the object.

  According to the second aspect of the present invention, it is possible to easily realize a highly accurate corrosion diagnosis of a steel underground structure by electrochemical impedance using a plurality of coupons.

  According to a third aspect of the present invention, the control means includes an electrochemical impedance between the underground buried structure and the ground electrode, and between the underground buried structure to which the coupon is connected and the ground electrode. When the electrochemical impedance is different from a predetermined impedance characteristic, it is determined that the underground structure is abnormal.

  According to the third aspect of the present invention, only the change in the impedance shape is used as the determination material, so that the corrosion diagnosis can be performed even if the diagnosis practitioner does not have specialized knowledge of impedance analysis.

  The invention described in claim 4 is characterized in that the control means determines the degree of deterioration of the underground buried structure based on the surface area of the coupon buried in soil.

  According to the invention described in claim 4, since only the change in impedance shape corresponding to the surface area of the coupon is used as the determination material, the corrosion diagnosis can be performed even if the diagnosis practitioner has no specialized knowledge of impedance analysis. . Further, the degree of corrosion can be grasped with high accuracy.

  The invention described in claim 5 is characterized in that the plurality of coupons have the same surface area or different surface areas.

  According to the fifth aspect of the present invention, connection wiring in a plurality of coupons can be easily formed, and the degree to which an underground buried structure is corroded can be grasped with high accuracy using a plurality of coupons. Can do.

  The invention described in claim 6 is characterized in that it has a coupon moving means for moving the coupon in order to change the surface area in contact with the soil of the coupon.

  According to invention of Claim 6, the surface area of the coupon which touches soil can be changed quickly and reliably. Thereby, the corroded area | region of an underground buried structure can be grasped | ascertained with high precision.

  The invention described in claim 7 is a corrosion diagnosis method for diagnosing corrosion of an underground buried structure, wherein the steel underground buried structure whose outer surface is coated with a predetermined material, and the underground buried structure A first measurement step for measuring an electrochemical impedance between a ground electrode embedded at a distant position; and a material of the same kind as the underground buried object, and electrically connected to the underground buried structure. Second measurement for measuring electrochemical impedance between the underground electrode and the ground electrode in a state in which a coupon embedded in an uncovered state in the vicinity of the underground object is electrically connected And a diagnosis step of diagnosing corrosion of the underground structure based on the electrochemical impedance obtained by the first measurement step and the second measurement step. And features.

  According to the seventh aspect of the present invention, it is possible to easily realize high-precision corrosion diagnosis of steel underground structures by electrochemical impedance.

  The invention described in claim 8 is a corrosion diagnosis method for diagnosing the corrosion of an underground buried structure, comprising a steel underground buried structure whose outer surface is coated with a predetermined material, and the underground buried structure. A first measurement step for measuring an electrochemical impedance between a ground electrode embedded at a distant position; and a material of the same kind as the underground buried object, and electrically connected to the underground buried structure. Electrochemical impedance between the underground buried structure and the ground electrode in a state where at least one of a plurality of coupons buried without being covered in the vicinity of the underground buried structure is electrically connected And diagnosing corrosion of the underground structure on the basis of a second measurement step for measuring the impedance, and an electrochemical impedance obtained by the first measurement step and the second measurement step. And having a diagnostic step that.

  According to the eighth aspect of the present invention, it is possible to easily realize a highly accurate corrosion diagnosis of a steel underground structure by electrochemical impedance using a plurality of coupons.

  According to a ninth aspect of the present invention, in the diagnosis step, the electrochemical impedance between the underground buried structure and the ground electrode, and the underground buried structure to which the coupon is connected and the ground electrode When the electrochemical impedance is different from a predetermined impedance characteristic, it is diagnosed that the underground structure is abnormal.

  According to the ninth aspect of the present invention, since only the change in impedance shape is used as the judgment material, the corrosion diagnosis can be performed even if the diagnosis operator does not have specialized knowledge of impedance analysis. The invention described in claim 10 is characterized in that the diagnosis step determines the degree of deterioration of the underground buried structure based on the surface area of the coupon buried in soil.

  According to the invention described in claim 10, since only the change in impedance shape corresponding to the surface area of the coupon is used as the judgment material, the corrosion diagnosis can be performed without the diagnosis operator having specialized knowledge of impedance analysis. . Further, the degree of corrosion can be grasped with high accuracy.

  ADVANTAGE OF THE INVENTION According to this invention, the corrosion diagnosis of steel underground buried structure with high precision can be implement | achieved easily.

<Outline of the present invention>
The present invention provides a diagnostic apparatus for corrosion of underground tanks and the like, to which an electrochemical impedance method is applied. That is, the surface state of the underground structure is measured by the electrochemical impedance method, and the corrosion state of the underground structure is diagnosed from the result. Here, the electrochemical impedance method is the measurement of the electrochemical impedance between the underground buried structure to be diagnosed and the electrode or probe buried underground, and the measurement object in contact with the soil, that is, the surface of the underground buried structure. It is a way to know the state.

  In the electrochemical impedance method, a weak AC electrical signal is applied between the underground structure to be diagnosed and the electrode or probe buried underground, so that the diagnostic object can be inspected nondestructively. is there. Therefore, the electrochemical impedance method is applied to monitoring of underground tanks as underground structures such as gas stations and underground pipes connected to the tanks, thereby diagnosing corrosion and the like.

<Embodiment>
Below, the form which carried out suitably the corrosion diagnostic apparatus and corrosion diagnostic method of an underground burial structure in the present invention is explained in detail using a drawing.

<First embodiment>
FIG. 1 is a diagram illustrating an example of a schematic configuration of a corrosion diagnostic apparatus in the first embodiment. A corrosion diagnostic apparatus 10 shown in FIG. 1 includes a coupon (coupon electrode) 11, a ground (probe) 12 that is a ground electrode, a measuring unit 13, and a control unit 14.

  Here, in FIG. 1, as an example, an underground tank 1 is embedded in the underground soil 2 as a steel underground structure. The underground tank 1 is made of steel, and a predetermined coating 1a is provided so as to cover the outer surface of the tank.

  The coating 1a is, for example, covered with a predetermined coating material that does not oxidize, and is coated with an epoxy resin to form a coating layer having a certain thickness or more. The outer surface of the underground tank 1 and the soil 2 are electrically connected. It is insulated and protects the outer surface of the steel underground tank 1. Note that the covering means for covering the underground tank 1 is not necessarily coating, and other covering means may be used as long as it electrically insulates the outer surface of the underground tank 1 and the soil 2. May be.

  In addition, the underground tank 1 stores the atmosphere and the interior so that the tank is stored in fuel oil such as gasoline, kerosene, light oil, heavy oil, the stored fuel oil is discharged, and the tank is kept at atmospheric pressure. Has at least one pipe 1b.

  A part or all of the pipe 1b is an underground pipe, and is made of, for example, steel. Further, the outer surface of the underground pipe 1 b is covered with a resin coating in the same manner as the underground tank 1. In the present embodiment, the underground tank 1, the underground pipe 1b, or both constitute an underground buried structure.

  The coupon 11 is made of the same material as the underground tank 1. That is, in the above-mentioned embodiment, it consists of steel materials. The coupon 11 is buried in the vicinity of the underground tank 1. The coupon 11 is preferably made of the same material as the underground tank 1, but may be of the same type, that is, an iron-based material.

  In addition, at least one earth 12 is embedded at a predetermined distance from the underground tank 1. For example, a copper grounding rod or the like can be used as the ground 12. The measuring means 13 measures the electrochemical impedance between the ground 12 and an object such as the coupon 11 or the underground tank 1 (hereinafter, the electrochemical impedance is simply referred to as impedance).

  Further, the measuring means 13 has a “−” current terminal Lc and a potentio terminal Lp, and another current terminal Hc and a potentio terminal Hp. Hc and Lc indicate current terminals, and Hp and Lp indicate voltage terminals. Further, the measuring means 13 connects Lp and Lc to the underground tank 1 and connects Hp and Hc to the ground 12.

  Specifically, the underground tank 1 is electrically connected to the current terminal Lc via the wiring 21-21A, and is electrically connected to the potention terminal Lp via the wiring 21-21B. On the other hand, the ground 12, which is a ground electrode, is electrically connected to the current terminal Hc via the wiring 22-22A, and is also electrically connected to the potention terminal Hp via the wiring 22-22B.

  The measuring means 13 applies an AC voltage between Lp and Hp under the control of the control means 14 and measures the current flowing between Lc and Hc. Moreover, the impedance between the underground tank 1 and the earth 12 is determined by measuring the ratio between the alternating voltage and the alternating current at each frequency. In the impedance measurement in the measuring means 13, for example, Hioki Electric Co., Ltd. LCR high testers 3532-50 and 3522-50 can be used.

  Further, the control means 14 causes the measurement means 13 to perform corrosion measurement, inputs the measurement result from the measurement means 13, and whether or not corrosion or the like has occurred on the surface of the underground tank 1 as an underground buried structure. Diagnose etc.

  The control unit 14 can be realized using a general-purpose personal computer, a server, or the like. In this case, the control means 14 includes an input means for receiving input from the user and instruction information, an output means for outputting execution progress and diagnosis results by display and voice, calculation of measurement results by the measurement means 13, and general diagnosis processing. It has a CPU (Central Processing Unit) for controlling the above, an accumulating means for accumulating various data, etc., and controls the overall corrosion diagnosis apparatus.

  Further, the control means 14 can generate various graphs such as a Nyquist diagram, which will be described later, based on the measurement result by the measurement means 13 and display the graph by the output means.

  Moreover, the coupon 11 has switching means 23 such as a switch, and is selectively connected to the wiring 21 by the switching means 23. Note that switching of the switch ON / OFF by the switching unit 23 is controlled by the control unit 14.

<Diagnostic processing procedure in the first embodiment>
Diagnosis procedure>
Next, the diagnostic processing procedure by the corrosion diagnosis apparatus 10 for the steel underground structure described above will be described. FIG. 2 is a diagram illustrating an example of a diagnostic processing procedure in the first embodiment.

  Here, in the present embodiment, an alternating current having a predetermined voltage is applied to the current terminals Lc and Hc, and the impedance is measured by the potentio terminals LP and HP.

  First, the impedance between the underground tank 1 and the earth 12 is measured. Specifically, the measurement means 13 measures the impedance by applying an alternating current between the underground tank 1 and the earth 12 under the control from the control means 14 while changing the frequency from low to high. Diagnose corrosion of underground tank 1.

  That is, the impedance between the underground tank 1 and the earth 12 is measured (S01), and it is determined whether or not the impedance characteristic is a preset normal characteristic (state without deterioration) (S02).

  Here, FIG. 3 is a diagram for explaining impedance characteristics when there is no deterioration such as corrosion in the underground tank (when sound). Moreover, FIG. 4 is a figure which shows an example which replaced the relationship between an underground tank, earth | ground, and soil with the equivalent circuit. The curve shown in FIG. 3 shows the impedance characteristic when the coating of the underground tank 1 is not deteriorated and is completely covered with a Nyquist diagram. Further, the horizontal axis of the graph shown in FIG. 3 indicates the real component (Z ′) of the impedance, and the vertical axis indicates the imaginary component (Z ″) of the impedance.

  As shown in FIG. 3, a capacitive semicircle corresponding to the impedance of the earth / soil interface is seen on the locus of the impedance in the high frequency range. Here, the diameter of the capacitive semicircle becomes the charge transfer resistance Rctp at the earth / soil interface, and the convergence point at the high frequency limit becomes the soil resistance Rsol1 between the earth 12 and the underground tank 1. Further, the impedance in the low frequency region is a locus parallel to the imaginary axis. This is due to the capacitor component at the healthy underground tank / soil interface.

  In other words, when there is no abnormality in the coating 1a for the underground tank 1, that is, when the outer surface is completely covered, as shown in FIG. A parallel trajectory) tendency. In addition, when there is a deteriorated portion in the underground tank 1, that is, when the impedance characteristic is not normal (NO in S02), two capacitive semicircles appear in the Nyquist diagram. 1 is determined to be abnormal (deteriorated) (S03). The difference in impedance with the underground tank 1 in a healthy state can be clearly grasped by the impedance characteristics described above.

  If normal impedance characteristics are obtained in the process of S02 (YES in S02), then the switch 17 is turned on to connect the coupon 11 to the underground tank 1 (S04). Measure (S05). Further, after the measurement, it is determined whether or not the impedance characteristic is normal and predetermined (S06).

  In this case, since the coupon 11 is not covered at all, the coupon 11 with the outer surface made of the same material as the underground tank 1 with the outer surface exposed is added to the underground tank 1 which is a completely covered object. Will be. Therefore, if the underground tank 1 is normal, it does not rise vertically in the Nyquist diagram of the impedance characteristic, and further rises in a quadratic curve at a constant frequency.

  That is, when the impedance characteristic draws the above-described locus, it is determined that the impedance characteristic is an English-speaking predetermined impedance characteristic (YES in S06) and is normal (S07). If the impedance characteristics are not normal (NO in S06), it is determined that there is an abnormality (S03). In the case of abnormality, the user is notified by display or voice using the output means of the control means 14.

  As described above, when the underground tank 1 and the earth 12 are connected, the vertical tank stands up vertically, and when the coupon 11 is connected to the underground tank 1 and shows a tendency to rise in a quadratic curve state when measured, The coating 1a of the underground tank 1 itself can be diagnosed as having no deterioration on the outer surface of the underground tank 1.

  Here, the equivalent circuit of FIG. 4 will be specifically described. The equivalent circuit 30 shown in FIG. 4 includes a resistance element Rctp of the soil 2 near the surface of the earth 12, a capacitor element Cdlp near the surface of the earth 12, and a resistance element Rsol1 of the soil 2 between the earth 12 and the underground tank 1 When the outer surface of the underground tank 1 is soundly protected by the coating 1a, and when the underground tank 1 and the soil 2 are electrically insulated, the capacitor element is used as a capacitor having a large volume. Cp is shown.

  Here, when the coating 1a of the underground tank 1 is deteriorated and the external surface of the underground tank 1 is partially in electrical contact with the soil 2, the equivalent circuit shown in FIG. Can be expressed as: FIG. 5 is a diagram showing an example of an equivalent circuit showing a situation where the external surface of the underground tank is partially in electrical contact with the soil.

  That is, when a part of the underground tank 1 is in electrical contact with the soil 2, the resistance element Rsol2 + Rct2 and the capacitor element Cdl2 of the contact part are added (dotted line 31 shown in FIG. 5).

  Here, FIG. 6 is a diagram illustrating an example of an impedance measurement result when the underground tank and the ground are connected in a state where the external surface of the underground tank is partially in electrical contact with the soil.

  As a result of the deterioration of the coating 1a, the impedance measurement result in the state where the underground tank 1 and the ground 12 in a state where the outside of the underground tank 1 is partially in electrical contact with the soil 2 is connected is shown in the Nyquist diagram. As shown, for example, as shown in FIG. 6 (A), after a predetermined frequency, there is a tendency to rise in a quadratic curve without rising vertically.

  In this case, the coupon 11 is connected to the underground tank 1 by switching the switch by the switching means 23, and a specific corrosion diagnosis measurement is performed. Specifically, in the impedance characteristic when the coupon 11 is connected, the degree of deterioration is diagnosed by the slope of the quadratic curve after a predetermined frequency.

  For example, when there is no change in the slope of the quadratic curve after a predetermined frequency, diagnosis is made that the coating 1a has already deteriorated and is in electrical contact with the soil 2 in an area sufficiently larger than the surface area of the coupon 11. Can do.

  In addition, as shown in FIG. 6B, when there is a change in the slope of the quadratic curve after the predetermined frequency with the coupon 11, in this case, the coating 1a having the same surface area as the surface area of the coupon 11 is provided. It can be estimated that it has deteriorated and is in electrical contact with the soil 2.

  As described above, in the above-described embodiment, it is possible to diagnose the deterioration state of the coating 1a in the underground tank 1 from the change in the impedance characteristics. Therefore, it can be diagnosed from this diagnosis result whether or not the conditions for starting corrosion are in place for the underground tank 1.

  Here, the diagnostic processing procedure of the underground structure using the coupon 11 as described above will be described using a flowchart. FIG. 7 is a flowchart illustrating an example of a diagnostic processing procedure using a coupon.

  In the diagnostic processing procedure shown in FIG. 7, first, the impedance between the underground tank 1 and the ground 12 is measured (S11), and it is determined whether or not the impedance characteristic is normal (S12). Next, when the impedance characteristic is not normal (NO in S12), the coupon 11 is connected to the underground tank 1 (S13), and the impedance is measured with the coupon 11 connected (S14).

  Here, it is determined whether or not there is a change in the slopes of the two quadratic curves in the presence or absence of the coupon 11 (S15). If there is no change (YES in S15), the underground tank 1 is equal to or larger than the surface area of the coupon 11. It is determined that the area has deteriorated (S16). Moreover, in the process of S15, when there is a change in the slopes of the two quadratic curves in the presence or absence of the coupon 11 (NO in S15), it is determined that the area equivalent to the surface area of the coupon 11 has deteriorated (S17). ). Note that the presence or absence of a change in S15 is determined using a preset allowable range (threshold).

  If there is a normal impedance characteristic in the processing of S12 (YES in S12), it is determined as normal (S18). Thereby, it is possible to estimate the state (range) of corrosion of the underground tank to some extent.

  In the present embodiment, the corrosion diagnosis procedure has been described with respect to the relationship between the underground tank 1 and the earth 12. However, the present invention is not limited to this. For example, the diagnosis procedure described above with respect to the relationship between the pipe 1 b and the earth 12 is used. You may go. Further, the corrosion diagnosis may be performed with the underground tank 1 and the underground pipe 1b as one underground buried structure.

<Second embodiment>
Next, a second embodiment of the corrosion diagnostic apparatus according to the present invention will be described with reference to the drawings. FIG. 8 is a diagram illustrating an example of a schematic configuration of the corrosion diagnosis apparatus according to the second embodiment. In addition, the same number is given about the structure similar to 1st Example mentioned above, and description here is abbreviate | omitted.

  In the corrosion diagnosis apparatus 40 shown in FIG. 8, a plurality of coupons 41A, 41B, and 41C having the same surface area are embedded at different depths. In addition, there is no restriction | limiting in particular about the number of coupons, Moreover, the embedment position of a coupon is not specified but can be installed arbitrarily.

  In addition, the value of impedance is so small that the coupon 41 embed | buried deeply with respect to the soil 2 is so small that it is embed | buried shallowly. This is because the amount of water contained in the soil 2 varies depending on the depth in the ground. The closer to the ground surface, the smaller the amount of water in the soil 2, and the farther from the ground surface, the greater the amount of water.

  In the second embodiment, the switching means 42 such as a switch can be selectively connected to the four terminals. The four terminals are a terminal connected to the coupon 41A, a terminal connected to the coupons 41A and 41B, a terminal connected to the coupons 41A, 41B and 41C, and a terminal not connected to any coupon. . The switching means 42 can be connected to any one of the terminals described above. The switching control in the switching unit 42 is performed by control from the control unit 14.

<Measurement Process for Impedance Characteristics in Second Embodiment>
Next, the impedance characteristic measurement process in the second embodiment will be described. First, impedance characteristics in a state where only the underground tank 1 and the ground 12 are connected are measured. Next, the impedance of the underground tank 1 and the ground 12 is measured in a state where the coupons 41 are sequentially connected to the underground tank 1.

  Specifically, the impedance characteristic is measured with the coupon 41A connected first, then the impedance characteristic is measured with the coupon 41A and 41B connected, and then the coupon 41A, 41B and 41C is connected. Measure impedance characteristics.

  That is, each impedance characteristic is measured while sequentially increasing the total surface area of the coupon 41. In the above-described measurement of impedance characteristics, the order of increase / decrease in the total surface area is not particularly limited as long as the coupons are connected so that the surface areas of the coupons are sequentially different.

  Here, FIG. 9 is a diagram illustrating an example of the impedance measurement result when the underground tank and the ground are connected in the second embodiment. The horizontal axis of the graph shown in FIG. 9 indicates the real component (Z ′) of the impedance, and the vertical axis indicates the imaginary component (Z ″) of the impedance.

  In the Nyquist diagram shown in FIG. 9, the Nyquist diagram based on the impedance measurement result by connecting only the underground tank 1 and the earth 12 has a tendency to rise vertically at a predetermined frequency when there is no deterioration due to corrosion. (FIG. 9A). Moreover, when there is deterioration due to corrosion such as the coating 1a of the underground tank 1 being peeled off in a state where the coupon 11 is not yet inserted, different quadratic curves are formed at frequencies after a predetermined frequency. (FIG. 9B).

  Here, in order to measure the degree of deterioration when the underground tank 1 is deteriorated, the impedance characteristics are measured while changing the surface area of the coupon using the coupons 41A, 41B, and 41C. Specifically, when the underground tank 1 is deteriorated, the impedance becomes a locus of a quadratic curve as shown in FIG. At this time, the combined impedance value Z of the impedance value Z generated by the underground tank 1 and the impedance Z2 of the coupon 11 has a relationship of Z = 1 / ((1 / Z1) + (1 / Z2)).

  Therefore, assuming that the distance from the position of the frequency at which the locus of the quadratic curve in FIG. 9B starts to the portion that draws the quadratic curve and touches the horizontal axis (the real component of impedance) is L, the underground tank 1 and the coupon When the surface area sizes of the two are the same, the distance L from the frequency at which the locus of the quadratic curve starts to the portion that draws the quadratic curve and touches the horizontal axis is 1 / 2L. That is, the surface area of the coupon when it becomes 1 / 2L becomes the surface area of the defective portion due to deterioration of the underground tank 1 or the like.

  9 will be described in detail. FIG. 9C shows impedance characteristics in a state where the deteriorated underground tank 1 and the coupon 41A are connected in the above-described corrosion diagnostic apparatus 40. FIG. (D) shows the impedance characteristic in the state in which the deteriorated underground tank 1 and the coupons 41A and 41B are connected, and FIG. 9 (E) shows the state in which the underground tank 1 and the coupons 41A, 41B, and 41C are connected. The impedance characteristics are shown.

  In addition, when the distance from the frequency at which the locus of the quadratic curve starts in FIG. 9E to the part that draws the quadratic curve and touches the horizontal axis is about ½ of the distance L described above, From the relational expression of the synthetic impedance value Z described above, it can be diagnosed that the deteriorated region of the underground tank 1 is equivalent to the total total surface area of the coupons 41A, 41B, 41C.

  In addition, the Nyquist diagram in the impedance characteristics rises in a quadratic curve after a predetermined frequency, as shown in FIG. 9B, with the measurement result obtained by connecting only the underground tank 1 and the earth 12. Show a tendency to Further, when a quadratic curve is obtained after a predetermined frequency, the characteristics after the predetermined frequency when the coupon connected to the underground tank 1 by the cobons 41A, 41B, 41C is increased and sequentially connected are measured. When there is no change, it can be estimated that the area where the coating 1a is deteriorated is larger than the total surface area of the most influential coupons 41A, 41B and 41C.

  As shown in the second embodiment described above, by providing a plurality of coupons 11 (three in the above example), the measurement result on the surface area of any coupon is obtained, and the degree of corrosion deterioration of the underground tank 1 is grasped with high accuracy. can do.

<Diagnostic processing procedure in the second embodiment>
Here, the diagnostic processing procedure in the second embodiment will be described with reference to a flowchart. FIG. 10 is a flowchart showing an example of a diagnostic processing procedure in the second embodiment. In FIG. 10, first, the impedance between the underground tank 1 and the earth 12 is measured (S21), and it is determined whether or not the impedance characteristic is normal (S22). Next, when the impedance characteristics are not normal (NO in S22), the coupon 41 is connected to the underground tank (S23), and the impedance is measured with the coupon 41 connected (S24).

  Here, it is determined whether or not the impedance characteristic is a predetermined impedance characteristic from the impedance measurement result (S25). Specifically, it is determined whether or not a predetermined impedance characteristic is obtained in which the quadratic curve measured in S24 is ½ of the distance L of the quadratic curve measured in S21. Here, when it is not a predetermined impedance characteristic (in S25, NO), the surface area of the coupon 41 is changed (S27), it returns to S24, and the process mentioned above with the changed coupon 41 is performed. Further, in the process of S25, when the measured impedance characteristic is the above-described predetermined impedance characteristic (YES in S25), the surface area of the coupon 41 at the present time is determined as the deterioration area of the underground tank (S26). If the impedance characteristic is normal in S22 (YES in S22), it is determined as normal (S28).

  Thereby, the degree (range) of corrosion of the underground tank can be grasped with high accuracy.

<Configuration example of other coupons>
Here, in the example of the coupon in the present invention described above, a plurality of coupons having the same surface area may be provided as described above, but the impedance may be measured by sequentially changing the surface area of the coupon by another method. .

  FIG. 11 is a diagram for explaining another coupon example in the present invention. FIG. 11 shows only the switching means, coupon, ground, and underground structure.

  As an example of the coupon, for example, as shown in FIG. 11A, coupons 51A, 51B, and 51C having different surface areas are provided. Therefore, the impedance characteristics can be measured by sequentially switching the coupons by the switching means 52. Of the surface coupons 51A, 51B, and 51C having different surface areas, a plurality of the surface coupons 51A, 51B, and 51C may be connected to measure impedance characteristics. Note that the switching control in the switching means 52 described above is performed by control from the control means 14.

  Moreover, as shown in FIG.11 (b), you may provide the cylindrical or stick-shaped coupon 61 and the coupon moving means 62 to which the coupon 61 is moved. In this case, when the underground tank 1 is deteriorated due to the impedance characteristics between the underground tank 1 and the ground 12, the switch is turned on by the switching means 63. Then, the coupon moving means 62 measures the impedance characteristics while burying the coupon 61 at every predetermined depth and sequentially changing the surface area in contact with the soil 2. Thereby, the degree (range) of deterioration in the underground tank 1 can be easily grasped in more detail and simply.

  In the above-described embodiment, the description has been made using an underground tank as an example of an underground buried structure. However, the present invention is not limited to this. For example, an underground buried structure in which only a pipe or a combination of an underground tank and a pipe is used. The present invention can also be applied to products.

  In this case, particularly when the underground tank and the pipe are electrically connected, it is necessary to consider the following points regarding the relationship between impedance and corrosion detection. When there is a deteriorated part (defect part) in the underground tank or pipe, since the deteriorated part / soil interface impedance is small, the response current due to the applied voltage selectively flows to the deteriorated part. Here, when there is no deterioration in the piping, since the impedance of the piping is large, even if the underground tank and the piping are electrically connected, there is no influence on the determination of the presence or absence of deterioration in the underground tank.

  On the other hand, when a deteriorated portion exists in the pipe, the impedance of the pipe becomes small. Therefore, when the underground tank and the pipe are electrically connected, the impedance of the deteriorated pipe is added to the impedance of the underground tank.

  Furthermore, when the underground tank is not single and a plurality of underground tanks (and / or pipes) are embedded, the present invention can be applied by connecting to each underground tank. In addition, even when the underground tank is divided into several rooms and each stores different fuels, the present invention can be applied by regarding the underground tank as a single underground structure. it can.

  As described above, according to the present invention, highly accurate corrosion diagnosis of steel underground structures can be realized. Specifically, by measuring the impedance of the underground buried structure between the probes, setting an equivalent circuit and comparing it with the impedance, the soil resistance and the corrosion resistance of the buried structure can be obtained. In addition, it is possible to detect deterioration of a simple steel underground structure using a coupon electrode. That is, in the present invention, only the change in the impedance shape is used as the judgment material, so that the corrosion diagnosis can be performed even if the user who is the diagnosis person has no specialized knowledge of impedance analysis.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to such specific embodiments, and various modifications, within the scope of the gist of the present invention described in the claims, It can be changed.

It is a figure which shows an example of schematic structure of the corrosion diagnostic apparatus in 1st Example. It is a figure which shows an example of the diagnostic processing procedure in 1st Example. It is a figure for demonstrating the impedance characteristic when there is no deterioration, such as corrosion, in an underground tank (when healthy). It is a figure which shows an example which replaced the relationship between an underground tank, earth | ground, and soil with the equivalent circuit. It is a figure which shows an example of the equivalent circuit which shows the condition where the external surface of an underground tank is partially in contact with the soil. It is a figure which shows an example of an impedance measurement result when the underground tank and the earth | ground are connected in the state in which the external surface of an underground tank is partially in electrical contact with soil. It is a flowchart which shows an example of the diagnostic processing procedure using a coupon. It is a figure which shows an example of schematic structure of the corrosion diagnostic apparatus in 2nd Example. It is a figure which shows an example of an impedance measurement result when the underground tank and earth | ground are connected in 2nd Example. It is a flowchart which shows an example of the diagnostic processing procedure in 2nd Example. It is a figure for demonstrating the example of another coupon in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Underground tank 1a Coating layer 1b Piping 2 Soil 10,40 Corrosion diagnostic device 11,41,51,61 Coupon 12 Ground (grounding electrode)
DESCRIPTION OF SYMBOLS 13 Measuring means 14 Control means 21,22 Wiring 23,42,52,63 Switching means 30 Equivalent circuit 31 Dotted line 62 Coupon moving means

Claims (10)

A corrosion diagnostic device for diagnosing the corrosion of underground structures,
A steel underground structure whose outer surface is coated with a predetermined material;
A coupon made of the same kind of material as the underground buried object, electrically connected to the underground buried structure, and embedded in an uncovered state in the vicinity of the underground buried structure,
A ground electrode embedded in a position away from the underground embedded structure;
Measuring means for measuring electrochemical impedance between the underground structure and the ground electrode;
Electrochemical impedance between the underground buried structure and the ground electrode obtained by the measuring means, and electrochemical impedance between the underground buried structure and the ground electrode in a state where the coupon is electrically connected And a control means for diagnosing the corrosion of the underground structure. A corrosion diagnostic device for diagnosing the corrosion of underground structures,
A steel underground structure whose outer surface is coated with a predetermined material;
A plurality of coupons made of the same kind of material as the underground buried object, electrically connected to the underground buried structure, and embedded without being covered in the vicinity of the underground buried structure,
A ground electrode embedded in a position away from the underground embedded structure;
Measuring means for measuring electrochemical impedance between the underground structure and the ground electrode;
Electrochemical impedance between the underground buried structure and the ground electrode obtained by measuring means, and the underground buried structure and the ground electrode in a state where at least one of the plurality of coupons is electrically connected And a control means for diagnosing the corrosion of the underground structure from the electrochemical impedance between them. The control means includes
The electrochemical impedance between the underground buried structure and the ground electrode and the electrochemical impedance between the underground buried structure to which the coupon is connected and the ground electrode are different from predetermined impedance characteristics, respectively. The corrosion diagnosing apparatus according to claim 1, wherein it is determined that the underground structure is abnormal. The control means includes
The corrosion diagnosis apparatus according to claim 3, wherein the degree of deterioration of the underground buried structure is determined based on a surface area of the coupon buried in soil.   The corrosion diagnosis apparatus according to claim 2, wherein the plurality of coupons have the same surface area or different surface areas.   The corrosion diagnosis apparatus according to claim 1, further comprising a coupon moving unit configured to move the coupon in order to change a surface area in contact with soil of the coupon. A corrosion diagnosis method for diagnosing the corrosion of underground structures,
A first measurement step of measuring an electrochemical impedance between a steel underground buried structure whose outer surface is coated with a predetermined material and a ground electrode buried in a position away from the underground buried structure;
Made of the same kind of material as the underground buried object, electrically connected to the underground buried structure, and a coupon buried in an uncovered state in the vicinity of the underground buried structure was electrically connected A second measuring step for measuring an electrochemical impedance between the grounded underground structure and the ground electrode;
And a diagnostic step of diagnosing the corrosion of the underground structure based on the electrochemical impedance obtained by the first measurement step and the second measurement step. A corrosion diagnosis method for diagnosing the corrosion of underground structures,
A first measurement step of measuring an electrochemical impedance between a steel underground buried structure whose outer surface is coated with a predetermined material and a ground electrode buried in a position away from the underground buried structure;
It is made of the same kind of material as the underground buried object, and is electrically connected to the underground buried structure and at least one of a plurality of coupons buried without being covered in the vicinity of the underground buried structure is A second measuring step for measuring an electrochemical impedance between the underground buried structure and the ground electrode in an electrically connected state;
And a diagnostic step of diagnosing the corrosion of the underground structure based on the electrochemical impedance obtained by the first measurement step and the second measurement step. The diagnostic step includes
The electrochemical impedance between the underground buried structure and the ground electrode and the electrochemical impedance between the underground buried structure to which the coupon is connected and the ground electrode are different from predetermined impedance characteristics, respectively. In this case, the corrosion diagnosis method according to claim 7 or 8, wherein the underground buried structure is diagnosed as having an abnormality. The diagnostic step includes
The corrosion diagnosis method according to claim 9, wherein a degree of deterioration of the underground buried structure is determined based on a surface area of the coupon buried in soil.

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