A method for evaluating the detection area of ​​in-situ sensors for metal soil corrosion

Abstract

The present invention provides a method for evaluating the detection area of ​​a metal soil corrosion in-situ sensor, wherein a plurality of metal plates are prepared and laid in the soil, and are sequentially connected to a detection device through a wire, and a metal plate is added for a round of measurement until the average value and deviation of the obtained charge transfer resistance are within a set range. The present invention adopts a strategy of breaking the whole into parts, avoids the movement of a large-sized metal component as a working electrode during the measurement process, overcomes the detection error caused by the change in the properties of the soil medium caused by the movement of the electrode, and improves the accuracy of the monitoring area evaluation of the metal soil corrosion in-situ sensor.

Description

Technical Field

[0001] The invention relates to the field of corrosion sensors, and in particular to a detection area evaluation method for a metal soil corrosion in-situ detection sensor. Background Art

[0002] With the acceleration of my country's economic development and urbanization, the number of buried metal engineering components has shown a rapid growth trend, such as the grounding grid of power facilities, oil and gas pipelines, and various underground pipe networks in cities. Facilities buried underground for a long time will inevitably be affected by soil corrosion. If the anti-corrosion layer of underground facilities is damaged or aged and deteriorated, the main body will be directly corroded by the soil medium, resulting in corrosion thinning, perforation and even corrosion accidents. Metal soil corrosion has the characteristics of spontaneity and concealment. It is difficult to operate and maintain after commissioning, and once an accident occurs, it often causes huge losses. Early detection, diagnosis and effective prevention and control measures are important components of corrosion protection of metal components. Corrosion monitoring technology can provide an evaluation basis for the rationality of material selection, the effectiveness of protection measures and environmental conditions. By monitoring the corrosion rate of metal components, mastering the corrosion state, corrosion development speed and law of production facilities and structures, and taking targeted and timely corrosion protection measures, the life of components can be extended, the normal operation time can be maintained, and the service safety of components can be ensured.

[0003] The corrosion development of metal components serving in the soil is not only affected by the corrosiveness of the soil, but also by the service conditions. In order to accurately grasp the corrosion development of metal components in the soil, in-situ detection methods with metal components as the detection object have emerged. In recent years, with the rapid development of intelligent sensing technology, a variety of in-situ detection systems for soil corrosion of metal components have been made public. Since electrochemical corrosion is the main form of metal soil corrosion, the in-situ detection sensors for metal soil corrosion are mostly developed based on electrochemical principles. Electrochemical sensors for in-situ detection of metal soil corrosion usually use the metal component to be tested as the working electrode, including an auxiliary electrode and a reference electrode. Since the area of ​​the metal component is much larger than the auxiliary electrode, the electrical signal applied to the conductor through the auxiliary electrode is not confined to the metal segment to be tested, which makes the polarized metal area uncertain, resulting in a large error in the calculation of the corrosion current density. Therefore, determining the detection area of ​​the in-situ sensor for metal soil corrosion is of great significance for accurately detecting the corrosion rate of metal soil.

[0004] After searching, the document "Research on Electrochemical Grounding Grid Corrosion Detection Method" discloses a method for determining the detection area of ​​a metal component soil corrosion in-situ detection sensor based on the concept of effective test area, that is, the ratio of the polarization resistivity of the test metal to the polarization resistance of the metal electrode measured by the sensor is defined as the effective test area of ​​the sensor, where the polarization resistivity of the metal is determined by the material and the medium, and for large-scale research objects, the medium is assumed to be uniform. However, under actual conditions, the soil medium is not uniform everywhere, and the water content, salt content, and compactness of the soil will affect the measurement of the effective test area. Therefore, the sensor detection area determination method based on the effective test area has a large error in metal soil corrosion detection. The document "Constant current charging curve technology to measure the corrosion rate of carbon steel grounding grid" discloses a method for determining the detection area of ​​a metal component soil corrosion in-situ detection sensor by the lifting method, that is, the sample buried in the soil is continuously pulled out to reduce the area of ​​the sample buried in the soil. Under each sample buried area, electrochemical measurement is performed, and the polarization resistance value of the corresponding area is analyzed. When the polarization resistance value suddenly changes, the area at this time is the effective test area of ​​the sensor. However, in the process of pulling outward, the compactness of the soil will be affected, causing changes in the conductivity of the medium and introducing errors in the calculation of the effective test area. Summary of the invention

[0005] The purpose of the present invention is to provide a method for evaluating the detection area of ​​a metal soil corrosion in-situ sensor, which can solve the problem of detection errors caused by changes in soil medium properties due to electrode movement.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for evaluating the detection area of ​​metal soil corrosion in-situ sensors comprises the following steps:

[0008] S1. Prepare a metal plate numbered M0 with an area of ​​S0 and n metal plates numbered M1 to M2. n metal plate, S0 is the theoretical detection area of ​​the metal soil corrosion in-situ sensor;

[0009] S2. Place the low-resistance metal wire in contact with the metal plate to make the two electrically connected;

[0010] S3. Use corrosion-resistant materials to seal the contact points between the wire and the metal plate to prevent the exposed metal section of the metal wire and the overlapping parts of dissimilar metals from contacting the medium;

[0011] S4. Measure the remaining exposed area of ​​the metal plate after sealing, and record it as S'0, S1'…S' n ;

[0012] S5. Install the sensor on the metal plate M0 and lay it in the soil.n Lay the metal plates in the soil in order from near to far from M0, so that the soil completely covers the metal plates;

[0013] S6. Connect the other end of the metal wire connected to the metal plate M0 and the lead wire of the sensor to the corresponding interface of the detection device respectively;

[0014] S7. Connect the metal plate M0 to the detection device, measure three times continuously, and obtain the average value and deviation of the charge transfer resistance obtained by fitting the equivalent circuit of the three AC impedance spectra;

[0015] S8. While keeping the metal plate M0 connected to the detector, add another metal plate and M0 as the working electrode and connect them to the detector. Repeat the measurement steps of S7 until x i-1 -d i-1 ≤x i ≤x i-1 +d i-1 , where x i d i Add the last M i The average value and deviation of the charge transfer resistance when adding a metal plate, i>1, if it is not satisfied, continue to add a metal plate and measure again;

[0016] S9. Define the metal plate added at the end as M t , then the sum of the metal plate areas S = S'0 + S1' + ... + S t ' -1 It is the detection area of ​​the in-situ sensor.

[0017] Preferably, the contact method in step S2 is specifically as follows: a hole is opened at the edge of the metal plate, one end of the wire is passed through the hole and wrapped around, so that the metal segment of the metal wire contacts the metal plate.

[0018] Preferably, the wire is provided with a rigid casing.

[0019] Furthermore, one end of the rigid shell has a groove, the width of the groove is greater than the thickness of the metal plate, and the depth is greater than the sum of the diameter of the metal plate opening and the distance between the outer edge of the opening and the edge of the metal plate, so that after the metal plate is placed in the groove of the rigid shell, the rigid shell can completely cover the metal plate opening.

[0020] Preferably, the distance between the edge of the opening and the edge of the metal plate is between 5-10 mm, and the diameter of the opening does not exceed 5 mm.

[0021] Preferably, the metal plates M0 to M n There is a gap between them, which should not exceed 10mm, and the distance between the upper surface of the soil and the top of the sensor should be greater than 3cm.

[0022] Preferably, the metal plates M0 to M nThe center points are on the same horizontal line.

[0023] Preferably, the corrosion-resistant material is epoxy resin or polyvinyl chloride, which has a fixed volume after curing.

[0024] Preferably, the number of inlet holes of the connector is not less than n+1, and the number of outlet holes is not less than 1. The connector is provided with control switches equal to the number of inlet holes, which can control the connection and conduction of the incoming wires and the outgoing wires respectively.

[0025] Preferably, the measurement method adopts the alternating current impedance method of electrochemical measurement, the measurement frequency is 100kHz to 0.1Hz, and the excitation amplitude is 10mV.

[0026] The advantages of the present invention are that multiple metal plates are used to break the whole into parts, which not only ensures the accuracy of the test of large-sized metal components, but also avoids the movement of large-sized metal components serving as working electrodes during the measurement process of the prior art, overcomes the detection error caused by the change of soil medium properties caused by the movement of the electrode, and ensures the stability of the system during the measurement process to the greatest extent. It is generally applicable to various electrochemical sensors and soil media, and greatly improves the accuracy of the detection area evaluation of the metal soil corrosion in-situ sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of a method for evaluating the detection area of ​​an in-situ sensor for metal soil corrosion according to Example 1 of the present invention;

[0028] Figure 2 This is a connection diagram of the metal soil corrosion in-situ sensor detection area assessment system according to Example 1 of the present invention;

[0029] Figure 3 This is a schematic diagram of a zinc plate with a corner opening and a copper wire wound thereon according to Example 1 of the present invention;

[0030] Figure 4 This is a schematic diagram of the zinc plate and the rigid housing after being assembled in Example 1 of the present invention;

[0031] Among them, 1-circular hole, 2-zinc plate, 3-copper wire, 4-epoxy resin, 5-sensor, 6-connector, 7-lead wire, 8-auxiliary electrode, 9-reference electrode, 10-working electrode interface, 11-auxiliary electrode interface, 12-reference electrode interface, 13-wire switch, 14-rigid shell, 20-first zinc plate, 21-second zinc plate, 22-third zinc plate, 23-fourth zinc plate, 24-fifth zinc plate, 131 first wire switch, 132-second wire switch, 133-third wire switch, 134-fourth wire switch, 135-fifth wire switch, 136-sixth wire switch, 137-seventh wire switch. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0033] Example 1

[0034] This embodiment discloses a method for evaluating the detection area of ​​metal soil corrosion in-situ sensors. For the specific process, please refer to Figure 1 , please refer to the connection relationship of each device Figure 2 .

[0035] Step 1: Prepare a zinc plate 2 with a round hole 1 in one corner. The zinc plate 2 includes a zinc plate 20 numbered M0 with an area of ​​8×8 cm and five zinc plates 21-25 numbered M1-M5 with an area of ​​15×20 cm. The surfaces are polished to remove corrosion products.

[0036] Step 2: Please refer to Figure 3 , prepare 6 copper wires 3 with a length of 50 cm and with insulating sleeves, pass one end of the metal segment of the copper wire 3 through the opening 1 and wrap it, so that the metal segment of the copper wire 3 is fully in contact with the zinc plate 2. Use epoxy resin or polyvinyl chloride-like viscous material with a fixed volume after curing to seal the contact point. In this embodiment, epoxy resin 4 is preferably used to seal the contact point between the copper wire 3 and the zinc plate 2 to prevent the metal exposed segment of the copper wire 3 and the overlap between the wire and the zinc plate 2 from contacting the medium. The wire is covered with a rigid shell 14 made of polyvinyl chloride. One end of the rigid shell has a groove, the groove width is greater than the thickness of the zinc plate, and the depth is greater than the sum of the diameter of the zinc plate opening 1 and the distance between the outer edge of the opening and the edge of the metal plate, so that after the zinc plate is placed in the groove of the rigid shell, the rigid shell 14 can completely cover the metal plate opening 1.

[0037] Step 3: Wrap the copper wire 3 around the other five zinc plates 21-25 in the same way and seal them. Measure the remaining exposed area of ​​each zinc plate 2 after sealing. The area of ​​the zinc plate 20 (number M0) is 62.5 cm 2 The areas of zinc plates 21-25 (numbered M1 to M5) are 298.0 cm 2 、298.3cm 2 、298.8cm 2 、298.5cm 2 、299.1cm 2 .

[0038] Step 4: Set the detection area to 8×8cm. The theoretical detection area is 64cm 2 The sensor 5 is installed on the zinc plate 20 and laid in the soil. M1 to M5 are laid in the soil in order from near to far from M0. There is a gap between the metal plates, and the gap distance is 5mm. The metal plates are completely covered with soil, and the distance between the upper surface of the soil and the top of the sensor is 3cm, and M0 to M5 are laid in the soil in order from near to far.n The center points are on the same horizontal line.

[0039] Step 5: Connect the other ends of the copper wires connecting the metal plates M0~M5 to the access ports of the connector 6 respectively, and connect the lead wires 7 of the connector and the lead wires of the sensor auxiliary electrode 8 and reference electrode 9 to the working electrode interface 10, auxiliary electrode interface 11 and reference electrode interface 12 of the detection device respectively.

[0040] Step 6: Turn on the switch 131 (number g0) on the connector that connects the M0 wire, so that the M0 wire is connected to the lead wire 7. Using the AC impedance method, the measurement frequency is 100kHz~0.1Hz, the excitation amplitude is 10mV, the AC impedance spectrum is measured, the equivalent circuit is fitted, and the charge transfer resistance is analyzed. After three consecutive measurements, the average value x1 of the charge transfer resistance is 4409Ω·cm 2 , the deviation d1 is 353Ω·cm 2 .

[0041] Step 7: On the basis of keeping the first wire switch 131 turned on, open the second wire switch 132 (number g1) connected to M1 on the connector, so that the M0 wire and the M1 wire are connected to the lead wire 7 at the same time, that is, M0 and M1 are used as working electrodes of the sensor together, and repeat the measurement method of step 6 to obtain the average value x2 of the charge transfer resistance of 3863Ω·cm 2 , the deviation d2 is 377Ω·cm 2 .

[0042] Step 9: Compare x2 with x1±d1. Since 3863<(4409-353), the third wire switch 133 (number g2) connected to M2 on the connector is opened, and the metal plates M0 and M1 currently connected to the detector together form a working electrode, that is, M2 and M0, M1 together serve as the working electrode of the sensor. Repeat the measurement method of step 6 to obtain the average value of the charge transfer resistance x3 of 3002Ω·cm 2 , the deviation d3 is 410Ω·cm 2 .

[0043] Step 10: Compare x3 with x2±d2. Since 3002<(3863-377), the switch 134 (number g3) connected to the M3 wire on the connector is turned on. The metal plate M2, M0 and M1 that are currently connected to the detector together form a working electrode. That is, M3 and M0, M1 and M2 together serve as the working electrode of the sensor. Repeat the measurement method of step 6 to obtain the average value of the charge transfer resistance x4 of 2718Ω·cm 2 , the deviation d4 is 397Ω·cm 2 .

[0044] Step 11: Compare x4 and x3±d3, (3002-410)≤2718≤(3002+410), that is, increasing the working electrode area does not affect the result, so the detection area of ​​the metal soil corrosion in-situ sensor is judged to be 658.8cm 2 .

[0045] The measurement results are shown in Table 1.

[0046] Table 1 Electrochemical impedance spectroscopy fitting results for different working electrode compositions

[0047]

[0048]

[0049] Example 2

[0050] Other steps Based on Example 1, in order to make the metal segment of the copper wire 3 fully contact with the zinc plate 2, other connection methods can also be used, such as setting a mushroom-shaped metal hook on the zinc plate and fully winding the copper wire on the hook; or setting one end of the wire as a clip to clamp it on the metal plate, etc.

[0051] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for evaluating the detection area of ​​metal soil corrosion in-situ sensors, characterized in that: Includes steps: S1. Prepare 1 block numbered The area is The metal plates and n blocks are numbered as follows of metal sheets, The theoretical detection area of ​​the in-situ sensor for metal soil corrosion; S2. Put the low-resistance metal wire in contact with the metal plate to make the two electrically connected; S3. Use corrosion-resistant materials to seal the contact points between the wire and the metal plate to prevent the exposed metal section of the metal wire and the overlapping parts of dissimilar metals from contacting the medium; S4. Measure the remaining exposed area of ​​the metal plate after sealing and record it as ; S5. Install the sensor on the metal plate on and laid in the soil, According to distance Lay them in the soil from near to far, so that the soil completely covers the metal plates and sensors; S6. Connect the metal plates The other ends of the metal wires are connected to the access ports of the connectors respectively, and the lead wires of the connectors and the lead wires of the auxiliary electrode and the reference electrode of the sensor are connected to the working electrode interface, the auxiliary electrode interface and the reference electrode interface of the detection device respectively; S7. Conductive metal plate The detection device was used to measure three times in a row to obtain the average value of the charge transfer resistance obtained by fitting the equivalent circuit of the three AC impedance spectra. and deviation ; S8. Keep the metal plate On the basis of connecting with the detector, add a metal plate and Connect them to the detector as working electrodes and repeat the measurement steps of S7 until ,in , Add the last The average and deviation of the charge transfer resistance when the metal plate is If it is not satisfied, add another metal plate and measure again; S9. Define the number of the metal plate added at the end as , then the sum of the areas of the metal plates is It is the detection area of ​​the in-situ sensor.

2. The metal soil corrosion in-situ sensor detection area assessment method according to claim 1 is characterized in that: The contact method in step S2 is specifically as follows: a hole is opened at the edge of the metal plate, one end of the wire is passed through the hole and wrapped around, so that the metal segment of the metal wire contacts the metal plate.

3. The metal soil corrosion in-situ sensor detection area assessment method according to claim 2 is characterized in that: The wire is provided with a rigid casing.

4. The metal soil corrosion in-situ sensor detection area assessment method according to claim 3 is characterized in that: The rigid shell has a groove at one end, the width of the groove is greater than the thickness of the metal plate, and the depth is greater than the sum of the diameter of the metal plate opening and the distance between the outer edge of the opening and the edge of the metal plate, so that after the metal plate is placed in the groove of the rigid shell, the rigid shell can completely cover the metal plate opening.

5. The metal soil corrosion in-situ sensor detection area assessment method according to claim 2 is characterized in that: The distance between the edge of the opening and the edge of the metal plate is between 5-10 mm, and the diameter of the opening does not exceed 5 mm.

6. The metal soil corrosion in-situ sensor detection area assessment method according to claim 1 is characterized in that: The metal plate There is a gap between them, which should not exceed 10mm, and the distance between the upper surface of the soil and the top of the sensor should be greater than 3cm.

7. The metal soil corrosion in-situ sensor detection area assessment method according to claim 1 is characterized in that: The metal plate The center points are on the same horizontal line.

8. The metal soil corrosion in-situ sensor detection area assessment method according to claim 1 is characterized in that: The corrosion-resistant material is epoxy resin or polyvinyl chloride and has a fixed volume after being cured.

9. The metal soil corrosion in-situ sensor detection area assessment method according to claim 1, characterized in that: The number of the inlet holes of the connector is not less than n+1, and the number of the outlet holes is not less than 1. The connector is provided with control switches equal to the number of the inlet holes, which can respectively control the connection and conduction of the incoming wires and the outgoing wires.

10. The metal soil corrosion in-situ sensor detection area assessment method according to claim 1, characterized in that: The measurement method adopts the alternating current impedance method of electrochemical measurement, the measurement frequency is 100kHz~0.1Hz, and the excitation amplitude is 10mV.

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