Corrosion monitoring sensor and method for suppressing corrosion

Abstract

To provide a corrosion monitoring sensor and a method for suppressing corrosion which can precisely derive the rate of corrosion of metal.SOLUTION: The corrosion monitoring sensor includes: a pair of electrodes 20 for measuring the polarization resistance of metal exposed to corrosive environments; and a piezoelectric element 30 for measuring the rate of corrosion of the metal.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a corrosion monitoring sensor and a corrosion inhibition method.

Background Art

[0002] There is a corrosion monitoring sensor as a device for measuring the corrosion state of a metal to be evaluated in a corrosive environment. The corrosion monitoring sensor, for example, exposes an electrode made of the metal to be evaluated to the corrosive environment and analyzes the corrosion rate by electrochemical measurement. In Patent Document 1, for the purpose of enabling stable use and facilitating handling such as transportation, an electrode part base, which is an insulator, is attached to a part of the side surface of a metal probe so as not to divide the probe in the longitudinal direction, and a corrosion monitoring sensor is disclosed in which a reference electrode is provided on the electrode part base together with a sample electrode made of the above-mentioned metal to be evaluated and its counter electrode. In Patent Document 2, for the purpose of preventing crevice corrosion and performing accurate electrochemical measurement, a pair of electrode members each having an electrode surface exposed to a dew point corrosion environment, and a holder for embedding and holding the pair of electrode members in an adjacent state are provided, and a liquid junction forming part for forming a liquid junction of condensed water is formed between the electrode surfaces in an acid dew point environment, and a corrosion monitoring sensor in which a part of the holder covering the electrode member is made of a water-repellent resin material is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Documents 1 and 2, it is stated that the corrosion rate of a metal can be detected by obtaining the polarization resistance correlated with the corrosion rate of the metal. In Patent Document 1, it is stated that if the relationship between the corrosion rate of the metal and the polarization resistance is obtained in advance, the corrosion rate can be derived from the polarization resistance. Here, when the polarization resistance of the metal is Rp and the proportionality constant is K, the corrosion current density icorr of the metal is given by the Stern - Geary equation icorr = K / Rp and is obtained by this equation. The proportionality constant K is said to depend on the type of the metal to be evaluated and the corrosion environment in which the metal to be evaluated is placed. In the conventional corrosion monitoring sensor, the proportionality constant K is experimentally determined from the corrosion current density icorr obtained from the result of measuring the amount of corrosion reduction of the metal over a certain period and the polarization resistance Rp during that period. That is, in the conventional corrosion monitoring sensor, for example, the corrosion current density icorr of the metal is obtained by placing a metal sample in an actual corrosion environment or an experimental environment simulating the actual environment for a certain period. For this reason, for example, it takes time to measure the corrosion current density icorr and it is inefficient. Also, it is difficult to obtain the corrosion current density icorr that changes at any time due to changes in the corrosion environment, etc. in real time. Therefore, it is difficult to accurately reflect changes in the corrosion rate due to changes in the corrosion environment and the progress of corrosion. Thus, there is a problem in the derivation accuracy of the corrosion current density icorr of the metal.

[0005] The present invention has been made in view of the above - described circumstances, and an object thereof is to provide a corrosion monitoring sensor and a corrosion suppression method capable of accurately deriving the corrosion rate of a metal.

Means for Solving the Problems

[0006] <1>The corrosion monitoring sensor according to Embodiment 1 of the present invention is characterized by including a pair of electrodes capable of measuring the polarization resistance of a metal exposed to a corrosion environment and a piezoelectric element capable of measuring the corrosion rate of the metal.

[0007] According to the present invention, it includes a pair of electrodes capable of measuring the polarization resistance of a metal exposed to a corrosive environment, and a piezoelectric element capable of measuring the corrosion rate of the metal. In addition to making it possible to measure the polarization resistance of the metal with a pair of electrodes, by making it possible to measure the corrosion rate of the metal with a piezoelectric element, the proportionality constant K in the above-mentioned Stern-Geary equation can be derived in real time. That is, the proportionality constant K, whose value changes due to changes in the corrosive environment, materials, etc., can be obtained on-site immediately. Therefore, for example, when deriving the proportionality constant K, compared with the case where the corrosion current density icorr is based on the result of measuring the corrosion of the metal for a certain period, it is possible to accurately reflect changes in the corrosive environment and changes in the corrosion rate due to the progress of corrosion. For this reason, the proportionality constant K can be derived in real time on-site. Thus, the derivation of the corrosion rate of the metal can be carried out with high accuracy.

[0008] <2>The corrosion monitoring sensor according to Aspect 2 of the present invention is the corrosion monitoring sensor according to Aspect 1, further comprising an exposed member, wherein the exposed member has an exposed portion that is the portion exposed to the corrosive environment and a non-exposed portion that is the portion other than the exposed portion, and the piezoelectric element is provided in the non-exposed portion.

[0009] According to the present invention, the exposed member has an exposed portion that is the portion exposed to the corrosive environment and a non-exposed portion that is the portion other than the exposed portion. The piezoelectric element is provided in the non-exposed portion. Thereby, for example, compared with the case where the piezoelectric element is provided in the exposed portion of the exposed member, the arrangement of the piezoelectric element can be easily performed.

[0010] <3>The corrosion monitoring sensor according to Aspect 3 of the present invention is the corrosion monitoring sensor according to Aspect 2, wherein a part of each of the pair of electrodes is exposed to the corrosive environment, and the non-exposed portion is the portion of each of the pair of electrodes other than the part exposed to the corrosive environment.

[0011] According to the present invention, the non-exposed portion of the exposed member is a portion of each of the pair of electrodes other than a portion that is exposed to the corrosion environment. Therefore, the piezoelectric element is provided in a portion of each of the pair of electrodes other than a portion that is exposed to the corrosion environment. By providing the piezoelectric element on the pair of electrodes in this way, for example, the temperature condition of the piezoelectric element can be made close to the temperature conditions of each of the pair of electrodes. Therefore, for example, the measurement of the corrosion rate of the metal by the piezoelectric element can be performed with higher accuracy.

[0012] <4>The corrosion monitoring sensor according to Aspect 4 of the present invention is the corrosion monitoring sensor according to Aspect 2, wherein the non-exposed portion is a portion of the metal other than a portion that is exposed to the corrosion environment.

[0013] According to the present invention, the non-exposed portion of the exposed member is a portion of the metal other than a portion that is exposed to the corrosion environment. Therefore, the piezoelectric element is provided in a portion of the metal other than a portion that is exposed to the corrosion environment. By providing the piezoelectric element in a part of the metal in this way, for example, the corrosion rate of the metal whose polarization resistance is measured by a pair of electrodes can be measured. Therefore, for example, the polarization resistance and the corrosion rate in the metal exposed to the corrosion environment can be measured simultaneously.

[0014] <5>The corrosion monitoring sensor according to Aspect 5 of the present invention is the corrosion monitoring sensor according to any one of Aspects 1 to 4, wherein the portion of the metal that is exposed to the corrosion environment includes a corrosion-prone portion that is relatively easy to corrode and a corrosion-resistant portion that is relatively difficult to corrode.

[0015] Here, for example, when measuring the thickness of a metal by ultrasonic thickness measurement, the speed at which ultrasonic waves propagate inside the metal may change due to a change in the temperature of the metal. As a result, for example, it may affect the accuracy when measuring the change in the thickness of the metal due to corrosion by ultrasonic thickness measurement.

[0016] According to the present invention, a metal part that is exposed to a corrosive environment includes a corrosion-prone part that is relatively prone to corrosion and a corrosion-resistant part that is relatively resistant to corrosion. Thereby, for example, in a metal, a part that is likely to change in thickness due to corrosion and a part that is unlikely to change in thickness can be provided.

[0017] Therefore, for example, when measuring the corrosion-prone part of a metal by ultrasonic thickness measurement, even if the measurement result changes due to a change in temperature or the like, based on the change amount of the measurement result of the corrosion-resistant part that is unlikely to change in thickness due to corrosion, the measurement result can be corrected. Therefore, even when the temperature of the metal changes, the corrosion rate of the corrosion-prone part can be accurately measured. Thus, the measurement of the corrosion rate of the metal can be carried out with higher precision.

[0018] <6>The corrosion monitoring sensor according to Aspect 6 of the present invention is the corrosion monitoring sensor according to Aspect 5, wherein the piezoelectric element includes a first piezoelectric element and a second piezoelectric element, the first piezoelectric element is located at a position corresponding to the corrosion-prone part, and the second piezoelectric element is located at a position corresponding to the corrosion-resistant part.

[0019] According to the present invention, the piezoelectric element includes a first piezoelectric element and a second piezoelectric element. The first piezoelectric element is located at a position corresponding to a portion of the metal that is relatively easily corroded, i.e., an easily corroded portion, and the second piezoelectric element is located at a position corresponding to a portion of the metal that is relatively difficult to corrode, i.e., a difficult-to-corrode portion. By providing piezoelectric elements individually for each of the easily corroded portion and the difficult-to-corrode portion in this way, for example, the correction of the measurement result of the ultrasonic thickness measurement of the easily corroded portion based on the measurement result of the ultrasonic thickness measurement of the difficult-to-corrode portion described above can be performed more reliably. Therefore, for example, the measurement of the corrosion rate of the easily corroded portion can be performed with higher accuracy. Also, when performing ultrasonic thickness measurement with one piezoelectric element, when the temperature of the measurement unit changes, it is necessary to correct (temperature correction) the information on the speed of sound used for thickness calculation each time. On the other hand, by arranging the first piezoelectric element and the second piezoelectric element as described above, it is possible to perform ultrasonic thickness measurement while grasping the change in the speed of sound in real time and always using the latest information on the speed of sound. That is, it is possible to eliminate the need to perform temperature correction each time with the change in temperature. Therefore, the efficiency of ultrasonic thickness measurement can be further improved.

[0020] <7>The corrosion monitoring sensor according to aspect 7 of the present invention is the corrosion monitoring sensor according to any one of aspects 1 to 6, wherein the metal has a first distance portion which is a portion of the metal and the distance from the portion of the metal exposed to the corrosion environment to the portion of the metal on the opposite side of the portion of the metal exposed to the corrosion environment is a first distance, and a second distance portion which is a portion of the metal and the distance from the portion of the metal exposed to the corrosion environment to the portion of the metal on the opposite side of the portion of the metal exposed to the corrosion environment is a second distance, and the first distance and the second distance are different.

[0021] According to the present invention, the metal has a first distance portion which is a portion of the metal and the distance from the portion of the metal exposed to the corrosion environment to the portion of the metal on the opposite side of the portion of the metal exposed to the corrosion environment is a first distance, and a second distance portion which is a portion of the metal and the distance from the portion of the metal exposed to the corrosion environment to the portion of the metal on the opposite side of the portion of the metal exposed to the corrosion environment is a second distance. The first distance and the second distance are different. Accordingly, for example, in the first distance portion and the second distance portion, if the metal portions exposed to the corrosive environment are flush, even if the first distance and the second distance change due to corrosion, the difference between the first distance and the second distance can be prevented from changing.

[0022] Therefore, for example, when the first distance portion and the second distance portion in the metal are measured by ultrasonic thickness measurement respectively, even if the respective measurement results change due to temperature change or the like, the measurement results can be corrected based on the change amount of the difference between the measurement result of the first distance portion and the measurement result of the second distance portion. Therefore, for example, even when the temperature of the metal changes, the first distance and the second distance can be measured more accurately. Thus, based on these measurement results, the corrosion rate of the metal can be measured with higher precision.

[0023] <8>The corrosion monitoring sensor according to aspect 8 of the present invention is the corrosion monitoring sensor according to aspect 7, wherein the piezoelectric element includes a first piezoelectric element and a second piezoelectric element, the first piezoelectric element is located at a position corresponding to the first distance portion, and the second piezoelectric element is located at a position corresponding to the second distance portion.

[0024] According to this invention, the piezoelectric element includes a first piezoelectric element and a second piezoelectric element. The first piezoelectric element is located at a position corresponding to the first distance portion, and the second piezoelectric element is located at a position corresponding to the second distance portion. By providing piezoelectric elements individually at positions corresponding to the first distance portion and the second distance portion in this way, for example, the correction of the measurement results based on the difference between the measurement result of the ultrasonic thickness measurement of the first distance portion and the measurement result of the ultrasonic thickness measurement of the second distance portion described above can be performed more reliably. Therefore, for example, the corrosion rate of the first distance portion or the second distance portion can be measured with higher precision.

[0025] <9>The corrosion monitoring sensor according to aspect 9 of the present invention is the corrosion monitoring sensor according to any one of aspects 1 to 8, wherein a gap is provided between a portion of the metal that is exposed to the corrosion environment and a portion of the metal that is on the opposite side of the portion exposed to the corrosion environment.

[0026] According to this invention, a gap is provided between a portion of the metal that is exposed to the corrosion environment and a portion of the metal that is on the opposite side of the portion exposed to the corrosion environment. By providing such a gap, it is possible to suppress a change in thickness of a portion of the metal located on the side opposite to the side exposed to the corrosion environment with respect to the gap due to corrosion of the metal.

[0027] Therefore, for example, when measuring a position different from the position corresponding to the gap in the metal by ultrasonic thickness measurement, even if the measurement result changes due to a change in temperature or the like, based on the change amount of the measurement result of the portion of the metal located on the side opposite to the side exposed to the corrosion environment with respect to the gap at the position corresponding to the gap in the metal, the measurement result can be corrected. Therefore, for example, even when the temperature of the metal changes, it is possible to accurately measure the change in thickness of a position different from the position corresponding to the gap in the metal more accurately. Thus, the measurement of the corrosion rate of the metal can be carried out with higher accuracy.

[0028] <10>The corrosion monitoring sensor according to aspect 10 of the present invention is the corrosion monitoring sensor according to aspect 9, wherein the piezoelectric element includes a first piezoelectric element and a second piezoelectric element, the first piezoelectric element is located at a position corresponding to the gap, and the second piezoelectric element is located at a position different from the position corresponding to the gap.

[0029] According to the present invention, the piezoelectric element includes a first piezoelectric element and a second piezoelectric element. The first piezoelectric element is located at a position corresponding to a gap provided in the metal, and the second piezoelectric element is located at a position different from the position corresponding to the gap provided in the metal. In this way, by individually providing piezoelectric elements at each of the position corresponding to the gap in the metal and the position different from the position corresponding to the gap in the metal, for example, the measurement result of the ultrasonic thickness measurement at the position corresponding to the gap in the metal described above can be used to more reliably correct the measurement result of the ultrasonic thickness measurement at the position different from the position corresponding to the gap in the metal. Therefore, for example, the corrosion rate at a position different from the position corresponding to the gap can be measured with higher accuracy.

[0030] <11>The corrosion monitoring sensor according to aspect 11 of the present invention is the corrosion monitoring sensor according to any one of aspects 1 to 10, wherein the pair of electrodes can measure the polarization resistance of the metal by electrochemical measurement, and the piezoelectric element can measure the corrosion rate of the metal by ultrasonic thickness measurement.

[0031] According to the present invention, the pair of electrodes can measure the polarization resistance of the metal by electrochemical measurement. The piezoelectric element can measure the corrosion rate of the metal by ultrasonic thickness measurement. In this way, by individually measuring the polarization resistance and the corrosion rate of the metal with the pair of electrodes and the piezoelectric element respectively, the measurement of the polarization resistance and the corrosion rate of the metal can be reliably performed.

[0032] <12>The corrosion monitoring sensor according to aspect 12 of the present invention is the corrosion monitoring sensor according to aspect 11, wherein the result of the ultrasonic thickness measurement is corrected for the speed of sound according to the temperature of the corrosion environment.

[0033] According to the present invention, the result of the ultrasonic thickness measurement is corrected for the speed of sound according to the temperature of the corrosion environment. Thereby, for example, the corrosion rate of the metal can be accurately measured according to the temperature of the corrosion environment where the metal is placed.

[0034] <13>The corrosion inhibition method according to aspect 13 of the present invention is a corrosion inhibition method using the corrosion monitoring sensor according to any one of aspects 1 to 12, wherein when the peak of the phase of the impedance measured by the electrochemical measurement is 10 Hz or less, or when the change in the phase from 10 Hz to 10 kHz is gentle and there is a peak in the phase in the low-frequency region of 10 Hz or less, it includes a blowing step of blowing a corrosion inhibitor into the corrosion environment.

[0035] Here, in the corrosion environment of a metal, when the peak of the phase of the impedance measured by electrochemical measurement becomes 10 Hz or less, the corrosion rate of the metal rapidly accelerates. According to this invention, when the peak of the phase of the impedance measured by electrochemical measurement is 10 Hz or less, or when the change in the phase from 10 Hz to 10 kHz is gentle and there is a peak in the phase in the low-frequency region of 10 Hz or less, it includes a blowing step of blowing a corrosion inhibitor into the corrosion environment. In this way, by blowing the corrosion inhibitor into the corrosion environment when the condition for the rapid acceleration of the corrosion rate of the metal is met, the corrosion of the metal can be effectively suppressed.

[0036] <14>The corrosion inhibition method according to aspect 14 of the present invention is a corrosion inhibition method using the corrosion monitoring sensor according to any one of aspects 1 to 12, wherein when the resistance measured on the high-frequency side (1 kHz to 10 kHz) obtained by electrochemical measurement becomes 100 Ω or less, it includes a blowing step of blowing a corrosion inhibitor into the corrosion environment.

[0037] Here, in the corrosion environment of a metal, when the resistance measured on the high-frequency side (1 kHz to 10 kHz) obtained by electrochemical measurement becomes 100 Ω or less, the corrosion rate of the metal rapidly accelerates. According to the present invention, when the resistance measured on the high-frequency side (1 kHz to 10 kHz) obtained by electrochemical measurement becomes 100 Ω or less, a blowing step of blowing a corrosion inhibitor into the corrosion environment is provided. In this way, by blowing the corrosion inhibitor into the corrosion environment when the corrosion rate of the metal suddenly accelerates, the corrosion of the metal can be effectively suppressed.

[0038] <15>The corrosion monitoring sensor according to aspect 15 of the present invention is the corrosion monitoring sensor according to any one of aspects 1 to 12, wherein the measurement of the polarization resistance by the pair of electrodes and the measurement of the corrosion rate by the piezoelectric element are simultaneously performed.

[0039] Here, in the corrosion environment of the metal, the conditions of the corrosion environment in the metal may change due to changes in temperature or the like depending on the time zone or the like. According to the present invention, the measurement of the polarization resistance by the pair of electrodes and the measurement of the corrosion rate by the piezoelectric element are simultaneously performed. Thereby, the situation of the corrosion environment when measuring the polarization resistance and the situation of the corrosion environment when measuring the corrosion rate can be made closer. Therefore, for example, even when the conditions of the corrosion environment in the metal change, the corrosion rate of the metal can be measured with higher accuracy.

[0040] <16>The corrosion monitoring sensor according to aspect 16 of the present invention is the corrosion monitoring sensor according to any one of aspects 1 to 12, further comprising an insulator holder for embedding and holding the adjacent pair of electrodes.

[0041] According to the present invention, an insulator holder for embedding and holding the adjacent pair of electrodes is further provided. In this way, by embedding the electrodes for measuring the polarization resistance in the insulator holder, it is possible to suppress the electrodes from being affected by the surrounding conductors. Therefore, the polarization resistance of the metal can be measured more reliably by the electrodes. Therefore, for example, the corrosion rate of the metal can be measured with higher accuracy.

[0042] <17>The corrosion monitoring sensor according to aspect 17 of the present invention is the corrosion monitoring sensor according to aspect 16, further comprising an exposed member, wherein the exposed member has an exposed portion that is a portion exposed to the corrosion environment and a non-exposed portion that is a portion other than the exposed portion, the piezoelectric element is provided in the non-exposed portion, and the non-exposed portion is provided in the holder.

[0043] According to the present invention, the piezoelectric element is provided in a non-exposed portion that is a portion of the exposed member other than the exposed portion, and the non-exposed portion is provided in the holder. In this way, by providing the piezoelectric element in the non-exposed portion of the exposed member provided in the insulator holder, it is possible to suppress the piezoelectric element from being affected by surrounding conductors. Therefore, the measurement of the corrosion rate by the piezoelectric element can be performed in an environment close to the corrosion environment of the exposed member that is partially exposed to the corrosion environment.

[0044] <18>The corrosion monitoring sensor according to aspect 18 of the present invention is the corrosion monitoring sensor according to any one of aspects 1 to 17, further comprising a measurement unit for measuring the temperature of the pair of electrodes, and a temperature adjustment unit for adjusting the temperature of the pair of electrodes based on the measurement result of the measurement unit.

[0045] According to the present invention, it further comprises a measurement unit for measuring the temperature of the pair of electrodes, and a temperature adjustment unit for adjusting the temperature of the pair of electrodes based on the measurement result of the measurement unit. Thereby, for example, based on the temperature of the electrodes measured by the measurement unit, the temperature of the electrodes can be adjusted by the temperature adjustment unit. By adjusting the temperature of the electrodes, for example, the electrodes can be set to a temperature suitable for measuring the polarization resistance and plate thickness of the metal exposed to the corrosion environment. Therefore, for example, the measurement of the corrosion rate of the metal can be carried out with higher accuracy.

Effect of the Invention

[0046] According to the present invention, it is possible to provide a corrosion monitoring sensor and a corrosion suppression method capable of accurately deriving the corrosion rate of a metal.

Brief Description of the Drawings

[0047]

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Modes for Carrying Out the Invention

[0048] (First Embodiment) Hereinafter, with reference to the drawings, a corrosion monitoring sensor 100 according to an embodiment of the present invention will be described. The corrosion monitoring sensor 100 according to this embodiment is disposed in a corrosion environment E. By doing so, the corrosion monitoring sensor 100 derives the corrosion rate of the metal in the corrosion environment E.

[0049] The corrosion environment E in this embodiment is, for example, inside the incinerator I of a waste treatment facility as shown in FIG. 1. The incinerator I of the waste treatment facility is, for example, in a heated state by being exposed to the exhaust gas when incinerating waste. At this time, in the superheater tubes (not shown) installed in the boiler of the incinerator I made of metal, problems such as low-temperature corrosion due to the condensation of acid in the exhaust gas and high-temperature corrosion due to high-temperature molten salt caused by ash contained in the exhaust gas occur.

[0050] In this embodiment, the corrosion monitoring sensor 100 is disposed, for example, as shown in FIG. 1, in a probe pipe P disposed inside the incinerator I. The corrosion monitoring sensor 100 measures the corrosion rate of the metal on the surface of the probe pipe P. By doing so, the corrosion monitoring sensor 100 enables the state inside the incinerator I to be grasped. Specifically, based on the measurement result of the corrosion rate of the metal on the surface of the probe pipe P, it is possible to grasp the corrosion rate of the superheater tubes installed in the boiler of the incinerator I. In the following description, as shown in FIG. 1, the longitudinal direction of the probe pipe P is referred to as the first direction D1. The direction in the radial direction of the probe pipe P (the direction orthogonal to the axis of the probe pipe P) and passing through the corrosion monitoring sensor 100 is referred to as the second direction D2. As shown in FIG. 2, in the radial direction of the probe pipe P, the direction orthogonal to the second direction D2 (the direction orthogonal to both the first direction and the second direction) is referred to as the third direction D3.

[0051] Here, when the polarization resistance of the metal is Rp and the proportionality constant is K, the corrosion current density icorr of the metal is given by the Stern - Geary equation icorr = K / Rp and is obtained by this formula. The corrosion rate of the metal is predicted, for example, as follows. First, the polarization resistance Rp of the metal on the surface of the probe pipe P disposed inside the incinerator I is measured by the corrosion monitoring sensor 100. From this and the corrosion current density icorr calculated from the metal thickness reduction amount on the surface of the probe pipe P measured by the piezoelectric element 30 described later, a proportionality constant K is obtained. The corrosion rate of the superheater tube installed in the boiler of the incinerator I is predicted from this proportionality constant K and the polarization resistance Rp.

[0052] In this embodiment, it is preferable that cooling air is sent to the probe pipe P disposed inside the incinerator I. By this, it is preferable to suppress extreme changes in the temperature of the metal on the surface of the probe pipe P. Alternatively, it is preferable to adjust the temperature of the probe pipe P to a temperature suitable for measuring the corrosion rate and polarization resistance of the metal on the surface of the probe pipe P by the corrosion monitoring sensor 100. A configuration for adjusting the temperature of the metal on the surface of the probe pipe P will be described later.

[0053] Further, as shown in FIGS. 1 and 2, a plurality of wirings C for transferring various measurement information by the corrosion monitoring sensor 100 to a processing device or the like are connected to the corrosion monitoring sensor 100. The plurality of wirings C are aggregated in the wiring aggregation part CA. In order to aggregate and protect the thus aggregated wirings C, it is preferable to dispose a wiring aggregation protection pipe CP inside the probe pipe P. Specifically, as shown in FIG. 2, the wiring C is disposed inside the heat-resistant insulator CI. Then, the heat-resistant insulator CI is disposed inside the wiring aggregation protection pipe CP. In this embodiment, the wiring aggregation protection pipe CP is formed of, for example, a metal such as stainless steel. By disposing the wiring C connected to the corrosion monitoring sensor 100 inside the wiring aggregation protection pipe CP, it is preferable to suppress the movement of the wiring C inside the probe pipe P, for example, when the cooling air sent into the probe pipe P hits the wiring C.

[0054] As shown in FIGS. 1, 2, 3, and 4, the corrosion monitoring sensor 100 includes an exposed member 10, electrodes 20, a piezoelectric element 30, a holder 40, a measurement unit 50, and a temperature adjustment unit 60. The exposed member 10 is disposed on a part of the probe pipe P. That is, the exposed member 10 is disposed, for example, in a through hole Ph formed to penetrate from the inner peripheral surface to the outer peripheral surface of the probe pipe P as shown in FIG. 2. Thus, the exposed member 10 has an exposed portion 11 that is a portion exposed to the corrosion environment E. Further, the exposed member 10 has a non-exposed portion 12 that is a portion of the exposed member 10 other than the exposed portion 11. In the present embodiment, the non-exposed portion 12 of the exposed member 10 is, for example, a portion of each of the pair of electrodes 20 other than a part exposed to the corrosion environment E. That is, in the present embodiment, the exposed member 10 is, for example, the electrode 20.

[0055] As shown in FIG. 3, the electrodes 20 are provided in a pair in the corrosion monitoring sensor 100. In the present embodiment, the electrode 20 which is the exposed member 10 is preferably provided, for example, inside a holder 40 described later. The electrode 20 is fixed to the holder 40 by an adhesive (not shown), for example. Further, a first bolt B1 and a second bolt B2 are provided on the electrode 20 (details will be described later).

[0056] The pair of electrodes 20 can measure, for example, the polarization resistance of a metal exposed to the corrosion environment E. Further, the pair of electrodes 20 can also measure the resistance of deposits such as liquids and solids adhering to the electrodes 20. Specifically, the pair of electrodes 20 can measure, for example, the polarization resistance of the metal on the surface of the probe pipe P and the resistance of the deposits adhering to the electrodes 20 by electrochemical measurement. In the present embodiment, the pair of electrodes 20 are, for example, a working electrode 21 and a counter electrode 22. Note that the working electrode 21 and the counter electrode 22 have the same configuration, but are classified as the working electrode 21 and the counter electrode 22 depending on the use. In the present embodiment, when it is not necessary to distinguish between the working electrode 21 and the counter electrode 22, they are referred to as the electrode 20.

[0057] In the present embodiment, the working electrode 21 and the counter electrode 22 are arranged, for example, as shown in FIG. 3, so as to be aligned in the first direction D1. Alternatively, the working electrode 21 and the counter electrode 22 may be arranged so as to be aligned in the third direction D3. Further, a pair of electrodes 20 composed of the working electrode 21 and the counter electrode 22 arranged in this manner are provided, for example, as shown in FIG. 3, in two sets so as to be aligned in the third direction D3. This enables, for example, sound velocity correction when measuring the thickness of the metal of the probe pipe P by ultrasonic thickness measurement (details will be described later). As shown in FIGS. 2 and 4, a part of each of the pair of electrodes 20 is exposed to the corrosion environment E. That is, in the present embodiment, a part of each of the pair of electrodes 20 faces the outside of the probe pipe P as shown in FIG. 2.

[0058] The piezoelectric element 30 can measure the corrosion rate of the metal exposed to the corrosion environment E. Specifically, the piezoelectric element 30 can measure the corrosion rate of the metal on the surface of the probe pipe P by ultrasonic thickness measurement. In the present embodiment, the result of the ultrasonic thickness measurement is corrected for the sound velocity according to the temperature of the corrosion environment E (details will be described later).

[0059] In the present embodiment, the piezoelectric element 30 includes a first piezoelectric element 31 and a second piezoelectric element 32. Hereinafter, when the first piezoelectric element 31 and the second piezoelectric element 32 are not distinguished, it is referred to as the piezoelectric element 30. In the present embodiment, the first piezoelectric element 31 and the second piezoelectric element 32 are arranged, for example, as shown in FIG. 3, so as to be aligned in the third direction D3. Further, a combination of the first piezoelectric element 31 and the second piezoelectric element 32 arranged in this manner is provided, for example, as shown in FIG. 3, in two sets so as to be aligned in the first direction D1.

[0060] By arranging the working electrode 21, the counter electrode 22, the first piezoelectric element 31, and the second piezoelectric element 32 in this way, in the corrosion monitoring sensor 100 shown in FIG. 3, four combinations are provided: the combination of the working electrode 21 and the first piezoelectric element 31, the combination of the counter electrode 22 and the first piezoelectric element 31, the combination of the working electrode 21 and the second piezoelectric element 32, and the combination of the counter electrode 22 and the second piezoelectric element 32. Hereinafter, in the present embodiment, each of the above-described combinations shown in FIG. 3 will be referred to as follows. That is, in FIG. 3, the combination of the working electrode 21 and the first piezoelectric element 31 is referred to as the first set PA. The combination of the counter electrode 22 and the first piezoelectric element 31 is referred to as the second set PB. The combination of the working electrode 21 and the second piezoelectric element 32 is referred to as the third set PC. The combination of the counter electrode 22 and the second piezoelectric element 32 is referred to as the fourth set PD.

[0061] The piezoelectric element 30 is provided, for example, in the non-exposed portion 12 of the exposed member 10 in the corrosion monitoring sensor 100. More specifically, the piezoelectric element 30 is provided, for example, in the non-exposed portion 12 of the exposed member 10 provided in the holder 40. Here, as described above, in the present embodiment, the exposed member 10 is the electrode 20. That is, the piezoelectric element 30 is provided in the portion of the electrode 20 that does not face the corrosion environment E, as shown in FIGS. 2, 3, and 4.

[0062] Thus, for example, it is preferable to integrate the electrode 20 for electrochemical measurement and the piezoelectric element 30 for measuring the corrosion rate. Thereby, it is preferable to enable the measurement of the corrosion rate of the metal on the surface of the probe pipe P by the piezoelectric element 30 under conditions close to the corrosion environment E in which the pair of electrodes 20 are arranged. The size of the piezoelectric element 30 is preferably determined appropriately according to the size of the electrode 20, for example.

[0063] The piezoelectric element 30 is arranged on the surface of the electrode 20, for example, as shown in FIG. 4. Further, a piezoelectric element electrode 30e is arranged on the surface of the piezoelectric element 30. On the surface of the piezoelectric element electrode 30e, as shown in FIG. 4, a silver paste 30p is disposed. Inside the thus disposed silver paste 30p, one end of either the first wiring C1 or the second wiring C2 is embedded. By covering the periphery of the piezoelectric element 30, the piezoelectric element electrode 30e, and the silver paste 30p arranged as described above with the inorganic adhesive Z, each of the above-described components is fixed on the electrode 20. Note that any material may be used for fixing the piezoelectric element 30 as long as it can withstand the operating environment temperature in the present embodiment and does not deteriorate the piezoelectric element 30. The above-described form is common to the first set PA to the fourth set PD described above.

[0064] One end of each of the first wiring C1 and the second wiring C2 is connected to the piezoelectric element 30 according to the above-described form. The other end of the first wiring C1 is connected to the first bolt B1 as shown in FIG. 4. The other end of the second wiring C2 is connected to the second bolt B2.

[0065] The first wiring C1 is connected to the first bolt B1 according to the above-described form. Thus, the first wiring C1 is fixed to the piezoelectric element 30. That is, by connecting the other end of the first wiring C1 to the first bolt B1, during the use of the corrosion monitoring sensor 100, the displacement of the first wiring C1 and the breakage of the first wiring C1 are suppressed. The first wiring C1 connected to the first bolt B1 is connected to a measurement device (not shown) using, for example, a cable or the like. Thus, the magnitude of the current flowing through the piezoelectric element 30 can be measured. For this reason, the first bolt B1 is preferably insulatable from the electrode 20. For this reason, a ceramic bolt, for example, is preferably used for the first bolt B1.

[0066] The second wiring C2 is connected to the second bolt B2 in the above-described manner. By this, the second wiring C2 is fixed to the piezoelectric element 30. That is, by connecting the other end of the second wiring C2 to the second bolt B2, during the use of the corrosion monitoring sensor 100, it is possible to suppress the displacement of the second wiring C2 and the breakage of the second wiring C2. The second bolt B2 is used, for example, as the ground of the piezoelectric element 30. Further, the second bolt B2 is connected to a measurement device (not shown) using a cable or the like, and is used as a conducting wire when measuring the polarization resistance. When measuring the polarization resistance, it is preferable to connect the second bolts B2 provided in each of the working electrode 21 and the counter electrode 22 and apply an alternating voltage. For the second bolt B2, for example, a metal bolt is preferably used.

[0067] In the present embodiment, it is preferable that the measurement of the polarization resistance by the pair of electrodes 20 and the measurement of the corrosion rate by the piezoelectric element 30 are, for example, simultaneously performed. By this, it is preferable to make the situation of the corrosion environment E when measuring the polarization resistance of the metal of the probe pipe P and the situation of the corrosion environment E when measuring the corrosion rate closer.

[0068] The holder 40 holds the exposed member 10. That is, in the present embodiment, the holder 40 embeds and holds the adjacent pair of electrodes 20. The holder 40 is disposed between the inner peripheral surface of the through hole Ph formed in the probe pipe P and the electrode 20 disposed inside the through hole Ph. The holder 40 is formed of, for example, resin or an insulator. By this, it is preferable to suppress the influence on the electrode 20 by the surrounding conductors. The holder 40 is preferably formed such that the surface of the exposed member 10 (electrode 20) and the surface of the probe pipe P are flush.

[0069] The measurement unit 50 is provided for measuring the temperature of the electrode 20. In the present embodiment, the measurement unit 50 is provided on the electrode 20 as shown in FIG. 3, for example. Alternatively, the measurement unit 50 may be provided on the holder 40 as shown in FIG. 7. Hereinafter, two examples of the installation of the measurement unit 50 will be described.

[0070] As a first example of the installation of the measurement unit 50, the measurement unit 50 is provided on the electrode 20 as shown in FIG. 3. That is, in the first example, the measurement unit 50 is provided on either the working electrode 21 or the counter electrode 22. In the example shown in FIG. 3, the measurement unit 50 is provided on the working electrode 21 of the first set PA. The electrode 20 on which the measurement unit 50 is provided, like the working electrode 21 of the first set PA in FIG. 3, may be formed larger than the other electrodes 20. That is, for example, the dimension of the electrode 20 in the third direction D3 on which the measurement unit 50 is provided may be larger than that of the other electrodes 20. In the following description of the first example, the measurement unit 50 will be described as being attached to the electrode 20.

[0071] In the first example of the installation of the measurement unit 50, the measurement unit 50 includes, for example, a thermocouple 51 and a heat-resistant insulating material 52 as shown in FIG. 5. The thermocouple 51 has a known configuration. The portion of the thermocouple 51 attached to the electrode 20 is, for example, linear as shown in FIG. 5. This ensures the portion of the thermocouple 51 attached to the electrode 20. Once the portion of the thermocouple 51 attached to the electrode 20 is ensured, the thermocouple 51 may be curved, for example, as it moves away from the electrode 20. The heat-resistant insulating material 52 is disposed between the thermocouple 51 and the electrode 20. This insulates the thermocouple 51 and the electrode 20 so that various measurements by the electrode 20 can be accurately performed. The heat-resistant insulating material 52 is a bottomed cylindrical member. The heat-resistant insulating material 52 is formed, for example, by an alumina protection tube or the like. On the outside of the heat-resistant insulating material 52, for example, a screwing portion 52S is formed. The electrode 20 and the heat-resistant insulating material 52 are fixed by screwing the screwing portion 52S. The thermocouple 51 and the heat-resistant insulating material 52 are fixed, for example, by being adhered with an inorganic adhesive Z in a state where the thermocouple 51 is inserted inside the heat-resistant insulating material 52.

[0072] In the first example of the installation of the measuring unit 50, the measuring unit 50 may further include a metal screw 53 in addition to the thermocouple 51 and the heat-resistant insulating material 52, for example, as shown in FIG. 6. In the example shown in FIG. 6, the thermocouple 51 and the heat-resistant insulating material 52 are the same as those in the example shown in FIG. 5. The metal screw 53 is provided between the thermocouple 51 and the heat-resistant insulating material 52. The metal screw 53 is a bottomed cylindrical member. The metal screw 53 is formed of, for example, SUS310S or the like. On the outside of the metal screw 53, a threaded portion 53S is formed, for example. The heat-resistant insulating material 52 and the metal screw 53 are fixed by screwing the threaded portion 53S. The thermocouple 51 and the metal screw 53 are fixed, for example, by silver brazing with silver brazing alloy Ag in a state where the thermocouple 51 is inserted into the metal screw 53. In the first example of the installation of the measuring unit 50, it is preferable to prevent ash or the like from accumulating around the connection portion between the electrode 20 and the measuring unit 50. By this, it is preferable to suppress conduction between the electrode 20 and the thermocouple 51 due to the ash or the like. That is, as shown in FIG. 5, for example, the heat-resistant insulating material 52 is preferably bottomed cylindrical as described above. In addition, in order to secure the bonding area when bonding the thermocouple 51 and the heat-resistant insulating material 52 with the inorganic adhesive Z, as shown in FIG. 5, the end of the heat-resistant insulating material 52 preferably protrudes from the surface of the electrode 20 along the thermocouple 51. In addition, in order to secure the brazing area when brazing the thermocouple 51 and the metal screw 53 with silver brazing alloy Ag, as shown in FIG. 6, the end of the metal screw 53 preferably protrudes from the surface of the electrode 20 along the thermocouple 51. Also, in order to secure the length of screwing between the heat-resistant insulating material 52 and the metal screw 53, as shown in FIG. 6, the end of the heat-resistant insulating material 52 also preferably protrudes from the surface of the electrode 20 along the thermocouple 51.

[0073] As a second example of the installation of the measurement unit 50, the measurement unit 50 is provided on the holder 40 as shown in FIG. 7. In the example shown in FIG. 7, the measurement unit 50 is provided near the second set of PB. Alternatively, the measurement unit 50 may be provided at any part of the holder 40 as long as it is a position where the temperature of the electrode 20 can be measured. In the second example of the installation of the measurement unit 50, the measurement unit 50 includes, for example, a thermocouple 51 and a metal screw 53 as shown in FIG. 8. The thermocouple 51 and the metal screw 53 have the same configuration as that of the first example of the installation of the measurement unit 50 described above. When the measurement unit 50 is provided on the holder 40 as in the second example of the installation of the measurement unit 50, the insulation between the measurement unit 50 and the electrode 20 is achieved by the holder 40, so the heat-resistant insulating material 52 becomes unnecessary. For this reason, in the second example of the installation of the measurement unit 50, the holder 40 and the metal screw 53 are fixed by screwing the screwing portion 53S. The thermocouple 51 and the metal screw 53 are fixed, for example, by being silver brazed with silver brazing Ag in a state where the thermocouple 51 is inserted inside the metal screw 53.

[0074] The temperature adjustment unit 60 is provided, for example, at the end of the probe pipe P on the side opposite to the side disposed inside the incinerator I, as shown in FIG. 1. The temperature adjustment unit 60 adjusts the temperature of the pair of electrodes 20 based on the measurement result of the measurement unit 50. That is, the temperature adjustment unit 60 feeds, for example, cooling air for cooling the metal on the surface of the corrosion monitoring sensor 100 to the probe pipe P. As shown in FIG. 1, the temperature adjustment unit 60 includes a cooling air supply device 61 that generates cooling air, and a blower 62 that blows the generated cooling air. The temperature of the cooling air is appropriately determined by the cooling air supply device 61 based on the measurement result of the measurement unit 50. By blowing the cooling air generated in the cooling air supply device 61 toward the probe pipe P by the blower 62, the temperature of the metal on the surface of the corrosion monitoring sensor 100 to the probe pipe P becomes closer to the temperature of the steam inside the incinerator I than the temperature of the boiler of the incinerator I. The difference between the temperature of the metal on the surface of the corrosion monitoring sensor 100 to the probe pipe P and the temperature of the steam inside the incinerator I is preferably, for example, 20° or less. In this way, it is preferably possible to adjust the temperature to a suitable temperature for measuring the corrosion rate and the polarization resistance Rp of the metal on the surface of the probe pipe P.

[0075] In the present embodiment, when adjusting the temperature of the metal on the surface of the corrosion monitoring sensor 100 to the probe pipe P, in addition to the temperature of the electrode 20 measured by the measurement unit 50, the temperature of the boiler of the incinerator I and the temperature of the steam inside the incinerator I are measured respectively. The temperature of the cooling air is determined after comparing these temperatures. In the present embodiment, the temperature of the boiler of the incinerator I is preferably measured, for example, by a known suction pyrometer (not shown). The temperature of the steam inside the incinerator I is preferably measured, for example, by existing equipment (not shown) in the incinerator I. Alternatively, these temperatures may be appropriately calculated by calculation or the like.

[0076] The corrosion monitoring sensor 100 having each of the above-described configurations measures the corrosion rate and polarization resistance of the metal on the surface of the probe pipe P as described above. The corrosion rate of the metal can be obtained, for example, by continuously measuring the thickness of the metal on the surface of the probe pipe P and calculating the elapsed time and the change in thickness. In addition, the measurement of the thickness of the metal of the probe pipe P can be performed, for example, by using any one of the first set PA to the fourth set PD of the combination of the electrode 20 and the piezoelectric element 30 described above. In this case, a measurement device (not shown) is connected to the first bolt B1 and the second bolt B2 of any one of the first set PA to the fourth set PD to apply a voltage, thereby enabling the measurement of the thickness. When performing an electrochemical test on the metal of the probe pipe P, it is possible to use the first set PA and the third set PC on the premise that all of the first set PA to the fourth set PD are at the same temperature. Alternatively, it is also possible to use the second set PB and the fourth set PD. That is, a measurement device (not shown) is connected to the second bolts of the first set PA and the third set PC, or the second bolts of the second set PB and the fourth set PD to apply a voltage, thereby enabling an electrochemical test on the metal.

[0077] Here, when measuring the thickness of the metal of the probe pipe P or the change in the thickness of the metal of the probe pipe P due to corrosion by ultrasonic thickness measurement, if the temperature of the metal of the probe pipe P changes, the speed at which ultrasonic waves propagate inside the metal changes, and as a result, the result of the ultrasonic thickness measurement may change. As a result, for example, it may become impossible to accurately measure the change in the thickness of the metal.

[0078] Therefore, it is preferable that the result of the ultrasonic thickness measurement is corrected for the speed of sound according to the temperature of the corrosion environment E. In the present embodiment, the probe pipe P is provided with a speed-of-sound correction structure, which is a structure that enables the speed-of-sound correction of the result of the ultrasonic thickness measurement. Hereinafter, three examples of the speed-of-sound correction structure according to the present embodiment will be described.

[0079] (First Example of Speed-of-Sound Correction Structure) In the first example of the sonic speed correction structure shown in FIG. 9, the metal of the probe pipe P includes a readily corrodible portion P1 and a hardly corrodible portion P2. At this time, the first piezoelectric element 31 is located at a position corresponding to the readily corrodible portion P1, and the second piezoelectric element 32 is located at a position corresponding to the hardly corrodible portion P2. The readily corrodible portion P1 is a portion of the metal of the probe pipe P that is exposed to the corrosion environment E and is relatively easily corroded. The hardly corrodible portion P2 is a portion of the metal of the probe pipe P that is exposed to the corrosion environment E and is relatively difficult to corrode. The hardly corrodible portion P2 is formed, for example, by covering the surface of the metal of the probe pipe P with a coating M. The coating M is, for example, gold plating or platinum plating.

[0080] In the probe pipe P having the above-described configuration, as shown in FIG. 9, the thickness t1 of the readily corrodible portion P1 before corrosion and the thickness t1' of the readily corrodible portion P1 after corrosion are measured by ultrasonic thickness measurement, and the change Δt1 in the thickness of the readily corrodible portion P1 per unit time is obtained to measure the corrosion rate when the readily corrodible portion P1 corrodes.

[0081] In the sonic speed correction structure according to the first example, sonic speed correction is performed as follows. That is, first, the temperature of an arbitrary metal is defined as the reference temperature. Then, the thickness t2 of the hardly corrodible portion P2 at the reference temperature is measured in advance by ultrasonic thickness measurement. By this, when the temperature of the metal of the probe pipe P changes from the reference temperature, the measurement result of the thickness of the readily corrodible portion P1 is corrected based on the change in the measurement result of the thickness t2 of the hardly corrodible portion P2.

[0082] Specifically, for example, the ratio between the measurement result of the thickness t2 of the hardly corrodible portion P2 at the reference temperature and the measurement result of the thickness t2 of the hardly corrodible portion P2 after changing from the reference temperature is applied to the measurement result of the thickness t1 or t1' of the readily corrodible portion P1 after changing from the reference temperature to correct the measurement result of the thickness t1 or t1' of the hardly corrodible portion P2. By this, the thickness t1 or t1' of the readily corrodible portion P1 and the change Δt1 in the thickness of the readily corrodible portion P1 can be accurately grasped.

[0083] (Second Example of Sonic Velocity Correction Structure) In the second example of the sonic velocity correction structure shown in FIG. 10, the probe pipe P has a flat outer peripheral surface. That is, in the probe pipe P according to the second example, the metal portions of the probe pipe P that are exposed to the corrosion environment E are flush. As shown in FIG. 10, the probe pipe P according to the second example has a stepped portion D on its inner peripheral surface. The stepped portion D is formed, for example, by notching the inner peripheral surface of the probe pipe P. By this, in the probe pipe P, two portions with different metal thicknesses are formed. That is, by providing the above-described stepped portion D, the metal of the probe pipe P according to the second example has, as shown in FIG. 10, a first distance portion P3 and a second distance portion P4. At this time, the first piezoelectric element 31 is located at a position corresponding to the first distance portion P3, and the second piezoelectric element 32 is located at a position corresponding to the second distance portion P4.

[0084] Among the probe pipes P having the above-described shape, the first distance portion P3 is the portion where the distance from the portion of the metal of the probe pipe P that is exposed to the corrosion environment E to the portion on the opposite side of the portion of the metal of the probe pipe P that is exposed to the corrosion environment E is the first distance t3. The second distance portion P4 is the portion where the distance from the portion of the metal of the probe pipe P that is exposed to the corrosion environment E to the portion on the opposite side of the portion of the metal of the probe pipe P that is exposed to the corrosion environment E is the second distance t4.

[0085] In the present embodiment, the first distance t3 and the second distance t4 are different. That is, the first distance portion P3 and the second distance portion P4 are two portions in the probe pipe P where the metal thicknesses are different from each other. Hereinafter, in the present embodiment, the portion with the thinner thickness of the probe pipe P is taken as the first distance portion P3, and the portion with the thicker thickness is taken as the second distance portion P4. In other words, the second distance t4 is larger than the first distance t3.

[0086] In the sonic velocity correction structure according to the second example, the outer peripheral surface of the probe pipe P facing the corrosion environment E corrodes evenly without distinction between, for example, the first distance portion P3 and the second distance portion P4. That is, the change in the first distance t3 before corrosion and the first distance t3' after corrosion, and the change in the second distance t4 before corrosion and the second distance t4' after corrosion are both equal to Δt2 shown in FIG. 10.

[0087] At this time, the inner peripheral surface of the probe pipe P does not face the corrosion environment E and does not corrode. Therefore, even after the outer peripheral surface of the probe pipe P corrodes, the thickness δ1 of the step portion D, that is, δ1 which is the difference in the thickness of the probe pipe P between the first distance portion P3 and the second distance portion P4 shown in FIG. 10, does not change. In other words, in the first distance portion P3 and the second distance portion P4 shown in FIG. 10, δ1=t4 - t3=t4' - t3' the relationship holds.

[0088] In the probe pipe P having the above-described configuration, as shown in FIG. 10, the first distance t3 or the second distance t4 before corrosion and the first distance t3' or the second distance t4' after corrosion are measured by ultrasonic thickness measurement, and the change Δt2 in the thickness of the first distance portion P3 or the second distance portion P4 per unit time is obtained to measure the corrosion rate when the probe pipe P corrodes.

[0089] In the sonic velocity correction structure according to the second example, sonic velocity correction is performed as follows. That is, first, the temperature of an arbitrary metal is determined as the reference temperature. Then, by ultrasonic thickness measurement, the thickness δ1 of the step portion D at the reference temperature, that is, the difference between the thickness of the first distance portion P3 and the thickness of the second distance portion P4, is measured in advance. By this, when the temperature of the metal of the probe pipe P changes from the reference temperature, the measurement results of the thicknesses of the first distance portion P3 and the second distance portion P4 are corrected based on the change in the measurement result of the thickness δ1 of the step portion D.

[0090] Specifically, for example, the ratio between the measurement result of the thickness δ1 of the step portion D at the reference temperature and the measurement result of the thickness δ1 of the step portion D after the change from the reference temperature is applied to the measurement results of the thicknesses of the first distance portion P3 and the second distance portion P4 after the change from the reference temperature, thereby correcting the measurement results of the thicknesses of the first distance portion P3 and the second distance portion P4. By doing this, the thicknesses of the first distance portion P3 and the second distance portion P4, and the thickness change Δt2 can be accurately grasped.

[0091] (Third Example of the Sonic Velocity Correction Structure) In the third example of the sonic velocity correction structure shown in FIG. 11, the probe pipe P has a flat outer peripheral surface. That is, in the probe pipe P according to the third example, the metal portions of the probe pipe P that are exposed to the corrosion environment E are flush. As shown in FIG. 11, the probe pipe P according to the third example has a gap S provided in the metal. By doing this, a reference portion P5 is formed in the probe pipe P according to the third example. Specifically, the gap S is provided between the metal portion of the probe pipe P that is exposed to the corrosion environment E and the portion on the opposite side of the metal portion that is exposed to the corrosion environment E. The gap S is formed, for example, by notching the metal of the probe pipe P along the axial direction of the probe pipe P. The reference portion P5 is the portion of the metal of the probe pipe P that is located on the opposite side of the portion that is more exposed to the corrosion environment E than the gap S provided in the probe pipe P. At this time, the first piezoelectric element 31 is located at a position corresponding to the gap S, and the second piezoelectric element 32 is provided at a position different from the position corresponding to the gap S.

[0092] In the sonic velocity correction structure according to the third example, the outer peripheral surface of the probe pipe P facing the corrosion environment E corrodes evenly regardless of the position of the gap S. At this time, the reference portion P5 does not face the corrosion environment E and does not corrode. Therefore, even after the outer peripheral surface of the probe pipe P corrodes, the thickness of the reference portion P5 does not change.

[0093] In the probe pipe P having the above-described configuration, as shown in FIG. 11, at a position different from the position corresponding to the gap S, the thickness t5 before corrosion and the thickness t5' after corrosion are measured by ultrasonic thickness measurement, and the corrosion rate when the probe pipe P corrodes is measured by obtaining the change Δt3 in thickness per unit time.

[0094] In the sound velocity correction structure according to the third example, the sound velocity correction is performed as follows. That is, first, the temperature of an arbitrary metal is defined as the reference temperature. Then, the thickness δ2 of the reference portion P5 is measured in advance by ultrasonic thickness measurement. By this, when the temperature of the metal of the probe pipe P changes from the reference temperature, the measurement result of the thickness of the metal of the probe pipe P is corrected based on the change in the measurement result of the thickness δ2 of the reference portion P5.

[0095] Specifically, for example, by applying the ratio between the measurement result of the thickness δ2 of the reference portion P5 at the reference temperature and the measurement result of the thickness δ2 of the reference portion P5 after changing from the reference temperature to the measurement result of the thickness t5 or t5' at a position different from the position corresponding to the gap S after changing from the reference temperature, the measurement result of the thickness t5 or t5' at a position different from the position corresponding to the gap S is corrected. By this, it becomes possible to accurately grasp the thickness t5 or t5' at a position different from the position corresponding to the gap S and the change Δt3 in the thickness at a position different from the position corresponding to the gap S.

[0096] Note that the sound velocity correction structures according to the above-described three examples may be provided on the electrode 20. That is, as the electrode 20 having a structure corresponding to the sound velocity correction structure according to the first example described above, as shown in FIG. 12, the electrode 20 to which the second wiring C2 is connected may be used as the corrosion-prone portion P1, and the electrode 20 to which the first wiring C1 is connected may be used as the corrosion-resistant portion P2. That is, by providing the coating M on the electrode 20 to which the first wiring C1 is connected, a sound velocity correction structure corresponding to the first example may be provided. Note that t6 and t6' shown in FIG. 12 respectively correspond to t1 and t1' shown in FIG. 9. t7 shown in FIG. 12 corresponds to t2 shown in FIG. 9. Δt4 shown in FIG. 12 corresponds to Δt1 shown in FIG. 9. That is, in the probe pipe P having the configuration shown in FIG. 12, the thickness t6 before corrosion and the thickness t6' after corrosion of the electrode 20 corresponding to the easily corroded portion P1 are measured by ultrasonic thickness measurement, and the change Δt4 in the thickness of the electrode 20 corresponding to the easily corroded portion P1 per unit time is obtained to measure the corrosion rate when the easily corroded portion P1 corrodes. Then, appropriate sound velocity correction is performed by the method described above. Thus, sound velocity correction corresponding to the above-described first example may be performed.

[0097] As the electrode 20 having a structure corresponding to the sound velocity correction structure according to the second example described above, as shown in FIG. 13, the electrode 20 to which the second wiring C2 is connected may be used as the second distance portion P4, and the electrode 20 to which the first wiring C1 is connected may be used as the first distance portion P3. That is, two electrodes 20 having different thicknesses may be provided. Note that t8 and t8' shown in FIG. 13 correspond to t4 and t4' shown in FIG. 10, respectively. t9 and t9' shown in FIG. 13 correspond to t3 and t3' shown in FIG. 10, respectively. Δt5 shown in FIG. 13 corresponds to Δt2 shown in FIG. 10. In other words, in the first distance portion P3 and the second distance portion P4 shown in FIG. 13, δ1 = t8 - t9 = t8' - t9' holds. That is, in the probe pipe P having the configuration shown in FIG. 13, t8 and t9 before corrosion and t8' and t9' after corrosion are measured by ultrasonic thickness measurement, and the change Δt5 in t8 or t9 per unit time is obtained to measure the corrosion rate when the probe pipe P corrodes. Then, appropriate sound velocity correction is performed by the method described above. Thus, sound velocity correction corresponding to the above-described second example may be performed.

[0098] As the electrode 20 having a structure corresponding to the sound velocity correction structure according to the third example described above, as shown in FIG. 14, a gap S may be provided in the electrode 20 to which the first wiring C1 is connected. Thus, a reference portion P5 may be formed in the electrode 20 to which the first wiring C1 is connected. Note that t10 and t10' shown in FIG. 14 correspond to t5 and t5' shown in FIG. 11, respectively. Δt6 shown in FIG. 14 corresponds to Δt3 shown in FIG. 10. That is, in the probe pipe P having the configuration shown in FIG. 14, the thickness t10 before corrosion and the thickness t10' after corrosion are measured by ultrasonic thickness measurement, and the corrosion rate when the probe pipe P corrodes is measured by obtaining the change Δt6 in thickness per unit time. Then, appropriate sound speed correction is performed by using the previously measured thickness δ2 according to the method described above. By this, sound speed correction corresponding to the above-described third example may be performed.

[0099] (Corrosion inhibition method) Next, a corrosion inhibition method using the corrosion monitoring sensor 100 according to the present embodiment will be described. The corrosion inhibition method according to the present embodiment includes a blowing step. The blowing step is a step of blowing a corrosion inhibitor into the corrosion environment E in which the metal is disposed when the following conditions are satisfied.

[0100] The condition for executing the blowing step is, for example, when the resistance measured on the high frequency side (1 kHz to 10 kHz) obtained by electrochemical measurement becomes 100 Ω or less. Such a condition is satisfied, for example, when the fly ash attached to the electrode 20 melts and molten salt corrosion starts. The condition for executing the blowing step is, for example, when the peak of the phase of the impedance measured by electrochemical measurement is 10 Hz or less, or when the change in phase in the range of 10 Hz to 10 kHz is gentle and there is a peak in the phase in the low frequency region of 10 Hz or less. Such a condition is satisfied, for example, when the molten salt corrosion is faster than expected and the corrosion resistance of the electrode 20 is low. When such a condition is satisfied, there are many defects in the corrosion product formed on the surface of the electrode 20 and there is no protection, so that the molten salt penetrates into the metal interface and corrosion is likely to accelerate. As described above, the aforementioned conditions are, for example, conditions under which the corrosion rate of the metal in the corrosion environment E rapidly accelerates. When the corrosion inhibitor is blown into the corrosion environment E when such conditions are satisfied, it is preferable to effectively suppress the corrosion of the metal.

[0101] As described above, according to the corrosion monitoring sensor 100 according to the present embodiment, a pair of electrodes 20 capable of measuring the polarization resistance Rp of a metal exposed to the corrosion environment E and a piezoelectric element 30 capable of measuring the corrosion rate of the metal are provided. In addition to being able to measure the polarization resistance Rp of the metal by the pair of electrodes 20, by being able to measure the corrosion rate of the metal by the piezoelectric element 30, the proportionality constant K in the above-mentioned Stern-Geary equation can be derived in real time. That is, the proportionality constant K, whose value changes depending on changes in the corrosion environment E and materials, etc., can be obtained on-site immediately. Therefore, for example, when deriving the proportionality constant K, compared with the case where the corrosion current density icorr is based on the result of measuring the corrosion of the metal for a certain period, changes in the corrosion rate due to changes in the corrosion environment E and the progress of corrosion can be reflected with high accuracy. For this reason, the proportionality constant K can be derived in real time on-site. Thus, the derivation of the corrosion rate of the metal can be carried out with high accuracy.

[0102] Further, the exposed member 10 has an exposed portion 11 that is a portion exposed to the corrosion environment E and a non-exposed portion 12 that is a portion other than the exposed portion 11. The piezoelectric element 30 is provided in the non-exposed portion 12. Thereby, for example, compared with the case where the piezoelectric element 30 is provided in the exposed portion 11 of the exposed member 10, the piezoelectric element 30 can be more easily arranged.

[0103] Further, the non-exposed portion 12 of the exposed member 10 is a portion of each of the pair of electrodes 20 other than a part that is exposed to the corrosion environment E. Therefore, the piezoelectric element 30 is provided in a portion of each of the pair of electrodes 20 other than a part that is exposed to the corrosion environment E. By providing the piezoelectric element 30 on the pair of electrodes 20 in this way, for example, the temperature condition of the piezoelectric element 30 can be made close to the temperature condition of each of the pair of electrodes 20. Thus, for example, the measurement of the corrosion rate of the metal by the piezoelectric element 30 can be carried out with higher accuracy.

[0104] Here, for example, when measuring the thickness of a metal by ultrasonic thickness measurement, the speed at which ultrasonic waves propagate through the interior of the metal may change due to a change in the temperature of the metal. As a result, for example, it may affect the accuracy when measuring the change in the thickness of the metal due to corrosion by ultrasonic thickness measurement.

[0105] The portion of the metal that is exposed to the corrosion environment E includes a corrosion-prone part P1 that is relatively prone to corrosion and a corrosion-resistant part P2 that is relatively resistant to corrosion. As a result, for example, in a metal, it is possible to provide a portion where the thickness is likely to change due to corrosion and a portion where the thickness is less likely to change.

[0106] Therefore, for example, when measuring the corrosion-prone part P1 in a metal by ultrasonic thickness measurement, even if the measurement result changes due to a change in temperature or the like, the measurement result can be corrected based on the change amount of the measurement result of the corrosion-resistant part P2 where the thickness is less likely to change due to corrosion. Therefore, even when the temperature of the metal changes, the corrosion rate of the corrosion-prone part P1 can be accurately measured. Thus, the measurement of the corrosion rate of the metal can be carried out with higher precision.

[0107] The piezoelectric element 30 also includes a first piezoelectric element 31 and a second piezoelectric element 32. The first piezoelectric element 31 is located at a position corresponding to a readily corrodible portion P1, which is a relatively easily corrodible portion among the metals, and the second piezoelectric element 32 is located at a position corresponding to a difficult-to-corrode portion P2, which is a relatively difficult-to-corrode portion among the metals. In this way, by providing the piezoelectric element 30 individually for each of the readily corrodible portion P1 and the difficult-to-corrode portion P2, for example, the correction of the measurement result of the ultrasonic thickness measurement of the readily corrodible portion P1 based on the measurement result of the ultrasonic thickness measurement of the difficult-to-corrode portion P2 described above can be performed more reliably. Therefore, for example, the corrosion rate of the readily corrodible portion P1 can be measured with higher accuracy. Further, when performing ultrasonic thickness measurement with one piezoelectric element 30, when the temperature of the measurement unit changes, it is necessary to correct (temperature correction) the information on the sound velocity used for the thickness calculation each time. On the other hand, by arranging the first piezoelectric element 31 and the second piezoelectric element 32 as described above, it is possible to grasp the change in the sound velocity in real time and perform ultrasonic thickness measurement using the latest sound velocity information at all times. That is, it is possible to eliminate the need to perform temperature correction each time with the change in temperature. Therefore, the efficiency of ultrasonic thickness measurement can be further improved.

[0108] Further, the metal has a first distance portion P3, which is a portion of the metal where the distance from the portion of the metal exposed to the corrosion environment E to the portion of the metal on the opposite side of the portion of the metal exposed to the corrosion environment E is the first distance t3, and a second distance portion P4, which is a portion of the second distance t4. The first distance t3 and the second distance t4 are different. Thereby, for example, in the first distance portion P3 and the second distance portion P4, when the portions of the metal exposed to the corrosion environment E are flush, even if the first distance t3 and the second distance t4 change due to corrosion, the difference between the first distance t3 and the second distance t4 can be prevented from changing.

[0109] Therefore, for example, when the first distance portion P3 and the second distance portion P4 in the metal are measured by ultrasonic thickness measurement respectively, even if the measurement results change due to temperature changes or the like, the measurement results can be corrected based on the change in the difference between the measurement result of the first distance portion P3 and the measurement result of the second distance portion P4. Therefore, for example, even when the temperature of the metal changes, the first distance t3 and the second distance t4 can be measured more accurately. Therefore, based on these measurement results, the corrosion rate of the metal can be measured with higher precision.

[0110] Further, the piezoelectric element 30 includes a first piezoelectric element 31 and a second piezoelectric element 32. The first piezoelectric element 31 is located at a position corresponding to the first distance portion P3, and the second piezoelectric element 32 is located at a position corresponding to the second distance portion P4. In this way, by individually providing the piezoelectric element 30 at positions corresponding to the first distance portion P3 and the second distance portion P4 respectively, for example, the correction of the measurement result based on the difference between the measurement result of the ultrasonic thickness measurement of the first distance portion P3 and the measurement result of the ultrasonic thickness measurement of the second distance portion P4 described above can be performed more reliably. Therefore, for example, the corrosion rate of the first distance portion P3 or the second distance portion P4 can be measured with higher precision.

[0111] Further, a gap S is provided between a portion of the metal that is exposed to the corrosion environment E and a portion of the metal that is on the opposite side of the portion exposed to the corrosion environment E. By providing the gap S in this way, it is possible to suppress a change in the thickness of the portion of the metal located on the side opposite to the side exposed to the corrosion environment E with respect to the gap S due to the corrosion of the metal.

[0112] Therefore, for example, when measuring a position different from the position corresponding to the gap S in the metal by ultrasonic thickness measurement, even if the measurement result changes due to temperature changes or the like, the measurement result can be corrected based on the change in the measurement result of the portion of the metal located on the side opposite to the side exposed to the corrosion environment E with respect to the gap S at the position corresponding to the gap S in the metal. Therefore, even when the temperature of the metal changes, for example, it is possible to accurately measure the change in thickness at a position different from the position corresponding to the gap S in the metal. Thus, the corrosion rate of the metal can be measured with higher precision.

[0113] Further, the piezoelectric element 30 includes a first piezoelectric element 31 and a second piezoelectric element 32. The first piezoelectric element 31 is located at a position corresponding to the gap S provided in the metal, and the second piezoelectric element 32 is located at a position different from the position corresponding to the gap S provided in the metal. By providing the piezoelectric element 30 individually at each of the position corresponding to the gap S in the metal and the position different from the position corresponding to the gap S in the metal, for example, the correction of the measurement result of the ultrasonic thickness measurement at the position different from the position corresponding to the gap S in the metal based on the measurement result of the ultrasonic thickness measurement at the position corresponding to the gap S in the metal described above can be performed more reliably. Thus, for example, the corrosion rate at a position different from the position corresponding to the gap S can be measured with higher precision.

[0114] Also, the pair of electrodes 20 can measure the polarization resistance Rp of the metal by electrochemical measurement. The piezoelectric element 30 can measure the corrosion rate of the metal by ultrasonic thickness measurement. By performing the measurement of the polarization resistance Rp and the corrosion rate of the metal individually by the pair of electrodes 20 and the piezoelectric element 30, respectively, the measurement of the polarization resistance Rp and the corrosion rate of the metal can be surely performed.

[0115] Further, the result of the ultrasonic thickness measurement is corrected for the sound speed according to the temperature of the corrosion environment E. Thereby, for example, the corrosion rate of the metal can be accurately measured according to the temperature of the corrosion environment E in which the metal is placed.

[0116] Here, in the corrosion environment E of the metal, when the resistance measured on the high frequency side (1 kHz to 10 kHz) obtained by electrochemical measurement becomes 100 Ω or less, the corrosion rate of the metal rapidly accelerates. Such conditions are satisfied, for example, when the fly ash attached to the electrode 20 melts and molten salt corrosion starts. When the resistance measured at the high-frequency side (1 kHz to 10 kHz) obtained by electrochemical measurement becomes 100 Ω or less, a blowing step of blowing a corrosion inhibitor into the corrosion environment E is provided. In this way, by blowing the corrosion inhibitor into the corrosion environment E when the corrosion rate of the metal becomes a condition of rapid acceleration, the corrosion of the metal can be effectively suppressed.

[0117] Here, in the corrosion environment E of the metal, when the peak of the phase of the impedance measured by electrochemical measurement becomes 10 Hz or less, the corrosion rate of the metal rapidly accelerates. Such conditions are satisfied, for example, when the molten salt corrosion is faster than expected and the corrosion resistance of the electrode 20 is low. When such conditions are satisfied, there are many defects in the corrosion products formed on the surface of the electrode 20 and there is no protection, so that the molten salt penetrates into the metal interface and the corrosion is likely to accelerate. When the peak of the phase of the impedance measured by electrochemical measurement is 10 Hz or less, or when the change in the phase from 10 Hz to 10 kHz is gentle and there is a peak in the phase in the low-frequency region of 10 Hz or less, a blowing step of blowing a corrosion inhibitor into the corrosion environment E is provided. In this way, by blowing the corrosion inhibitor into the corrosion environment E when the corrosion rate of the metal becomes a condition of rapid acceleration, the corrosion of the metal can be effectively suppressed.

[0118] Here, in the corrosion environment E of the metal, the conditions of the corrosion environment E in the metal may change due to changes in temperature or the like depending on the time zone or the like. The measurement of the polarization resistance Rp by the pair of electrodes 20 and the measurement of the corrosion rate by the piezoelectric element 30 are performed simultaneously. Thereby, the situation of the corrosion environment E when measuring the polarization resistance Rp and the situation of the corrosion environment E when measuring the corrosion rate can be made closer. Therefore, for example, even when the conditions of the corrosion environment E in the metal change, the measurement of the corrosion rate of the metal can be performed with higher accuracy.

[0119] Furthermore, it further includes an insulator holder 40 that embeds and holds a pair of adjacent electrodes 20. In this way, by embedding the electrode 20 for measuring the polarization resistance Rp in the insulator holder 40, it is possible to suppress the electrode 20 from being affected by surrounding conductors. Therefore, the polarization resistance Rp of the metal can be more reliably measured by the electrode 20. Thus, for example, the measurement of the corrosion rate of the metal can be carried out with higher precision.

[0120] Also, the piezoelectric element 30 is provided in the non-exposed portion 12 which is a portion of the exposed member 10 other than the exposed portion 11, and the non-exposed portion 12 is provided in the holder 40. In this way, by providing the piezoelectric element 30 in the non-exposed portion 12 of the exposed member 10 provided in the insulator holder 40, it is possible to suppress the piezoelectric element 30 from being affected by surrounding conductors. Therefore, the measurement of the corrosion rate by the piezoelectric element 30 can be carried out in an environment close to the corrosion environment E of the exposed member 10 that is partially exposed to the corrosion environment E.

[0121] Furthermore, it further includes a measurement unit 50 for measuring the temperature of the pair of electrodes 20, and a temperature adjustment unit 60 for adjusting the temperature of the pair of electrodes 20 based on the measurement result of the measurement unit 50. Thereby, for example, based on the temperature of the electrode 20 measured by the measurement unit 50, the temperature of the electrode 20 can be adjusted by the temperature adjustment unit 60. By adjusting the temperature of the electrode 20, for example, the electrode 20 can be set to a temperature suitable for measuring the polarization resistance Rp and the plate thickness of the metal exposed to the corrosion environment E. Thus, for example, the measurement of the corrosion rate of the metal can be carried out with higher precision.

[0122] (Second Embodiment) Next, the second corrosion monitoring sensor 200 according to the second embodiment of the present invention will be described with reference to FIG. 15. In this second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted, and only the different points will be described. In the second corrosion monitoring sensor 200 according to the second embodiment, as shown in FIG. 15, the non-exposed portion 12 of the exposed member 10 is different from the corrosion monitoring sensor 100 in that, for example, it is a portion of the metal of the probe pipe P other than the portion exposed to the corrosion environment E. That is, in the second embodiment, the exposed member 10 is the probe pipe P. That is, in the second corrosion monitoring sensor 200, the piezoelectric element 30 is arranged to contact the inner peripheral surface of the probe pipe P. This is different from the corrosion monitoring sensor 100 in this regard.

[0123] As described above, according to the second corrosion monitoring sensor 200 according to the second embodiment, the non-exposed portion 12 of the exposed member 10 is a portion of the metal other than the portion exposed to the corrosion environment E. Therefore, the piezoelectric element 30 is provided in a portion of the metal other than the portion exposed to the corrosion environment E. By providing the piezoelectric element 30 in a part of the metal in this way, for example, the corrosion rate of the metal in which the polarization resistance Rp is measured by a pair of electrodes 20 can be measured. Therefore, for example, the polarization resistance Rp and the corrosion rate in the metal exposed to the corrosion environment E can be measured simultaneously.

[0124] Note that the technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the probe pipe P according to the present embodiment may be provided at a location other than the above-described incinerator I.

[0125] In addition, without departing from the spirit of the present invention, it is possible to appropriately replace the components in the above-described embodiment with well-known components, and the above-described modification examples may be appropriately combined.

Explanation of Reference Numerals

[0126] 10 Exposed member 11 Exposed portion 12 Non-exposed portion 20 Electrode 21 Working electrode 22 Counter electrode 30 Piezoelectric element 31 First piezoelectric element 32 Second piezoelectric element 40 Holder 50 Measuring unit 51 Thermocouple 52 Heat-resistant insulating material 53 Metal screw 60 Temperature adjustment unit 100 Corrosion monitoring sensor 200 Second corrosion monitoring sensor B1 First bolt B2 Second bolt C Wiring CA Wiring aggregation part CP Wiring aggregation protection pipe D Step part E Corrosion environment I Incinerator M Coating P Probe pipe P1 Corrosion-prone part P2 Corrosion-resistant part P3 First distance part P4 Second distance part Ph Through hole P5 Reference part Rp Polarization resistance S Gap t3 First distance t4 Second distance Z Inorganic adhesive

Claims

1. A pair of electrodes capable of measuring the polarization resistance of a metal exposed to a corrosive environment, A piezoelectric element capable of measuring the corrosion rate of the metal, Comprising, A corrosion monitoring sensor characterized by this.

2. An exposed member, Further comprising, The exposed member has an exposed portion that is the portion exposed to the corrosive environment and a non-exposed portion that is the portion other than the exposed portion, The piezoelectric element is provided in the non-exposed portion, The corrosion monitoring sensor according to claim 1, characterized by this.

3. A part of each of the pair of electrodes is exposed to the corrosive environment, The non-exposed portion is a portion of each of the pair of electrodes other than the part exposed to the corrosive environment, The corrosion monitoring sensor according to claim 2, characterized by this.

4. The non-exposed portion is a portion of the metal other than the portion exposed to the corrosive environment, The corrosion monitoring sensor according to claim 2, characterized by this.

5. The portion of the metal that is exposed to the corrosive environment includes a corrosion-prone portion that is a portion relatively prone to corrosion and a corrosion-resistant portion that is a portion relatively resistant to corrosion, The corrosion monitoring sensor according to claim 4, characterized by this.

6. The piezoelectric element includes a first piezoelectric element and a second piezoelectric element, The first piezoelectric element is located at a position corresponding to the corrosion-prone portion, The second piezoelectric element is located at a position corresponding to the corrosion-resistant portion, The corrosion monitoring sensor according to claim 5, characterized by this.

7. The metal has a first distance portion that is a portion of the metal from the portion exposed to the corrosive environment to the portion on the opposite side of the portion of the metal exposed to the corrosive environment and has a first distance, and a second distance portion that is a portion of the metal from the portion exposed to the corrosive environment to the portion on the opposite side of the portion of the metal exposed to the corrosive environment and has a second distance, The first distance and the second distance are different, The corrosion monitoring sensor according to claim 4, characterized by this.

8. The piezoelectric element includes a first piezoelectric element and a second piezoelectric element, The first piezoelectric element is located at a position corresponding to the first distance portion, The second piezoelectric element is located at a position corresponding to the second distance portion, The corrosion monitoring sensor according to claim 7, characterized by this.

9. A gap is provided between a portion of the metal that is exposed to the corrosion environment and a portion of the metal that is on the opposite side of the portion exposed to the corrosion environment. The corrosion monitoring sensor according to claim 4, characterized in that.

10. The piezoelectric element includes a first piezoelectric element and a second piezoelectric element. The first piezoelectric element is located at a position corresponding to the gap. The second piezoelectric element is located at a position different from the position corresponding to the gap. The corrosion monitoring sensor according to claim 9, characterized in that.

11. The pair of electrodes can measure the polarization resistance of the metal by electrochemical measurement. The piezoelectric element can measure the corrosion rate of the metal by ultrasonic thickness measurement. The corrosion monitoring sensor according to any one of claims 1 to 10, characterized in that.

12. The result of the ultrasonic thickness measurement is corrected for the speed of sound according to the temperature of the corrosion environment. The corrosion monitoring sensor according to claim 11, characterized in that.

13. A corrosion suppression method using the corrosion monitoring sensor according to claim 11, comprising: A blowing step of blowing a corrosion inhibitor into the corrosion environment when the peak of the phase of the impedance measured by the electrochemical measurement is 10 Hz or less, or when the change in phase in the range of 10 Hz to 10 kHz is gentle and there is a peak in the phase in the low frequency region of 10 Hz or less. Comprising. The corrosion suppression method, characterized in that.

14. A corrosion suppression method using the corrosion monitoring sensor according to claim 11, comprising: A blowing step of blowing a corrosion inhibitor into the corrosion environment when the resistance measured on the high frequency side (1 kHz to 10 kHz) obtained by electrochemical measurement becomes 100 Ω or less. Comprising. The corrosion suppression method, characterized in that.

15. The measurement of the polarization resistance by the pair of electrodes and the measurement of the corrosion rate by the piezoelectric element are performed simultaneously. The corrosion monitoring sensor according to any one of claims 1 to 10, characterized in that.

16. Further comprising an insulator holder for embedding and holding the adjacent pair of electrodes. The corrosion monitoring sensor according to any one of claims 1 to 9, characterized in that.

17. An exposed member. Further comprising. The exposed member has an exposed portion that is a portion exposed to the corrosion environment and a non-exposed portion that is a portion other than the exposed portion. The piezoelectric element is provided in the non-exposed portion, The non-exposed portion is provided in the holder, The corrosion monitoring sensor according to claim 16, characterized in that.

18. A measuring unit for measuring the temperature of the pair of electrodes, A temperature adjusting unit for adjusting the temperature of the pair of electrodes based on the measurement result of the measuring unit, The corrosion monitoring sensor according to any one of claims 1 to 10, further comprising.

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