JP7743300B2 - CORROSION POTENTIAL SENSOR AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Description

The present invention relates to an electrochemical corrosion potential sensor and a method for manufacturing an electrochemical corrosion potential sensor.

One example of an electrochemical corrosion potential sensor that can more accurately measure the corrosion potential of structural components is the technology described in Patent Document 1. The electrochemical corrosion potential sensor in Patent Document 1 includes a reference electrode, an insulator, a measured electrode, and a sensor body. The zirconium metal reference electrode is fixed within a zirconium oxide insulator. A stainless steel sensor body is attached to the insulator, surrounding one end of the insulator. The measured electrode is attached to the surface of the insulator so as to cover the side and the periphery of the insulator's tip. The measured electrode is made of the same material as the structural component of the nuclear power plant, whose electrochemical corrosion potential is being measured. A zirconium electrode wire passes through the insulator and is connected to the reference electrode. The core wire of a mineral insulated cable inserted into the sensor body is connected to the zirconium electrode wire, and the metal outer tube of the mineral insulated cable is connected to the sensor body.

JP 2013-079830 A

In nuclear power plants, structural components such as equipment and piping are made from structural materials such as stainless steel and nickel-based alloys. These structural materials are susceptible to stress corrosion cracking (SCC) under certain conditions. Therefore, to maintain the integrity of nuclear power plants, SCC countermeasures are applied to the structural components of nuclear power plants.

In recent years, SCC countermeasures have also been applied to structural components of nuclear power plants in order to improve economic efficiency, such as by increasing the capacity factor and extending the lifespan of nuclear power plants.

Technologies aimed at improving the corrosion resistance of materials, improving stress, or mitigating the corrosive environment are being applied as countermeasures against SCC. In boiling water reactors (BWRs), hydrogen injection is widely used both domestically and internationally as one of the countermeasures against SCC based on improving the corrosive environment of the reactor coolant (reactor water) to which structural components are exposed.

Reactor water contains oxygen and hydrogen peroxide, which are produced by radiolysis of water inside the reactor pressure vessel (inside the reactor), and these create a corrosive environment for the reactor water. Hydrogen injection involves adding hydrogen to the reactor water by adding it to the feedwater, which then reacts with the oxygen and hydrogen peroxide, turning them back into water. As a result of the reduced oxygen and hydrogen peroxide concentrations in the reactor water, the electrochemical corrosion potential (ECP) of structural components is reduced, suppressing the occurrence of SCC.

Furthermore, one technology that promotes the reduction of ECP during hydrogen injection is to inject platinum group precious metal elements into the reactor water, which act as a catalyst on the electrochemical reaction of hydrogen, thereby significantly reducing the ECP of structural components during hydrogen injection.

In applying these technologies, it is necessary to accurately know the ECP of structural components that come into contact with reactor water in nuclear power plants. ECP is expressed as the potential relative to a reference electrode used. The standard hydrogen electrode potential is widely used as the reference, and "vs. SHE (versus Standard Hydrogen Electrode)," which is set to 0 V at each temperature, is added after V, the unit of potential difference.

ECP is measured by installing a corrosion potential sensor inside the reactor or on piping connected to the reactor, and measuring the potential difference between this corrosion potential sensor and the structural component. The corrosion potential sensor generates a constant potential (reference potential) that serves as the basis for ECP measurement under the conditions of use. For this reason, the corrosion potential sensor is also called a standard electrode or reference electrode. The ECP of a structural component can be determined by using an electrometer to measure the potential difference between the potential of the structural component under the conditions of reactor water temperature, oxygen concentration, hydrogen peroxide concentration, and reactor water flow rate and the reference potential of the corrosion potential sensor.

When attempting to measure the ECP of a BWR plant in situ, it is necessary to install an ECP sensor directly on piping or equipment and immerse it in the reactor water. For example, when installing an ECP sensor on a recirculation system piping, the ECP sensor is inserted into a cylindrical measurement seat (flange) attached to the recirculation system piping, so that the tip of the ECP sensor (detection part) comes into contact with the reactor water flowing through the recirculation system piping. The measurement seat is made of the same material as the recirculation system piping: 304 stainless steel or 316NG steel (nuclear grade of 316L steel).

However, if the COP sensor is attached to the measurement seat with its detection section reaching inside the inner surface of the recirculation system piping, the flow of reactor water in the recirculation system piping will hit the COP sensor and cause disturbances at the tip of the sensor. Furthermore, because the COP sensor is perpendicular to the high-velocity flow of reactor water in the recirculation system piping, there is a risk that the COP sensor will be damaged by flow vibrations.

Therefore, it is necessary to align the tip of the corrosion potential sensor with the inner surface of the recirculation system piping and attach the corrosion potential sensor to the measurement seat. When the corrosion potential sensor is attached to the measurement seat in this way, the space between the corrosion potential sensor and the inner surface of the measurement seat is also filled with reactor water flowing through the recirculation system piping.

When the tip of the corrosion potential sensor is inserted into and attached to a measurement seat provided in the recirculation system piping and aligned with the inner surface of the recirculation system piping, if the width of the gap formed between the tip of the corrosion potential sensor and the inner surface of the measurement seat is large, the corrosion potential sensor will measure the ECP of the surface of the metal casing of the corrosion potential sensor, rather than the ECP of the inner surface of the recirculation system piping.

The reason for this is that ECP is measured by measuring the potential difference between the corrosion potential sensor and the surface of the piping and structural materials, but the piping and structural materials, the corrosion potential sensor's signal wire, and the corrosion potential sensor's housing are all installed in the reactor water in an electrically conductive state.

Because BWR reactor water is pure water and has high liquid resistance, if the distance between the COP sensor tip and the piping surface becomes longer than the distance between the COP sensor tip and the COP sensor housing, the COP sensor housing becomes the closest ground surface to the COP sensor tip. As a result, the COP sensor measures the potential of the COP sensor housing. As a result, the COP sensor will no longer be able to accurately measure the ECP of the structural components.

Therefore, in order for the electrochemical corrosion potential sensor to accurately measure the ECP of a structural component, the distance between the side of the detection part at the tip of the electrochemical corrosion potential sensor and the inner surface of the measurement seat must be sufficiently smaller than the distance between the detection part at the tip of the electrochemical corrosion potential sensor and the metal casing of the electrochemical corrosion potential sensor.

As described in Patent Document 1 above, an electrochemical corrosion potential sensor has been developed that includes an insulator, a reference electrode disposed within the insulator, and a metal housing attached to the insulator and surrounding one end of the insulator, with a cage-shaped or cylindrical electrode to be measured disposed on the side of the detection section of the electrochemical corrosion potential sensor. The electrode to be measured is made of the same material as the object to be ECP measured, such as recirculation system piping. This allows the potential difference between the detection section of the electrochemical corrosion potential sensor and the electrode to be measured to more accurately measure the ECP of the object to be ECP measured.

However, boiling water nuclear power plants use a variety of metallic materials, such as carbon steel, stainless steel, and nickel-based alloys, for their structural components, and the material of the electrode being measured by the corrosion potential sensor must be changed to suit each ECP measurement target, which is extremely difficult.

In addition, although the ECP of the test electrode, which is made of the same material as the structural member, is measured inside the furnace, care must be taken when treating the measured ECP of the test electrode as the ECP of the structural member, as this does not measure the ECP of the actual structural member.

The object of the present invention is to provide an electrochemical corrosion potential sensor and a method for manufacturing an electrochemical corrosion potential sensor that can measure the ECP of a structural member more accurately than conventional methods, regardless of the distance between the electrochemical corrosion potential sensor and the structural member.

The present invention includes multiple means for solving the above-mentioned problems, and one example is an electrochemical corrosion potential sensor comprising: a hollow metal housing; a reference electrode arranged in the longitudinal direction of the metal housing and protruding from one end of the metal housing; an insulator formed on one end of the metal housing and covering at least a portion of the reference electrode; a first metal oxide coating covering the joint between the metal housing and the insulator; and a second metal oxide coating directly covering at least a portion of the first metal oxide coating and at least a portion of the outer periphery of one end of the metal housing on which the first metal oxide coating is formed.

According to the present invention, the ECP of a structural member can be measured more accurately than conventional methods, regardless of the distance between the corrosion potential sensor and the structural member. Other issues, configurations, and advantages will become clearer from the description of the following examples.

FIG. 2 is an explanatory diagram showing an example of an installation state of an electrochemical corrosion potential sensor on a pipe. FIG. 1 is an explanatory diagram showing a detection unit at the tip of an electrochemical corrosion potential sensor of a related art and its installation state in a pipe. 1 is an explanatory diagram showing a detection unit of an electrochemical corrosion potential sensor according to an embodiment and its installation state in a pipe. FIG. 1 is a characteristic diagram showing the relationship between the distance L between a pipe and an electrochemical corrosion potential sensor and the potential detected by the electrochemical corrosion potential sensor. FIG. 1 is a cross-sectional schematic view of an electrochemical corrosion potential sensor according to an embodiment of the present invention. FIG. 10 is a cross-sectional schematic view of an electrochemical corrosion potential sensor according to a modified example of the embodiment of the present invention. FIG. 10 is a cross-sectional schematic view of an electrochemical corrosion potential sensor according to another modified example of the embodiment of the present invention.

Examples of the electrochemical corrosion potential sensor and electrochemical corrosion potential sensor manufacturing method of the present invention will be described using Figures 1 to 7. Note that in the drawings used in this specification, identical or corresponding components are designated by the same or similar reference numerals, and repeated description of these components may be omitted.

First, I will explain how we came to this invention.

The inventors investigated the configuration of an electrochemical corrosion potential sensor that can suppress the influence of ECP on the surface of the metal casing of an electrochemical corrosion potential sensor when installed on a structural component of a nuclear power plant, and can accurately measure the ECP on the surface of the structural component.

First, an example of the installation location of an electrochemical corrosion potential sensor in a boiling water reactor (BWR) will be described using Figures 1 to 3. Figure 1 is an explanatory diagram showing an example of the installation state of an electrochemical corrosion potential sensor on a pipe, Figure 2 is an explanatory diagram showing the detection unit at the tip of an electrochemical corrosion potential sensor of the reference technology and its installation state on the pipe, and Figure 3 is an explanatory diagram showing the detection unit of an electrochemical corrosion potential sensor of the embodiment and its installation state on the pipe.

As shown in Figure 1, the corrosion potential sensor 101 is inserted into a measurement seat 13 welded to a hole formed in the recirculation system piping 12 or bottom drain piping 12 of a BWR, so that the detection part at the tip of the corrosion potential sensor 101 comes into contact with the reactor water flowing through the piping 12, thereby measuring the ECP of the piping 12.

The measurement seat 13 installed on the recirculation system piping 12 is called a flange type and has a diameter of approximately φ80 to 300 mm. The measurement seat 13 installed on the bottom drain piping 12 is called a manifold type and has a diameter of approximately φ25 to 30 mm.

The dimensions of the electrochemical corrosion potential sensor 101 are approximately 150 mm x approximately φ10 mm. Therefore, when the electrochemical corrosion potential sensor 101 is installed on the measurement seat 13, the distance between the measurement seat 13 or piping 12 and the detection part of the electrochemical corrosion potential sensor 101 is several tens to several hundred mm for the flange type, and several mm for the manifold type.

1 and 2 has a cylindrical insulator 103 made of zirconia (zirconium oxide: ZrO ₂ ) located in the detection section of the sensor and joined to a metal housing 102 by a brazing section 104. The area inside the insulator 103 filled with platinum black powder 108 serves as a reference electrode 105 for ECP measurement. A reference electrode 105 made of a platinum core wire is inserted into the insulator 103 filled with platinum black powder 108, and the reference electrode 105 is led to the outside via a metal wire 107 inside a mineral insulated cable.

As shown in Figure 1, this corrosion potential sensor 101 is inserted into a measurement seat 13 welded to a pipe 12 (e.g., a recirculation system pipe) or into a hole formed in the pipe 12.

At this time, the detection unit at the tip of the corrosion potential sensor 101 is positioned on the inner surface of the pipe 12. The ECP of the pipe 12 is measured by connecting the metal wire 107 connected to the reference electrode 105 and located inside the metal casing 102, and the wiring 15 connected to the pipe 12, to, for example, an electrometer 14, and using the electrometer 14 to measure the potential difference between the reference electrode 105 and the pipe 12.

As shown in FIG. 2, when the distance L between the detection unit of the electrochemical corrosion potential sensor 101 and the pipe 12 is small, the electrochemical corrosion potential sensor 101 detects the ECP of the pipe 12. On the other hand, when the distance L between the detection unit of the electrochemical corrosion potential sensor 101 and the pipe 12 is large and exceeds the distance M between the detection unit of the electrochemical corrosion potential sensor 101 and the metal casing 102, the electrochemical corrosion potential sensor 101 detects the ECP of the metal casing 102.

The inventors therefore considered the relationship between the distance L between the detection unit of the electrochemical corrosion potential sensor 101 and the pipe 12, the distance M between the detection unit of the electrochemical corrosion potential sensor 101 and the metal housing 102, and the ECP detected by the electrochemical corrosion potential sensor 101, and came up with the idea of covering the surface of the metal housing 2 of the electrochemical corrosion potential sensor 1 with an insulating metal oxide coating 6, as shown in Figure 3.

As a result, the ECP of the metal housing 2 is blocked by the metal oxide coating 6, preventing the electrochemical corrosion potential sensor 1 from detecting the ECP of the metal housing 2. Even if the distance L between the detection unit of the electrochemical corrosion potential sensor 1 and the piping 12 is greater than the distance M between the detection unit of the electrochemical corrosion potential sensor 1 and the metal housing 2, the electrochemical corrosion potential sensor 1 can detect the ECP of the piping 12.

The electrochemical corrosion potential sensor 101 shown in Figure 2 can detect the ECP of the metal component closest to the electrochemical corrosion potential sensor 101's detection unit, such as the pipe 12 or the electrochemical corrosion potential sensor 101's metal casing 102, because the range of the electric potential is extremely limited in reactor water environments with low electrical conductivity, such as BWRs.

The relationship between the distance L between the detection unit of the electrochemical corrosion potential sensor 101 and the pipe 12, the distance M between the detection unit of the electrochemical corrosion potential sensor 101 and the metal casing 102, and the potential E detected by the electrochemical corrosion potential sensor 101 is expressed by the following equation (1).

In equation (1), ECP _p represents the ECP of the pipe 12, ECP _m represents the ECP of the metal casing 2 of the corrosion potential sensor 1, and ρ _w represents the resistivity of the reactor water.

In contrast, as shown in Figure 3, if the surface of the metal casing 2 of the electrochemical corrosion potential sensor 1 is covered with a metal oxide coating 6, the potential E detected by the electrochemical corrosion potential sensor 1 can be expressed by the following equation (2):

In formula (2), ρ _c represents the resistivity of the metal oxide film 6 , and N represents the film thickness of the metal oxide film 6 .

Figure 4 is a characteristic diagram showing the relationship between the distance L between the pipe and the electrochemical corrosion potential sensor and the potential detected by the electrochemical corrosion potential sensor. The characteristics shown in Figure 4 show the results of a trial calculation based on equations (1) and (2) of the relationship between the distance L between the pipe 12 and the electrochemical corrosion potential sensor 1 and the potential detected by the electrochemical corrosion potential sensor 1 when the distance M between the detection unit of the electrochemical corrosion potential sensor 1 and the metal housing 2 is 30 mm.

In Figure 4, the horizontal axis represents the distance L between the pipe 12 and the detection unit of the electrochemical corrosion potential sensor 1, and the vertical axis represents the potential detected by the electrochemical corrosion potential sensor 1, with the bottom end of the vertical axis corresponding to the ECP of the pipe 12 and the top end corresponding to the ECP of the metal casing 2 of the electrochemical corrosion potential sensor 1. In other words, the closer the detected potential of the electrochemical corrosion potential sensor 1 is to the bottom end of the vertical axis, the more accurately the electrochemical corrosion potential sensor 1 can measure the ECP of the pipe 12, and the closer it is to the top end, the more the potential detected by the electrochemical corrosion potential sensor 1 becomes a composite potential of the ECP of the pipe 12 and the ECP of the metal casing 2.

First, we will explain the electrochemical corrosion potential sensor of the reference technology shown in Figure 2, which does not have a metal oxide coating on the surface of the metal casing. If the distance L between the pipe 12 and the electrochemical corrosion potential sensor 101 is within a few mm, the ECP contamination from the metal casing 102 that constitutes the electrochemical corrosion potential sensor 101 is small, and the electrochemical corrosion potential sensor 101 can accurately measure the ECP of the pipe 12.

On the other hand, if the distance L between the pipe 12 and the electrochemical corrosion potential sensor 101 exceeds 20 mm, the influence of the ECP of the metal casing 102 that constitutes the electrochemical corrosion potential sensor 101 becomes greater, and the detected potential of the electrochemical corrosion potential sensor 101 becomes a mixture of the ECP of the pipe 12 and the ECP of the metal casing 102.

For this reason, in order to accurately measure the ECP of the pipe 12 using the electrochemical corrosion potential sensor 101 of the reference technology shown in Figure 2, the distance L between the pipe 12 and the electrochemical corrosion potential sensor 101 needs to be within a few mm. Therefore, with a flange-type measurement seat where the distance between the pipe 12 and the detection part of the electrochemical corrosion potential sensor 101 is several tens to several hundred mm, there is a risk that the ECP of the pipe 12 may not be measured accurately, which places limitations on the conditions for measuring the electrochemical corrosion potential using the electrochemical corrosion potential sensor.

On the other hand, in the case of an electrochemical corrosion potential sensor 1 having a metal oxide coating 6 applied to the surface of a metal housing 2 as shown in Figure 3, even when the distance L between the piping 12 and the electrochemical corrosion potential sensor 1 is 100 mm, the ECP contamination originating from the metal housing 2 that constitutes the electrochemical corrosion potential sensor 1 is small, and the electrochemical corrosion potential sensor 1 can accurately measure the ECP of the piping 12.

Therefore, by using the electrochemical corrosion potential sensor 1 shown in Figure 3, it is possible to accurately measure the ECP of a pipe even when using a flange-type measurement seat where the distance between the pipe 12 and the detection part of the electrochemical corrosion potential sensor 1 is several tens to several hundreds of mm.

The configuration of an electrochemical corrosion potential sensor according to an embodiment of the present invention, which reflects the results of the above study, will be described using Figures 5 to 7. Figures 5 to 7 are schematic cross-sectional views of the electrochemical corrosion potential sensor according to this embodiment.

The electrochemical corrosion potential sensor 1 of this embodiment shown in Figure 5 comprises an insulator 3 formed at one end of a metal housing 2 and covering at least a portion of the reference electrode 5, a hollow metal housing 2, a reference electrode 5 arranged in the longitudinal direction of the metal housing 2 and protruding from one end of the metal housing 2, a metal wire (lead wire) 7, metal/metal oxide powder 8, a sealing plug 9, a mineral insulated cable 10, a first metal oxide coating 6a covering the joint between the metal housing 2 and the insulator 3, and a second metal oxide coating 6b covering at least a portion of the outer periphery of one end of the metal housing 2 on the side where the first metal oxide coating 6a is formed.

The insulator 3 and metal casing 2 are joined at the brazing portion 4.

One end of the reference electrode 5 is connected to the metal wire 7 at a joint 11 inside the insulator 3 or the metal housing 2. The other end of the reference electrode 5, which serves as the detection section, is located inside the insulator 3 filled with metal/metal oxide powder 8 and is covered by the insulator 3 via the metal/metal oxide powder 8. The metal/metal oxide powder 8 inside the insulator 3 is sealed from the metal housing 2 side of the electrochemical corrosion potential sensor 1 by a hollow sealing plug 9.

In the electrochemical corrosion potential sensor 1 of this embodiment, as shown in FIG. 5, the outer surface of the portion where the insulator 3 and the metal housing 2 are joined by the brazing portion 4 is covered with a first metal oxide coating 6a, and a portion of the outer surface of the metal housing 2 is covered with a second metal oxide coating 6b.

Furthermore, the second metal oxide coating 6b covers at least a portion of the first metal oxide coating 6a. Figure 5 shows a configuration in which one surface of the first metal oxide coating 6a facing the second metal oxide coating 6b is covered by the second metal oxide coating 6b.

As described above with reference to Figures 2 and 3, the distance M between the detection part (end of the reference electrode 5) of the electrochemical corrosion potential sensor 1 and the metal housing 2 is approximately 30 mm, so it is necessary to form a first metal oxide coating 6a and a second metal oxide coating 6b on the brazed part 4 and part of the outer surface of the metal housing 2, depending on the distance L between the piping 12 and the electrochemical corrosion potential sensor 1.

For example, if the distance L between the piping 12 and the electrochemical corrosion potential sensor 1 is 100 mm, it is desirable to cover the outer periphery of the metal casing 2 from the brazed portion 4 for at least 100 mm in the longitudinal direction with the first metal oxide coating 6a and the second metal oxide coating 6b. The insulating first metal oxide coating 6a and the second metal oxide coating 6b insulate the potential of the brazed portion 4 and the metal casing 2, thereby suppressing ECP hybridization originating from the brazed portion 4 and the metal casing 2, allowing the electrochemical corrosion potential sensor 1 to accurately measure the ECP of the piping.

The electrochemical corrosion potential sensor of this embodiment is not limited to the structure shown in Figure 5; other examples of configurations will be described below using Figures 6 and 7.

The electrochemical corrosion potential sensor 1A shown in Figure 6 has a configuration in which the second metal oxide coating 6b1 covers the entire outer periphery of the metal casing 2, and is suitable for installing the electrochemical corrosion potential sensor in a flange-type measurement seat with a diameter of more than 100 mm. In the electrochemical corrosion potential sensor 1A shown in Figure 6, it is desirable that the brazed portion 4 is also covered with the insulating first metal oxide coating 6a, as shown in Figure 6.

The electrochemical corrosion potential sensor 1B shown in Figure 7 has an insulator 3b, a metal housing 2, a reference electrode 5b, a metal wire (lead wire) 7, a first metal oxide coating 6a2 covering the joint between the metal housing 2 and the insulator 3b, and a second metal oxide coating 6b2 covering at least a portion of the outer periphery of one end of the metal housing 2 on the side where the first metal oxide coating 6a is formed.

In the corrosion potential sensor 1B shown in Figure 7, the reference electrode 5b is exposed on the opposite side of the insulator 3b from the metal casing 2, and is configured so that the reference electrode 5b is in direct contact with the reactor water.

Even in a configuration in which the reference electrode 5b is in direct contact with reactor water, such as the electrochemical corrosion potential sensor 1B shown in Figure 7, the second metal oxide coating 6b2 can cover the entire outer periphery of the metal casing 2, as shown in Figure 6. Also, the junction between the reference electrode 5b and the insulator 3b can be covered with an insulating first metal oxide coating 6a2.

The metal housing 2 in the electrochemical corrosion potential sensors 1, 1A, and 1B shown in Figures 5 to 7 is made of at least one of nickel-based alloys and stainless steels, and in particular can be made of nickel-based alloy 42 (42 alloy) and 316L stainless steel (SUS316L).

The insulators 3, 3b can be made of at least one of zirconia, yttrium oxide (Y ₂ O ₃ , yttria), aluminum oxide (Al ₂ O ₃ , alumina), partially stabilized zirconia (PSZ), yttria-stabilized zirconia (YSZ), and the like.

The reference electrodes 5, 5b can be made of one or more of the following: iron, silver/silver chloride electrode, platinum electrode, zirconium electrode, etc.

Furthermore, like the insulators 3 and 3b, the first metal oxide coatings 6a and 6a2 and the second metal oxide coatings 6b, 6b1 and 6b2 can be made of at least one of zirconia, yttria, alumina, partially stabilized zirconia, yttria-stabilized zirconia, etc.

Next, we will explain the method for forming the first metal oxide coatings 6a and 6a2 and the method for forming the second metal oxide coatings 6b, 6b1, and 6b2 on the outer surface of the metal casing 2, which are part of the manufacturing method for the electrochemical corrosion potential sensors 1, 1A, and 1B according to this embodiment.

The first metal oxide coating 6a, 6a2 and the second metal oxide coating 6b, 6b1, 6b2 can be formed on the outer surfaces of the brazing portion 4 and the metal casing 2, respectively, using any of the following methods: physical vapor deposition (PVD), chemical vapor deposition (CVD), thermal spraying, sol-gel, metal organic decomposition (MOD), and coating.

Furthermore, it is preferable that the first metal oxide coatings 6a, 6a2 and the second metal oxide coatings 6b, 6b1, 6b2 are formed simultaneously using the above-mentioned formation method.

Next, we will explain the effects of this embodiment.

The electrochemical corrosion potential sensors 1, 1A, 1B of the present embodiment described above comprise a hollow metal housing 2, a reference electrode 5, 5b disposed longitudinally of the metal housing 2 and protruding from one end of the metal housing 2, an insulator 3, 3b formed at one end of the metal housing 2 and covering at least a portion of the reference electrode 5, 5b, a first metal oxide coating 6a, 6a2 covering the joint between the metal housing 2 and the insulator 3, 3b, and a second metal oxide coating 6b, 6b1, 6b2 covering at least a portion of the outer periphery of the end of the metal housing 2 on the side where the first metal oxide coating 6a, 6a2 is formed.

In this way, by covering at least the side of the outer periphery of the metal casing 2 closest to the reference electrode 5, 5b with the second metal oxide coating 6b, 6b1, 6b2, the side of the surface of the metal casing 2 closest to the reference electrode 5, 5b is insulated, preventing the electrochemical corrosion potential sensors 1, 1A, 1B from measuring the ECP of the surface of the metal casing 2 that constitutes the sensor. Therefore, even if the distance between the side of the reference electrode 5, 5b, which is the detection unit of the electrochemical corrosion potential sensor 1, 1A, 1B, and the inner surface of the measurement seat is greater than the distance between the detection unit of the electrochemical corrosion potential sensor 1, 1A, 1B and the metal casing 2, the electrochemical corrosion potential sensor 1, 1A, 1B can accurately measure the ECP of the structural member. This relaxes the constraints on the distance between the electrochemical corrosion potential sensor and the ECP measurement target, allowing for more accurate measurement of the ECP of the structural member of the plant that is the ECP measurement target.

Such corrosion potential sensors 1, 1A, and 1B can be installed on other piping in a BWR plant (e.g., reactor cleanup system piping, drain piping and feedwater piping connected to the bottom of the reactor, etc.) and used to measure the ECP of the corresponding piping. Furthermore, they can be used to measure the ECP of piping in pressurized water nuclear power plants and thermal power plants, and are particularly suitable for measuring the corrosion potential of structural members made of carbon steel, iron-based alloys, or nickel-based alloys whose surfaces come into contact with the reactor's cooling water. Specifically, they are corrosion potential sensors suitable for measuring the corrosion potential that serves as an indicator of water chemistry conditions for stress corrosion cracking (SCC) of stainless steel and nickel-based alloys or flow-accelerated corrosion (FAC) of carbon steel and nickel-based alloys.

In addition, because the second metal oxide coatings 6b, 6b1, and 6b2 cover at least a portion of the first metal oxide coatings 6a and 6a2, the areas where the metal casing 2 is exposed can be reduced, enabling more accurate ECP measurements.

Furthermore, because the second metal oxide coating 6b1 covers the entire outer periphery of the metal casing 2, the possibility of the reference electrode 5, 5b measuring the ECP of the metal casing 2 is further reduced, resulting in a structure that can accurately measure the ECP of plant structural components even if the distance to the inner surface of the measurement seat is very large.

Furthermore, by simultaneously forming the first metal oxide coatings 6a, 6a2 and the second metal oxide coatings 6b, 6b1, 6b2, the time required for coating formation can be shortened, improving the manufacturing efficiency of the electrochemical corrosion potential sensors 1, 1A, 1B.

<Others>
The present invention is not limited to the above-described embodiment, and various modifications and applications are possible. The above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to having all of the described configurations.

101, 1, 1A, 1B... ECP sensor 102, 2... Metal housing 103, 3, 3b... Insulator 104, 4... Brazed portion 105, 5, 5b... Reference electrode 6... Metal oxide coating 6a, 6a2... First metal oxide coating 6b, 6b1, 6b2... Second metal oxide coating 107, 7... Metal wire 108, 8... Metal/metal oxide powder 9... Sealing plug 10... Mineral insulated cable 11... Joint between reference electrode and metal wire 12... Piping 13... Measurement seat 14... Electrometer 15... Wiring

Claims (10)

1. An electrochemical corrosion potential sensor comprising:
A hollow metal housing,
a reference electrode provided in the longitudinal direction of the metal housing and protruding from one end of the metal housing;
an insulator formed at one end of the metal housing and covering at least a portion of the reference electrode;
a first metal oxide coating covering a joint between the metal housing and the insulator;
a second metal oxide coating that directly covers at least a portion of the first metal oxide coating and at least a portion of the outer periphery of one end of the metal casing on which the first metal oxide coating is formed. The electrochemical corrosion potential sensor according to claim 1,
The electrochemical corrosion potential sensor according to claim 1, wherein the second metal oxide coating covers the entire outer periphery of the metal casing. 2. The electrochemical corrosion potential sensor according to claim 1,
The electrochemical corrosion potential sensor according to claim 1, wherein the insulator covers an end of the reference electrode. 2. The electrochemical corrosion potential sensor according to claim 1,
The electrochemical corrosion potential sensor according to claim 1, wherein the reference electrode is exposed on the opposite side of the insulator from the metal housing. The electrochemical corrosion potential sensor according to claim 1,
a first metal oxide film and a second metal oxide film each containing at least one of zirconium oxide, yttrium oxide, and partially stabilized zirconia; 2. The electrochemical corrosion potential sensor according to claim 1,
10. The electrochemical corrosion potential sensor according to claim 9, wherein the reference electrode is made of any one of silver/silver chloride, iron, zirconium, and platinum. The electrochemical corrosion potential sensor according to claim 1,
The electrochemical corrosion potential sensor according to claim 1, wherein the insulator contains at least one of zirconium oxide, yttrium oxide, and aluminum oxide. A method for manufacturing an electrochemical corrosion potential sensor having a hollow metal housing, a reference electrode provided in a longitudinal direction of the metal housing and protruding from one end of the metal housing, and an insulator formed on the one end of the metal housing and covering at least a portion of the reference electrode,
forming a first metal oxide coating that covers a joint between the metal housing and the insulator;
forming a second metal oxide coating that directly covers at least a portion of the first metal oxide coating and at least a portion of the outer periphery of one end of the metal casing on the side where the first metal oxide coating is formed. 9. The method for manufacturing an electrochemical corrosion potential sensor according to claim 8 ,
a method for manufacturing an electrochemical corrosion potential sensor, the method comprising forming the first metal oxide coating and the second metal oxide coating by at least one method selected from the group consisting of physical vapor deposition (PVD), chemical vapor deposition (CVD), thermal spraying, a sol-gel process, metal organic decomposition (MOD), and a coating method. 9. The method for manufacturing an electrochemical corrosion potential sensor according to claim 8 ,
a first metal oxide film and a second metal oxide film formed on the first electrode and the second electrode simultaneously;