JPH03100451A - Method and device for monitoring environmental crack and method and device for controlling corrosive environment - Google Patents

Abstract

PURPOSE:To easily and accurately monitor the stress corrosion crack and environmental crack of a structure made of a metallic material exposed to corrosive environment by comparing the potential difference between the spacing part of the metallic structure and other part with a preset reference value. CONSTITUTION:The structure 1 of a potential measuring cell has a cylindrical external cell 3 and a cylindrical internal cell 7 disposed apart a prescribed annular spacing part 5 in the external cell 3 and is constituted of the same material as the material of the structure in a light water reactor. Respective electrodes 27, 29 for potential measurement are provided in and out of the spacing part 5 in the corrosive environment. A detector 35 measures the difference in the potential in the two electrodes 27, 29. A comparing means 37 makes comparison between the potential difference and the preset reference value (critical potential difference) concerning the generation and progression of the crack in the corrosive environment. A warning command signal to a warning device 39 is outputted when the potential difference is larger than the reference value. The stress corrosion crack and environmental crack of the structure made of the metallic material exposed to the corrosive environment are easily and accurately monitored in this way.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is applicable to structures in nuclear power plants, thermal power plants, chemical plants, etc., in environments such as stress corrosion cracking (SCC). The present invention relates to a method and apparatus for monitoring cracks, as well as an environmental control method and apparatus for improving the health of structures exposed to corrosive environments.

(Conventional technology) Like nuclear power plants, thermal power plants, chemical plants, etc.
In plants with relatively large structures, especially in nuclear power plants with light water reactor structures in contact with high-temperature pure water, it is important to ensure that the structures are in a healthy condition for long-term effective use. It is strongly desired to avoid this occurrence as much as possible and to extend its life as much as possible.

Particularly in structures that come into contact with a corrosive environment such as reactor water, cracks occur in the structure at a stress lower than the fracture stress of the structure due to the corrosive environment, and environmental cracking, which progresses, becomes a problem. This environmental cracking progresses gradually with almost no change in appearance and leads to destruction, so advanced technology is required to detect it, and periodic inspections are needed to identify areas where there is a risk of environmental cracking. It would be inefficient to investigate each item one by one.

Environmental cracking is often stress corrosion cracking, and stress corrosion cracking is a phenomenon caused by a combination of three factors: material, environment, and stress.

Therefore, conventional measures have been taken to suppress or avoid the occurrence of stress corrosion cracking in structures by removing material factors such as changing the materials constituting the structure, and reducing stress by changing the structure. Currently, in nuclear power plants, 5U
Changes have been made from stainless steel such as S304 to pond materials that do not cause stress corrosion cracking, and removal of residual stress through heat treatment. However, it is difficult to eliminate residual stress in welded parts and the like, and it is almost impossible to change the material of the reactor internals to other materials. Furthermore, it would be extremely costly to take these measures for all locations where stress corrosion cracking is likely to occur.

In response, it has been considered to control the environment itself to a state where environmental cracking such as stress corrosion cracking does not occur, and this is equally effective at each of the many locations where environmental cracking is likely to occur. However, it is the most rational measure.

In view of this, it is important to establish technology to control the environment so that environmental cracks do not occur, and to monitor environmental cracks as part of this control.

Corrosion environment monitoring systems currently being implemented in BWRs (boiling water reactors) overseas include Epri, N, and B352.
1 (EPRI-NP-3521198415), EPRI, N, B 3517 (EPRI-NP-35171
98415), Corrosion-83 PAPER NUMB
ER122), Corrosion-83 Vapor Number 12
9 (Corrosion“83 PAPERNUM
As described in BER129), environmental corrosion monitoring, that is, environmental cracking risk is determined by measuring the corrosion potential of stainless steel in secondary cooling water (reactor water) using a reference electrode. things are being done. According to this,
It is said that if the corrosion potential of stainless steel is 1230 mV vs SHE or less, stress corrosion cracking will not occur in the stainless steel.

In order to prevent stress corrosion cracking, measures have been taken to prevent stress corrosion cracking by injecting hydrogen into the reactor water and regulating the oxygen concentration in the secondary cooling water. When dealing with this stress corrosion cracking, the amount of hydrogen injected into the reactor water is important. If the amount of hydrogen injected is too large, hydrogen embrittlement will occur in the sub-cooling system equipment and members, and there is a risk of hydrogen-induced cracking. This also causes the problem that the amount of hydrogen in the exhaust gas increases. On the contrary, if the amount of hydrogen injected into the reactor water is small, the effect of preventing stress corrosion cracking will be reduced.

As a method to keep the amount of hydrogen injected into the reactor water at an appropriate value,
As described in Japanese Patent Publication No. 63-19838,
-Measure the corrosion potential, dissolved hydrogen concentration, and dissolved hydrogen concentration of the stainless steel that constitutes the secondary cooling system, and
mV ~-600mV, dissolved hydrogen concentration 10-50pp
b. A method is known in which the amount of hydrogen injection is controlled so that the residual hydrogen concentration is 150 ppb or less.

(Problems to be Solved by the Invention) The prior art as described above controls the hydrogen concentration in the primary cooling water in order to maintain the corrosion potential of stainless steel, the dissolved hydrogen concentration, and the dissolved hydrogen concentration in the secondary cooling water at predetermined values. , is characterized by preventing the occurrence of stress corrosion cracking, but the relationship between stress corrosion cracking and corrosion potential fluctuates under the influence of the conductivity of the primary cooling water. If it is set too much on the safe side, excessive hydrogen will be injected into the secondary cooling water, resulting in problems such as the risk of hydrogen-induced cracking and an increase in hydrogen in the exhaust gas. In the conventional technology as described above, it is difficult to find a universally appropriate value for this critical potential, and in reality, the appropriate potential width must be set relatively wide, making it difficult to determine the optimal amount of hydrogen injection. Have difficulty.

Generally, the interior of a crack caused by stress corrosion cracking is a type of pore environment, which is a different environment from the bulk, and the water quality inside this crack is directly involved in stress corrosion cracking. Therefore, it is not necessarily appropriate to control the amount of hydrogen injection based on the corrosion potential of stainless steel immersed in bulk water, and it is important to fully understand the water quality inside cracks to reliably assess the risk of stress corrosion cracking. essential for finding out.

In addition, a highly stable and long-life reference electrode is required to measure the corrosion potential, but no suitable electrode has been developed at present.

SUMMARY OF THE INVENTION In view of the above-mentioned problems and circumstances, it is an object of the present invention to provide a highly reliable method and device for monitoring environmental cracks, a monitoring device with a warning device, and an environmental control method and device.

[Structure of the Invention] (Means for Solving the Problems) According to the present invention, the above object is to provide an artificial gap in a metal structure that is in contact with a corrosive environment, and to An environmental crack monitoring method, comprising: measuring a difference in potential between a gap and other parts; and comparing this potential difference with a preset reference value regarding the occurrence and growth of cracks in the metal structure; The apparatus used to carry out this method includes a double-tube structure disposed in a corrosive environment, with an artificial gap formed by the double-tube structure; Electrodes for potential measurement are provided inside the gap and outside the gap, a potential difference measuring means for measuring the potential difference between the two electrodes, and a potential difference measuring means for measuring the difference in potential between the two electrodes, and a method for measuring the difference in potential and the occurrence and growth of cracks in a corrosive environment. An environmental crack monitoring device having a comparison device for comparing with a preset reference value, or an electrode having an artificial gap and an electrode having no gap in a corrosive environment, This is achieved by an environmental crack monitoring device having a potential difference measuring means for measuring the potential difference of the electrodes, and a comparing means for comparing the potential difference with a preset reference value regarding crack initiation and propagation in a corrosive environment.

The difference in corrosion potential between the gap and the outside of the gap can be detected by measuring the potentials of the gap and other parts, or by detecting the difference between the potentials of the gap and other parts. It may also be detected by direct measurement of the potential difference.

The reference value may be determined depending on the environmental cracking sensitivity determined by the material of the member sensitive to environmental cracking, particularly the sulfur content.

In addition, when a corrosive environment comes into contact with an aqueous solution, the water quality of this aqueous solution is measured both in the gap and outside the gap, and the difference in water quality is compared with a predetermined reference value regarding the occurrence and propagation of cracks in a corrosive environment. The above-mentioned monitoring of environmental cracks may be performed in consideration of the comparison. In this case, water quality measurements include dissolved hydrogen concentration,
The measurement may be performed for molten hydrogen concentration, hydrogen peroxide concentration, sulfur oxide concentration, Cl concentration, pH concentration, etc.

Also, measuring the difference in conductivity between the gap and the outside of the gap,
Environmental cracking may be monitored as described above by comparing this conductivity difference with a preset reference value regarding the occurrence and growth of cracks in a corrosive environment.

Another object of the present invention is to provide an environmental crack monitoring device as described above, in which at least one of the potential group or the potential difference, the water quality difference, and the conductivity difference is greater than a reference value by the comparison means. This is achieved by an environmental crack monitoring device having a warning means for issuing a warning when a comparison is reached.

Another object of the present invention is to add a corrosion inhibitor such as hydrogen, oxygen, or nitrogen oxide to a corrosive environment according to the results of comparison using the above-mentioned environmental crack monitoring method or device. A corrosive environment control method and a device used to carry out this method include a corrosion inhibitor addition device that adds a corrosion inhibitor to a corrosive environment according to the results of a comparison using the above-mentioned environmental crack monitoring method or device. This can be achieved by a corrosive environment control device such as

The environmental crack risk control device as described above may be used in a nuclear power plant, a thermal power plant, or a chemical plant.

(Function) The cause of stress corrosion cracking is not directly related to the potential of the metal itself in contact with the corrosive environment, such as stainless steel, but due to the impurity that comes into contact with the aqueous solution according to the potential gradient between the potential in the gap and other parts. It is caused by the ion, So-1Cl-, moving into the interstitial space and condensing, resulting in a pH-lowering force phenomenon.

Therefore, stress corrosion cracking susceptibility (SCC susceptibility) is correlated with the potential difference between the gap and other parts, and the smaller this potential difference, the less likely stress corrosion cracking will occur. That is, the potential difference is an index for SCC susceptibility, and the potential difference is the IR loss caused by the current generated by the macrocell based on the difference between the corrosion process inside and outside the gap, and the existence of this potential difference indicates that some corrosion process is occurring inside and outside the gap. This is thought to be the cause of the difference. Stress corrosion cracking is a corrosion phenomenon in a physically limited space within a gap.
There is an identified correlation between this potential difference and stress corrosion cracking.

Therefore, environmental cracks can be monitored based on the potential difference between the gap and other parts without using a reference electrode and without being affected by conductivity.

In addition, by controlling the amount of corrosion inhibitor injected according to the potential difference, water quality difference, and conductivity difference, stress corrosion cracking in the structure can be reliably avoided without causing other problems. Become so.

(Example) The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows one embodiment of an environmental crack monitoring device according to the present invention. In FIG. 1, reference numeral 1 indicates a potential measuring cell structure of an environmental crack monitoring device.

The potential measuring cell structure 1 has a cylindrical vertical cell 3 and a cylindrical internal cell having a predetermined annular gap 5 in the external cell 3. When installed in the reactor water circulation system of a light water reactor, it is constructed of the same material as the structural material inside the light water reactor. This material includes low alloy steel,
Examples include stainless steel and Inconel 600 alloy.

The inner self is composed of a cylindrical body having an outer diameter one smaller than the inner diameter of the outer cell 3, and is connected to the cap member 11 by an insulating connector 9, and the cap member 3 is screwed to one end of the outer cell 3. External cell 3
The annular gap portion 5 is fixedly arranged concentrically within the cell and the outer cell 3 to form the annular gap portion 5 therebetween.

A reactor water inlet 13 is provided at the other end of the outer cell 3, and a reactor water outlet 15 is provided in the cap member 11, so that the reactor water flowing into the outer cell 3 from the reactor water inlet 13 is It fills the outer cell 3 including the gap 5 and flows through the inner self and the inner passages 15,17 of the insulating connector 9 towards the reactor water outlet 15.

The internal self acts as a specimen, which includes specimen electrode wire 2.
1 is electrically connected. Further, the external cell 3 is provided with a reference electrode boat 23 for measuring the corrosion potential in the annular gap 5 and a reference electrode boat 25 for measuring the corrosion potential in the area outside the gap 5. ing. Each of these reference electrode boats 23.25 has a reference electrode 27.2.
is installed. The reference electrodes 27 and 29 may be either external reference electrodes or internal reference electrodes, but are preferably external reference electrodes from the viewpoint of leakage of reactor water and long-term stability.

Collation type f! 27 and 29 are conductively connected to the potential difference detection device 35 together with the sample electrode wire 21 by electrode wires 31 and 33, respectively. The potential difference detection means 35 takes in the potential at the annular gap 7 taken out from the reference electrode 27 and the potential outside the gap taken out from two other reference electrodes, and calculates the potential difference between these two potentials. Then, this is output to the comparing means 37.

The comparison means 37 compares the potential difference with a preset reference value (limit potential difference) regarding the occurrence and growth of cracks in a corrosive environment, and outputs a warning command signal to the warning device 39 when the potential difference is larger than the reference value. It is supposed to be done.

As a result, the warning device 39 issues a warning, display, etc. when the potential difference is larger than the reference value to warn that there is a risk of environmental cracking occurring.

FIGS. 2 and 3 show the relationship between the potential difference inside and outside the gap and the stress corrosion cracking fracture rate, that is, the environmental cracking risk, as calculated as described above.

Figure 2 shows the potential difference between the inside and outside of the gap in low alloy a (0,004 wt% S) for pressure vessels in high-temperature pure water at 288°C, and the smooth test piece with the gap applied at a low strain rate of 10-68-1.
The above relationship, that is, SCC susceptibility, obtained by conducting a tensile test (SSRT test) is shown. FIG. 3 shows the test results when a similar test piece was made of stainless steel (304 stainless steel) sensitized by chromium carbide precipitation.

From any of these tests, the potential difference inside and outside the gap and the SC
It will be appreciated that there is a specific correlation between C sensitivity.

Figure 4 shows a cell structure as shown in Figure 1 made of a low alloy for pressure vessels, and a 5SRT test similar to that shown in Figures 2 or 3 carried out on the alloy steel. This figure shows the relationship between the potential difference at the stress corrosion cracking limit obtained by varying the sulfur content from 0.014% by weight to 0°004% by weight and the sulfur content in the alloy steel.

In FIG. 4, O indicates the absence of environmental cracking, . indicates the presence of environmental cracking, and the numerical value in parentheses indicates the environmentally promoted fracture surface ratio.

Therefore, the environmental crack occurrence limit value determined by the sulfur content of alloy steel for pressure vessels in various plants as shown in FIG. 4 and the potential difference detected by the potential difference detection means 35 as described above in an actual plant. If this potential difference exceeds the limit potential difference, the warning device 39 may be activated to issue a warning.

Figure 5 shows a cell structure having the above-mentioned structure made of 304 stainless steel, and a 5SRT test similar to that shown in Figures 2 or 3 conducted to increase the sensitivity of the material to environmental corrosion cracking. The results shown are the results obtained by varying the intensity. Note that the degree of sensitization uses the maximum grain boundary erosion depth after Strauss test as a parameter, and the test results show that as the degree of sensitization increases, the limit potential difference tends to decrease. Therefore, if the degree of sensitization in the target part of each plant is recognized, the limit potential difference as defined in FIG. The potential difference may be compared with the potential difference, and if this potential difference exceeds the limit potential difference, a warning may be issued.

As mentioned above, in the present invention, environmental cracking is monitored based on the potential difference between the inside and outside of the gap, so even if the conductivity of the reactor water changes, stress corrosion cracking may occur as a comparison standard. The appropriate value does not change.

Figure 6 shows the occurrence of stress corrosion cracking in the simple relationship between corrosion potential and conductivity of reactor water.

In Figure 8, the ○ marks indicate that stress corrosion cracking does not occur.
The mark indicates that stress corrosion cracking has occurred. As is clear from this graph, it will be understood that with only a simple corrosion potential, the critical potential for stress corrosion cracking changes greatly depending on the conductivity.

FIG. 7 shows the occurrence of stress corrosion cracking in the relationship between the potential difference inside and outside the gap and the conductivity of the reactor water as described above. Also in FIG. 7, the O mark indicates that stress corrosion cracking does not occur, and the * mark indicates that stress corrosion cracking occurs. In this case, the critical potential difference for stress corrosion cracking becomes approximately constant regardless of the conductivity. That is, the appropriate value of the comparison reference value does not change depending on the conductivity, and can be uniquely determined.

FIG. 8 shows one embodiment in which the environmental crack monitoring device according to the present invention is incorporated into a light water reactor nuclear power plant. 6th
In the figure, numeral 41 indicates the light water reactor pressure vessel, numeral 43 indicates the reactor water recirculation system piping, and the reactor water is supplied to the reactor water pump 4.
5, the reactor water flows through the reactor water recirculation system piping 43 and is recirculated and supplied into the light water reactor pressure vessel 41.

A bypass reactor water circulation pipe 46 is branched from the middle of the reactor water circulation system pipe 10, and two potential measurement cell structures 1 are equally installed in parallel with each other in this pipe 46 for double check. ing.

In this embodiment, the potential signals taken out from each of the potential measuring cell structures 1 are taken in by an electronic control unit 47 including a microcomputer having a general structure. The slave control device 47 detects the potential difference between the inside and outside of the gap based on the potential signal from the potential detection cell structure 1, and detects the potential difference between the inside and outside of the gap and the preset limit regarding crack occurrence and propagation in a corrosive environment as described above. The potential difference is compared with a reference value, and if the potential difference exceeds the reference value, an activation command is output to the warning device 49. Therefore, if the potential difference rises above the reference value, the warning device 49 will issue a warning.

As mentioned above, the metal constituting the potential measurement cell structure 1 connected to the piping is made of the same metal used for the reactor wall and core, such as light alloy steel, stainless steel, and nickel-based metal steel. However, if the correlation between the SCC susceptibility of the cell constituent metal and the SCC susceptibility of the target metal is known, the cell structure 1 may be made of other metal materials.

The flow rate of reactor water flowing into cell structure #1 is not particularly specified, but if the flow rate of reactor water is too fast, it may have a disturbance effect on the potential in the gap, so in reality it is 3 to 10%. A value of the order of liters/hour would be suitable.

FIG. 9 shows one embodiment of the corrosive environment control device for environmental cracking according to the present invention. In FIG. 9, parts corresponding to those in FIG. 8 are indicated by the same reference numerals as in FIG.

The environmental control device is provided with a hydrogen injection device 55 that injects hydrogen into a water supply pipe 53 to the light water reactor pressure vessel 41 using a hydrogen injection pipe 51. Hydrogen injection device 5
5 receives a control signal from the electronic control device 47, and when the potential difference between the inside and outside of the gap, determined based on the potential detected by the potential measurement cell structure 1, rises above the reference value, the hydrogen is supplied to the water supply pipe. It is designed to be injected into 53.

As a result, hydrogen injection control can be carried out appropriately depending on the risk of environmental cracking found from the potential difference between the inside and outside of the gap.

In addition, in FIG. 9, 57 indicates the main steam piping.

FIG. 10 shows another embodiment of a nuclear power plant equipped with a corrosive environment control device according to the present invention. In Fig. 10, 61 is the light water reactor pressure vessel, 63 is the in-core instrumentation pipe installed in the light water reactor pressure vessel 61, 65 is the reactor water recirculation system piping with a pump 67 in the middle, and β9 is the water supply water supply pipe. plumbing,
Reference numeral 71 indicates a reactor water purification system piping having a bongua 3 and a demineralizer 75 for purifying reactor water in the middle. The light water reactor pressure vessel 61 is provided with an electrode combination structure tree 81 for potential difference measurement through the in-core instrumentation pipe 63, and each of the reactor water recirculation system pipe 65, six water supply pipes, and reactor water purification system pipe 71 is provided with an electrode assembly structure tree 81 for measuring potential difference. An electrode combination structure 91 for potential difference measurement is provided.

As clearly shown in FIG. 11, the electrode combination m body 81 for potential difference measurement has a gap between llll13! Part 85
A rectangular electrode member 83 having a cutout and a rectangular electrode member 87 having no notch are provided close to each other. The electrode members 83 and 87 are made of the same metal as the metal that constitutes the reactor wall of the light water reactor pressure vessel 61.
3, as shown in FIG. 12, the other exposed parts of the furnace except for the gap 85 formed by the notch are covered with an electrically insulating layer 8.
It is insulated by two layers. The electrical insulating layer 89 is a CV
It is composed of a coating layer of Z r O2 by method D. Note that this electrical insulating layer 89 is formed by Z
r In addition to the O2 coating layer, it may be formed by a thermal spraying method, PVD method, electrophoresis method, cluster ion beam method, ion mixing method, etc. Also, as the electrical insulating material, in addition to ZrO□, Al2O2, 5i02 Other oxides may also be used.

As described above, since the outer surface of the electrode member 83 except for the gap 85 is electrically insulated, only the potential at the gap 85 is extracted from the electrode member 83.
The area of the 0-gap portion 85, which prevents the potential taken out from this electrode member from becoming a mixed potential including the potential of portions other than the gap portion 85, is larger than the area of other portions of the electrode member 83. Since the potential taken out from this electrode member 83 is the mixed potential, this electrode member 83
The potential extracted from the electrode member 8 having no gap 85
7, the potential is almost the same as the potential extracted by 7, and the gap 85
becomes virtually impossible to detect. For this reason, in the device of the present invention, the gap 85 is
In order to extract only the potential at the gap 85, the electrode member 83 is coated with an electrically insulating coating except for the gap 85.

Electrode wires 101 are connected to each of the electrode members 83 and 87, and the electrode wires are taken out of the furnace through an in-furnace instrumentation tube 63 and connected to an electrometer 103. The electrometer 103 is a potential difference measuring means having a high internal resistance, and is adapted to detect the potential difference between the electrode members 83 and 87.

As clearly shown in FIG. 13, the electrode combination structure 91 for potential difference measurement that is incorporated into various piping systems includes a rectangular electrode member 93 having a gap 95 formed by a notch, and a rectangular electrode member 93 having a gap 95 formed by a notch. These electrode members are constructed in the same manner as the electrode members of the electrode combination structure 81 for potential difference measurement described above. That is, the electrode members 93 and 97 are each made of the same metal as the metal that constitutes the reactor wall of the light water reactor pressure vessel 61, and the outer surface of the electrode member 93 except for the gap 95 is coated with electrical insulation.

Electrode wires 105 are connected to the electrode members 93 and 97, respectively, and the electric f! The wires 105 pass through the piping member 107 and are taken out to the outside, and are each connected to an electrometer 109 that is the same as the electrometer 103. The electrometers 109 are configured to detect the potential difference between the electrode members 93 and 97 of the potential difference measuring electrode combination structure 91 that is incorporated in each piping system.

The potential difference between the electrode members 83 and 87 or between the electrode members 93 and 97 detected by the electrometers 103 and 109 is the potential difference between the inside and outside of the gap 85 or the gap 95.
This is a potential difference between inside and outside, and information regarding this potential difference is sent to a central processing control unit 111 including a microcomputer.

The central processing control unit 111 uses predetermined reference values regarding the occurrence and growth of cracks in a corrosive environment and each electrometer 1.
03 or 109, and if the potential difference exceeds the reference value, or if it is estimated that there is a risk of the potential difference exceeding the reference value through statistical processing or learning control, a warning is sent to the warning device 113. It is designed to output a command signal. As a result, if the risk of environmental cracking increases, the warning device 113 will display the location and issue a warning.

Furthermore, in the present invention, in addition to the potential difference between the inside and outside of the gap as described above, environmental cracks may be monitored according to the water quality difference inside and outside the gap and changes in conductivity. An example of a means for measuring conductivity difference is shown.

In this embodiment, a test piece 121 having a notch gap 121a is provided in the piping system of a nuclear power plant, and SO4-ion concentration sensors 123a and 123b are installed in the notch gap 121 and in the normal pipe, respectively. , C1 ion concentration sensors 125a, 125b, H2O2-02-H2 simultaneous analysis sensors 127a, 127b, and pH droplet level sensor 12.
9a, 129b and conductivity meters 131a, 131b are respectively arranged.

The test piece 121 is made of the same metal as the wall of the light water reactor pressure vessel or the metal forming the reactor water piping. 504-Ion concentration sensor 123a, 123b
The Cl- ion concentration sensors 125a and 125b may be composed of AgC19 electrodes that do not use an internal liquid.H2020
The 2-H2 simultaneous analysis sensors 127a and 127b perform simultaneous quantitative analysis of the concentrations of H2O2, H2, and 02 by performing pulse portammetry using platinum microelectrodes with a radius of several tens of μm or less. For this analytical sensor, a three-electrode system combining a platinum electrode, a reference electrode, and a platinum counter electrode is suitable.

For the PH sensors 129a and 129b, a three-electrode system combining a TlO2 semiconductor electrode, a reference electrode, and a platinum electrode is suitable.

Information signals from various sensors and conductivity meters as described above are sent to a potentiostat 133 or an electrometer 135.
etc. are connected to measuring instruments such as

Information signals from various sensors taken into the potentiostat 133 are sent to a frequency response converter 137 or an arbitrary function generator 139, where appropriate signal conversion processing is performed, and the signals are sent to the microcomputer 140. It has become. Various information signals from the microcomputer 140 and the electrometer 135 are sent to the statistical processing device 1.
Sent to 41.

The statistical processing device 141 is given the various information signals described above and information regarding the potential difference detected as described above, and compares these data with past data, changes over time of each data, and compares these data with each reference value. A warning command signal is output to the warning generating device 143 if even one of the data values exceeds or is likely to exceed the reference value. The warning device 143 is configured to issue a danger display and alarm in response to a command signal from the statistical processing device 141.

FIGS. 15 to 17 show the relationship between the water quality difference in the reactor water inside and outside the gap and the stress corrosion cracking fracture rate.

These exhibit SCC susceptibility through a tensile test at a low strain rate in high-temperature water at 288°C containing minute amounts of Cl- ions, 804- ions, and N O2- impurities. It will be understood that the greater the difference in water quality, the more likely stress corrosion cracking will occur.

Therefore, as described above, by constantly detecting these water quality differences, it becomes possible to monitor the SCC susceptibility of the structure. Since the various water quality differences described above are interrelated, if any one of them exceeds the reference value or if a large variation occurs, it may be determined that SCC susceptibility increases.

FIG. 18 shows an example in which a corrosion environment control device consisting of a combination of the environmental crack monitoring device and the corrosion inhibitor injection device shown in FIGS. 10 and 14 is applied to the piping system of a nuclear power plant. . In FIG. 18, parts corresponding to those in FIG. 10 are designated by the same reference numerals as in FIG. 10. In FIG. 18, reference numeral 151 designates a measuring cell structure incorporated in each piping system, which is used for potential difference measurement tf! as shown in FIG. Combination structure 81
Alternatively, it may be configured as a composite structure of 91 and the sensor assembly for water quality and conductivity measurement shown in FIG. The data are individually taken into a data analysis device 153 including a statistical processing device, and sent from there to the statistical processing device 141. The statistical processing device 141 may be the same as that in the embodiment described above, and it outputs a command signal to the warning generating device 143 and also outputs a command signal to the H2 injection device 155.0□ injection device 157, NOx injection device 157.
A command signal is output to a corrosion inhibitor injection device such as the injection device 159.

These corrosive injection devices are equipped with H2,0□ for each piping system.
, to inject corrosion inhibitors such as NOx.

Therefore, if at least one of the potential difference between the inside and outside of the gap, various types of water quality, and electrical conductivity exceeds the standard value, or if there is a risk of exceeding the standard value, each corrosion inhibitor is automatically injected into that location to prevent stress corrosion cracking. The risk of occurrence of this will be reduced.

FIGS. 19 and 20 show the results of a test on changes over time in the potential difference inside and outside the gap and the amount of hydrogen injected to confirm the effectiveness of the environment control device shown in FIG. 18. Furthermore, the first
In Figure 9, the mark indicates the occurrence of a warning. From these two graphs, a warning is issued and hydrogen injection begins when the potential difference exceeds the reference value, and the amount of hydrogen injection changes depending on the size of the potential difference, reaching the maximum potential difference. The amount of hydrogen injection is at its maximum during this period. Thereafter, as the potential difference became smaller, the amount of hydrogen injection also decreased, and the plant operated stably after 400 hours. The amount of hydrogen injection at this time should be quantitatively controlled by feedback control so that the potential difference is equal to the critical potential difference for stress corrosion cracking multiplied by a certain safety factor. The water quality of the reactor water will be appropriately controlled to prevent cracking and stress corrosion cracking.

The above-described method and apparatus according to the present invention are not limited to nuclear power plants, but can be widely applied to structures where there is a risk of environmental cracking, such as thermal power plants or chemical plants.

Although the present invention has been described in detail with respect to specific embodiments above, the present invention is not limited thereto.
It will be apparent to those skilled in the art that various embodiments are possible within the scope of the invention.

[Effects of the Invention] As is clear from the above explanation, according to the method and apparatus of the present invention, stress corrosion cracking of a structure made of a metal material exposed to a corrosive environment, or in other words, environmental cracking, can be easily and precisely corrected. By controlling the injection of corrosion inhibitors into the corrosive environment based on this information, it becomes possible to optimally control the water quality of the corrosive environment and improve the integrity of the structure. Become a figurehead.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view showing one embodiment of a potential measuring cell structure used in an environmental crack monitoring device according to the present invention, and FIG.
Figures 3 and 3 are graphs showing the relationship between the potential difference inside and outside the gap and the stress corrosion cracking fracture rate as a susceptibility to environmental cracking, and Figure 4 shows the relationship between the sulfur content of the metal and the potential difference inside and outside the gap. Figure 5 is a graph showing the occurrence of stress corrosion cracking in relation to the grain boundary erosion depth as the degree of sensitization of stainless steel and the potential difference inside and outside the gap. Figure 6 is a graph showing the relationship between electrical conductivity and RFL corrosion potential, Figure 7 is a graph showing the relationship between electrical conductivity and the potential difference inside and outside the gap, and Figure 8 is a graph showing the relationship between electrical conductivity and the potential difference inside and outside the gap. FIG. 9 is a schematic configuration diagram showing an example of incorporating the corrosive environment control device according to the present invention into a nuclear power plant. FIG. A schematic configuration diagram showing another example in which a control device is incorporated into a nuclear power plant,
Fig. 11 is a schematic configuration diagram showing an example of an electrode combination structure for potential difference measurement provided in a furnace, Fig. 12 is a vertical sectional view showing an enlarged gap of the gap electrode, and Fig. 13 is a piping FIG. 14 is a schematic configuration diagram showing an embodiment of an electrode assembly for measuring a potential difference that is incorporated into a system, and FIG. A schematic configuration diagram showing an example, FIG. 15 shows Cl- and 50
4- is a graph showing the relationship between the total ion concentration difference and the stress corrosion cracking fracture surface ratio, and FIG. 17th
The figure is a graph showing the relationship between the dissolved hydrogen concentration inside and outside the gap and stress corrosion cracking, and Figure 18 is a schematic diagram showing another embodiment in which the corrosion environment control device according to the present invention is incorporated into a nuclear power plant. , Fig. 19 is a graph showing the temporal change in the potential difference inside and outside the gap in a simulated nuclear power plant, and Fig. 20 is a graph showing the temporal change in the amount of hydrogen injection under the temporal change in the potential difference shown in Fig. 19. This is a graph showing. 1... Potential measurement cell structure 5... Annular gap 27, 29... Reference electrode 41... Light water r pressure vessel 43... Reactor water recirculation system piping 47... Electronic control device 49...Warning device 55.
...Hydrogen injection device 61...Light water reactor pressure vessel 81.
91... Electrode combination structure for potential difference measurement 83... Electrode member 85... Gap portion 7... Electrode member
93... Electrode member 5... Gap portion 97
... Electrode member 03.109 ... Electrometer 11 ... Central processing control unit 13 ... Warning device! 23a to 129a...Various sensors 23a to 129b...Various sensors 39a, 139b =...Conductivity meter 51...Measurement cell structure Applicant: Hitachi, Ltd.

Claims (19)

[Claims] (1) An artificial gap is provided in a metal structure that is in contact with a corrosive environment, and the difference in potential between the gap and other parts of the metal structure is measured, and this potential difference and the An environmental crack monitoring method characterized by comparing crack occurrence and progression with preset reference values. (2) The environmental crack monitoring method according to claim 1, wherein the reference value is determined in accordance with the environmental crack sensitivity determined by the material of the member that is sensitive to the environmental crack action. (3) The environmental crack monitoring method according to claim 2, wherein the environmental crack sensitivity is determined by the sulfur content of the member. (4) In the environmental crack monitoring method according to any one of claims 1 to 3, the corrosive environment exists in an aqueous solution, and the water quality of the aqueous solution is measured in the gap and other parts, respectively; An environmental crack monitoring method characterized by further comparing this water quality difference with a preset reference value regarding the occurrence and progression of cracks in the metal structure. (5) In the environmental crack monitoring method according to claim 4, the water quality is measured for at least one of dissolved oxygen concentration, dissolved hydrogen concentration, hydrogen peroxide concentration, sulfur oxide concentration, Cl concentration, and pH concentration. An environmental crack monitoring method characterized by: (6) In the environmental crack monitoring method according to any one of claims 1 to 5, a difference in electrical conductivity between the gap and other parts is measured, and this electrical conductivity difference and the difference in electrical conductivity of the metal structure are measured. An environmental crack monitoring method characterized by further comparing crack occurrence and progression with preset reference values. (7) It has a double pipe structure disposed in a corrosive environment, and an artificial gap is formed by the double pipe structure, and in the corrosive environment, an artificial gap is formed between the inside of the gap and the outside of the gap. are each provided with an electrode for potential measurement, a potential difference measuring means for measuring the difference in potential between the two electrodes, and a reference value set in advance regarding the difference in potential and the occurrence and growth of cracks in a corrosive environment. An environmental crack monitoring device characterized by having a comparison means for comparison. (8) An electrode having an artificial gap and an electrode having no gap are arranged in a corrosive environment, a potential difference measuring means for measuring the potential difference between the two electrodes, and cracking occurring between the potential difference and the corrosive environment. and a comparison means for comparing the progress with a preset reference value. (9) The environmental crack monitoring device according to claim 8, wherein the electrode having the gap has a portion other than the gap covered with an electrically insulating coating. (10) In the environmental crack monitoring device according to any one of claims 7 to 9, the water quality is detected by each of the water quality detection means provided in the gap and outside the gap, and the water quality detection means. An environmental crack monitoring device characterized by having a comparison means for comparing a difference in water quality with a preset reference value regarding the occurrence and progression of cracks in a corrosive environment. (11) In the environmental crack monitoring device according to claim 10, the water quality detection means includes an O_2 sensor, an H_2 sensor, an H_
An environmental crack monitoring device comprising at least one of a 2O sensor, a SO_4^-ion sensor, a Cl^-ion sensor, and a pH sensor. (12) In the environmental crack monitoring device according to any one of claims 7 to 11, the detection is performed by each of the conductivity detection means provided in the gap and outside the gap, and the conductivity detection means. 1. An environmental crack monitoring device, comprising comparison means for comparing the difference in electrical conductivity between the conductivity and a preset reference value regarding the occurrence and propagation of cracks in a corrosive environment. (13) In the environmental crack monitoring device according to any one of claims 7 to 11, at least one of the potential difference, the potential difference, the water quality difference, and the conductivity difference reaches a reference value or more by the comparison means. An environmental crack monitoring device characterized by having a warning generating means for issuing a warning when a comparison is made between the two. (14) A method for controlling a corrosive environment, which comprises adding a corrosion inhibitor to a corrosive environment according to a comparison result using the environmental crack monitoring method or device according to any one of claims 1 to 13. (15) At least one of the potential difference, the water quality difference, and the conductivity difference measured by the environmental crack monitoring method or device according to any one of claims 1 to 13 is below a reference value. 1. A method for controlling a corrosive environment, comprising controlling the amount of a corrosion inhibitor added to a corrosive environment so that (16) The method for controlling a corrosive environment according to claim 14 or 15, wherein the corrosion inhibitor is at least one of hydrogen, oxygen, and nitrogen oxide. Method. (17) It has a corrosion inhibitor addition device that adds a corrosion inhibitor to a corrosive environment according to the environmental cracking risk measured by the environmental cracking monitoring method or device according to any one of claims 1 to 13. A corrosive environment control device featuring: (18) The environmental crack monitoring device according to any one of claims 7 to 13 is provided in at least one location within the reactor and in the piping system, and corrosion is suppressed in the reactor water according to the comparison result of the environmental crack monitoring device. A nuclear power plant characterized in that it is provided with a corrosion inhibitor addition device for adding a corrosion inhibitor. (19) A nuclear power plant, a thermal power plant, or a chemical plant, comprising the corrosive environment control device according to claim 17.