JP2680697B2 - Environmental crack monitoring method and apparatus and corrosion environment control method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an environment such as stress corrosion cracking (SCC) in a structure in a nuclear power plant, a thermal power plant, a chemical plant or the like. The present invention relates to a method and an apparatus for monitoring cracks, and an environmental control method and apparatus for improving the soundness of a structure exposed to a corrosive environment.

(Prior Art) In a plant having a relatively large structure such as a nuclear power plant, a thermal power plant, and a chemical plant, in particular, in a nuclear power plant having a light water reactor structure in contact with high temperature pure water, the structure is It is strongly desired to avoid the damage to the structure as much as possible and to extend the life of the structure as much as possible for long-term effective utilization of the sound condition of the structure.

Especially for structures that are exposed to corrosive environments such as reactor water,
Due to the corrosive environment, a crack is generated in the structure at a stress lower than the fracture stress of the structure, and the environmental crack that develops this becomes a problem. This environmental crack gradually progresses with almost no change in appearance and leads to destruction. Therefore, advanced technology is required to detect this, and there is a possibility that environmental cracks will occur during regular inspection. It is inefficient to look at each 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, conventionally, measures have been taken to suppress or avoid the occurrence of stress corrosion cracking in a structure by removing material factors such as changing the material forming the structure and reducing the stress by changing the structure. Currently, in nuclear power plants, SU
Changes are being made from stainless steel such as S304 to other materials that do not cause stress corrosion cracking, and removal of residual stress by heat treatment. However, it is difficult to remove the residual stress in the welded part, etc., and it is almost impossible to change the internal structure of the furnace to other materials. In addition, it is enormously expensive to take these measures for all the places where stress corrosion cracking may occur.

On the other hand, it is considered to control the environment itself to a state where environmental cracks such as stress corrosion cracking do not occur, and this is to exert its effect equally in many places where environmental cracks may occur. Since, it is the most rational measure. Therefore, it is important to establish a technology for controlling the environment so that environmental cracking does not occur and a technology for monitoring the environmental crack for this control.

Currently, EPRI, N, P 3521 are used in the corrosive environment monitoring system currently used in BWRs (boiling water reactors) overseas.
(EPRI / NP-3521 1984/5), Epri, N, P 3517
(EPRI · NP-3517 1984/5) , corrosion ^- 83, Paper number 122 (Corrosion ^- 83 PAPER NUMBER 12
2), corrosion ^- 83 paper number 129 (Corrosion
^- As described in 83 PAPER NUMBER 129) or the like,
Environmental corrosion monitoring, that is, the risk of environmental cracking has been found by measuring the corrosion potential of stainless steel in primary system cooling water (reactor water) using a reference electrode.
According to this, the corrosion potential of stainless steel is −230 mV vs SHE.
It is assumed that stress corrosion cracking does not occur in the stainless steel if the following is satisfied.

Further, in order to prevent stress corrosion cracking, measures are taken to prevent stress corrosion cracking by injecting hydrogen into the reactor water and regulating the oxygen concentration in the primary cooling water. To prevent 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 primary cooling system equipment, members, etc., and there is a risk of hydrogen-induced cracking. In addition, there is a problem that the amount of hydrogen in the exhaust gas increases. On the contrary, when the amount of hydrogen injected into the reactor water is small, the effect of preventing stress corrosion cracking is reduced.

As a method of keeping the hydrogen injection amount to the reactor water at an appropriate value, as described in JP-B-63-19838, the corrosion potential, the dissolved oxygen concentration and the dissolved hydrogen concentration of the stainless steel constituting the primary cooling system are measured. The corrosion potential is -250 mV
-600 mV, dissolved oxygen concentration 10 to 50 ppb, residual hydrogen concentration 15
A method of controlling the hydrogen injection amount so that it becomes 0 ppb or less is known.

(Problems to be solved by the invention) As described above, the conventional technique controls the hydrogen concentration in the primary cooling water so as to keep the corrosion potential, the dissolved oxygen concentration, and the dissolved hydrogen concentration of the stainless steel in the primary cooling water at a predetermined value. It is characterized by preventing the occurrence of corrosion cracking, but the relationship between stress corrosion cracking and corrosion potential fluctuates under the influence of the electrical conductivity of the primary cooling water, and the comparative reference value for this, that is, the limiting potential is too small. If it is set too high on the safe side, hydrogen will be excessively injected into the primary cooling water, and problems such as the risk of hydrogen-induced cracking and the increase of hydrogen in exhaust gas will occur. In the conventional technology as described above, it is difficult to find a universally appropriate value of this limiting potential, and in practice, the appropriate potential width has to be set relatively wide, and the optimum hydrogen injection amount can be determined. Have difficulty.

Further, generally, the inside of a crack generated by stress corrosion cracking or the like is a kind of void environment, which is an environment different from the bulk, and the water quality inside this crack is directly involved in the stress corrosion cracking. Therefore, it is not always appropriate to control the hydrogen injection amount by the corrosion potential of the stainless steel immersed in the water quality in the bulk, and it is not appropriate to grasp the water quality inside the crack so that the risk of stress corrosion cracking is highly reliable. It is essential to find out.

Further, a reference electrode having excellent stability and long life is required for measuring the corrosion potential, but at present, an electrode suitable for the reference electrode has not been developed.

The present invention has been made in view of the above problems and circumstances, and an object of the present invention is to provide a method and a device for monitoring environmental cracks with high reliability, a monitoring device with a warning device, and an environmental control method and device.

[Means for Solving the Problems] (Means for Solving the Problems) According to the present invention, the above-described object is to provide an artificial gap portion in a metal structure in contact with a corrosive environment, An environmental crack monitoring method characterized by measuring a potential difference between a gap and another portion, and comparing this potential difference with a preset reference value for crack generation and progress of the metal structure, and As a device used to carry out this method, having a dual-function structure arranged in a corrosive environment,
An artificial gap is formed by the double-function structure, and electrodes for potential measurement are provided inside the gap and outside the gap in a corrosive environment, and a potential difference between the electrodes is provided. And an environmental crack monitoring device such as a potential difference measuring means for measuring the potential difference, and a comparison device for comparing the potential difference with a preset reference value for crack generation and progress in a corrosive environment, or artificial in a corrosive environment An electrode having a gap and an electrode not having a gap are provided, and a potential difference measuring means for measuring a potential difference between the electrodes, and a preset reference for the potential difference and crack initiation and progress in a corrosive environment Environmental crack monitoring device, such as with a comparison means for comparing the values.

The difference in corrosion potential between the gap portion and the outside of the gap portion may be detected by measuring the potential of each of the gap portion and other portions, or may be detected from the difference between the two potentials, or between the gap portion and other portions. It may also be detected by direct measurement of the potential difference.

The reference value may be determined according to the environmental cracking susceptibility determined by the material of the member that is susceptible to environmental cracking, particularly according to the sulfur content.

When the corrosive environment is in contact with an aqueous solution, the water quality of the aqueous solution is measured at each of the gap portion and the outside of the gap portion, and the difference between the water quality and a predetermined reference value for crack generation and progress in the corrosive environment The above-mentioned environmental crack monitoring may be performed in consideration of the comparison. The water quality in this case is measured by dissolved oxygen concentration, molten hydrogen concentration, hydrogen peroxide concentration, sulfur oxide concentration, C1
Concentration, pH concentration, etc. may be performed.

In addition, the difference in conductivity between the gap and the outside of the gap is measured, and the difference in conductivity and a reference value set in advance for crack generation and progress in a corrosive environment are taken into consideration in comparison with the environment described above. Cracking may be monitored.

Another object of the present invention is to provide an environment crack monitoring device as described above, wherein at least one of the potential difference or the potential difference and the difference between the water quality and the conductivity reaches a reference value or more by the comparison means. This is accomplished by an environmental crack monitoring system having warning means that alert when compared to the following.

Another object of the present invention is to add a corrosion inhibitor such as hydrogen, oxygen or nitric oxide to the corrosive environment according to the comparison result in the environmental crack monitoring method or apparatus as described above. Corrosion environment control method, and as an apparatus used for carrying out this method, there is a corrosion inhibitor addition device for adding a corrosion inhibitor to the corrosion environment according to the comparison result in the environment crack monitoring method or apparatus as described above. Such as a corrosive environment control device.

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.

(Action) The cause of stress corrosion cracking is not directly related to the potential of the metal itself that is in contact with a corrosive environment such as stainless steel, but to the impure substance that contacts the aqueous solution according to the potential gradient between the gap and other parts. It occurs when ions, SO ₄ ²⁻ , and Ol ⁻ move into the gap and condense to cause a phenomenon such as pH decrease. Therefore, stress corrosion cracking susceptibility (SCC susceptibility)
Has a correlation with the potential difference between the gap and the other portion, and if this potential difference is small, stress corrosion cracking is less likely to occur. That is, the potential difference is an index for SCC sensitivity, the potential difference is an IR loss caused by the current generated by the macrocell based on the difference in the corrosion process inside and outside the gap, the presence of this potential difference of the corrosion process inside and outside the gap. It is considered that there is a difference. Since stress corrosion cracking is a corrosion phenomenon in a physically limited space within a gap, there is a specified correlation between this potential difference and stress corrosion cracking.

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

Further, by controlling the injection amount of the corrosion inhibitor according to the potential difference, further the difference in water quality, and the difference in conductivity, the occurrence of stress corrosion cracking in the structure can be reliably avoided without causing other obstacles. Become so.

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

FIG. 1 shows one embodiment of the environmental crack monitoring device according to the present invention. In FIG. 1, reference numeral 1 denotes a potential measuring cell structure of the environmental crack monitoring device. The potential measuring cell structure 1 has a cylindrical outer cell 3 and a cylindrical inner cell 7 arranged in the outer cell 3 with a predetermined annular gap 5 therebetween. When it is provided in the water circulation system, it is made of the same material as the structural material in the system water reactor.
Examples of this material include low alloy steel, stainless steel, Inconel 600 alloy and the like.

The inner cell 7 is composed of a tubular body having an outer diameter slightly smaller than the inner diameter of the outer cell 3, is connected to a cap member 11 by an insulating connector 9, and the cap member 11 is screwed to one end of the outer cell 3. External cell 3
The annular gap portion 5 is fixedly disposed in the inside of the inner cell and fixed to the outer cell 3.

The other end of the outer cell 3 is provided with a reactor water inlet 13, and the cap member 11 is provided with a reactor water outlet 15, so that the reactor water flowing from the reactor water inlet 13 into the outer cell 3 is The outer cell 3 including the gap 5 is filled and flows through the inner cell 7 and the inner passages 15 and 17 of the insulating connector 9 toward the reactor water outlet 15.

The internal cell 7 acts as a test material, which is the test material electrode wire.
21 is conductively connected. The external cell 3 has a reference electrode port for measuring the corrosion potential in the annular gap 5.
23 and a reference electrode port 25 for measuring the corrosion potential outside the gap 5. Reference electrodes 27 and 29 are attached to the reference electrode ports 23 and 25, respectively. The reference electrodes 27, 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.

The verification electrodes 27 and 29 are conductively connected to the potential difference detection device 35 together with the sample material electrode line 21 by electrode lines 31 and 33, respectively.
The potential difference detecting means 35 respectively takes in the potential in the annular gap portion 7 taken out from the reference electrode 27 and the potential outside the gap portion taken out from the other reference electrode 29, and calculates the potential difference between these two potentials. This is output to the comparison means 37.

The comparing means 37 compares the potential difference with a preset reference value (limit potential difference) with respect to crack generation and progress 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 do.

As a result, the warning device 39 warns the user that there is a risk of environmental cracking by warning or displaying when the potential difference is larger than the reference value.

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

Fig. 2 shows the potential difference between the inside and outside of the gap and the smooth test piece with the gap in low-pressure alloy steel (0.004 wt% S) in high-temperature pure water at 288 ° C, and the strain rate was reduced to 10 ^-6 S ^-1 . Tensile test (S
SRT test) shows the above-mentioned relationship obtained, that is, SCC sensitivity. FIG. 3 shows the test results when a similar test piece was made of sensitized stainless steel (304 stainless steel) by chromium carbide precipitation or the like.

From all of these tests, the potential difference between the inside and outside of the gap and the SC
It will be appreciated that there is a particular correlation with C susceptibility.

FIG. 4 shows a cell structure as shown in FIG. 1 manufactured with a pressure vessel low alloy, and the SSRT test similar to that shown in FIG. The content is 0.
Fig. 3 shows the relationship between the potential difference of the stress corrosion cracking limit and the sulfur content in alloy steel, which was obtained by changing the amount from 014% by weight to 0.004% by weight. In Figure 4
Indicates that there is no environmental cracking, ● indicates that there is environmental cracking, and the value in parentheses indicates the environmentally-promoted fracture rate.

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

FIG. 5 shows a cell structure having the above-mentioned structure manufactured using 304 stainless steel, and the SSRT test similar to that shown in FIG. 2 or 3 was performed to sensitize the material to environmental corrosion cracking. The results are shown in different degrees.
The degree of sensitization was determined by using the maximum grain boundary erosion depth after the Strauss test as a parameter. From this test result, it is seen that the limit potential difference tends to decrease as the degree of sensitization increases. Therefore, if the degree of sensitization in the target portion of each plant is recognized, the limit potential difference as determined by FIG. 5 is detected by the degree of sensitization and the potential difference detecting means 35 as described above in the actual plant. A warning may be issued when the potential difference is compared and the potential difference exceeds the limit potential difference.

As described above, in the present invention, since environmental cracks are monitored based on the potential difference between the inside and outside of the gap, there is a risk that stress corrosion cracking may occur even if the conductivity of the reactor water changes. The appropriate value does not change.

FIG. 6 shows the occurrence of stress corrosion cracking in the relation between the simple corrosion potential and the conductivity of reactor water. In FIG. 6, a circle indicates that stress corrosion cracking did not occur, and a circle indicates that stress corrosion cracking occurred. As is clear from this graph, it will be understood that a simple corrosion potential alone greatly changes the critical potential of stress corrosion cracking depending on the conductivity.

FIG. 7 shows the state of occurrence of stress corrosion cracking in the relationship between the electric potential difference inside and outside the gap and the electric conductivity of the reactor water as described above. In FIG. 7 as well, the 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 of stress corrosion cracking becomes almost 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 an embodiment in which the environmental crack monitoring device according to the present invention is incorporated in a light water reactor nuclear plant. In FIG. 8, reference numeral 41 indicates a light water reactor pressure vessel, and reference numeral 43 indicates a reactor water recirculation system pipe. Reactor water flows through the reactor water recirculation system pipe 43 by the reactor water pump 45 and the light water reactor pressure is shown. It is adapted to be recirculated and supplied into the container 41.

A bypass reactor water circulation pipe 46 is branched from the middle of the reactor water circulation system pipe 10, and two potential measuring cell structures 1 are provided in parallel in the pipe 46 for double check. ing.

In this embodiment, the potential signals taken out from each of the potentiometric cell structures 1 are taken into an electronic control unit 47 containing a microcomputer of general construction. The electronic control unit 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 this and the limit potential difference set in advance as to the crack generation and progress in the corrosive environment as described above, That is, compared with the reference value, if the potential difference exceeds the reference value, an operation command is output to the warning device 49. Therefore, if the potential difference rises above the reference value, the warning device 49 will give a warning.

Potential measuring cell structure 1 connected in the pipe as described above
It is preferable that the metal composing the same is composed of the same metal as the metal used for the furnace wall and the core, such as light alloy steel, stainless steel, nickel-base alloy steel, etc. The cell structure 1 may be made of another metal material as long as the correlation with the SCC sensitivity of the metal is known.

The flow rate of the reactor water flowing into the cell structure 1 is not particularly specified. However, if the reactor water flow velocity is too fast, the potential in the gap may be disturbed, so in practice, 3 to 10 liters is actually used. / Hour will be suitable.

FIG. 9 shows one embodiment of the corrosion environment control system for environmental cracks according to the present invention. Incidentally, in FIG. 9, portions corresponding to those in FIG. 8 are designated by the same reference numerals as those in FIG.

In the environment control device, a hydrogen injection device 55 for injecting hydrogen into the water supply pipe 53 for the light water reactor pressure vessel 41 with the hydrogen injection pipe 51 is provided. The hydrogen injection device 55 receives a control signal from the electronic control device 47, and when the potential difference between the inside and the outside of the gap obtained based on the potential detected by the potential measuring cell structure 1 exceeds the reference value, hydrogen is injected. Is injected into the water supply pipe 53. As a result, the hydrogen injection control can be properly performed without error according to the risk of environmental cracking found from the potential difference between the inside and outside of the gap.

 Incidentally, in FIG. 9, 57 indicates a main steam pipe.

FIG. 10 shows another embodiment of a nuclear power plant equipped with the corrosion environment control device according to the present invention. In FIG. 10, 61 is a light water reactor pressure vessel, 63 is an in-core instrumentation pipe installed in the light water reactor pressure vessel 61, 65 is a reactor water recirculation system pipe having a pump 67 in the middle, and 69 is a water supply. Reference numeral 71 denotes a piping for the reactor water purification system, which has a pump 73 and a desalinator 75 for reactor water purification in the middle. The light water reactor pressure vessel 61 is provided with an electrode combination structure 81 for measuring a potential difference by means of an in-reactor instrumentation pipe 63, and also in each of the reactor water recirculation system pipe 65, the water supply pipe 69 and the reactor water purification system pipe 71. A potential difference measuring electrode combination structure 91 is provided.

The potential difference measuring electrode combination structure 81, as well shown in FIG. 11, is a rectangular electrode member 83 having a gap 85 formed by a notch, and a rectangular electrode member 87 having no notch.
And are close to each other. The electrode members 83 and 87 are made of the same metal as the metal forming the furnace wall of the light water reactor pressure vessel 61, and the electrode member 83 has a gap 85 formed by a notch as well shown in FIG. Except for this, other exposed parts in the furnace are insulation-coated with an electric insulating layer 89. The electrical insulating layer 89 is composed of a coating layer of ZrO _{2 formed} by the CVD method. In addition, this electrical insulating layer 89 is Z by the CVD method.
Besides coating layer and rO _2, spraying method, PVD method, an electrophoresis method, a cluster ion beam method, may be formed by ion mixing method, etc., and as the electric insulating material, ZrO ₂
Besides, oxides such as Al ₂ O ₃ and SiO ₂ may be used.

As described above, since the electrode member 83 is electrically insulated on the outer surface of the other parts except the gap 85, the electrode member 83
In this case, only the electric potential in the gap portion 85 is taken out, and the electric potential taken out from this electrode member is prevented from becoming a mixed potential including the electric potential of the portion other than the gap portion 85. Since the area of the gap 85 is very small as compared with the areas of other portions of the electrode member 83, if the potential extracted from this electrode member 83 is the mixed potential, it is extracted from this electrode member 83. Potential becomes almost the same as the potential taken out by the electrode member 87 having no gap 85, and it becomes substantially impossible to detect the potential of the gap 85. For this reason, in the device of the present invention, as described above, only the electric potential in the gap 85 is taken out, so that the electrode member 83 is electrically insulating coated except for the gap 85.

An electrode wire 101 is connected to each of the electrode members 83 and 87, and this electrode wire is taken out of the furnace by 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.

The potential difference measuring electrode combination structure 91 incorporated in various piping systems, as well shown in FIG. 13, is a rectangular electrode member 93 having a gap 95 by a notch, and a rectangular electrode member 93 having no gap. Of the electrode member 97 and the electrode member 97 of the same are arranged in the same manner as the electrode member of the potential difference measuring electrode combination structure 81 described above. That is, the electrode members 93 and 97
Are made of the same metal as the metal forming the furnace wall of the light water reactor pressure vessel 61, and the electrode member 93 has the outer surface other than the gap 95 covered with the insulation.

Electrode wires 93 are connected to the electrode members 93 and 97, respectively, and the electrode wire 105 penetrates the piping member 107 and is taken out to the outside thereof, and is connected to the electrometer 109 which is the same as the electrometer 103. . The electrometer 109 is an electrode combination structure for measuring the potential difference, which is incorporated in each piping system.
The potential difference between the electrode members 93 and 97 of 91 is detected.

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 inside / outside the gap 85 or the potential difference inside / outside the gap 95. It is adapted to be sent to a central processing control unit 111 including a microcomputer.

The central processing control unit 111 uses a predetermined reference value for each crack generation and progress in the corrosive environment and each electrometer 10
3 or 109 compared with the potential difference, if the potential difference exceeds the reference value or statistical processing, if it is estimated by the learning process that the potential difference may exceed the reference value, the warning device 113 is warned. It is designed to output a command signal. As a result, if the risk of environmental cracking increases, the warning device 113 displays the location and issues a warning.

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

In this example, a test piece 121 having a notch gap portion 121a is arranged in the piping system of a nuclear power plant, and each of the notch gap portion 121 and a normal pipe has a SO ₄ ^2- ion concentration sensor 123a. , 123b, Cl ^- ion concentration sensors 125a, 125b, H
₂ O ₂ —O ₂ —H ₂ simultaneous analysis sensors 127a and 127b, pH concentration sensors 129a and 129b, and conductivity meters 131a and 131b are arranged, respectively.

The test piece 121 is made of the same metal as the metal forming the wall surface of the LWR pressure vessel or the metal forming the reactor water pipe. The SO ₄ ²⁻ ion concentration sensors 123a and 123b may be composed of AgSO ₄ electrodes. Cl ^- ion concentration sensor 125
The a and 125b may be composed of AgCl electrodes that do not use an internal solution. H ₂ O ₂ -O ₂ -H ₂ simultaneous mechanic analysis sensor 127a, 127b
Uses H ₂ O ₂ and H ₂ and O ₂ by pulse voltammetry using a platinum microelectrode with a radius of several tens of μm or less.
May be adapted for simultaneous quantitative analysis of the concentrations of. For this analytical sensor, a three-electrode system in which a platinum electrode, a reference electrode and a platinum counter electrode are combined is suitable.

As the pH sensors 129a and 129b, a three-electrode system in which a TiO ₂ semiconductor electrode, a reference electrode and a platinum electrode are combined is suitable.

Information signals from the various sensors and the conductivity meter as described above are connected to a measuring instrument such as the potentiostat 133 or the electrometer 135. Information signals from various sensors taken in the potentiostat 133 are sent to the frequency response converter 137 or the arbitrary function generator 139, where appropriate signal conversion processing is performed, and the microcomputer 140
To be sent to Microcomputer 14
0 and various information signals from the electrometer 135 are sent to the statistical processing unit 141, respectively.

The statistical processing device 141 is provided with the above-mentioned various information signals and information about the potential difference detected as described above, collates with these past data, the time change state of each data, and compares with each reference value of these data. And the like, a warning command signal is output to the warning generation device 143 when the reference value of one of the data values is exceeded or is likely to be exceeded. Warning device 1
Reference numeral 43 is configured to issue a danger display and an alarm in response to a command signal from the statistical processing device 141.

Figures 15 to 17 show the relationship between the water quality difference of reactor water inside and outside the gap and the stress corrosion cracking surface area ratio. This is very small amount of Cl ^- containing impurities ^- ions and SO ₄ ^2-ions and NO ₂
It shows SCC susceptibility in a tensile test at a low strain rate in high-temperature water at 288 ° C, and it will be understood that stress corrosion cracking is more likely to occur if the water quality difference between the inside and outside of the gap is larger than these.

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

FIG. 18 shows an embodiment in which the corrosion environment control device comprising the combination of the environment crack monitoring device and the corrosion inhibitor injection device shown in FIGS. 10 and 14 is applied to the nuclear power plant piping system. . Incidentally, in FIG. 18, portions corresponding to those in FIG. 10 are designated by the same reference numerals as those in FIG.
In FIG. 18, reference numeral 151 denotes a measuring cell structure incorporated in each piping system, which is a potential difference measuring electrode combination structure 81 or 91 as shown in FIG. 13 and FIG. It is constructed as a composite structure with a sensor combination for water quality and conductivity measurement shown in Fig. 3, and information signals from these are data including various measuring instruments, signal converters, microcomputers, statistical processing devices as described above. The data is individually taken into the analysis device 153 and then sent to the statistical processing device 141. The statistical processing device 141 may be the same as that of the above-described embodiment, which outputs a command signal to the warning generation device 143 and also H ₂ injection device 155, O ₂ injection device 157,
A command signal is output to the corrosion suppression injection device such as the NOx injection device 159. These corrosion injecting devices are designed to inject corrosion inhibitors such as H ₂ , O ₂ and NOx into each piping system.

Therefore, if at least one of the potential difference inside and outside the gap, various water qualities, and the conductivity exceeds or is likely to exceed the reference value, each corrosion inhibitor is automatically injected into that location, and stress corrosion cracking occurs. The risk of occurrence of is reduced.

FIG. 19 and FIG. 20 show the results of a change-over-time test of the potential difference inside and outside the gap and the hydrogen injection amount for confirming the effectiveness of the environment control device shown in FIG. Incidentally, in FIG. 19, the mark ● indicates that a warning has occurred. From these two graphs, when the potential difference exceeds the reference value, a warning is issued and hydrogen injection is started, and the hydrogen injection amount changes according to the magnitude of the potential difference, and the potential difference becomes maximum. The amount of hydrogen injection is maximum during the period. After that, as the potential difference decreased, the hydrogen injection amount also decreased.
The plant operation is stable in the operation after 0 hours. The hydrogen injection amount at this time may be quantitatively controlled by feedback control so that the voltage difference becomes a value obtained by multiplying the critical potential difference for stress corrosion cracking by a safety factor. From this fact, the water quality of the reactor water can be appropriately controlled so that stress corrosion cracking does not occur without causing hydrogen embrittlement cracking due to excessive hydrogen injection.

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 such as thermal power plants or chemical plants where environmental cracks may occur.

In the above, the present invention has been described in detail with reference to specific embodiments. However, the present invention is not limited to these, and it is understood that various embodiments are possible within the scope of the present invention. It will be clear to the trader.

[Effects of the Invention] As is clear from the above description, 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, in other words, environmental cracking, can be performed easily and accurately. The quality of the structure is improved by controlling the injection of the corrosion inhibitor into the corrosive environment based on this, which enables optimal control of the water quality of the corrosive environment. Will be available.

[Brief description of the 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.
Figures and 3 are graphs showing the relationship between the potential difference inside and outside the gap and the stress corrosion cracking surface area ratio as the susceptibility to environmental cracking. Fig. 4 shows the relationship between the sulfur content of the metal and the potential difference inside and outside the gap. Fig. 5 is a graph showing the stress corrosion cracking occurrence state in Fig. 5, and Fig. 5 is a graph showing the stress corrosion cracking occurrence state in relation to the grain boundary erosion depth as the sensitization degree of stainless steel and the potential difference inside and outside the gap, FIG. 6 is a graph showing the relationship between electrical conductivity and corrosion potential, FIG. 7 is a graph showing the relationship between electrical conductivity and potential difference inside and outside the gap, and FIG. 8 is an environmental crack monitoring device according to the present invention installed in a nuclear power plant. FIG. 9 is a schematic configuration diagram showing an incorporated embodiment, and FIG. 9 is a schematic configuration diagram showing an embodiment in which a corrosion environment control device according to the present invention is incorporated in a nuclear plant.
FIG. 10 is a schematic configuration diagram showing another embodiment in which the corrosion environment control device according to the present invention is incorporated in a nuclear plant,
Figure is a schematic configuration diagram showing one embodiment of an electrode combination structure for potentiometric measurement provided in the furnace, Figure 12 is an enlarged vertical cross-sectional view showing the gap portion of the gap electrode, Figure 13 is a piping system FIG. 14 is a schematic configuration diagram showing one embodiment of a potential difference measuring electrode assembly to be incorporated, and FIG. 14 is a schematic configuration showing one embodiment of measuring means for measuring water quality and conductivity difference in the corrosion environment control device according to the present invention. Figures and 15 are graphs showing the relationship between the total ion concentration difference between Cl ^-1 and SO ₄ ^2- and the stress corrosion cracking surface ratio, and Figure 16 is the pH concentration difference inside and outside the gap and stress corrosion cracking. A graph showing the relationship with the fracture rate, FIG. 17 is a graph showing the relationship between the dissolved oxygen concentration inside and outside the gap and stress corrosion cracking, and FIG. 18 is a corrosion environment control device according to the present invention incorporated into a nuclear power plant. FIG. 19 is a schematic configuration diagram showing another embodiment, and FIG. 19 shows the electric power inside and outside the gap in the simulated nuclear power plant. Graph showing the change over time in the difference, FIG. 20 is a graph showing the change over time in the in the hydrogen injection quantity under potential time course shown in Figure 19. 1 …… Potential measuring cell structure 5 …… Annular gap 27, 29 …… Reference electrode 41 …… Light water reactor pressure vessel 43 …… Reactor water recirculation system piping 47 …… Electric 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 87 …… Electrode member, 93 …… Electrode member 95 …… Gap Part, 97 ... Electrode member 103, 109 ... Electrometer 111 ... Central processing control device 113 ... Warning device 123a-129a ... Various sensors 123a-129b ... Various sensors 139a, 139b ... Conductivity meter 151 ... ... Measuring cell structure

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takuya Takahashi 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Ltd. (72) Yoshinao Urayama 4026 Kuji Town, Hitachi City, Ibaraki Hitachi Research Institute, Hitachi Ltd. In-house (72) Eiji Kikuchi 4026 Kuji-machi, Hitachi, Hitachi, Ibaraki 4026 Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Jiro Kuniya 4026, Kuji-cho, Hitachi, Ibaraki Hitachi, Ltd. (72) Inventor, Hitachi Michiyoshi Yamamoto 3-1, 1-1 Saiwaicho, Hitachi City, Ibaraki Hitachi Ltd., Hitachi Factory (72) Inventor Naruo Hattori 3-1-1, Saiwaicho, Hitachi City, Ibaraki Hitachi Ltd. (72) ) Inventor Katsumi Otsuka 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory (5 6) References JP-A-57-190261 (JP, A) JP-A-57-6350 (JP, A)

Claims (11)

(57) [Claims] 1. A metal structure in contact with a corrosive environment is provided with an artificial gap portion, and a potential difference between an aqueous solution existing in the gap portion of the metal structure and an aqueous solution existing in another portion is set. An environmental crack monitoring method comprising measuring and comparing this potential difference with a reference value set in advance for crack initiation and progress of the metal structure. 2. A double pipe structure disposed in a corrosive environment, wherein the double pipe structure forms a artificial gap.
Electrodes for measuring potential are provided inside and outside the gap in a corrosive environment, and a potential difference measuring means for measuring a potential difference between the two electrodes, and a potential difference between the potential and the corrosive environment. An environmental crack monitoring device, comprising: a comparison unit that compares a reference value set in advance with respect to the occurrence and progress of cracks. 3. An electrode having an artificial gap portion and an electrode having no gap portion are arranged in a corrosive environment, and a potential difference measuring means for measuring a potential difference between the both electrodes, and a potential difference between the potential difference and the corrosive environment. Comparing means for comparing a reference value set in advance with respect to crack generation and progress, water quality detecting means provided in each of the gap portion and outside the gap portion, and difference in water quality detected by each of the water quality detecting means And an comparing means for comparing a reference value set in advance with respect to occurrence and progress of cracks in a corrosive environment. 4. The environmental crack monitoring device according to claim 3, wherein the water quality detecting means is an O ₂ sensor, H ₂ sensor, H ₂ O ₂ sensor, SO ₄ ²⁻ ion sensor, Cl ^{2 −} ion sensor. , An environmental crack monitoring device comprising at least one of a pH sensor. 5. The environmental crack monitoring device according to claim 2, wherein each of the conductivity detecting means and the conductivity detecting means provided in each of the gap portion and outside the gap portion. An environmental crack monitoring device, comprising: a comparison unit that compares a difference in conductivity detected by the sensor with a preset reference value for crack generation and progress in a corrosive environment. 6. The environmental crack monitoring device according to claim 2, wherein at least one of the potential difference or the potential difference and the difference between the water quality and the conductivity is a reference value or more by the comparison means. An environmental crack monitoring device having a warning generating means for issuing a warning when compared with the above. 7. An artificial gap portion is provided in a metal structure in contact with a corrosive environment, and a potential difference between an aqueous solution existing in the gap and an aqueous solution existing in another portion of the metal structure is measured. However, this potential difference is compared with a reference value set in advance for crack generation and progress of the metal structure, and a corrosion inhibitor characterized in that a corrosion inhibitor is added to the corrosion environment according to the comparison result. Control method. 8. The method for controlling a corrosive environment according to claim 7, wherein the corrosion inhibitor is at least one of hydrogen, oxygen and nitric oxide. 9. A double-tube structure disposed in a corrosive environment, the double-tube structure forming an artificial gap,
Electrodes for measuring potential are provided inside and outside the gap in a corrosive environment, and a potential difference measuring means for measuring a potential difference between the two electrodes, and a potential difference between the potential and the corrosive environment. Comparing means for comparing with a preset reference value regarding the occurrence and progress of cracks, and a corrosion inhibitor adding device for adding a corrosion inhibitor to the corrosive environment according to the environmental crack risk based on the comparison result of the comparing means And a corrosive environment control device. 10. The environmental crack monitoring device according to any one of claims 2 to 6 is provided in at least one location inside a furnace and in a piping system, and the environmental crack monitoring device is placed in reactor water in accordance with a comparison result of the environmental crack monitoring device. A nuclear power plant comprising a corrosion inhibitor addition device for adding a corrosion inhibitor. 11. A nuclear power plant, a thermal power plant, or a chemical plant comprising the corrosion environment control device according to claim 9.