JPH0868731A - Method and device for predicting life of plant structure - Google Patents

Abstract

PURPOSE: To predict the life of a structure by installing a sensor part consisting of a same metal material near a plant structure under a corrosive environment and guiding hydrogen through the sensor part after being generated due to corrosion to the outside of the structure and then measuring the amount of transmission of hydrogen in unit time. CONSTITUTION: A plurality of sensor parts formed by the same metal material as that of a plant structure placed under a corrosive environment is provided in an actual environment near the structure for forming a clearance. Hydrogen which is generated due to corrosion is transmitted through each sensor part and is guided to the outside from the structure. The amount of transmitted hydrogen per unit time is measured for cases where there is clearance and there is no clearance at the sensor part and the hydrogen concentration in metal for the presence or absence of clearance is estimated based on the result. A crack tip hydrogen concentration is obtained from the result and the three-axis stress at the crack tip which is assumed in the structure. The time change of crack length is obtained from the time integration of the sum of the crack progress speed of the same metal under the concentration and the crack progress speed due to corrosion solution and the time when the crack reaches a limit depth is obtained, thus predicting life.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for preventing damage to a structure in contact with a corrosive environment and extending its life, and particularly to a method for predicting the life of a plant structure when stress corrosion cracking involving hydrogen occurs in the plant structure. And its equipment.

[0002]

2. Description of the Related Art In order to make effective use of plant equipment and structures, there is a tendency to extend the life of the equipment as much as possible, and there is a strong demand for a technology that operates as long as possible without damaging the structures. Particularly, in a structure that is in contact with a corrosive environment, stress corrosion cracking (SCC) in which a crack is generated and propagates with a relatively low stress depending on the environment becomes a problem.
Since this SCC has little change in appearance and gradually progresses, it is difficult to detect it. Also, it is inefficient to examine each of these points where they may occur during regular inspection. is there.

This SCC is a phenomenon involving three factors of material, environment and stress. Especially, there are many unclear points about the environmental factors, and there is a possibility that the estimation may be erroneous only by the life estimation from the laboratory test. . Therefore, it is often attempted to put the test piece directly into the environment of the actual machine and evaluate the life from its behavior. However, most of them are based on the correlation based on empirical experimental data, and their application is naturally limited, so that it is required to establish a prediction technique based on more mechanism.

For example, a sensor capable of monitoring the crack growth of the same material as that used in the actual machine is inserted, and the possibility of the SCC development under the reactor water environment is judged based on its behavior based on the mechanism, and A method of controlling water quality has been proposed (FP Ford et al, Pape
r presented to Forth International Symposium on Env
ironmental Degradation of Materials in Nuclear Pow
er Systems-WaterReactors, August 6-10, 1989, Je
ykll Island, Gorgia).

This method has been proposed on the premise that crack propagation occurs due to dissolution of a new surface at the crack tip. However, the actual mechanism of cracking is not limited to dissolution, and the effect of hydrogen penetrating into the metal due to the corrosion reaction is well known. The effect of hydrogen depends on the temperature. Above about 450 ° C, so-called hydrogen attack causes embrittlement by methane due to the reaction between hydrogen and carbon, and at temperatures below that, hydrogen directly weakens the ductility of the metal, so-called hydrogen embrittlement. The phenomenon occurs. In particular, in order to evaluate the life due to hydrogen embrittlement type cracking, it is important to know the amount of hydrogen that has penetrated into the material.

In order to predict such cracking due to hydrogen, an attempt has already been made to quantify hydrogen that has been generated by corrosion and has penetrated and penetrated into the material by providing a hydrogen permeation detection sensor on the wall surface of the actual machine. .

[0007]

However, it is known that what is actually important is the local permeation of hydrogen such as the inner surface of the crack (for example, Yamakawa et al., Iron and Steel).
74th (1988) No. 4, p151). For this reason,
As described above, it cannot be denied that the evaluation by the method of providing the hydrogen permeation detection sensor on the wall surface of the actual machine has a limit. Moreover, it cannot be said that a method for evaluating the life of the actual machine based on the obtained information has been established. Therefore, in the conventional technique, it is difficult to predict the life by monitoring the SCC generated by hydrogen in the actual machine.

It is an object of the present invention to quantitatively grasp the SCC generation life of a plant structure in a corrosive environment and predict the life of the structure in consideration of environmental changes during plant operation. An object of the present invention is to provide a method of predicting the life of an object and an apparatus thereof.

[0009]

In order to achieve the above object, the method of predicting the life of the present invention is such that a sensor section constituted by using the same metal material as that of a plant structure placed under a corrosive environment is used. Installed in the actual environment near the object, guide the hydrogen generated by corrosion and transmitted through the sensor unit to the outside from the structure, measure the amount of hydrogen permeation per unit time, and based on the measurement result Predicting the life of the structure due to environmental cracking.

Two or more of the sensor units are installed, and a gap is formed in at least one of them.
The hydrogen generated by corrosion and permeating through each of the sensor parts is guided to the outside from the structure, and the amount of permeated hydrogen per unit time is measured at the same time with and without a gap in the sensor part, The life of the structure due to environmental cracking may be predicted based on the measurement result.

Further, if two or more sensor portions having a gap formed in at least one of them are installed, hydrogen generated by corrosion and permeating through each of the sensor portions is guided to the outside from the structure and permeated. The amount of hydrogen per unit time is measured at the same time when there is a gap in the sensor part and when there is no gap, and the hydrogen concentration in the metal with respect to the presence or absence of a gap is estimated based on the measurement result. The crack tip hydrogen concentration is calculated from the triaxial stress of the crack tip assumed in the structure,
The time change of the crack length is calculated from the time integration of the sum of the crack growth rate of the same metal at the crack tip hydrogen concentration and the crack growth rate due to corrosion dissolution of the crack tip, and the time until it reaches the limit depth is calculated. It can be calculated, which can also predict the life of the structure due to environmental cracking.

Further, the plant operating method of the present invention is to determine the operating conditions such as water quality so that the life of the plant structure becomes a predetermined value or longer using each of the above life prediction results.

Further, the plant structure life predicting apparatus of the present invention is constructed by using the same metal material as that of the plant structure placed in a corrosive environment, and the sensor installed in the actual environment near the structure. Section, derivation means for guiding hydrogen generated by corrosion and permeating through the sensor section to the outside from the structure, measuring means for measuring the amount of permeated hydrogen per unit time, and the structure based on the measurement result. It is provided with a predicting means for predicting the life of an object due to environmental cracking.

Further, the plant operating apparatus of the present invention controls the plant operation while monitoring the operating conditions such as the water quality so that the life of the plant structure becomes a predetermined value or longer based on the prediction result from the above-mentioned prediction means. It is a thing.

[0015]

FIG. 1 shows a flowchart of the life prediction procedure of the present invention. First, the hydrogen permeation amount of each sensor is input, and based on the hydrogen permeation amount, hydrogen in the bulk of the evaluation site and the surface of the gap is calculated. The hydrogen concentration C on the metal surface due to hydrogen entering from the bulk environment is the permeated hydrogen amount J of the metal piece and the plate thickness B of the metal piece.
And the lattice diffusion coefficient D of hydrogen at the temperature to which the metal piece is exposed, can be obtained by the following equation (1).

C = BJ / D (1) From this and the flow stress σ _f of the material in the evaluation part and the stress intensity factor value, the hypothesis due to hydrogen coming from the bulk environment is calculated by the following formula. The crack tip hydrogen concentration C _HB in the evaluation part (sensor part) estimated by static or non-destructive inspection is calculated from the equation (2).

C _HB = C · exp (σ _kk V _h / RT) (2) where σ _kk = (1 + π) σ _f / √3 Further, V _h is a partial molecular volume of hydrogen, R is a gas constant.

On the other hand, the hydrogen concentration C _L on the metal surface at the gap structure portion or the local portion such as a latent defect can be obtained by inserting the amount of hydrogen that permeates the metal piece provided with the gap into the equation (1). it can. The hydrogen concentration C _HL at the crack tip due to hydrogen entering from the local area is calculated by the equation (3).

C _HL = α · C _L exp (σ _kk V _h / RT) (3) Here, α is a correction coefficient in consideration of hydrogen associated with new surface dissolution at the crack tip. It is difficult to obtain this α by calculation, and it is realistic to determine it so as to match the crack growth data. The crack tip hydrogen concentration C _HT as a whole is obtained by adding C _HB and C _HL . From the C _HT and the stress in the evaluation part and the stress intensity factor K of the assumed crack in the evaluation part, the crack growth rate by hydrogen is calculated based on the database.
On the other hand, the progress of the crack due to the dissolution of the new surface of the crack tip is
already given by dresen and Ford (M
aterial Science and Engineering, A103 (1988) p16
7), use it. The crack growth rate is added and the two are integrated over time to determine the change over time in the crack size, and the life is defined as the time when it reaches a limit value.

[0020]

EXAMPLES Examples of the present invention will be described in detail below. [Example 1] The results of examination on the correlation between hydrogen permeability and crack growth behavior are shown. The material is 621 ° C./25 h + 9 after solution treatment in austenitic stainless steel SUS304.
After the carbide precipitation treatment at 50 ° C / 25h, the temperature is about 15
Rolled to a hardness of about Hv320 at 0 ° C, then 500 ° C / 4
The crystal grain boundary Cr deficiency treatment of h was used. Hydrogen permeation was performed using the apparatus shown in FIG. A hollow cylinder test piece was used as the evaluation test piece 1, and high temperature water was circulated in the evaluation cell 2 for testing. The test was carried out with and without a gap in the evaluation area. The test in high temperature water was performed using a test piece called a compact tension test piece shown in FIG.

FIG. 4 shows the test results showing the dependence of the crack growth rate and hydrogen permeation behavior on the dissolved oxygen concentration. Hydrogen permeation was not observed without a gap, only with a gap. A good correlation is observed between the crack growth rate and the hydrogen permeation amount, which shows the validity of the present invention.

Example 2 In order to quantitatively examine the results of Example 1, the same material as that used in Example 1 was used.
The crack growth behavior was investigated in hydrogen gas at ℃ and compared with the crack growth behavior in high temperature water as a function of hydrogen concentration at the crack tip. FIG. 5 shows the crack growth rate in high temperature hydrogen gas as a function of the crack tip hydrogen concentration and the crack tip strain rate. The crack growth rate in high temperature hydrogen gas can be well organized by these parameters. FIG. 6 compares the results with the crack growth rate by hydrogen and the crack growth rate in high temperature water calculated based on the equation (3) based on the active dissolution and hydrogen permeation amount. By setting the correction coefficient α of hydrogen at the crack tip due to dissolution of the newly formed crack tip to 5, the two agree well.

[Embodiment 3] FIG. 7 shows an example of a shape of a metal piece and an evaluation method for evaluating the amount of hydrogen permeation. The sensor unit 3 has a hollow cylindrical shape, and sensitivity and responsiveness can be enhanced by reducing the outer diameter of the evaluation unit (upper part of the drawing). The amount of hydrogen permeating into the hollow portion is evacuated by connecting the hollow portion and the measuring portion introducing pipe 5 connected thereto to a vacuum, or by connecting the hollow portion and the measuring portion introducing pipe 5 connected thereto to a vacuum. After sealing, the change in the degree of vacuum inside the container is monitored by using a vacuum gauge.

Further, by covering the evaluation portion with the gap cap 4, a sensor portion with a gap can be formed.
When the gap cap 4 is put on, the evaluation portion and the gap cap 4
A gap is formed between them.

[Embodiment 4] FIG. 8 shows another example of the shape of the metal piece and the evaluation method for evaluating the hydrogen permeation amount. The sensor unit 6 has a disk shape, and is fixed to the sensor fixing unit 7 by welding or using an O-ring. The evaluation part is the sensor part 6, and the sensor part 6 and the sensor fixing part 7 form a hollow part. The amount of hydrogen permeating into the hollow portion is determined by pulling the hollow portion and the measuring portion introducing pipe 8 connected thereto into a vacuum and connecting it to the mass spectrometer, or by evacuating the hollow portion and the measuring portion introducing pipe 8 connected thereto. After sealing, the change in the degree of vacuum inside the container is monitored by using a vacuum gauge.

A gap cap 9 is provided above the sensor section 6.
It is possible to form a sensor unit with a gap by covering the sensor unit with the cover. When the gap cap 9 is put on, the sensor unit 6
A gap is formed between the gap cap 9 and the gap cap 9.

[Embodiment 5] A case where the present invention is applied to stress corrosion cracking life evaluation of a light water reactor plant and its water quality control will be described with reference to FIG. The sensor 10 is made of stainless steel SUS304 or SUS316 used for the internal structure of the reactor and is of the same system as that used in the actual machine, and at least three of them are prepared. At least one of them is the amount of hydrogen that permeates from the bulk environment.
At least one of the rest is calibrated for the amount of hydrogen that enters from the gap using a sensor with a gap, and for the rest that is calibrated for hydrogen that comes out from outside the sensor site due to corrosion, etc. It is for. These sensors are inserted into the core 12 through the neutron instrumentation tube 11.

Then, the amount of hydrogen passing through the sensor 10 is analyzed by the mass analyzer and the computer 13 connected thereto, and the life is estimated based on the irradiation amount and the stress estimated from the operation history of the evaluation section. To do.

FIG. 10 and FIG. 11 show screen images of the life diagnostic apparatus for the furnace and the internal structural materials. First, as shown in FIG. 10, a portion to be evaluated by the actual machine is shown on the screen on the schematic diagram of the actual machine. When the site to be evaluated is selected from these, the life prediction result for the site to be evaluated is displayed on the screen. Figure 11
10 is a life prediction result when a shroud is selected in FIG. There, the name of the evaluation target is shown, and it can be confirmed that the evaluation site is the same as the desired one. There is a column on the screen that displays the dose and stress required for life evaluation, and the data on the dose and stress for these structures are output from the database. It is also possible to enter data or estimated values there as needed. The estimated SCC generation life based on these display data and the current hydrogen permeation data is displayed. At the same time, the change in the hydrogen permeation agent and the change in the estimated remaining life value are displayed on the screen at the same time, giving useful information for determining whether or not countermeasures should be taken.

Further, based on this value, the turbine 15 is provided by the gas and chemical injection system 14 so as to have a predetermined life or longer.
Determine the water quality of the condensate from the water supply pipe 1 in the pressure vessel 16
It is also possible to put the water in through 7 and operate the plant while monitoring the hydrogen permeation amount so as to satisfy a predetermined life. In FIG. 9, 18 is a reactor water recirculation system piping, 19 is a reactor water purification system piping, 20 is a switching valve,
Reference numeral 21 denotes a vacuum pump.

[0031]

As described above, according to the present invention,
In addition to being able to quantitatively understand the SCC generation life of a plant structure in a corrosive environment, environmental measures can be taken based on the result to prevent SCC damage to the actual equipment and reduce loss due to damage accidents It is possible to extend the life.

Further, since the permeated hydrogen is led out from the structure and the amount of permeated hydrogen per unit time is measured, the life is always predicted even if the permeated hydrogen amount increases or decreases. It is possible.

[Brief description of drawings]

FIG. 1 is a flowchart showing a life prediction method of the present invention.

FIG. 2 is a schematic view of an apparatus for setting a test piece for evaluation.

FIG. 3 is a diagram showing the shape and dimensions of a compact tension test piece.

FIG. 4 is a diagram showing the dissolved oxygen concentration dependence of crack growth behavior and hydrogen permeation behavior in high temperature water.

FIG. 5 is a diagram showing the dependence of the crack growth rate in hydrogen on the hydrogen concentration at the crack tip.

FIG. 6 is a diagram showing a comparison result between a predicted value and a measured value of a crack growth rate in high temperature water.

FIG. 7 is a diagram illustrating an example of a sensor unit.

FIG. 8 is a diagram showing another example of the sensor unit.

FIG. 9 is a diagram showing an example in which the present invention is applied to a light water reactor plant.

FIG. 10 is a diagram showing an example of a screen image of the life prediction apparatus.

FIG. 11 is a diagram showing another example of a screen image of the life diagnosis apparatus.

[Explanation of symbols]

 1 Test piece for hydrogen permeation evaluation 2 Evaluation cell 3,6 Hydrogen permeation evaluation sensor section 4,9 Gap cap 5,8 Measuring section introduction tube 7 Sensor fixing section 10 Hydrogen permeation evaluation sensor 11 Neutron instrumentation tube 12 Reactor core 13 Mass spectrometer And computer 14 Gas and chemical injection system 15 Turbine 16 Reactor pressure vessel 17 Reactor water supply piping 18 Reactor water recirculation system piping 19 Reactor water purification system piping 20 Switching valve 21 Vacuum pump

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyotomo Nakata 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Jiro Kuniya 7-chome, Omika-cho, Hitachi-shi, Ibaraki No. 1 in Hitachi, Ltd. Hitachi Research Laboratory

Claims (9)

[Claims] 1. A sensor unit made of the same metal material as that of a plant structure placed in a corrosive environment is installed in an actual environment near the structure, and is generated by corrosion and penetrates the sensor unit. Leading hydrogen out of the structure,
A method for predicting the life of a plant structure, which measures the amount of hydrogen permeation per unit time and predicts the life of the structure due to environmental cracks based on the measurement result. 2. At least two sensor units, which are made of the same metal material as the plant structure placed in a corrosive environment, are installed in the actual environment near the structure, and at least one of the sensor units is used. First, a gap is formed, and hydrogen generated by corrosion and permeating through each of the sensor parts is guided to the outside from the structure, and the amount of permeated hydrogen per unit time is calculated as A method for predicting the life of a plant structure, in which the life of the structure due to environmental cracks is predicted based on the measurement results obtained by simultaneously measuring the case with and without the case. 3. Two or more sensor units configured by using the same metal material as the plant structure placed in a corrosive environment are installed in an actual environment near the structure, and at least one of the sensor units is provided. First, a gap is formed, and hydrogen generated by corrosion and permeating through each of the sensor parts is guided to the outside from the structure, and the amount of permeated hydrogen per unit time is calculated as Simultaneously measuring with and without the presence, the hydrogen concentration in the metal with respect to the presence or absence of a gap is estimated based on the measurement result, and then from the estimation result and the triaxial stress at the crack tip assumed in the structure The crack tip hydrogen concentration is calculated, and the time change of the crack length is calculated from the time integration of the sum of the crack growth rate of the same metal at the crack tip hydrogen concentration and the crack growth rate due to corrosion dissolution of the crack tip, and that is the limit. Until the depth A method for predicting the life of a plant structure, in which the life of the structure due to environmental cracking is predicted by calculating the time. 4. A method of operating a plant, which uses the life prediction result according to any one of claims 1 to 3 to determine an operating condition such as water quality so that the life of the plant structure is equal to or longer than a predetermined value. 5. A sensor part, which is constructed by using the same metal material as that of a plant structure placed in a corrosive environment and is installed in an actual environment near the structure, and a sensor part which is generated by corrosion and permeates the sensor part. And a derivation means for guiding hydrogen from the structure to the outside, a measurement means for measuring the amount of permeated hydrogen per unit time, and a prediction means for predicting the life of the structure due to environmental cracking based on the measurement result. , A plant structure life prediction device provided. 6. The life prediction apparatus according to claim 5,
Two or more of the sensor units are provided, and a gap is formed in at least one of them, and the measuring unit simultaneously measures the amount of permeated hydrogen when the sensor unit has a gap and when there is no gap. Life prediction system for plant structures. 7. The life prediction apparatus according to claim 6,
The sensor part is formed in a cylindrical shape with one end closed, and the other end opening of the cylindrical shape is connected to the lead-out means, while the closing part of the sensor part is covered with a cap, and between the closing part and the cap. A life predicting apparatus for a plant structure, wherein a sensor portion having a gap is formed by providing the gap. 8. The life prediction device according to claim 5,
A life predicting apparatus for a plant structure, wherein the measuring unit is a mass spectrometer or a vacuum gauge. 9. A plant operating device for performing plant operation control while monitoring operating conditions such as water quality so that the life of the plant structure is at least a predetermined value based on the prediction result from the prediction means according to claim 5. .