JP2006010427A - Method and apparatus for manufacturing stress corrosion crack test specimen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a stress corrosion crack test specimen capable of easily manufacturing an SCC test specimen in a short time, and a manufacturing apparatus therefor. <P>SOLUTION: This manufacturing method of the stress corrosion crack test specimen has a process S1 for preliminarily measuring the correlation of the depth of a crack with an indication value by a crack development measuring instrument, a process S3 for applying load to a test specimen material, a process S4 for immersing the test specimen material to which load is applied in an accelerated corrosion solution, a process S5 for measuring the depth of the crack of the test specimen material developed in the accelerated corrosion solution during immersion on the basis of the measured correlation of the depth of the crack with the indication value and a process S6 for taking out the test specimen material when the measured depth of the crack of the test specimen material reaches a predetermined value to manufacture the test specimen. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a manufacturing method and a manufacturing apparatus for a stress corrosion cracking specimen for technical development or improvement of a crack inspection method related to stress corrosion cracking (hereinafter referred to as “SCC”).

  Conventionally, in the case of nuclear equipment, in order to make the plant more robust and to extend the life of the plant, it should be possible to apply it to the material surface of nuclear equipment exposed to the primary water of the reactor. In the event of an abnormality such as a crack caused by SCC, the development of a technique that predicts the progress life related to the crack caused by SCC with high accuracy and is useful for plant soundness evaluation and preventive diagnosis has been advanced.

  In general, SCC refers to a crack in an alloy material caused by the combined action of stress and corrosion. This cracking occurs when a material that is prone to corrosion under stress is under tensile stress and is in a specific corrosive environment.

  In nuclear power equipment, austenitic stainless steel is widely used for the purpose of avoiding corrosion generation associated with the use of carbon steel. When this austenitic stainless steel is placed in a liquid containing chlorine ions, SCC may be generated, but SCC may also be generated in a pure water environment in which the chlorine ions are controlled. That is, in the case of austenitic stainless steel, SCC occurs only when the three factors of stress, material, and environment overlap.

  Examples of the stress factor include primary stress such as its own weight and internal pressure, secondary stress such as welding residual stress, stress due to thermal expansion, and stress due to installation. This stress loading state is also said to change the chemical properties of the material surface.

  Examples of the material factor include a weld heat affected zone, a grinder processed layer, and an alloy composition. When austenitic stainless steel is held at 600 to 800 ° C., chromium carbide precipitates at grain boundaries, and the chromium concentration supporting the original corrosion resistance decreases in the vicinity (sensitization). Sensitization proceeds when carbide nuclei are present in advance even at low temperatures such as the operating temperature of a boiling water reactor. This sensitization can be mitigated by reducing the carbon content. In addition, when the material surface is processed, it exhibits mechanical and chemical properties different from those inside the base material.

  Examples of environmental factors include dissolved oxygen, hydrogen peroxide, temperature, pH, and the like. The corrosion pattern and corrosion rate of the surface layer or new surface depends on the corrosive power of the environment. Even if the formed film is stable in the initial stage, it may become unstable due to local aging of the environment.

  As described above, since SCC generated on the material surface of nuclear equipment is affected by three factors of stress, material, and environment, it is necessary to use an SCC specimen to accurately evaluate the progress life of cracks caused by SCC. Inspection is required.

  In order to obtain an SCC specimen simulating this SCC, it was necessary to immerse a material having enhanced SCC sensitivity in high-temperature and high-pressure water and to immerse it for a long time.

Further, in a water environment simulating a reactor coolant, a high temperature and high pressure of 70 to 150 kgf / cm ² is obtained at 288 to 350 ° C., which requires a large amount of test equipment, and it is difficult to produce a large specimen. there were.

  In addition, when a defect is imparted by a simple method, there is a method of imparting a defect due to fatigue. However, since the crack shape is different from that of SCC, the reliability as a specimen is insufficient.

In addition, a technique is also disclosed in which a test specimen is brought into contact with a tetrathionate solution that is an accelerated corrosion solution to generate and propagate intergranular stress corrosion cracking in the specimen (see, for example, Patent Document 1). In this technique, a test specimen to which stress is applied is immersed in a tetrathionate solution that is an accelerated corrosion solution, and stress corrosion cracks are generated and propagated in the test specimen.
JP 2002-333397 A

  However, in the above-described conventional method and apparatus for producing a stress corrosion cracking specimen, in order to produce an SCC specimen, the specimen material with increased SCC sensitivity must be immersed in high-temperature and high-pressure water. However, there is a problem to be solved that soaking is necessary for a long time because of the slow progress rate.

  In addition, when the test specimen is immersed in the tetrathionate solution that is an accelerated corrosion solution, a load may be applied to the specimen material and a crack may be applied while monitoring in a state immersed in the accelerated corrosion solution. Since this is not possible, there is a problem to be solved that it is difficult to manufacture the SCC specimen accurately and easily.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method and an apparatus for manufacturing a stress corrosion cracking test body that can easily manufacture an SCC test body in a short time.

  In order to achieve the above object, in the method of manufacturing a stress corrosion cracking specimen of the present invention, a step of measuring the correlation between the crack depth and the indicated value with a crack growth measuring instrument in advance, and a load on the specimen material. A test that progresses during immersion in the accelerated corrosion solution based on the correlation between the step of applying, the step of immersing the specimen material to which the load is applied in the accelerated corrosion solution, and the measured defect depth and indicated value A step of measuring the crack depth of the body material with a crack propagation measuring instrument, and a step of taking out the measured specimen when the crack depth of the specimen material reaches a predetermined value and manufacturing a test body; , Characterized by having.

    In order to achieve the above object, in the apparatus for producing a stress corrosion cracking specimen of the present invention, a test tank storing an accelerated corrosion solution, a load applying mechanism provided outside the test tank, and the load applying And a crack monitor that monitors the depth of a crack generated in the specimen material that has been loaded by the mechanism and immersed in the accelerated corrosion solution.

  According to the present invention, since a crack can be applied while applying a load to the specimen material and monitoring in a state of being immersed in an accelerated corrosion solution, an SCC specimen can be easily manufactured in a short time. it can.

  Thereby, since the crack of the SCC specimen can be accurately measured, it is possible to improve the defect detection technique related to SCC and to operate a safe nuclear reactor plant.

  Embodiments of a method for manufacturing a stress corrosion cracking specimen and a manufacturing apparatus according to the present invention will be described below with reference to FIGS. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

  FIG. 1 is a flowchart showing a procedure of a method for manufacturing a stress corrosion cracking test specimen according to an embodiment of the present invention. As shown in the figure, in step S1, the correlation between the SCC or fatigue crack defect depth and the indicated value is measured in advance by a crack growth measuring instrument. By measuring the correlation between the SCC or fatigue crack defect depth and the indicated value, a method for estimating the defect depth is established.

  Next, in step S2, heat treatment or cold working or the like is added in order to easily generate SCC in the specimen material. Furthermore, in step S3, in order to make it easy to generate SCC in the specimen material, a load is applied and a tensile stress is generated in the specimen material.

  In step S4, the specimen is immersed in an accelerated corrosion solution suitable for the specimen material in a state where a load is applied, and based on the correlation between the depth of the SCC or fatigue crack defect measured in step S1 and the indicated value. SCC or fatigue cracks, which are intended defects, are imparted to the material.

  Next, the crack meter (crack growth measuring instrument) is calibrated as necessary, and in step S5, cracks that have developed in the specimen material are immersed in the accelerated corrosion solution to give defects. The depth is measured with a crack growth measuring instrument.

  In step S6, when the depth of the crack in the specimen material reaches a predetermined value, the specimen is taken out to produce a specimen.

  In the present embodiment formed as described above, a technique for estimating the depth of the defect is previously established by measuring the correlation between the defect depth and the indicated value using a crack propagation measuring instrument. Next, the specimen is immersed in an accelerated corrosion solution suitable for the specimen material with a load applied. Furthermore, based on the correlation between the defect depth measured by the crack growth measuring instrument and the indicated value, this specimen material was measured while measuring the crack depth of the specimen material that was developed during immersion in this accelerated corrosion solution. When the crack depth reaches a predetermined value, the specimen can be taken out to obtain a specimen.

According to the present embodiment, the cracks that are generated can have a growth rate on the order of 10 ⁻⁵ mm / s. Usually, the growth rate of a crack generated in high-temperature water is on the order of 10 ⁻⁶ to 10 ⁻⁸ mm / s. Therefore, the stress corrosion cracking test specimen can be manufactured at a rate of 10 to 1000 times the crack propagation speed according to the present embodiment as compared with the conventional case. Moreover, since the temperature is from room temperature to 135 ° C. and atmospheric pressure, the stress corrosion cracking test specimen manufacturing apparatus is simplified and a large stress corrosion cracking test specimen can be manufactured.

  Next, an apparatus for manufacturing a stress corrosion cracking test specimen according to this embodiment will be described. FIG. 2 is a schematic longitudinal sectional view showing an apparatus for producing a stress corrosion cracking specimen.

  The apparatus for producing a stress corrosion cracking test specimen is composed of a test tank 13 in which an accelerated corrosion solution 14 is stored. As this accelerated corrosion solution 14, a tetrathionic acid solution is used as an example.

  This tetrathionic acid solution generally has a concentration of 0.10 to 5%. When the concentration is less than 0.10% and exceeds 5%, SCC tends to hardly occur in the specimen material. This corrosive solution is used for imparting SCC to sensitized 304 steel having SCC sensitivity or sensitized Ni-based alloy. Since the grain boundary type SCC (IGSCC) can be easily provided at room temperature and atmospheric pressure, the applicability is great also for the production of a large-sized stress corrosion cracking specimen.

  In this tetrathionic acid solution, the pH of tetrathionic acid is adjusted to 1 to 4. When the pH is less than 1 and when the pH exceeds 4, there is a tendency that SCC hardly occurs in the specimen material. In this way, the conditions are regulated so that the pH of tetrathionic acid is adjusted to suppress the overall corrosion and to give only SCC.

  As the accelerated corrosion solution 14, a solution obtained by adding a 0.01 to 1% chloride solution to a tetrathionic acid solution is used. This is because corrosion holes are formed and SCC is accelerated. If it is less than 0.01% or more than 1%, the tendency to form corrosion holes and accelerate SCC is poor.

  Thus, by using a solution obtained by adding a 0.01 to 1% chloride solution to a tetrathionic acid solution, SCC can be imparted to a material having a slightly low SCC sensitivity.

  A tension jig 15 for applying a tensile load is installed outside the test tank 13 as a load applying mechanism.

  A tensile load is applied to the specimen material 11 by the tension jig 15. The specimen material 11 in a state where the tensile load is applied is immersed in a tetrathionic acid solution stored in the test tank 13.

  A lead wire 16a is connected to the specimen material 11 to which this tensile load is applied and immersed in the tetrathionic acid solution. The condition of the crack 12 generated in the specimen material 11 is monitored by a crack monitor 16 which is a crack growth measuring instrument provided outside the test tank 13 through a lead wire 16a. That is, a method of measuring the depth of the crack 12 from the resistance value of the current flowing through the specimen material 11 by the AC potential difference method or the DC potential difference method is used as a crack growth measuring instrument. According to this method, it is possible to arbitrarily measure a crack 12 having an arbitrary depth.

  Data on the crack 12 generated in the monitored specimen material 11 is stored in the data collection device 17.

  In addition, the crack 12 which generate | occur | produces in the test body material 11 can also be provided by a fatigue crack by electric discharge machining or after electric discharge machining, a load can be concentrated and the crack concerning SCC can also be provided to a specific location.

  According to the present embodiment, a tetrathionic acid solution is used as the accelerated corrosion solution 14, a tensile load is applied from the outside of the test tank 13, and the crack 12 is monitored while monitoring the depth of the crack 12 of the specimen material 11. Therefore, when it is determined that the depth of the crack 12 has reached the desired value, the specimen material 11 can be taken out and a stress corrosion cracking specimen can be easily manufactured in a short time.

  In addition, according to the present embodiment, the stress corrosion cracking test specimen is manufactured under atmospheric pressure at a test temperature of about room temperature to 135 ° C. Therefore, the manufacturing apparatus for the stress corrosion cracking test specimen is simplified and large-sized. A stress corrosion cracking specimen can be manufactured.

  Next, an apparatus for producing a stress corrosion cracking specimen according to another embodiment of the present invention will be described. FIG. 3 is a schematic longitudinal sectional view showing an apparatus for producing a stress corrosion cracking test specimen according to another embodiment. In FIG. 3, the same or similar parts as in FIG.

  The apparatus for producing a stress corrosion cracking test specimen is composed of a test tank 13 in which an accelerated corrosion solution 14 is stored. In the present embodiment, a boiling magnesium chloride solution is used as the accelerated corrosion solution 14. As the boiling magnesium chloride solution, a solution of approximately 42% is used if the concentration is 41% to 43%. When the concentration is less than 41% and when the concentration exceeds 43%, SCC tends to hardly occur in the specimen material.

  This boiling magnesium chloride solution having a concentration of about 42% can cause SCC cracks to propagate at a high rate even for materials with extremely low SCC sensitivity.

  As another example of the accelerated corrosion solution 14, a high temperature sodium oxide solution having a concentration of 10 to 60% and a temperature of 150 to 350 ° C. was used. When the concentration is less than 9% and exceeds 60%, when the temperature is less than 150 and when the temperature exceeds 350 ° C., SCC tends to hardly occur in the specimen material.

  A high-temperature sodium oxide solution having a concentration of 10 to 60% and a temperature of 150 to 350 ° C. can cause an SCC crack to propagate at a high rate even for a material having extremely low SCC sensitivity. This solution, like the approximately 42% boiling magnesium chloride solution, can propagate SCC cracks at a high rate even for materials with very low SCC sensitivity. The difference from the approximately 42% boiling magnesium chloride solution is that the SCC form is a grain boundary type.

  Next, a bending jig 19 that applies a bending load as a load applying mechanism is installed outside the test tank 13. The bending jig 19 is for applying a bending load by pressing both ends of the specimen material 11a with a bolt 19a against a convex jig.

  Thus, by using a three-point bending or four-point bending jig 19, by applying a bending stress, SCC can be easily applied without using a large-scale apparatus.

  Since a boiling magnesium chloride solution is used as the accelerated corrosion solution 14, a cooler 18 is provided at the upper part of the test tank 13 to prevent a change in liquid concentration due to evaporation, and a stress corrosion cracking specimen is manufactured while circulating. ing.

  A lead wire 16a is connected to the specimen material 11a that has been subjected to this bending load and immersed in the tetrathionic acid solution. The state of cracks occurring in the specimen material 11a is monitored by a crack monitor 16 provided outside the test tank 13 via the lead wire 16a.

  In the present embodiment configured as described above, a tetrathionic acid solution is used as the accelerated corrosion solution 14, a bending load is applied from the outside of the test tank 13, and the crack depth of the specimen material 11a is monitored. Since the crack can be applied, when it is determined that the depth of the crack has reached the desired value, the specimen material 11a can be taken out and a stress corrosion cracking specimen can be manufactured.

  Next, an apparatus for producing a stress corrosion cracking specimen according to another embodiment of the present invention will be described. FIG. 4 is a schematic longitudinal sectional view showing an apparatus for producing a stress corrosion cracking test specimen according to another embodiment. 4, parts that are the same as or similar to those in FIG.

  In the embodiment of the present invention, a bending jig 20 that applies a bending load is installed as a load applying mechanism. The bending jig 20 is a jig that supports both ends of the test specimen material 11b with both ends of the bending jig 20, and applies a bending load by pressing the central portion of the test specimen material 11b with a bolt 20b in this supported state.

  A solution holding cell 13a storing the accelerated corrosion solution 14a is installed on the upper part of the test body material 11b. That is, the solution holding cell 13a is installed in the vicinity of the portion where the bending load 20 is applied by the bending jig 20 which is a load applying mechanism and the crack 12 of the specimen material 11b is generated, and accelerated corrosion in the solution holding cell 13a. Solution 14a is wetted.

  This solution holding cell 13a is comprised from a small container compared with FIG. This is because only the portion of the specimen material 11b where the crack occurs and the vicinity thereof are in contact with the accelerated corrosion solution 14a.

  The leaked accelerated corrosion solution 14 a is collected by the liquid receiver 21 installed at the lower end of the bending jig 20.

  A lead wire 16a is connected to the specimen material 11b that has been subjected to this bending load and immersed in the tetrathionic acid solution. The condition of the crack 12 generated in the specimen material 11b is monitored by a crack monitor 16 provided outside the solution holding cell 13a via a lead wire 16a.

  In this embodiment configured as described above, a tetrathionic acid solution is used as the accelerated corrosion solution 14a, a bending load is applied from the outside of the solution holding cell 13a, and the depth of the crack 12 of the specimen material 11b is monitored. However, since the crack 12 can be applied, when it is determined that the depth of the crack 12 has reached the desired value, the specimen material 11b can be taken out to produce a stress corrosion cracking specimen.

  According to the present embodiment, a portion to which a crack is applied by applying a bending load to a specimen material to which a crack has been applied in advance by a bending jig and installing the solution holding cell 13a on the specimen material 11b. Further, only the vicinity thereof is in contact with the liquid so that the accelerated corrosion solution is reduced. In addition, for the production of a large-scale stress corrosion cracking specimen, it is possible to propagate a crack while applying a load from the outside by using this embodiment.

The flowchart which shows the procedure of the manufacturing method of the stress corrosion cracking test body of embodiment of this invention. The schematic longitudinal cross-sectional view which shows the manufacturing apparatus of the stress corrosion cracking test body of embodiment of this invention. The schematic longitudinal cross-sectional view which shows the manufacturing apparatus of the stress corrosion cracking test body of other embodiment of this invention. The schematic longitudinal cross-sectional view which shows the manufacturing apparatus of the stress corrosion cracking test body of other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Specimen material, 12 ... Crack, 13 ... Test tank, 13a ... Solution holding cell, 14 ... Accelerated corrosion solution, 15 ... Tensile jig (loading mechanism), DESCRIPTION OF SYMBOLS 16 ... Crack monitor (crack growth measuring device), 17 ... Data collection device, 18 ... Cooler, 19, 20 ... Bending jig (loading mechanism), 21 ... Liquid received

Claims (15)

Measuring the correlation between the crack depth and the indicated value with a crack growth measuring instrument in advance,
Applying a load to the specimen material;
Immersing the specimen material to which this load is applied in an accelerated corrosion solution;
Based on the correlation between the measured defect depth and the indicated value, a step of measuring the crack depth of the specimen material that progresses during immersion in the accelerated corrosion solution with a crack growth measuring instrument;
A step of taking out the measured specimen material when the crack depth reaches a predetermined value and manufacturing the specimen,
A method for producing a stress corrosion cracking specimen characterized by comprising:   2. The method for producing a stress corrosion cracking specimen according to claim 1, wherein the accelerated corrosion solution is a tetrathionic acid solution having a concentration of 0.1 to 5%.   The method for producing a stress corrosion cracking specimen according to claim 2, wherein the accelerated corrosion solution is adjusted to have a pH of the tetrathionic acid of 1 to 4.   4. The method for producing a stress corrosion cracking test specimen according to claim 2, wherein the accelerated corrosion solution is a 0.01 to 1% chloride solution added to the tetrathionic acid.   2. The method for producing a stress corrosion cracking specimen according to claim 1, wherein the accelerated corrosion solution is a boiling magnesium chloride solution having a concentration of 41 to 43%.   2. The method for producing a stress corrosion cracking specimen according to claim 1, wherein the accelerated corrosion solution is a high-temperature sodium oxide solution having a concentration of 10 to 60% and a temperature of 150 to 350 ° C.   2. The production of a stress corrosion cracking specimen according to claim 1, wherein, in the step of immersing in the accelerated corrosion solution, only the portion of the specimen material to be cracked and the vicinity thereof are in contact with the accelerated corrosion solution. Method.   2. The method for producing a stress corrosion cracking specimen according to claim 1, wherein in the step of applying the load, a bending load is applied using a bending jig.   2. The stress corrosion cracking specimen according to claim 1, wherein the crack growth measuring instrument measures the depth of the crack from the resistance value of the current flowing through the specimen material by an AC potential difference method or a DC potential difference method. Production method.   2. The method for producing a stress corrosion cracking specimen according to claim 1, wherein the crack of the specimen material is applied by electric discharge machining or by fatigue cracking after electric discharge machining. A test chamber storing an accelerated corrosion solution;
A load applying mechanism provided outside the test tank;
A crack monitor that monitors the depth of a crack generated in a specimen material that is loaded by this load applying mechanism and is immersed in the accelerated corrosion solution;
An apparatus for producing a stress corrosion cracking specimen characterized by comprising:   The apparatus for producing a stress corrosion cracking specimen according to claim 11, wherein the load application mechanism is a tension jig that applies a tensile load to the specimen material.   12. The apparatus for producing a stress corrosion cracking specimen according to claim 11, wherein the load application mechanism is a bending jig that applies a bending load to the specimen material.   The test tank is provided with means for bringing only the portion where the crack is generated in the specimen material loaded by the load applying mechanism and the vicinity thereof into contact with the accelerated corrosion solution. 11. An apparatus for producing a stress corrosion cracking specimen according to 11.   12. The apparatus for producing a stress corrosion cracking specimen according to claim 11, further comprising a data collecting device for storing data relating to a crack generated in the specimen material monitored by the crack monitor.

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