Stress corrosion cracking testing apparatus and stress corrosion cracking testing method

Abstract

To detect an SCC occurrence within a practical test time for highly corrosion-resistant materials and accurately evaluate the integrity of structures.SOLUTION: A stress corrosion cracking test device 10 includes a loading section 30 for gripping and loading both ends of a test piece 20, a load control section 11 for controlling a tensile stress σ applied to the test piece 20, a detection section 12 for detecting electrical characteristics of the test piece 20 to recognize an SCC occurrence, and a container 16 sealed with a liquid 15 for immersing the test piece 20.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Embodiments of the present invention relate to a stress corrosion cracking test technique for evaluating corrosion-resistant materials. [Background technology]

[0002] As nuclear power generation facilities age and their lifespans are extended, the risk of age-related degradation events increases, making countermeasures increasingly important. Improving the operational stability and utilization rate of nuclear power generation facilities is also important from the perspective of power generation efficiency and stable power supply. For this reason, in nuclear power generation facilities, the integrity of in-core structures and piping is assessed by analyzing the progression of stress corrosion cracking (SCC). This SCC progression analysis is performed by creating test specimens of corrosion-resistant materials and obtaining data on the progression rate. In other words, the degree of SCC progression in in-core structures and piping is used to confirm the risk of damage, and highly corrosion-resistant materials with excellent SCC resistance are applied as maintenance measures.

[0003] In addition to the test methods specified in industrial standards such as JIS, test methods have been used to evaluate the susceptibility and occurrence of SCC in materials in the high-temperature, high-pressure water environment of light water reactors. These include constant-strain type tests such as the creased bent beam (CBB) test, C-ring test, and U-bend test, as well as external-load type tests such as the slow-strain rate technique (SSRT) test and the uniaxial constant load (UCL) test. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] JIS G0576 "Test Method for Stress Corrosion Cracking of Stainless Steel" [Overview of the project] [Problems that the invention aims to solve]

[0005] In the constant-strain type test described above, the test specimen loaded in a jig is immersed in the test environment for a predetermined time, then removed, and the surface and cross-section of the specimen are observed to evaluate SCC cracking. For this reason, it is difficult to accurately evaluate the SCC initiation time in the constant-strain type test. On the other hand, the CBB test accelerates the corrosion reaction by forming gaps on the surface of the test specimen, making it an effective method for initiating SCC in a relatively short time, and it also has a proven track record as a test method in a BWR simulated environment. However, because the CBB test is structured to press the gap-forming material with a jig, it is extremely difficult to detect cracks from the outside.

[0006] Furthermore, in the external load application type test described above, it is difficult to simultaneously test a large number of specimens necessary for statistical evaluation of the lifespan of SCC occurrence. In addition, the SSRT test forcibly applies a predetermined amount of low-speed tensile strain to a specimen in a test environment or until fracture occurs, and evaluates SCC susceptibility based on mechanical properties such as the number and length of cracks that occur in the specimen, the fracture surface ratio of SCC on the fracture surface, and the tensile strength.

[0007] For this reason, SSRT testing is an effective and proven method for evaluating SCC susceptibility in a relatively short time. However, like constant-strain testing, it is difficult to accurately evaluate the SCC occurrence time with SSRT testing. Furthermore, because SSRT testing dynamically increases the displacement of the specimen, it is difficult to identify the strain and stress conditions in the specimen at the time of SCC occurrence, and it is not easy to correlate the SCC occurrence time with the mechanical conditions.

[0008] On the other hand, UCL testing involves applying a predetermined load to a test specimen in a test environment and evaluating the time it takes for the specimen to fracture due to stress-induced corrosion cracking (SCC). For this reason, UCL testing is an effective method for evaluating SCC occurrence time and the stress required for its occurrence (generated stress), and it has a proven track record as a testing method in light water reactor environments. However, with highly corrosion-resistant materials, it is difficult to induce SCC within a realistic test time in UCL testing, and the test time is generally prolonged.

[0009] For this reason, methods such as installing gap-forming fixtures on the specimen surface have been proposed for UCL testing to accelerate the occurrence of SCC, but, as with CBB testing, detecting cracks from the outside is extremely difficult. Furthermore, while the susceptibility and occurrence of SCC are generally evaluated by the time it takes for the specimen to fracture, it is difficult to pinpoint the exact occurrence time with conventional methods, making it extremely difficult to accurately assess the soundness of the structure.

[0010] Thus, with conventional SCC testing methods, it has become difficult to experimentally induce SCC within a realistic test time for highly corrosion-resistant materials that exhibit excellent SCC resistance. As a result, it has become impossible to determine the degree of improvement in SCC occurrence life (FOI: Factor of Improvement) compared to conventional materials. In this way, when the time from the start of use of highly corrosion-resistant materials until SCC occurs (occurrence life) is unknown, it becomes necessary to conservatively assume the occurrence of SCC, resulting in an extremely strict soundness assessment that is far removed from reality.

[0011] Embodiments of the present invention have been made in consideration of these circumstances, and provide a stress corrosion cracking testing technique that allows for the recognition of SCC occurrence within a practical test time for highly corrosion-resistant materials and accurately evaluates the structural integrity of the structure. [Means for solving the problem]

[0012] A stress corrosion cracking testing apparatus according to an embodiment comprises: a loading unit for gripping and loading both ends of a test specimen; a load control unit for controlling the tensile stress applied to the test specimen; a detection unit for detecting the electrical characteristics of the test specimen to recognize the occurrence of SCC; and a container in which a liquid is sealed for immersing the test specimen. 、 The loading unit grips one end of the test piece. And a pair of first protrusions are formed. The first gripping member grips the other end of the test piece. And a pair of second protrusions are formed. The second gripping member and The first gripping member is provided with a first hole that engages with the first projection, and the second gripping member is provided with a second hole that loosely fits onto the second projection and engages with the second projection when the test piece breaks. Even if the test piece breaks, the first gripping part Material and the second gripping part Material It comprises a support member that supports both so as not to separate, Multiple loading units are connected and apply the tensile stress to multiple test pieces arranged in series. . [Effects of the Invention]

[0013] According to the embodiment of the present invention, a stress corrosion cracking test technique is provided that enables the recognition of SCC occurrence in high corrosion-resistant materials within a practical test time and accurately evaluates the soundness of structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] [Figure 1] Longitudinal cross-sectional view of the stress corrosion cracking test apparatus according to the first embodiment of the present invention. [Figure 2] (A) Front longitudinal cross-sectional view of the loading section holding the test specimen in the first embodiment, (B) Front longitudinal cross-sectional view of the loading section after the test specimen is fractured, (C) Side view of the loading section holding the test specimen, (D) Side view of the loading section after the test specimen is fractured. [Figure 3] Explanatory diagram of the test specimen and connection wiring. [Figure 4] Graph showing tensile stress applied to the test specimen versus test time. [Figure 5] Longitudinal cross-sectional view of the stress corrosion cracking test apparatus according to the second embodiment. [Figure 6] (A) Front longitudinal cross-sectional view of the loading section holding the test specimen in the second embodiment, (B) Side view of the loading section holding the test specimen. [Figure 7] Graph showing test results for two materials with different SCC resistance in an example using the stress corrosion cracking test apparatus according to the present embodiment. [Figure 8] Graph showing normalized potential difference varying with SCC propagation versus test time. [Figure 9] Graph plotting cumulative hazard function against SCC occurrence time and fracture time of test specimen. MODE FOR CARRYING OUT THE INVENTION

[0015] (First Embodiment) Embodiments of the present invention will be described below with reference to the attached drawings. Figure 1 is a longitudinal cross-sectional view of a stress corrosion cracking test apparatus 10A(10) (hereinafter simply referred to as "test apparatus 10A") according to the first embodiment of the present invention. As shown, the test apparatus 10A includes a loading unit 30 for gripping and loading both ends of a test piece 20, a load control unit 11 for controlling the tensile stress σ applied to the test piece 20, a detection unit 12 for detecting the electrical characteristics of the test piece 20 to recognize the occurrence of SCC, and a container 16 in which a liquid 15 is sealed to immerse the test piece 20.

[0016] In the test apparatus 10A, a beam member 23 is spanned horizontally across a pair of support columns 22 erected on the foundation 21. A portion of this beam member 23 is connected to one end of the loading section 30, which grips the test specimen 20, and fixes it in place. Furthermore, although not shown in the figure, a load control unit 11 is also fixed to the foundation 21. The load control unit 11 is equipped with a mechanism for controlling a rod 24, the tip of which is connected to the other end of the loading section 30, and transmits tensile stress σ to the test specimen 20.

[0017] Furthermore, the base section 21 is provided with a watertight and airtight container 16 to prevent leakage of the liquid 15 that is sealed under high pressure inside the container 16 while the support columns 22, beam members 23, and loading section 30 are housed inside the container 16. Similarly, the part of the base section 21 where the rod 24 passes through and slides between the side where the liquid 15 is sealed and the side facing the atmosphere is also treated to be watertight.

[0018] Furthermore, the test apparatus 10A includes a temperature control unit (not shown) for adjusting the temperature of the sealed liquid 15, and a water quality adjustment unit 17 for adjusting the concentration of corrosive ions in the sealed liquid 15. The circulation path 13, which has both ends opening into the inside of the container 16, injects the liquid 15 into the inside of the container 16 from one inlet 13a and discharges the liquid 15 to the outside of the container 16 from the other outlet 13b. Normally, SCC tests are performed based on a sealed state in which the container 16 is filled with liquid 15.

[0019] The water quality adjustment unit 17 is incorporated into the circulation path 13, and a chemical solution containing a predetermined amount of corrosive ions is injected from the chemical solution injection unit 18 to accelerate the occurrence of SCC in the test specimen 20. These corrosive ions can chemically reduce the stability of the film formed on the surface of the test specimen 20.

[0020] The corrosive ions that can be injected include sulfate ions, hydrochloride ions, nitrate ions, and combinations thereof. However, it is desirable to set the corrosive ions and their concentrations in a way that minimizes their impact on the SCC generation mechanism and the oxidation-reduction reaction of corrosion in test specimen 20.

[0021] Furthermore, the appropriate setting conditions for generating SCC in the water quality adjustment unit 17 are the same as those for the load control unit 11 described later, but they also differ depending on the SCC resistance of the target material. For this reason, the conditions for adding corrosive ions in the water quality adjustment unit 17 can be arbitrarily adjusted depending on the SCC resistance of the material and the SCC generation time desired by the operator.

[0022] The temperature control unit (not shown) is not particularly limited in its installation location as long as it can heat the liquid 15, and may be located in the water quality adjustment unit 17 or inside the container 16. When the liquid 15 is heated in a sealed system, a pressure of 1 atmosphere is applied if the set temperature is 100°C or below, but if it exceeds 100°C, a pressure equivalent to the saturated vapor pressure of water at that set temperature is applied. In this embodiment, the test was described using liquid 15, but it is also possible to conduct the test in a gas phase or vapor environment.

[0023] Figure 2(A) is a front longitudinal cross-sectional view of the loading section 30 holding the test piece 20 in the first embodiment. Figure 2(B) is a front longitudinal cross-sectional view of the loading section 30 with the test piece 20 broken. Figure 2(C) is a side view of the loading section 30 holding the test piece 20. Figure 2(D) is a side view of the loading section 30 with the test piece 20 broken.

[0024] The loading unit 30 includes a first gripping member 31 for gripping one end of the test piece 20, a second gripping member 32 for gripping the other end of the test piece 20, and a support member 35 that supports both the first gripping member 31 and the second gripping member 32 so that they do not separate even if the test piece 20 breaks.

[0025] As shown in Figure 2(A), the first gripping member 31 grips one end of the test piece 20, while the other end is connected to and fixed to a part of the beam member 23. A pair of first projections 41 are formed on both sides of the first gripping member 31, and the support member 35 engages with them.

[0026] Similarly, the second gripping member 32 grips the other end of the test piece 20, while its opposite end is connected to and fixed to the tip of the rod 24. A pair of second projections 42 are also formed on both sides of this second gripping member 32, and the support member 35 is loosely fitted into them.

[0027] As shown in Figure 2(C), the support member 35 is provided with a first hole 38 that engages with the first projection 41 of the first gripping member 31, and a second hole 39 that loosely fits with the second projection 42 of the second gripping member 32. Before the test piece 20 breaks, the support member 35 is unloaded, but as shown from Figure 2(A) to Figure 2(B) or from Figure 2(C) to Figure 2(D), it supports both the first gripping member 31 and the second gripping member 32 so that they do not separate even when the test piece 20 breaks. When the test piece 20 breaks, the support member 35 is under load from the load control unit 11.

[0028] The test piece 20 has threads 27 (Figure 3) for fastening nuts 26 at both ends. The first gripping member 31 and the second gripping member 32 are provided with contact surfaces 28 that the nuts 26 contact via an electrical insulator 25.

[0029] By making the contact surface 28 a spherical seat structure, the load can be uniformly transmitted from the gripping members 31 and 32 even when there is no stress distribution on the test piece 20. Furthermore, because the contact surface 28 has a spherical seat structure, even if there is a fluctuation in the tensile stress σ applied to the test piece 20 (see Figure 4), axial displacement of the test piece 20 is prevented. Also, as described in the second embodiment, even when multiple test pieces 20 are connected in multiple layers and inspected at once, axial displacement of the test piece 20 is prevented even if one of the test pieces 20 breaks and a sudden displacement change occurs throughout the loading section 30.

[0030] Figure 3 is an explanatory diagram of the test piece 20 and connecting wiring (reference numerals 45-49). The test piece 20 used in the embodiment described later has a reference section with a diameter of 8 mm and a test section 44 with a diameter of 4 mm and a length of 5 mm, forming a round bar. Both ends of the test piece 20 are engraved with screws 27 for fastening nuts 26 (Figure 2). A constant current controlled current is supplied from the current supply lines 45 and 46 connected to both ends of the test piece 20.

[0031] Then, the potential difference V of the reference section 43 is measured using the potential difference measurement lines 47 and 49. REF The potential difference V of the test section 44 was measured using the potential difference measurement lines 47 and 48. ACT The potential difference V associated with the change in surface properties of a test specimen 20 immersed in a high-temperature, high-pressure, corrosive liquid 15 is measured. ACT The effect on the reference potential difference V REF The normalized potential difference is calculated by excluding the correction applied.

[0032] Furthermore, when evaluating the test data, the reference potential difference V changes during the test. REF If the effect is negligible, the potential difference V ACT The evaluation may also be performed using the test specimen directly. Furthermore, the shape and dimensions of the test specimen 20 can be arbitrarily changed within the range that allows it to be attached to the loading section 30, depending on the strength of the material and measurement convenience. In addition, notches or notches may be provided in advance in the test section 44 of the test specimen 20 in order to accelerate the occurrence of SCC due to stress concentration.

[0033] Figure 4 is a graph showing the tensile stress σ applied to the test specimen 20 as a function of the test time. In this way, the load control unit 11 periodically varies the tensile stress σ and applies it to the test specimen 20. By applying a periodically varying tensile stress σ in this manner, the mechanical failure of the film formed on the surface of the test specimen 20 can be promoted, and the occurrence of SCC can be accelerated.

[0034] Furthermore, the variable tensile stress σ is not limited to a trapezoidal wave; triangular waves, square waves, sawtooth waves, sinusoidal waves, and other types of stress application methods, such as those used in SSRT tests that increase tensile stress at a low strain rate, may be combined with periodic unloading. Thus, the conditions for adding corrosive ions and applying variable stress in the embodiment can be arbitrarily adjusted depending on the material's resistance to SCC and the SCC occurrence time desired by the implementer. The load control unit 11 may be a servo motor or the like, but is not limited to such mechanical mechanisms; mechanisms using pressure or thermal load may also be used.

[0035] The detection unit 12 detects the electrical characteristics of the test piece 20 to recognize the occurrence of SCC. In each embodiment, by applying a current controlled to a constant value to the test piece 20, changes in the electrical characteristics of the test piece 20 associated with the occurrence and progression of SCC are detected as changes in potential difference. By employing such a potential difference method, the occurrence of SCC can be detected in real time.

[0036] Furthermore, the detection method for SCCs is not limited to this potentiometric method. For example, other detection methods using electrical measurement include directly measuring the resistance change associated with the occurrence of SCCs, or constructing a database of the time evolution of the potentiometer and obtaining a correlation between the occurrence of SCCs and the slope of the trend line of the potentiometer evolution or the absolute value of the potentiometer. In addition to detecting electrical characteristics in this way, ultrasonic testing and acoustic emission methods are also being considered for recognizing SCCs that have occurred on the test piece 20.

[0037] (Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. 5. FIG. 5 is a longitudinal cross-sectional view of a stress corrosion cracking test apparatus 10B(10) (hereinafter simply referred to as "test apparatus 10B") according to the second embodiment. The test apparatus 10B of the second embodiment includes the loading unit 30 which is a component of the first embodiment described above n (n=1 to 7 in the illustration) connected in plurality, and a plurality of test pieces 20 arranged in series n (n=1 to 7 in the illustration) is configured to apply tensile stress σ. In FIG. 5, parts having the same configuration or function as those in FIG. 1 are denoted by the same reference numerals, and overlapping descriptions are omitted.

[0038] In the second embodiment, a large number of test pieces 20 can be processed at one time n a multi-coupled test method that allows loading and testing is adopted. Accordingly, even after part of the test pieces 20 n have broken, tensile stress σ is continuously applied to the other remaining test pieces 20 n Furthermore, by enabling testing of a large number of test pieces 20 at one time n this method is effective for statistical evaluation of material life.

[0039] FIG. 6(A) shows the loading unit 30 holding the test piece 20 in the second embodiment n (n=1 to N in the illustration) is a front longitudinal cross-sectional view. FIG. 6(B) shows the loading unit 30 holding the test piece 20 n (n=1 to N in the illustration) is a side view. As described above, adjacent loading units 30 n and the loading unit 30 n-1 are connected by pins 40. As described in the first embodiment, the nuts 26 fastened to both ends of the test piece 20 are supported by the contact surfaces 28 of the gripping members 31 and 32. Accordingly, load is uniformly transmitted from the gripping members 31 and 32 to all of the plurality of test pieces 20 connected in series without any uneven stress distribution.

Examples

[0040] Next, we will describe an example in which the effects of this embodiment were confirmed. Figure 7 is a graph showing the test results for two materials A and B with different SCC resistance, in an example of an SCC test using the test apparatus 10 of this embodiment.

[0041] Material A is a nickel (Ni)-based alloy weld metal containing approximately 20% chromium (Cr), a corrosion-resistant element, and has been conventionally used in light water reactors due to its excellent resistance to SCC (Steel Chloride Corrosion). It is also known that it is difficult to induce SCC in conventional UCL (Urgent Corrosion Collision) tests using Material A. Furthermore, in CBB (Cold-Blocked Battering) tests, Material A is known to exhibit SCC after prolonged immersion of approximately 2,000 hours under harsh test conditions that combine cold working of the material's strength with a gap environment created by graphite wool.

[0042] In contrast, material B is a nickel-based alloy weld metal with a composition that is approximately 10% higher than material A, containing 30% chromium, a corrosion-resistant element. Material B has a similar chemical composition to materials widely used in pressurized water reactors (PWRs), and is known to exhibit superior SCC resistance compared to material A, even in BWR environments.

[0043] In this test, for material A, the change in normalized potential difference observed up to approximately 500 hours confirmed the occurrence of SCC at 415 hours using the determination method described later, and fracture of the test specimen occurred at 1600 hours. In contrast, for material B, no occurrence of SCC was observed even after approximately 2300 hours of testing under the same test conditions.

[0044] The settings for the water quality adjustment unit 17 and the load control unit 11 in the test shown in Figure 7 were set so that the occurrence of SCC could be observed within the 500-hour test period commonly used in conventional CBB tests.

[0045] Figure 8 is a graph showing the normalized potential difference as SCC progresses, against the test time. Figure 8 was created by adjusting the settings of the temperature control unit, water quality control unit 17, and load control unit 11 compared to Figure 7, so that the occurrence of SCC could be detected in a relatively short test time of about 300 hours.

[0046] In the test shown in Figure 8, the temperature control unit and water quality control unit 17 were set to simulate the normal water quality environment in a BWR, with a temperature of 288°C, a pressure of 9 MPa, and a dissolved oxygen concentration of approximately 8.5 ppm. Furthermore, sulfate ions were added as corrosive ions to a concentration of 1.0 ppm. This amount of addition reduces the stability of the corrosion-resistant film formed on the material surface of the test specimen 20 without affecting the oxidation-reduction reaction of corrosion.

[0047] Furthermore, in the load control unit 11, a test stress (1.04σy) slightly exceeding the yield stress σy of the material was defined, and a tensile stress σ equal to 10% of this test stress was periodically deloaded with a 90-minute period, thereby applying a trapezoidal wave-shaped tensile stress σ through load control.

[0048] Figure 8 shows the time course of the normalized potential difference, revealing the existence of a singularity Y where the slope changes at 295 hours. Observation of the surface of specimen 20 after passing this singularity Y revealed fine cracks presumed to be SCCs. On the other hand, no such cracks were observed on the surface of specimen 20 before passing singularity Y. This suggests a causal relationship between the singularity Y where the rate of change in the electrical properties of specimen 20 changes and the time at which SCCs occur.

[0049] According to the test conditions in the example shown in Figure 8, the SCC occurrence time for material A was determined to be approximately 295 hours, which is sufficiently short and practical for performance evaluation. For comparison, under test conditions where the sulfate ion concentration injected as a chemical solution was 350 ppb and the fluctuating stress relief period was 6 hours, SCC could not be induced in material A within the target test time of 500 hours.

[0050] Figure 9 is a graph plotting the cumulative hazard function H(t) against the SCC occurrence time and the fracture time of the test specimen 20. From this graph, the SCC occurrence lifetime and fracture lifetime of the material constituting the test specimen 20 can be evaluated. Here, the cumulative hazard function H(t) was derived from the equation shown in Figure 9 based on the test results using the test apparatus 10B of the second embodiment.

[0051] From the graph in Figure 9, it can be said that the relationship between SCC occurrence time, fracture time, and the cumulative hazard function H(t) shows a good regression line. From this, the SCC occurrence lifetime is estimated to be approximately 211 hours from the intersection of the SCC occurrence evaluation line P and the horizontal axis of time. Similarly, the fracture lifetime is estimated to be approximately 1111 hours from the intersection of the fracture occurrence evaluation line Q and the horizontal axis of time. Furthermore, by fitting the evaluation result of the cumulative hazard function H(t) to a probability distribution such as the Weibull distribution, it is possible to evaluate the occurrence lifetime corresponding to a desired probability.

[0052] According to the stress corrosion cracking testing apparatus of at least one embodiment described above, a controlled tensile stress is applied to a test specimen immersed in a liquid sealed in a container, and its electrical properties are detected. This makes it possible to recognize the occurrence of SCC within a practical testing time and accurately evaluate the structural integrity.

[0053] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, modifications, and combinations are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0054] 10 (10A, 10B)... Stress corrosion cracking test apparatus (test apparatus), 11... Load control unit, 12... Detection unit, 13... Circulation path, 13b... Discharge port, 13a... Inlet, 15... Liquid, 16... Container, 17... Water quality adjustment unit, 18... Chemical injection unit, 20... Test piece, 21... Foundation unit, 22... Support column, 23... Beam member, 24... Rod, 25... Electrical insulator, 26... Nut, 27... Screw, 28... Contact surface, 30... Loading unit, 31... First gripping member, 32... Second gripping member, 35... Support member, 38... Hole, 39... Hole, 40... Pin, 41... First projection, 42... Second projection, 43... Reference unit, 44... Test unit, 45... Current supply line, 47... Potential difference measurement line.

Claims

1. A loading section that grips both ends of the test piece and loads it, A load control unit for controlling the tensile stress applied to the test specimen, A detection unit for detecting the electrical characteristics of the test piece in order to recognize the occurrence of SCC, The system comprises a container in which a liquid is sealed so as to immerse the test piece, The loading section includes a first gripping member that grips one end of the test piece and has a pair of first protrusions formed on it, A second gripping member, which grips the other end of the aforementioned test piece and has a pair of second protrusions formed thereon, The first gripping member has a first hole that engages with the first projection, and the second gripping member has a second hole that loosely fits onto the second projection and engages with the second projection when the test piece breaks, and the support member supports both the first gripping member and the second gripping member so that they do not separate even when the test piece breaks, The aforementioned loading section is connected in multiple units, and the stress corrosion cracking test apparatus applies the aforementioned tensile stress to multiple test pieces arranged in series.

2. In the stress corrosion cracking test apparatus according to claim 1, The ends of the aforementioned test piece are engraved with threads for fastening nuts. A stress corrosion cracking testing apparatus is provided in which the first gripping member and the second gripping member have contact surfaces to which the nut abuts via an electrical insulator.

3. In the stress corrosion cracking test apparatus according to claim 1 or claim 2, The load control unit is a stress corrosion cracking test apparatus that periodically varies and applies the tensile stress.

4. In the stress corrosion cracking test apparatus according to claim 1 or claim 2, A first adjustment unit for adjusting the concentration of corrosive ions in the sealed liquid, A stress corrosion cracking test apparatus comprising a second adjustment unit for adjusting the temperature of the sealed liquid.

5. A loading unit comprising a plurality of connected loading units, each comprising: a first gripping member for gripping one end of a test piece and having a pair of first protrusions formed thereon; a second gripping member for gripping the other end of the test piece and having a pair of second protrusions formed thereon; a support member provided with a first hole for engaging with the first protrusions of the first gripping member and a second hole for loosely fitting into the second protrusions of the second gripping member and engaging with the second protrusions when the test piece breaks, and supporting both the first gripping member and the second gripping member so as not to separate even when the test piece breaks; and the step of gripping both ends of a test piece into the plurality of loading units, A step in which a liquid is sealed in a container so as to immerse the test piece, A step of controlling the tensile stress applied to a plurality of test specimens arranged in series, A stress corrosion cracking test method comprising the step of detecting the electrical properties of the test specimen in order to recognize the occurrence of SCC.

6. In the stress corrosion cracking test method described in claim 5, A stress corrosion cracking test method in which the singularity at which the rate of change of the electrical characteristics switches is defined as the time of occurrence of SCC.

7. In the stress corrosion cracking test method described in claim 6, A stress corrosion cracking test method for deriving at least one of the SCC occurrence time and fracture time from a regression line between at least one of the SCC occurrence time and fracture time and a cumulative hazard function.

Images