Stress corrosion cracking test device and stress corrosion cracking test 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] SUMMARY OF THE INVENTION Embodiments of the present invention relate to stress corrosion cracking testing techniques 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 phenomena increases, making it increasingly important to address these issues. Improving the operational stability and availability of nuclear power generation facilities is important from the perspective of power generation efficiency and a stable supply of electricity. For this reason, the integrity of reactor internal structures and piping is assessed through stress corrosion cracking (SCC) propagation analysis. This SCC propagation analysis is performed by creating test specimens made of corrosion-resistant materials and obtaining propagation rate data. In other words, the risk of damage to reactor internal structures and piping is confirmed based on the degree of SCC propagation, and highly corrosion-resistant materials with excellent SCC resistance are applied as a maintenance measure.

[0003] Testing methods used to evaluate the susceptibility and occurrence of SCC in materials in the high-temperature, high-pressure water environment of light water reactors include test methods specified in industrial standards such as JIS, as well as constant strain-applying tests such as the Creviced Bent Beam (CBB) test, C-ring test, and U-bend test, and external load-applying 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 G 0576 "Stress corrosion cracking test method for stainless steel" Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-mentioned constant strain test, a test specimen loaded into a jig is immersed in the test environment for a specified 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 time to SCC initiation using constant strain tests. In addition, the CBB test accelerates the corrosion reaction by forming a crevice on the surface of the test specimen, making it an effective method for inducing SCC in a relatively short period of time. It has also been used as a test method in simulated BWR environments. However, because the CBB test uses a jig to press the crevice-forming material, it is extremely difficult to detect cracks from the outside.

[0006] Furthermore, with the external load test described above, it is difficult to simultaneously test the large number of specimens required for statistical evaluation of SCC initiation life. The SSRT test forcibly applies a low-rate tensile strain to a specimen in a test environment until a specified amount 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 SCC fracture area ratio on the fracture surface, and tensile strength.

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

[0008] On the other hand, the UCL test applies a specified load to a test specimen in a test environment and evaluates the time until the specimen fractures due to SCC. Therefore, the UCL test is effective as a method for evaluating the time to SCC onset and the stress required for SCC onset (generated stress), and has a proven track record in light water reactor environments. However, with highly corrosion-resistant materials, it is difficult to induce SCC within a realistic test time, so the test time is generally long.

[0009] For this reason, methods have been proposed for the UCL test, such as installing a gap-forming jig on the surface of the test specimen to accelerate the onset of SCC, but as with the CBB test, this makes it extremely difficult to detect cracks from the outside.In addition, evaluation of SCC susceptibility and onset is generally based on the time it takes for the test specimen to break, but with conventional methods it is difficult to precisely identify the onset time, making it extremely difficult to accurately evaluate the soundness of the structure.

[0010] As a result, it has become difficult to experimentally induce SCC in highly corrosion-resistant materials with excellent SCC resistance within a realistic test time using conventional SCC testing methods. This has made it impossible to determine the degree of improvement in the initiation life (FOI: Factor of Improvement) compared to conventional materials. When the time from the start of service of a highly corrosion-resistant material until SCC occurs (initiation life) is unknown, it becomes necessary to make conservative assumptions about SCC occurrence, resulting in an extremely strict integrity assessment that is far removed from reality.

[0011] The embodiments of the present invention have been made in consideration of these circumstances, and provide a stress corrosion cracking testing technology that enables the occurrence of SCC in highly corrosion-resistant materials to be detected within a practical testing time and accurately evaluates the soundness of structures. [Means for solving the problem]

[0012] The stress corrosion cracking testing device according to the embodiment includes a loading unit that holds both ends of a test piece and loads it, a load control unit that controls the tensile stress applied to the test piece, a detection unit that detects the electrical characteristics of the test piece to recognize the occurrence of SCC, and a container in which a liquid is sealed so that the test piece can be immersed. [Effects of the Invention]

[0013] According to an embodiment of the present invention, a stress corrosion cracking testing technique is provided that can detect the occurrence of SCC in highly corrosion-resistant materials within a practical testing time and accurately evaluate the soundness of a structure. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a longitudinal sectional view of a stress corrosion cracking testing device according to a first embodiment of the present invention. [Figure 2] (A) A front longitudinal cross-sectional view of the loading section holding the test piece in the first embodiment, (B) a front longitudinal cross-sectional view of the loading section that broke the test piece, (C) a side view of the loading section holding the test piece, and (D) a side view of the loading section that broke the test piece. [Figure 3] FIG. 2 is an explanatory diagram of a test piece and connecting wiring. [Figure 4] 1 is a graph showing the tensile stress applied to the test piece versus the test time. [Figure 5] FIG. 6 is a longitudinal sectional view of a stress corrosion cracking testing device according to a second embodiment. [Figure 6] FIG. 10(A) is a front vertical cross-sectional view of a loading section gripping a test piece in the second embodiment, and FIG. 10(B) is a side view of the loading section gripping a test piece. [Figure 7] 1 is a graph showing test results for two materials with different SCC resistances, which are examples using the stress corrosion cracking test device according to the present embodiment. [Figure 8] 1 is a graph showing the normalized potential difference that changes with the progression of SCC versus test time. [Figure 9] Graph plotting cumulative hazard function against SCC initiation time and specimen rupture time. DETAILED DESCRIPTION OF THE INVENTION

[0015] (First embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a longitudinal sectional view of a stress corrosion cracking testing apparatus 10A (10) (hereinafter simply referred to as "testing apparatus 10A") according to a first embodiment of the present invention. As described above, the testing apparatus 10A includes a loading unit 30 that grips both ends of a test specimen 20 and loads it, a load control unit 11 that controls the tensile stress σ applied to the test specimen 20, a detection unit 12 that detects the electrical characteristics of the test specimen 20 to detect the occurrence of SCC, and a container 16 that contains a liquid 15 so that the test specimen 20 can be immersed.

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

[0017] Furthermore, the container 16 is provided in the base 21 in a watertight and airtight manner so that the liquid 15 sealed under high pressure does not leak when the columns 22, beam members 23, and loading section 30 are housed inside the container 16. Similarly, the portions of the base 21 where the rod 24 passes and slides between the side where the liquid 15 is sealed and the atmospheric side are also treated to be watertight.

[0018] Furthermore, the test apparatus 10A is equipped with a temperature adjustment unit (not shown) that adjusts the temperature of the enclosed liquid 15, and a water quality adjustment unit 17 that adjusts the concentration of corrosive ions in the enclosed liquid 15. The circulation path 13 has both ends that open into the interior of the container 16, and injects the liquid 15 into the container 16 from one inlet 13a and discharges the liquid 15 from the other outlet 13b to the outside of the container 16. Note that an SCC test is usually performed with the container 16 basically filled with the liquid 15 and sealed.

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

[0020] The corrosive ions to be injected include sulfate ions, hydrochloride ions, nitrate ions, and combinations thereof, but it is desirable to select corrosive ions and their concentrations that have as little effect as possible on the SCC generation mechanism and corrosion redox reaction in the test piece 20.

[0021] The appropriate setting conditions for causing SCC in the water quality adjusting unit 17 are the same as those for the load control unit 11 described below, but also vary depending on the SCC resistance of the target material. Therefore, the conditions for adding corrosive ions in the water quality adjusting unit 17 are adjusted as desired depending on the SCC resistance of the material and the SCC occurrence time desired by the operator.

[0022] The temperature adjustment unit (not shown) may be installed in any location as long as it can heat liquid 15, and may be in water quality adjustment unit 17 or inside container 16. Liquid 15 heated in a sealed system is subjected to a pressure of 1 atmosphere if the set temperature is 100°C or lower, but if the temperature exceeds 100°C, it is subjected to a pressure equivalent to the saturated vapor pressure of water at this set temperature. Note that although the present example describes a test using liquid 15, it is also possible to perform the test in a gas phase or steam environment.

[0023] Fig. 2(A) is a front vertical cross-sectional view of the loading part 30 gripping the test piece 20 in the first embodiment. Fig. 2(B) is a front vertical cross-sectional view of the loading part 30 after breaking the test piece 20. Fig. 2(C) is a side view of the loading part 30 gripping the test piece 20. Fig. 2(D) is a side view of the loading part 30 after breaking the test piece 20.

[0024] The loading section 30 includes a first gripping member 31 that grips one end of the test piece 20, a second gripping member 32 that grips the other end of the test piece 20, and a support member 35 that supports 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] 2(A), the first gripping member 31 grips one end of the test piece 20, while the opposite end is connected to and fixed to a part of the beam member 23. A pair of first protrusions 41 are formed on both sides of the first gripping member 31, and a support member 35 is engaged therewith.

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

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

[0028] Threads 27 (FIG. 3) for fastening nuts 26 are formed on both ends of the test piece 20. The first gripping member 31 and the second gripping member 32 are provided with abutment surfaces 28 against which the nuts 26 abut via the electrical insulator 25.

[0029] By providing this contact surface 28 with a spherical seat structure, the load can be transmitted uniformly from the gripping members 31, 32 without any stress distribution on the test piece 20. Furthermore, by providing the contact surface 28 with a spherical seat structure, even if fluctuations occur in the tensile stress σ applied to the test piece 20 (see FIG. 4), axial displacement of the test piece 20 is prevented. Also, as will be described in the second embodiment, even when multiple test pieces 20 are connected in multiple units and inspected at the same time, even if one of the test pieces 20 breaks and a sudden change in displacement occurs in the entire loading section 30, axial displacement of the test piece 20 is prevented.

[0030] 3 is an explanatory diagram of the test piece 20 and connecting wires (reference numerals 45 to 49). The test piece 20 used in the examples described below is a round rod-shaped test piece 44 with a diameter of 4 mm and a length of 5 mm, and a reference portion 8 mm in diameter. Threads 27 for fastening nuts 26 (FIG. 2) are formed on both ends of the test piece 20. A constant current is supplied from current supply lines 45 and 46 connected to both ends of the test piece 20.

[0031] The potential difference V of the reference part 43 is measured by the potential difference measurement lines 47 and 49. REF The potential difference V of the test section 44 is measured by the potential difference measurement lines 47 and 48. ACT The potential difference V due to the change in the surface properties of the test piece 20 immersed in the 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 correcting the difference.

[0032] In evaluating the test data, the reference potential difference V REF If the effect of can be ignored, the potential difference V ACT Alternatively, the test piece 20 may be directly evaluated using the specimen 20. The shape and dimensions of the test piece 20 may be arbitrarily changed depending on the strength of the material, convenience of measurement, and the like, as long as it can be attached to the loading part 30. In addition, a notch or cutout may be provided in advance in the test part 44 of the test piece 20 in order to accelerate the occurrence of SCC due to stress concentration.

[0033] 4 is a graph showing the tensile stress σ applied to the test piece 20 versus the test time. In this way, the load control unit 11 periodically varies the tensile stress σ and applies it to the test piece 20. By applying the tensile stress σ that is periodically varied in this way, it is possible to promote mechanical destruction of the film formed on the surface of the test piece 20 and accelerate the occurrence of SCC.

[0034] Furthermore, the fluctuating tensile stress σ is not limited to a trapezoidal wave, but may be a triangular wave, a rectangular wave, a sawtooth wave, a sine wave, or a combination of a low strain rate tensile stress increasing stress application mode and periodic unloading in the SSRT test. Thus, the conditions for adding corrosive ions and applying fluctuating stress in the embodiment can be adjusted arbitrarily depending on the SCC resistance of the material and the SCC occurrence time desired by the operator. While the load control unit 11 may be a servo motor or the like, it is not limited to such mechanical mechanisms and may also use a mechanism that applies pressure or thermal load.

[0035] The detection unit 12 detects the electrical characteristics of the test piece 20 to recognize the occurrence of SCC. In each embodiment, a current controlled to a constant value is passed through the test piece 20, and 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] However, the detection method for SCC is not limited to the potential difference method. For example, other detection methods using electrical measurements include directly measuring the change in resistance associated with SCC occurrence, or constructing a database of the time course of potential difference and obtaining a correlation between SCC occurrence and the slope of the trend line of the potential difference course or the absolute value of the potential difference. In addition to detecting electrical characteristics in this way, ultrasonic flaw detection and acoustic emission methods are also being considered for identifying SCC that has occurred in 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 sectional view of a stress corrosion cracking testing apparatus 10B (10) (hereinafter simply referred to as "testing apparatus 10B") according to the second embodiment. The testing apparatus 10B of the second embodiment has a loading section 30, which is a component of the first embodiment described above. n (n=1 to 7 in the figure) are connected together and arranged in series. n (n=1 to 7 in the drawing) to apply a tensile stress σ to the wires 11. In Fig. 5, parts having the same structure or function as those in Fig. 1 are designated by the same reference numerals, and redundant explanations will be omitted.

[0038] In the second embodiment, a large number of test pieces 20 n This allows for a multi-connection test method in which 20 test pieces can be loaded and tested. n Even after some of the test pieces broke, the remaining 20 n The tensile stress σ is continuously applied to the specimen. n This makes it possible to carry out tests such as these, which is useful for statistical evaluation of material life.

[0039] FIG. 6(A) shows the loading section 30 holding the test piece 20 in the second embodiment. n (n=1 to N) in the figure. FIG. 6(B) shows the front vertical cross section of the loading section 30 holding the test piece 20. n (n=1 to N in the figure) is a side view of the loading section 30 adjacent to each other. n and loading section 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. This allows the load to be transmitted uniformly from the gripping members 31 and 32 to all of the multiple test pieces 20 connected in series without any stress distribution. [Example]

[0040] Next, an example in which the effects of this embodiment were confirmed will be described. Fig. 7 is a graph showing the test results of an example of an SCC test using the test device 10 of this embodiment, for two materials A and B that have different SCC resistance.

[0041] Material A is a nickel (Ni)-based alloy weld metal containing approximately 20% of the corrosion-resistant element chromium (Cr), and has traditionally been used in light water reactors for its excellent SCC resistance. It is known that it is difficult to induce SCC in Material A using conventional UCL testing. Material A is also known to exhibit SCC after long-term immersion of approximately 2,000 hours in CBB testing, which combines the harsh test conditions of cold working the material's strength with the crevice environment created by graphite wool.

[0042] In contrast, Material B is a Ni-based alloy weld metal with a 30% Cr content, a corrosion-resistant element, which is approximately 10% higher than Material A. Material B has the same chemical composition as materials widely used in pressurized water reactors (PWRs), and is known to exhibit superior SCC resistance to Material A even in BWR environments.

[0043] Here, for Material A, the occurrence of SCC was confirmed at 415 hours using the determination method described below based on the change in normalized potential difference observed up to about 500 hours, and the test piece fractured 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 conditions set for the water quality adjusting unit 17 and the load control unit 11 in the test of FIG. 7 were set so that the occurrence of SCC could be observed within the 500-hour test time generally employed in conventional CBB tests.

[0045] Figure 8 is a graph showing the normalized potential difference that changes with the progression of SCC versus test time. Figure 8 shows a graph in which the setting conditions of the temperature adjustment unit, water quality adjustment unit 17, and load control unit 11 are adjusted compared to Figure 7, so that the occurrence of SCC can be detected in a relatively short test time of about 300 hours.

[0046] In the test shown in Figure 8, the temperature and water quality control units 17 were set to simulate the typical water chemistry environment in a BWR: 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 can reduce the stability of the corrosion-resistant film formed on the material surface of the test piece 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 of 10% of this test stress was periodically unloaded in a 90-minute cycle, thereby applying a trapezoidal wave-shaped tensile stress σ by load control.

[0048] Looking at the time progression of the normalized potential difference in Figure 8, the presence of singular point Y, where the slope switches, is confirmed at 295 hours. When the surface of test piece 20 is observed after passing singular point Y, fine cracks presumed to be SCC are confirmed. On the other hand, when the surface of test piece 20 is observed before passing singular point Y, no such cracks are confirmed. This suggests a causal relationship between singular point Y, where the rate of change of the electrical properties of test piece 20 switches, and the time when SCC occurs.

[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 a sufficiently short and practical test time for performance evaluation. Note that, as a comparative example, under test conditions in which the concentration of sulfate ions injected as a chemical solution was 350 ppb and the cycle of unloading the fluctuating stress was 6 hours, SCC was not able to occur in Material A within the target test time of 500 hours.

[0050] 9 is a graph plotting the cumulative hazard function H(t) against the SCC initiation time and the fracture time of the test specimen 20. From this graph, the SCC initiation life and fracture life of the material constituting the test specimen 20 can be evaluated. The cumulative hazard function H(t) was derived from the equation shown in FIG. 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 seen that the relationship between the SCC initiation time, fracture time, and cumulative hazard function H(t) shows a good regression line. From this, the SCC initiation life is estimated to be approximately 211 hours from the intersection of the SCC initiation evaluation line P and the time on the horizontal axis. Similarly, the fracture initiation life is estimated to be approximately 1111 hours from the intersection of the fracture initiation evaluation line Q and the time on the horizontal axis. Furthermore, by fitting the evaluation results of the cumulative hazard function H(t) to a probability distribution such as the Weibull distribution, it is possible to evaluate the initiation life corresponding to a desired probability.

[0052] According to at least one of the embodiments of the stress corrosion cracking testing device described above, a controlled tensile stress is applied to a test piece immersed in a liquid sealed in a container, and the electrical characteristics are detected, thereby making it possible to recognize the occurrence of SCC within a practical testing time and accurately evaluate the soundness of the structure.

[0053] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as the inventions described in the claims and their equivalents. [Explanation of symbols]

[0054] 10 (10A, 10B)...Stress corrosion cracking test apparatus (test apparatus), 11...Load control section, 12...Detection section, 13...Circulation path, 13b...Outlet, 13a...Inlet, 15...Liquid, 16...Container, 17...Water quality adjustment section, 18...Chemical solution injection section, 20...Test piece, 21...Foundation section, 22...Support, 23...Beam member, 24...Rod, 25...Electrical insulator, 26...Nut, 27...Screw, 28...Abutment surface, 30...Loading section, 31...First gripping member, 32...Second gripping member, 35...Support member, 38...Hole section, 39...Hole section, 40...Pin, 41...First protrusion section, 42...Second protrusion section, 43...Reference section, 44...Test section, 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 that controls the tensile stress applied to the test piece; a detection unit that detects electrical characteristics of the test piece to recognize the occurrence of SCC; A stress corrosion cracking test device comprising: a container in which a liquid is sealed so that the test piece is immersed.

2. The stress corrosion cracking testing device according to claim 1, The loading section includes a first gripping member that grips one end of the test strip; a second gripping member that grips the other end of the test piece; a support member that supports the first gripping portion and the second gripping portion so that they do not separate even if the test piece breaks.

3. 3. The stress corrosion cracking testing apparatus according to claim 2, Both ends of the test piece are provided with threads for fastening nuts, The stress corrosion cracking testing device, wherein the first gripping member and the second gripping member are provided with a contact surface against which the nut abuts via an electrical insulator.

4. The stress corrosion cracking testing device according to any one of claims 1 to 3, A stress corrosion cracking testing device in which a plurality of the loading sections are connected and the tensile stress is applied to a plurality of the test pieces arranged in series.

5. The stress corrosion cracking testing device according to any one of claims 1 to 3, The load control unit is a stress corrosion cracking testing device that applies the tensile stress by periodically varying it.

6. The stress corrosion cracking testing device according to any one of claims 1 to 3, a first adjusting unit that adjusts the concentration of corrosive ions in the enclosed liquid; A stress corrosion cracking testing device comprising: a second adjustment unit that adjusts the temperature of the enclosed liquid.

7. a step of gripping both ends of the test piece and loading it into the loading section; a step of sealing a liquid in a container so as to immerse the test piece; controlling the tensile stress applied to the test piece; detecting electrical properties of the test specimen to recognize the occurrence of SCC.

8. The stress corrosion cracking test method according to claim 7, A stress corrosion cracking test method in which the singular point at which the rate of change of the electrical characteristics switches is determined as the time when the SCC occurs.

9. The stress corrosion cracking test method according to claim 8, A stress corrosion cracking test method for deriving at least one of the SCC initiation life and the rupture life from a regression line between the cumulative hazard function and at least one of the SCC initiation time and the rupture time.

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