JP6470716B2 - Method for calculating test piece area and test cell size in hydrogen embrittlement property evaluation test - Google Patents

Description

  The present invention relates to a test piece area calculation method and a test cell size calculation method in a hydrogen embrittlement test for determining a test piece area for evaluating hydrogen embrittlement characteristics of a reinforcing bar and a test cell size of a test apparatus.

  Rebars absorb hydrogen in certain use environments, lose ductility, and can significantly reduce strength. This phenomenon is called hydrogen embrittlement (see Non-Patent Document 1), and is known to occur, for example, in reinforcing bars (PC reinforcing bars) in prestressed concrete structures (see Non-Patent Document 2).

  A hydrogen embrittlement characteristic test has been conducted on PC rebars in order to evaluate that they have a certain resistance to hydrogen embrittlement. As a hydrogen embrittlement test, there is a method in which hydrogen is absorbed from the outside to a reinforcing bar loaded with load, and the presence or absence of breakage and the breakage time are confirmed. For example, “Method for hydrogen embrittlement of PC steel in 20% ammonium thiocyanate solution” (hereinafter referred to as test for PC steel) described in Non-Patent Document 3 and “delayed fracture of high strength bolt” There are test methods described in the “Characteristics Evaluation Guidebook” (hereinafter, testing for high-strength bolts), and (a) sample selection, (b) test cell, and (c) hydrogen charge test conditions are defined as shown in Table 1. ing.

  These conventional hydrogen embrittlement resistance tests have different test conditions, and each has unique characteristics as shown in Table 1. A test cell is essential for the test, and optimization according to the test solution and hydrogen charge conditions is necessary. For example, in the test for PC steel materials, there is a rule that the immersion length is 200 mm or more with respect to the contact area (immersion length) of the test piece that determines the device shape of the hydrogen embrittlement test (see Non-Patent Document 3). In this standard, when the immersion length is shortened, the rupture time tends to become longer experimentally, but it does not prescribe a sufficient immersion length that can break. Therefore, in the hydrogen embrittlement characteristic test, even if the same conditions and equipment are used, the quality of the PC rebar is not strictly uniform. Therefore, the rebar always breaks within the predetermined test time or does not necessarily break. Not exclusively.

  Therefore, in order to evaluate the quality of PC rebars, if there are rebars that break within the test time and rebars that do not break, increasing the area through which hydrogen can enter the rebar ensures a sufficient area where the rebar can break. A method of clarifying the presence or absence of breakage due to individual differences of test pieces can be considered.

Nagumo Michihiko, “Effect of Hydrogen on the Mechanical Behavior of Steel”, Iron and Steel, 2004, Vol. 90, no. 10, p. 766-775 Tetsuo Shirakami, “Hydrogen embrittlement in steel materials”, Materials and Environment, 2011, 60, 236-240 “Hydrogen embrittlement test method for PC steel in 20% ammonium thiocyanate solution”, Corrosion and Corrosion Protection Association, 2012, JSCE S 1201, p. 6-7 “Guidebook for Evaluation of Delayed Fracture Characteristics of High Strength Bolt”, Japan Steel Structure Association, 2010, JSSC Technical Report No. 91, p. 6-7, p. 126-127 Atsushi Komatsu, Atsushi Nishikata, Toru Water Flow, “Quantification of Hydrogen Accumulated in Steel Materials Under Repeated Wet and Wet Corrosion Environment by Electrochemical Measurement”, Materials and Environment, 2009, Vol. 58, no. 7, p. 269-273 Yasuhiko Omura, Takahiro Kushida, Ikuo Kudo, Fukukazu Nakazato, Ryo Watanabe, “Environmental factors affecting hydrogen penetration into steel”, Materials and the Environment, 2005, Vol. 54, no. 2, p. 61-67 Sato Noriyuki, Uchida Kenichiro, Yokoi Katsunori, Nonaka Motohiro, “Fundamental Study on Detailed Evaluation Technology of Concrete Neutralization by Phenolphthalein Method”, Annual Report of Concrete Engineering, 2009, Vol. 31, no. 1, p. 2023-2028 Yasuhiko Omura, Hiroshi Suzuki, Tsukasa Okamura, and 13 others, “Hydrogen Charging Method of Low Alloy Steel Simulating Air and High Pressure Hydrogen Gas Environment”, Iron and Steel, Vol. 100, no. 10, p. 1289-1297

  However, in consideration of controlling the temperature of the test solution, in order to shorten the preparation time until the start of the test, the test cell of the test apparatus must be a minimum size so that the amount of the test solution used is reduced. However, there has been no method for appropriately setting the size of the test apparatus so far.

  The present invention has been made in view of such problems, and the object of the present invention is to break within a predetermined test time without unnecessarily increasing the size of a test apparatus in a hydrogen embrittlement characteristic test of a reinforcing bar. An object of the present invention is to provide a test piece area calculation method and a test cell size calculation method in a hydrogen embrittlement test that can improve the probability of the test.

  In order to solve the above problems, the present invention is a method for calculating the area of a test piece in a hydrogen embrittlement characteristic evaluation test, wherein a hydrogen embrittlement test was performed a plurality of times by immersing a rebar test piece in a test solution. Sometimes, a step of obtaining a first test piece area where the test piece comes into contact with the test solution without causing a bias in a distribution of breakage positions of the test pieces of the reinforcing bars due to hydrogen embrittlement; Determining the probability of breakage of a test piece of a reinforcing bar of the test piece area, calculating the probability of break per unit area from the break probability and the first test piece area, and the calculated per unit area A second test piece in which the test piece comes into contact with the test solution, wherein the test piece obtains a probability of breakage in an arbitrary test piece area where the test piece comes into contact with the test solution based on the probability of breakage. Calculate area And steps, and having the steps of: calculating a size of the test cell of the test piece and the the test solution is contacted with the test strip area of the calculated hydrogen embrittlement characteristics evaluation test apparatus.

According to a second aspect of the present invention, in the method for calculating a test piece area in the hydrogen embrittlement property evaluation test according to the first aspect, the step of calculating the fracture probability per unit area includes the fracture probability per unit area. X is calculated as X = 1− (1−X _k ) ^{1 / k} from the breaking probability X _{k at which} the reinforcing bar test piece having the first test piece area is broken.

According to a third aspect of the present invention, in the method for calculating a test piece area in the hydrogen embrittlement characteristic evaluation test according to the first or second aspect, the second test piece area in which the fracture probability is a desired value is calculated. The step is characterized in that the fracture probability X _n in the arbitrary specimen area is calculated from the fracture probability X per unit area as X _n = 1− (1−X) ⁿ .

  The invention according to claim 4 is the test piece area calculation method in the hydrogen embrittlement characteristic evaluation test according to any one of claims 1 to 3, wherein the hydrogen embrittlement test is a test used in the hydrogen embrittlement test. It is a hydrogen embrittlement test by cathodic charging in which a negative potential is applied to the rebar with respect to the solution.

  The invention according to claim 5 is a method of calculating a test cell size in a hydrogen embrittlement characteristic evaluation test, and as test conditions for a hydrogen embrittlement characteristic evaluation test, a test piece, a test solution in which the test piece is immersed, A hydrogen charging method for the test piece immersed in a test solution, a first step of determining a load stress applied to the test piece during the hydrogen charge, a second step of determining an electrode used for the hydrogen charge, and the test piece A third step of determining a test piece area in contact with the test solution, a fourth step of determining a specific liquid amount of the test solution with respect to the test piece, and contacting the test piece and the determined electrode with each other. And a fifth step of calculating a test cell size that can be inserted without causing the test piece to realize the test piece area and the specific liquid amount.

  According to a sixth aspect of the present invention, in the test cell size calculation method in the hydrogen embrittlement characteristic evaluation test according to the fifth aspect, the area of the test piece determined in the third step is any one of the first to fourth aspects. It is the said 2nd test piece area calculated by the calculation method of the test piece area in the hydrogen embrittlement characteristic evaluation test of a crab.

  The invention according to claim 7 is the method for calculating the test cell size in the hydrogen embrittlement characteristic evaluation test according to claim 5 or 6, wherein the specific liquid amount determined in the fourth step is hydrogen under the test conditions. It is characterized in that the change amount of the liquid property of the test solution when the embrittlement characteristic evaluation test is performed for a predetermined time is determined to be smaller than a predetermined value.

  If the test equipment designed and manufactured based on the test piece area determined according to the present invention is used, the probability of fracture within a predetermined test time without unnecessarily increasing the size of the test equipment in the hydrogen embrittlement characteristic test of reinforcing steel Can be improved.

It is a flowchart of the calculation method of the test piece area in the hydrogen embrittlement test which concerns on one Embodiment of this invention. It is a figure which shows the relationship between the frequency | count of a fracture | rupture and a fracture | rupture position when a hydrogen embrittlement test is performed 12 times with respect to the PC reinforcement taken out from the prestressed concrete structure. It is a figure which shows the outline | summary of a hydrogen embrittlement test apparatus. It is the conceptual diagram which showed the relationship between immersion length n and the fracture | rupture probability X. FIG. It is the figure plotted based on the function obtained by substituting X = 0.356 into fracture probability _Xn = 1- (1-X) ⁿ in case of immersion length n. It is a schematic diagram of an evaluation test apparatus for evaluating hydrogen embrittlement resistance. It is a figure which shows the time-dependent change of pH with respect to the time of hydrogen charge of the test solution in each specific liquid amount. It is a figure which shows an example of the test cell shape in the hydrogen embrittlement resistance evaluation method of PC steel materials.

  In the present invention, by using a test cell determined according to the following procedure for each of various test conditions, a stable result can be obtained without unnecessarily increasing the size of the test apparatus in the hydrogen embrittlement characteristic test of the reinforcing bar. The number of times can be reduced, the probability of fracture within a predetermined test time can be improved, and the total test time required for evaluating the hydrogen embrittlement resistance of PC steel can be shortened.

(Test cell shape determination procedure)
[1] Determination of test conditions [2] Selection of electrodes to be inserted into the test cell [3] Determination of immersion length [4] Determination of specific liquid volume [5] Determination of test cell shape

[1] Determination of test conditions The sample (test piece) should be selected according to the purpose of the test. For example, a new PC steel material with a notch or a PC steel material taken out from a structure (extracted PC steel material) can be used as the test piece. The test solution may be a buffer solution having a pH of 7.8 to 8.3, and 0 to 1 w% ammonium thiocyanate may be added to the test solution. The hydrogen charge can be selected from an immersion method in which a test piece is brought into contact with a corrosive solution or a cathodic charge method in which electrochemical control is performed on the surface of the test piece. In the cathode charging method, the applied potential and current density are controlled. The load on the test piece in the hydrogen embrittlement resistance test can be, for example, 0.7 times the tensile strength of the test piece.

[2] Selection of electrode to be inserted into test cell As the reference electrode and the counter electrode when the cathode charging method is adopted, for example, a silver-silver chloride electrode may be used as the reference electrode and a platinum black electrode may be used as the counter electrode.

[3] Determine the immersion length.
Determine the shape parameters (contact area, or immersion length) of the test equipment. What is necessary is just to obtain | require optimal immersion length from the fracture | rupture probability in immersion length as immersion length. Hereinafter, a method of calculating the test piece area where the test piece comes into contact with the test solution in the hydrogen embrittlement test of the PC rebar will be described. The method for calculating the test piece area in the hydrogen embrittlement test of the present invention consists of the following three procedures.

<1> Evaluation of Effective Specimen Area <2> Calculation of Fracture Probability per Unit Area <3> Determination of Specimen Area FIG. 1 shows calculation of test piece area in a hydrogen embrittlement test according to an embodiment of the present invention. A flow chart of the method is shown. First, as an evaluation of <1> effective test piece area, an effective test piece area in which breakage due to hydrogen embrittlement occurs in a specific region of the test piece without deviation is obtained (step 101). Next, <2> as the calculation of the failure ratio per unit area, it calculates the failure ratio X _k to the effective test area from multiple experiments (step 102), the unit immersed length from failure ratio X _k to the effective test area The breaking probability X = 1− (1−X _k ) ^{1 / k} is calculated (step 103). And <3> as the determination of the test piece area, from the function obtained by substituting the fracture probability X per unit immersion length into the fracture probability X _n = 1− (1-X) ⁿ when the immersion length ⁿ Then, the immersion length at which a desired breaking probability is obtained is calculated (step 104).

  Each procedure will be described in detail below.

<1> Evaluation of Effective Specimen Area Effective specimen area here refers to the specimen area where fracture due to hydrogen embrittlement actually occurs evenly in a specific area of the specimen when hydrogen embrittlement characteristics are evaluated. It is defined as For the effective test piece area, a hydrogen embrittlement test is performed a plurality of times under predetermined conditions, and the area where the test piece is broken for each test is recorded to evaluate the distribution of the broken area.

  In FIG. 2, the relationship between the frequency | count of a fracture | rupture and a fracture | rupture position at the time of performing a hydrogen embrittlement test 12 times with respect to the PC reinforcement taken out from the prestressed concrete structure is shown. FIG. 3 shows an outline of a test piece and an electrochemical cell (test cell) in the hydrogen embrittlement test apparatus used for the hydrogen embrittlement test. As shown in FIG. 3, since the hydrogen embrittlement test is performed on a PC rebar with an electrochemical cell attached, in order to simplify the notation, FIG. 2 shows the fracture position of the PC rebar in contact with the PC rebar and an aqueous solution. It was shown by the distance from the lower end.

  From the results shown in FIG. 2, the breaking position is broken regardless of the center portion or the end portion. In this experiment, the contact area per unit length between the PC reinforcing bar and the test solution can be regarded as the effective test piece area. I confirmed that I can do it.

The experimental conditions of the hydrogen embrittlement test were as follows: PC rebar loaded with a load 0.7 times the tensile strength (1420 MPa) according to JIS standards was applied to 1M (mol) sodium hydrogen carbonate (NaHCO ₃ ). It is immersed in an aqueous solution to which 1 wt% ammonium thiocyanate (NH ₄ SCN) is added, and the contact area of the PC rebar and the aqueous solution is 42.4 cm ² (deformed round bar, diameter 0.9 cm, immersion length 15 cm), -1000 mVvs. Hydrogen was absorbed by applying a potential of SSE, and the test time was 6 hours at maximum.

<2> Calculation of fracture probability with respect to effective test piece area The fracture probability with respect to the effective test piece area is calculated based on the fracture probability under the conditions of a hydrogen embrittlement test in which there are rebars that break and rebars that do not break. The method of calculating the fracture probability with respect to the effective test area will be described using the following experimental results. In order to simplify the calculation, the unit was calculated not by area but by immersion length.

(Experimental result)
When the contact area between the PC rebar and the test solution was 8.48 mm ² (diameter: 0.9 cm, immersion length: 3 cm), the test was performed 30 times under the hydrogen embrittlement test conditions used in the evaluation of the effective test piece area. Of these, 22 fractures occurred.

(Calculation method)
FIG. 4 is a conceptual diagram showing the relationship between the immersion length n and the fracture probability X in order to consider the fracture probability when the immersion length is n, where X is the fracture probability per unit immersion length. For example, the breakage probability X2 when the immersion length is ₂ is the probability that the breakage occurs in any region of the immersion length of 0 to 1 or 1 or ₂ , so that the immersion length is 0 to 1 or 1 to 2. The probability of not breaking in any of the areas is a value obtained by subtracting from 1. Therefore, in the case where the contact area per unit length is the effective test piece area, since the rupture occurs without being biased to a specific region, the rupture probability is the same in all regions, so it can be expressed as follows: it can.

Fracture probability X ₂ = 1− (1-X) ² when immersion length is ²
Similarly, when the immersion length 3 or later is described,
Fracture probability X ₃ = 1− (1-X) ³ when the immersion length is ³
Fracture probability X _k = 1− (1-X) ^k when the immersion length is k (1)
Therefore, it can be considered that the fracture probability per unit immersion length can be expressed by the following formula when the fracture probability is an arbitrary immersion length k.

Fracture probability per unit immersion length X = 1− (1−X _k ) ^{1 / k} (2)
Based on this formula (2), when the fracture probability X per unit immersion length (1 cm) is determined from the fracture probability 73.3% (= 22/30) at the immersion length of 3 cm obtained in the above experimental results, 35. 6%. A function obtained by substituting this value into the equation (1), that is, obtained by substituting X = 0.356 into the fracture probability X _n = 1− (1-X) ⁿ when the immersion length is n. From the function, the plot shown in FIG. 5 is obtained.

<3> Determination of test piece area From the plot of FIG. 5, if the immersion length is 10 cm or more in the present reinforcing bars and test conditions, it can be expected that all test pieces will break in about 10 test times. In fact, using a cell that can be tested at an immersion length of 10 cm and tested 12 times, it broke 11 times.

[4] Determine the specific liquid amount.
For the specific liquid volume, prepare test cells with different specific liquid volumes, charge the test piece with hydrogen under the determined test conditions, check the liquid property change during the test time, and make sure that the change volume is below the specified value. To decide. For example, if a test solution is used to simulate an actual environment, the judgment standard is based on a pH of 11 or less at which concrete neutralization progresses and rebar corrosion progresses (see Non-Patent Document 7).

[5] Determine the test cell shape.
The test cell shape may be determined for each test condition determined in [1]. For example, a buffer solution having a pH of 7.8 to 8.3 in which 0 to 1 wt% ammonium thiocyanate is added to the test solution, and the control potential is −700 to −1000 mVvs. In the method for evaluating hydrogen embrittlement resistance of PC steel, characterized in that the electric potential is SSE or higher and the temperature of the test solution is 35 to 50 ° C., the immersion length is 15 cm or more and the specific liquid volume is 3 ml / cm ^2. Any test cell shape that can ensure the above is sufficient. The material of the test cell need not affect the liquidity of the test solution. For example, acrylic may be selected.

(Test example)
Hereinafter, examples for evaluating the hydrogen embrittlement resistance of the test pieces are shown. FIG. 6 shows a schematic diagram of an evaluation test apparatus for evaluating hydrogen embrittlement resistance. The experiment was carried out under the test conditions shown in Table 2 using the evaluation test apparatus schematically shown in FIG.

  The taken out PC steel was used for the test piece. The test piece length was 45 cm in total length, and the length of the test piece immersed in the solution (immersion length) was 15 cm.

  Here, the test temperature is set to room temperature (about 20 ° C.), but may be set to a high temperature of about 35 to 50 ° C. by controlling the temperature of the test solution according to the purpose of the test (when an accelerated test is performed).

  With the evaluation test apparatus shown in FIG. 6, a load is applied to the test piece 5 with a weight 6 or the like, the test piece 5 is immersed in the solution in the container 1, the test piece 5 is used as a working electrode, and the potentiostat 2 Then, hydrogen charging was performed using the reference electrode 3 and the counter electrode 4. That is, hydrogen was charged while stress was applied to the test piece 5.

The solution in the container 1 was a 1M NaHCO ₃ aqueous solution (initial pH = 7.8 to 8.3) to which 1 wt% NH ₄ SCN was added. A silver / silver chloride electrode (SSE) was used as the reference electrode 3, and a platinum wire was used as the counter electrode 4. The potential is -1000 mVvs. Controlled to SSE. Under such an environment, the test piece 5 was charged with hydrogen.

  In addition, in the cathode charging method in a test solution to which an ammonium thiocyanate aqueous solution is added, which is a conventional technique, a change in liquid property due to ammonium thiocyanate has been pointed out. Therefore, it can be estimated that the smaller the amount of ammonium thiocyanate added, the smaller the effect. Therefore, it is clear that the effect of suppressing the influence of the liquid property change caused by ammonium thiocyanate can be obtained if the addition amount is less than 1% mentioned in this example.

  The potential was also -1000 mVvs. If it is higher than SSE, the current flowing by the electrochemical reaction is small, and since the influence on the pH of the test solution is small, it is clear that the effect of suppressing the influence of the liquid property change can be obtained.

(Specific liquid volume)
Using test cells with different specific liquid amounts, charge the hydrogen, and determine the specific liquid amount from the range where it was confirmed that the pH of the test solution was within the predetermined criteria. Stable test results can be obtained without doing so. Since the test solution used in this example is characterized by simulating an actual environment, the judgment standard is based on pH 11 or less at which the neutralization of concrete proceeds and the corrosion of reinforcing bars proceeds.

As a test example, a test cell having a specific liquid volume of 3, 6, 12, 18 ml / cm ² is prepared, and hydrogen charging is performed under the test conditions shown in Table 2 (no stress load). The change in pH of the test solution was investigated from 42 hours after the start.

FIG. 7 shows the change over time in pH with respect to the time of hydrogen charging of the test solution at each specific solution amount. In any specific liquid amount, the pH is 11 or less at which corrosion of reinforcing bars proceeds. Although the pH increases with time, the amount of change is 0.7, and does not exceed the amount of fluctuation 2 (after 48 hours) in conventional research (see Non-Patent Document 8). If it is ² or more, the fluctuation amount of pH can be suppressed to 1 or less.

In addition, since the influence of the electrochemical reaction on the pH of the test solution is smaller as the specific liquid volume increases, it is clear that the same effect can be obtained if there is a specific liquid volume of 18 ml / cm ² or more that has been verified. It is.

(Test cell shape)
The test cell is determined for each test condition determined in [1], and has a shape that can secure the immersion length determined in [3] and the specific liquid amount determined in [4]. In FIG. 8, an example of the test cell shape in the hydrogen embrittlement resistance evaluation method of PC steel materials is shown. Here, for example, a buffer solution having a pH of 7.8 to 8.3 in which 0 to 1 wt% ammonium thiocyanate is added to the test solution, and the control potential is −700 to −1000 mVvs. The potential is SSE or higher, and the temperature of the test solution is 35-50 ° C.

Since the immersion length is 15 cm or more, the test cell height is 20 cm. The specific liquid volume may be 3 ml / cm ² or more, but a silver silver chloride electrode having a diameter of 10.3 mm and a height of 148 mm is used as the reference electrode 3, and a platinum black electrode having a diameter of 7 cm and a height of 20 cm is used as the counter electrode 4 Since the inner diameter is 8 cm, the specific liquid amount is 18 ml / cm ² . The counter electrode 4 is formed by rolling a platinum black mesh sheet into a cylindrical shape, and is arranged along the inner wall surface of the container 1 so that the reference electrode 3, the counter electrode 4, and the test piece 5 do not contact each other. For example, the distance between the counter electrode 4 and the test piece 5 can be set to about 3 cm, and the distance between the reference electrode 3 and the counter electrode 4 can be set to about 1 to 2 cm.

  The test cell container 1 is made of acrylic that does not affect the liquidity of the test solution, and the container 1 is controlled so that the temperature of the test solution is kept constant by circulating temperature-adjusted water between the outer tank and the inner tank. Use a constant temperature bath. The thickness of the outer tub is 5 mm to ensure strength, and the thickness of the inner tub is 3 mm for quick temperature control. The distance between the outer tank and the inner tank is set to 1 to 2 cm.

  By using a test cell determined according to the procedure of the present invention, the test result is stabilized without using a test cell larger than necessary, and the test time required for temperature control is further suppressed, as compared with the conventional technique. Can do. A material suitable for the PC steel used for the structure can be selected more accurately and in a short time, which can contribute to the improvement of the long-term reliability of the structure.

It should be noted that the present invention is not limited to the embodiment described above, and it is obvious that many modifications can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is. For example, the rebar potential is controlled in order to allow the rebar to absorb hydrogen, but the present invention can also be applied to a test in which the rebar is corroded or exposed to a high-pressure hydrogen gas environment such as an NH ₄ SCN aqueous solution.

  Thus, in the present invention, in the hydrogen embrittlement test, when there is a reinforcing bar that does not break and a reinforcing bar that does not break, the fracture probability per unit test piece area is calculated, and the test piece area is determined from the predetermined number of tests. By using a test apparatus in which a test cell is designed and manufactured based on the area of the test piece, the probability of breaking within a predetermined test time can be improved without unnecessarily increasing the test apparatus. The test cell only needs to have a volume and shape that allow the determined test piece area to be brought into contact with the test solution reliably, and may be designed in consideration of fluctuations in the liquid level due to temperature changes and the like.

Claims (7)

When a hydrogen embrittlement test is performed a plurality of times by immersing a rebar test piece in a test solution, there is no bias in the distribution of breakage positions of the rebar test piece due to hydrogen embrittlement. Determining a first specimen area in contact with the solution;
Determining the probability of breakage of the rebar test piece of the first test piece area determined;
Calculating a fracture probability per unit area from the fracture probability and the first specimen area;
Based on the calculated fracture probability per unit area, the fracture probability at any test piece area where the test piece comes into contact with the test solution is obtained, and the test piece becomes the desired value. Calculating a second test piece area in contact;
A method of calculating a test piece area in a hydrogen embrittlement characteristic evaluation test characterized by comprising: In the step of calculating the fracture probability per unit area, the fracture probability X per unit area is calculated from X = 1− (the fracture probability X _{k at which the} specimen of the reinforcing bar having the first test piece area is broken. It calculates as 1- _Xk ) ^{1 / k} , The calculation method of the test piece area in the hydrogen embrittlement characteristic evaluation test of Claim 1 characterized by the above-mentioned. The step of calculating the second specimen area in which the fracture probability takes a desired value includes the fracture probability X _n in the arbitrary specimen area, from the fracture probability X per unit area to X _n = 1− (1 -X) The calculation method of the test piece area in the hydrogen embrittlement property evaluation test according to claim 1 or 2, wherein the calculation is performed as ⁿ .   4. The hydrogen embrittlement test according to claim 1, wherein the hydrogen embrittlement test is a hydrogen embrittlement test by cathode charging in which a negative potential is applied to the reinforcing bar with respect to a test solution used in the hydrogen embrittlement test. The calculation method of the test piece area in the hydrogen embrittlement property evaluation test described. As test conditions for the hydrogen embrittlement characteristic evaluation test, a test piece, a test solution in which the test piece is immersed, a hydrogen charging method for the test piece immersed in the test solution, and a load stress applied to the test piece during the hydrogen charge A first step to be determined;
A second step of determining an electrode used for the hydrogen charge;
A third step of determining a test strip area where the test strip comes into contact with the test solution;
A fourth step of determining a specific amount of the test solution with respect to the test piece;
A fifth step of calculating a test cell size in which the test piece and the determined electrode can be inserted without contacting each other, and the test piece area and the specific liquid amount can be realized;
A test cell size calculation method in a hydrogen embrittlement property evaluation test, comprising:   The test piece area determined in the third step is the second test piece area calculated by the test piece area calculation method in the hydrogen embrittlement property evaluation test according to any one of claims 1 to 4. The method for calculating the test cell size in the hydrogen embrittlement characteristic evaluation test according to claim 5.   The specific liquid amount determined in the fourth step is determined so that the amount of change in the liquid property of the test solution when a hydrogen embrittlement characteristic evaluation test is performed for a predetermined time under the test conditions is smaller than a predetermined value. The method for calculating the test cell size in the hydrogen embrittlement characteristic evaluation test according to claim 5 or 6.

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