Tank toughness reliability evaluation method

Abstract

A method for evaluating the toughness reliability of a tank, comprising the steps of: acquiring a required fracture toughness value on the basis of the change over time of a stress amplification factor and the design life of the tank; a step of acquiring a transition temperature of the material from a Charpy transition curve based on a Charpy impact test of the tank; acquiring a fracture toughness value according to a fracture toughness test of the material of the tank; a step for acquiring design tolerance conditions on the basis of the relationship between a temperature index, which is the reciprocal of the difference between each test temperature and the transition temperature, and the fracture toughness value at each test temperature; acquiring a required temperature index according to the design allowable condition and the required fracture toughness value; a step of acquiring an allowable Charpy transition curve having a required transition temperature based on the required temperature index; and a step for evaluating the toughness reliability of the material of the can on the basis of the allowable Charpy transition curve.

Description

Technical Field

[0001] The invention relates to a method for evaluating the toughness reliability of a tank.

[0002] This application claims priority to Japanese Patent Application No. 2022-118784 filed in Japan on July 26, 2022, and the contents are incorporated herein by reference. Background Art

[0003] Various articles manufactured using metal materials are required to have strength and toughness required for the articles. For example, Patent Document 1 discloses a method for manufacturing steel having excellent low-temperature toughness of a heat-affected portion due to welding.

[0004] Previous technical literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Publication No. 5-247531 Summary of the invention

[0007] Technical issues to be solved by the invention

[0008] However, in tanks storing liquefied gases such as LPG (liquefied petroleum gas), the thickness, strength, toughness, etc. of the material forming the tank are determined according to regulations. In contrast, the pressure inside a tank storing liquefied carbon dioxide is the same as that of a tank storing LPG, and the temperature inside the tank is lower. Therefore, if materials such as high-tensile steel used for LPG tanks are directly applied to tanks storing liquefied carbon dioxide, the required toughness may not be ensured.

[0009] Therefore, it is possible to use new materials to replace existing materials for liquefied carbon dioxide tanks, but the actual situation is that the rules such as toughness requirements related to new materials have not yet been determined.

[0010] Furthermore, the fracture toughness value is affected by temperature and stress state. Therefore, when investigating the toughness by simulating the actual machine state, a large-scale fracture toughness test is required. As a result, it is sometimes difficult to obtain the toughness under the conditions close to the actual machine state in terms of cost, equipment, and time.

[0011] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a can toughness reliability evaluation method capable of appropriately and easily evaluating the toughness of the can.

[0012] Means for solving technical problems

[0013] In order to solve the above-mentioned problems, the toughness reliability evaluation method of the tank according to the present invention includes the following steps: a step of obtaining a required fracture toughness value; a step of obtaining a material transition temperature; a step of obtaining a fracture toughness value; a step of obtaining a design allowable condition; a step of obtaining a required temperature index; a step of obtaining an allowable Charpy transformation curve; and a step of evaluating the toughness reliability of the material. In the step of obtaining the required fracture toughness value, the required fracture toughness value is obtained based on a predetermined temporal change of a stress magnification factor and a design life of the tank. In the step of obtaining the material transition temperature, the material transition temperature is obtained from a Charpy transformation curve based on a Charpy impact test at each test temperature of the material of the tank. In the step of obtaining the fracture toughness value, the fracture toughness value at each test temperature is obtained based on a fracture toughness test at each test temperature of the material of the tank. In the step of obtaining the design allowable condition, the design allowable condition for satisfying the fracture toughness characteristics with each temperature index is obtained based on the relationship between the temperature index and the fracture toughness value at each test temperature. The temperature index is the reciprocal of the difference between each test temperature and the transition temperature. In the step of acquiring the required temperature index, the required temperature index is acquired based on the design allowable condition and the required fracture toughness value. In the step of acquiring the allowable Charpy transformation curve, an allowable Charpy transformation curve having a required transformation temperature based on the required temperature index is acquired. In the step of evaluating the toughness reliability of the material, the toughness reliability of the material of the tank is evaluated based on the allowable Charpy transformation curve.

[0014] The toughness reliability evaluation method of a tank according to the present invention evaluates the toughness reliability of the tank based on the transition temperature of the material obtained from the Charpy transition curve of the Charpy impact test at each test temperature of the tank material and the fracture toughness value at each test temperature obtained from the fracture toughness test at each test temperature of the tank material. The toughness reliability evaluation method of the tank includes: a step of obtaining a required fracture toughness value; a step of obtaining a design allowable condition; a step of obtaining a required temperature index; a step of obtaining an allowable Charpy transition curve; and a step of evaluating the toughness reliability of the material. In the step of obtaining the required fracture toughness value, the required fracture toughness value is obtained based on the time change of a predetermined stress magnification factor and the design life of the tank. In the step of obtaining the design allowable condition, the design allowable condition that satisfies the fracture toughness characteristics with each temperature index is obtained based on the relationship between the temperature index and the fracture toughness value at each test temperature. The temperature index is the reciprocal of the difference between each test temperature and the transition temperature. In the step of obtaining the required temperature index, the required temperature index is obtained based on the design allowable condition and the required fracture toughness value. In the step of acquiring the allowable Charpy transformation curve, an allowable Charpy transformation curve having a required transformation temperature based on the required temperature index is acquired. In the step of evaluating the toughness reliability of the material, the toughness reliability of the material of the tank is evaluated based on the allowable Charpy transformation curve.

[0015] Effects of the Invention

[0016] According to the can toughness reliability evaluation method of the present invention, the toughness of the can can be appropriately and easily evaluated. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a cross-sectional view showing an example of a tank to be evaluated by the tank toughness reliability evaluation method according to the embodiment of the present invention.

[0018] Figure 2 This is a flowchart showing the procedure of a tank toughness reliability evaluation method according to an embodiment of the present invention.

[0019] Figure 3 This is a diagram showing an example of a Charpy transformation curve obtained in the step of obtaining the transformation temperature of the material according to the embodiment of the present invention.

[0020] Figure 4 This is a graph showing the correlation between the test temperature and the fracture toughness value obtained in the step of obtaining the fracture toughness value according to the embodiment of the present invention.

[0021] Figure 5This is a diagram showing the correlation between the elapsed period and the stress amplification factor obtained in the step of obtaining the required fracture toughness value according to the embodiment of the present invention.

[0022] Figure 6 This is a diagram showing the correlation between the temperature index and the fracture toughness value and the design line diagram obtained in the step of obtaining the allowable conditions according to the embodiment of the present invention.

[0023] Figure 7 This is a diagram showing an allowable Charpy transition curve acquired in the step of acquiring the allowable Charpy transition curve according to the embodiment of the present invention.

[0024] Figure 8 This is a diagram showing material evaluation based on an allowable Charpy transformation curve in the step of evaluating the toughness reliability of the material according to the embodiment of the present invention.

[0025] Fig. 9 This is a flowchart showing the steps of a method for evaluating the toughness reliability of a tank according to a modification of the embodiment of the present invention. DETAILED DESCRIPTION

[0026] Below, reference Figures 1 to 8 , a method for evaluating the toughness reliability of a tank according to an embodiment of the present invention is described.

[0027] (Structure of the tank)

[0028] like Figure 1 As shown, the tank 1 that is the evaluation object of the toughness reliability evaluation method of the tank in this embodiment can store liquefied gases such as liquefied carbon dioxide. The tank 1 is installed on the hull of a ship, the floating body of an offshore floating device, a liquefied gas storage facility on land, etc. The tank 1 is, for example, cylindrical. The tank 1 has a cylindrical portion 2 and an end plate portion 3. The cylindrical portion 2 extends along its central axis direction Dc. In this embodiment, the cylindrical portion 2 is formed into a cylindrical shape, and the cross-sectional shape orthogonal to its central axis direction Dc is circular. The end plate portions 3 are respectively arranged at the two end portions of the central axis direction Dc of the cylindrical portion 2. Each end plate portion 3 is hemispherical and closes the opening of the central axis direction Dc of the cylindrical portion 2. In addition, the tank 1 is not limited to a cylindrical shape, and can also be other shapes such as a sphere and a square. The tank 1 is formed by welding a plurality of steel plates.

[0029] (Sequence of the reliability evaluation method for tank toughness)

[0030] Figure 2 This is a flowchart showing the procedure of a tank toughness reliability evaluation method according to an embodiment of the present invention.

[0031] like Figure 2As shown, the toughness reliability evaluation method S10 of the tank includes: step S11 of obtaining the transformation temperature of the material, step S12 of obtaining the fracture toughness value, step S13 of obtaining the required fracture toughness value, step S14 of obtaining the design allowable condition, step S15 of obtaining the required temperature index, step S16 of obtaining the allowable Charpy transformation curve, and step S17 of evaluating the toughness reliability of the material.

[0032] Figure 3 This is a diagram showing an example of a Charpy transformation curve obtained in the step of obtaining the transformation temperature of the material according to the embodiment of the present invention.

[0033] In step S11 of obtaining the transition temperature of the material, a Charpy impact test is performed on the material used in the tank 1. The Charpy impact test is performed by applying an impact to a test piece of the material used in the tank 1 with a hammer to break the test piece, and the amount of energy required to break the test piece is obtained as the absorbed energy E. In this embodiment, Figure 3 As shown, the Charpy impact test is performed at a plurality of test temperatures (for example, test temperatures T1 to T5) including a use temperature range of the tank 1 assumed in a state where liquefied carbon dioxide is stored in the tank 1. In the present embodiment, at each of the test temperatures T1 to T5, for example, three Charpy impact tests are performed. At each of the test temperatures T1 to T5, the average value of the absorbed energy E in the three Charpy impact tests is set as a representative value of the absorbed energy E at each of the test temperatures T1 to T5. In addition, the test temperature of the Charpy impact test performed in this step S11 and the number of tests in each test number can be appropriately changed.

[0034] Next, in the step S11 of obtaining the transition temperature of the material, the Charpy transition curve L1 is obtained based on the correlation between the multiple test temperatures T1 to T5 and the magnitude of the absorbed energy E at each test temperature T1 to T5 of the material of the tank 1. In addition, in the obtained Charpy transition curve L1, the transition temperature vTrE of the material of the tank 1 is obtained. Among them, the intermediate value Em between the upper limit value Eu and the lower limit value Eb of the absorbed energy E in the Charpy transition curve L1 is obtained. On the Charpy transition curve L1, the temperature at the obtained intermediate value Em is obtained as the transition temperature vTrE. Here, the intermediate value Em is (upper limit value Eu+lower limit value Eb) / 2.

[0035] Figure 4 This is a graph showing the correlation between the test temperature and the fracture toughness value obtained in the step of obtaining the fracture toughness value according to the embodiment of the present invention.

[0036] In step S12 of obtaining the fracture toughness value, a fracture toughness test is performed on the material used in the tank 1. In the fracture toughness test, a notch is formed on a test piece of the material used in the tank 1, and a load is applied to the test piece. The stress magnification factor when the test piece breaks due to a crack extending from the notch is obtained as the fracture toughness value Z. The stress magnification factor indicates the strength of the stress distribution near the front end of the crack. In this embodiment, Figure 4 As shown, the fracture toughness test is performed at each of the test temperatures T1 to T5 which are the same as the Charpy impact test performed in step S11. In step S12, the fracture toughness value Z at each test temperature T1 to T5 is obtained based on the fracture toughness test at each test temperature T1 to T5 of the material of the tank 1.

[0037] The above-mentioned step S11 and step S12 can be performed by the manufacturer of the tank 1 at the manufacturing site of the tank 1, or can be performed by the material manufacturer of the steel plate used to manufacture the tank 1. As long as it is a material manufacturer, it has equipment for performing a Charpy impact test and a fracture toughness test. Therefore, at the manufacturing site of the tank 1, the necessity of performing a fracture toughness test is particularly suppressed.

[0038] Figure 5 This is a diagram showing the correlation between the elapsed period and the stress amplification factor K obtained in the step of obtaining the required fracture toughness value according to the embodiment of the present invention.

[0039] In step S13 of obtaining the required fracture toughness value, the required fracture toughness value Zr is obtained based on the temporal change of the predetermined stress magnification factor K and the design life of the tank 1. Specifically, in the tank 1, when cracks of a predetermined size already exist from the initial stage, the temporal change of the cracks when the tank 1 is used is predicted by simulation. The simulation is performed based on the history of the predetermined stress. Based on the prediction result based on the simulation, as shown in FIG. Figure 5 As shown, a correlation curve L2 is obtained showing the correlation between the elapsed time from the start of use of the tank 1 and the stress magnification factor K. In the obtained correlation curve L2, the magnitude of the stress magnification factor K at the preset design life Te of the tank 1 is obtained as the required fracture toughness value Zr.

[0040] Figure 6 This is a diagram showing the correlation between the temperature index and the fracture toughness value and the design line diagram acquired in the step of acquiring the design allowable conditions according to the embodiment of the present invention.

[0041] In step S14 of acquiring the design permissible conditions, first, the temperature index Y is acquired. The temperature index Y is calculated by the following formula (1) based on the test temperatures T1 to T5 used in steps S11 and S12 and the transition temperature vTrE acquired in step S11. As shown in formula (1), the temperature index Y is the reciprocal of the difference between each test temperature T1 to T5 and the transition temperature vTrE. The temperature index Y is calculated corresponding to each of the test temperatures T1 to T5.

[0042] Temperature index Y = (test temperature (T1 ~ T5) - transition temperature vTrE) -1 …… (1)

[0043] Then, in step S14 , a correlation graph L3 is acquired which shows the correlation between the calculated temperature index Y corresponding to each of the test temperatures T1 to T5 and the fracture toughness value Z at each of the test temperatures T1 to T5 acquired in step S12 .

[0044] In step S14, the design line diagram L4 indicating the design allowable conditions is obtained based on the obtained correlation line diagram L3. The design line diagram L4 is set at a predetermined interval with respect to the correlation line diagram L3, with the predetermined safety estimated. The fracture toughness value Z of each temperature index Y in the design line diagram L4 is lower than the fracture toughness value Z in the correlation line diagram L3. Figure 6 , the design line graph L4 is set in parallel with the correlation line graph L3.

[0045] In the step S15 of acquiring the required temperature index, the required temperature index Yr is acquired based on the required fracture toughness value Zr acquired in the step S13 and the design line diagram L4 indicating the design allowable conditions set in the step S14. Here, the value of the temperature index Y corresponding to the required fracture toughness value Zr is acquired as the required temperature index Yr based on the design line diagram L4.

[0046] Figure 7 This is a diagram showing an allowable Charpy transition curve acquired in the step of acquiring the allowable Charpy transition curve according to the embodiment of the present invention.

[0047] In step S16 of acquiring the permissible Charpy transition curve, the required transition temperature Tr is acquired by the following equation (2) based on the required temperature index Yr acquired in step S15 and the preset lower limit of the design temperature. Here, the transition temperature vTrE obtained based on the required temperature index Yr is acquired as the required transition temperature Tr.

[0048] Required temperature index Yr = (lower limit of design temperature - required transformation temperature Tr) -1 …… (2)

[0049] Here, the above-mentioned design temperature lower limit is the lower limit value of the design temperature of the tank 1 .

[0050] In step S16, the allowable Charpy transition curve L5 is obtained based on the intermediate value Em between the upper limit value Eu and the lower limit value Eb of the absorbed energy E in the Charpy transition curve L1 obtained in step S11 and the obtained required transition temperature Tr. The allowable Charpy transition curve L5 is expressed by a preset function.

[0051] Figure 8 This is a diagram of material evaluation based on an allowable Charpy transformation curve in the step of evaluating the toughness reliability of the material according to the embodiment of the present invention.

[0052] In step S17 of evaluating the toughness reliability of the material, Figure 8 As shown, the toughness reliability of the material of the tank 1 is evaluated based on the allowable Charpy transformation curve L5 obtained in step S16. Step S17 is implemented, for example, when the tank 1 is actually manufactured. In this case, a test piece is taken out from the actually manufactured tank 1. An object in which the metal materials used in the tank 1 are joined by welding can also be used as a test piece.

[0053] In addition, step S17 can be implemented, for example, at the design stage of the tank 1. In step S17, for example, candidate materials that can be adopted as the material of the tank 1 are evaluated as test pieces.

[0054] The evaluation of the toughness reliability of the material is implemented by performing a Charpy impact test on the test piece. At this time, the set test temperature Tt of the Charpy impact test in step S17 is set to, for example, the lower limit of the design temperature. In addition, the set test temperature Tt can be set according to the thickness of the test piece. Specifically, for example, when the thickness t of the test piece is 25<t≤30, the set test temperature Tt is set to a temperature 10°C lower than the design temperature of the tank 1 or a temperature lower than -20°C. And, when the thickness t of the test piece is 30<t≤35, the set test temperature Tt is set to a temperature 15°C lower than the design temperature of the tank 1 or a temperature lower than -20°C. When the thickness t of the test piece is 35<t≤40, the set test temperature Tt is set to a temperature 20°C lower than the design temperature of the tank 1. In addition, the set test temperature Tt shown here is only an example and can be appropriately changed.

[0055] In the present embodiment, the set test temperature Tt of the Charpy impact test in step S17 is set to only one determined as described above, for example. That is, the Charpy impact test in step S17 is performed at only one set test temperature Tt.

[0056] The toughness reliability of the material of the tank 1 is evaluated based on the allowable Charpy transformation curve L5. Specifically, it is evaluated based on the required absorbed energy Et corresponding to the set test temperature Tt for implementing the Charpy impact test in the allowable Charpy transformation curve L5. That is, the result of the Charpy impact test of the test piece at the set test temperature Tt is used to determine whether the obtained absorbed energy E exceeds the required absorbed energy Et at the set test temperature Tt. As a result, if the absorbed energy E of the Charpy impact test at the set test temperature Tt in the test piece exceeds the required absorbed energy Et, it is determined that the toughness reliability of the material used in the test piece meets the requirements. And, in the case where the absorbed energy E of the Charpy impact test in the test piece does not exceed the required absorbed energy Et, it is determined that the toughness reliability of the material used in the test piece does not meet the requirements. In the case where it is determined that the requirements are not met, the designer (manufacturer) of the tank 1 changes the composition, plate thickness, etc. of the material used in the tank 1 and evaluates it again.

[0057] (Effect)

[0058] In the toughness reliability evaluation method S10 of the tank 1 of the above-mentioned embodiment, the material of the tank 1 is subjected to a Charpy impact test and a fracture toughness test to obtain the material's transition temperature vTrE and fracture toughness value Z. In addition, with respect to the tank 1, the required fracture toughness value Zr is obtained based on the temporal change of the predetermined stress magnification factor K and the design life of the tank 1. On this basis, the design allowable conditions for satisfying the fracture toughness characteristics with each temperature index Y are obtained based on the relationship between the reciprocal of the difference between each test temperature T1 to T5 and the transition temperature vTrE, that is, the temperature index Y and the fracture toughness value Z at each test temperature T1 to T5. In addition, the required temperature index Yr is obtained based on the design allowable conditions and the required fracture toughness value Zr. Then, the allowable Charpy transformation curve L5 having the required transformation temperature Tr based on the required temperature index Yr is obtained. The toughness reliability of the material of the tank 1 can be appropriately evaluated based on the allowable Charpy transformation curve L5 obtained in this way.

[0059] Therefore, if the allowable Charpy transformation curve L5 is obtained in advance, the toughness reliability of the material used in the tank 1 can be evaluated by performing a Charpy test. That is, it is not necessarily necessary to perform a large-scale fracture toughness test at the manufacturing site of the tank 1.

[0060] Therefore, according to the toughness reliability evaluation method of the tank 1 of the present embodiment, the toughness of the tank 1 can be appropriately and easily evaluated.

[0061] In the above-described embodiment, based on the temporal change of the stress magnification factor K, the stress magnification factor K at the time when the tank 1 reaches the end of its design life can be obtained as the required fracture toughness value Zr.

[0062] In the above embodiment, the Charpy transformation curve L1 can be obtained based on the correlation between each test temperature T1 to T5 and the absorbed energy E when the Charpy impact test is performed at each test temperature T1 to T5. In addition, in the Charpy transformation curve L1, the temperature at the intermediate value Em between the upper limit value Eu and the lower limit value Eb of the absorbed energy E in the material of the tank 1 can be obtained as the transformation temperature vTrE of the material.

[0063] In the above embodiment, the correlation graph L3 can be obtained based on the relationship between the temperature index Y, which is the inverse of the difference between each test temperature T1 to T5 and the transition temperature vTrE, and the fracture toughness value Z at each test temperature T1 to T5. The design graph L4 can be set at a predetermined interval relative to the obtained correlation graph L3. The design graph L4 set in this way can be set as a design allowable condition.

[0064] In the above-described embodiment, the temperature index Y corresponding to the required fracture toughness value Zr is acquired as the required temperature index Yr in the design line diagram L4 as the design allowable condition.

[0065] In the above-described embodiment, by acquiring the transition temperature vTrE obtained based on the required temperature index Yr as the required transition temperature Tr, the allowable Charpy transition curve L5 can be acquired based on the required transition temperature Tr.

[0066] In the above embodiment, a test piece is taken out from the actually manufactured tank 1 and subjected to the Charpy impact test. Then, the set test temperature Tt and the absorbed energy E values ​​of the test piece obtained by the Charpy impact test are determined based on the allowable Charpy transformation curve L5, so that the toughness reliability of the test piece can be evaluated.

[0067] In the above-described embodiment, the test piece only needs to be subjected to the Charpy impact test at the set test temperature Tt, and thus the toughness reliability of the can 1 can be easily evaluated.

[0068] (Other Implementations)

[0069] As mentioned above, although the embodiment of the present invention is described in detail with reference to the drawings, the specific structure is not limited to this embodiment, and design changes and the like that do not depart from the scope of the gist of the present invention are also included.

[0070] Furthermore, in the above-described embodiment, the procedure of the toughness reliability evaluation method S10 of the tank 1 has been described, but the procedure may be appropriately changed.

[0071] Furthermore, in the above embodiment, steps S11 to S17 are shown as the toughness reliability evaluation method S10 of the tank 1, but for example, the material manufacturer that provides the material used in the tank 1 may perform the step S11 of obtaining the material transition temperature and the step S12 of obtaining the fracture toughness value in advance. In this case, the material manufacturer provides the obtained data of the material transition temperature vTrE and the fracture toughness value Z to the manufacturer of the tank 1.

[0072] Fig. 9 This is a flowchart showing the procedure of a method for evaluating the toughness reliability of a tank according to a modification of the embodiment of the present invention.

[0073] In this case, the manufacturer of the tank 1 determines the transition temperature vTrE and the fracture toughness value Z obtained in advance from the material manufacturer of the tank 1. Fig. 9 In the toughness reliability evaluation method S20 of the tank 1 shown, the same steps S13 to S17 as those in the above-described embodiment are implemented.

[0074] <Note>

[0075] The toughness reliability evaluation methods S10 and S20 of the tank 1 described in the embodiment can be understood, for example, as follows.

[0076] (1) The toughness reliability evaluation method S10 of the tank 1 according to the first embodiment includes the following steps:

[0077] Step S13, obtaining a required fracture toughness value Zr according to a predetermined temporal change of a stress amplification factor K and a design life of the tank 1;

[0078] Step S11, obtaining the transition temperature of the material from a Charpy transition curve L1 of a Charpy impact test at various test temperatures T1 to T5 of the material of the tank 1;

[0079] Step S12, obtaining fracture toughness values ​​at each of the test temperatures T1 to T5 according to the fracture toughness test of the material of the tank 1 at each of the test temperatures T1 to T5;

[0080] Step S14, according to the relationship between the temperature index Y, which is the inverse of the difference between each of the test temperatures T1 to T5 and the transition temperature vTrE, and the fracture toughness value Z at each of the test temperatures T1 to T5, obtaining the design allowable conditions for satisfying the fracture toughness characteristics with each temperature index Y;

[0081] Step S15, obtaining a required temperature index according to the design allowable condition and the required fracture toughness value Zr;

[0082] Step S16, obtaining an allowable Charpy transition curve L5 having a required transition temperature Tr based on the required temperature index Yr; and

[0083] Step S17, evaluating the toughness reliability of the material of the tank 1 according to the allowable Charpy transformation curve L5.

[0084] The toughness reliability evaluation method S10 of the tank 1 performs a Charpy impact test and a fracture toughness test on the material of the tank 1 to obtain the transformation temperature vTrE and the fracture toughness value Z of the material. In addition, with respect to the tank 1, the required fracture toughness value Zr is obtained based on the temporal change of the predetermined stress magnification coefficient K and the design life of the tank 1. On this basis, the design allowable conditions for satisfying the fracture toughness characteristics with each temperature index Y are obtained based on the relationship between the reciprocal of the difference between each test temperature T1 to T5 and the transformation temperature vTrE and the fracture toughness value Z at each test temperature T1 to T5. In addition, the required temperature index Yr is obtained based on the design allowable conditions and the required fracture toughness value Zr. Then, the allowable Charpy transformation curve L5 having the required transformation temperature Tr based on the required temperature index Yr is obtained. The toughness reliability of the material of the tank 1 can be appropriately evaluated based on the allowable Charpy transformation curve L5 obtained in this way.

[0085] Therefore, if the allowable Charpy transformation curve L5 is obtained in advance, the toughness reliability of the material used in the tank 1 can be evaluated by performing a Charpy test.

[0086] As a result, the toughness evaluation of the can 1 can be appropriately and easily performed.

[0087] (2) A second embodiment of the toughness reliability evaluation method S10 of the tank 1 is the toughness reliability evaluation method S10 of the tank 1 according to (1), wherein:

[0088] In the step S13 of obtaining the required fracture toughness value Zr, the stress magnification factor K when the tank 1 reaches its design life is obtained as the required fracture toughness value Zr based on the temporal change of the stress magnification factor K.

[0089] Thus, based on the temporal change of the stress magnification factor K, the stress magnification factor K at the time when the tank 1 reaches the designed life can be obtained as the required fracture toughness value Zr.

[0090] (3) The toughness reliability evaluation method S10 of the tank 1 according to the third aspect is the toughness reliability evaluation method S10 of the tank 1 according to (1) or (2), wherein:

[0091] In step S11 of obtaining the transition temperature of the material,

[0092] The Charpy transformation curve L1 is obtained according to the correlation between each of the test temperatures T1 to T5 and the absorbed energy E when the Charpy impact test is performed at each of the test temperatures T1 to T5.

[0093] The temperature at the intermediate value Em between the upper limit value Eu and the lower limit value Eb of the absorbed energy E in the material of the can 1 is obtained from the Charpy transition curve L1 as the transition temperature vTrE of the material.

[0094] Thus, the Charpy transformation curve L1 can be obtained based on the correlation between each test temperature T1 to T5 and the absorbed energy E when the Charpy impact test is performed at each test temperature T1 to T5. In addition, in the Charpy transformation curve L1, the temperature at the intermediate value Em between the upper limit value Eu and the lower limit value Eb of the absorbed energy E in the material of the tank 1 can be obtained as the material transformation temperature vTrE.

[0095] (4) The toughness reliability evaluation method S10 of the tank 1 according to the fourth aspect is any one of the toughness reliability evaluation methods S10 of the tank 1 described in (1) to (3), wherein:

[0096] In step S14 of obtaining the design permissible conditions,

[0097] A design line diagram L4 set at a specified interval relative to the correlation line diagram L3 is obtained as the design allowable condition, and the correlation line diagram L3 is obtained based on the relationship between the inverse of the difference between each of the test temperatures T1~T5 and the transition temperature vTrE, that is, the temperature index Y and the fracture toughness value Z at each of the test temperatures T1~T5.

[0098] Thus, the correlation diagram L3 can be obtained based on the relationship between the temperature index Y, which is the inverse of the difference between each test temperature T1 to T5 and the transition temperature vTrE, and the fracture toughness value Z at each test temperature T1 to T5. The design diagram L4 can be set at a predetermined interval relative to the obtained correlation diagram L3. The design diagram L4 set in this way can be set as a design allowable condition.

[0099] (5) A fifth aspect of the toughness reliability evaluation method S10 of the tank 1 is the toughness reliability evaluation method S10 of the tank 1 according to (4), wherein:

[0100] In step S15 of obtaining the required temperature index,

[0101] Based on the design line diagram L4 as the design allowable condition, the temperature index Y corresponding to the required fracture toughness value Zr is acquired as the required temperature index Yr.

[0102] Thus, in the design line diagram L4 as the design allowable condition, the temperature index Y corresponding to the required fracture toughness value Zr is acquired as the required temperature index Yr.

[0103] (6) The toughness reliability evaluation method S10 of the tank 1 according to the sixth aspect is any one of the toughness reliability evaluation methods S10 of the tank 1 described in (1) to (5), wherein:

[0104] In step S16 of obtaining the allowable Charpy transition curve L5,

[0105] Obtaining the transition temperature vTrE obtained according to the required temperature index Yr as the required transition temperature Tr,

[0106] The allowable Charpy transition curve L5 is obtained according to the required transition temperature Tr.

[0107] Thus, by acquiring the transition temperature vTrE obtained from the required temperature index Yr as the required transition temperature Tr, the allowable Charpy transition curve L5 can be acquired from the required transition temperature Tr.

[0108] (7) The toughness reliability evaluation method S10 of the tank 1 according to the seventh aspect is any one of the toughness reliability evaluation methods S10 of the tank 1 described in (1) to (6), wherein:

[0109] In step S17 of evaluating the toughness reliability of the material,

[0110] A test piece was taken out from the actually manufactured can 1 and subjected to the Charpy impact test.

[0111] The set test temperatures T1 to T5 and the absorbed energy E values ​​in the test piece obtained by the Charpy impact test are determined based on the allowable Charpy transformation curve L5.

[0112] Thus, the Charpy impact test is performed on the material actually used in the tank 1 as a test piece. Then, the test temperatures T1 to T5 and the absorbed energy E values ​​of the test piece obtained by the Charpy impact test are determined based on the allowable Charpy transformation curve L5, thereby evaluating the toughness reliability of the test piece.

[0113] (8) The toughness reliability evaluation method S10 of the tank 1 according to the eighth aspect is the toughness reliability evaluation method S10 of the tank 1 according to (7), wherein:

[0114] In the toughness reliability evaluation step S17 of the material,

[0115] The Charpy impact test is performed on the test piece at a preset test temperature Tt.

[0116] Thus, the test piece only needs to be subjected to the Charpy impact test at the set test temperature Tt, and the toughness reliability of the can 1 can be easily evaluated.

[0117] (9) The toughness reliability evaluation method S20 of the tank 1 according to the ninth aspect evaluates the toughness reliability of the tank 1 based on the transition temperature vTrE of the material obtained from the Charpy transition curve L1 of the Charpy impact test at each test temperature T1 to T5 of the material of the tank 1 and the fracture toughness value Z at each test temperature T1 to T5 obtained from the fracture toughness test at each test temperature T1 to T5 of the material of the tank 1. The toughness reliability evaluation method S20 of the tank 1 comprises the following steps:

[0118] Step S13, obtaining a required fracture toughness value Zr according to a predetermined temporal change of a stress amplification factor K and a design life of the tank 1;

[0119] Step S14, according to the relationship between the temperature index Y, which is the inverse of the difference between each of the test temperatures T1 to T5 and the transition temperature vTrE, and the fracture toughness value Z at each of the test temperatures T1 to T5, obtaining the design allowable conditions for satisfying the fracture toughness characteristics with each temperature index Y;

[0120] Step S15, obtaining a required temperature index according to the design allowable condition and the required fracture toughness value Zr;

[0121] Step S16, obtaining an allowable Charpy transition curve L5 having a required transition temperature Tr based on the required temperature index Yr; and

[0122] Step S17, evaluating the toughness reliability of the material of the tank 1 according to the allowable Charpy transformation curve L5.

[0123] In the toughness reliability evaluation method S20 of the tank 1, the material of the tank 1 is subjected to a Charpy impact test and a fracture toughness test in advance to obtain the material's transition temperature vTrE and fracture toughness value Z. In addition, with respect to the tank 1, the required fracture toughness value Zr is obtained based on the temporal change of the predetermined stress magnification coefficient K and the design life of the tank 1. On this basis, the design allowable conditions for satisfying the fracture toughness characteristics with each temperature index Y are obtained based on the relationship between the reciprocal of the difference between each test temperature T1 to T5 and the transition temperature vTrE, that is, the temperature index Y and the fracture toughness value Z at each test temperature T1 to T5. In addition, the required temperature index Yr is obtained based on the design allowable conditions and the required fracture toughness value Zr. Then, the allowable Charpy transformation curve L5 having the required transformation temperature Tr based on the required temperature index Yr is obtained. The toughness reliability of the material of the tank 1 can be appropriately evaluated based on the allowable Charpy transformation curve L5 obtained in this way.

[0124] Therefore, if the allowable Charpy transformation curve L5 is obtained in advance, the toughness reliability of the material used in the tank 1 can be evaluated by performing a Charpy test.

[0125] As a result, the toughness evaluation of the can 1 can be appropriately and easily performed.

[0126] Industrial Applicability

[0127] According to the can toughness reliability evaluation method of the present invention, the toughness of the can can be appropriately and easily evaluated.

[0128] Explanation of symbols

[0129] 1-tank, 2-cylindrical portion, 3-end plate portion, Dc-central axis direction, E-absorbed energy, Eu-upper limit value, Eb-lower limit value, Em-middle value, Et-required absorbed energy, K-stress magnification factor, L1-Charpy transformation curve, L2-correlation curve, L3-correlation line diagram, L4-design line diagram, L5-allowable Charpy transformation curve, S10, S20-toughness reliability evaluation method of tank, S11-step of obtaining the transformation temperature of the material, S12-step of obtaining the fracture toughness value, S13-step of obtaining required fracture toughness value, S14-step of obtaining design allowable conditions, S15-step of obtaining required temperature index, S16-step of obtaining allowable Charpy transformation curve, S17-step of evaluating toughness reliability of material, T1~T5-test temperature, Te-design life, Tr-required transformation temperature, vTrE-transformation temperature, Tt-set test temperature, Y-temperature index, Yr-required temperature index, Z-fracture toughness value, Zr-required fracture toughness value.

Claims

1. A method for evaluating the toughness reliability of a tank, comprising the following steps: The step of obtaining a required fracture toughness value based on a predetermined time variation of a stress magnification factor and a design life of the tank; A step of obtaining a transition temperature of the material from a Charpy transition curve based on a Charpy impact test at various test temperatures of the material of the can; A step of obtaining fracture toughness values ​​at each of the test temperatures according to a fracture toughness test of the material of the tank at each of the test temperatures; A step of obtaining a design allowable condition for satisfying fracture toughness characteristics at each temperature index based on a relationship between a temperature index that is a reciprocal of a difference between each test temperature and the transition temperature and a fracture toughness value at each test temperature; The step of obtaining a required temperature index according to the design allowable condition and the required fracture toughness value; The step of obtaining an allowable Charpy transformation curve having a required transformation temperature based on the required temperature indicator; and The step of evaluating the toughness reliability of the material of the tank according to the allowable Charpy transformation curve.

2. The tank toughness reliability evaluation method according to claim 1, wherein: In the step of obtaining the required fracture toughness value, the stress magnification factor when the tank reaches the design life is obtained as the required fracture toughness value based on the temporal change of the stress magnification factor.

3. The method for evaluating the toughness reliability of a tank according to claim 1 or 2, wherein: In the step of obtaining the transition temperature of the material, The Charpy transformation curve is obtained according to the correlation between each of the test temperatures and the absorbed energy when the Charpy impact test is performed at each of the test temperatures. A temperature that is an intermediate value between an upper limit value and a lower limit value of the absorbed energy in the material of the can is obtained from the Charpy transition curve as a transition temperature of the material.

4. The method for evaluating the toughness reliability of a tank according to claim 1 or 2, wherein: In the step of obtaining the design allowable conditions, A design line diagram set at a predetermined interval relative to a correlation line diagram is acquired as the design allowable condition, wherein the correlation line diagram is acquired based on the relationship between a temperature index which is the inverse of the difference between each of the test temperatures and the transformation temperature and a fracture toughness value at each of the test temperatures.

5. The method for evaluating the toughness reliability of a tank according to claim 4, wherein: In the step of obtaining the required temperature index, The temperature index corresponding to the required fracture toughness value is acquired as the required temperature index based on the design line diagram as the design allowable condition.

6. The tank toughness reliability evaluation method according to claim 1 or 2, wherein: In the step of obtaining the allowable Charpy transition curve, obtaining a transition temperature obtained according to the required temperature index as the required transition temperature, The allowable Charpy transition curve is obtained according to the required transition temperature.

7. The tank toughness reliability evaluation method according to claim 1 or 2, wherein: In the step of evaluating the toughness reliability of the material, A test piece was taken from the actually manufactured can and subjected to the Charpy impact test. The set test temperature and the absorbed energy values ​​in the test piece obtained by the Charpy impact test are determined based on the allowable Charpy transformation curve.

8. The tank toughness reliability evaluation method according to claim 7, wherein: In the step of evaluating the toughness reliability of the material, The Charpy impact test is performed on the test piece at a preset test temperature.

9. A method for evaluating the toughness reliability of a tank, wherein the method evaluates the toughness reliability of the tank according to a transition temperature of the material obtained from a Charpy transition curve of a Charpy impact test at each test temperature of the material of the tank and a fracture toughness value at each test temperature obtained from a fracture toughness test at each test temperature of the material of the tank, the method comprising the following steps: The step of obtaining a required fracture toughness value based on a predetermined change in stress magnification factor over time and the design life of the tank; A step of obtaining a design allowable condition for satisfying fracture toughness characteristics at each temperature index based on a relationship between a temperature index that is a reciprocal of a difference between each test temperature and the transition temperature and a fracture toughness value at each test temperature; The step of obtaining a required temperature index according to the design allowable condition and the required fracture toughness value; The step of obtaining an allowable Charpy transformation curve having a required transformation temperature based on the required temperature indicator; and The step of evaluating the toughness reliability of the material of the tank according to the allowable Charpy transformation curve.

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