Metal environment fatigue correction factor prediction method considering load retention effect

Abstract

The invention discloses a metal environment fatigue correction factor prediction method considering a load retention effect. The method comprises the following steps: preparing a tubular fatigue sample and a high-temperature and high-pressure water corrosion fatigue test simulation device; after a plurality of factors such as the loading strain rate, the loading strain amplitude, the temperature, the oxygen concentration and the load keeping are controlled to be fixed, a fatigue test is carried out on the austenitic stainless steel material, so that the influence of each factor on the fatigue life of the austenitic stainless steel is researched; based on a fatigue life curve of the austenitic stainless steel in ASME room temperature air, according to a fatigue test result in a high-temperature and high-pressure water environment, an austenitic stainless steel environment fatigue correction factor prediction model is established by combining the influence of factors such as a loading strain rate, a loading strain amplitude, temperature and oxygen concentration on the fatigue life; and establishing an austenitic stainless steel environmental fatigue correction factor prediction model considering the load retention effect by introducing the influence of a load type and retention time.

Description

Technical Field

[0001] This patent relates to the technical field of environmental fatigue experiments and numerical prediction of metal materials, and specifically relates to a method for predicting the environmental fatigue correction factor of metals considering the load hold effect. Background Art

[0002] During the operation of a pressurized water reactor nuclear power plant, in the coolant water environment, due to the changes in temperature and pressure during shutdown / startup transients and operation transients, the pressure boundaries such as steam generators, pressure vessels, and main pipelines may suffer from corrosion fatigue failure problems. The operating experience of nuclear power plants shows that the number of fatigue failure cases gradually increases with the increase in the service life of the nuclear power plant, which is related to the increase in fatigue cumulative damage of components with the increase in service time. When the corrosion fatigue life reaches the limit, it will evolve into crack initiation. When the crack penetrates the wall thickness of the service component under complex load conditions, leakage or instantaneous fracture will occur, with unthinkable consequences, seriously affecting the economy and safety of nuclear power plant operation.

[0003] Currently, many research institutions have studied the corrosion fatigue tests of nuclear power structure materials in high-temperature and high-pressure circulating water and the prediction models of environmental correction factors. The research found that the fatigue life of austenitic stainless steel may decrease by 10 - 100 times considering factors such as loading strain rate, loading strain amplitude, and different water chemistries (dissolved oxygen, temperature). Through literature research, it is found that the load hold effect still has an obvious impact on the environmental fatigue life of austenitic stainless steel. Therefore, to further obtain a more accurate environmental fatigue correction factor, conduct environmental fatigue life tests of austenitic stainless steel considering the load hold effect and establish a corresponding correction factor model, which is of great significance for designing the fatigue life of pressurized water reactor nuclear power plants, ensuring their safe operation, and life extension management. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for predicting the environmental fatigue correction factor of metals considering the load hold effect, so as to realize the prediction of the environmental fatigue correction factor of austenitic stainless steel under the coupling action of factors such as loading strain rate, loading strain amplitude, temperature, oxygen concentration, and load hold, and then obtain the fatigue life considering environmental correction based on the fatigue life in air, providing a basis for engineering structure design.

[0005] The technical solution of the present invention is as follows: A method for predicting the environmental fatigue correction factor of metals considering the load hold effect, comprising the following steps:

[0006] S1: Prepare tubular fatigue specimens of austenitic stainless steel;

[0007] S2: Prepare a simulation device for high-temperature and high-pressure circulating water corrosion fatigue tests;

[0008] S3: Under the condition of high-temperature and high-pressure water environment inside the specimen in S1, load the specimen to study different loading strain rates Under the conditions of load hold effect, oxygen concentration and temperature, the fatigue life N and the strain amplitude ε a Relationship between them;

[0009] S4: Based on the fatigue test data obtained in step S3, analyze the effects of factors such as loading strain rate, loading strain amplitude, temperature, oxygen concentration and load hold on the fatigue life of the specimen, and use the Langer equation to fit to obtain the specimen curve under high-temperature and high-pressure water environment, and the expression is formula (2)

[0010]

[0011] Among them, ε a Is the strain amplitude, N is the fatigue life, and A1, A2 and n1 are fitting parameters.

[0012] S5: Define the environmental fatigue correction factor F en , and the expression is formula (4)

[0013]

[0014] Among them, N air And N water Respectively represent the fatigue life in room-temperature air environment and the fatigue life coupling various environments; N air Is known;

[0015] S6: Fit the fatigue life prediction model of the specimen in room-temperature air, such as formula (5)

[0016] ln(N air ) = 6.954 - 2ln(ε a - 0.128) (5)

[0017] S7: Based on the test data in S3, establish the relationship between the loading strain rate And the fatigue correction factor of the loading strain rate , such as formula (6)

[0018]

[0019] S8: Based on the test data in S3, establish the relational expression between the temperature T and the temperature fatigue correction factor F en-T , such as formula (7)

[0020] ln(F en-T ) = 0.00572·(T - 100) (7)

[0021] S9: Based on the test data in S3, establish the relationship between the dissolved oxygen concentration DO and the oxygen concentration fatigue correction factor F en-o ;

[0022] S10: Based on steps S5 - S9, combine the formula to obtain the environmental fatigue factor F en of austenitic stainless steel material, and the expression is:

[0023]

[0024] T * = 0 (T ≤ 100°C)

[0025] T * = 0.00101(T - 100) (100°C ≤ T ≤ 325°C)

[0026] T * = 0.227 (T ≥ 325°C)

[0027] O * = 1 (DO < 20 ppb)

[0028] O * = 0.5 (DO ≥ 20 ppb)

[0029] S11: Considering the influence of load type and holding time, based on the high-temperature and high-pressure water environment fatigue correction factor F en establish a prediction model for the environmental fatigue correction factor F en-hold considering the hold-time effect

[0030] F en-hold = F hold ·F en

[0031] In the above S1, samples are taken axially at a position 1 / 4 wall thickness from the inner or outer surface of the main pipe. The gauge length of the sample is 20 mm, the outer diameter is 10 mm, and the inner diameter is 5 mm.

[0032] The surface roughness of the sample is better than 0.8 μm.

[0033] In the above S2, the water chemical environment solution medium of the simulated high-temperature and high-pressure cyclic water corrosion fatigue test device is selected as 500 ppb B 3+ , 2 ppm Li + ; the maximum temperature is 360°C; the control accuracy is ±1°C; the maximum pressure is 20 MPa; the dissolved oxygen concentration range is 10 ppb - 200 ppb.

[0034] In the above S3, the applied strain ratio is -1.

[0035] The above S3 includes

[0036] S3.1: Control the loading strain rate Keep the strain rate at 0.04% / s, the temperature at 325 °C, and the oxygen concentration < 10 ppb fixed, and study the effect of different loading strain amplitudes ε a on the fatigue life of the specimen;

[0037] S3.2: Control the loading strain amplitude ε a Keep it at 0.6%, the temperature at 325 °C, and the oxygen concentration < 10 ppb fixed, and study the relationship between the fatigue life N of the specimen and the loading strain amplitude ε a under different loading strain rates;

[0038] S3.3: Control the loading strain rate at 0.04% / s, the loading strain amplitude at 0.6%, and the oxygen concentration < 10 ppb fixed, and study the relationship between the fatigue life N of the specimen and the loading strain amplitude ε a at different temperatures;

[0039] S3.4: Control the loading strain rate at 0.04% / s, the loading strain amplitude at 0.6%, and the temperature at 325 °C fixed, and study the relationship between the fatigue life N of the specimen and the loading strain amplitude ε a under different oxygen concentrations;

[0040] S3.5: Control the loading strain rate at 0.04% / s, the loading strain amplitude at 0.6%, the temperature at 325 °C, and the oxygen concentration < 10 ppb fixed, and study the relationship between the fatigue life N of the specimen and the loading strain amplitude ε a under different load types and holding times;

[0041] In S3.1, different loading strain amplitudes ε a include 0.0004% / s, 0.004% / s, 0.01% / s, 0.4% / s, 4% / s.

[0042] In S3.2, different temperatures include 100 °C, 150 °C, 250 °C, 325 °C.

[0043] In S3.4, different oxygen concentrations include 10 ppb, 20 ppb, 50 ppb, 100 ppb, 200 ppb.

[0044] S3.5 includes:

[0045] S3.5.1: Conduct a triangular wave test at a temperature of 325 °C. When the fatigue life reaches 1 / 4 of the fatigue life in air, stop the test when the strain is 0, unload, drain the high-temperature and high-pressure water inside the specimen, turn on the heating furnace, raise the temperature to 420 °C, maintain the temperature and pressure for 36 h, and then restart the fatigue test at 325 °C until the specimen fails;

[0046] S3.5.2: Conduct a triangular wave test at a temperature of 325 °C. When the fatigue life reaches 1 / 4 of the fatigue life in air, stop the test by controlling the strain at the target peak value. Drain the high-temperature and high-pressure water inside the specimen, turn on the heating furnace, raise the temperature to 420 °C, maintain the temperature and pressure for 36 h, and then restart the fatigue test at 325 °C;

[0047] S3.5.3: Conduct a trapezoidal wave test at a temperature of 325 °C, maintain the peak temperature and pressure for 0.278 h, and directly carry out the fatigue test.

[0048] In S4, the fitting confidence level is greater than or equal to 0.97.

[0049] In S7, when the strain rate is lower than 0.0004% / s set it as a fixed value. When calculate the upper limit of the strain rate as 6.8% / s.

[0050] In S9, when the oxygen concentration ≥ 20 ppb, the fatigue life is about 2 times that under the condition of oxygen concentration < 10 ppb.

[0051] Therefore, in S11, F hold take 1.56.

[0052] The remarkable effect of the present invention lies in: obtaining an environmental fatigue correction factor calculation model by introducing the influences of factors such as loading strain rate, loading strain amplitude, temperature, oxygen concentration, and load holding, so as to predict the fatigue life of austenitic stainless steel materials in a coolant environment, which can provide guiding significance for revealing the environmental fatigue mechanism of austenitic stainless steel and the structural reliability design. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 Schematic diagram of the prediction process of the environmental fatigue correction factor of austenitic stainless steel considering the load holding effect

[0054] Figure 2 Schematic diagram of the geometric dimensions of a tubular fatigue specimen

[0055] Figure 3 Schematic diagram of the triangular wave load holding fatigue test procedure

[0056] Figure 4 Schematic diagram of the trapezoidal wave load holding fatigue test procedure

[0057] Figure 5 Fatigue life curves of austenitic stainless steel under different loading strain rate conditions

[0058] Figure 6 Environmental fatigue life curve of austenitic stainless steel considering the load holding effect

[0059] Figure 7 Comparison Curve between Environmental Fatigue Life Prediction Results Considering Load Retention Effect and Test Results Specific Embodiments

[0060] Numerous specific details are set forth in the following description in order to provide a thorough understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the connotation of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.

[0061] The terms used in one or more embodiments of the present application are for the purpose of describing specific embodiments only and are not intended to limit one or more embodiments of the present application. The singular forms "a", "the", and "said" used in one or more embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly dictates otherwise. It should also be understood that the term "and / or" used in one or more embodiments of the present application refers to and includes any or all possible combinations of one or more of the associated listed items.

[0062] It should be understood that although the terms first, second, etc. may be used in one or more embodiments of the present application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of one or more embodiments of the present application, the first may also be referred to as the second, and similarly, the second may also be referred to as the first.

[0063] The specific process implemented by the present invention is as Figure 1 shown. An embodiment for predicting the environmental fatigue factor of austenitic stainless steel considering the effects of loading strain rate, loading strain amplitude, temperature, oxygen concentration, and load retention effect is presented as follows:

[0064] S1: Prepare a tubular fatigue specimen of austenitic stainless steel, take a sample axially at a position 1 / 4 wall thickness from the inner or outer surface of the main pipeline. The gauge length of the specimen is 20 mm, the outer diameter is 10 mm, and the inner diameter is 5 mm, as Figure 2 shown.

[0065] In step S1, in order to better obtain the required test data, the fatigue specimen needs to consider the following preferred conditions:

[0066] 1. Preferably, the surface roughness of the specimen inside and outside is better than 0.8 μm.

[0067] 2. Preferably, after the specimen is processed, dimensional inspection is carried out to ensure compliance with the requirements.

[0068] S2: The simulated high-temperature and high-pressure circulating water corrosion fatigue test device includes four parts: a high-temperature and high-pressure circulating water circuit, an autoclave, a fatigue testing machine, and a control system. Among them, the water environment can precisely control the temperature and oxygen content.

[0069] In step S2, to better obtain the required test data, the test device needs to consider the following preferred conditions: The water flows inside the pipeline, and various conditions refer to those inside the specimen.

[0070] 1. Preferably, an Epsilon high-temperature extensometer is used to in-situ measure the strain of the gauge section of the fatigue specimen.

[0071] 2. Preferably, the water chemical environment solution medium is selected as 500 ppb B 3+ , 2 ppm Li + .

[0072] 3. Preferably, the high-temperature and high-pressure circulating water corrosion fatigue test device can achieve a maximum temperature of 360 °C with a control accuracy of ±1 °C; a maximum pressure of 20 MPa; and an oxygen concentration range of 10 ppb - 200 ppb.

[0073] S3: Under the high-temperature and high-pressure water environment inside the specimen in S1, the specimen is loaded in a strain-controlled manner until the specimen fails. Considering the fatigue life N (i.e., the number of fatigue cycles) and the strain amplitude ε under the conditions of different loading strain rates a , load hold effect, oxygen concentration, and temperature, the relationship is formed Figure 5 , 6 ;

[0074] The following sequence is adopted during the test:

[0075] S3.1: Control the loading strain rate to be 0.04% / s, the temperature to be 325 °C, and the oxygen concentration to be <10 ppb and keep them fixed, and study the influence of different loading strain amplitudes ε a (0.25%, 0.4%, 0.6%, 0.8%, 1.0%) on the fatigue life of the specimen;

[0076] S3.2: Control the loading strain amplitude ε a to be 0.6%, the temperature to be 325 °C, and the oxygen concentration to be <10 ppb and keep them fixed, and study the relationship between the fatigue life N of the specimen and the loading strain amplitude ε a under different loading strain rates (0.0004% / s, 0.004% / s, 0.01% / s, 0.4% / s, 4% / s);

[0077] S3.3: Keep the controlled loading strain rate at 0.04% / s, the loading strain amplitude at 0.6%, and the oxygen concentration < 10 ppb fixed, and study the relationship between the fatigue life N of the specimen and the loading strain amplitude ε at different temperatures (100 °C, 150 °C, 250 °C, 325 °C). a and the relationship;

[0078] S3.4: Keep the controlled loading strain rate at 0.04% / s, the loading strain amplitude at 0.6%, and the temperature at 325 °C fixed, and study the relationship between the fatigue life N of the specimen and the loading strain amplitude ε at different oxygen concentrations (10 ppb, 20 ppb, 50 ppb, 100 ppb, 200 ppb). a and the relationship;

[0079] S3.5: Keep the controlled loading strain rate at 0.04% / s, the loading strain amplitude at 0.6%, the temperature at 325 °C, and the oxygen concentration < 10 ppb fixed, and study the relationship between the fatigue life N of the specimen and the loading strain amplitude ε under different load types and holding times; Preferably, in the hold-time test, to consider the influence of different load types, the following load application forms are adopted, and the specific steps include: a and the relationship;

[0080] S3.5.1: Adopt a triangular-wave test at a temperature of 325 °C. When the fatigue life reaches 1 / 4 of the fatigue life in air (the fatigue life of the specimen in air is known), stop the test when the strain is 0, unload, drain the high-temperature and high-pressure water inside the tubular specimen, turn on the heating furnace, raise the temperature to 420 °C, maintain the temperature and pressure for 36 h, and then restart the fatigue test at 325 °C until the specimen fails; As shown Figure 3 in;

[0081] S3.5.2: Adopt a triangular-wave test at a temperature of 325 °C. When the fatigue life reaches 1 / 4 of the fatigue life in air, stop the test by controlling the strain at the target peak value, drain the high-temperature and high-pressure water inside the tubular specimen, turn on the heating furnace, raise the temperature to 420 °C, maintain the temperature and pressure for 36 h, and then restart the fatigue test at 325 °C;

[0082] S3.5.3: Adopt a trapezoidal-wave test at a temperature of 325 °C, maintain the peak temperature and pressure for 0.278 h, and directly carry out the fatigue test, as shown Figure 4 in;

[0083] Preferably, in the triangular-wave hold-time test, an equivalent acceleration test is adopted based on the thermal activation mechanism of nuclear-grade stainless steel materials. The Arrhenius relationship followed by the thermal activation process is Equation (1).

[0084]

[0085] Among them, t1 = 36 h and t2 = 567 h are the aging times at temperatures T1 = 420 °C and T2 = 325 °C respectively, Q is the activation energy, R is the gas constant, and the time equivalence coefficient at these two temperatures is 15.75.

[0086] In the embodiment, the loading strain amplitude is controlled at 0.6%, the temperature is 325 °C, and the oxygen concentration < 10 ppb is kept fixed. The fatigue life N curves of the specimens at different loading strain rates are as Figure 5 shown; the loading strain rate is controlled at 0.04% / s, the loading strain amplitude is 0.6%, the temperature is 325 °C, and the oxygen concentration < 10 ppb is kept fixed. The fatigue life curves of austenitic stainless steel under different load types and holding times are as Figure 6 shown.

[0087] Preferably, a strain-controlled fatigue test is carried out, and the strain ratio of the loading is -1.

[0088] S4: Based on the fatigue test data obtained in step S3, analyze the effects of factors such as loading strain rate, loading strain amplitude, temperature, oxygen concentration, and load holding on the fatigue life of austenitic stainless steel, and use the Langer equation to fit to obtain the best fitting curve of austenitic stainless steel material in a high-temperature and high-pressure water environment. The expression is formula (2)

[0089]

[0090] where ε a is the strain amplitude, N is the fatigue life, and A1, A2, and n1 are fitting parameters. The confidence level of the fitting satisfies R 2 = 0.97

[0091] Among them, when the loading strain rate is 0.04% / s, the temperature is 325 °C, and the oxygen concentration < 10 ppb, A1 = 14.5, A2 = 0.112, and n1 = -0.47.

[0092] S5: Use regression analysis to evaluate the degree of agreement between the fitting result and the experimental data. The expression of the confidence level R 2 is formula (3)

[0093]

[0094] where y i is the experimental value of the i-th sample, is the mean value of the experimental values, is the predicted value of the model. The closer R 2 is to 1, the better the fitting result of the model. The calculated confidence level R 2 = 0.97.

[0095] S6: Adopt the idea of introducing an environmental fatigue correction factor based on the fatigue life N of the specimen in air, that is, consider the effects of factors such as loading strain rate, loading strain amplitude, temperature, oxygen concentration, and load holding. Define the environmental fatigue correction factor F as the ratio of the fatigue life at room temperature in air to the fatigue life under various coupled environments (at the same strain amplitude). en , the fatigue life of the known specimen in air, that is, N air is known

[0096] The expression is Equation (4)

[0097]

[0098] Among them, N air and N water respectively represent the fatigue life in the room temperature air environment and the fatigue life under various coupled environments.

[0099] S7: The fatigue life prediction model of the specimen in room temperature air adopts the best-fit curve in the ASME code, such as Equation (5)

[0100] ln(N air ) = 6.954 - 2ln(ε a - 0.128) (5)

[0101] S8: Based on the test data in S3, establish the relationship between the loading strain rate and the fatigue correction factor of the loading strain rate , such as Equation (6)

[0102]

[0103] Among them, when the strain rate is lower than 0.0004% / s set as a fixed value, when the upper limit of the strain rate can be calculated as 6.8% / s.

[0104] S9: Based on the test data in S3, establish the relationship between the temperature T and the temperature fatigue correction factor F en-T , such as Equation (7)

[0105] ln(F en-T ) = 0.00572·(T - 100) (7)

[0106] Among them, since the maximum temperature in the high-temperature and high-pressure water environment is 325°C, and when the temperature is 100°C, the high-temperature and high-pressure water environment has almost no effect on the environmental fatigue life of the specimen. Therefore, set F en-T to 1 when the temperature is less than 100°C, and set F en-T to a fixed value when the temperature is higher than 325°C.

[0107] S10: Based on the test data in S3, establish the relationship between the oxygen concentration DO and the oxygen concentration fatigue correction factor F en-o The test data shows that when the oxygen concentration ≥ 20 ppb, the fatigue life is about twice that under the condition of oxygen concentration < 10 ppb.

[0108] S11: Based on steps S6 - S10, combine the formula to obtain the environmental fatigue factor F en The expression is

[0109]

[0110] T * = 0 (T ≤ 100 °C)

[0111] T * = 0.00101(T - 100) (100 °C ≤ T ≤ 325 °C)

[0112] T * = 0.227 (T ≥ 325 °C)

[0113] O * = 1 (DO < 20 ppb)

[0114] O * = 0.5 (DO ≥ 20 ppb)

[0115] S12: Considering the influence of the load type and the holding time, based on the high - temperature and high - pressure water environment fatigue correction factor F en establish a prediction model for the environmental fatigue correction factor F en-hold considering the hold - load effect

[0116] F en-hold = F hold ·F en

[0117] F hold is the ratio of the fatigue life without the temperature and pressure holding process in S3 to the fatigue life with the temperature and pressure holding process in S3, that is, comparing the fatigue life obtained from S3.1 - S3.4 with that of S3.5. The result shows that the fatigue life obtained from S3.1 - S3.4 is about 1.56 times that of S3.5. Therefore, dl F oh is taken as 1.56.

[0118] The above - mentioned are only the preferred embodiments of this patent and are not intended to limit this patent. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this patent shall be included within the protection scope of this patent.

[0119] It should be noted that for the foregoing method embodiments, for the sake of simplicity of description, they are all expressed as a series of action combinations. However, those skilled in the art should know that this application is not limited by the described action sequence, because according to this application, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily essential to this application.

[0120] In the above embodiments, the descriptions of the respective embodiments have their own emphases. For parts not detailed in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0121] The preferred embodiments of the present application disclosed above are only used to help explain the present application. The alternative embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this application. These embodiments are selected and specifically described in this application to better explain the principle and practical application of this application, so that those skilled in the art can well understand and utilize this application.

Claims

1. A prediction method for the metal environmental fatigue correction factor considering the load holding effect, characterized in that: It includes the following steps: S1: Prepare a tubular fatigue specimen of austenitic stainless steel; S2: Prepare a simulation device for high-temperature and high-pressure cyclic water corrosion fatigue test; S3: Under the condition of a high-temperature and high-pressure water environment inside the specimen in S1, load the specimen to study different loading strain rates Under the conditions of load holding effect, oxygen concentration, and temperature, the relationship between the fatigue life N and the strain amplitude ε a therebetween; S4: Based on the fatigue test data obtained in step S3, analyze the effects of factors such as loading strain rate, loading strain amplitude, temperature, oxygen concentration, and load holding on the fatigue life of the specimen, and use the Langer equation to fit to obtain the specimen curve under high-temperature and high-pressure water environment, and the expression is formula (2) where ε a is the strain amplitude, N is the fatigue life, and A1, A2, and n1 are fitting parameters. S5: Define the environmental fatigue correction factor F en , and the expression is Equation (4) Among them, N air and N water respectively represent the fatigue life in the room-temperature air environment and the fatigue life under various coupled environments; N air is known; S6: Fit the fatigue life prediction model of the specimen in room-temperature air, such as formula (5) ln(N air ) = 6.954 - 2ln(ε a - 0.128) (5) S7: Based on the test data in S3, establish the relationship between the loading strain rate and the fatigue correction factor of the loading strain rate as shown in Equation (6). S8: Based on the test data in S3, establish the relationship between temperature T and temperature fatigue correction factor F en-T as shown in Equation (7) ln(F en-T ) = 0.00572·(T - 100) (7) S9: Based on the test data in S3, establish the relationship between the oxygen concentration DO and the oxygen concentration fatigue correction factor F en-o ; S10: Based on steps S5 - S9, combine the formula to obtain the environmental fatigue factor F of the austenitic stainless steel material en The expression is: T * = 0 (T ≤ 100 °C) T * = 0.00101(T - 100) (100 °C ≤ T ≤ 325 °C) T * = 0.227 (T ≥ 325 °C) O * = 1 (DO < 20 ppb) O * = 0.5 (DO ≥ 20 ppb) S11: Considering the influence of load type and holding time, based on the high-temperature and high-pressure water environment fatigue correction factor F en Establish an environmental fatigue correction factor F considering the hold load effect en-hold Prediction model F en-hold = F hold ·F en 。 2. The prediction method of the metal environmental fatigue correction factor considering the load holding effect according to claim 1, wherein: In the above S1, samples are taken axially at a position 1 / 4 wall thickness from the inner surface or the outer surface of the main pipeline. The gauge length of the specimen is 20 mm, the outer diameter is 10 mm, and the inner diameter is 5 mm.

3. A method for predicting the metal environmental fatigue correction factor considering the load holding effect according to claim 2, characterized in that: The surface roughness of the specimen inside and outside is better than 0.8 μm.

4. A prediction method for the metal environmental fatigue correction factor considering the load holding effect according to claim 1, characterized in that: In S2, the aqueous chemical environment solution medium of the simulated high-temperature and high-pressure circulating water corrosion fatigue test device is selected as 500 ppb B 3+ , 2 ppm Li + ; the maximum temperature is 360 °C; the control accuracy is ±1 °C; the maximum pressure is 20 MPa; the oxygen concentration range is 10 ppb - 200 ppb.

5. A method for predicting a metal environmental fatigue correction factor considering the load holding effect according to claim 1, characterized in that: In the above S3, the strain ratio of the loading is -1.

6. A method for predicting a metal environmental fatigue correction factor considering the load retention effect according to claim 1, characterized in that: The above S3 includes S3.1: Control the loading strain rate Keep the loading strain rate at 0.04% / s, the temperature at 325 °C, and the oxygen concentration < 10 ppb fixed, and study the effect of different loading strain amplitudes ε a on the fatigue life of the specimen; S3.2: Control the applied strain amplitude ε a Keep the applied strain amplitude ε at 0.6%, temperature at 325 °C, and oxygen concentration < 10 ppb fixed, and study the relationship between the fatigue life N of the specimen and the applied strain amplitude ε a under different applied strain rates; S3.3: Keep the controlled loading strain rate at 0.04% / s, the loading strain amplitude at 0.6%, and the oxygen concentration < 10 ppb fixed, and study the relationship between the fatigue life N of the specimen and the loading strain amplitude ε a at different temperatures; S3.4: Control the loading strain rate at 0.04% / s, the loading strain amplitude at 0.6%, and the temperature at 325°C to remain fixed, and study the relationship between the fatigue life N of the specimen and the loading strain amplitude ε a under different oxygen concentrations; S3.5: Keep the controlled loading strain rate at 0.04% / s, the loading strain amplitude at 0.6%, the temperature at 325 °C, and the oxygen concentration < 10 ppb fixed, and study the relationship between the fatigue life N of the specimen and the loading strain amplitude ε a under different load types and holding times.

7. A prediction method for a metal environmental fatigue correction factor considering the load holding effect according to claim 6, characterized in that: In S3.1, different loading strain amplitudes ε a include 0.0004% / s, 0.004% / s, 0.01% / s, 0.4% / s, 4% / s.

8. A prediction method for the metal environmental fatigue correction factor considering the load holding effect according to claim 6, characterized in that: In S3.2, the same temperatures include 100 °C, 150 °C, 250 °C, and 325 °C.

9. A method for predicting the metal environmental fatigue correction factor considering the load holding effect according to claim 6, characterized in that: In S3.4, the different oxygen concentrations include 10 ppb, 20 ppb, 50 ppb, 100 ppb, and 200 ppb.

10. A prediction method for a metal environmental fatigue correction factor considering the load holding effect according to claim 6, characterized in that: S3.5 includes: S3.5.1: Adopt a triangular wave test, the temperature is 325 °C. When the fatigue life reaches 1 / 4 of the fatigue life in air, stop the test when the strain is 0, unload, drain the high-temperature and high-pressure water inside the specimen, turn on the heating furnace, heat up to 420 °C, maintain the temperature and pressure for 36 h, and then restart the fatigue test at 325 °C until the specimen fails; S3.5.2: Adopt a triangular wave test, the temperature is 325 °C. When the fatigue life reaches 1 / 4 of the fatigue life in air, stop the test by controlling the strain at the target peak value, drain the high-temperature and high-pressure water inside the specimen, turn on the heating furnace, heat up to 420 °C, maintain the temperature and pressure for 36 h, and then restart the fatigue test at 325 °C; S3.5.3: Adopt a trapezoidal wave test, the temperature is 325 °C, maintain the peak temperature and pressure for 0.278 h, and directly carry out the fatigue test.

11. A prediction method for a metal environmental fatigue correction factor considering the load holding effect according to claim 1, characterized in that: In the above S4, the confidence level of the fitting is greater than or equal to 0.

97.

12. A prediction method for a metal environmental fatigue correction factor considering the load holding effect according to claim 1, characterized in that: In the above S7, when the strain rate is lower than 0.0004% / s it is set as a fixed value. When is reached, the upper limit of the strain rate is calculated to be 6.8% / s.

13. A prediction method for a metal environmental fatigue correction factor considering the load holding effect according to claim 1, characterized in that: In the above S9, when the oxygen concentration ≥ 20 ppb, the fatigue life is about 2 times that under the condition of oxygen concentration < 10 ppb.

14. A prediction method for a metal environmental fatigue correction factor considering the load holding effect according to claim 1, characterized in that: In S11, F hold Take 1.56.

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