Method for evaluating service life of alloy seamless pipe for nuclear power heat exchanger

Abstract

The application discloses a kind of alloy seamless pipe service life evaluation methods for nuclear power heat exchanger, belong to nuclear power technical field, including the following steps: step 1, alloy seamless pipe sample is treated for long-term aging;Step 2, the alloy seamless pipe sample after long-term aging treatment is processed into alternating load creep sample;Step 3, alternating load creep sample is carried out alternating load creep experiment, and alternating load creep experimental data are obtained;Step 4, alternating load creep experimental data are substituted into life formula, and the fitting curve of stress and sample fracture time is obtained;Step 5, the fitting curve of stress and sample fracture time is calculated by isotherm extrapolation method, and the service life of alloy seamless pipe is obtained, and the service life of alloy seamless pipe can be more comprehensively evaluated by the evaluation method, and the accuracy of alloy seamless pipe service life evaluation is improved.

Description

A method for assessing the service life of alloy seamless tubes for nuclear power heat exchangers Technical Field

[0001] This invention belongs to the field of nuclear power technology, and in particular to a method for assessing the service life of seamless alloy tubes used in nuclear power heat exchangers. Background Technology

[0002] Nuclear energy, as a clean, efficient, and renewable new energy source, is being widely promoted and applied globally. Nuclear power heat exchangers are one of the most crucial components in nuclear power plants, used to transfer heat generated by the nuclear reactor to the working medium. Alloy seamless tubes are the core component of nuclear power heat exchangers. During nuclear power plant operation, these tubes endure harsh working environments such as high temperature, high pressure, and radiation, making them susceptible to corrosion, fatigue, and stress corrosion cracking. If the lifespan of the alloy seamless tubes cannot be accurately predicted, it may lead to sudden failures and leaks, endangering personnel and environmental safety. By assessing the service life of alloy seamless tubes, potential problems can be detected in a timely manner, allowing for necessary repair and replacement measures to ensure the safe operation of the nuclear power plant.

[0003] Currently, the finished product inspection and life prediction of alloy seamless tubes used in nuclear power heat exchangers mainly focus on short-term experimental data such as tensile properties, yield strength, and impact toughness, or simply refer to single fatigue and creep test data. However, these traditional evaluation methods lack performance evaluation standards for alloy seamless tubes under complex long-term service environments, and cannot accurately assess their reliability in the long-term operation of nuclear power plants.

[0004] Therefore, there is an urgent need to provide a life assessment method that comprehensively considers multiple factors to evaluate the service life of alloy seamless tubes. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for assessing the service life of alloy seamless tubes for nuclear power heat exchangers, which improves the accuracy of service life assessment of alloy seamless tubes.

[0006] This invention is achieved through the following technical solution:

[0007] Step 1: Perform long-term aging treatment on the alloy seamless tube sample;

[0008] Step 2: Process the alloy seamless tube sample after long-term aging treatment into a variable load creep sample.

[0009] Step 3: Conduct an alternating load creep test on the alternating load creep specimen to obtain alternating load creep test data;

[0010] The alternating load creep test data are stress and specimen fracture time;

[0011] The load cycling mode of the alternating load creep experiment is a rectangular wave cyclic load;

[0012] Step 4: Substitute the alternating load creep test data into the life formula to obtain the fitting curve of stress versus specimen fracture time.

[0013] Step 5: Calculate the service life of the alloy seamless tube by using the isothermal extrapolation method on the fitted curve of stress versus fracture time of the sample.

[0014] Preferably, the long-term aging treatment temperature in step 1 is 650~750℃.

[0015] Preferably, the long-term aging treatment time in step 1 is 5000~10000h.

[0016] Preferably, the experimental temperature for the alternating load creep test in step 3 is 500~700℃.

[0017] Preferably, the cyclic load stress in the alternating load creep test in step 3 is 200~400MPa.

[0018] Preferably, the cyclic load strain in the alternating load creep test in step 3 is 0.1~0.2.

[0019] Preferably, the cyclic load strain rate of the alternating load creep test in step 3 is 0.1~1s. -1 .

[0020] Preferably, the cyclic load stress relaxation time in the alternating load creep test in step 3 is 200s.

[0021] Preferably, the lifespan formula in step 4 is:

[0022] lgσ=lgk+mlgt

[0023] In the formula, σ is the stress, t is the fracture time of the specimen, and k and m are material constants.

[0024] In summary, the beneficial effects of this invention are as follows: This evaluation method comprehensively considers the factors of long-term aging and alternating loads. It performs long-term aging treatment and alternating load creep tests on the samples, and substitutes the alternating load creep test data into the life formula to obtain a fitting curve of stress versus sample fracture time. The service life of the alloy seamless tube is calculated using the isothermal extrapolation method, enabling a more comprehensive assessment of the alloy seamless tube's lifespan. By combining experimental data and theoretical models, the accuracy of the service life assessment of alloy seamless tubes is improved. Furthermore, this evaluation method optimizes the parameters in the long-term aging treatment and alternating load creep tests, as well as the load cycle mode of the alternating load creep tests, better adapting to practical application needs and improving the reliability and practicality of the evaluation method. Attached Figure Description

[0025] Figure 1 is a structural diagram of the alternating load creep specimen of the present invention;

[0026] Figure 2 is a curve showing the fitting relationship between stress and specimen fracture time according to the present invention. Detailed Implementation

[0027] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0028] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be further described below with reference to specific embodiments.

[0029] Example 1

[0030] A finished alloy seamless tube made of GH1059 material was selected. A rectangular alloy seamless tube sample was taken from the finished alloy seamless tube. The alloy seamless tube sample size was 190mm×15mm×15mm.

[0031] (1) The alloy seamless tube sample was placed in a heat treatment boiler for long-term aging treatment, and the treatment temperature was set to 650℃ and the treatment time was 5000h.

[0032] (2) The alloy seamless tube sample after long-term aging treatment was processed into an alternating load creep sample as shown in Figure 1.

[0033] (3) The alternating load creep specimen was clamped on the Gleeble 3500 thermal simulation testing machine to carry out the alternating load creep test. The test temperature was set to 600℃, the load cycle mode was rectangular wave cyclic load, the cyclic load stress was 250MPa and 300MPa, the cyclic load strain was 0.12, and the cyclic load strain rate was 1s. -1 The stress relaxation time under cyclic load was 200s. After the alternating load creep test, the experimental data of stress and specimen fracture time were obtained.

[0034] (4) Substituting the stress and specimen fracture time data into the life formula lgσ=lgk+mlgt, the specimen fracture time is calculated to be t1=0.2867, t2=0.0885, k=205.92, m=-0.0674, and the specimen life formula at 600℃ is lgσ=2.3137-0.0674lgt. The fitting curve of stress and specimen fracture time is shown in Figure 2.

[0035] Where σ is the stress, t is the fracture time of the specimen, and k and m are material constants;

[0036] (5) The isothermal extrapolation method was used to calculate the stress-fracture time of the specimen. When the stress was 110 MPa, the fracture time of the specimen was 10000 h; when the stress was 130 MPa, the fracture time of the specimen was 1000 h; and when the stress was 150 MPa, the fracture time of the specimen was 100 h.

[0037] In summary, the material is GH1059 finished alloy seamless tube, which can still operate for 10,000 hours under a pressure of 110MPa after a long-term aging treatment of 5000 hours.

[0038] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and all such equivalent transformations fall within the protection scope of the present invention.

Claims

1. A method for assessing the service life of seamless alloy tubes used in nuclear power plant heat exchangers, characterized in that, Includes the following steps: Step 1: Perform long-term aging treatment on the alloy seamless tube sample; In step 1, the long-term aging treatment temperature is 650~750℃, and the long-term aging treatment time is 5000~10000h. In step 2, the alloy seamless tube sample after long-term aging is processed into an alternating load creep test sample. In step 3, an alternating load creep test is conducted on the alternating load creep test sample to obtain alternating load creep test data. The alternating load creep test data consists of stress and sample fracture time. The load cycle mode of the alternating load creep test is a rectangular wave cyclic load. The test temperature in step 3 is 500~700℃. In step 4, the alternating load creep test data is substituted into the life formula to obtain a fitting curve of stress versus sample fracture time. The life formula in step 4 is: lgσ=lgk+mlgt, where σ is stress, t is sample fracture time, and k and m are material constants. In step 5, the service life of the alloy seamless tube is calculated using the isothermal extrapolation method on the fitting curve of stress versus sample fracture time.

2. The method for assessing the service life of seamless alloy tubes for nuclear power plant heat exchangers according to claim 1, characterized in that, The cyclic load stress in the alternating load creep test in step 3 is 200~400MPa.

3. The method for assessing the service life of seamless alloy tubes for nuclear power plant heat exchangers according to claim 1, characterized in that, The cyclic load strain in the alternating load creep test in step 3 is 0.1~0.

2.

4. The method for evaluating the service life of seamless alloy tubes for nuclear power heat exchangers according to claim 1, characterized in that, The cyclic load strain rate in the alternating load creep test in step 3 is 0.1~1s. -1 .

5. The method for evaluating the service life of seamless alloy tubes for nuclear power plant heat exchangers according to claim 1, characterized in that, The cyclic load stress relaxation time in the alternating load creep experiment in step 3 is 200s.

Images