Microscopic rapid evaluation method for long-time thermal service state of nuclear power pressure vessel material

Abstract

The invention belongs to the technical field of safety evaluation of service materials, and particularly relates to a microscopic rapid evaluation method for a long-time thermal service state of a nuclear power pressure vessel material, which comprises the following steps of: 1, selecting a pressure vessel micro-area material in a certain service state; 2, a specific corrosive liquid is selected for corrosion for a certain time, and a state monitoring sample piece is obtained; step 3, the microscopic morphology of the state monitoring sample piece is shot through a microscope; 4, counting the percentage composition of the corrosion area; and 5, evaluating the thermal service state of the material according to the linear relationship between the percentage composition of the corrosion area and the thermal aging time. According to the microscopic rapid evaluation method for the long-time thermal service state of the nuclear power pressure vessel material, thermal aging degradation damage of the pressure vessel material is presented through an over-corrosion method, rapid evaluation of the thermal aging state can be achieved only by obtaining a local monitoring material, and the microscopic rapid evaluation method still has a good prediction effect on long-time thermal service equipment.

Description

Technical Field

[0001] This invention relates to the field of safety evaluation technology for in-service materials, and in particular to a microscopic rapid evaluation method for the long-term thermal service status of nuclear power pressure vessel materials. Background Technology

[0002] For structural materials in nuclear power pressure vessels, thermal service is a crucial operating condition for long-term component operation. Taking pressurized water reactors as an example, nuclear power pressure vessel materials need to serve at high temperatures for 60 to 80 years. However, thermal service often leads to material embrittlement, manifested as a decrease in plasticity and toughness, thus reducing the service life of the equipment. Therefore, conducting a safety assessment of the thermal service status of in-service equipment is an important engineering issue. However, the materials for service monitoring inside pressure vessels are limited and large-area cutting is not permitted. Traditional evaluation methods based on impact energy are no longer sufficient for a comprehensive assessment of material properties. Therefore, microstructure analysis has become an important evaluation method. For nuclear power pressure vessel materials, the evolution of their metallographic structure with thermal aging time is not very obvious, making it difficult to accurately assess early damage and thermal aging status.

[0003] The performance degradation of pressure vessel materials after long-term thermal service is related to the evolution of their microstructure. However, traditional metallographic methods have limited characterization of the microstructure evolution of pressure vessel materials during thermal aging. If the degradation structure that should be visible can be reflected by improving corrosion conditions and methods, the shortcomings of existing evaluation methods can be effectively overcome. Summary of the Invention

[0004] Based on existing technical problems, this invention proposes a rapid microscopic evaluation method for the long-term thermal service status of nuclear power pressure vessel materials. Starting from the microscopic damage of materials during thermal service, a microscopic corrosion scheme is proposed, and a relationship curve between the percentage of micro-area corrosion area and the duration of thermal service is established to achieve rapid evaluation of thermal service status. This method overcomes the shortcomings of traditional thermal service status evaluation methods, such as high destructiveness, waste of samples, insufficient accuracy, and single monitoring methods, and provides a brand-new technical path for predicting thermal service status under engineering conditions.

[0005] The present invention proposes a rapid microscopic evaluation method for the long-term thermal service status of nuclear power pressure vessel materials, comprising the following steps;

[0006] Step 1: Selection of micro-region materials after hot service;

[0007] Step 2: Prepare a suitable etching solution and determine the etching time;

[0008] Step 3: Take micro-area images of the monitored samples and calculate the percentage of corrosion area;

[0009] Step 4: Fit a straight line relating the percentage of corrosion area to the duration of hot service.

[0010] Step 5: Hot Service Status Evaluation.

[0011] Preferably, in step one, the hot service micro-region material to be evaluated is cut according to engineering needs, that is, the pressure vessel micro-region material in a certain service state is selected.

[0012] Preferably, in step two, the corrosion is carried out using a super-corrosion method.

[0013] Preferably, a specific etchant is used to etch the sample for a certain period of time to obtain a condition monitoring sample. The etchant is a 4% nitric acid ethanol solution, and the etching time is 2 minutes.

[0014] Preferably, in step three, the microscopic morphology of the state monitoring sample is captured by microscopic imaging.

[0015] Considering the non-uniformity of the micro-area surface after corrosion, multiple locations of the micro-area corrosion sample were photographed using an optical microscope or scanning electron microscope. The percentage of micro-area corrosion area was statistically analyzed using image processing software to obtain the percentage of micro-area corrosion area at different locations.

[0016] Preferably, in step four, after statistically analyzing the percentage of corrosion area, a linear relationship between the percentage of micro-area corrosion area and the thermal service time is fitted, and the percentage of corrosion area is positively linearly correlated with the thermal aging time.

[0017] Preferably, in step five, the thermal service condition of the material is evaluated based on the linear relationship between the percentage of corrosion area and the thermal aging time. The thermal service condition is predicted using a linear relationship graph between the percentage of micro-area corrosion area and the thermal service time.

[0018] The beneficial effects of this invention are as follows:

[0019] This method for rapid microscopic evaluation of the long-term thermal service status of nuclear power pressure vessel materials only requires measuring the percentage of corrosion area in a micro-region of the thermally serviced equipment. It can evaluate the thermal aging status according to a linear formula, accurately predicting the service status of pressure vessel materials. This prediction presents the thermal aging deterioration damage of pressure vessel materials through a hypercorrosion method. It only requires obtaining local monitoring materials to achieve rapid assessment of the thermal aging status, and still has a good predictive effect on equipment with long-term thermal service. Attached Figure Description

[0020] Figure 1 This is a flowchart of a rapid microscopic evaluation method for the long-term thermal service state of nuclear power pressure vessel materials proposed in this invention;

[0021] Figure 2 The images show the microscopic metallographic morphology of samples after corrosion at different aging times, which are part of a rapid microscopic evaluation method for the long-term thermal service state of nuclear power pressure vessel materials proposed in this invention.

[0022] Figure 3 This is a linear relationship between the percentage of corrosion area and different service durations after statistical analysis of the microscopic rapid evaluation method for the long-term thermal service state of nuclear power pressure vessel materials proposed in this invention. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0024] Reference Figure 1-3 A rapid microscopic evaluation method for the long-term thermal service status of nuclear power pressure vessel materials, comprising the following steps;

[0025] Step 1: Selection of micro-region materials after hot service; according to engineering needs, the micro-region materials to be evaluated after hot service are cut out. Specifically, the micro-region materials of the nuclear power pressure vessel after hot service are cut out. In this embodiment, the original sample and four accelerated hot service samples are cut out, and the thermal aging times of the accelerated service samples are 5000 h, 10000 h, 15000 h and 20000 h, respectively.

[0026] Step 2: Prepare a suitable etching solution and determine the etching time; the etching method used is over-etching, the etching solution is a 4% nitric acid-ethanol solution, and the etching time is 2 minutes. Specifically, a 4% nitric acid-ethanol solution is prepared and used to immerse and etch micro-area samples with different thermal aging states after surface grinding and polishing to a mirror finish, with an etching time of 2 minutes. The over-etching method reveals the thermal aging deterioration damage of the pressure vessel material.

[0027] Step 3: Take pictures of the micro-area of ​​the monitoring sample and count the percentage of corrosion area; Considering the non-uniformity of the micro-area surface after corrosion, take pictures of multiple locations of the micro-area corrosion sample with an optical microscope or scanning electron microscope, and use image processing software such as Image-Pro to count the percentage of micro-area corrosion area to obtain the percentage of micro-area corrosion area at different locations.

[0028] Specifically, an optical microscope with a large field of view was used to take at least five photographs of the monitored micro-area sample at different locations, with a magnification of 1000x. Figure 2 As shown, the percentage of area of ​​corrosion in the photographed images was statistically analyzed.

[0029] Step 4: Fit the percentage of corrosion area With thermal service life Relationship line ;in, The slope, typically a positive value, represents the percentage increase in thermal aging time per unit corrosion area. The intercept is used to fit the linear relationship between the percentage of micro-area corrosion area and the thermal service time. The percentage of corrosion area is positively linearly correlated with the thermal aging time.

[0030] Specifically, a linear relationship is established between the percentage of corrosion area and the thermal service duration under different service durations, where the percentage of corrosion area is on a logarithmic scale and the service duration is on a linear scale, such as... Figure 3 As shown, this enables the prediction of service life, i.e., the evaluation of hot service status:

[0031] .

[0032] This experimental scheme uses over-corrosion to evaluate the thermal aging state by the percentage of corrosion area. Compared with traditional mechanical evaluation methods such as impact energy and tensile strength, as well as microscopic metallographic and hardness methods, this method has the characteristics of being less destructive and having significant regularity. Figure 3 It can be seen that this method has good fitting results not only for early thermal service damage but also for long-term thermal service conditions.

[0033] Step 5: Thermal Service Condition Evaluation; Using the linear relationship between the percentage of micro-area corrosion area and thermal service duration, the thermal service condition is predicted. Based on current test results for accelerated aging samples, samples aged 5000 h, 10000 h, 15000 h, and 20000 h correspond to approximately 12, 24, 36, and 48 years of service at 350°C, respectively. Therefore, this model has good predictive results for data within 48 years of accelerated thermal service, with a coefficient of determination R0. 2 =0.96.

[0034] This method for rapid microscopic evaluation of the long-term thermal service status of nuclear power pressure vessel materials can effectively demonstrate the impact of thermal aging on microstructure. By establishing a quantitative linear model to correlate the percentage of micro-corrosion area after thermal service with the duration of thermal service, it can predict the duration of thermal service. It has the advantages of low destructiveness of micro-area sampling, simple form and fewer parameters.

[0035] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A rapid microscopic evaluation method for the long-term thermal service status of nuclear power pressure vessel materials, characterized in that: Includes the following steps; Step 1: Selection of materials for micro-regions after hot service; Step 2: Prepare a suitable etching solution and determine the etching time; Step 3: Take micro-area images of the monitored samples and calculate the percentage of corrosion area; Step 4: Fit a straight line relating the percentage of corrosion area to the duration of hot service. Step 5: Hot Service Status Evaluation.

2. The rapid microscopic evaluation method for the long-term thermal service status of nuclear power pressure vessel materials according to claim 1, characterized in that: In step one, the hot service micro-region material to be evaluated is cut according to engineering needs.

3. The rapid microscopic evaluation method for the long-term thermal service status of nuclear power pressure vessel materials according to claim 1, characterized in that: In step two, the corrosion is carried out using an over-corrosion method.

4. The rapid microscopic evaluation method for the long-term thermal service status of nuclear power pressure vessel materials according to claim 3, characterized in that: The corrosion solution used is a 4% nitric acid ethanol solution, and the corrosion time is 2 minutes.

5. The rapid microscopic evaluation method for the long-term thermal service status of nuclear power pressure vessel materials according to claim 1, characterized in that: In step three, considering the non-uniformity of the micro-area surface after corrosion, multiple locations of the micro-area corrosion sample are photographed using an optical microscope or scanning electron microscope, and the percentage of micro-area corrosion area is statistically analyzed using image processing software to obtain the percentage of micro-area corrosion area at different locations.

6. The rapid microscopic evaluation method for the long-term thermal service status of nuclear power pressure vessel materials according to claim 1, characterized in that: In step four, a straight line is fitted to show the relationship between the percentage of micro-area corrosion area and the thermal service time, and the percentage of corrosion area is positively linearly correlated with the thermal aging time.

7. The rapid microscopic evaluation method for the long-term thermal service status of nuclear power pressure vessel materials according to claim 1, characterized in that: In step five, the thermal service status is predicted by using the linear relationship between the percentage of micro-area corrosion area and the thermal service duration.

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