Steam generator heat transfer pipe inspection and pipe blockage management method based on risk classification
By adopting a risk-based inspection method for heat transfer tubes in steam generators, which utilizes flow-induced vibration analysis to classify risk levels and differentiate inspections, the problems of resource waste and safety hazards in heat transfer tube inspections are solved, achieving efficient heat transfer tube management and economic benefits.
Patent Information
- Application Number
- CN202511460735.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-14
- Publication Date
- 2026-02-13
AI Technical Summary
In the existing technology, the inspection and blockage management of heat transfer tubes in steam generators lacks scientific basis, which leads to waste of inspection resources or potential safety hazards. Moreover, the full inspection method increases the shutdown waiting time of nuclear power plants and reduces economic efficiency.
A risk-based classification method is adopted to calculate the fluid stability ratio (FSR) of heat transfer tubes through flow-induced vibration analysis, classifying them into high, medium, and low risk areas. The inspection frequency and coverage are adjusted according to the risk level, and the inspection method is dynamically adjusted to ensure the safety of high-risk areas and the economy of low-risk areas.
It achieves full monitoring of high-risk areas, reduces waste of inspection resources in low-risk areas, shortens shutdown waiting time, improves the economic efficiency of nuclear power plants, and the number of inspections is only 20% of that of full inspection, while the detection effect reaches 80% of that of full inspection.
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Figure CN121526031A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of maintenance and management of nuclear power plant steam generators, and particularly relates to a steam generator heat pipe inspection and blocked pipe management method based on risk classification. BACKGROUND
[0002] In the prior art, the in-service inspection and blocked pipe management of steam generator heat pipes are usually based on fixed time intervals or inspection frequencies determined by experience. The determination of inspection coverage and frequency often lacks scientific basis and mainly relies on past inspection experience or industry standards. For example, the EPRI Steam Generator Structural Integrity Assessment Guidelines and the NEI 97-06 Steam Generator Program Guidelines provide guidance for the inspection and blocked pipe management of steam generator heat pipes. These standards usually determine the inspection coverage and frequency based on experience, without fully considering the actual wear risks faced by different heat pipes.
[0003] In practical applications, the damage and degradation of heat pipes are not uniform. Due to factors such as fluid scouring, vibration, or chemical corrosion, the damage degree and speed of heat pipes in different areas are different. Heat pipes in high-risk areas may develop serious defects in a short period of time, while heat pipes in low-risk areas remain in good condition even after long-term operation. The existing fixed inspection strategy cannot balance the safety of high-risk areas and the economy of low-risk areas, resulting in waste of inspection resources or potential safety hazards.
[0004] Currently, the heat pipe inspection strategy during the overhaul of nuclear power plants often adopts a 100% full inspection method due to the lack of understanding of the wear risk of heat pipes in steam generators. This method takes a long time, increases the downtime of nuclear power plants, and reduces the economic benefits of nuclear power plants. SUMMARY
[0005] The purpose of the present application is to overcome the defects of the prior art and provide a steam generator heat pipe inspection and blocked pipe management method based on risk classification, which can dynamically adjust the inspection frequency and coverage according to the risk level of the heat pipes (high risk, medium risk, and low risk), ensure that high-risk areas are fully monitored, and avoid excessive inspection of low-risk areas, thereby improving the utilization efficiency of inspection resources.
[0006] To achieve the above purpose, the present application provides the following technical solutions:
[0007] A steam generator heat pipe inspection and blocked pipe management method based on risk classification, comprising:
[0008] Step 1: Calculate the FSR of each heat pipe, divide the risk level into high-risk areas, medium-risk areas, and low-risk areas, and clarify the differences in wear risk of each area;
[0009] Step 2: Employ differentiated inspections based on both frequency and coverage for different risk levels;
[0010] Step 3: Reassess the risk level of each heat transfer tube based on the inspection results and adjust the corresponding inspection methods accordingly;
[0011] Step 4: Perform dynamic adjustment and inspection on the detected worn and blocked heat transfer tubes.
[0012] As an feasible approach, the FSR should be ≥0.7 for high-risk areas, 0.5≤FSR<0.7 for medium-risk areas, and <0.5 for low-risk areas.
[0013] As an feasible approach, the FSR of each heat transfer tube is calculated through flow-induced vibration analysis.
[0014] As an feasible approach, heat transfer pipes in high-risk areas should be inspected annually, with each inspection covering at least 50% of the area.
[0015] As an feasible approach, heat transfer pipes in medium-risk areas should be inspected every two years, with an inspection coverage rate of no less than 25%.
[0016] As an feasible approach, heat transfer pipes in low-risk areas should be inspected every three years, with an inspection coverage rate of no less than 12.5%.
[0017] As an feasible approach, the worn / blocked heat transfer tube and its surrounding area should be inspected three times consecutively until the wear stabilizes.
[0018] As an feasible approach, the inspection results can be divided into:
[0019] Category C-1: The number of heat transfer tubes with defects having a depth greater than 20% of the wall thickness is less than 5% of the total number of heat transfer tubes inspected.
[0020] Category C-2: The number of heat transfer tubes with defects having a depth greater than 20% of the wall thickness is in the range of 5%-10% of the total number of heat transfer tubes inspected.
[0021] Category C-3: The number of heat transfer tubes with wall thickness defects greater than 20% in depth exceeds 10% of the total number of heat transfer tubes under inspection, or the number of heat transfer tubes exceeding the acceptance criteria exceeds 1% of the total number of heat transfer tubes under inspection.
[0022] As an feasible approach, the original inspection method is maintained for Category C-1, additional inspection is performed on the steam generator for Category C-2, and additional inspection is performed on the steam generator and the steam generator in the same unit for Category C-3.
[0023] As an implementable manner, for the detected worn heat transfer tube, it is detected according to the original risk area division method; for the plugged heat transfer tube, a layer of heat transfer tubes around the plugged heat transfer tube is detected during continuous three shutdown refueling overhauls, whether the worn heat transfer tube appears wear and tear and the change of the wear and tear amount are observed, until the wear and tear amount is no longer deepened, and the worn heat transfer tube is detected according to the original risk area division method.
[0024] Compared with the prior art, the steam generator heat transfer tube inspection and plugged tube management method based on risk classification provided by the application has the following beneficial effects:
[0025] The application can scientifically evaluate the risk of each heat transfer tube according to the actual operating condition of the heat transfer tube, and divide the heat transfer tube into three grades of high risk, medium risk and low risk. Through this risk classification method, the application can adopt differentiated inspection methods for heat transfer tubes of different risk grades, ensure that the heat transfer tubes in the high-risk area are subjected to higher inspection coverage and frequency, and at the same time, reduce unnecessary inspection in the medium-risk and low-risk areas, and save inspection resources.
[0026] The application detects the number of worn heat transfer tubes and plugged heat transfer tubes, which is about 80% of the total detection, and the detection number is only 20% of the total detection. Under the premise of ensuring safety, the waiting time for shutdown is greatly shortened, and the economic benefit of the nuclear power plant is ensured. BRIEF DESCRIPTION OF DRAWINGS
[0027] In order to more clearly illustrate the technical solutions of the application, the following will briefly introduce the drawings needed to be used in the technical description.
[0028] Figure 1 The flowchart of the steam generator heat transfer tube inspection and plugged tube management method based on risk classification provided by the application. DETAILED DESCRIPTION
[0029] The following will be further described in detail through specific embodiments.
[0030] As shown in the drawings, Figure 1 The application provides a steam generator heat transfer tube inspection and plugged tube management method based on risk classification, which is based on flow-induced vibration analysis (FIV), classifies the steam generator heat transfer tube through calculation of flow stability ratio (FSR), and adopts differentiated inspection methods for heat transfer tubes of different risk grades. Through this dynamic risk classification and inspection method, the application ensures the safety of the heat transfer tubes in the high-risk area, while effectively reducing the inspection frequency in the low-risk area, and maximizes the saving of inspection resources. The method comprises the following steps:
[0031] Step 1: Initial full inspection risk. Calculate the flow bullet stability ratio (FSR) of each heat transfer tube through flow-induced vibration analysis, and divide it into high-risk area (FSR≥0.7), medium-risk area (0.5≤FSR<0.7), and low-risk area (FSR<0.5). Calculate the FSR of each heat transfer tube using the formula for FSR in ASME B&PVC Code, Volume III, Appendix N, and determine the difference in wear risk in each area.
[0032] Step 2: Differentiate sampling inspection according to risk level. Adopt "frequency + coverage" dual differentiation for different risk levels. For high-risk areas, check ≥50% per year; for medium-risk areas, check ≥25% per year; for low-risk areas, check ≥12.5% per year; and for worn / blocked heat transfer tubes and their surroundings, conduct continuous three mandatory inspections until the wear stabilizes.
[0033] Step 3: Dynamic adjustment of inspection result classification. Trigger additional inspection based on inspection results (C-1 / C-2 / C-3 categories). For C-1 (low risk), maintain the original method; for C-2 (medium risk), add inspection to the steam generator; for C-3 (high risk), add inspection to the steam generator and other steam generators in the same unit.
[0034] Step 4: Update risk level cycle optimization. Through dynamic updating of risk level, ensure sufficient monitoring of high-risk areas (safety) and reduce resource waste in low-risk areas (economy), achieving a balance between detection quantity (only 20% of full inspection) and detection effect (80% of full inspection).
[0035] In Step 1, the risk classification of steam generator heat transfer tubes is based on the results of flow-induced vibration analysis, with the flow bullet stability ratio (FSR) selected as the key risk assessment indicator. The flow bullet stability ratio is an important parameter for measuring the impact of fluid vibration effects on the stability of heat transfer tubes. It is calculated using the flow field data of the steam generator during normal operation, using the formula in ASME B&PVC Code, Volume III, Appendix N. Specifically, the heat transfer tubes are divided into the following three risk levels:
[0036] (1) High-risk area: When the flow bullet stability ratio (FSR) of the heat transfer tube is greater than or equal to 0.7, it is determined that the heat transfer tube in this area faces a higher risk of wear and fatigue. These heat transfer tubes are more susceptible to damage and cracking due to fluid erosion, vibration, or turbulent flow effects.
[0037] (2) Medium-risk area: When the flow bullet stability ratio (FSR) of the heat transfer tube is between 0.5 and 0.7, it is determined that the risk of these heat transfer tubes is moderate. They are affected to some extent by fluid erosion and vibration, but the damage rate is relatively low.
[0038] (3) Low risk area: when the flow bullet stability ratio (FSR) of the heat transfer tube is less than 0.5, it is judged that the heat transfer tube in this area has the lowest risk of wear and fatigue. They are less affected by fluid scouring and vibration, and are less likely to have serious defects during long-term operation.
[0039] The fluid-induced vibration of the heat transfer tube in the present application mainly refers to the vibration of the heat transfer tube excited by the secondary side transverse flow. Fluid-elastic instability caused by fluid-elastic excitation is a self-excited vibration phenomenon after the coupling of flowing fluid and heat transfer tube vibration. When the fluid flow velocity approaches or reaches the flow bullet instability critical flow velocity, the heat transfer tube enters the fluid-elastic state. At this time, the fluid and the heat transfer tube structure are strongly coupled, the fluid-elastic excitation causes the heat transfer tube to have a large displacement from its original equilibrium position, and the vibration displacement of the heat transfer tube affects the fluid flow in turn, further aggravating the vibration of the heat transfer tube, and the amplitude of the heat transfer tube increases significantly. The heat transfer tube may have significant wear. In the present application, the flow bullet stability ratio calculation formula in the ASME B&PVC specification is used to calculate the flow bullet stability ratio of all heat transfer tubes in the steam generator under operating conditions. The greater the flow bullet stability ratio, the greater the possibility and depth of wear of the heat transfer tube.
[0040] In the present application, the flow bullet stability ratio (FSR) of each heat transfer tube is calculated by fluid-induced vibration analysis, and the heat transfer tube is divided into three risk levels: high risk, medium risk and low risk. The heat transfer tube in the high risk area is usually significantly affected by fluid scouring and vibration, and has a high risk of wear and fatigue damage; the heat transfer tube in the medium risk area is moderately affected by the fluid, and has a moderate risk of wear and fatigue damage; the heat transfer tube in the low risk area is less affected by the fluid, and has the lowest risk of wear and fatigue damage.
[0041] In step 2, in order to ensure the safety of the high-risk area, the present application sets that the heat transfer tube in the high-risk area is checked once a year, and the coverage rate of each check is not less than 50%, that is, more than half of the high-risk heat transfer tube is checked in each check. For the heat transfer tube in the medium risk area, the present application sets that it is checked once every two years, and the coverage rate of the check is not less than 25%, which effectively saves the cost of checking while ensuring safety. For the heat transfer tube in the low risk area, the present application sets that it is checked once every three years, and the coverage rate of the check is not less than 12.5%, and this low-frequency checking method avoids waste of resources.
[0042] In step 3, a dynamic checking method is used. After each check, the risk level of each heat transfer tube is re-evaluated according to the check results, and the corresponding checking method is adjusted. This dynamic adjustment ensures that the checking method can always reflect the actual state of the heat transfer tube.
[0043] At the first outage, all the heat transfer tubes are detected to determine the initial state of the steam generator, and at the subsequent outages, the heat transfer tubes are divided into risk areas according to the flow bullet stability ratio, and the detection frequency and range are determined according to the above method.
[0044] At each inspection, the inspection results are divided into three categories: C-1, C-2, and C-3.
[0045] (1) C-1 refers to the number of heat transfer tubes with defects greater than 20% of the wall thickness in the inspected heat transfer tubes is less than 5% of the total number of inspected heat transfer tubes, but there are no defects exceeding the acceptance standard.
[0046] (2) C-2 refers to the number of heat transfer tubes with defects greater than 20% of the wall thickness in the inspected heat transfer tubes is within the range of 5%-10% of the total number of inspected heat transfer tubes; or one or several heat transfer tubes are detected to exceed the acceptance standard, but the number is less than 1% of the total number of inspected heat transfer tubes.
[0047] (3) C-3 refers to the number of heat transfer tubes with defects greater than 20% of the wall thickness in the inspected heat transfer tubes exceeds 10% of the total number of inspected heat transfer tubes; or the number of heat transfer tubes exceeding the acceptance standard is greater than 1% of the total number of inspected heat transfer tubes.
[0048] If the in-service inspection result is C-1, no expanded inspection is required; if the inspection result is C-2, the steam generator is additionally inspected for the remaining 20% of the heat transfer tubes or heat transfer tube bundles with the same degradation mechanism; if the inspection result is C-3, the steam generator is additionally inspected for all the remaining heat transfer tubes or heat transfer tube bundles with the same degradation mechanism. At least 20% of the heat transfer tube bundles with the same degradation mechanism are additionally inspected for other steam generators.
[0049] The present application is dynamic. Specifically, by evaluating the state of the heat transfer tubes after each inspection, the risk level of each heat transfer tube and its corresponding inspection method are dynamically adjusted according to the inspection results. For high-risk areas, the inspection frequency is high and the inspection coverage is large to ensure timely detection of possible defects; for medium-risk areas, the inspection frequency and coverage are moderate, balancing safety and economy; and for low-risk areas, the inspection frequency and coverage are the lowest to maximize the saving of inspection resources.
[0050] In Step 4, the inspection method is dynamically adjusted for the worn and plugged heat transfer tubes detected in the in-service inspection. For the detected worn heat transfer tubes, their wear is observed during the detection in the subsequent three consecutive refueling outages until the wear no longer deepens, and then they are detected according to the original risk area division method. For the plugged heat transfer tubes, the surrounding layer of heat transfer tubes is detected during the three consecutive refueling outages, and whether the wear appears and the change of the wear are observed until the wear no longer deepens, and then they are detected according to the original risk area division method.
[0051] The present application adopts the non-destructive testing (NDT) technology to inspect the heat transfer tubes of the steam generator. The non-destructive testing is a detection method that can obtain the internal state of the equipment or material without damaging it, mainly including eddy current testing (ECT). The eddy current testing is the preferred method for inspecting the heat transfer tubes in the high-risk area in the present application, and has the advantages of high detection sensitivity and can effectively identify the small cracks, perforations and wall thickness thinning in the heat transfer tubes, especially for the high-risk area, the eddy current testing can ensure the timely discovery of potential defects.
[0052] All inspection data are recorded and archived for subsequent risk assessment and inspection method adjustment. The data record after each inspection will serve as the basis for the next inspection method adjustment.
[0053] In implementation, firstly, the flow-induced vibration analysis is performed on all heat transfer tubes, the flow elastic stability ratio (FSR) of each heat transfer tube is calculated, and the heat transfer tubes are divided into high-risk, medium-risk and low-risk areas according to the FSR. When the present application is implemented for the first time, 100% coverage inspection should be performed on all heat transfer tubes to determine their initial risk level. The inspection results will serve as a reference for subsequent inspection and dynamic adjustment.
[0054] In subsequent inspections, the inspection method of each risk area will be implemented according to the following principles:
[0055] The heat transfer tubes in the high-risk area are inspected once a year, with an inspection coverage rate of not less than 50%, mainly using eddy current testing (ECT). The heat transfer tubes in the medium-risk area are inspected once every two years, with an inspection coverage rate of not less than 25%, mainly using eddy current testing (ECT). The heat transfer tubes in the low-risk area are inspected once every three years, with an inspection coverage rate of not less than 12.5%, mainly using eddy current testing (ECT). After each inspection, the risk level and inspection method of each heat transfer tube are dynamically adjusted according to the inspection results. If the detection result is C-1, the original method is maintained. If the detection result is C-2, additional inspection is performed on the steam generator. If the detection result is C-3, in addition to the additional inspection on the steam generator, additional inspection is also required on the remaining steam generators of the same unit.
[0056] Embodiment
[0057] According to the nondestructive inspection data obtained from the full inspection of all the heat transfer tubes of a steam generator in a certain power plant during the first three shutdowns for refueling overhaul, the simulation detection results obtained by using the method of the application are compared, and it is found that the data detection amount and detection effect of the application are good.
[0058] According to the detection method proposed in the application, all the heat transfer tubes are detected during the first shutdown for refueling overhaul, and the detection method and the obtained results are consistent with the actual situation of the power plant. The detection method proposed in the application has a detection amount of 100% of the full inspection, and the number of detected worn heat transfer tubes and blocked heat transfer tubes is 100% of the full inspection.
[0059] During the second shutdown for refueling overhaul, according to the detection method proposed in the application, first, all the worn heat transfer tubes detected during the first shutdown for refueling overhaul and the heat transfer tubes around the blocked heat transfer tubes during the first overhaul are detected. Second, 1 / 2 of the high-risk area heat transfer tubes, 1 / 4 of the medium-risk area heat transfer tubes and 1 / 8 of the low-risk area heat transfer tubes are randomly selected. According to the flow bullet stability ratio calculation results of the power plant, there are 1089 high-risk heat transfer tubes, 2070 medium-risk heat transfer tubes and 6866 low-risk heat transfer tubes. Comparing the simulation detection results with the full inspection results, the detection amount is 19% of the full inspection, the number of detected worn heat transfer tubes is 75% of the full inspection, and the number of blocked tubes is 90% of the full inspection.
[0060] During the third shutdown for refueling overhaul, according to the detection method proposed in the application, first, all the worn heat transfer tubes detected during the first and second shutdowns for refueling overhaul and the heat transfer tubes around the blocked heat transfer tubes are detected. Second, 1 / 2 of the high-risk area heat transfer tubes, 1 / 4 of the medium-risk area heat transfer tubes and 1 / 8 of the low-risk area heat transfer tubes not detected during the second overhaul are randomly selected. Comparing the simulation detection results with the full inspection results, the detection amount is about 21% of the full inspection, the number of detected worn heat transfer tubes is 85% of the full inspection, and the number of blocked tubes is 88% of the full inspection.
[0061] As can be found from the above examples, compared with 100% full inspection, the detection amount of the detection method proposed in the application is only 20% of the full inspection without excessive reduction of the wear detection rate and the blocked tube rate, which can effectively reduce the nondestructive detection cost of the heat transfer tubes, shorten the shutdown waiting time of the unit during the overhaul, and has good economic benefits.
[0062] The above is only a specific embodiment of the application, but the protection scope of the application is not limited thereto, and any changes or replacements easily thought of by those skilled in the art within the technical scope disclosed in the application should be covered within the protection scope of the application.
Claims
1. A method for inspecting and managing blockages in heat transfer tubes of a steam generator based on risk classification, characterized in that, include: Step 1: Calculate the FSR of each heat transfer tube, divide the risk level into high-risk, medium-risk and low-risk areas, and clarify the differences in wear risk in each area; Step 2: Employ differentiated inspections based on both frequency and coverage for different risk levels; Step 3: Reassess the risk level of each heat transfer tube based on the inspection results and adjust the corresponding inspection methods accordingly; Step 4: Perform dynamic adjustment and inspection on the detected worn and blocked heat transfer tubes.
2. The method for inspecting and managing heat transfer tube blockages in a steam generator based on risk classification according to claim 1, characterized in that, In step 1, the FSR of high-risk areas is ≥0.7, the FSR of medium-risk areas is 0.5≤FSR<0.7, and the FSR of low-risk areas is <0.
5.
3. The method for inspecting and managing heat transfer tube blockages in a steam generator based on risk classification according to claim 1, characterized in that, In step 1, the FSR of each heat transfer tube is calculated through flow-induced vibration analysis.
4. The method for inspecting and managing heat transfer tube blockages in a steam generator based on risk classification according to claim 1, characterized in that, In step 2, heat transfer pipes in high-risk areas should be inspected annually, with each inspection covering at least 50% of the area.
5. The method for inspecting and managing heat transfer tube blockages in a steam generator based on risk classification according to claim 1, characterized in that, In step 2, heat transfer pipes in medium-risk areas should be inspected every two years, with an inspection coverage rate of no less than 25%.
6. The method for inspecting and managing heat transfer tube blockages in a steam generator based on risk classification according to claim 1, characterized in that, In step 2, heat transfer pipes in low-risk areas should be inspected every three years, with an inspection coverage rate of no less than 12.5%.
7. The method for inspecting and managing heat transfer tube blockages in a steam generator based on risk classification according to claim 1, characterized in that, In step 2, the worn / blocked heat transfer tube and its surrounding area are inspected three times consecutively until the wear stabilizes.
8. The method for inspecting and managing heat transfer tube blockages in a steam generator based on risk classification according to claim 1, characterized in that, In step 3, the inspection results are divided into: Category C-1: The number of heat transfer tubes with defects having a depth greater than 20% of the wall thickness is less than 5% of the total number of heat transfer tubes inspected. Category C-2: The number of heat transfer tubes with defects having a depth greater than 20% of the wall thickness is in the range of 5%-10% of the total number of heat transfer tubes inspected. Category C-3: The number of heat transfer tubes with wall thickness defects greater than 20% in depth exceeds 10% of the total number of heat transfer tubes under inspection, or the number of heat transfer tubes exceeding the acceptance criteria exceeds 1% of the total number of heat transfer tubes under inspection.
9. The method for inspecting and managing heat transfer tube blockages in a steam generator based on risk classification according to claim 8, characterized in that, For category C-1, the original inspection method shall be maintained; for category C-2, additional inspection shall be carried out on the steam generator; and for category C-3, additional inspection shall be carried out on the steam generator and the steam generator of the same unit.
10. The method for inspecting and managing heat transfer tube blockages in a steam generator based on risk classification according to claim 1, characterized in that, In step 4, for the detected worn heat transfer tubes, they are inspected according to the original risk area division method; for the blocked heat transfer tubes, during three consecutive reactor shutdowns and refueling overhauls, the heat transfer tubes in the surrounding layer are inspected to observe whether wear occurs and the change in the amount of wear, until the amount of wear no longer increases, and then they are inspected according to the original risk area division method.