A method and system for on-line detection of defects in nuclear power plant pipes

Abstract

The application provides a nuclear power plant pipe defect online detection method and system, electromagnetic ultrasonic waves are sent to the cold side pipeline of the nuclear power plant during cooling circulation, echo signals of the cold side pipeline are collected, and a frequency dispersion curve offset feature of the echo signals is determined; a dynamic stability criterion model of the critical speed of steam during gas-liquid flow type conversion is established through the steam flow rate and the frequency dispersion curve offset feature, and a gas-liquid interface instability region in the cold side pipeline is screened out according to the dynamic stability criterion model; flow damping to gas film flow in the cold side pipeline is identified according to the gradient change of the temperature data; the identification boundary of the gas-liquid interface instability region is corrected based on the flow damping, and a defect region of the cold side pipeline under the cold-heat cycle alternating working condition is determined according to the reflection signal of the electromagnetic ultrasonic wave in the corrected gas-liquid interface instability region; the above scheme can correct the oscillation region boundary of the steam in combination with the surface tension distribution, and realize accurate positioning of the pipeline defect under complex working conditions.

Description

Technical Field

[0001] This application relates to the field of defect detection technology, and more specifically, to an online detection method and system for defects in nuclear power plant pipe fittings. Background Technology

[0002] During the cooling cycle, the cold-side piping of a nuclear power plant generates a two-phase flow of gas and liquid due to alternating hot and cold temperatures. A vapor film easily forms at the gas-liquid interface, triggering high-frequency oscillations. Long-term operation may lead to defects such as fatigue cracks and corrosion in the piping. Under these conditions, the uneven distribution of the gas film inside the piping and the dynamic changes in the flow pattern make it difficult for traditional detection methods to accurately identify unstable areas at the gas-liquid interface and the location of defects. Therefore, there is an urgent need for an online detection technology adapted to complex flow field environments to achieve precise detection of gas film characteristics, flow pattern stability, and defects.

[0003] While single electromagnetic ultrasonic testing can acquire pipeline echo signals, it struggles to distinguish between film noise and defect signals, and its dispersion feature extraction is significantly affected by gas-liquid interface fluctuations. Single-parameter detection methods based on flow velocity or temperature cannot fully reflect the dynamic stability of gas-liquid flow pattern transitions or the inhibitory effect of surface tension on film flow, leading to potential misjudgments. Furthermore, traditional methods lack dynamic boundary correction mechanisms for gas-liquid interface instability zones, making them ill-suited for adapting to flow field changes under thermal cycling conditions. Therefore, how to integrate multi-source data such as electromagnetic ultrasonic dispersion characteristics, steam velocity, and temperature gradients to establish a dynamic stability criterion model for gas-liquid flow pattern transitions, and how to incorporate surface tension distribution to correct the boundary of steam oscillation zones, thereby achieving accurate pipeline defect localization under complex conditions, has become a major challenge in the industry. Summary of the Invention

[0004] This application provides an online detection method and system for defects in nuclear power plant pipe fittings, which can correct the boundary of the steam oscillation zone by combining surface tension distribution, and achieve accurate positioning of pipeline defects under complex operating conditions.

[0005] In a first aspect, this application provides an online detection method for defects in nuclear power plant pipe fittings, comprising the following steps:

[0006] Electromagnetic ultrasonic waves are sent to the cold-side pipes of the nuclear power plant during the cooling cycle, and the echo signals of the cold-side pipes are collected.

[0007] Determine the dispersion curve offset characteristics of the echo signal when a steam model is generated during a hot and cold cycle;

[0008] The steam velocity at the gas-liquid interface in the cold-side pipe is collected by a flow velocity sensor, and a dynamic stability criterion model for the critical steam velocity during gas-liquid flow pattern conversion is established by the steam velocity and the dispersion curve offset characteristics. Then, the gas-liquid interface instability zone with potential high-frequency steam oscillation in the cold-side pipe is screened out according to the dynamic stability criterion model.

[0009] Temperature data of the cold-side pipe is collected by a temperature sensor, and then the surface tension distribution of the condensate in the cold-side pipe is used to identify the flow damping of the gas film flow based on the gradient change of the temperature data.

[0010] The identification boundary of the gas-liquid interface instability zone is corrected based on the flow damping, and the defect area of ​​the cold-side pipeline under alternating hot and cold cycles is determined based on the reflected electromagnetic ultrasonic signal in the gas-liquid interface instability zone after correction.

[0011] In some embodiments, determining the dispersion curve shift characteristics of the echo signal when a steam model is generated during a thermal cycle specifically includes:

[0012] Determine the time-frequency distribution of the echo signal;

[0013] Based on the time-frequency distribution diagram, the dispersion curve offset characteristics of the steam model generated during the cold and hot cycle are extracted from the echo signal.

[0014] In some embodiments, establishing a dynamic stability criterion model for the critical steam velocity during gas-liquid flow pattern transition based on the steam velocity and the dispersion curve offset characteristics specifically includes:

[0015] The gas film characteristics at the gas-liquid interface are determined based on the dispersion curve offset characteristics.

[0016] The flow pattern conversion threshold at the gas-liquid interface is determined by the steam flow rate.

[0017] The critical instability velocity of steam during gas-liquid flow pattern transition is determined based on the aforementioned gas film characteristics;

[0018] A dynamic stability criterion model for the critical velocity of steam during gas-liquid flow pattern switching is established based on the flow pattern switching threshold and the instability critical velocity.

[0019] In some embodiments, the gas-liquid interface instability zone with potential high-frequency steam oscillations in the cold-side pipeline, screened according to the dynamic stability criterion model, specifically includes:

[0020] Spatial mapping of the cold-side pipe yields multiple membrane motion criterion units;

[0021] Determine the instability velocity of each membrane motion criterion unit;

[0022] Based on the dynamic stability criterion model and all instability velocities, multiple instability units with potential high-frequency steam oscillations were screened out.

[0023] Based on all the instability units, the gas-liquid interface instability zone of potential high-frequency steam oscillation in the cold-side pipe is determined.

[0024] In some embodiments, identifying the flow damping of the gas film flow by the surface tension distribution of the condensate in the cold-side pipe based on the gradient change of the temperature data specifically includes:

[0025] Determine the gradient change of the temperature data;

[0026] The surface tension distribution of the condensate in the cold-side pipe under various temperature changes is determined based on the gradient change.

[0027] Based on the tension distribution, the surface tension gradient is used to determine multiple suppressive stresses at the gas-liquid interface;

[0028] The surface tension distribution of the condensate in the cold-side pipe is determined based on all the suppressing stresses to damp the flow of the gas film flow.

[0029] In some embodiments, correcting the identification boundary of the gas-liquid interface instability region based on the flow damping specifically includes:

[0030] Determine the damping distribution diagram of the cold-side pipe;

[0031] The identification boundary of the gas-liquid interface instability zone is determined based on the flow damping and the damping distribution diagram.

[0032] The identification boundary is corrected.

[0033] In some embodiments, determining the defect region of the cold-side pipeline under alternating hot and cold cycling conditions based on the reflected signal of electromagnetic ultrasonic waves within the modified gas-liquid interface instability region specifically includes:

[0034] Adjust the transmission frequency of the electromagnetic ultrasound and re-emit the electromagnetic ultrasound to the corrected gas-liquid interface instability region, and re-acquire the reflected signal of the electromagnetic ultrasound.

[0035] The defect area of ​​the cold-side pipeline under alternating hot and cold cycles is determined based on the reflected signal.

[0036] Secondly, this application provides an online defect detection system for nuclear power plant pipe fittings, comprising:

[0037] The acquisition module is used to send electromagnetic ultrasonic waves to the cold-side pipes of the nuclear power plant during the cooling cycle and to acquire the echo signals of the cold-side pipes.

[0038] The processing module is used to determine the dispersion curve offset characteristics of the echo signal when the steam model is generated by the cold and hot cycle;

[0039] The processing module is also used to collect the steam velocity at the gas-liquid interface in the cold-side pipe through a flow velocity sensor, and to establish a dynamic stability criterion model of the steam critical velocity during the gas-liquid flow pattern conversion based on the steam velocity and the dispersion curve offset characteristics, and then to screen out the gas-liquid interface instability zone with potential high-frequency steam oscillation in the cold-side pipe according to the dynamic stability criterion model.

[0040] The processing module is also used to collect temperature data of the cold-side pipe by a temperature sensor, and then identify the flow damping of the surface tension distribution of the condensate in the cold-side pipe on the gas film flow based on the gradient change of the temperature data.

[0041] The execution module is used to correct the identification boundary of the gas-liquid interface instability zone based on the flow damping, and to determine the defect area of ​​the cold-side pipeline under alternating hot and cold cycles based on the reflected electromagnetic ultrasonic signal in the gas-liquid interface instability zone after correction.

[0042] Thirdly, this application provides a computer device, the computer device including a memory and a processor, the memory storing code, and the processor being configured to acquire the code and execute the above-described online detection method for defects in nuclear power plant pipe fittings.

[0043] Fourthly, this application provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described online detection method for defects in nuclear power plant pipe fittings.

[0044] The technical solutions provided by the embodiments disclosed in this application have the following beneficial effects:

[0045] The online detection method and system for nuclear power plant pipe defects provided in this application firstly sends electromagnetic ultrasonic waves to the cold-side pipes of the nuclear power plant during cooling cycles and collects the echo signals of the cold-side pipes; determines the dispersion curve shift characteristics of the echo signals when steam is generated during the hot and cold cycles; collects the steam velocity at the gas-liquid interface in the cold-side pipes using a flow velocity sensor, and establishes a dynamic stability criterion model for the critical steam velocity during gas-liquid flow pattern conversion based on the steam velocity and the dispersion curve shift characteristics; then, based on the dynamic stability criterion model, filters out the gas-liquid interface instability zone with potential high-frequency steam oscillation in the cold-side pipes; collects temperature data of the cold-side pipes using a temperature sensor, and then identifies the flow damping of the surface tension distribution of the condensate in the cold-side pipes on the gas film flow based on the gradient change of the temperature data; corrects the identification boundary of the gas-liquid interface instability zone based on the flow damping; and determines the defect area of ​​the cold-side pipes under alternating hot and cold cycle conditions based on the reflected signals of electromagnetic ultrasonic waves in the corrected gas-liquid interface instability zone.

[0046] Therefore, in the online defect detection method for nuclear power plant pipe fittings of this application, firstly, electromagnetic ultrasonic waves are sent to the cold-side pipes of the nuclear power plant during cooling cycles to collect the echo signals of the cold-side pipes; the dispersion curve shift characteristics of the echo signals when steam is generated during the hot and cold cycles are determined; secondly, the steam velocity at the gas-liquid interface in the cold-side pipes is collected by a flow velocity sensor, and a dynamic stability criterion model of the critical steam velocity during gas-liquid flow pattern conversion is established based on the steam velocity and the dispersion curve shift characteristics. Then, based on the dynamic stability criterion model, potential gas-liquid interface instability zones with high-frequency steam oscillations in the cold-side pipes are screened out; wherein, the gas-liquid interface instability zone refers to a continuous region where the steam velocity exceeds the critical value, causing high-frequency oscillations at the gas-liquid interface, caused by unstable membrane dynamics. Criterion unit clustering is used to locate high-risk areas of gas-liquid interface instability, facilitating the narrowing of the scanning range for subsequent electromagnetic ultrasonic testing. Temperature data from the cold-side pipe is collected by a temperature sensor, and the surface tension distribution of the condensate in the cold-side pipe is used to identify the flow damping of the gas film flow based on the gradient changes in the temperature data. This flow damping is a parameter describing the inhibitory effect of the condensate surface tension distribution on gas film flow, reflecting the suppression of gas film oscillations and facilitating subsequent correction of the identification boundary of the gas-liquid interface instability zone. Based on the flow damping, the identification boundary of the gas-liquid interface instability zone is corrected, and the defect area of ​​the cold-side pipe under alternating hot and cold cycles is determined based on the reflected signal of electromagnetic ultrasonic waves within the corrected gas-liquid interface instability zone. This scheme can combine surface tension distribution to correct the boundary of the steam oscillation zone, achieving accurate location of pipeline defects under complex operating conditions. Attached Figure Description

[0047] Figure 1 This is an exemplary flowchart of an online defect detection method for nuclear power plant pipe fittings according to some embodiments of this application;

[0048] Figure 2 This is an exemplary flowchart illustrating the determination of dispersion curve offset characteristics according to some embodiments of this application;

[0049] Figure 3 This is a schematic diagram of the structure of a temperature sensor according to some embodiments of this application;

[0050] Figure 4 This is a schematic diagram of the structure of an online detection system for defects in nuclear power plant pipe fittings, as shown in some embodiments of this application;

[0051] Figure 5 This is a schematic diagram of the structure of a computer device for implementing an online detection method for defects in nuclear power plant pipe fittings, according to some embodiments of this application. Detailed Implementation

[0052] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0053] refer to Figure 1 The figure is an exemplary flowchart of an online detection method for defects in nuclear power plant pipe fittings according to some embodiments of this application. The online detection method 100 for defects in nuclear power plant pipe fittings mainly includes the following steps:

[0054] In step 101, electromagnetic ultrasonic waves are sent to the cold-side pipes of the nuclear power plant during the cooling cycle, and the echo signals of the cold-side pipes are collected.

[0055] In practice, a broadband ultrasonic wave is emitted into the cold-side pipe during the cooling cycle via an electromagnetic ultrasonic probe. The probe uses a non-contact electromagnetic coupling method to adapt to the high-temperature and high-pressure environment of nuclear power plant pipes. A multi-channel data acquisition system is configured simultaneously to acquire mixed echo signals including the pipe body and the gas film interface. Software synchronization ensures that the transmission and acquisition timing are consistent to avoid signal aliasing. The acquisition frequency is 200MHz.

[0056] In step 102, the dispersion curve offset characteristics of the echo signal when the steam model is generated by the hot and cold cycle are determined.

[0057] In some embodiments, reference Figure 2 The figure described is an exemplary flowchart for determining the dispersion curve offset characteristics in some embodiments of this application. In this embodiment, determining the dispersion curve offset characteristics of the echo signal when a steam model is generated by a thermal cycle can be achieved by the following steps:

[0058] First, in step 1021, the time-frequency distribution diagram of the echo signal is determined;

[0059] Secondly, in step 1022, the dispersion curve offset characteristics of the steam model generated during the cold and hot cycle are extracted from the echo signal according to the time-frequency distribution diagram.

[0060] In specific implementation, the time-frequency distribution map of the echo signal can be determined in the following way: First, the echo signal is transformed in the time and space domain by short-time Fourier transform; second, a balance is achieved between the time domain and frequency domain resolution by setting the window function length, thereby obtaining the time-frequency distribution map of the echo signal. The time-frequency distribution map is an image describing the wavenumber of electromagnetic ultrasound as a function of frequency. The window function length is usually set to 5 to 10 periods, and the window function length in this application is set to 6 periods. Other methods can be used to determine the distribution map in other embodiments, which are not limited here.

[0061] In specific implementation, the dispersion curve offset characteristics of the steam vapor model generated during the cold and hot cycle can be extracted from the echo signal based on the time-frequency distribution diagram using the following method: The propagation characteristics of electromagnetic ultrasound are calculated using physical field simulation software (such as COMSOL Multiphysics, COMSOL) in conjunction with the time-frequency distribution diagram to obtain the dispersion curve. The dispersion curve is a schematic diagram describing the relationship between the propagation speed and frequency of electromagnetic ultrasound; one frequency corresponds to one propagation speed. A propagation speed is selected from the dispersion curve as the chosen propagation speed. The propagation speed of electromagnetic ultrasound in water without a vapor film at the frequency corresponding to the chosen propagation speed is obtained from the database of the nuclear power plant pipe component defect online detection system. Based on the selected propagation speed… The relative wave velocity change rate of the selected propagation speed is calculated from the propagation speed and the above-mentioned propagation speed. The relative wave velocity change rate is a parameter value describing the change of the propagation speed of electromagnetic ultrasound in a condensate with an air film relative to the propagation speed in a condensate without an air film. The relative wave velocity change rate of the selected propagation speed is judged. If the relative wave velocity change rate of the selected propagation speed is greater than the change threshold, the selected propagation speed and the frequency corresponding to the selected propagation speed are both used as dispersion curve offset features. The dispersion curve offset features of the remaining propagation speeds in the dispersion curve are further determined. The change threshold can be set according to specific measurement requirements. In this application, the change threshold is set to 3%. Other methods can be used to determine it in other embodiments, which are not limited here.

[0062] It should be noted that the dispersion curve shift feature in this application refers to the difference between the propagation speed of electromagnetic ultrasonic waves and the frequency when the electromagnetic ultrasonic waves propagate in a condensate containing an air film and the condition without an air film. It is used to describe the influence of the presence of an air film on the electromagnetic ultrasonic wave characteristics, so as to lay a data foundation for subsequent flow pattern stability analysis.

[0063] In step 103, the steam velocity at the gas-liquid interface in the cold-side pipe is collected by a flow velocity sensor, and a dynamic stability criterion model for the critical steam velocity during gas-liquid flow pattern conversion is established by the steam velocity and the dispersion curve offset characteristics. Then, the gas-liquid interface instability zone with potential high-frequency steam oscillation in the cold-side pipe is screened out according to the dynamic stability criterion model.

[0064] In practice, a flow velocity sensor (such as an ultrasonic Doppler velocimeter) is installed in the gas-liquid interface area of ​​the cold-side pipeline. The sensor axis is perpendicular to the pipeline axis to obtain the steam flow velocity at the gas-liquid interface. The flow velocity data is synchronized with the ultrasonic detection system through a time synchronization module (such as a clock) to ensure that the acquisition timing and spatial location of the flow velocity data and the dispersion signal are consistent. A sliding window filter (such as a mean filter) is used to remove high-frequency noise from the acquired steam flow velocity signal to obtain the steam flow velocity at the gas-liquid interface in the cold-side pipeline.

[0065] In some embodiments, the dynamic stability criterion model for the critical steam velocity during gas-liquid flow pattern transition, established by means of the steam velocity and the dispersion curve offset characteristics, can be implemented using the following steps:

[0066] The gas film characteristics at the gas-liquid interface are determined based on the dispersion curve offset characteristics.

[0067] The flow pattern conversion threshold at the gas-liquid interface is determined by the steam flow rate.

[0068] The critical instability velocity of steam during gas-liquid flow pattern transition is determined based on the aforementioned gas film characteristics;

[0069] A dynamic stability criterion model for the critical velocity of steam during gas-liquid flow pattern switching is established based on the flow pattern switching threshold and the instability critical velocity.

[0070] In specific implementation, determining the gas film characteristics at the gas-liquid interface based on the dispersion curve shift characteristics can be achieved in the following way: Initialize a gas film characteristic model, using all propagation velocities in the dispersion curve shift characteristics as initialization parameters of the gas film characteristic model, and using all frequencies in the dispersion curve shift characteristics as constraint parameters of the gas film characteristic model. Then, obtain the gas film characteristics at the gas-liquid interface through this gas film characteristic model. The gas film characteristic model is a model of gas film characteristics established using machine learning algorithms (such as decision trees, neural networks, etc.). For example, the model is: Gas film feature = all propagation velocities (i.e., initialization parameters) in the dispersion curve offset feature * A + all frequencies (i.e., initialization parameters) in the dispersion curve offset feature * B, where A and B are weighting coefficients. A and B can be determined by fitting the historical dataset of the training gas film feature using a multiple linear regression method (such as the least squares method). The gas film feature describes the characteristics of the vapor film generated at the gas-liquid interface, including gas film thickness, gas film density, and gas film equivalent radius. Other methods can also be used to determine these characteristics in other embodiments, which are not limited here.

[0071] It should be noted that the propagation speed and frequency distribution of electromagnetic ultrasound in air-film pipelines are modulated by the geometric and physical properties of the air film. By determining the weighting coefficients through multiple linear regression (such as the least squares method), this modulation relationship can be quantified, thereby inverting the air film characteristics from the dispersive signal and providing basic parameters for subsequent flow pattern analysis.

[0072] In specific implementation, the flow pattern conversion threshold of the gas-liquid flow pattern at the gas-liquid interface can be determined by the following method: the equivalent radius of the gas film, the gas film density, and the steam velocity in the gas film characteristics are all known operands, and then the critical Weber number of the gas-liquid flow pattern at the gas-liquid interface is calculated by combining the Weber number calculation formula, and the above critical Weber number is used as the flow pattern conversion threshold of the gas-liquid flow pattern; other methods can also be used to determine it in other embodiments, which are not limited here.

[0073] It should be noted that the flow pattern conversion threshold in this application is a parameter value describing the critical condition for the flow pattern of a fluid (steam and condensate) to change from a stable subsurface flow to an intermittent flow. When the steam velocity increases, the inertial force dominates the fluid motion, which intensifies the interfacial fluctuations at the gas-liquid interface and causes the fluid flow pattern to change from a stable subsurface flow to an intermittent flow. The critical Weber number is calculated using the equivalent radius of the gas film, density, and steam velocity. When the critical Weber number exceeds the critical value, the risk of gas film instability at the gas-liquid interface increases significantly. This threshold transforms the interfacial stability theory in fluid mechanics into a calculable quantitative index, which can provide a criterion for flow pattern conversion.

[0074] In specific implementation, the instability critical velocity of steam during the gas-liquid flow pattern transition can be determined by the following method: obtaining the density of condensate from the database of the nuclear power plant pipe defect online detection system, and using the density of condensate, the equivalent radius of the gas film in the gas film characteristics, and the gas film density in the gas film characteristics as known parameters, and combining them with the critical velocity formula to calculate the instability critical velocity; other methods can also be used to determine it in other embodiments, which are not limited here.

[0075] It should be noted that when the steam velocity exceeds the critical value, the minute disturbances at the gas-liquid interface will be amplified and trigger high-frequency oscillations of the gas film. The critical velocity formula, which combines the condensate density, the equivalent radius of the gas film, and the gas film density, quantifies the balance between surface tension and inertial force at the gas-liquid interface: the thinner and lower the density of the gas film, or the higher the density of the condensate, the lower the critical velocity, and the more easily the gas film at the gas-liquid interface becomes unstable. The instability critical velocity is a parameter value describing the critical velocity condition at which the gas-liquid interface ruptures due to the transition of the fluid (steam and condensate) flow pattern from a stable split laminar flow to an intermittent flow. It is used to judge the instability of the gas film caused by local flow velocity.

[0076] In specific implementation, the dynamic stability criterion model for the steam critical velocity during gas-liquid flow pattern transition, based on the flow pattern transition threshold and the instability critical velocity, can be implemented in the following way: Obtain pipe geometric parameters from the database of the nuclear power plant pipe fitting defect online detection system; use the flow pattern transition threshold and the instability critical velocity as known input variables; combine the basic equations of fluid dynamics to establish a multi-parameter dynamic stability criterion model; and then use the established multi-parameter dynamic stability criterion model as the dynamic stability criterion model in this application. As a preferred embodiment, a forward modeling method based on instability theory (such as Helmholtz instability theory) can be used to construct a model with the gas phase velocity and the equivalent radius of the gas film as... The critical velocity function of the variables is used to simulate the triggering conditions for gas-liquid interface instability under different subcooling and wall temperatures, thereby describing the dynamic stability criterion for the transition of steam and condensate flow patterns from stratified flow to intermittent flow. The input variables of the multi-parameter dynamic stability criterion model include the flow pattern transition threshold, the critical instability velocity, the steam velocity at each point in the cold-side pipe, and the instability velocity at each point in the cold-side pipe; the output is the critical stability index of the gas-liquid flow pattern transition. This model is constructed based on the conservation laws of fluid mechanics and the theory of interface instability, considering the dynamic balance between gas phase momentum transfer and surface tension, and solving the gas-liquid interface stability through numerical methods (such as the finite volume method). Other methods can also be used to determine the stability in other embodiments, which are not limited here.

[0077] It should be noted that the dynamic stability criterion model in this application is based on the theory of interface instability, integrating the characteristic parameters of gas-liquid two-phase flow and pipeline geometry. It achieves quantitative prediction of the critical conditions for flow pattern transformation through numerical simulation (such as multiphase flow model). This model is applicable to the identification of gas-liquid interface instability zones in cold-side pipelines of nuclear power plants under alternating hot and cold cycles. When the local steam velocity exceeds the critical velocity or the flow pattern transformation threshold is exceeded, the stability of the interface at the gas-liquid junction is destroyed, triggering a warning of gas film oscillation risk, and providing a core criterion for screening gas-liquid interface instability zones.

[0078] In some embodiments, the following steps can be used to screen out the gas-liquid interface instability zone of potential high-frequency steam oscillation in the cold-side pipeline according to the dynamic stability criterion model:

[0079] Spatial mapping of the cold-side pipe yields multiple membrane motion criterion units;

[0080] Determine the instability velocity of each membrane motion criterion unit;

[0081] Based on the dynamic stability criterion model and all instability velocities, multiple instability units with potential high-frequency steam oscillations were screened out.

[0082] Based on all the instability units, the gas-liquid interface instability zone of potential high-frequency steam oscillation in the cold-side pipe is determined.

[0083] The membrane dynamics criterion unit refers to the basic analysis unit formed after spatial discretization of the cold-side pipeline of a nuclear power plant. By decomposing the complex flow field into quantifiable basic units, a refined assessment of the stability of the gas-liquid interface can be achieved. Specifically, the cold-side pipeline is spatially mapped to obtain multiple membrane dynamics criterion units, which can be achieved in the following way: obtain the pipeline geometric parameters (such as length and width) from the database of the nuclear power plant pipe defect online detection system, and divide the cold-side pipeline into multiple equally spaced grid units along the axial direction using structured mesh generation technology (such as a three-dimensional finite element mesh generator, Gmsh) in combination with the pipeline geometric parameters. Then, through a time synchronization module (such as hardware clock synchronization), the flow velocity sensor (such as an electromagnetic flowmeter) and electromagnetic ultrasonic probe are mapped to the corresponding grid units according to spatial coordinates, and all grid units are used as membrane dynamics criterion units. In other embodiments, other methods can also be used to determine the membrane dynamics criterion units, which are not limited here.

[0084] In specific implementation, the instability velocity of each membrane kinetic criterion unit can be determined as follows: A membrane kinetic criterion unit is selected as the chosen membrane kinetic criterion unit. The gas film geometric parameters at the chosen membrane kinetic criterion unit are calculated using a gas film model combined with electromagnetic and ultrasonic signals from that unit. These parameters include the thickness, density, and equivalent radius of the gas film at the chosen unit. The density, equivalent radius, and density of the condensate at the chosen unit are then substituted into the critical velocity formula as known operands to calculate the instability velocity of the chosen membrane kinetic criterion unit. This instability velocity is a critical parameter value describing the vapor velocity at the gas-liquid interface of the membrane kinetic criterion unit when it loses its stable state. The instability velocities of the remaining membrane kinetic criterion units are then determined. Other methods can also be used in other embodiments, which are not limited here.

[0085] In specific implementation, the selection of multiple unstable units with potential high-frequency steam oscillations based on the dynamic stability criterion model and all unstable velocities can be achieved in the following way: Select a membrane dynamics criterion unit as the selected membrane dynamics criterion unit, and input the unstable velocity of the selected membrane dynamics criterion unit, the steam velocity at the selected membrane dynamics criterion unit, the flow pattern transition threshold, and the critical unstable velocity as input parameters into the dynamic stability criterion model. Judge the critical stability index of the gas-liquid flow pattern transition output by the dynamic stability criterion model. If the above critical stability index is greater than or equal to 1, then mark the selected membrane dynamics criterion unit as a potentially unstable unit with high-frequency steam oscillations, and continue to judge the remaining membrane dynamics criterion units; in other embodiments, other methods can also be used to determine this, which are not limited here.

[0086] It should be noted that the measured steam velocity, calculated instability velocity, and flow pattern conversion threshold of each membrane dynamics criterion unit are input into the dynamic stability criterion model. The unstable units are screened by comparing the actual working conditions with the critical conditions. If the critical stability index output by the model is ≥1, it indicates that the steam velocity of the membrane dynamics criterion unit has exceeded the critical threshold for interface instability, which will lead to increased interfacial fluctuations at the gas-liquid interface under the dominance of inertial force, forming a potential high-frequency oscillation source.

[0087] In specific implementation, the gas-liquid interface instability region with potential high-frequency steam oscillation in the cold-side pipeline can be determined based on all instable units in the following manner: using the Connected Component Labelling (CCL) algorithm, clustering the membrane motion criterion units marked as unstable based on the four-neighbor or eight-neighbor criteria, merging adjacent units to form a continuous region, and filling and smoothing the boundaries of the formed continuous region through morphological closing operations, thereby obtaining the gas-liquid interface instability region with potential high-frequency steam oscillation in the cold-side pipeline; other methods can also be used in other embodiments, which are not limited here.

[0088] It should be noted that the gas-liquid interface instability region in this application refers to a continuous region where the vapor velocity exceeds the critical value, causing high-frequency oscillations at the gas-liquid interface. It is formed by clustering unstable membrane dynamics criterion units and is used to locate high-risk areas of gas-liquid interface instability, which facilitates narrowing the scanning range of subsequent electromagnetic ultrasonic testing.

[0089] In step 104, temperature data of the cold-side pipe is collected by a temperature sensor, and then the surface tension distribution of the condensate in the cold-side pipe is identified as the flow damping of the gas film flow based on the gradient change of the temperature data.

[0090] For specific implementation, refer to Figure 3 The figure is a schematic diagram of the temperature sensor structure in some embodiments of this application. In this application, a temperature sensor (such as an infrared thermal imager) is arranged along the axial direction of the cold-side pipe. The temperature sensor scans the circumferential temperature distribution through the pipe window and records the temperature value of each spatial position (spatial position interval 0.5-1m) in real time. The temperature value is then mapped to the membrane motion criterion unit through the pipe geometric model. Median filtering is used to remove pulse noise to obtain the temperature data of the cold-side pipe.

[0091] In some embodiments, identifying the flow damping of the gas film flow by the surface tension distribution of the condensate in the cold-side pipe based on the gradient change of the temperature data can be achieved by the following steps:

[0092] Determine the gradient change of the temperature data;

[0093] The surface tension distribution of the condensate in the cold-side pipe under various temperature changes is determined based on the gradient change.

[0094] Based on the tension distribution, the surface tension gradient is used to determine multiple suppressive stresses at the gas-liquid interface;

[0095] The surface tension distribution of the condensate in the cold-side pipe is determined based on all the suppressing stresses to damp the flow of the gas film flow.

[0096] In specific implementation, the gradient change of the temperature data can be determined by the following steps: select any two membrane motion criteria units as the two selected membrane motion criteria units, use the temperature corresponding to the two selected membrane motion criteria units and the spatial coordinates of the two selected membrane motion criteria units as known operands, calculate the axial temperature gradient between the two selected membrane motion criteria units, continue to determine the temperature gradient between the remaining two arbitrary membrane motion criteria units, and use the set of all obtained temperature gradients as the gradient change of the temperature data; in other embodiments, other methods can also be used to determine it, which are not limited here.

[0097] In specific implementation, determining the surface tension distribution of condensate in the cold-side pipe under various temperature changes based on the gradient changes can be achieved through the following steps: Select a membrane kinetic criterion unit as the selected membrane kinetic criterion unit; obtain the working fluid characteristic constant from the database of the power plant pipe defect online detection system, wherein the working fluid characteristic constant refers to a constant reflecting the thermodynamic properties of the working fluid in the nuclear power plant; use the working fluid characteristic constant and the mean of all temperature gradients corresponding to the selected membrane kinetic criterion unit as known operands; calculate the surface tension of the selected membrane kinetic criterion unit by combining the physical property relationship of water surface tension with temperature change (such as Etworth's rule); continue to determine the surface tension of the remaining membrane kinetic criterion units; and use the set of all obtained surface tensions and the spatial coordinates of each membrane kinetic criterion unit as the surface tension distribution of condensate in the cold-side pipe under various temperature changes, wherein the tension distribution describes the distribution of surface tension of condensate at the gas-liquid interface at each membrane kinetic criterion unit in the cold-side pipe; other methods can also be used in other embodiments, which are not limited here.

[0098] It should be noted that during the cooling cycle of a nuclear power plant, the temperature gradient of the cold-side pipes reflects the local temperature value of each membrane kinetic criterion unit in the cold-side pipes. The surface tension of each membrane kinetic criterion unit is a function of temperature. By using the thermodynamic constant of the working fluid (such as the surface tension temperature coefficient of pure water), the temperature distribution can be transformed into the spatial distribution of surface tension, providing basic data for analyzing the inhibitory effect of the surface tension gradient on the gas film, thereby inversely deriving the condensate surface tension of each membrane kinetic criterion unit.

[0099] In specific implementation, determining the surface tension gradient's suppression stress at the gas-liquid interface based on the tension distribution can be achieved through the following steps: Select a membrane dynamics criterion unit as the selected membrane dynamics criterion unit, use the surface tension corresponding to the selected membrane dynamics criterion unit in the tension distribution as a known parameter, and calculate the suppression stress at the gas-liquid interface of the selected membrane dynamics criterion unit using the shear relationship of surface tension on the gas-liquid interface (such as the Marangoni stress formula). Continue to determine the suppression stress of the remaining membrane dynamics criterion units, wherein the suppression stress describes the stress of the surface tension of the condensate at the gas-liquid interface suppressing the unstable flow of the gas film; other methods can also be used in other embodiments, which are not limited here.

[0100] It should be noted that the surface tension of the condensate at the gas-liquid interface generates shear stress, which inhibits the unstable flow of the gas film. The surface tension value of each membrane kinetic criterion unit is converted into interfacial shear stress using the Marangoni stress formula. The physical effect of this shear stress is that when the gas film flow causes uneven interfacial temperature, the surface tension gradient will form a reverse stress, which hinders the excessive oscillation of the gas film. Therefore, calculating the suppression stress of each membrane kinetic criterion unit can quantify the stabilizing ability of surface tension on the gas film flow.

[0101] In specific implementation, the flow damping of the surface tension distribution of the condensate in the cold-side pipe on the gas film flow can be determined by the following steps based on all the suppressing stresses: Select one suppressing stress as the selected suppressing stress, substitute the selected suppressing stress and the area of ​​the membrane kinetic criterion unit corresponding to the selected suppressing stress as known parameters into the equivalent damping coefficient calculation formula, and obtain the equivalent damping coefficient of the surface tension of the condensate at the membrane kinetic criterion unit corresponding to the selected suppressing stress on the gas film flow. Continue to determine the equivalent damping coefficient of the membrane kinetic criterion unit corresponding to the remaining suppressing stresses, and take the average of all obtained equivalent damping coefficients as the flow damping of the surface tension distribution of the condensate in the cold-side pipe on the gas film flow. In other embodiments, other methods can also be used to determine this, which are not limited here.

[0102] It should be noted that the flow damping in this application is a parameter value describing the inhibitory effect of the surface tension distribution of the condensate in the cold-side pipe on the gas film flow. It is used to reflect the situation where gas film oscillation is suppressed, which facilitates the subsequent correction of the identification boundary of the gas-liquid interface instability zone. Among them, the shear stress generated by the surface tension gradient of the condensate in the cold-side pipe is essentially a viscous damping force. By averaging the damping effect of all film motion criterion units, the comprehensive damping effect of the condensate surface tension distribution in the entire cold-side pipe on the gas film flow can be obtained. The higher the damping coefficient, the easier it is to suppress the gas film flow and the lower the oscillation risk, thus providing a key parameter for correcting the boundary of the gas-liquid interface instability zone (e.g., a high-damping region can reduce the range of the oscillation zone).

[0103] In step 105, the identification boundary of the gas-liquid interface instability zone is corrected based on the flow damping, and the defect area of ​​the cold-side pipeline under alternating hot and cold cycles is determined based on the reflected electromagnetic ultrasonic signal in the gas-liquid interface instability zone after correction.

[0104] In some embodiments, the correction of the identification boundary of the gas-liquid interface instability region based on the flow damping can be achieved by the following steps:

[0105] Determine the damping distribution diagram of the cold-side pipe;

[0106] The identification boundary of the gas-liquid interface instability zone is determined based on the flow damping and the damping distribution diagram.

[0107] The identification boundary is corrected.

[0108] In specific implementation, the damping distribution diagram of the cold-side pipe can be determined by the following steps: the damping distribution diagram of the cold-side pipe is obtained by combining the spatial coordinates of each membrane motion criterion unit and the equivalent damping coefficient of each membrane motion criterion unit with mathematical modeling software (such as MATrix LABoratory, MATLAB); other methods can also be used to determine it in other embodiments, which are not limited here.

[0109] In specific implementation, the identification boundary of the gas-liquid interface instability zone can be determined based on the flow damping and the damping distribution map using the following steps: using flow damping as a judgment index, the candidate regions composed of membrane dynamics criterion units corresponding to all equivalent damping coefficients greater than or equal to the flow damping in the damping distribution map are filled with the boundaries of the candidate regions through morphological closing operations, and the filled boundary is taken as the identification boundary of the gas-liquid interface instability zone. Here, the identification boundary refers to the boundary of the gas-liquid interface instability zone. In other embodiments, other methods can also be used to determine it, which are not limited here.

[0110] In specific implementation, the correction of the recognition boundary can be achieved by the following steps: the recognition boundary of the candidate region is removed by morphological closing operation (such as filling holes) and connected component analysis to eliminate isolated regions in the candidate region, so as to obtain continuous recognition boundary; other methods can also be used to determine it in other embodiments, which are not limited here.

[0111] In some embodiments, determining the defect region of the cold-side pipeline under alternating hot and cold cycling conditions based on the reflected signal of electromagnetic ultrasonic waves within the modified gas-liquid interface instability region can be achieved using the following steps:

[0112] Adjust the transmission frequency of the electromagnetic ultrasound and re-emit the electromagnetic ultrasound to the corrected gas-liquid interface instability region, and re-acquire the reflected signal of the electromagnetic ultrasound.

[0113] The defect area of ​​the cold-side pipeline under alternating hot and cold cycles is determined based on the reflected signal.

[0114] In specific implementation, adjusting the transmission frequency of the electromagnetic ultrasonic wave to re-emit the electromagnetic ultrasonic wave towards the corrected gas-liquid interface instability region and re-acquiring the reflected signal of the electromagnetic ultrasonic wave can be achieved through the following steps: Based on the gas film geometry parameters and gas film density of the gas-liquid interface instability region, the surface tension at the gas-liquid interface, and the sound wave propagation model at the gas-liquid interface, the optimal detection frequency matching the gas film vibration characteristics is calculated. The optimal detection frequency enables the electromagnetic ultrasonic wave to generate effective coupling at the gas-liquid interface, reduces signal attenuation, and enhances the characteristic identification of the reflected signal. Thus, the electromagnetic ultrasonic wave with the optimal detection frequency is emitted towards the corrected gas-liquid interface instability region, and the reflected signal carrying information about the gas film boundary and defects is acquired. In other embodiments, other methods can also be used to determine the frequency, which are not limited here.

[0115] In specific implementation, determining the defect area of ​​the cold-side pipeline under alternating hot and cold cycles based on the reflected signal can be achieved through the following steps: First, the collected reflected signal is preprocessed for noise reduction (e.g., wavelet threshold denoising), defect feature signals (e.g., abrupt echoes) are extracted, and the signal is spatially located using the time reversal method. The defect location coordinates are calculated in combination with the pipeline geometric parameters. Then, pattern matching is performed based on the defect feature library (e.g., echo amplitude-time delay template), and a machine learning classifier (e.g., support vector machine) is used to identify the defect type, thereby obtaining the defect area of ​​the cold-side pipeline under alternating hot and cold cycles. In other embodiments, other methods can also be used to determine the defect area, which are not limited here.

[0116] In another aspect, in some embodiments, this application provides an online defect detection system for nuclear power plant piping components, with reference to... Figure 4 The figure is a schematic diagram of the structure of an online detection system for defects in nuclear power plant pipe fittings according to some embodiments of this application. The online detection system 400 for defects in nuclear power plant pipe fittings includes: a data acquisition module 401, a processing module 402, and an execution module 403, which are described below:

[0117] Acquisition module 401, in this application, is mainly used to send electromagnetic ultrasonic waves to the cold-side pipes of the nuclear power plant during the cooling cycle and to acquire the echo signals of the cold-side pipes.

[0118] Processing module 402, in this application, is used to determine the dispersion curve offset characteristics of the echo signal when a steam model is generated by a cold and hot cycle;

[0119] It should be noted that the processing module 402 in this application is also used to collect the steam flow velocity at the gas-liquid interface in the cold side pipe through the flow velocity sensor, and to establish a dynamic stability criterion model of the steam critical velocity when the gas-liquid flow pattern is converted by the steam flow velocity and the dispersion curve offset characteristics, and then screen out the gas-liquid interface instability zone with potential high-frequency steam oscillation in the cold side pipe according to the dynamic stability criterion model.

[0120] Additionally, it should be noted that the processing module 402 in this application is also used to collect temperature data of the cold-side pipe by a temperature sensor, and then identify the flow damping of the surface tension distribution of the condensate in the cold-side pipe on the gas film flow based on the gradient change of the temperature data.

[0121] The execution module 403 in this application is mainly used to correct the identification boundary of the gas-liquid interface instability zone based on the flow damping, and to determine the defect area of ​​the cold side pipeline under alternating hot and cold cycles based on the reflected electromagnetic ultrasonic signal in the gas-liquid interface instability zone after correction.

[0122] In addition, this application also provides a computer device, which includes a memory and a processor. The memory stores code, and the processor is configured to acquire the code and execute the above-described online detection method for defects in nuclear power plant pipe fittings.

[0123] In some embodiments, reference Figure 5 The figure is a schematic diagram of the structure of a computer device for implementing an online defect detection method for nuclear power plant pipe fittings according to some embodiments of this application. The online defect detection method for nuclear power plant pipe fittings in the above embodiments can... Figure 5 The computer device shown is used to implement this, and the computer device 500 includes at least one processor 501, a communication bus 502, a memory 503, and at least one communication interface 504.

[0124] Processor 501 can be a general-purpose central processing unit (CPU) or an application-specific integrated circuit (ASIC).

[0125] The communication bus 502 can be used to transmit information between the aforementioned components.

[0126] Memory 503 may be a read-only memory (ROM) or other type of static storage device capable of storing static information and instructions, random access memory (RAM) or other type of dynamic storage device capable of storing information and instructions, or electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM) or other optical disc storage, optical disc storage (including compressed optical discs, laser discs, optical discs, digital versatile optical discs, Blu-ray discs, etc.), magnetic disks or other magnetic storage devices, or any other medium capable of carrying or storing desired program code in the form of instructions or data structures and accessible by a computer, but not limited thereto. Memory 503 may exist independently and be connected to processor 501 via communication bus 502. Memory 503 may also be integrated with processor 501.

[0127] The memory 503 stores program code for executing the scheme of this application, and its execution is controlled by the processor 501. The processor 501 executes the program code stored in the memory 503. The program code may include one or more software modules. The method used in the above embodiments can be implemented by the processor 501 and one or more software modules in the program code in the memory 503.

[0128] Communication interface 504 uses any transceiver-like device to communicate with other devices or communication networks, such as Ethernet, radio access network (RAN), wireless local area networks (WLAN), etc.

[0129] In a specific implementation, as one example, a computer device may include multiple processors, each of which may be a single-core (single-CPU) processor or a multi-core (multi-CPU) processor. Here, a processor may refer to one or more devices, circuits, and / or processing cores used to process data (e.g., computer program instructions).

[0130] The aforementioned computer device can be a general-purpose computer device or a special-purpose computer device. In specific implementations, the computer device can be a desktop computer, a portable computer, a network server, a handheld digital assistant (PDA), a mobile phone, a tablet computer, a wireless terminal device, a communication device, or an embedded device. This application does not limit the type of computer device.

[0131] In addition, this application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described online detection method for defects in nuclear power plant pipe fittings.

[0132] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0133] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for on-line detection of defects in a nuclear power plant pipe, characterized in that, Includes the following steps: Electromagnetic ultrasonic waves are sent to the cold-side pipes of the nuclear power plant during the cooling cycle, and the echo signals of the cold-side pipes are collected. Determine the dispersion curve offset characteristics of the echo signal when a steam model is generated during a hot and cold cycle; The steam velocity at the gas-liquid interface in the cold-side pipe is collected by a flow velocity sensor, and a dynamic stability criterion model for the critical steam velocity during gas-liquid flow pattern conversion is established by the steam velocity and the dispersion curve offset characteristics. Then, the gas-liquid interface instability zone with potential high-frequency steam oscillation in the cold-side pipe is screened out according to the dynamic stability criterion model. Temperature data of the cold-side pipe is collected by a temperature sensor, and then the surface tension distribution of the condensate in the cold-side pipe is used to identify the flow damping of the gas film flow based on the gradient change of the temperature data. Based on the flow damping, the identification boundary of the gas-liquid interface instability zone is corrected, and the defect area of ​​the cold side pipeline under alternating hot and cold cycles is determined according to the reflected signal of electromagnetic ultrasonic waves in the gas-liquid interface instability zone after correction. Specifically, the dynamic stability criterion model for establishing the critical steam velocity during gas-liquid flow pattern transition based on the steam velocity and the dispersion curve offset characteristics includes: The gas film characteristics at the gas-liquid interface are determined based on the dispersion curve offset characteristics. The flow pattern conversion threshold at the gas-liquid interface is determined by the steam flow rate. The critical instability velocity of steam during gas-liquid flow pattern transition is determined based on the aforementioned gas film characteristics; A dynamic stability criterion model for the critical velocity of steam during gas-liquid flow pattern switching is established based on the flow pattern switching threshold and the instability critical velocity.

2. The method as described in claim 1, characterized in that, The specific characteristics of the dispersion curve shift of the echo signal when the steam model is generated by the thermal cycle include: Determine the time-frequency distribution of the echo signal; Based on the time-frequency distribution diagram, the dispersion curve offset characteristics of the steam model generated during the cold and hot cycle are extracted from the echo signal.

3. The method as described in claim 1, characterized in that, Based on the dynamic stability criterion model, the specific gas-liquid interface instability zones with potential high-frequency steam oscillations in the cold-side pipeline include: Spatial mapping of the cold-side pipe yields multiple membrane motion criterion units; Determine the instability velocity of each membrane motion criterion unit; Based on the dynamic stability criterion model and all instability velocities, multiple instability units with potential high-frequency steam oscillations were screened out. Based on all the instability units, the gas-liquid interface instability zone of potential high-frequency steam oscillation in the cold-side pipe is determined.

4. The method as described in claim 1, characterized in that, The flow damping effect of the surface tension distribution of the condensate in the cold-side pipe on the gas film flow, based on the gradient change of the temperature data, specifically includes: Determine the gradient change of the temperature data; The surface tension distribution of the condensate in the cold-side pipe under various temperature changes is determined based on the gradient change. Based on the tension distribution, the surface tension gradient is used to determine multiple suppressive stresses at the gas-liquid interface; The surface tension distribution of the condensate in the cold-side pipe is determined based on all the suppressing stresses to damp the flow of the gas film flow.

5. The method as described in claim 1, characterized in that, The correction of the identification boundary of the gas-liquid interface instability region based on the aforementioned flow damping specifically includes: Determine the damping distribution diagram of the cold-side pipe; The identification boundary of the gas-liquid interface instability zone is determined based on the flow damping and the damping distribution diagram. The identification boundary is corrected.

6. The method as described in claim 1, characterized in that, Based on the reflected electromagnetic ultrasonic signals within the corrected gas-liquid interface instability zone, the specific defect areas of the cold-side pipeline under alternating hot and cold cycling conditions are determined as follows: Adjust the transmission frequency of the electromagnetic ultrasound and re-emit the electromagnetic ultrasound to the corrected gas-liquid interface instability region, and re-acquire the reflected signal of the electromagnetic ultrasound. The defect area of ​​the cold-side pipeline under alternating hot and cold cycles is determined based on the reflected signal.

7. An online defect detection system for nuclear power plant pipe fittings, comprising performing online defect detection of nuclear power plant pipe fittings using the method described in any one of claims 1 to 6, characterized in that, The system includes: The acquisition module is used to send electromagnetic ultrasonic waves to the cold-side pipes of the nuclear power plant during the cooling cycle and to acquire the echo signals of the cold-side pipes. The processing module is used to determine the dispersion curve offset characteristics of the echo signal when the steam model is generated by the cold and hot cycle; The processing module is also used to collect the steam velocity at the gas-liquid interface in the cold-side pipe through a flow velocity sensor, and to establish a dynamic stability criterion model of the steam critical velocity during the gas-liquid flow pattern conversion based on the steam velocity and the dispersion curve offset characteristics, and then to screen out the gas-liquid interface instability zone with potential high-frequency steam oscillation in the cold-side pipe according to the dynamic stability criterion model. The processing module is also used to collect temperature data of the cold-side pipe by a temperature sensor, and then identify the flow damping of the surface tension distribution of the condensate in the cold-side pipe on the gas film flow based on the gradient change of the temperature data. The execution module is used to correct the identification boundary of the gas-liquid interface instability zone based on the flow damping, and to determine the defect area of ​​the cold-side pipeline under alternating hot and cold cycles based on the reflected electromagnetic ultrasonic signal in the gas-liquid interface instability zone after correction.

8. A computer device, characterized in that, The computer device includes a memory and a processor, the memory storing code, and the processor being configured to acquire the code and execute the online detection method for defects in nuclear power plant pipe fittings as described in any one of claims 1 to 6.

9. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the online detection method for defects in nuclear power plant pipe fittings as described in any one of claims 1 to 6.

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