Nuclear power plant small branch pipe weld defect identification system and method

Abstract

The invention belongs to the field of defect recognition, and particularly relates to a nuclear power plant small branch pipe weld defect recognition system and method.The system comprises an acceleration measuring system, a control collecting and processing system and a pulse excitation system; the acceleration measuring system is installed on a small branch pipe welding seam, and the acceleration measuring system and the pulse excitation system are connected with the control collecting and processing system. The pulse excitation system applies excitation to the welding seam of the small branch pipe, the control acquisition and processing system acquires measurement data of the acceleration measurement system and excitation data applied by the pulse excitation system, and the measurement data and the excitation data are analyzed and calculated to obtain a frequency response function. According to the method, the small branch pipe welding seam defect is recognized by obtaining the frequency response function difference value of the small branch pipe under different excitations, recognition is rapid and effective, and the defect that manual inspection and visual inspection are insufficient in precision is overcome.

Description

Technical Field

[0001] The invention belongs to the field of defect recognition, and in particular relates to a system and method for identifying defects in weld seams of small branch pipes in nuclear power plants. Background Art

[0002] In recent years, in response to the incidents of small branch pipes breaking and causing unit shutdown in nuclear power plants, China's nuclear power system organized vibration fatigue screening, and formulated the reliability management guidelines and supervision plan for small branch pipes in the conventional island and nuclear island based on the screening results. During the implementation of the above work, some problems were found, that is, after relying on existing standards (including ASME and relevant domestic standards) to screen sensitive pipes, some small branch pipes that were not included in the sensitive pipe list still broke. Recently, the cracking of the weld of the steam drain pipe of a steam turbine in a power plant was listed as a Class A incident in China's nuclear power, affecting production work.

[0003] After a long period of tracking and analysis, as well as a lot of research work, it is currently believed that the root cause of the above problems is that some small branches already have initial defects before fatigue evaluation, such as welding defects or fatigue cracks. Under the influence of alternating stress, fatigue fracture will occur earlier than ordinary small branches, and then the original evaluation method will no longer be applicable. Therefore, these small branches with initial defects should be removed before the vibration screening of small branches. In general, the vibration screening list of small branches of each unit in each nuclear power plant is about 2,000, and the use of non-destructive testing methods such as X-rays or ultrasound is not efficient, time-consuming and labor-intensive. Manual visual inspection is not accurate enough, and a fast and effective inspection method is urgently needed. Summary of the invention

[0004] The purpose of the present invention is to provide a system and method for identifying defects in small branch pipe welds in nuclear power plants. The method identifies defects in small branch pipe welds by obtaining the difference in frequency response functions of small branch pipes under different excitations. The identification is fast and effective, making up for the defect of insufficient accuracy of manual visual inspection.

[0005] The technical solution to achieve the purpose of the present invention is:

[0006] A nuclear power plant small branch pipe weld defect identification system, the system comprising: an acceleration measurement system, a control acquisition processing system, and a pulse excitation system; the acceleration measurement system is installed on the small branch pipe weld, and the acceleration measurement system and the pulse excitation system are respectively connected to the control acquisition processing system; the pulse excitation system applies excitation to the small branch pipe weld, the control acquisition processing system collects measurement data of the acceleration measurement system and excitation data applied by the pulse excitation system, analyzes and calculates the measurement data and the excitation data, and obtains a frequency response function.

[0007] The pulse excitation system includes an exciter and a force sensor. The exciter, the force sensor, and the control acquisition processing system are connected in sequence. The exciter is used to apply excitation to the small branch pipe weld. The force sensor collects the excitation data applied by the exciter and sends the excitation data to the control acquisition processing system.

[0008] The acceleration measurement system adopts an acceleration sensor, the control acquisition processing system adopts a portable data acquisition and analysis system with a frequency response function calculation function, and the vibration exciter adopts a hard plastic head hammer.

[0009] The bandwidth of the data acquisition and analysis system is selected to be 1000 Hz, and the resolution is not less than 1 Hz.

[0010] A method for identifying weld defects of a small branch pipe in a nuclear power plant, the method comprising:

[0011] Step 1: Install the acceleration measurement system on the weld of the small branch pipe, and connect the acceleration measurement system and the pulse excitation system to the control acquisition processing system respectively;

[0012] Step 2: The pulse excitation system applies excitation to the small branch pipe weld, and the control acquisition processing system collects the measurement data of the acceleration measurement system and the excitation data applied by the pulse excitation system;

[0013] Step 3: Control the acquisition and processing system to analyze the measurement data and excitation data, calculate the frequency response function, and obtain the defect index;

[0014] Step 4: Identify small branch pipe welds based on defect indicators.

[0015] The step 2 includes using a vibrator in a pulse excitation system to tap the small branch pipe weld multiple times, the tapping includes light tapping and heavy tapping, the reference peak value of the light tapping is 16N, and the reference peak value of the heavy tapping is 40N.

[0016] The step 3 comprises:

[0017] Step 3.1, when the small branch pipe weld is damaged, after introducing cubic nonlinear stiffness, the harmonic balance method is used to obtain the nonlinear structural frequency response function;

[0018] Step 3.2, using a nonlinear frequency response difference extraction method to calculate a nonlinear frequency response difference characteristic curve;

[0019] Step 3.3: Calculate the defect index based on the nonlinear frequency response difference characteristic curve.

[0020] The calculation formula of the nonlinear structural frequency response function in step 3.1 is:

[0021]

[0022] Where H(ω) is the nonlinear structural frequency response function, k is the system linear stiffness, m is the oscillator mass, j is the imaginary unit, c is the system damping, ω is the excitation angular frequency, and A is the excitation amplitude.

[0023] The calculation formula of the nonlinear frequency response difference characteristic curve in step 3.2 is:

[0024]

[0025] H i,0 =H i -H

[0026] In the formula, H m is the nonlinear frequency response difference characteristic curve, H i,0 is the nonlinear frequency response difference, H0 is the frequency response function under the minimum excitation amplitude, H i For different excitation amplitudes A i Frequency response function under (i=0,1,…,N).

[0027] The calculation formula of the defect index in step 3.3 is:

[0028]

[0029] In the formula, DI is the defect index, H m (j) is the nonlinear frequency response difference characteristic curve of the jth sampling point, and n is the number of sampling points.

[0030] The beneficial technical effects of the present invention are:

[0031] 1. The present invention provides a method for identifying defects in weld seams of small branch pipes in nuclear power plants. The method uses portable vibration measuring equipment to obtain the difference in frequency response functions of small branch pipes under different excitations to achieve the purpose of identifying initial defects of small branch pipes.

[0032] 2. The invention provides a method for identifying weld defects of small branch pipes in nuclear power plants. The method has a simple testing process and is suitable as a supplementary means for visual defect inspection of small branch pipes in nuclear power plants, thereby providing assistance for reliability management of small branch pipes in nuclear power plants.

[0033] 3. The method for identifying weld defects of small branch pipes in nuclear power plants provided by the present invention is more sensitive to socket welding defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of a nuclear power plant small branch pipe weld defect identification system provided by the present invention;

[0035] Figure 2 A field layout diagram of a nuclear power plant small branch pipe weld defect identification system provided by the present invention;

[0036] Figure 3 This is a test data diagram of the frequency response function of a small branch pipe without defects in an embodiment of the present invention;

[0037] Figure 4 This is a test data diagram of the frequency response function of a defective small branch pipe in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0039] like Figure 1 As shown, the present invention provides a nuclear power plant small branch pipe weld defect identification system, including: an acceleration measurement system, a control acquisition processing system, and a pulse excitation system; the acceleration measurement system is installed on the small branch pipe weld, and the acceleration measurement system and the pulse excitation system are respectively connected to the control acquisition processing system; the pulse excitation system applies excitation to the small branch pipe weld, and the control acquisition processing system collects measurement data of the acceleration measurement system and excitation data applied by the pulse excitation system, analyzes and calculates the measurement data and the excitation data, and obtains a frequency response function.

[0040] The pulse excitation system includes an exciter and a force sensor. The exciter, the force sensor, and the control acquisition processing system are connected in sequence. The exciter is used to apply excitation to the small branch pipe weld. The force sensor collects the excitation data applied by the exciter and sends the excitation data to the control acquisition processing system.

[0041] In a specific implementation, the acceleration measurement system uses an acceleration sensor, the control acquisition processing system uses a data acquisition and analysis system, the data acquisition and analysis system uses a portable data acquisition and analysis instrument with a frequency response function calculation function, and the exciter uses a hard plastic head hammer.

[0042] A method for identifying weld defects of small branch pipes in a nuclear power plant comprises the following steps:

[0043] Step 1: Install the acceleration measurement system on the weld of the small branch pipe, and connect the acceleration measurement system and the pulse excitation system to the control acquisition processing system respectively;

[0044] Install the acceleration sensor at one end of the small branch pipe weld. The acceleration sensor and the exciter are connected to the data acquisition and analysis system respectively. The layout diagram is as follows: Figure 2 shown.

[0045] Step 2: The pulse excitation system applies excitation to the small branch pipe weld, and the control acquisition processing system collects the measurement data of the acceleration measurement system and the excitation data applied by the pulse excitation system;

[0046] Use the exciter in the pulse excitation system, such as a hard plastic head hammer, to knock the other end of the small branch pipe weld multiple times. The force sensor obtains the excitation data, the acceleration sensor obtains the measurement data, and the data acquisition and analysis system collects the excitation data and the measurement data.

[0047] In a specific embodiment, a hard plastic head hammer is used to perform light tapping and heavy tapping on the other end of the small branch pipe weld, with the reference peak value of the light tapping being 16N and the reference peak value of the heavy tapping being 40N.

[0048] The bandwidth of the data acquisition and analysis system is selected to be 1000Hz, and the resolution is not less than 1Hz.

[0049] Step 3: Control the acquisition and processing system to analyze the measurement data and excitation data, calculate the frequency response function, and obtain the defect index;

[0050] Step 3.1: When the small branch pipe weld is damaged, after introducing cubic nonlinear stiffness, the harmonic balance method is used to obtain the nonlinear structural frequency response function. The calculation formula of the nonlinear structural frequency response function is:

[0051]

[0052] Where H(ω) is the nonlinear structural frequency response function, k is the system linear stiffness, m is the oscillator mass, j is the imaginary unit, c is the system damping, ω is the excitation angular frequency, and A is the excitation amplitude.

[0053] Step 3.2: Use the nonlinear frequency response difference extraction method to calculate the nonlinear frequency response difference characteristic curve

[0054] The nonlinear frequency response difference extraction method is a method to identify nonlinear defects by using the dependence of the nonlinear structure frequency response function on the excitation amplitude. i (i=0,1,…,N) different excitations with the same frequency and phase. The corresponding frequency response function H can be obtained i (i=0,1,…,N). Using the direct subtraction method, the frequency response function H under different excitation amplitudes is i Subtract the frequency response function H0 under the minimum excitation amplitude to obtain the nonlinear frequency response difference. The calculation formula of the nonlinear frequency response difference is:

[0055] H i,0 =H i -H0

[0056] Where H0 is the frequency response function under the minimum excitation amplitude, H i For different excitation amplitudes A i Frequency response function under (i=0,1,…,N), H i,0 is the nonlinear frequency response difference;

[0057] Then the obtained nonlinear frequency response difference is summed and averaged to obtain a difference curve that can represent the strength of the structural nonlinearity. This curve is called the nonlinear frequency response difference characteristic curve, denoted by H m ,Right now:

[0058]

[0059] Step 3.3: Calculate the defect index based on the nonlinear frequency response difference characteristic curve

[0060] H m The energy density DI of the function can be used as a defect index to effectively characterize the nonlinear defect degree of the small branch pipe. The calculation formula of the defect index is:

[0061]

[0062] In the formula, DI is the defect index, H m (j) is the nonlinear frequency response difference characteristic curve of the jth sampling point, and n is the number of sampling points.

[0063] Step 4: Identify small branch pipe welds based on defect indicators

[0064] The calculated defect index is compared with the preset defect index threshold. When the calculated defect index is greater than or equal to the preset defect index threshold, the small branch pipe weld is judged to be defective; when the calculated defect index is less than the preset defect index threshold, the small branch pipe weld is judged to be non-defective. Figure 3 As shown in the figure, the test data of the frequency response function of the defective small branch pipe is as follows: Figure 4 shown.

[0065] In actual testing, two amplitude pulse excitations can be used to obtain the frequency response function of the small branch pipe, and the frequency response function difference can be calculated by the nonlinear frequency response difference extraction method to obtain the defect index and achieve the purpose of identifying the initial defect. The test data proves that this method is more sensitive to the socket welding defects.

[0066] The present invention is described in detail above with reference to the accompanying drawings and embodiments, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of ordinary technicians in the field without departing from the purpose of the present invention. The contents not described in detail in the present invention can adopt the existing technology.

Claims

1. A nuclear power plant small branch pipe weld defect identification system, characterized in that: The system comprises: an acceleration measurement system, a control acquisition processing system, and a pulse excitation system; the acceleration measurement system is installed on the small branch pipe weld, and the acceleration measurement system and the pulse excitation system are respectively connected to the control acquisition processing system; the pulse excitation system applies excitation to the small branch pipe weld, and the control acquisition processing system collects measurement data of the acceleration measurement system and excitation data applied by the pulse excitation system, analyzes and calculates the measurement data and the excitation data, and obtains a frequency response function.

2. A nuclear power plant small branch pipe weld defect identification system according to claim 1, characterized in that: The pulse excitation system includes an exciter and a force sensor. The exciter, the force sensor, and the control acquisition processing system are connected in sequence. The exciter is used to apply excitation to the small branch pipe weld. The force sensor collects the excitation data applied by the exciter and sends the excitation data to the control acquisition processing system.

3. A nuclear power plant small branch pipe weld defect identification system according to claim 2, characterized in that: The acceleration measurement system adopts an acceleration sensor, the control acquisition processing system adopts a portable data acquisition and analysis system with a frequency response function calculation function, and the vibration exciter adopts a hard plastic head hammer.

4. A nuclear power plant small branch pipe weld defect identification system according to claim 3, characterized in that: The bandwidth of the data acquisition and analysis system is selected to be 1000 Hz, and the resolution is not less than 1 Hz.

5. A method for identifying weld defects of small branch pipes in nuclear power plants, using a system for identifying weld defects of small branch pipes in nuclear power plants according to claim 1, characterized in that: The method comprises: Step 1: Install the acceleration measurement system on the weld of the small branch pipe, and connect the acceleration measurement system and the pulse excitation system to the control acquisition processing system respectively; Step 2: The pulse excitation system applies excitation to the small branch pipe weld, and the control acquisition processing system collects the measurement data of the acceleration measurement system and the excitation data applied by the pulse excitation system; Step 3: Control the acquisition and processing system to analyze the measurement data and excitation data, calculate the frequency response function, and obtain the defect index; Step 4: Identify small branch pipe welds based on defect indicators.

6. A method for identifying weld defects of small branch pipes in nuclear power plants according to claim 5, characterized in that: The step 2 includes using a vibrator in a pulse excitation system to tap the small branch pipe weld multiple times, the tapping includes light tapping and heavy tapping, the reference peak value of the light tapping is 16N, and the reference peak value of the heavy tapping is 40N.

7. A method for identifying weld defects of small branch pipes in nuclear power plants according to claim 5, characterized in that: The step 3 comprises: Step 3.1, when the small branch pipe weld is damaged, after introducing cubic nonlinear stiffness, the harmonic balance method is used to obtain the nonlinear structural frequency response function; Step 3.2, using a nonlinear frequency response difference extraction method to calculate a nonlinear frequency response difference characteristic curve; Step 3.3: Calculate the defect index based on the nonlinear frequency response difference characteristic curve.

8. A method for identifying weld defects of small branch pipes in nuclear power plants according to claim 7, characterized in that: The calculation formula of the nonlinear structural frequency response function in step 3.1 is: Where H(ω) is the nonlinear structural frequency response function, k is the system linear stiffness, m is the oscillator mass, j is the imaginary unit, c is the system damping, ω is the excitation angular frequency, and A is the excitation amplitude.

9. A method for identifying weld defects of small branch pipes in nuclear power plants according to claim 8, characterized in that: The calculation formula of the nonlinear frequency response difference characteristic curve in step 3.2 is: H i，0 =H i -H0 In the formula, H m is the nonlinear frequency response difference characteristic curve, H i,0 is the nonlinear frequency response difference, H0 is the frequency response function under the minimum excitation amplitude, H i For different excitation amplitudes A i Frequency response function under (i=0,1,…,N).

10. A method for identifying weld defects of small branch pipes in nuclear power plants according to claim 9, characterized in that: The calculation formula of the defect index in step 3.3 is: In the formula, DI is the defect index, H m (j) is the nonlinear frequency response difference characteristic curve of the jth sampling point, and n is the number of sampling points.

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