A correction method for affecting the accuracy of eddy current evaluation of pipeline defects
By designing an eddy current probe and optimizing signal excitation parameters, a quantitative relationship between eddy current signal amplitude and gain was established, which solved the problem of the influence of eddy current signal excitation gain on defect accuracy, realized the accurate correction of defect size in eddy current evaluation, and improved the accuracy of quantitative eddy current evaluation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CNNC NUCLEAR POWER OPERATION MANAGEMENT CO LTD
- Filing Date
- 2026-02-10
- Publication Date
- 2026-07-31
AI Technical Summary
When evaluating the size of pipe defects, existing eddy current technology lacks an effective solution to the factors affecting the excitation gain of eddy current signals, making it difficult to guarantee the accuracy of defect assessment.
By designing an eddy current probe and optimizing signal excitation parameters, a quantitative relationship between the amplitude and gain of the eddy current signal is established. Combined with mathematical fitting, the amplitude of the eddy current signal is corrected to determine the defect size.
This improved the accuracy of defect size assessment in eddy current evaluation, thereby enhancing the accuracy of quantitative eddy current evaluation.
Smart Images
Figure CN122487488A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of eddy current nondestructive testing technology, specifically relating to a method for correcting defects in pipelines that affect the accuracy of eddy current testing. Background Technology
[0002] Eddy current technology is a conventional technique for non-destructive evaluation of defects, achieving quantitative assessment based on the magnitude of the defect signal. However, numerous factors influence the accuracy of defect size evaluation using eddy current technology, with the excitation gain of the eddy current signal (i.e., the excitation energy of the eddy current signal, or simply gain) being a significant factor, for which no effective solution has yet been found. Therefore, this invention, targeting the evaluation of defects in the inner wall of pipelines, proposes a method to correct the influence of excitation gain on defect size evaluation using eddy current technology. Summary of the Invention
[0003] The purpose of this invention is to provide a correction method for the impact of eddy current evaluation on the accuracy of pipeline defects, and to solve the problem of accurate and non-destructive evaluation of invisible defects on the inner wall of pipelines.
[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A correction method for affecting the accuracy of eddy current evaluation of pipeline defects, comprising the following steps: Step 1: Select a circular pipe sample of a certain length that has the same characteristics as the pipeline used in nuclear power plants, and process defects on its inner surface; Step 2: Design and manufacture the corresponding eddy current probe based on the pipe size characteristics; Step 3: Optimize and fix the excitation parameters of the eddy current signal, and change the excitation gain of the eddy current signal in sequence to obtain the eddy current signal of the defect. Step 4: Extract the amplitude of the eddy current signal, calculate the difference between the amplitude corresponding to the minimum gain and other amplitudes, and fit it with a mathematical formula to obtain a quantitative relationship between the amplitude difference of the eddy current signal and the gain. Step 5: Using the same eddy current signal excitation parameters as in Step 3, and fixing the excitation gain of the eddy current signal, sequentially collect eddy current signals from defects of different sizes. Step 6: Extract the amplitude of the eddy current signal from the defect, obtain the correlation between the amplitude of the eddy current signal and the defect size, and fit it with a mathematical formula to obtain a quantitative relationship between the amplitude of the eddy current signal and the defect size. Step 7: Using the same eddy current signal excitation parameters as in Step 3, acquire the eddy current signal of any defect, adjust its eddy current signal amplitude, determine its gain, and calculate the difference between this gain and the excitation gain of the eddy current signal in Step 5. Step 8: Substitute the gain difference from Step 7 into the relationship in Step 4 to obtain the difference in the amplitude of the corresponding eddy current signal. Step 9: Superimpose the difference in eddy current signal amplitude from Step 8 with the amplitude of the defect eddy current signal from Step 7, and substitute it into the quantitative relationship from Step 6 to obtain the true size of the defect.
[0005] Step one involves machining defects on the inner surface of the circular tube sample using mechanical processing methods.
[0006] Step three, the excitation parameters, include the elevation of the eddy current probe and the filtering method.
[0007] In step one, the number of defects shall not be less than 5, and the size of the defects shall only vary along the wall thickness direction.
[0008] In step three, the amplitude of the eddy current signal under any gain shall not exceed 100% of the screen and shall not be less than 60% of the screen.
[0009] In step four, the difference in the amplitude of the eddy current signal must be positive and the number must be no less than five.
[0010] In steps five and six, the difference in amplitude between adjacent defect eddy current signals shall not be less than 10%.
[0011] The defect type in step seven is the same as the defect type in step one.
[0012] Step seven states that the gain is the absolute value of the difference between two gains.
[0013] In steps eight and nine, the difference in amplitude of the eddy current signal has the same sign as the gain difference in step seven.
[0014] The amplitude of the eddy current signal obtained after superposition in step nine does not exceed 100mV.
[0015] The beneficial effects achieved by this invention are as follows: This invention proposes a technical means to solve the problem of the influence of eddy current signal excitation gain on the results of quantitative evaluation of eddy current waves, thereby improving the accuracy of quantitative evaluation of eddy current defects. Attached Figure Description
[0016] Figure 1 This is a graph showing the relationship between the excitation gain difference of an eddy current signal and the difference in its signal amplitude. Figure 2 This is a graph showing the relationship between the amplitude of the eddy current signal and the depth of the rectangular groove. Detailed Implementation
[0017] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.
[0018] A correction method for affecting the accuracy of eddy current evaluation of pipe defects includes the following steps: Step 1: Select a circular pipe sample of a certain length that has the same characteristics as the pipeline used in nuclear power plants, and use mechanical processing methods to process defects on its inner surface; Step 2: Based on the pipe size characteristics, design and manufacture the corresponding eddy current probe (eddy current frequency and size). Step 3: Optimize and fix the excitation parameters of the eddy current signal (elevation of the eddy current probe, filtering method), and change the excitation gain of the eddy current signal (defined as gain) in sequence to obtain the eddy current signal of the defect. Step 4: Extract the amplitude of the eddy current signal, calculate the difference between the amplitude corresponding to the minimum gain and other amplitudes, and fit it with a mathematical formula to obtain a quantitative relationship between the amplitude difference of the eddy current signal and the gain. Step 5: Using the same eddy current signal excitation parameters as in Step 3, and fixing the excitation gain of the eddy current signal, sequentially collect eddy current signals from defects of different sizes. Step 6: Extract the amplitude of the eddy current signal from the defect, obtain the correlation between the amplitude of the eddy current signal and the defect size, and fit it with a mathematical formula to obtain a quantitative relationship between the amplitude of the eddy current signal and the defect size. Step 7: Using the same eddy current signal excitation parameters as in Step 3, acquire the eddy current signal of any defect, adjust its eddy current signal amplitude, determine its gain, and calculate the difference between this gain and the excitation gain of the eddy current signal in Step 5. Step 8: Substitute the gain difference from Step 7 into the relationship in Step 4 to obtain the difference in the amplitude of the corresponding eddy current signal. Step 9: Superimpose the difference in eddy current signal amplitude from Step 8 with the amplitude of the defect eddy current signal from Step 7, and substitute it into the quantitative relationship from Step 6 to obtain the true size of the defect.
[0019] In step one, the number of defects shall not be less than 5, and the size of the defects shall only vary along the wall thickness direction.
[0020] In step three, the amplitude of the eddy current signal at any gain does not exceed the screen (i.e., 100% of the screen) and is not less than 60% of the screen.
[0021] In step four, the difference in the amplitude of the eddy current signal is positive and the number is no less than 5.
[0022] The difference in amplitude between adjacent defect eddy current signals in steps five and six shall not be less than 10%.
[0023] The defect type in step seven is the same as the defect type in step one.
[0024] The gain in step seven is the absolute value of the difference between the two gains.
[0025] The amplitude difference of the eddy current signal in steps eight and nine has the same sign as the gain difference in step seven.
[0026] The amplitude of the eddy current signal calculated after superposition in step nine does not exceed 100mV.
[0027] Example: Taking a pipeline made of Q235 steel as an example, the specific process of a correction method for affecting the accuracy of pipeline defects in eddy current evaluation is as follows: Step 1: Select Q235 steel as the material, with the following dimensions: length 700mm, wall thickness 6mm, and outer diameter 60mm. Using wire EDM technology, machine five circumferentially distributed rectangular grooves (pre-fabricated defects) into the inner wall of the pipe. The grooves have a constant width of 0.5mm, a constant length of 10mm, and depths of 1.0mm, 1.5mm, 2.0mm, 2.5mm, and 3.0mm, respectively. The spacing between adjacent rectangular grooves is 100mm.
[0028] Step 2: Based on the pipe size, defect size and distribution in Step 1, eddy current is used to detect prefabricated defects. The center frequency range of the probe is 64Hz-5MHz. Four impedance planes are selected, the automatic mixing function is turned on, and a low-pass filter of 5KHz is used.
[0029] Step 3: Connect the eddy current probe to the eddy current detector using wires. Optimize and fix the excitation parameters of the eddy current signal, fixing the eddy current lift-off height at 1.0 mm. Ensure the amplitude of the eddy current signal in the rectangular slot does not exceed 80% of the full screen and is not lower than 50% of the screen. Detect a rectangular slot with a depth of 1.5 mm using low-pass filtering. Based on this, select excitation gains of 10 dB, 12 dB, 14 dB, 16 dB, 18 dB, and 20 dB for the eddy current signal, and acquire their eddy current wave signals respectively.
[0030] Step four: Extract the amplitudes of the eddy current signals at six different gains, namely 63.2mV, 75.3mV, 86.9mV, 91.6mV, 95.2mV, and 96.7mV. The differences between these amplitudes and the amplitudes at a gain of 10dB are 12.1mV, 23.7mV, 28.4mV, 32mV, and 33.5mV, respectively, thus establishing their correlation. Based on this, a nonlinear function is used to fit the amplitudes, yielding a quantitative relationship between the amplitude differences of the eddy current signals and the excitation gain of the eddy current signals, as shown in equation (1).
[0031] (1) In the formula, A is the amplitude of the eddy current signal (mV), and E is the excitation gain of the eddy current signal (db).
[0032] Step 5: Using the same eddy current signal excitation parameters as in Step 3, select an excitation gain of 16dB for the eddy current signal and sequentially collect eddy current signals from the rectangular grooves with depths of 1.0mm, 1.5mm, 2.0mm, 2.5mm, and 3.0mm from Step 1.
[0033] Step six: Extract the amplitudes of the eddy current signal from the rectangular slot in step five, which are 16.5mV, 91.6mV, 62.7mV, 71.9mV, and 76.3mV, respectively. (See...) Figure 2 The eddy current signal amplitude and the defect size were fitted by a nonlinear function to obtain a quantitative relationship between the eddy current signal amplitude and the defect size, as shown in equation (2).
[0034] (2) In the formula, A is the amplitude of the eddy current signal (mV) and D is the depth of the rectangular groove (mm).
[0035] Step 7: Use the same detection parameters as in Step 3 to detect any long-term service pipeline and obtain the defect eddy current signal, which has an amplitude of 69.3mV and a gain (excitation gain of the eddy current signal) of 13.1dB, which is 2.9dB different from the gain of 16dB in Step 5.
[0036] Step 8: Substitute the gain difference of 2.9dB from Step 7 into Equation (1) in Step 4 to calculate the difference in amplitude of the corresponding eddy current signal, which is 18.12mV.
[0037] Step 9: The difference in eddy current signal amplitude of 18.12mV in Step 8 is superimposed with the amplitude of defect eddy current signal of 69.3mV in Step 7 to calculate 87.42mV. This value is then substituted into Equation (2) in Step 6 to calculate the defect depth as 1.26mm.
Claims
1. A correction method for affecting the accuracy of eddy current evaluation of pipeline defects, characterized in that: The steps are as follows: Step 1: Select a circular pipe sample of a certain length that has the same characteristics as the pipeline used in nuclear power plants, and process defects on its inner surface; Step 2: Design and manufacture the corresponding eddy current probe based on the pipe size characteristics; Step 3: Optimize and fix the excitation parameters of the eddy current signal, and change the excitation gain of the eddy current signal in sequence to obtain the eddy current signal of the defect. Step 4: Extract the amplitude of the eddy current signal, calculate the difference between the amplitude corresponding to the minimum gain and other amplitudes, and fit it with a mathematical formula to obtain a quantitative relationship between the amplitude difference of the eddy current signal and the gain. Step 5: Using the same eddy current signal excitation parameters as in Step 3, and fixing the excitation gain of the eddy current signal, sequentially collect eddy current signals from defects of different sizes. Step 6: Extract the amplitude of the eddy current signal from the defect, obtain the correlation between the amplitude of the eddy current signal and the defect size, and fit it with a mathematical formula to obtain a quantitative relationship between the amplitude of the eddy current signal and the defect size. Step 7: Using the same eddy current signal excitation parameters as in Step 3, acquire the eddy current signal of any defect, adjust its eddy current signal amplitude, determine its gain, and calculate the difference between this gain and the excitation gain of the eddy current signal in Step 5. Step 8: Substitute the gain difference from Step 7 into the relationship in Step 4 to obtain the difference in the amplitude of the corresponding eddy current signal. Step 9: Superimpose the difference in eddy current signal amplitude from Step 8 with the amplitude of the defect eddy current signal from Step 7, and substitute it into the quantitative relationship from Step 6 to obtain the true size of the defect.
2. The correction method for the impact of eddy current on the accuracy of pipeline defect evaluation according to claim 1, characterized in that: Step one involves machining defects on the inner surface of the circular tube sample using mechanical processing methods.
3. The correction method for the impact of eddy current on the accuracy of pipeline defect evaluation according to claim 1, characterized in that: Step three, the excitation parameters, include the elevation of the eddy current probe and the filtering method.
4. The correction method for the impact of eddy current on the accuracy of pipeline defect evaluation according to claim 1, characterized in that: In step one, the number of defects shall not be less than 5, and the size of the defects shall only vary along the wall thickness direction.
5. The correction method for affecting the accuracy of eddy current evaluation of pipeline defects according to claim 1, characterized in that: In step three, the amplitude of the eddy current signal under any gain shall not exceed 100% of the screen and shall not be less than 60% of the screen.
6. The correction method for the impact on the accuracy of eddy current evaluation of pipeline defects according to claim 1, characterized in that: In step four, the difference in the amplitude of the eddy current signal must be positive and the number must be no less than five.
7. The correction method for the impact of eddy current on the accuracy of pipeline defect evaluation according to claim 1, characterized in that: In steps five and six, the difference in amplitude between adjacent defect eddy current signals shall not be less than 10%.
8. The correction method for the impact of eddy current evaluation on the accuracy of pipeline defects according to claim 1, characterized in that: The defect type in step seven is the same as the defect type in step one.
9. The correction method for the impact of eddy current on the accuracy of pipeline defect evaluation according to claim 1, characterized in that: Step seven states that the gain is the absolute value of the difference between two gains.
10. The correction method for the impact of eddy current on the accuracy of pipeline defect evaluation according to claim 1, characterized in that: In steps eight and nine, the difference in amplitude of the eddy current signal has the same sign as the gain difference in step seven.
11. The correction method for the impact of eddy current on the accuracy of pipeline defect evaluation according to claim 1, characterized in that: The amplitude of the eddy current signal obtained after superposition in step nine does not exceed 100mV.