CN102661995B - Electromagnetic acoustic and magnetic leakage compounded detection method - Google Patents

Abstract

The invention relates to a combined detection method of electromagnetic ultrasonic and magnetic flux leakage, relating to a nondestructive detection method. Based on the basic principle of magnetic flux leakage detection, an EMAT excitation coil capable of generating a dynamic alternating magnetic field and an EMAT detection coil capable of receiving ultrasonic echoes are added. When the pulse current is excited in the EMAT excitation coil, electromagnetic ultrasonic waves propagating to the other side of the steel plate under test are generated. When the electromagnetic ultrasonic waves encounter the outer wall of the steel plate to be tested, ultrasonic echoes will be generated, and the EMAT detection coil is used to pick up the ultrasonic echoes. By analyzing the picked-up ultrasonic echoes, the position of the defect can be known, and the positioning of the inner and outer wall layers can be realized. Finally, by fusing the defect shape information provided by the magnetic flux leakage detection signal, the effect of "composite non-destructive testing" can be formed, thereby reconstructing the actual shape and depth of the defect. It effectively overcomes the disadvantages of unsatisfactory defect determination and low accuracy in the prior art, and has a simple structure and non-contact measurement.

Description

A combined detection method of electromagnetic ultrasonic and magnetic flux leakage

technical field

The invention relates to a non-destructive testing method, in particular to a testing method based on electromagnetic ultrasonic and magnetic flux leakage composite.

Background technique

As the magnetic flux leakage method is widely used in the detection of steel plates such as storage tanks and pipelines, the location of defect depth is becoming more and more important. On the one hand, it is beneficial to accurately describe the cause of corrosion defects in the flaw detection report; on the other hand, with the positioning of the corrosion inner and outer wall layers (ie depth), the detection signal can be more accurately evaluated and the quantitative accuracy of the detection results can be improved. The magnetic flux leakage detection method widely used at present, because similar leakage magnetic fields can be generated on both sides of the steel plate to be tested, it is difficult to evaluate the specific depth of corrosion. For the method of distinguishing the inner and outer walls of magnetic flux leakage detection, foreign countries use the idea of signal filtering to realize it. But in fact, it is not only the location of the corrosion that causes the frequency characteristic of the signal to change, but also the detection speed and the geometric shape of the corrosion will also be reflected on the signal waveform and frequency. Therefore, the traditional idea of signal filtering is not ideal, and the accuracy rate is hovering. At 50%, it is difficult to promote in practical engineering applications.

Chinese patent CN101354380A discloses a combined eddy current and electromagnetic ultrasonic non-destructive testing method, which uses eddy current testing to be sensitive to defects on the surface and subsurface of the object to be tested, and compared with eddy current testing, electromagnetic ultrasonic can detect much thicker material. By combining eddy current testing and electromagnetic ultrasonic testing, the mutual inspection of the detection results of the measured object is realized, and at the same time, mutual compensation can be achieved, so as to achieve the purpose of detecting surface and deeper defects of the measured object. However, this method can only obtain the information of whether there is a defect on the surface of the measured object and the information of the depth of the surface of the measured object and below, and cannot obtain the actual shape information of the defect.

Contents of the invention

The object of the present invention is to provide an electromagnetic ultrasonic and magnetic flux leakage composite detection device in order to overcome the above-mentioned deficiencies in the prior art.

Another object of the present invention is to provide a combined detection method of electromagnetic ultrasonic and magnetic flux leakage

The electromagnetic ultrasonic and magnetic flux leakage composite detection device is provided with a magnetic core, a permanent magnet, an EMAT excitation coil, an EMAT detection coil, and a magnetic flux leakage detection element. The permanent magnet is fixed on the thinner end of the magnetic core, and the EMAT excitation coil, EMAT detection The coil is fixed directly below the permanent magnet and above the steel plate to be tested; the magnetic flux leakage detection element is fixed in the middle of the two ends of the probe and placed above the steel plate to be tested.

The magnetic core can be an L-shaped magnetic core or a U-shaped magnetic core.

The electromagnetic ultrasonic and magnetic flux leakage composite detection method adopts the electromagnetic ultrasonic and magnetic flux leakage composite detection device, and the detection method includes the following steps:

1) Place the electromagnetic ultrasonic and magnetic flux leakage composite detection device on the surface of the steel plate to be tested, and scan and detect the steel plate to be tested according to the set lift-off value H1, among which, the permanent magnet, EMAT excitation coil, EMAT detection coil and the steel plate to be tested Constitute an electromagnetic ultrasonic transducer (Electromagnetic Acoustic Transducer, referred to as EMAT), an electromagnetic ultrasonic transducer is a transducer that excites and receives ultrasonic waves in a conductor;

2) Apply an excitation signal to the EMAT excitation coil to form an electromagnetic ultrasonic wave incident perpendicular to the surface of the steel plate to be tested. The electromagnetic wave propagates to the other side of the steel plate to be tested. When encountering the outer wall of the steel plate to be tested, an ultrasonic echo will be generated. At the same time , under the action of the permanent magnet, the steel plate to be tested is partially magnetized to a saturated state, and a leakage magnetic field will be generated at the defect;

3) Use the EMAT detection coil to pick up the ultrasonic echo generated in step 2), and at the same time, use the magnetic flux leakage detection element to measure the leakage magnetic field generated in step 2) with the set lift-off value H2, and the picked up ultrasonic echo The wave signal and the output signal of the magnetic flux leakage detection element (that is, the magnetic flux leakage signal) are sent to the signal processing unit;

4) Amplify and filter the echo signal sent into the ultrasonic echo signal channel and the magnetic flux leakage signal sent into the magnetic flux leakage signal channel, and then convert the processed data into digital signals through the A/D converter After that, they are sent to the information processing system respectively;

5) In the information processing system, after analyzing and processing the received digital signal, the waveform diagram of the ultrasonic echo signal and the magnetic flux leakage signal is obtained. Since the signals are not synchronized, the two signals are achieved by shifting the magnetic flux leakage signal in time domain The purpose of synchronous display;

6) Further process the two kinds of signal waveform images that reflect different information of defects processed in step 5) into synchronous signals that can be displayed on the same interface and displayed on the display, and set the lower limit threshold A0 of the first echo amplitude and the lower threshold T0 of the time taken to receive the first echo;

7) Under the premise of magnetic flux leakage signal, analyze the ultrasonic echo signal image, and compare the amplitude A and the time T of the first echo signal obtained with the set thresholds A0 and T0; if A< A0, the defect is located on the inner wall of the steel plate; if T<T0, the defect is located on the outer wall or inside of the steel plate; then through the analysis of the magnetic flux leakage signal image, the conventional magnetic flux leakage detection and analysis method is used to obtain the shape information of the defect, so that it can be realized at the same time Know the actual shape of the defect and locate the inner and outer wall layers (ie depth), reconstruct the actual shape and depth of the defect, and complete a defect detection.

In step 1), the EMAT excitation coil and the EMAT detection coil can be made of two coils respectively, or can be an integrated transceiver coil.

In step 3), the signal processing unit may be provided with an ultrasonic echo signal channel, a magnetic flux leakage signal channel, an amplification and filtering module, an A/D converter and an information processing system.

In step 4), the information processing system may use a single chip microcomputer, DSP, PC, etc.

The lift-off value H1 can be 1-4mm, and H2 is 0.2-3mm; the electromagnetic ultrasonic signal is excited in the gap between conventional magnetic flux leakage detection signal sampling; the excitation signal is excited by a sine wave pulse with a frequency of 50kHz-2MHz signal; the magnetic flux leakage detection element is a magnetic sensitive element.

On the basis of the basic principle of magnetic flux leakage detection, the present invention adds an EMAT excitation coil capable of generating a dynamic alternating magnetic field and an EMAT detection coil for receiving ultrasonic echoes; The characteristic of this non-destructive testing method is to use two independent testing units to detect the same defect. Using the lift-off effect of electromagnetic ultrasound and the principle of ultrasonic echo measurement, the depth information of the defect can be obtained from the electromagnetic ultrasonic echo signal, so that the "complementarity" of the information provided by the two detection methods can be used effectively on the basis of magnetic flux leakage detection. Realize the positioning of the inner and outer wall layers accurately, and realize the simultaneous acquisition of the actual shape and depth information of the defect. In addition, both electromagnetic ultrasonic and magnetic flux leakage testing belong to "non-contact" non-destructive testing technology, so the new non-destructive testing technology combined by the two technologies is still "non-contact" type, which can meet the requirements of actual testing. The invention also has the characteristics of simple structure, fast and convenient measurement, no coupling agent and the like.

Description of drawings

Figure 1 is a schematic diagram of the combined detection of electromagnetic ultrasound and magnetic flux leakage; where: the thin direction line represents the magnetic force line, and the thick direction line represents the vertically incident ultrasonic wave excited by the EMAT coil.

Fig. 2 is a schematic diagram of the principle of using electromagnetic ultrasonic to detect defects when the steel plate has no defects.

Figure 3 is a u-t diagram of the signal waveform received by the EMAT detection coil when the steel plate has no defects. In Figure 3, u is the received ultrasonic echo amplitude (mV), and t is the time (μs).

Fig. 4 is a schematic diagram of the defect detection principle using electromagnetic ultrasonic when the defect is located on the inner wall of the steel plate.

Figure 5 is a u-t diagram of the signal waveform received by the EMAT detection coil when the defect is located on the inner wall of the steel plate. In Figure 5, u is the received ultrasonic echo amplitude (mV), and t is the time (μs).

Fig. 6 is a schematic diagram of the principle of using electromagnetic ultrasonic to detect defects when the defects are located on the outer wall or inside of the steel plate.

Figure 7 is a u-t diagram of the signal waveform received by the EMAT detection coil when the defect is located on the outer wall or inside of the steel plate. In Figure 7, u is the received ultrasonic echo amplitude (mV), and t is the time (μs).

Figure 8 and Figure 9 are schematic diagrams of defect detection using magnetic flux leakage.

In Figures 1 to 9, each mark is: L-shaped magnetic core 1, permanent magnet 2, EMAT excitation coil 3, magnetic flux leakage detection element 4, steel plate to be tested 5, lift-off value H1, lift-off value H2, scanning direction A, Vertically incident ultrasonic waves and echoes B, Magnetic force lines C.

Detailed ways

Further illustrate the detection method provided by the present invention below in conjunction with accompanying drawing:

Figure 1 is a schematic diagram of the method detection device. The detection device of the present invention is mainly composed of an L-shaped magnetic core 1 , a permanent magnet 2 , an EMAT excitation coil 3 (also used as an EMAT detection coil), and a magnetic flux leakage detection element 4 . The permanent magnet 2 is fixed on the thinner end of the L-shaped magnetic core. The EMAT excitation coil 3 is fixed directly below the permanent magnet 2, and placed above the steel plate 5 to be tested with a certain lift-off value H1. The magnetic flux leakage detection element 4 is fixed in the middle of the two ends of the probe, and placed above the steel plate 5 to be tested with a certain lift-off value H2.

The detection principle of the method of the present invention is based on the basic principle of magnetic flux leakage detection, adding an EMAT excitation coil that can generate a dynamic alternating magnetic field and an EMAT detection coil that receives ultrasonic echoes, and utilizing the lift-off effect of electromagnetic ultrasonic waves and the principle of ultrasonic echo measurement , the depth information of the defect is obtained from the electromagnetic ultrasonic echo signal, and the location of the defect level of the inner and outer walls is realized. Combined with the magnetic flux leakage detection signal, the conventional magnetic flux leakage detection and analysis method is used to obtain the defect shape information, so as to achieve the purpose of reconstructing the actual shape and depth of the defect.

The electromagnetic ultrasonic testing part, as shown in FIGS. 2 to 7 , uses the vertically incident ultrasonic waves excited by the EMAT excitation coil 3 to detect the steel plate 5 to be tested. When there is no defect, the incident wave hits the bottom surface and generates an echo, as shown in Figures 2 and 3; when the defect is located on the inner surface of the steel plate under test, it is equivalent to changing the lift-off value of the EMAT excitation coil, thereby changing the value of the steel plate under test. The intensity of the eddy current formed on the surface will also significantly affect the intensity of the excited electromagnetic ultrasound. At this time, the first echo amplitude detected by the EMAT detection coil is smaller than the first echo amplitude in the case of no defect, as shown in Figure 4 and 5. When the defect is located on the outer surface or inside of the tested steel plate, it mainly affects the action time of the ultrasonic echo. Compared with the case of no defect, the EMAT detection coil will detect the first ultrasonic echo in advance, as shown in Figure 6 and 7. The depth information of the defect can be obtained by analyzing and processing the signal obtained by the EMAT detection coil.

For the magnetic flux leakage detection part, as shown in Figures 8 and 9, when the permanent magnet magnetizes the tested steel plate 5 to a saturated state, both inner surface and outer surface defects can excite magnetic flux leakage signals, and the magnetic flux leakage signals are different due to different shapes of defects. , and can be detected by the magnetic flux leakage detection element 4 placed above the inner surface. A row of closely arranged magnetic flux leakage detection elements is used to collect magnetic flux leakage signals, and the collected magnetic flux leakage signals are analyzed and processed by conventional magnetic flux leakage detection methods to obtain the shape information of defects.

Since electromagnetic ultrasound and magnetic flux leakage have different requirements on the direction of the bias magnetic field, the positions of the EMAT coil and the magnetic flux leakage detection element on the probe structure are also different. Therefore, when the probe moves in the scanning direction as shown in Figure 1, for the same defect, there is a certain fixed hysteresis in the signal of the magnetic flux leakage detection. This problem can be solved by shifting the signal in the time domain during the post-processing of the detection signal. After the two signals are synchronized, the actual shape and depth information of the defect can be reconstructed by analyzing the obtained electromagnetic ultrasonic signal and magnetic flux leakage signal, and the inner and outer wall defects can be effectively distinguished.

Example

The Q235 steel plate with a thickness of 8mm is selected as the detection object, and the permanent magnet is N35 NdFeB with a length of 50mm, a width of 30mm, and a thickness of 20mm. The EMAT excitation coil (also used as the EMAT detection coil) is a folded wire coil made of a printed circuit (PCB). The thickness of the PCB is 1mm, and the line width is 0.5mm. Place the probe structure above the steel plate to be tested with a lift-off value of 2 mm, use a Hall element of model AH3503 as the magnetic flux leakage detection element, and measure the magnetic field leakage on the surface of the steel plate with a lift-off value of 1 mm. The steel plate is scanned and detected at a certain detection speed (4m/min). A 1MHz sine wave pulse signal is applied to the EMAT excitation coil during the sampling gap of the magnetic flux leakage detection signal, and the echo signal is detected by the EMAT detection coil. The ultrasonic echo signal detected by the EMAT detection coil and the magnetic flux leakage signal detected by the Hall element are respectively sent to different channels for amplification and filtering processing, and then the processed data is converted into a digital signal by the A/D converter. Send them to the PC for processing and display the signal waveform synchronously on the monitor.

When no defect is set, the lower limit threshold A0 of the first echo amplitude is 200mV, and the time T0 used to receive the first echo is 10μs. Compare the amplitude A and time T of the first detected ultrasonic echo signal with A0 and T0 respectively. If A<200mV, the defect is located on the inner wall of the steel plate; if T<10μs, the defect is located on the outer wall of the steel plate or internal. Combined with the magnetic flux leakage detection signal, the defect shape information can be obtained by using the conventional magnetic flux leakage detection method, and the actual shape and depth of the defect can be reconstructed.

The foregoing embodiments are only used to further illustrate a detection method of electromagnetic ultrasound and magnetic flux leakage compounding of the present invention, but the present invention is not limited to the embodiments, and any simple modification or equivalent to the above embodiments is made according to the technical essence of the present invention Changes and modifications all fall within the protection scope of the technical solution of the present invention.

Claims (9)

1. An electromagnetic ultrasonic and magnetic flux leakage composite detection method is characterized in that an electromagnetic ultrasonic and magnetic flux leakage composite detection device is used, and the device is provided with a magnetic core, a permanent magnet, an EMAT excitation coil, an EMAT detection coil, and a magnetic flux leakage detection element, The permanent magnet is fixed on the thinner end of the magnetic core, and the EMAT excitation coil and the EMAT detection coil are fixed directly below the permanent magnet and above the steel plate to be tested; In the middle of the end and placed above the steel plate to be tested; The detection method comprises the following steps: 1) Place the electromagnetic ultrasonic and magnetic flux leakage composite detection device on the surface of the steel plate to be tested, and scan and detect the steel plate to be tested according to the set lift-off value H1, in which the permanent magnet, EMAT excitation coil, EMAT detection coil and the steel plate to be tested Constitute an electromagnetic ultrasonic transducer, an electromagnetic ultrasonic transducer is a transducer device that excites and receives ultrasonic waves in a conductor; 2) Apply an excitation signal to the EMAT excitation coil to form an incident electromagnetic ultrasonic wave perpendicular to the surface of the steel plate to be tested. The electromagnetic wave propagates to the other side of the steel plate to be tested. When encountering the outer wall of the steel plate to be tested, an ultrasonic echo will be generated. , under the action of the permanent magnet, the steel plate to be tested is partially magnetized to a saturated state, and a leakage magnetic field will be generated at the defect; 3) Use the EMAT detection coil to pick up the ultrasonic echo generated in step 2), and at the same time, use the magnetic flux leakage detection element to measure the leakage magnetic field generated in step 2) with the set lift-off value H2, and the picked up ultrasonic echo The wave signal and the output signal of the magnetic flux leakage detection element are sent to the signal processing unit; 4) Amplify and filter the echo signal sent into the ultrasonic echo signal channel and the magnetic flux leakage signal sent into the magnetic flux leakage signal channel, and then convert the processed data into a digital signal through the A/D converter After that, they are sent to the information processing system respectively; 5) In the information processing system, after analyzing and processing the received digital signal, the waveform diagram of the ultrasonic echo signal and the magnetic flux leakage signal is obtained. Since the signals are not synchronized, the two signals are achieved by shifting the magnetic flux leakage signal in time domain The purpose of synchronous display; 6) Further process the two kinds of signal waveform images that reflect different information of defects processed in step 5) into synchronous signals that can be displayed on the same interface and displayed on the display, and set the lower limit threshold A0 of the first echo amplitude and the lower threshold T0 of the time taken to receive the first echo; 7) Under the premise of magnetic flux leakage signal, analyze the ultrasonic echo signal image, and compare the amplitude A and the time T of the first echo signal obtained with the set thresholds A0 and T0; if A< A0, the defect is located on the inner wall of the steel plate; if T<T0, the defect is located on the outer wall or inside of the steel plate; then through the analysis of the magnetic flux leakage signal image, the conventional magnetic flux leakage detection and analysis method is used to obtain the shape information of the defect, so that it can be realized at the same time Acquire the actual shape of the defect and locate the inner and outer wall layers, reconstruct the actual shape and depth of the defect, and complete a defect detection. 2 . The combined detection method of electromagnetic ultrasound and magnetic flux leakage according to claim 1 , wherein the magnetic core is an L-shaped magnetic core or a U-shaped magnetic core. 3 . 3. A kind of electromagnetic ultrasonic and flux leakage compound detection method as claimed in claim 1, it is characterized in that in step 1), described EMAT excitation coil and EMAT detection coil are respectively made of two coils, or are one Transceiver integrated coil. 4 . The combined detection method of electromagnetic ultrasound and magnetic flux leakage according to claim 1 , wherein in step 1), the lift-off value H1 is 1-4 mm. 5 . The combined detection method of electromagnetic ultrasound and magnetic flux leakage according to claim 1 , wherein in step 2), the excitation signal is a sine wave pulse excitation signal with a frequency of 50 kHz to 2 MHz. 6 . 6. A kind of electromagnetic ultrasonic and magnetic flux leakage compound detection method as claimed in claim 1, is characterized in that in step 3), described signal processing unit is provided with ultrasonic echo signal channel, magnetic flux leakage signal channel, amplifying and filtering module , A/D converter and information processing system. 7 . The combined detection method of electromagnetic ultrasound and magnetic flux leakage according to claim 1 , wherein in step 3), the lift-off value H2 is 0.2-3 mm. 8 . The combined detection method of electromagnetic ultrasound and magnetic flux leakage according to claim 1 , wherein in step 3), the magnetic flux leakage detection element is a magnetic sensitive element. 9. A composite detection method of electromagnetic ultrasound and magnetic flux leakage as claimed in claim 1, characterized in that in step 4), the information processing system adopts a single-chip microcomputer, DSP or PC.