CN107153097A - A kind of supersonic guide-wave for many defects detections of pipeline is segmented self-focusing detection method - Google Patents

Abstract

The invention belongs to the field of ultrasonic non-destructive testing, and in particular discloses an ultrasonic guided wave segmented self-focusing testing method for multiple-defect testing of pipelines. The technical solution adopted in the present invention is to divide the area to be inspected of the pipeline into multiple intervals of appropriate width along the length direction, and adopt the method of arranging the conventional detection signals of each interval in reverse order to realize the self-focusing of the ultrasonic guided wave on the defect position of the corresponding interval to realize For the self-focusing detection in different intervals, compare the signal-to-noise ratio of the inspection results in each interval with the conventional guided wave inspection results to judge whether there is a defect in the interval. The beneficial effect of the present invention is that the self-focusing detection of different sections of the pipeline can not only effectively improve the detection ability of multiple small defects, but also avoid the complicated process of calculating the delay parameters of each channel when focusing on different points, effectively reducing the The point-by-point focusing scanning process of the defect-free position is realized.

Description

A self-focusing detection method of ultrasonic guided wave segmented for multi-defect detection in pipelines

technical field

The invention belongs to the field of ultrasonic non-destructive testing, and in particular discloses an ultrasonic guided wave segmented self-focusing testing method for multiple-defect testing of pipelines.

Background technique

Ultrasonic guided waves have the advantages of long propagation distance, small attenuation, and sound field covering the entire wall thickness in pipe structures, and are especially suitable for long-distance, large-scale and full-structure inspections of pipes. Low-frequency axisymmetric longitudinal mode L(0,2) or torsional mode T(0,1) is the current conventional ultrasonic guided wave testing technology due to the uniform energy distribution along the pipeline circumferential direction, which is convenient for the analysis and processing of defect echo signals. The main detection mode used. Since the energy distribution of the axisymmetric mode is uniform along the circumferential direction of the pipeline, the energy of the echo reflected by the defect is directly related to its section loss. When the section loss is large, the energy of the echo reflected by the defect is large; small. In actual engineering testing, multiple defects may exist in a pipeline at the same time, and for multiple defects with a small section loss rate, when the L(0,2) or T(0,1) mode is used as the detection mode The energy of the reflected echo will be very small, and may be submerged in noise on the time history curve, resulting in missed detection of defects.

The patent number is 201010610991.7, and the title of the invention is "A Pipeline Defect Detection Method and System Based on Ultrasonic Guided Wave Focusing". The position of the focus point of wave energy in the pipeline is tested multiple times at different positions to find defects. However, unlike the conventional bulk wave ultrasonic phased array, the delay time and amplitude coefficient of each channel of the guided wave phased array are nonlinear functions of the geometric size of the pipeline, the point to be focused, the size of the excitation source, and the frequency of the excitation signal. When this method is used for guided wave detection in pipes, it is first necessary to establish an accurate pipe detection model to calculate the energy distribution law of a specific bending mode guided wave at the axial position of the focus point, or to excite a single array element of the transducer array , and uniformly install a transducer array with sufficient array elements along the circumferential direction of the pipeline at the axial position of the focus point, and measure the distribution law of the bending mode guided wave energy in the circumferential direction of the focus point; combined with the deconvolution algorithm Calculate the amplitude coefficient and delay time of each channel when the guided wave energy is focused on the point to be focused. Furthermore, this focusing method can only realize the control of the guided wave mode, that is, it can only focus the guided wave of a specific bending mode on a predetermined position in the pipeline, but cannot realize the automatic control of the ultrasonic guided wave energy at the defect position. Therefore, this method can only adopt a point-by-point focusing scanning method for the detection process of the entire pipeline defect, and only when the defect is exactly located at the focus point of the adjusted guided wave energy can an effective detection result be obtained. In short, this method is not only complicated to obtain the amplitude coefficient and delay time of each focus point, but also the focus detection of different target positions in the tube leads to a lot of time wasted in focus scanning detection of many non-defective parts.

The application number is CN200610144294.0, and the title of the invention is "Ultrasonic guided wave time-reversal detection device and method for pipeline defects", which discloses a method for obtaining inversion excitation signals of each channel by using the same time starting point and the same width rectangular window to realize The time-space focusing of the guided wave energy at the defect position is achieved, which significantly improves the detection ability of a single small defect. However, in this method, the width of the rectangular window is set to a fixed value for each detection. When the rectangular window is wide and contains information between the excitation wave packet and the first end-face echo, for a relatively large defect that contains multiple defects Long pipes will cause multiple defect wave packets to superimpose, resulting in missed detection of defects; when the rectangular window is narrow, it is necessary to be able to pre-judge the approximate position of the defect from the conventional ultrasonic guided wave inspection results to ensure that the defect is contained in the rectangular window However, in practical engineering applications, the tiny defect information contained in the tube is often submerged in the noise and difficult to extract.

Contents of the invention

The invention overcomes the deficiencies in the prior art and provides an ultrasonic guided wave segmented self-focusing detection method for detecting multiple defects in pipelines. The technical problem to be solved by the present invention is how to control the waveform of the excitation signal of each channel in the array to self-focus the ultrasonic guided wave only in a certain section of the area to be inspected when performing segmented self-focus detection on the area to be inspected in the tube Instead of focusing on other positions of the pipeline, the method must not only realize the mode control of the ultrasonic guided wave, but also realize the self-focusing of the defect position of the ultrasonic guided wave in this interval.

In order to solve the above technical problems, the technical solution adopted by the present invention is: by dividing the pipeline into N (N>2) sections along the length direction, and corresponding to M (M>16) array elements simultaneously excited and M On the time history curve detected by the conventional guided wave detection method that the array elements receive at the same time, the waveform data points received by the M array elements in the N segment are normalized and arranged in reverse order to synthesize the excitation signals of the corresponding array elements. The reciprocity theorem, when the excitation waveform in a certain interval contains defect wave packet information, the excitation waveform emitted by each array element will return to the defect position, so as to realize the self-focusing of the ultrasonic guided wave to the defect position in this interval. When there is no defect in the interval, there is no self-focusing phenomenon when each array element emits the excitation waveform, so it can be judged whether there is a defect in a certain interval according to whether the signal-to-noise ratio of the superposition result of received signals of all array elements is better than the conventional ultrasonic guided wave detection result. For the self-focusing detection signal of a certain section whose signal-to-noise ratio is better than that of conventional ultrasonic guided wave testing, the detection signal can be analyzed to determine the specific position of the defect in this section. The method mainly includes the following steps:

(1) Simultaneously excite M transducer array elements distributed at equal intervals along the circumferential direction of the pipe end by using narrow-band pulse signals of shorter frequency in the time domain with the same amplitude, and trigger and start each receiving channel at the initial moment of excitation signal transmission Start to receive the echo signals detected by each array element respectively, and superimpose the signals received by each channel to obtain the conventional ultrasonic guided wave detection results.

(2) Divide the area to be inspected in the length direction of the pipeline into N sections. Considering the time when the detection instrument emits the excitation signal and the influence of the near-field area of the transducer, discard the time domain width of the excitation signal from the excitation end face minus half of the peak moment of the excitation signal wave packet multiplied by the detection mode at the center frequency of the excitation signal The self-focus detection of the area within the distance corresponding to the group velocity, and the cut-off point of this area is used as the starting point of the area to be inspected. Considering the influence of the end-face echo, the cut-off point of the area to be inspected is set to the distance from the time-domain width of the excitation signal at the other end of the pipeline plus the peak time of the wave packet of the excitation signal multiplied by the group velocity of the detection mode at the center frequency of the excitation signal. corresponding to half the length. Starting from the starting point of the area to be inspected, the duration of the excitation signal used in conventional guided wave inspection is times the group velocity of the detection mode at the center frequency of the excitation signal to divide the area to be tested, where Integer greater than 1, the last interval is regarded as a separate interval no matter the length is less than or equal to other intervals. Correspond the divided intervals to the time course curve of conventional ultrasonic guided wave detection, wherein the lengths of the first interval to the N-1th interval are equal, and the length of the Nth interval is less than or equal to the length of other intervals.

(3) Extract the waveform data points received by each receiving channel from the first interval to the Nth interval on the conventional ultrasonic guided wave detection time history curve, and obtain M×N waveform data point vectors, and use all waveform data points Each vector is normalized by the maximum value of , and the normalized M×N vectors are all arranged in reverse order.

(4) Synthesize the data points in the M reverse-ordered vectors corresponding to the first section into M excitation signals to stimulate the respective array elements at the same time, and trigger and start each receiving channel at the initial moment of excitation signal transmission. Start to receive the echo signals detected by each array element, and superimpose the signals received by each receiving channel as the result of the self-focus detection of the first section; similarly, obtain the self-focus detection results of the 2~N sections respectively.

(5) Analyze the self-focusing detection results of the first to Nth intervals. When the signal-to-noise ratio of the self-focusing detection results in a certain interval is better than the conventional ultrasonic guided wave inspection results, it can be considered that there are defects in this interval. By analyzing the self-focusing detection results of this section, the specific location of the defect can be determined; otherwise, it can be determined that there is no defect in this section of the section.

Compared with the prior art, the present invention has the following beneficial effects:

1. Automatic focus, simple calculation. Compared with the prior art, the present invention realizes that the ultrasonic guided wave is only automatically focused on the defect position in a certain section, which not only avoids the complicated process of calculating the delay parameters of each channel, but also reduces the need for defects in the tube. Point by point focus scanning detection process.

2. Segment detection, high detection ability. Compared with the prior art, the present invention can not only avoid the missed detection caused by the superimposition of multiple defect wave packets in the pipeline, but also overcome the disadvantage of needing to pre-judge the approximate position of the reflected echo wave packets of small defects submerged in the noise , for a pipeline with a long length and many defects, the invention can significantly improve the detection ability of multiple small defects in the pipe.

Description of drawings

Fig. 1 is a flow chart of an ultrasonic guided wave segmental self-focusing detection method for pipeline multi-defect detection;

Fig. 2 is a schematic diagram of the conventional ultrasonic guided wave detection and segmented self-focusing detection data acquisition process of the present invention;

Fig. 3 is the results of conventional ultrasonic guided wave detection of pipeline 1 containing double defects and the segmental self-focusing detection of the present invention; wherein: (a) conventional ultrasonic guided wave detection results; (b) self-focusing detection results of the first interval; (c ) The self-focus detection result of the second interval; (d) The self-focus detection result of the third interval; (e) The self-focus detection result of the fourth interval; (f) The self-focus detection result of the fifth interval;

Fig. 4 shows the results of conventional ultrasonic guided wave detection of pipeline 2 containing double defects and the segmented self-focusing detection of the present invention, in which the first defect is located exactly at the junction of the second and third intervals: (a) conventional ultrasonic guided wave detection results; ( b) The self-focus detection result of the first interval; (c) The self-focus detection result of the second interval; (d) The self-focus detection result of the third interval; (e) The self-focus detection result of the fourth interval; focus on test results;

Fig. 5 is the results of conventional ultrasonic guided wave detection of pipeline 3 containing three defects and the segmented self-focusing detection of the present invention: (a) conventional ultrasonic guided wave detection results; (b) self-focusing detection results of the first interval; (c) second Interval self-focus detection results; (d) self-focus detection results in the third interval; (e) self-focus detection results in the fourth interval; (f) self-focus detection results in the fifth interval.

detailed description

Below in conjunction with the accompanying drawings and examples, the specific implementation of the present invention will be further described in detail, the following examples are used to illustrate the present invention, but not to limit the scope of the present invention.

Figure 1 shows a flow chart of an ultrasonic guided wave segmented self-focusing detection method for multi-defect detection in pipelines, and the method can be implemented step by step according to the flow shown in Figure 1 .

FIG. 2 is a schematic diagram of the conventional ultrasonic guided wave detection and segmented self-focusing detection data acquisition process of the present invention. The method for obtaining the excitation signal during self-focus detection in each section and the process of performing self-focus detection for the i-th (1≤i≤N) section are described below in conjunction with FIG. 2 . In conventional ultrasonic guided wave detection, in order to excite low-order axisymmetric modes, the signals V ₁ (t)~V _M (t) of transducer elements 1~M in driving array 1 need to be simultaneously loaded with the same time-domain For excitation signals with a shorter frequency and narrow band, the transducer elements 1~M in array 2 respectively receive the reflected echo signals of multiple defects and end faces at the same time, and the received signals corresponding to transducer elements 1~M in array 2 can be respectively Denoted as R ₁ (t)~ _RM (t), the superposition result of the received signals of all transducer elements in array 2 is the conventional ultrasonic guided wave detection result. The method of obtaining the excitation signal during self-focus detection in each section: extract the received waveform data points from the first section to the Nth section on the time history curve of each receiving channel respectively, and obtain M×N waveform data point vectors, and use the waveform The maximum value of the data point normalizes each vector, corresponding to the i-th (1≤i≤N) interval, the normalized waveform data points received by channels 1~M are expressed as W _i1 (t)~W _iM (t). The process of self-focus detection for the i-th (1≤i≤N) interval: the normalized waveform data points W _i1 (t)~ After W _iM (t) is arranged in reverse order, V _i1 (t)~V _iM (t) can be obtained, and the waveform data points in V _i1 (t)~V _iM (t) are used to simultaneously stimulate 1~M in array 2 Array elements, the received signals of 1~M array elements in array 1 can be expressed as R _i1 (t)~R _iM (t), and the superposition result of all received signals is Focus on test results.

Embodiment 1: steel pipe pipeline 1, material density is , the modulus of elasticity is , Poisson's ratio is 0.286543. The pipe is 2.1m long, with an outer diameter of 70mm and an inner diameter of 63mm. There are two transparent cracks of the same size at 0.7m and 1.5m away from the end face of the pipe, respectively. The crack width is 2mm, and the expansion angle along the circumferential direction is 8º. The specific detection steps are:

(1) Use the 3-period sine wave with a center frequency of 100kHz plus a Hanning window modulation as the excitation signal for conventional guided wave detection, load it on 48 array elements uniformly distributed along the circumferential direction of the pipe end face, and extract one distance from the pipe end face 1 The information on 48 array nodes with an axial distance of 2.5mm and the same circumferential angle is used as echo signals, and the echo signals received by the 48 array nodes are superimposed as the conventional ultrasonic guided wave detection results. The detection results are shown in the figure 3(a).

(2) Divide the uninspected area of pipeline 1 into five uninspected intervals along the length direction, and the corresponding positions of each uninspected interval on the time history curve are the intervals divided by the vertical dotted lines in Figure 3(a). Since the time domain width of the 3-period plus Hanning window modulated sine wave excitation signal with a center frequency of 100kHz is 30us, and the peak time of the excitation signal appears at 13us, for a steel pipe with a wall thickness of 3.5mm, the L(0,2) modal guided wave is at The group velocity at 100kHz is 5.33mm/us. Considering the time when the detection instrument emits the excitation signal and the influence of the near-field area of the transducer, the self-focus detection of the area within the range of 125.3mm in length from the end face of the pipe is discarded, and the The cut-off point of the area is used as the starting point of the area to be checked. Considering the influence of the echo of the end face, the cut-off point of the area to be inspected is set at a distance of 114.6 mm from the end face 2. Starting from the starting point of the area to be inspected, divide it by 2.5 times the propagation distance of the L(0,2) mode guided wave packet in the time domain width of the excitation signal, and obtain 4 intervals with a length of 400mm. There is also an interval with a length of 260 mm between the cut-off point of each interval and the cut-off point of the area to be inspected, and this interval is regarded as the fifth interval. When calculating the position of the defect or end face, the time difference between the peak time of the echo wave packet of the defect or end face minus the peak time of the wave packet of the excitation signal is multiplied by the group velocity of the detection mode at the center frequency of the excitation signal to calculate the position of the defect or end face. Therefore, when corresponding the start and end points of the 1~5 intervals to the time history curve, it is necessary to divide the distance between the start and end points of each interval and the end face-1 by the L(0,2) modal guided wave at 100kHz After the group velocity at time, the time corresponding to the peak value of the wave packet of the excitation signal is added as the start and end points of each interval on the time course curve.

(3) From the time-history curves of conventional guided wave detection at 48 array nodes, extract 48×5 waveform data point vectors corresponding to the 1st to 5th intervals, normalize them with the maximum value, and reverse the sequence respectively arrangement.

(4) The 48 waveform data points arranged in reverse order corresponding to the first section respectively excite the corresponding array elements, and the data on the 2 array elements of the array are collected synchronously and superimposed, as the self-focus detection result of the first section, as shown in Figure 3(b) shows. Using the same method, the self-focus detection results of the 2nd, 3rd, 4th, and 5th intervals were obtained, respectively, as shown in Figure 3(c), Figure 3(d), Figure 3(e), and Figure 3(e). 3(f).

(5) From the test analysis, it can be seen that the signal-to-noise ratio of the self-focusing test results in the 2nd and 4th areas is better than that of the conventional ultrasonic guided wave test results, while the signal-to-noise ratio of the self-focusing test results in the 1st, 3rd and 5th areas is lower than that of the conventional ultrasound Based on the guided wave detection results, it is judged that there are defects in the 2nd section and the 4th section. According to the propagation time of the wave packet in Figure 3(c) and the group velocity of the L(0,2) mode guided wave at 100kHz, it can be calculated that the defect position in this interval is 699.56mm from the end face 1 of the pipeline, and the end face 2 2 The position is 2093.36m away from the pipe end face 1, and the error with the actual position is 0.06%, 0.32%. Therefore, it can be seen that when the self-focus detection is performed on the second section, the defect position and the end surface position located in this section can be accurately detected. According to the propagation time of the wave packet in Fig. 3(e) and the group velocity of the L(0,2) mode guided wave at 100kHz, it can be calculated that the defect position in this interval is 1493.73mm from the end face 1 of the pipeline, and the end face 2 2 The position is 2092.03m away from the pipe end face 1, and the error with the actual position is 0.42%, 0.38%. Therefore, it can be seen that when the self-focus detection is performed on the fourth section, the defect position and the end surface position in this section can be accurately detected.

Embodiment 2: steel pipe pipeline 2, material density is , the modulus of elasticity is , Poisson's ratio is 0.286543. The pipe is 2.1m long, with an outer diameter of 70mm and an inner diameter of 63mm. There are two transparent cracks of the same size at 0.925m and 1.5m away from the pipe end face 1 respectively, the crack width is 2mm, and the expansion angle along the circumferential direction is 8º.

(1) Use a 3-period sine wave with a center frequency of 100 kHz plus a Hanning window modulation as the excitation signal for conventional guided wave detection, load it on 48 array elements uniformly distributed along the circumferential direction at the end face of the pipeline, and extract the distance from the end face to 1 1 The information of 48 array elements with an axial distance of 2.5mm and the same circumferential angle is used as the echo signal, and the echo signals received by the 48 array nodes are superimposed as the conventional ultrasonic guided wave detection result, as shown in Figure 4(a) Show.

(2) Divide the uninspected area of pipeline 1 into five uninspected intervals along the length direction, and the corresponding positions of each uninspected interval on the time history curve are shown by the vertical dotted line in Figure 4(a). Since the time domain width of the 3-period plus Hanning window modulated sine wave excitation signal with a center frequency of 100kHz is 30us, and the peak time of the excitation signal appears at 13us, for a steel pipe with a wall thickness of 3.5mm, the L(0,2) modal guided wave is at The group velocity at 100kHz is 5.33mm/us. Considering the time when the detection instrument emits the excitation signal and the influence of the near-field area of the transducer, the self-focus detection of the area within the range of 125.3mm in length from the end face of the pipe is discarded, and the The cut-off point of the area is used as the starting point of the area to be checked. Considering the influence of the echo of the end face, the cut-off point of the area to be inspected is set at a distance of 114.6 mm from the end face 2. Starting from the starting point of the area to be inspected, divide it by 2.5 times the propagation distance of the L(0,2) mode guided wave packet in the time domain width of the excitation signal, and obtain 4 intervals with a length of 400mm. There is also an interval with a length of 260mm between the cut-off point of each interval and the cut-off point of the area to be tested, and this interval is regarded as the fifth interval. When calculating the position of the defect or end face, the time difference between the peak time of the echo wave packet of the defect or end face minus the peak time of the wave packet of the excitation signal is multiplied by the group velocity of the detection mode at the center frequency of the excitation signal to calculate the position of the defect or end face. Therefore, when corresponding the start and end points of the 1~5 intervals to the time history curve, it is necessary to divide the distance between the start and end points of each interval and the end face-1 by the L(0,2) modal guided wave at 100kHz After the group velocity at time, the time corresponding to the peak value of the wave packet of the excitation signal is added as the start and end points of each interval on the time course curve.

(3) From the time-history curves of conventional guided wave detection at 48 nodes, extract 48×5 waveform data point vectors corresponding to the 1st to 5th sections, normalize them according to the maximum value, and arrange them in reverse order .

(4) The 48 waveform data points arranged in reverse order corresponding to the first section respectively excite the corresponding array elements, and the data on the 2 array elements of the array are collected synchronously and superimposed, as the self-focus detection result of the first section, as shown in Figure 4(b) shows. Using the same method, the self-focus detection results of the 2nd, 3rd, 4th, and 5th intervals were obtained, respectively, as shown in Figure 4(c), Figure 4(d), Figure 4(e), and Figure 4(e). 4(f).

(5) From the detection analysis, it can be seen that the signal-to-noise ratio of the self-focusing detection results in the 3rd and 4th intervals is better than that of the conventional guided wave detection, while the signal-to-noise ratio of the self-focusing detection results in the 1st, 2nd and 5th intervals is lower than that of the conventional guided wave detection , so it is judged that there are defects in the 3rd and 4th intervals. According to the propagation time of the wave packet in Figure 4(c) and the group velocity of the L(0,2) mode guided wave, it can be calculated that the distance between the defect and the pipe end face 1 in this interval is 928.75 mm, and the distance between the end face 2 and the pipe end face 1 is 928.75 mm. 1 is 2092.03mm, and the actual error is 0.41%, 0.38%. It can be seen that when the self-focusing detection is performed on the third interval, since the third interval contains the second half of the L(0,2) mode of the previous defect reflection wave packet and the velocity is close to the L(0,2) mode High-order bending mode information, the guided wave with greater energy can automatically focus to the defect position during self-focusing detection, and the position of the defect and the end face 2 at the boundary position between this interval and the previous interval can be detected more accurately . According to the propagation time of the wave packet in Figure 4(e) and the group velocity of the L(0,2) mode guided wave, it can be calculated that the distance between the defect and the pipe end face 1 in this interval is 1496.4mm, and the distance between the end face 2 and the pipe end face 1 1 is 2090.69mm, and the actual error is 0.24%, 0.44%. Therefore, it can be seen that when the self-focusing detection is performed on the fourth section, the defect and the position of the end surface located in this section can be accurately detected.

Embodiment 3: steel pipe pipeline 3, material density is , the modulus of elasticity is , Poisson's ratio is 0.286543. The pipe is 2.1m long, with an outer diameter of 70mm and an inner diameter of 63mm. Three through holes with diameters of 2mm, 2.5mm and 3mm are respectively opened at 0.6m, 1.1m and 1.5m away from the end surface of the pipe.

(1) Use a 3-cycle sine wave with a center frequency of 100 kHz plus a Hanning window modulation as the excitation signal for conventional guided wave detection, and load it on the 48 array nodes uniformly distributed along the circumferential direction of the pipe end face-1, extract and compare the end face The information on 48 array nodes whose axial distance is 2.5mm and the same circumferential angle is used as the echo signal, and the echo signals received by the 48 array nodes are superimposed as the conventional ultrasonic guided wave detection result, as shown in Figure 5(a ) shown.

(2) Divide the uninspected area of pipeline 1 into five uninspected intervals along the length direction, and the corresponding positions of each uninspected interval on the time history curve are shown by the vertical dotted line in Figure 5(a). Since the time domain width of the 3-period plus Hanning window modulated sine wave excitation signal with a center frequency of 100kHz is 30us, and the peak time of the excitation signal appears at 13us, for a steel pipe with a wall thickness of 3.5mm L(0,2) mode guided wave The group velocity at 100kHz is 5.33mm/us. Considering the time when the detection instrument emits the excitation signal and the influence of the near-field area of the transducer, the self-focus detection of the area within the range of 125.3mm in length from the end face of the pipe is discarded, and the The cut-off point of this area is used as the starting point of the area to be checked. Considering the influence of the echo of the end face, the cut-off point of the area to be inspected is set at a distance of 114.6 mm from the end face 2. Starting from the starting point of the area to be inspected, divide it by 2.5 times the propagation distance of the L(0,2) mode guided wave packet in the time domain width of the excitation signal, and obtain 4 intervals with a length of 400mm. There is also an interval with a length of 260mm between the cut-off point of each interval and the cut-off point of the area to be tested, and this interval is regarded as the fifth interval. When calculating the position of the defect or end face, the time difference between the peak time of the echo wave packet of the defect or end face minus the peak time of the wave packet of the excitation signal is multiplied by the group velocity of the detection mode at the center frequency of the excitation signal to calculate the position of the defect or end face. Therefore, when corresponding the start and end points of the 1~5 intervals to the time history curve, it is necessary to divide the distance between the start and end points of each interval and the end face-1 by the L(0,2) modal guided wave at 100kHz After the group velocity at time, the time corresponding to the peak value of the wave packet of the excitation signal is added as the start and end points of each interval on the time course curve.

(3) From the time history curves of conventional guided wave detection at 48 array nodes, extract 48×5 waveform data point vectors corresponding to the 1st to 5th regions, normalize them according to the maximum value, and perform reverse order respectively arrangement.

(4) The 48 waveform data points arranged in reverse order corresponding to the first section excite the corresponding array elements respectively, and superimpose the synchronously collected data on the receiving array nodes as the result of self-focus detection in the first section, as shown in Figure 5(b) shows. Using the same method, the autofocus results of the 2nd, 3rd, 4th, and 5th intervals were obtained, respectively, as shown in Figure 5(c), Figure 5(d), Figure 5(e), and Figure 5 (f) shown.

(5) From the detection analysis, it can be seen that the SNR of the self-focusing detection results in the 2nd, 3rd and 4th intervals is better than that of the conventional guided wave detection results, while the signal-to-noise ratio of the self-focusing detection results in the 1st and 5th intervals is lower than that of the conventional guided wave As a result of the test, it is judged that there are defects in the 2nd, 3rd and 4th sections. According to the propagation time of the wave packet in Figure 5(c) and the group velocity of the L(0,2) mode guided wave, it can be calculated that the distance between the defect and the pipe end face 1 in this interval is 601.44mm, and the distance between the end face 2 and the pipe end face 1 1 is 2097mm, and the actual error is 0.24%, 0.14%. Therefore, it can be seen that when the self-focusing detection is performed on the second section, the defect position and the end surface 2 position located in this section can be accurately detected. According to the propagation time of the wave packet in Figure 5(d) and the group velocity of the L(0,2) mode guided wave, it can be calculated that the distance from the defect to the pipe end face 1 is 1098.17mm, and the distance from the end face 2 to the pipe end face 1 is 2097mm , and the actual error is 0.17%, 0.14%. Therefore, it can be seen that when the self-focus detection is performed on the third section, the defect position and the end surface position located in this section can be accurately detected. According to the propagation time of the wave packet in Fig. 5(e) and the group velocity of the L(0,2) mode guided wave, it can be calculated that the distance between the defect and the pipe end face 1 in this interval is 1498.23mm, and the distance between the end face 2 and the pipe end face 1 1 is 2095.64mm, and the actual error is 0.12%, 0.21%. Therefore, it can be seen that when the self-focus detection is performed on the fourth section, the defect position and the end surface position in this section can be accurately detected.

To sum up, the technical solution adopted by the ultrasonic guided wave segmental self-focusing detection method for pipeline multi-defect detection in the present invention is to divide the area to be inspected of the pipeline into multiple sections along the length direction, and divide each section corresponding to The echo signals are globally normalized and arranged in reverse order as the excitation signal of each array element, so as to realize the self-focusing of the ultrasonic guided wave on the defect position in this interval. The method can realize self-focusing detection of defects in a section of the pipeline in one detection, and avoids the disadvantage of point-by-point focusing scanning.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still understand the foregoing embodiments Modifications to the technical solutions described, or equivalent replacements for some of the technical features, within the spirit and principles of the present invention, any modifications, equivalent replacements, improvements, etc., shall be included in the scope of protection of the present invention Inside.

Claims (4)

1. An ultrasonic guided wave segmental self-focusing detection method for pipeline multi-defect detection, characterized in that, comprising the following steps: (1) Simultaneously excite M transducer array elements distributed at equal intervals along the circumferential direction of the pipe end by using narrow-band pulse signals of shorter frequency in the time domain with the same amplitude, and trigger and start each receiving channel at the initial moment of excitation signal transmission Respectively start to receive the echo signals detected by each array element, and superimpose the echo signals received by each receiving channel to obtain a conventional ultrasonic guided wave detection time history curve; (2) Divide the area to be inspected of the pipeline in the length direction into N sections, and map the N sections to the conventional ultrasonic guided wave detection time course curve in the step (1); (3) Extract the received waveform data points of each channel from the first interval to the Nth interval on the conventional ultrasonic guided wave detection time history curve respectively, and obtain M×N waveform data point vectors, and take the maximum value of all waveform data points Perform normalization processing on each vector, and arrange the normalized M×N vectors in reverse order; (4) Synthesize the data points in the M reverse-ordered vectors corresponding to the first section into M excitation signals to stimulate the respective array elements at the same time, and trigger and start each receiving channel at the initial moment of excitation signal transmission Start to receive the echo signals detected by each array element respectively, and superimpose the echo signals received by each channel as the self-focus detection result of the first segment; similarly, obtain the self-focus detection results of the 2-N segment respectively; (5) Analyze the self-focusing detection results of the first to Nth intervals. When the signal-to-noise ratio of the self-focusing detection results in a certain interval is better than the conventional ultrasonic guided wave inspection results, it can be considered that there are defects in this interval. By analyzing the self-focusing detection results of this section, the specific position of the defect in this section can be determined; otherwise, it can be determined that there is no defect in this section. 2. A kind of ultrasonic guided wave segmental self-focusing detection method for pipeline multi-defect detection as claimed in claim 1, characterized in that: the length of the distance from the array installation end face on the pipeline is the time domain width of the excitation signal minus the excitation signal Half of the wave packet peak time multiplied by the distance corresponding to the group velocity at the center frequency of the excitation signal of the detection mode is used as the starting point of the area to be inspected in the step (2), and the end point of the area to be inspected is the distance from the pipeline The tail length is the time domain width of the excitation signal plus the peak moment of the wave packet of the excitation signal multiplied by half the distance corresponding to the group velocity of the detection mode at the center frequency of the excitation signal. 3. A kind of ultrasonic guided wave segmented self-focusing detection method for pipeline multi-defect detection as claimed in claim 1 or 2, It is characterized in that: starting from the starting point of the area to be inspected, <math display = 'block'> of the excitation signal duration used in conventional guided wave detection <mrow> <mi>n</mi> <mo>&amp;sol;</mo> <mn>2</mn> </mrow> </math> multiply by The length corresponding to the group velocity of the detection mode at the center frequency of the excitation signal is used to divide the area to be detected, where <math display = 'block'> <mrow> <mi>n</mi> </mrow> </math> for big Integers greater than or equal to 1, the last segment is regarded as a separate segment no matter the length is less than or equal to the length of other intervals; the first segment The lengths of intervals from interval to N-1 are equal, and the length of interval N is less than or equal to other intervals. 4. An ultrasonic guided wave segmental self-focusing detection method for pipeline multi-defect detection according to claim 1, characterized in that: the number M of array elements distributed at equal intervals along the circumferential direction of the pipeline end >16.