Method and apparatus for ultrasonic testing of the inner wall of a boiler tube

Abstract

An ultrasonic testing method and apparatus for the inner wall of boiler pipes is disclosed. The testing method includes: placing a testing trolley on the inner wall of the pipe; the trolley has a left drive wheel, a right drive wheel, a coupling agent application head, an ultrasonic probe, and a camera; driving the left and right drive wheels with an initial speed difference, causing the trolley to move in a helical trajectory; applying coupling agent through the coupling agent application head during movement, detecting the applied area through the ultrasonic probe, and simultaneously acquiring an image containing the applied coupling agent area through the camera; processing the image to identify the overlap width of the coupling agent application area between two adjacent helical trajectories and comparing it with a preset target overlap width; adjusting the speed difference of the left and right drive wheels in real time based on the comparison result: decreasing the speed difference when the overlap width is greater than the target value, and increasing the speed difference when it is less than the target value; repeating the above steps to maintain the overlap width at the target value, thereby achieving continuous and uniform ultrasonic testing of the inner wall of the pipe. This invention can adapt to the geometric and motion uncertainties of the inner wall of the pipe, achieving high-efficiency and full-coverage ultrasonic testing.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing technology for boiler pipes, specifically to an ultrasonic testing method and apparatus for the inner wall of boiler pipes. Background Technology

[0002] Boiler pipelines operate under high temperature, high pressure, and corrosive environments for extended periods, making their inner walls prone to defects such as cracks, corrosion pits, and thinning. Regular non-destructive testing of the inner walls is crucial for ensuring safe operation. Ultrasonic testing is widely used due to its sensitivity to internal defects and its ability to detect deep penetrations.

[0003] For ultrasonic testing of pipe inner walls, various testing devices and methods based on helical travel have been proposed in the existing technology.

[0004] CN223868831U discloses a spiral carbon fiber centrifugal-driven pipeline flaw detection robot, which has an internal rotatable disk for ultrasonic testing. Driven by a eccentric motor, the robot moves forward in a spiral motion within the pipeline. The direction of rotation of the eccentric motor can be changed, allowing the robot to slow down or return when encountering insurmountable obstacles. This design achieves spiral movement through the eccentric motor, with the ultrasonic probe mounted on the internal rotatable disk. The disk's rotation drives the probe to scan circumferentially along the pipeline. CN117515318A discloses an adaptive spiral-driven pipeline defect detection robot, comprising a pre-detection module, an adaptive support module, a drive module, a spiral motion module, and a post-detection module connected in sequence. The spiral motion module enables the robot to move spirally within the pipeline, and the adaptive support module improves its adaptability to changes in pipe diameter. CN104865314A discloses a pipeline non-destructive testing device based on spiral measurement, integrating an ultrasonic distance sensor and a digital potentiometric angle sensor. Connected to a spiral pipeline robot, it conducts experimental research and achieves spiral measurement of the pipeline's inner wall by performing data inversion on a pipeline inner wall model.

[0005] However, the above-mentioned spiral-type ultrasonic testing scheme still has the following shortcomings in practical applications: The uniformity of helical trajectory coverage depends on the control precision of the driving parameters. In the aforementioned scheme, the ultrasonic probe is typically mounted on an internal rotatable disk, with circumferential scanning achieved by the disk's rotation. The helical motion of the detection device is driven by a eccentric motor, fan blades, or a helical motion module. The robot's linear movement and the probe's circumferential scanning are two relatively independent motions. When there are variable diameter sections, elliptic deformation, weld protrusions, or internal wall deposits inside the pipe, the actual travel speed and posture of the detection device will change unpredictably, leading to fluctuations in the pitch of the helical trajectory. This results in excessive overlap between adjacent helical trajectories, reducing detection efficiency, or insufficient coverage causing missed detection areas. Existing solutions mainly improve the transmission and throughput of helical motion through mechanical structure optimization, such as eccentric motor drive, fan blade drive, and adaptive support, but they fail to effectively solve the problem of real-time perception and active adjustment of helical coverage uniformity during the detection process. Summary of the Invention

[0006] The present invention aims to provide an ultrasonic testing method and apparatus for the inner wall of boiler pipes, so as to achieve adaptive, high-efficiency and full-coverage ultrasonic testing of the inner wall of boiler pipes.

[0007] To solve the above technical problems, the specific solution adopted by the present invention is as follows: an ultrasonic testing method for the inner wall of boiler pipes, comprising the following steps: The detection cart is placed inside the pipe wall. The cart has a left drive wheel, a right drive wheel, a coupling agent applicator, an ultrasonic probe, and a camera. The left and right drive wheels are driven by the initial speed difference, so that the trolley moves along the inner wall of the pipe in a spiral trajectory. During the process, coupling agent is applied to the inner wall of the pipe through a coupling agent application head; ultrasonic probe is used to perform ultrasonic testing on the area of ​​the inner wall of the pipe with the applied coupling agent, and at the same time, a camera is used to capture real-time images of the inner wall of the pipe, the images of which include the area with the applied coupling agent; The acquired images are processed to identify the overlap width of the coupling agent coating area between two adjacent spiral trajectories; The identified overlap width is compared with the preset target overlap width; The speed difference between the left and right drive wheels is adjusted in real time based on the comparison results: when the overlap width is greater than the target overlap width, the speed difference is reduced; when the overlap width is less than the target overlap width, the speed difference is increased. Repeat the above steps of acquisition, identification, comparison, and adjustment to maintain the overlap width at the target overlap width, thereby achieving continuous and uniform ultrasonic testing of the inner wall of the pipe.

[0008] Preferably, the target overlap width is a fixed value within the range of 0.5cm to 1.5cm.

[0009] Preferably, the initial speed difference is a speed difference that causes positive overlap between two adjacent spiral trajectories.

[0010] Preferably, the processing of the acquired image includes: converting the image into a grayscale image, extracting the boundary of the coupling agent application area through threshold segmentation, and calculating the overlap distance of the application areas of two adjacent trajectories along the pipe axis.

[0011] Preferably, the coupling agent contains a fluorescent tracer; when the camera acquires images, it is used in conjunction with an excitation light source and a filter of the corresponding wavelength, and automatic exposure control is performed to enhance the image contrast of the area where the coupling agent is applied.

[0012] An ultrasonic testing device for the inner wall of a boiler pipe used to implement the above-mentioned ultrasonic testing method includes: Car; The left and right drive wheels, located at the bottom of the vehicle, are each driven by an independent drive motor. A retractable support frame is installed on the top of the trolley and a follower wheel is installed on its top; The coupling agent application head, ultrasonic probe, and camera are mounted on the vehicle, with the coupling agent application head located in front of the ultrasonic probe. The controller is electrically connected to the camera, the drive motor of the left drive wheel, and the drive motor of the right drive wheel, respectively. The controller is used to: acquire images captured by the camera, identify the overlap width of the coupling agent coating area between two adjacent spiral trajectories, compare the overlap width with a preset target overlap width, and output a control signal based on the comparison result to adjust the speed difference between the left drive wheel and the right drive wheel in real time, so that the overlap width is maintained at the target overlap width.

[0013] Preferably, the coupling agent contains a fluorescent tracer; a bandpass filter corresponding to the emission wavelength of the fluorescent tracer is provided in front of the camera; the trolley is also provided with a ring-shaped LED illumination source whose emission wavelength matches the excitation wavelength of the fluorescent tracer; the controller also includes an automatic exposure control module for dynamically adjusting the camera exposure parameters according to the image brightness.

[0014] Preferably, the left drive wheel and the right drive wheel each independently include a drive motor and a transmission mechanism, and the follower wheel, the left travel wheel and the right travel wheel are all omnidirectional wheels.

[0015] Preferably, the optical axis of the camera points to the inner wall area of ​​the pipe behind the coupling agent applicator, and the field of view of the camera covers the trajectory just applied by the coupling agent applicator and the boundary area of ​​adjacent trajectories.

[0016] Beneficial effects Existing helical motion ultrasonic probe designs typically require an internal rotatable disk and a corresponding drive mechanism to achieve circumferential scanning, increasing the system's structural complexity and size. This invention utilizes differential drive to achieve the helical motion of the trolley. The ultrasonic probe is fixedly mounted on the trolley and moves helically along with it, eliminating the need for a separate probe rotation mechanism. This results in a simpler and more compact structure, making it suitable for use in smaller diameter boiler pipes and reducing manufacturing costs.

[0017] In existing helical ultrasonic testing solutions (such as CN223868831U, CN117515318A, CN104865314A, etc.), the ultrasonic probe is mounted on an internal rotatable disk, and circumferential scanning is achieved by the rotation of the disk. The robot's linear movement and the probe's circumferential scanning are two relatively independent movements. When there are variable diameter sections, elliptic deformation, weld protrusions, or internal wall deposits inside the pipe, the actual speed and posture of the testing device will change unpredictably, causing fluctuations in the pitch of the helical trajectory. This leads to problems such as excessive overlap between adjacent helical trajectories, reducing testing efficiency, or insufficient coverage, resulting in missed areas. This invention uses a controller to compare the identified overlap width with a preset target overlap width and adjusts the speed difference between the left and right drive wheels in real time based on the comparison result. When the overlap is too wide, the speed difference is reduced; when the overlap is insufficient, the speed difference is increased, thus forming a closed-loop control. This mechanism can automatically compensate for trajectory deviations caused by factors such as diameter changes, slippage, and weld protrusions, keeping the overlap width consistently near the preset target value. This avoids both the waste of coupling agent and the extended detection time caused by excessive overlap, and eliminates missed detection areas caused by insufficient overlap, thus achieving a balance between detection integrity and detection efficiency.

[0018] In existing spiral-type inspection solutions, to achieve the desired spiral coverage effect, it is usually necessary to pre-calculate or set driving parameters based on parameters such as pipe inner diameter, probe width, and desired pitch. When pipe specifications change or there are variable diameter sections, parameters need to be recalculated or adjusted, which is cumbersome and requires a high level of expertise from operators. This invention directly uses the actual overlap width detected visually as a feedback signal to dynamically adjust the differential speed, without the need to pre-measure pipe inner diameter, calculate pitch, or rely on precise kinematic models. For complex conditions commonly found in boiler pipes, such as reduced diameter transition sections, elliptical deformation, and local weld protrusions, the system can automatically adapt, significantly reducing the requirements for pre-parameter preparation and operator skills. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the detection vehicle in an embodiment of the present invention; Figure 2 for Figure 1 Schematic diagram of the AA-direction cross-section structure; The markings in the diagram are: 1. Pipe, 2. Sleeve, 3. Top caster wheel, 4. Telescopic rod, 5. Spring, 6. Camera, 7. Coupling agent applicator, 8. Ultrasonic probe, 9. Cart, 10. Right caster wheel, 11. Left caster wheel, 12. Left drive wheel. Detailed Implementation

[0020] like Figure 1 and Figure 2 As shown, an ultrasonic testing device for the inner wall of a boiler pipe 1 according to the present invention includes a trolley 9. A left drive wheel 12 and a left follower universal wheel 11 are located on the left side of the bottom of the trolley 9, and a right drive wheel and a right follower universal wheel 10 are located on the right side. The left drive wheel 12 is connected to a left drive motor, and the right drive wheel is connected to a right drive motor. Both motors (not shown in the figure) are DC servo motors, which can independently control their speed and direction. A telescopic support frame is provided on the top of the trolley 9. The support frame consists of a sleeve 2 fixed to the trolley 9 and a telescopic rod 4 slidably disposed in the sleeve 2. Multiple positioning holes are provided on the telescopic rod 4. When one positioning hole overlaps with another positioning hole on the sleeve 2 and a pin is inserted, the height of the support frame is fixed. A top follower universal wheel 3 is installed at the top of the telescopic rod 4. A compression spring 5 is provided inside the support frame, enabling it to adapt to changes in the inner diameter of the pipe 1 and always press the top follower universal wheel 3 tightly against the inner wall of the pipe 1, ensuring stable contact between the trolley 9 and the inner wall of the pipe 1. The left and right travel wheels and the top omnidirectional wheel 3 only serve as support and follow-up functions, and have no power.

[0021] The trolley 9 is equipped with a coupling agent applicator 7, an ultrasonic probe 8, and a camera 6, installed sequentially. The coupling agent applicator 7 is a sponge-shaped tube connected via a flexible tube to a coupling agent reservoir and a miniature peristaltic pump inside the trolley, allowing for the metered extrusion of coupling agent and application to the inner wall of pipe 1. The ultrasonic probe 8 is a contact-type longitudinal wave probe used to detect corrosion and cracks on the inner wall of pipe 1. The camera 6 is an industrial camera, its optical axis pointing approximately 3-5 cm behind the coupling agent applicator 7 on the inner wall of pipe 1, enabling simultaneous capture of the current application trajectory and the boundary of the adjacent previous trajectory. The trolley 9 also houses a controller, an embedded microprocessor. Its input is connected to the camera 6 and the current feedback terminals of the two drive motors, while its output is connected to the drive circuits of the left and right drive motors. The controller internally implements an image processing unit, a comparison unit, and a differential speed adjustment unit via software.

[0022] The detection method of the present invention will be described in detail below.

[0023] Before conducting the test, preparatory operations are performed. An ultrasonic coupling agent mixed with a fluorescent tracer is injected into the coupling agent storage tank. In this embodiment, Rhodamine B is used as the fluorescent tracer, with an excitation wavelength of 530 nm and an emission wavelength of 570 nm, added at a ratio of 0.1 g / L. The trolley 9 is placed into the boiler pipe 1 to be tested; in this embodiment, the inner diameter of pipe 1 is 100 mm. The telescopic support frame is adjusted so that the left drive wheel 12, right drive wheel, left follower universal wheel 11, right follower universal wheel 10, and top follower universal wheel 3 all press against the inner wall of pipe 1. The ring LED light source is activated, with a center wavelength of 530 nm, matching the excitation wavelength of the fluorescent tracer. Simultaneously, the automatic exposure function of the camera 6 is activated.

[0024] At the start of the inspection, the controller drives the left drive wheel 12 and the right drive wheel with an initial speed difference, causing the trolley 9 to travel along the inner wall of the pipe 1 in a spiral trajectory. The principle for selecting this initial speed difference is to ensure positive overlap between adjacent spiral trajectories, i.e., the overlap width is greater than zero. This avoids missed detection gaps in the initial stage. The specific value of the initial speed difference can be calibrated according to different pipe 1 diameters, wheel diameters, and desired travel speeds. The core requirement is to ensure that the spiral trajectory overlaps rather than separates at the beginning.

[0025] During the movement of the trolley 9, coupling agent is applied to the inner wall of pipe 1 through the coupling agent application head 7. Specifically, a peristaltic pump is activated, causing the coupling agent application head 7 to extrude coupling agent into the roller at a constant flow rate, which then applies the coupling agent to the inner wall of pipe 1. Simultaneously, an ultrasonic probe 8 performs ultrasonic testing on the area of ​​the inner wall of pipe 1 with the applied coupling agent, and the data is stored in real time in the controller's storage unit. At the same time, a camera 6 captures real-time images of the inner wall of pipe 1, including the area with the applied coupling agent. Because the coupling agent contains a fluorescent tracer and is excited by a ring LED light source, the applied area appears bright in the images, while the background of the inner wall of pipe 1, including metal, rust, and shadows, is dark, creating a significant contrast.

[0026] The controller processes the acquired images to identify the overlap width of the coupling agent application area between two adjacent spiral trajectories. Specifically, the processing involves: converting and binarizing the image to grayscale to extract the coupling agent application area; determining the coverage area of ​​the current application trajectory and the adjacent trajectory from the previous spiral trajectories along the axial direction of pipe 1; calculating the overlap length of the two areas along the axial direction; and converting this overlap length to the actual length based on a pre-calibrated pixel equivalent.

[0027] The controller compares the identified overlap width with the preset target overlap width. In this embodiment, the preset target overlap width is 1.0 cm. The specific value can be set by the user within the range of 0.5-1.5 cm before detection, based on the actual working conditions of pipe 1 and the probe parameters.

[0028] Based on the comparison results, the controller adjusts the speed difference between the left drive wheel 12 and the right drive wheel in real time. When the overlap width is greater than the target overlap width, the controller reduces the speed difference, increasing the pitch of the helical movement of the trolley 9 and decreasing the subsequent overlap width; when the overlap width is less than the target overlap width, the controller increases the speed difference, increasing the subsequent overlap width. The control cycle is 0.5 seconds, and a PID algorithm is used for adjustment.

[0029] The controller repeats the above steps of acquisition, identification, comparison, and adjustment to maintain the overlap width near the target overlap width. Experiments show that even when the inner diameter of pipe 1 gradually narrows from 100mm to 95mm, such as in the transition section of the simulated boiler pipe 1, or when the drive wheel briefly slips over the weld bead area, the visual feedback system can detect changes in overlap width within 1-2 control cycles and adjust the differential speed in time, thus maintaining uniform coverage. After the trolley 9 has traversed the entire length of pipe 1, it stops moving and applying the coating, saving the ultrasonic inspection data and image records for subsequent defect analysis.

[0030] In this embodiment, a water-based ultrasonic coupling agent containing Rhodamine B fluorescent tracer (addition ratio 0.1 g / L) is used. A ring-shaped LED light source with a center wavelength of 530 nm is installed around the camera 6, matching the excitation wavelength of Rhodamine B. A bandpass filter with a center wavelength of 570 nm and a half-bandwidth of ±10 nm is installed in front of the lens of the camera 6. This filter only allows fluorescent emission light to pass through, effectively blocking ambient light and excitation light reflection. Simultaneously, the controller incorporates an automatic exposure control module that monitors the overall brightness of the image in real time and dynamically adjusts the exposure time and gain of the camera 6 to ensure consistent image brightness under different pipe diameters and travel speeds, avoiding overexposure or underexposure. This combination results in a uniformly bright area in the image where the coupling agent is applied, while the background of the inner wall of pipe 1 is dark, greatly simplifying the threshold segmentation and ensuring the reliability of overlap width recognition.

Claims

1. An ultrasonic testing method for the inner wall of boiler pipes, characterized in that: Includes the following steps: The detection cart (9) is placed in the pipe (1). The cart (9) has a left drive wheel (12), a right drive wheel, a coupling agent applicator (7), an ultrasonic probe (8), and a camera (6). Drive the left drive wheel (12) and the right drive wheel with the initial speed difference, so that the trolley (9) moves along the inner wall of the pipe (1) in a spiral trajectory; During the process, coupling agent is applied to the inner wall of the pipe (1) through the coupling agent application head (7); ultrasonic detection is performed on the inner wall area of ​​the pipe (1) with the coupling agent applied through the ultrasonic probe (8), and at the same time, the inner wall image of the pipe (1) is acquired in real time through the camera (6), the image containing the area with the coupling agent applied; The acquired images are processed to identify the overlap width of the coupling agent coating area between two adjacent spiral trajectories; The identified overlap width is compared with the preset target overlap width; The speed difference between the left drive wheel (12) and the right drive wheel is adjusted in real time according to the comparison results: when the overlap width is greater than the target overlap width, the speed difference is reduced; when the overlap width is less than the target overlap width, the speed difference is increased. Repeat the above steps of acquisition, identification, comparison and adjustment to maintain the overlap width at the target overlap width and achieve continuous and uniform ultrasonic detection of the inner wall of the pipe (1).

2. The ultrasonic testing method for the inner wall of a boiler pipe according to claim 1, characterized in that: The target overlap width is a fixed value within the range of 0.5cm to 1.5cm.

3. The ultrasonic testing method for the inner wall of a boiler pipe according to claim 1, characterized in that: The initial speed difference is the speed difference that causes positive overlap between two adjacent spiral trajectories.

4. The ultrasonic testing method for the inner wall of a boiler pipe according to claim 1, characterized in that: The processing of the acquired image includes: converting the image into a grayscale image, extracting the boundary of the coupling agent coating area by threshold segmentation, and calculating the overlap distance of the coating areas of two adjacent trajectories along the axial direction of the pipe (1).

5. The ultrasonic testing method for the inner wall of a boiler pipe according to claim 1, characterized in that: The coupling agent contains a fluorescent tracer; when the camera (6) acquires images, it is used in conjunction with an excitation light source and a filter of the corresponding wavelength, and performs automatic exposure control to enhance the image contrast of the area coated with the coupling agent.

6. An ultrasonic testing device for the inner wall of a boiler pipe used to implement the ultrasonic testing method according to any one of claims 1-5, characterized in that: include: Car (9); The left drive wheel (12) and right drive wheel, which are located at the bottom of the trolley (9), are driven by independent drive motors respectively; A retractable support frame is installed on the top of the trolley (9) and a follower wheel is installed on its top; The coupling agent applicator (7), the ultrasonic probe (8), and the camera (6) are mounted on the trolley (9), with the coupling agent applicator (7) located in front of the ultrasonic probe (8); The controller is electrically connected to the camera (6), the drive motor of the left drive wheel (12), and the drive motor of the right drive wheel, respectively; The controller is used to: acquire images captured by the camera (6), identify the overlap width of the coupling agent coating area between two adjacent spiral trajectories, compare the overlap width with the preset target overlap width, and output a control signal according to the comparison result to adjust the speed difference between the left drive wheel (12) and the right drive wheel in real time, so that the overlap width is maintained at the target overlap width.

7. The ultrasonic testing device for the inner wall of a boiler pipe according to claim 6, characterized in that: The coupling agent contains a fluorescent tracer; a bandpass filter corresponding to the emission wavelength of the fluorescent tracer is provided in front of the camera (6); the trolley (9) is also provided with a ring LED lighting source, the emission wavelength of which matches the excitation wavelength of the fluorescent tracer; the controller also includes an automatic exposure control module, which is used to dynamically adjust the exposure parameters of the camera (6) according to the image brightness.

8. The ultrasonic testing device for the inner wall of a boiler pipe according to claim 6, characterized in that: The left drive wheel (12) and the right drive wheel each independently include a drive motor and a transmission mechanism, and the follower wheel, the left travel wheel and the right travel wheel are all omnidirectional wheels.

9. The ultrasonic testing device for the inner wall of a boiler pipe according to claim 6, characterized in that: The optical axis of the camera (6) points to the inner wall area of ​​the pipe (1) behind the coupling agent application head (7), and the field of view of the camera (6) covers the trajectory just applied by the coupling agent application head (7) and the boundary area of ​​the adjacent trajectory.

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