Mechanical scanning imaging method for inner layer ultra-thin composite pipe

Abstract

A kind of mechanical scanning imaging method of inner layer extremely thin bimetallic composite pipe, comprising the following steps:1) setting water coupling circulation system, install several jet coupling ultrasonic detection units on cylindrical coupling cavity along the circumference;Each detection unit is an ultrasonic detection channel, forming n ultrasonic detection channels;2) composite pipe passes through cylindrical coupling cavity, cavity and composite pipe axis coincide;3) start water coupling circulation system, drive composite pipe uniform speed in turn through each adjacent detection unit, dynamic water jet coupling ultrasonic wave enters composite pipe and carries out imaging detection, until composite pipe passes through detection unit completely.The application adopts multiple channels ultrasonic wave parallel detection, each channel is triggered by bimetallic composite pipe end in sequence, each adjacent channel is started to detect, after obtaining detection point signal, each channel mechanical scanning point position is reorganized, the ultrasonic wave detection contrast image of extremely thin inner layer of bimetallic composite pipe is formed, and the online detection of defect is realized.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, and in particular to a mechanical scanning imaging method for an ultra-thin inner layer composite tube. Background Technology

[0002] Currently, many industries urgently need high-performance, low-cost pipes. Besides meeting conventional mechanical performance requirements, these pipes also need to possess properties such as high-temperature resistance, corrosion resistance, erosion resistance, and oxidation resistance. However, it is particularly difficult for a single material to simultaneously possess all these comprehensive properties. Even expensive high-alloy steels, such as martensitic stainless steel, duplex stainless steel, nickel-based alloys, or titanium alloys, have their own shortcomings. With the development of manufacturing technology, various bimetallic composite pipes using different manufacturing processes have emerged to address this situation.

[0003] Bimetallic composite pipes are made of two different metal materials, using carbon steel or low-alloy steel pipes as the base pipe, with a corrosion-resistant alloy layer laminated to the inner and outer surfaces. They are manufactured through specific physical deformation or metallurgical bonding. Through special deformation and connection techniques, the base material and lining of the bimetallic composite pipe are tightly bonded together, maximizing the advantages of both metals, overcoming the performance defects of single-metal materials, and simultaneously reducing the overall cost of use.

[0004] See Figure 1 Bimetallic composite pipe 100 is a new type of steel pipe that combines a base steel pipe 10 and a cladding metal 20 by means of mechanical or metallurgical bonding, and 30 is the interface between the two.

[0005] The base steel pipe 10 primarily serves as a pressure-bearing and rigid support, while the cladding metal 20 provides functional corrosion protection, high-temperature oxidation resistance, and wear resistance. The bimetallic composite pipe retains the advantages of both the base pipe and the cladding metal while addressing their respective shortcomings. The base steel pipe 10 can have its diameter, wall thickness, and steel grade adjusted according to structural and service requirements, while the cladding metal 20 can be selected from different corrosion-resistant metals or alloys based on service conditions. Bimetallic composite pipes effectively reduce the cost of traditional high-alloy products, costing only 1 / 5 to 1 / 2 of pure corrosion-resistant alloy pipes. Comparative analysis of the comprehensive performance of various pipelines used for oil and gas transportation by domestic professional research institutions shows that bimetallic composite pipes rank among the best in terms of overall performance.

[0006] For novel steel pipe products like bimetallic composite pipes, where the inner layer metal is expensive, the thickness of the inner layer metal-clad metal 20mm layer will be designed and manufactured to a cost-effective level to meet the application scenario. The quality inspection targets and dimensional equivalent requirements will differ significantly from traditional flaw detection requirements. Previous quality inspection methods are no longer applicable, especially when the inner layer metal-clad metal 20mm layer is extremely thin. Figure 1Previous methods for detecting defects in steel pipes are no longer applicable to the quality inspection of bimetallic composite pipes.

[0007] We know that my country currently has mature national standards for the flaw detection of steel pipes, which stipulate corresponding methods for quality inspection. For example, GB / T 5777-2008 "Ultrasonic Testing Method for Seamless Steel Pipes" specifies the use of the refracted transverse wave flaw detection method. By incident ultrasonic waves at a certain angle to the surface of the steel pipe, the longitudinal waves are completely reflected, and the refracted transverse waves are used to enter the steel pipe for testing.

[0008] For bimetallic composite tubes with extremely thin inner metal layers, in order to reduce costs, the thickness of the inner metal layer can even be as thin as a few hundred micrometers, such as... Figure 1 As shown, the actual thickness of the inner metal-cladding metal 20 used is extremely thin, less than 1 mm. This means that existing conventional online flaw detection equipment either cannot detect defects at the junction of the inner and base layers due to their small size, or the signals are completely masked by the backwave signal. Consequently, existing flaw detection technology cannot identify manufacturing defects in composite steel pipes with such thin inner metal layers. Therefore, the quality inspection targets and dimensional equivalent requirements for flaw detection of composite pipes with extremely thin inner metal layers differ significantly from traditional flaw detection requirements. Previous quality inspection methods are no longer applicable, especially with extremely thin inner metal layers. For bimetallic composite pipes with extremely thin inner metal-cladding metal 20 layers, defects are often related to the manufacturing process, such as porosity in the inner metal and unbonded cracks at the bonding interface 30. These two types of defects are novel for traditional single-material steel pipes, and conventional flaw detection techniques cannot detect them. Furthermore, due to the small size of the defects, conventional flaw detection methods are also unable to guarantee sufficient sensitivity. Since bimetallic composite pipes with extremely thin inner metal layers are a new type of steel pipe product that has emerged under the current progress of the manufacturing industry, there are no corresponding mature technologies and experiences to draw upon for identifying and detecting the quality of their composite pipe functional layers and bonding surfaces.

[0009] Currently available non-destructive testing methods for steel pipes all have limitations:

[0010] 1. The pipe body is a bimetallic material with an extremely thin inner layer. Defects such as pores and poor bonding exist in the inner layer area, making conventional ultrasonic testing methods no longer applicable.

[0011] 2. Both magnetic particle and eddy current methods are difficult to use for automatic flaw detection of the inner layer of steel pipes;

[0012] 3. X-ray methods also struggle to achieve the sensitivity required to address the current problems.

[0013] 4. Even using ultrasonic guided wave methods, it is difficult to achieve the required flaw detection sensitivity level for bimetallic composite pipes, let alone realize online automatic flaw detection.

[0014] Chinese patent CN210639145U discloses a "composite pipe flaw detection device," which includes a testing platform with a probe mounted on top. The testing platform has a mounting base containing two rotating shafts. Each rotating shaft has a roller supporting the pipe. The rotating shafts are driven by a drive mechanism. A support plate is connected to the testing platform via a support frame. Vertical plates are located at the bottom of both ends of the support plate. A reciprocating screw and a sliding rod are located between the two vertical plates. The end of the reciprocating screw is rotatably mounted on the vertical plate, and a nut is attached to the screw. A slider is attached to the sliding rod, and the slider and nut are connected via a connecting plate. The probe is fixed to the connecting plate, and the reciprocating screw is connected to the output end of a reduction motor. This device has a simple structure and achieves comprehensive inspection.

[0015] As can be seen from this patent, the device is a flaw detection tool for steel pipe products produced by various conventional composite manufacturing processes. It does not involve the technical principles of online imaging detection, nor does it involve the characteristics of the tested object with an extremely thin inner layer of less than 1 mm.

[0016] Chinese Patent CN206497075U discloses an "ultrasonic flaw detection machine tool for composite pipes," which includes: a machine frame, a spindle box, a moving base, and a mounting bracket; a three-jaw chuck is mounted on the output shaft of the spindle box, and a circular gear ring is provided on the circumference of the three-jaw chuck; the moving base is slidably disposed in a groove located at the bottom of the machine frame, and a threaded through hole is provided on the moving base in a left-right direction, with a threaded rod disposed in the threaded through hole; the two ends of the threaded rod are respectively rotatably disposed on a fixed base and the spindle box; a gear is mounted at the left end of the threaded rod, and the gear meshes with the gear ring; the mounting bracket is welded and fixedly fixed to the top of the moving base, and an ultrasonic detector is fixedly mounted on the mounting bracket, with the probe of the ultrasonic detector pointing vertically downward. This utility model enables the ultrasonic detector to move horizontally simultaneously during the rotation of the composite pipe, eliminating the need for multiple pipe clamping or angle adjustments, thus greatly improving efficiency and ensuring no flaws are missed during flaw detection.

[0017] As can be seen from this patent, the device is also a flaw detection tool for composite steel pipe products using the contact water film method. It does not mention any ultrasonic detection technology or ultrasonic imaging detection technology, nor does it involve the technical principle of online imaging detection, nor does it address the characteristics of the tested object with an extremely thin inner layer of less than 1 mm.

[0018] Chinese patent CN208457441U discloses a "flaw detection device for stainless steel-lined composite pipes", which includes a pipe wall detector and a forming frame; a rolling gap for the pipe is provided between the forming frame and the pipe wall detector; the forming frame includes a supporting outer frame, the inner wall of which is provided with a circular support hole, and a supporting roller is arranged in a ring array inside the support hole; the pipe wall detector includes several sets of pressure plates arranged in a coaxial linear array, and the pressure plates are interconnected by an air booster; eight sets of air piston assemblies are arranged in a ring array on the pressure plates; the air piston assembly includes a cylinder body fixedly connected to the pressure plate, and a cylinder piston is floatingly connected inside the cylinder body; the bottom of the cylinder body is connected to the inside of the pressure plate through a connecting valve, a tension strain gauge is provided between the bottom of the cylinder piston and the bottom of the cylinder body, and a compression roller is rotatably connected to the top of the cylinder piston. As can be seen from this patent, the device is a stress detection tool that connects a tensile strain gauge to an ammeter via a bridge circuit. It does not involve the technical features of online ultrasonic imaging detection, nor does it address the characteristics of the test object with an extremely thin inner layer of less than 1 mm.

[0019] Therefore, in order to overcome the limitations of conventional ultrasonic testing methods for steel pipes and the technical principles of various testing methods such as eddy current, X-ray, infrared, microwave, and laser ultrasonic testing, and to realize online quality flaw detection of bimetallic composite pipes, new methods are necessary.

[0020] Although there are currently more than a dozen mature non-destructive testing methods and more than a thousand types of non-destructive testing instruments and equipment, most of the available non-destructive testing methods for steel pipes have limitations in their testing principles. This invention believes that only by using ultrasonic detection combined with mechanical imaging can a method that can be implemented in industrial applications and conduct online flaw detection on bimetallic composite pipes with extremely thin inner layers be realized.

[0021] The characteristic of mechanical imaging is that the detection results are typically a grid-like distribution map. For sheet metal or small round parts, this result is generally a two-dimensional planar distribution map or a three-dimensional spatial distribution map. The nodes of the grid represent the locations where detection was performed, or are considered the locations where detection signals were acquired. Adjacent nodes form adjacent points on the mechanical imaging result map, and the distance between adjacent nodes is the step size of the mechanical scan. Figure 2 As shown, the mechanical imaging detection of a plate is used as an example to illustrate the detection method. Figure 2 In this method, using a single channel and with the assistance of a servo motion control system, it is easy and quick to perform repeated mechanical scanning imaging of the plate sample. The step size can also be adjusted by setting the motion system to obtain mechanical imaging detection results of different resolutions.

[0022] However, using mechanical imaging to inspect extremely thin bimetallic composite pipes presents new challenges compared to plate or small round parts. While it's possible to use a single channel for mechanical imaging of extremely thin bimetallic composite pipes by employing a linear motion of the ultrasonic sensor relative to the pipe's axis, combined with the pipe's gradual rotation, the detection efficiency is extremely low and unsuitable for practical production applications. Using multiple channels for mechanical imaging results in excessively large sensor spacing, preventing the formation of a complete mechanical scan image. In other words, to achieve 100% flawless inspection, the effective area of ​​the ultrasonic detection points is limited, for example, less than 1 mm. 2 The spacing between adjacent nodes in a mechanical imaging grid must match this, also being on the same order of magnitude. However, it is difficult to achieve simultaneous side-by-side mechanical motion detection at such a small size between adjacent sensors in a multi-sensor group. This is determined by the actual manufacturing technology of each sensor. As a result, mechanical imaging detection cannot be performed. Summary of the Invention

[0023] The purpose of this invention is to provide a mechanical scanning imaging method for ultra-thin inner layer composite tubes, so as to realize mechanical scanning imaging detection of the unique defects of ultra-thin inner layer bimetallic composite tubes.

[0024] To achieve the above objectives, the technical solution of the present invention is as follows:

[0025] To address the difficulty of mechanical imaging detection of bimetallic composite pipes in multi-channel ultrasonic testing, this invention designs a method for acquiring signal data to generate ultrasonic mechanical scanning images. It employs multi-channel ultrasonic detection, sequentially triggering the detection of each adjacent channel at the pipe end. After obtaining the detection point signals, the positions of the mechanical scanning points in each channel are reorganized to form an ultrasonic contrast image of the extremely thin inner layer of the bimetallic composite pipe, thereby achieving online defect detection.

[0026] This invention utilizes dynamic water jet coupling to maintain good coupling within the water cavity during flaw detection. After the water jet coupling is complete, the jet naturally falls into the circulating water path and is recycled back to the water tower tank for reuse. This is done to meet the requirement that ultrasonic waves used in flaw detection must be coupled with water to enter the steel pipe body. Through the ultrasonic mechanical imaging method of this invention, a sufficient number of adjacent channels are used for perpendicular incidence on the extremely thin inner layer of the bimetallic composite pipe. Combined with controlled ultrasonic waves of a specific frequency band and sound field distribution as a detection probe, the quality detection of the composite pipe can be efficiently achieved. The frequency meets the requirements for detection sensitivity, and the size of the detection sound field focal spot can cover the entire composite layer area.

[0027] Specifically, the mechanical scanning imaging method for an ultra-thin inner bimetallic composite tube according to the present invention includes the following steps:

[0028] 1) A water-coupled circulation system is set up, and several jet-coupled ultrasonic detection units are installed circumferentially on a cylindrical coupling cavity. The central angles of each detection unit are the same, forming a fan-shaped distribution. They are also arranged at equal intervals along the axial direction of the cylindrical coupling cavity. The axial distance x between adjacent detection units is between 30 and 60 mm, and the radial distance y is between 5 and 10 mm, or the central angle between adjacent detection units is between 5° and 15°. Each detection unit is an ultrasonic detection channel, thus forming n ultrasonic detection channels. The concentric height of the detection units is adjustable.

[0029] 2) Pass the composite tube through the cylindrical coupling cavity, and adjust the height of the cylindrical coupling cavity so that the axis of the cavity and the composite tube are aligned.

[0030] 3) Start the water-coupled circulation system, driving the composite tube to pass through each adjacent detection unit at a uniform speed. Dynamic water jets couple ultrasonic waves into the composite tube for imaging detection until the entire composite tube has passed through the detection unit. As the composite tube sequentially enters the detection space below the sensors of each adjacent detection unit, the tube end enters a specific adjacent channel. This channel detects the ultrasonic signal reflected from the outer surface of the composite tube end. Since the ultrasonic sensors in each channel are at the same distance from the central axis through which the composite tube passes within the coupling cavity of the detection equipment, the transmission distance of the sound waves emitted from each channel to the surface of the composite tube is also the same. Therefore, the reflected signal of the ultrasonic waves generated on the surface of a sensor at the end of the composite tube can be used to trigger the detection program to execute the actual detection task and initiate the acquisition and storage of detection signal data. As the composite tube end sequentially activates the operation of each adjacent ultrasonic detection channel, subsequent channels detect and acquire data in the axial direction. The data conditions are identical. Each adjacent channel detects a detection line at its own angle. This detection line consists of detection points with a fixed step spacing, which are mechanical scanning points. Each scanning point corresponds to one ultrasonic detection. All detection points on the detection line of each channel form a series of detection waveform datasets that run through the entire length of the composite tube. Each waveform data corresponds to a mechanical scanning point, i.e., a detection point. Adjacent waveform data are measured from adjacent positions on the composite tube with a fixed step spacing. Each series of detection lines for each channel starts from the end of the composite tube and is formed by the same number of detection points. Thus, if there are n channels, each detection process of the composite tube passing through the coupling cavity will generate n detection lines of the same length. By aligning these detection lines of the same length appropriately and plotting the waveform data characteristics corresponding to each detection point, i.e., the maximum value of the reflected signal within the monitoring range, a graph can be plotted to obtain a mechanical scanning image of the quality of an ultra-thin inner layer bimetallic composite tube using multi-channel ultrasonic detection.

[0031] Furthermore, following step 3), all channels measure the same length of the detection lines, which are composed of the same number of detection points. Each pair of adjacent detection lines corresponds to the detection results of the adjacent channel on the composite tube at a certain angle, penetrating the head and tail of the composite tube. If the heads of each scanning line of adjacent channels are aligned, the n scanning lines of n channels are arranged in rows to form a mechanical scanning image for detecting the quality of the ultra-thin inner layer bimetallic composite tube. By changing the circumferential sector angle range of the composite tube covered by the ultrasonic channel, repeatedly detecting the composite tube, and redrawing it in the form of a two-dimensional planar diagram according to the above method, ultrasonic mechanical scanning imaging detection of the entire circumference of the ultra-thin inner layer bimetallic composite tube can be achieved.

[0032] When inspecting defect-free areas of the composite pipe, the physical state near the inner wall of the pipe is relatively uniform, and the waveform echo heights within this range of ultrasonic monitoring are basically consistent, resulting in minimal difference in contrast colors in mechanical imaging. However, if the inspection reaches a defective area, the waveform echo height within this range of ultrasonic monitoring will show a significant change compared to the signal height at defect-free locations. After the obtained detection data is quantized and defined using gradient colors (i.e., different colors are used to indicate different signal amplitudes), the image color at the defective location will have a large contrast with the color at the defect-free location. This enables ultrasonic mechanical scanning imaging inspection of the entire circumference of a bimetallic composite pipe with an extremely thin inner layer, utilizing the contrast difference to perform online imaging quality detection.

[0033] Furthermore, following step 3), since the scanning line results of each adjacent channel are obtained from the tube end, the detection position points of each channel are relatively aligned; since the image is formed by surface data, that is, by several lines, a long scanning line result of a certain channel is cut into several lines of fixed length, which are arranged and combined in sequence to form a planar image.

[0034] Preferably, the ultrasonic sound field employs point focusing or line focusing, with the bimetallic composite tube under test located midway between the sound source and the focal point or line, ensuring that the ultrasonic energy is concentrated in the extremely thin inner layer region of the bimetallic composite tube; wherein,

[0035] The point-focusing method involves the sound wave being incident into the interior of the composite tube by perpendicularly intersecting the central axis of the point-focused sound field with the radial central axis of the composite tube.

[0036] In the line focusing method, the symmetrical center plane of the line focusing sound field passes through the radial central axis of the composite tube, and the focal line remains parallel to it, so that the sound waves are incident into the interior of the composite tube.

[0037] Preferably, in step 1), the detection units are arranged at equal intervals along the axial direction of the cylindrical coupling cavity, with the axial spacing x between adjacent detection units being between 30 and 60 mm and the radial spacing y being between 5 and 10 mm, or the central angle between adjacent detection units being between 5° and 15°.

[0038] The aforementioned axial spacing x and radial spacing y refer to the distance between adjacent detection units in the axial and circumferential (or radial) directions. This is due to the relatively large processing dimensions of the detection units. By increasing the longitudinal spacing between adjacent detection units, it can be ensured that the distance between the detection focal spots is close enough to prevent missed detections.

[0039] Preferably, in step 1), the axial and circumferential spacing a and b of the adjacent detection points formed after the ultrasonic waves emitted by the adjacent detection units enter the composite pipe through water coupling and reach the composite interface are 0.5 to 2 mm respectively.

[0040] The aforementioned axial spacing 'a' and circumferential spacing 'b' refer to the spacing between the detected focal spots at the composite layer of the composite tube, in the axial and circumferential directions.

[0041] Equipped with a coupled water sensor, the ultrasonic waves emitted by the sensor are coupled through the water into the steel pipe and reach the composite interface via the jet-coupled ultrasonic detection unit. The distance between adjacent detection points (i.e., ultrasonic focal spots with a certain detection coverage area) is measured in both the axial and circumferential directions. These adjacent detection points are obtained by the same sensor transmitting and receiving signals in the axial direction, and their spacing can be determined by the sensor's signal pickup time interval (for example, based on the composite pipe's travel speed v and the signal pickup time t, the longitudinal spacing between adjacent detection points is vt). In the circumferential direction, it represents the distance between the focal spots of adjacent jet-coupled ultrasonic detection units on the composite layer interface.

[0042] The method for detecting defects in the extremely thin inner layer of a bimetallic composite tube using ultrasonic waves, as described in this invention, requires controlling the emission of ultrasonic waves as a detection probe to perform ultrasonic detection on the extremely thin inner layer of the bimetallic composite tube to achieve defect detection.

[0043] The ultrasonic sound field employs either point focusing or line focusing. When using point focusing, the central axis of the focused sound field intersects perpendicularly with the radial central axis of the composite tube, directing the sound waves into the interior of the composite tube. When using line focusing, the symmetrical central plane of the focused sound field passes through the radial central axis of the composite tube, with the focal line parallel to it, directing the sound waves into the interior of the composite tube. Positioning the bimetallic composite tube under inspection at a suitable midpoint between the sound source and the focal point (line) ensures that the ultrasonic energy is concentrated in the extremely thin inner layer of the bimetallic composite tube, facilitating defect detection.

[0044] This invention employs parallel ultrasonic detection with a sufficient number of channels. For each channel, the detection of each adjacent channel is triggered sequentially by the end of the bimetallic composite pipe. After obtaining the detection point signal, the positions of the mechanical scanning points of each channel are reorganized. Based on the actual needs of detecting and identifying defects, an ultrasonic contrast image of the extremely thin inner layer of the bimetallic composite pipe is formed, thereby realizing online detection of defects.

[0045] Due to limitations in actual sensor manufacturing technology, individual sensors are relatively large, typically exceeding 10 mm in diameter. In contrast, defects in the extremely thin inner layer of the bimetallic composite tube are very small, only a few hundred μm in size. Simultaneously, the effective coverage area of ​​the sensor is also on the order of several hundred μm. To ensure no missed detections, the spacing between adjacent nodes in the grid used for mechanical imaging between adjacent sensors must match this size. Therefore, the circumferential projection distance y between adjacent sensors is approximately several hundred μm, while the axial projection distance x between adjacent sensors is at least 10 mm, which is larger than the sensor size.

[0046] During testing, the composite tube only undergoes axial linear motion, while the multi-channel sensor array arranged on the composite tube remains stationary under fixed testing conditions. Thus, from a circumferential perspective, the projected distance y between adjacent detection units (sensors) is several hundred μm. From the perspective of ultrasonic mechanical imaging, this achieves full circumferential coverage with 100% detection accuracy. From the axial perspective of the composite tube's movement, the distance between adjacent points acquiring signals from each channel must also be several hundred μm. This can be achieved by using a servo motion system that drives the composite tube's linear motion, incorporating length measurement capabilities and external triggering. In this way, the overall detection effect achievable by all adjacent channels can cover the entire functional layer area of ​​the composite tube's inner wall.

[0047] Since the results of ultrasonic mechanical imaging detection using the above method may still differ from those of conventional mechanical scanning imaging, the detection results in each channel are long, misaligned scanning lines that cannot be aligned according to the specific position on the composite pipe, and thus cannot form a two-dimensional mechanical scanning image, the present invention preferably uses contrast analysis to achieve quality flaw detection.

[0048] Taking the detection of a composite steel pipe with an outer diameter of 100mm as an example, the detection is performed using a patented ultrasonic mechanical scanning image method with a matching design. For instance, the mechanical imaging grid spacing of the inner wall of the composite pipe must be no less than 1mm to avoid missed detections. If the pipe wall thickness is 10mm and the composite layer thickness is 1mm, then the composite layer is located on a circumference with a diameter of 80mm, and the inner diameter of the composite steel pipe is 78mm. To ensure that the detection of a composite pipe with a composite layer diameter of 80mm is not missed, if the detection task of one composite steel pipe is completed by 8 reciprocating passes, that is, one detection is completed within a 45-degree sector on the circumference, the detection of one composite steel pipe can be completed by reciprocating through 8 45-degree sectors on the circumference of the steel pipe. Then, the diameter of the detected circumference is 80mm, the circumference is approximately 251.2mm, and the length of each 45-degree sector is 31.4mm. Therefore, 32 channels can be used. Using 32 channels also means... Figure 3 There are 32 detection points in the middle. These 32 channels are evenly distributed in a sector of 45 degrees along the circumference of the composite steel pipe. Adjacent channels are arranged in sequence and numbered. The detection is carried out in the direction of the jet in each channel that is perpendicular to the axis of the steel pipe, that is, the angle between the directions of two adjacent jet channels is about 1.4°.

[0049] If the diameter of the designed circular water circulation cavity is 500mm, then its circumference is 1.57m. The corresponding length of the 45-degree sector around the composite pipe is 196.25mm. For a 32-channel detection system, the projected distance between any two adjacent channels around the composite pipe is approximately 6.13mm. Figure 3 In this case, y = 6.13 mm. If the diameter of the jet head is 40 mm, then the axial projection distance between any two adjacent channels in the composite pipe can also be 40 mm, i.e. Figure 3 In this case, x = 40 mm, and the total length of the 32 channels is less than 1.28 m. The angle between the probe line formed by all the probe points and the axis of the composite tube can be calculated and is approximately: arctg(6.13 / 40) = 8.7°.

[0050] The above describes the process of probing one composite steel pipe by reciprocating through eight 45-degree sectors around the circumference of the steel pipe. If the manufacturing cost of the equipment is to be reduced, or if the detection time is sufficient, the number of channels can be halved to 16 channels. In this case, if the diameter of the circular water circulation cavity is still 500 mm, its overall length will be less than 614 mm, and so on.

[0051] To address this, the present invention utilizes the end of the composite tube to trigger each adjacent detection channel sequentially, ensuring that the scan lines detected by each adjacent channel are aligned one by one. This is achieved because, during the arrangement of adjacent channel sensors, each adjacent sensor is equidistant along the axial direction of the composite tube at a spacing of x. Initially, the ultrasonic sensor group remains stationary in the fixed position of the detection device, but each channel detection system has already entered a pre-adjusted detection state. At this time, the end of the composite tube has not yet entered the channel; the channel can only detect noise signals, the detection is not actually performed, and data is not acquired or stored. Figure 7 As the steel pipes are linearly conveyed by the clamping rollers and sequentially enter the detection space below each adjacent sensor, the composite pipe end enters a certain adjacent channel. This channel detects the ultrasonic signal reflected back from the outer surface of the composite pipe end, thereby driving the actual detection and initiating the acquisition and storage of detection signal data. Figure 8 .

[0052] Because each adjacent ultrasonic detection channel is activated sequentially at the tube end, the conditions for subsequent channels to detect and acquire data in the axial direction are identical. This ensures that the scan lines obtained from each adjacent channel all start from the tube end, achieving alignment. Next, this invention presents the mechanical scanning image results in two ways:

[0053] A) Following the steps above, by aligning the scan results from adjacent ultrasonic sensors and redrawing them as a 2D planar diagram, ultrasonic mechanical scanning imaging detection of the entire circumference of an extremely thin inner bimetallic composite pipe is achieved. When no defects are detected in the steel pipe, the physical state near the inner wall is relatively uniform, and the contrast colors of the mechanical imaging are not significantly different. However, if a defect is detected, the obtained detection data, after being clearly color-coded, shows a large color contrast with the defect-free areas. This enables ultrasonic mechanical scanning imaging detection of the entire circumference of the extremely thin inner bimetallic composite pipe, utilizing the difference in contrast to perform online imaging quality detection.

[0054] B) This invention also presents mechanical scanning imaging results in another form, as follows: Figure 6 Since the scan lines obtained from each adjacent channel all start from the tube end, the detection points between channels are relatively aligned. Because the image is formed from surface data, and... Figure 6In the process of detecting a steel pipe of length AB passing through the detection unit, ultrasonic waves are emitted into the inside of the steel pipe at regular intervals y. The detection begins when the steel pipe enters the detection unit and ends when the steel pipe exits the detection unit. L detection data points are obtained at equal intervals along the axial direction of the steel pipe. In order to represent the detection results as an intuitive image, the data points of length L are plotted as a line for every M data points. Finally, an detection image of L / M = N lines can be obtained.

[0055] On a steel pipe of length AB, if a defect exists on the inner wall between segments c and d, after inspection by the detection unit, a detection data of length L is obtained. Since the steel pipe passes through the detection unit at a uniform speed, and ultrasonic testing is performed at fixed intervals y, the length of the steel pipe is proportional to the length of the data. The position of the defect along the length of the steel pipe corresponds one-to-one with its position in the data queue. On the steel pipe, the same continuous defect along the radial direction may appear as multiple defects after the detection results are visualized. Figure 9 The two forms that appear are: form one, in which the defect is drawn on the same line, and form two, in which it is drawn on two adjacent lines.

[0056] exist Figure 9 In the data queue A'B', segment c'd' corresponds to the location of the defect in segment cd on steel pipe AB. When there is no defect in the steel pipe, the physical state near the inner wall of the steel pipe is relatively consistent, and the contrast color of the mechanical imaging is not much different. However, if a defect is detected, the obtained detection data, after being clearly color-marked, has a large color contrast with the defect-free area. This enables ultrasonic mechanical scanning imaging detection of the entire circumference of the extremely thin inner layer of the bimetallic composite pipe. The difference in contrast can be used to perform online imaging quality detection.

[0057] The beneficial effects of this invention are:

[0058] The mechanical imaging method for bimetallic composite pipes with extremely thin inner layers described in this invention can solve the technical difficulty of not being able to perform ultrasonic mechanical imaging inspection in the current quality identification and detection technology of composite pipe functional layers and bonding surfaces. This enables the quality of bimetallic composite pipes to be inspected, eliminating the technical barriers to non-destructive testing of quality between innovative steel pipe products and their market application. Attached Figure Description

[0059] Figure 1 This shows the cross-sectional view of the bimetallic composite pipe;

[0060] Figure 2 This is a schematic diagram of a mechanical imaging method for sample detection.

[0061] Figure 3 This is a schematic diagram of the multi-channel sensor arrangement in an embodiment of the present invention;

[0062] Figure 4 for Figure 3 Side view;

[0063] Figure 5 This is a schematic diagram of the sector division for the bimetallic composite tube detection according to the present invention;

[0064] Figure 6 This is a flowchart of the method described in this invention;

[0065] Figure 7 This is a schematic diagram illustrating the reflected signal situation of the composite pipe end before it enters the channel in an embodiment of the present invention;

[0066] Figure 8 This is a schematic diagram showing the reflected signal of the composite pipe end after it has entered the channel in an embodiment of the present invention;

[0067] Figure 9 To convert the linear results obtained after ultrasonic testing of the inner layer of a bimetallic composite tube into a mechanical scanning image;

[0068] Figure 10 This is a complete mechanical scanning imaging result of an ultra-thin inner layer composite tube obtained using the method described in this invention. Detailed Implementation

[0069] See Figures 3 to 10 The mechanical scanning imaging method for the ultra-thin inner layer bimetallic composite tube of the present invention includes the following steps:

[0070] 1) A water-coupled circulation system is set up, and several jet-coupled ultrasonic detection units 1 and 1' are installed circumferentially on the cylindrical coupling cavity. The central angles of each detection unit 1 and 1' are the same, forming a fan-shaped distribution, and they are arranged at equal intervals along the axial direction of the cylindrical coupling cavity. Each detection unit is an ultrasonic detection channel, thereby forming n ultrasonic detection channels. The concentric height of the detection units is adjustable.

[0071] 2) Pass the composite tube 100 through the cylindrical coupling cavity, and adjust the height of the cylindrical coupling cavity so that the axis of the cavity and the composite tube are aligned.

[0072] 3) Start the water-coupled circulation system, driving the composite tube 100 to pass through each adjacent detection unit 1 and 1' at a uniform speed. Dynamic water jet coupling ultrasonic waves enter the composite tube body for imaging detection until the composite tube 100 has completely passed through detection units 1 and 1'. When the composite tube enters the detection space below the sensor of each adjacent detection unit one by one, the end of the composite tube enters a certain adjacent channel. This channel detects the ultrasonic signal reflected back from the outer surface of the end of the composite tube. Since the ultrasonic sensors of each channel are at the same distance from the central axis through which the composite tube passes in the coupling cavity of the detection device, this ensures that the transmission distance of the sound waves emitted by each channel to the surface of the composite tube is also the same. Therefore, the ultrasonic wave reflected on the surface by the end of the composite tube running on the acoustic path of a certain sensor can be used to trigger the detection program to execute the actual detection task and start the acquisition and storage of detection signal data. As the end of the composite tube successively starts the operation of each adjacent ultrasonic detection channel, the subsequent channels in the axial direction The conditions for upward detection and data acquisition are the same. Each adjacent channel detects a detection line at its own angle. This detection line consists of detection points with a fixed step spacing, which are mechanical scanning points. Each scanning point corresponds to an ultrasonic detection. All detection points on the detection line of each channel form a series of detection waveform datasets that run through the entire length of the composite tube. Each waveform data corresponds to a mechanical scanning point, i.e., a detection point. Adjacent waveform data are measured from adjacent positions on the composite tube with a fixed step spacing. Each series of detection lines for each channel starts from the end of the composite tube and is formed by the same number of detection points. Thus, if there are n channels, each detection process of the composite tube passing through the coupling cavity will generate n detection lines of the same length. By aligning these detection lines of the same length appropriately and plotting the waveform data characteristics corresponding to each detection point, i.e., the maximum value of the reflected signal within the monitoring range, a graph can be drawn to obtain a mechanical scanning image of the quality of an ultra-thin inner layer bimetallic composite tube using multi-channel ultrasonic detection.

[0073] Preferably, the ultrasonic sound field employs point focusing or line focusing, with the bimetallic composite tube under test located midway between the sound source and the focal point or line, ensuring that the ultrasonic energy is concentrated in the extremely thin inner layer region of the bimetallic composite tube; wherein,

[0074] The point-focusing method involves the sound wave being incident into the interior of the composite tube by perpendicularly intersecting the central axis of the point-focused sound field with the radial central axis of the composite tube.

[0075] In the line focusing method, the symmetrical center plane of the line focusing sound field passes through the radial central axis of the composite tube, and the focal line remains parallel to it, so that the sound waves are incident into the interior of the composite tube.

[0076] Preferably, in step 1), the detection units are arranged at equal intervals along the axial direction of the cylindrical coupling cavity, with the axial spacing x between adjacent detection units being between 30 and 60 mm and the radial spacing y being between 5 and 10 mm, or the central angle between adjacent detection units being between 5° and 15°.

[0077] See Figure 5 The circumference of the composite tube 100 is divided into several sectors 101 in the circumferential direction. For each sector, a series of jet-coupled ultrasonic testing units 1 and 1' that meet the circumferential resolution requirements of flaw detection are arranged to carry out the detection. The entire composite tube, including the tube end parts in all sectors, is detected by working in an axial reciprocating manner.

[0078] Taking the detection of a composite pipe with an outer diameter of 100mm as an example, to ensure no missed detections, the mechanical imaging grid spacing of the inner wall of the composite pipe must be no greater than 1mm. If the pipe wall thickness is 10mm and the composite layer thickness is 1mm, then the composite layer is located on a circumference with a diameter of 80mm, and the inner diameter of the composite steel pipe is 78mm. To ensure no missed detections of a composite pipe with a composite layer diameter of 80mm, the detection task of one composite steel pipe is completed in 8 reciprocating passes. This means that one detection is completed within a 45-degree sector on the circumference. Reciprocating through 8 45-degree sectors on the circumference of the steel pipe completes the detection of one composite steel pipe. Therefore, the diameter of the detected circumference is 80mm, and the circumference is approximately 251.2mm. The length of each 45-degree sector is 31.4mm, so 32 channels are used. Using 32 channels also means... Figure 3 There are 32 detection points in the middle. These 32 channels are evenly distributed in a sector of 45 degrees along the circumference of the composite steel pipe. Adjacent channels are arranged in sequence and numbered. The detection is carried out in the direction of the jet in each channel that is perpendicular to the axis of the steel pipe, that is, the angle between the directions of two adjacent jet channels is about 1.4°.

[0079] If the diameter of the designed circular water circulation cavity is 500mm, then its circumference is 1.57m. The corresponding length of the 45-degree sector around the composite pipe is 196.25mm. For a 32-channel detection system, the projected distance between any two adjacent channels around the composite pipe is approximately 6.13mm. Figure 3 In this case, y = 6.13 mm. If the diameter of the jet head is 40 mm, then the axial projection distance between any two adjacent channels in the composite pipe can also be 40 mm, i.e. Figure 3 In this case, x = 40 mm, and the total length of the 32 channels is less than 1.28 m. The angle between the probe line formed by all the probe points and the axis of the composite tube can be calculated and is approximately: arctg(6.13 / 40) = 8.7°.

[0080] The above describes the process of probing one composite steel pipe by reciprocating through eight 45-degree sectors around the circumference of the steel pipe. To reduce equipment manufacturing costs or if there is sufficient probing time, the number of channels can be halved to 16 channels. In this case, if the diameter of the circular water circulation chamber remains 500mm, its overall length will be less than 640mm, and so on.

[0081] In the method described in this invention,

[0082] A sufficient number of ultrasonic sensors arranged in adjacent rows are used to perform quality inspection on the extremely thin inner layer of bimetallic composite tubes; the arrangement of adjacent sensors is as follows: Figures 3-5 As shown; during detection, the composite tube only performs axial linear motion, while the multi-channel sensor group arranged on the composite tube remains stationary under fixed detection conditions.

[0083] The results of ultrasonic mechanical imaging inspection using the above method may still differ from those of conventional mechanical scanning imaging. In this case, each channel produces scan lines that are significantly misaligned with each other. These scan lines cannot be aligned based on their specific positions on the composite pipe, thus failing to form a two-dimensional mechanical scan image. Consequently, quality inspection cannot be achieved through contrast analysis.

[0084] As mentioned above, when using multi-channel ultrasonic testing to detect the quality of the extremely thin inner layer of bimetallic composite pipes, after obtaining signals from continuous mechanical position points along the entire length of the steel pipe through each channel, there is a problem that mechanical scanning images cannot be directly formed: when using many channels to perform mechanical imaging flaw detection, due to the large spacing between the sensors, the mechanical scanning linear series results measured by adjacent channel sensors at their respective angles (a large number of corresponding ultrasonic detection signals formed on a large number of continuous mechanical scanning points spaced one step apart) cannot be kept consistent with the actual relative positions of the scanning points on the steel pipe, and ultimately cannot form an image of the overall mechanical scanning surface.

[0085] Therefore, this invention employs a method during the detection process where the acoustic wave signal reflected from the end of the composite tube is used to trigger each adjacent detection channel to enter detection mode sequentially, ensuring that the scan lines detected by each adjacent channel are aligned one by one. This is achieved because, during the arrangement of adjacent channel sensors, each adjacent sensor is already equidistant along the axial direction of the composite tube at a spacing of x. Initially, the ultrasonic sensor group remains stationary in the fixed position of the detection equipment, but each channel's detection system has already entered the pre-adjusted detection state. At this time, the end of the composite tube has not yet entered the channel; this channel can only detect noise signals, the detection is not actually performed, and data is not acquired or stored. Figure 7 As shown.

[0086] As the composite tubes are linearly conveyed by the clamping rollers and sequentially enter the detection space below each adjacent sensor, the tube end enters a specific adjacent channel. This channel detects the ultrasonic signal reflected from the outer surface of the composite tube end. Since the ultrasonic sensors in each channel are equidistant from the central axis through which the composite tube passes within the coupling cavity of the detection equipment, the transmission distance of the sound waves emitted from each channel to the surface of the composite tube is also the same. Therefore, the reflected signal of the ultrasonic waves generated on the surface of a sensor as the composite tube end travels along that sensor's acoustic path (detection begins from the tube end and continues as long as the composite tube body remains within the sensor's acoustic path) can be used to trigger the detection program to execute the actual detection task and initiate the acquisition and storage of detection signal data. Figure 8 As shown.

[0087] Because each adjacent ultrasonic detection channel is activated sequentially at the end of the composite tube, the conditions for subsequent detection and data acquisition in the axial direction are identical for each channel. This ensures that each adjacent channel detects a detection line at its own angle. This detection line consists of detection points (i.e., mechanical scanning points) spaced at fixed intervals, with each scanning point corresponding to one ultrasonic detection. All detection points on the detection line of each channel form a series of detection waveform datasets spanning the entire length of the composite tube. Each waveform data corresponds to a mechanical scanning point (detection point), and adjacent waveform data are measured from adjacent points at fixed intervals on the composite tube. Each series of detection lines for each channel starts from the tube end and is formed by the same number of detection points. Thus, with 32 channels, each detection process as the composite tube passes through the coupling cavity will generate 32 detection lines of the same length. By properly aligning these detection lines of the same length and plotting the waveform data characteristics (maximum reflected signal value within the monitoring range) corresponding to each detection point, a mechanical scanning image for detecting the quality of an ultra-thin inner layer bimetallic composite tube using multi-channel ultrasonic waves can be obtained.

[0088] The present invention can also present the results of mechanical scanning imaging in the following two ways:

[0089] The first method, following the steps above, utilizes the fact that all channels measure the same probe line length, consisting of the same number of probe points. Each pair of adjacent probe lines corresponds to the probe results of the adjacent channel at a certain angle, penetrating the beginning and end of the composite tube. Therefore, by aligning the heads of each scan line from adjacent channels and arranging the 32 scan lines of the 32 channels in rows, a mechanical scanning image for detecting the quality of the ultra-thin inner layer bimetallic composite tube is formed. By changing the circumferential sector angle range of the composite tube covered by the ultrasonic channel, repeatedly probing the composite tube, and redrawing it in the form of a two-dimensional planar diagram according to the above method, ultrasonic mechanical scanning imaging detection of the entire circumference of the ultra-thin inner layer bimetallic composite tube is achieved.

[0090] When inspecting defect-free areas of a composite pipe, the physical state near the inner wall is relatively uniform. Under reasonable conditions, the waveform echo height within this area monitored by ultrasound is basically consistent, and the contrast color of the mechanical imaging is not significantly different. However, if a defect is detected, the waveform echo height within this area monitored by ultrasound will change significantly compared to the signal height at defect-free locations. After the obtained detection data is quantized and defined using gradient colors (different colors are used to indicate different signal amplitudes), the image color at the defective location contrasts significantly with the color at the defect-free location. This enables ultrasonic mechanical scanning imaging inspection of the entire circumference of a bimetallic composite pipe with an extremely thin inner layer. By utilizing the contrast difference, online imaging quality detection is performed, and the interpretation and judgment of the detection results are very clear and convenient.

[0091] The second method, since the scan line results for each adjacent channel all start from the tube end, means that the detection point results are relatively aligned between channels. Since the image is formed from surface data, i.e., composed of several lines, we can cut a long scan line result for a certain channel into several lines of fixed length, and arrange them sequentially to form a planar image. Figure 9 In the detection process, when a composite tube of length AB passes through the detection unit, ultrasonic waves are emitted into the interior of the composite tube at regular intervals y. The detection begins when the composite tube enters the detection unit and ends when the composite tube exits the detection unit. L detection waveform data points are obtained, which are evenly distributed along the axial direction of the composite tube. Each detection waveform data point corresponds to a mechanical scanning point. In order to present the detection results as an intuitive image, the data points of length L are plotted as a line every M data points. Finally, an L / M = N rows of detection images can be obtained.

[0092] On a composite pipe of length AB, if a defect exists on the inner wall between segments cd, after detection by the detection unit, detection data of length L is obtained. Since the composite pipe passes through a detection channel at a constant speed, and the step size between detection points is a fixed interval y, the length of the composite pipe is proportional to the length of the detected data line. The position of the defect along the length of the composite pipe corresponds to its position in the data queue. On the composite pipe, the same continuous defect along the radial direction may appear as multiple defects after the detection results are imaged. Figure 9 The two forms that appear are: form one, in which the defect is drawn on the same line, and form two, in which it is drawn on two adjacent lines.

[0093] exist Figure 9 The image shows the result of a data line measured from a certain angle, starting at end A of the composite tube and ending at end B. This data line consists of a large number of data points, with each adjacent data point corresponding to an adjacent detection position on the composite tube (the spacing is a step size). Corresponding to the length of the composite tube, the system measures a data line queue A'B' of a certain length, starting from data point A' and ending at data point B'. The waveform echo height within this location range is basically consistent during ultrasonic monitoring, and the contrast color of the mechanical imaging is not significantly different. If the segment from data point c' to data point d' in the data line queue corresponds to the location of a defect in segment cd on the composite tube, then the waveform echo height within this location range will show a significant change compared to the signal height at the defect-free location. After the obtained detection data is quantized and defined using gradient colors (different colors are used to indicate different signal amplitudes), the image color at the defective location contrasts significantly with the color at the defect-free location. This enables ultrasonic mechanical scanning imaging detection of the entire circumference of the extremely thin inner layer bimetallic composite tube, utilizing the difference in contrast. If the defect can be detected by multiple adjacent channels, then the same location in the ultrasonic mechanical scanning imaging results of each channel will show an image of the defect.

[0094] Once the entire circumference of the composite tube has been scanned by the detection channels, the ultrasonic mechanical scanning imaging inspection of the entire circumference of the bimetallic composite tube with its extremely thin inner layer is completed.

[0095] For a specific composite tube, according to the method described in this invention, a complete mechanical scanning image of the extremely thin inner layer of the composite tube can be obtained after detection. The defects and porosity of the composite layer are clearly displayed, such as... Figure 10 As shown. If there are pores or unbonded defects in the composite layer or functional layer, the amplitude of the defect reflection signal at the detection point can be quantized, and different echo amplitudes can be continuously defined by gradient colors to obtain the following result. Figure 10This provides a direct and intuitive mechanical scanning imaging result for the extremely thin inner layer of the composite tube. Thus, this invention overcomes the problem that when using multiple channels to perform mechanical imaging flaw detection, the spacing between sensors becomes too large, resulting in the mechanical scanning lines failing to form a complete mechanical scanning image.

Claims

1. A mechanical scanning imaging method for inner layer extremely thin bi-metal composite pipe, characterized in that, The method comprises the following steps: 1) setting a water coupling circulation system, installing a plurality of jet coupling ultrasonic detection units on the circumferential direction of the cylindrical coupling cavity, the central angles between each detection unit being the same, forming a fan-shaped distribution, and being arranged at equal intervals along the axial direction of the cylindrical coupling cavity; each detection unit is an ultrasonic detection channel, thereby forming n ultrasonic detection channels; the height of the detection unit is adjustable; 2) passing the composite pipe through the cylindrical coupling cavity, adjusting the height of the cylindrical coupling cavity so that the axes of the cavity and the composite pipe coincide; 3) starting the water coupling circulation system, driving the composite pipe to pass through each adjacent detection unit at a uniform speed, and dynamically coupling the water jet ultrasonic wave into the composite pipe for imaging detection until the composite pipe passes through all the detection units; when the composite pipe sequentially enters the detection space below each adjacent detection unit sensor, the end of the composite pipe enters a certain adjacent channel, and the channel detects the ultrasonic wave signal reflected from the outer surface of the end of the composite pipe; since the ultrasonic sensors of each channel are at the same distance from the central axis of the composite pipe passing through the coupling cavity of the detection device, the transmission distance of the sound wave emitted by each channel to the surface of the composite pipe is also the same, thereby using the reflection signal of the ultrasonic wave generated by the end of the composite pipe running on the sound path of a certain sensor to trigger the detection program to perform the actual detection task and start the acquisition and storage of the detection signal data; since the end of the composite pipe sequentially starts the work of each adjacent ultrasonic detection channel, the conditions for the subsequent channels to detect and acquire data in the axial direction are the same, and each adjacent channel detects a detection line at a respective angle, which is composed of detection points with a fixed step length, i.e. mechanical scanning points, and each scanning point corresponds to an ultrasonic detection; all the detection points on the detection line of each channel form a set of detection waveform data that penetrates the entire length of the composite pipe, each waveform data corresponds to a mechanical scanning point, i.e. a detection point, and adjacent waveform data is measured from adjacent position points on the composite pipe with a fixed step length; each set of detection line results of each channel starts from the end of the composite pipe and is formed by the same number of detection points; in this way, if there are n channels, the detection process of the composite pipe passing through the coupling cavity each time will produce n detection lines with the same length, aligning these detection lines with the same length, and drawing the waveform data features corresponding to each detection point, i.e. the maximum reflection signal in the monitoring range, can realize the mechanical scanning image of the quality of the extremely thin inner double-metal composite pipe using multi-channel ultrasonic detection.

2. The method of mechanically scanning the inner layer of the extremely thin bimetallic composite pipe according to claim 1, wherein the step of In the step 3), all the channel measured detection line length is the same, and is composed of the same number of detection points, and each adjacent two detection lines correspond to the detection result of the adjacent channel pair composite pipe at a certain angle and through the head and tail of the composite pipe; if the head of each scanning line of the adjacent channel is aligned, the n scanning lines of the n channels are arranged in rows to form a mechanical scanning image for detecting the quality of the extremely thin inner layer of the double-metal composite pipe; by changing the circumferential sector angle range of the composite pipe covered by the ultrasonic channel, repeatedly detecting the composite pipe, and re-drawing in the form of a two-dimensional plan view in the above manner, the full-body ultrasonic mechanical scanning imaging detection of the extremely thin inner layer of the double-metal composite pipe is realized. When there is no defect in the detected composite pipe, the physical state near the inner wall of the composite pipe is relatively consistent, the waveform echo height monitored by the ultrasonic wave in the position range is basically consistent, and the contrast color of the mechanical imaging is not much different; but if the detected composite pipe has a defect, the waveform echo height monitored by the ultrasonic wave in the position range will be obviously changed compared with the signal height at the position without defects, and after the detection data is quantified and defined by using the gradient color, i.e., different colors are used to identify different signal amplitudes, the image color of the defective position and the color of the non-defective position have a large contrast, thus realizing the ultrasonic mechanical scanning imaging detection of the full-body of the extremely thin inner layer of the double-metal composite pipe, and using the difference in contrast to perform online imaging quality detection.

3. The method of mechanically scanning the inner layer of the extremely thin bimetallic composite pipe according to claim 1, wherein In the step 3), the scanning line result of each adjacent channel is obtained from the pipe end, and the results of the detection position points between the channels are relatively aligned; since the image is formed by a plane of data, i.e., by a plurality of lines, the scanning line result of a very long channel is cut into a plurality of lines of fixed length, and sequentially arranged and combined to form a plan view.

4. The method of mechanically scanning the inner layer of the extremely thin bimetallic composite pipe according to claim 1, wherein The ultrasonic sound field adopts a point focusing or line focusing mode, the double-metal composite pipe to be detected is located at the middle position between the sound source and the focus or line, and the energy of the ultrasonic wave is concentrated in the extremely thin inner layer of the double-metal composite pipe; wherein, In the point focusing mode, the central axis of the point focusing sound field is perpendicular to the radial central axis of the composite pipe, and the sound wave is incident into the composite pipe; In the line focusing mode, the symmetry center plane of the line focusing sound field passes through the radial central axis of the composite pipe, and the focal line is parallel to the radial central axis, and the sound wave is incident into the composite pipe.

5. The method of mechanically scanning the inner layer of the extremely thin bimetallic composite pipe according to claim 1, characterized in that, In the step 1), the adjacent detection units are arranged at equal intervals along the axial direction of the cylindrical coupling cavity, the axial spacing x between the adjacent detection units is 30-60 mm, and the radial spacing y is 5-10 mm, or the central angle between the adjacent detection units is 5-15°.

6. The mechanical scanning imaging method of an inner layer extremely thin bi- metal composite pipe according to claim 1 or 5, characterized by, In the step 1), the ultrasonic waves emitted by the adjacent detection units enter the composite pipe through water coupling and reach the adjacent detection points formed after the composite interface, and the axial and circumferential spacings a and b are 0.5-2 mm.

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