Mechanical scanning imaging method for composite pipe with extremely thin inner layer

Abstract

A mechanical scanning imaging method of a bimetal composite pipe with an extremely thin inner layer comprises the following steps: 1) arranging a water coupling circulating system, and installing a plurality of jet coupling ultrasonic detection units on a cylindrical coupling cavity along the circumferential direction; each detection unit is an ultrasonic detection channel, and n ultrasonic detection channels are formed; (2) the composite pipe passes through a cylindrical coupling cavity, and the axis of the cavity and the axis of the composite pipe coincide and coincide; and (3) starting the water coupling circulating system, driving the composite pipe to sequentially penetrate through each adjacent detection unit at a constant speed, and enabling dynamic water jet coupling ultrasonic waves to enter the composite pipe for imaging detection until the composite pipe completely penetrates through the detection units. According to the method, multi-channel ultrasonic parallel detection is adopted, each adjacent channel is sequentially triggered by the pipe end of the bimetal composite pipe to start detection, the mechanical scanning point position of each channel is rearranged after a detection point signal is obtained, an ultrasonic detection contrast image of the ultra-thin inner layer of the bimetal composite pipe is formed, and online detection of defects is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of nondestructive testing, and in particular to a mechanical scanning imaging method for an extremely thin inner layer composite pipe. Background Art

[0002] At present, many industries are in urgent need of high-performance and low-cost pipes. In addition to conventional mechanical properties, pipes are also required to have high temperature resistance, corrosion resistance, erosion resistance, and oxidation resistance. However, it is particularly difficult for a single material to have the above comprehensive properties at the same time. 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, facing this situation, bimetallic composite pipes with various manufacturing processes have emerged.

[0003] Bimetallic composite pipe is a product made of two different metal materials, with carbon steel pipe or low alloy steel pipe as the base pipe, and a layer of corrosion-resistant alloy layer on its inner and outer surfaces, through certain physical deformation or metallurgical bonding. Bimetallic composite pipe uses special deformation and connection technology to closely combine the base and lining, maximize the advantages of the two metals, overcome the performance defects of a single metal material, and reduce the comprehensive use cost of the product at the same time.

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

[0005] The base steel pipe 10 mainly plays the role of pressure bearing and rigid support, while the role of the cladding metal 20 is functional corrosion resistance, high temperature oxidation resistance, wear resistance, etc. The bimetallic composite pipe retains the advantages of the base pipe and the cladding metal and makes up for the shortcomings. The base steel pipe 10 can adjust the pipe diameter, wall thickness and steel grade according to the structure and service requirements, and the cladding metal 20 can use different corrosion-resistant metals or alloys according to the service conditions. Bimetallic composite pipes can effectively reduce the cost of the original high-alloy products, and the cost is only 1 / 5 to 1 / 2 of that of pure corrosion-resistant alloy pipes. The analysis and comparison of the comprehensive performance of various pipelines for oil and gas transportation by domestic professional research institutions shows that the comprehensive performance of bimetallic composite pipes ranks among the best.

[0006] For new steel pipe products such as bimetallic composite pipes, if the inner metal is expensive, the thickness of the inner metal-cladding metal 20 will be designed and manufactured to a lower cost thickness level that can meet the use according to the application scenario. The quality inspection objectives and dimensional equivalent requirements will be very different from the traditional flaw detection requirements. The previous quality inspection methods are no longer applicable, especially when the inner metal-cladding metal 20 is extremely thin, such as Figure 1, the previous steel pipe flaw detection method is no longer applicable to the quality inspection of bimetallic composite pipes.

[0007] We know that my country's steel pipe flaw detection currently has mature national standards that stipulate corresponding methods for quality inspection, such as GB / T 5777-2008 "Ultrasonic Flaw Detection of Seamless Steel Pipes". This standard stipulates the use of refracted shear wave flaw detection method, which is to make the incident ultrasonic wave enter the steel pipe at a certain angle to the steel pipe surface, so as to achieve the purpose of fully reflecting the longitudinal wave and using the refracted shear wave to enter the steel pipe for inspection.

[0008] For bimetallic composite pipes with extremely thin inner metal layers, the thickness of the inner metal layer can even be as thin as a few hundred microns in order to reduce costs. Figure 1 As shown, the thickness of the inner metal-cladding metal 20 actually used is very thin, less than 1mm, resulting in the existing conventional technical performance online flaw detection equipment, because the defect target at the junction of the inner layer and the substrate layer is too small, either it cannot be found, or the signal is completely covered in the bottom wave signal, causing the existing flaw detection technology equipment to be unable to identify the manufacturing defects of the composite steel pipe product with such a thin inner layer. Therefore, with regard to the flaw detection problem of composite pipes with extremely thin inner metal layers, the quality inspection targets and size equivalent requirements are very different from the traditional flaw detection requirements. The previous quality inspection methods are no longer applicable, especially when the inner metal layer is extremely thin. For bimetallic composite pipes with extremely thin inner metal-cladding metal 20, the defects are often pores in the inner metal layer related to the manufacturing process, and unbonded cracks on the bonding interface 30. These two types of defects are new defects for traditional single-material steel pipes. Conventional flaw detection technology processes cannot detect them. At the same time, due to the small size of the defects, the sensitivity of conventional flaw detection methods is also difficult to guarantee. Since the bimetallic composite pipe with extremely thin inner metal layer is a new steel pipe product that has emerged under the current situation of manufacturing industry progress, there is no corresponding mature technology and experience to draw on for the quality identification and detection technology of the functional layer and joint surface of the composite pipe.

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

[0010] 1. The tube body is a bimetal with an extremely thin inner layer. Defects such as pores and poor bonding exist in the inner layer area, making conventional ultrasonic flaw detection methods no longer applicable;

[0011] 2. It is difficult to automatically detect the inner layer of steel pipes by magnetic powder and eddy current;

[0012] 3. It is also difficult for the X-ray method to achieve the sensitivity required by the current problems;

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

[0014] The "composite pipe flaw detection device" disclosed in Chinese patent CN210639145U provides a composite pipe flaw detection device, including a detection table, a probe is arranged above the detection table, a mounting seat is arranged on the detection table, two rotating shafts are arranged in the mounting seat, a roller supporting the pipe is arranged on the rotating shaft, and the rotating shaft is driven by a driving mechanism. The detection table is connected to a support plate through a support frame, and vertical plates are arranged at the bottom of both ends of the support plate. A reciprocating screw and a sliding rod are arranged between the two vertical plates. The end of the reciprocating screw is rotatably mounted on the vertical plate, a nut matching with the reciprocating screw is arranged on the reciprocating screw, and a sliding block is arranged on the sliding block. The sliding block is connected to the nut through a connecting plate, and the probe is fixed on the connecting plate. The reciprocating screw is connected to the output end of the reduction motor. The device has a simple structure and realizes comprehensive detection.

[0015] It can be seen from the patent that 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 object being tested with an extremely thin inner layer of less than 1 mm thickness.

[0016] Chinese patent CN206497075U discloses a "composite pipe ultrasonic flaw detection machine tool", which includes: a machine tool frame, a spindle box, a moving seat and a mounting frame; a three-jaw chuck is installed on the output shaft of the spindle box, a circular ring of gear is arranged on the circumference of the three-jaw chuck, the moving seat is slidably arranged in a slide groove located at the bottom of the machine tool frame, a left-right threaded through hole is arranged on the moving seat, a threaded rod is arranged in the threaded through hole, two ends of the threaded rod are rotatably arranged on the fixed seat and the spindle box respectively, a gear is installed at the left end of the threaded rod, and the gear is meshed with the gear ring; the mounting frame is welded and fixed on the top of the moving seat, and an ultrasonic detector is fixedly installed on the mounting frame, and the probe of the ultrasonic detector is vertically downward. The utility model enables the ultrasonic detector to move horizontally at the same time during the rotation of the composite pipe, without the need to clamp the pipe or adjust the angle multiple times, so the efficiency is greatly improved and it is guaranteed that there is no omission in the flaw detection.

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

[0018] Chinese patent CN208457441U discloses "a flaw detection device for lined stainless steel composite pipes", which includes a pipe wall detector and a forming frame; a pipe rolling gap is set between the forming frame and the pipe wall detector; the forming frame includes a supporting outer frame, the inner wall of the supporting outer frame is provided with a circular hole-shaped supporting hole, and a supporting roller is arranged in a circular array in the supporting hole; the pipe wall detector includes a plurality of groups of pressure plates arranged in a coaxial linear array, and the pressure plates are connected to each other through an air booster; 8 groups of air piston assemblies are arranged in a circular array on the pressure plate; the air piston assembly includes a cylinder body fixedly connected to the pressure plate, and a cylinder piston is floatingly connected in the cylinder body; the bottom of the cylinder body is connected to the inside of the pressure plate through a connecting valve, a tensile strain gauge is arranged between the bottom of the cylinder piston and the bottom of the cylinder body, and an extrusion rod is rotatably connected to the top of the cylinder piston. It can be seen from the patent that the patented device is a stress detection tool in which a tensile strain gauge is connected to an ammeter through a bridge circuit. It does not involve the technical features of online ultrasonic imaging detection, nor does it involve the characteristics of the object to be measured with an extremely thin inner layer of less than 1 mm thickness.

[0019] It can be seen that in order to break through the technical principle limitations of conventional steel pipe ultrasonic flaw detection methods and current detection methods such as eddy current, X-ray, infrared detection, microwave detection, and laser ultrasound, and to achieve online quality flaw detection of bimetallic composite pipes, new methods must be used.

[0020] Although there are 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 different non-destructive testing methods that can be used for steel pipes have limitations in detection principles. The present invention believes that the method of online flaw detection for bimetallic composite pipes with extremely thin inner layers that can be applied industrially can only be achieved by using ultrasonic detection combined with mechanical imaging.

[0021] The characteristic of mechanical imaging is that the detection result is usually a grid-shaped detection result distribution map. For plates or small round materials, the result is generally a two-dimensional plane distribution map, or a three-dimensional space distribution map. The nodes of the grid are the locations where detection is carried out, or are regarded as the locations where detection signals are obtained. Adjacent nodes of the grid form adjacent points on the mechanical imaging result map. The distance between adjacent nodes of the grid is the step length of the mechanical scanning, such as Figure 2 As shown, the method of performing detection is described by taking mechanical imaging detection of a plate as an example. Figure 2 In the process, one channel is used and with the cooperation of the servo motion control system, it is possible to quickly and easily realize repeated mechanical scanning and imaging of the plate sample. The step size can also be adjusted by setting the motion system to obtain mechanical imaging detection results with different resolutions.

[0022] However, if mechanical imaging is used to detect bimetallic composite pipes with extremely thin inner layers, new situations different from those for plates or small round materials will arise. If one channel is used to detect bimetallic composite pipes with extremely thin inner layers, it is indeed possible to use the ultrasonic sensor to move linearly relative to the axial direction of the steel pipe, and the steel pipe to gradually rotate, to achieve mechanical imaging flaw detection, but its detection efficiency is extremely low and is not suitable for actual production applications. If many channels are used to perform mechanical imaging flaw detection, there will be a problem that the spacing between sensors is too large, resulting in the problem that the results of the mechanical scanning line cannot ultimately form an overall mechanical scanning image. In other words, in order to achieve the effect of 100% non-missing flaw detection, due to the limited effective area of ​​the ultrasonic detection point, for example, less than about 1mm 2 , the spacing between adjacent nodes of the mechanical imaging grid must match it, and is also of this order of magnitude, but it is difficult for adjacent sensors in a multi-sensor group to achieve such a small size of simultaneous side-by-side mechanical motion detection, which 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 object of the present invention is to provide a mechanical scanning imaging method for a composite tube with an extremely thin inner layer, so as to realize mechanical scanning imaging detection of the unique defects of a bimetallic composite tube with an extremely thin inner layer.

[0024] To achieve the above object, the technical solution of the present invention is:

[0025] In view of the difficulties in mechanical imaging detection of bimetallic composite pipes in multi-channel ultrasonic detection, the present invention designs a method of acquiring signal data to generate ultrasonic mechanical scanning images, adopts multi-channel ultrasonic detection, and the pipe end sequentially triggers each adjacent channel to start detection. After obtaining the detection point signal, the position of the mechanical scanning point of each channel is rearranged to form an ultrasonic detection contrast image of the extremely thin inner layer of the bimetallic composite pipe, thereby realizing online detection of defects.

[0026] The present invention can maintain good coupling in the water cavity during the flaw detection process through dynamic water jet coupling. After the jet water coupling is completed, it naturally falls into the circulating water circuit and is recycled to the water tower water tank for reuse. The purpose of this is to meet the requirement that ultrasonic waves must be used to couple sound waves into the steel pipe body when flaw detection is performed. Through the ultrasonic mechanical imaging method of the present invention, a sufficient number of adjacent channels are used in a vertical incidence mode to act on the bimetallic composite pipe with an extremely thin inner layer, and the ultrasonic wave with a certain frequency band and a certain sound field distribution form is controlled to be used as a detection probe, so that the quality detection of the composite pipe can be efficiently realized, wherein the frequency can meet the requirements of 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 of a bimetallic composite tube with an extremely thin inner layer described in the present invention comprises the following steps:

[0028] 1) A water coupling circulation system is provided, and a plurality of jet coupling ultrasonic detection units are installed along the circumferential direction of a cylindrical coupling cavity, wherein the central angles of the detection units are the same, forming a fan-shaped distribution, and the detection units are arranged at equal intervals along the axial direction of the cylindrical coupling cavity, wherein the axial spacing x between adjacent detection units is between 30 and 60 mm, and the radial spacing y is between 5 and 10 mm, or the central angles of the adjacent detection units are between 5° and 15°; each detection unit is an ultrasonic detection channel, thereby forming n ultrasonic detection channels; and the concentric height of the detection unit 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 coincide with each other;

[0030] 3) Start the water coupling circulation system, drive the composite pipe to pass through each adjacent detection unit in turn at a uniform speed, and use the dynamic water jet to couple the ultrasonic wave into the composite pipe body for imaging detection until the composite pipe passes through all the detection units; when the composite pipe enters the detection space below the sensor of each adjacent detection unit one by one, the end of the composite pipe enters a certain adjacent channel, and the channel detects the ultrasonic 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 through which the composite pipe passes in the coupling cavity of the detection equipment, this ensures that the transmission distance of the sound waves emitted from each channel to the surface of the composite pipe is also the same, so that the ultrasonic wave reflected on the surface generated by the end of the composite pipe running to a certain sensor sound path can be used 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 starts the work of each adjacent ultrasonic detection channel one by one, each subsequent channel detects and acquires in the axial direction The conditions of the data are the same, and each adjacent channel detects a detection line at its own angle. The detection line is composed of detection points with a fixed step length, namely 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 series of detection waveform data sets throughout the entire length of the composite pipe, and each waveform data corresponds to a mechanical scanning point, namely a detection point, and adjacent waveform data are measured from adjacent position points with a fixed step length on the composite pipe; each series 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, each detection process in which the composite pipe passes through the coupling cavity will generate n detection lines of the same length. These detection lines of the same length are reasonably aligned, and the waveform data characteristics corresponding to each detection point, namely the maximum value of the reflected signal within the monitoring range, are plotted into a graph, so that a mechanical scanning image of the quality of the extremely thin inner layer bimetallic composite pipe can be realized by using multi-channel ultrasonic detection.

[0031] Further, following the step 3), the lengths of the detection lines measured by all channels are the same, and they are composed of the same number of detection points. Each of the two adjacent detection lines corresponds to the detection results of the adjacent channels on the composite pipe at a certain angle and through the head and tail of the composite pipe; if the heads of each scanning line of the adjacent channels are 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 bimetallic composite pipe; the circumferential sector angle range of the composite pipe covered by the ultrasonic channel is changed, the composite pipe is repeatedly detected, and it is re-drawn in the form of a two-dimensional plane diagram according to the above method, so as to realize the ultrasonic mechanical scanning imaging detection of the entire body of the bimetallic composite pipe with an extremely thin inner layer;

[0032] When inspecting a composite pipe without defective positions, the physical state near the inner wall of the composite pipe is relatively consistent, the waveform echo height within the ultrasonic monitoring range of the position is basically consistent, and the contrast color of the mechanical imaging is not much different; however, if the composite pipe is inspected to a defective position, the waveform echo height within the ultrasonic monitoring range of the position will be significantly different from the signal height at the position without defect. After the obtained inspection data is quantified by using gradient colors to define the signal amplitude, that is, different colors are used to identify different signal amplitudes, the image color at the defective position has a large contrast with the color at the non-defective position. At this point, ultrasonic mechanical scanning imaging inspection of the entire body of the bimetallic composite pipe with an extremely thin inner layer is realized, and the imaging quality detection is performed online using the difference in contrast.

[0033] Furthermore, continuing with step 3), since the scanning line results of each adjacent channel detected start from the tube end, the results of the detection position points between the channels are relatively aligned; since the image is formed by the data of a surface, that is, formed by a number of lines, the scanning line results of a very long channel are cut into a number of fixed-length lines, which are arranged in sequence to form a plane diagram.

[0034] Preferably, the ultrasonic sound field adopts a point focusing or line focusing method, and the inspected bimetallic composite tube is located in the middle position between the sound source and the focus or line, so as to ensure that the energy of the ultrasonic wave is concentrated on the extremely thin inner layer area of ​​the bimetallic composite tube; wherein,

[0035] Point focusing method, in which the central axis of the point focusing sound field intersects perpendicularly with the radial central axis of the composite tube, so that the sound wave is incident into the interior of the composite tube;

[0036] Line focusing method: the symmetric center plane of the line focusing sound field passes through the radial center axis of the composite tube, and the focal line remains parallel to it, so that the sound wave is 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, the axial spacing x between adjacent detection units is between 30 and 60 mm, the radial spacing y is between 5 and 10 mm, or the central angle between adjacent detection units is 5° to 15°.

[0038] The above-mentioned axial spacing x and radial spacing y refer to the distances between adjacent detection units in the axial and circumferential directions (or radial directions), which is due to the larger processing size of the detection units. After the adjacent detection units are spaced apart in the longitudinal direction, it can be ensured that the distances between the detection focal spots are close enough to ensure that no detection is missed.

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

[0040] The above-mentioned axial spacing a and circumferential spacing b refer to the spacing between the detection focal spots at the composite layer of the composite pipe in the axial direction and the circumferential direction.

[0041] Equipped with a coupled water sensor, the ultrasonic wave emitted by the sensor passes through the jet-coupled ultrasonic detection unit, enters the steel pipe through water coupling and reaches the composite interface, and the spacing between adjacent detection points (i.e., ultrasonic focal spots with a certain detection coverage area) in 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 time interval of the sensor's detection signal pickup (for example, according to the composite pipe's travel speed v, the signal pickup time t, the longitudinal adjacent detection point spacing is vt); in the circumferential direction, it is the spacing between the focal spots of adjacent jet-coupled ultrasonic detection units on the composite layer interface.

[0042] The method of using ultrasonic waves to detect defects in the extremely thin inner layer of a bimetallic composite pipe of the present invention requires controlling the emission of ultrasonic waves as a detection probe to act on the extremely thin inner layer of the bimetallic composite pipe in an ultrasonic detection manner to achieve defect detection.

[0043] The ultrasonic sound field adopts point focusing or line focusing. When the point focusing method is adopted, the sound wave is incident into the inside of the composite pipe in a manner that the central axis of the point focusing sound field intersects perpendicularly with the radial central axis of the composite pipe; when the line focusing method is adopted, the sound wave is incident into the inside of the composite pipe in a manner that the symmetrical central plane of the line focusing sound field passes through the radial central axis of the composite pipe and the focal line is kept parallel to it. The inspected bimetallic composite pipe is located in a reasonable middle position between the sound source and the focal point (line), which can ensure that the energy of the ultrasonic wave can be concentrated in the extremely thin inner layer area of ​​the bimetallic composite pipe, which is conducive to the detection of defects.

[0044] The present invention adopts ultrasonic parallel detection of sufficiently many channels, and for each channel, the end of the bimetallic composite pipe sequentially triggers each adjacent channel to start detection. After obtaining the detection point signal, the position of the mechanical scanning point of each channel is re-arranged, and according to the actual needs of facilitating the detection and identification of defects, an ultrasonic detection contrast image of the extremely thin inner layer of the bimetallic composite pipe is formed to realize online detection of defects.

[0045] Due to the actual sensor manufacturing technology, the size of a single sensor is relatively large, with a diameter of usually more than 10mm, while the defect size at the extremely thin inner layer of the bimetallic composite tube is very small, as small as a few hundred μm. At the same time, the effective coverage area of ​​the sensor is also on the order of hundreds of μm. In order to achieve no missed detection, the spacing between adjacent nodes of the grid used for mechanical imaging between adjacent sensors must match this size. Therefore, the projection spacing y of adjacent sensors in the circumferential direction is about a few hundred μm, while the projection spacing x of adjacent sensors in the axial direction is at least 10mm, which is larger than the size of the sensor.

[0046] During the inspection, the composite pipe only makes axial linear motion, while the multi-channel sensor group arranged on the composite pipe remains stationary while maintaining fixed detection conditions. From the circumferential point of view, the projection spacing y of adjacent detection units (sensors) in the circumferential direction is several hundred μm. From the requirements of ultrasonic mechanical imaging, the circumferential range has been fully covered, with 100% no missed detection. From the axial point of view of the composite pipe operation, the spacing between adjacent position points of the signal collected by each channel must also be several hundred μm. This can be achieved by providing the servo motion system that drives the composite pipe to move linearly with a length measurement function and combining it with an external trigger. In this way, the detection effect that can be achieved by all adjacent channels as a whole can already cover the functional layer area of ​​the entire inner wall of the composite pipe.

[0047] Since the results of ultrasonic mechanical imaging detection using the above method may still be different from conventional mechanical scanning imaging, the detection results of each channel are scan lines that are offset from each other by a long distance, and the scan lines cannot be aligned according to the specific positions on the composite pipe body, and a two-dimensional image of mechanical scanning cannot be formed. Therefore, the present invention preferably implements quality flaw detection through contrast analysis.

[0048] Taking the detection of composite steel pipes with an outer diameter of 100mm as an example, the patented method of ultrasonic mechanical scanning images designed in conjunction is used to perform the detection. For example, we must meet the requirement that the mechanical imaging grid spacing of the inner wall of the composite pipe to be detected is not less than 1mm to avoid missed detection. If the pipe wall thickness is 10mm and the composite layer thickness is 1mm, then the position of the composite layer is on a circle with a diameter of 80mm, and the inner diameter of the composite steel pipe is 78mm. To ensure that the detection of composite pipes with a composite layer diameter of 80mm is not missed, if 8 reciprocating times are used to complete the detection task of a composite steel pipe, that is, one detection is completed in a sector with a 45-degree angle in the circumference, and the detection of a composite steel pipe can be completed by reciprocating the detection of 8 45-degree sectors of the steel pipe circumference. Then, the diameter of the circle to be detected is 80mm, and the circumference is approximately 251.2mm, corresponding to the length of each 45-degree sector of 31.4mm, then 32 channels can be used. Using 32 channels, also Figure 3 There are 32 detection points. On the circumference of the composite steel pipe, the 32 channels are evenly distributed in a 45-degree sector, and adjacent channels are numbered in sequence. The detection is carried out when the jet direction of each channel 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 500 mm, then its circumference is 1.57 m, and the length of the 45-degree angle sector of the composite pipe is 196.25 mm. For a 32-channel detection system, the projection spacing between every two adjacent channels on the circumference of the composite pipe is about 6.13 mm, that is, Figure 3 If the diameter of the jet head is 40 mm, then the projection distance between each two adjacent channels in the axial direction of the composite tube can also be 40 mm, that is, Figure 3 x=40mm, and the total length of 32 channels is less than 1.28m. The angle between the detection line formed by all detection points and the axis of the composite pipe can be calculated, which is approximately: arctg(6.13 / 40)=8.7゜.

[0050] The above is a case of completing the detection of a composite steel pipe by reciprocatingly detecting 8 45-degree angle sectors of the circumference of the steel pipe. If you want to reduce the equipment manufacturing cost, or if the detection time is sufficient, the number of channels can be halved, that is, 16 channels. If the diameter of the above circular water circulation cavity is still 500mm, its overall length will be less than 614mm, and so on.

[0051] To this end, the present invention is designed to use the end of the composite pipe to trigger each adjacent detection channel one by one, so that the scanning lines detected by each adjacent channel can be aligned one by one. The implementation method is that when arranging the adjacent channel sensors, each adjacent sensor has been arranged equidistantly in the axial direction of the composite pipe according to a spacing of x. At the beginning of the detection, the ultrasonic sensor group is in a fixed position of the detection device and remains motionless, but the detection system of each channel has entered a detection state in which various conditions have been adjusted. At this time, the end of the composite pipe has not yet entered the channel, and the channel can only detect noise signals. The detection is not actually performed, and the data is not acquired and stored. Figure 7 When the steel pipe is transported in a straight line by the clamping roller and enters the detection space below each adjacent sensor one by one, the end of the composite pipe enters an adjacent channel, which detects the ultrasonic signal reflected from the outer surface of the end of the composite pipe, thereby driving the actual detection and starting the acquisition and storage of the detection signal data. Figure 8 .

[0052] Since the pipe end starts the work of each adjacent ultrasonic detection channel one by one, the conditions for subsequent detection and data acquisition in the axial direction of each channel are the same, so that the scanning line results obtained by each adjacent channel detection are all aligned starting from the pipe end. Next, the present invention adopts two methods to present the results of mechanical scanning imaging:

[0053] A) Following the above steps, by aligning the scanning results of adjacent ultrasonic sensors and redrawing them in the form of a 2D plane, ultrasonic mechanical scanning imaging detection of the entire bimetallic composite pipe with an extremely thin inner layer can be achieved. 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 defective position is detected, the obtained test data will have a large color contrast with the color of the defect-free position after obvious color marking, thus achieving ultrasonic mechanical scanning imaging detection of the entire bimetallic composite pipe with an extremely thin inner layer, and using the difference in contrast, online imaging quality detection is performed.

[0054] B) The present invention also takes another form to present the mechanical scanning imaging result, the process is as follows Figure 6 Since the scan line results obtained by each adjacent channel detection start from the tube end, it can be said that the detection position results of each channel are relatively aligned. Figure 6In the process of detecting a steel pipe with a length of AB passing through the detection unit, ultrasonic waves are emitted to the inside of the steel pipe at a certain interval y. The detection starts from the time the steel pipe enters the detection unit and ends when the steel pipe passes through the detection unit. L detection data with equal intervals along the axial direction of the steel pipe can be obtained. In order to present the detection results as an intuitive image, the data points with a length of L are drawn as a line for every M data points, so that L / M=N rows of detection images can be obtained in the end.

[0055] If there is a defect on the inner wall of a steel pipe with a length of AB between the cd segments, after the detection unit is tested, the test data with a length of L is obtained. Since the steel pipe passes through the test unit at a constant speed and the ultrasonic test is performed at a fixed interval y, the length of the steel pipe is proportional to the length of the data. The position of the defect in the length direction of the steel pipe corresponds to the position in the data queue. Fig. 9 There are two forms in which the defect is drawn on the same line, and form two is drawn on two adjacent lines.

[0056] exist Fig. 9 In the data queue A'B', the c'd' segment corresponds to the position where the defect exists in the cd segment on the steel pipe AB. When the steel pipe is detected without defective positions, 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 defective position is detected, the obtained detection data will have a large color contrast with the color of the defect-free position after obvious color marking, thus realizing ultrasonic mechanical scanning imaging detection of the entire body of the bimetallic composite pipe with an extremely thin inner layer. The difference in contrast can be used to perform imaging quality detection online.

[0057] Beneficial effects of the present invention:

[0058] The mechanical imaging method for the bimetallic composite pipe with an extremely thin inner layer described in the present invention can solve the technical difficulties in the current quality identification and detection technology of the functional layer and the joint surface of the composite pipe, which cannot implement ultrasonic mechanical imaging detection, so that the quality of the bimetallic composite pipe can be detected, and the technical obstacles of non-destructive quality detection existing between the innovative products of steel pipes and their market application are eliminated. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 is the cross-section of the bimetallic composite pipe;

[0060] Figure 2 This is a schematic diagram of the sample detection method using mechanical imaging;

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

[0062] Figure 4 for Figure 3 Side view of

[0063] Figure 5 It is a schematic diagram of the sector division of the bimetallic composite pipe detection of the present invention;

[0064] Figure 6 is a flow chart of the method of the present invention;

[0065] Figure 7 Schematic diagram of the reflection signal of the composite pipe end before the composite pipe end enters the channel in the embodiment of the present invention;

[0066] Figure 8 Schematic diagram of the reflection signal of the composite pipe end after the composite pipe end has entered the channel in an embodiment of the present invention;

[0067] Fig. 9 The linear results obtained after testing the inner layer of a bimetallic composite pipe through an ultrasonic channel are converted into a mechanical scanning diagram;

[0068] Fig.10 This is a complete mechanical scanning imaging result of an extremely thin inner layer composite tube obtained by the method of the present invention. DETAILED DESCRIPTION

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

[0070] 1) A water coupling circulation system is provided, and a plurality of jet coupling ultrasonic detection units 1, 1' are installed circumferentially on a cylindrical coupling cavity, wherein the central angles of the detection units 1, 1' are the same, forming a fan-shaped distribution, and the detection units 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; and the concentric height of the detection unit 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 coincide with each other;

[0072] 3) Start the water coupling circulation system, drive the composite pipe 100 to pass through each adjacent detection unit 1, 1' at a uniform speed in turn, and the dynamic water jet couples the ultrasonic wave into the composite pipe body for imaging detection until the composite pipe 100 passes through the detection units 1, 1' completely; when the composite pipe enters the detection space below the sensor of each adjacent detection unit one by one, the end of the composite pipe enters a certain adjacent channel, and the channel detects the ultrasonic 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 through which the composite pipe passes in the coupling cavity of the detection device, this ensures that the transmission distance of the sound waves emitted from each channel to the surface of the composite pipe is also the same, so that the ultrasonic wave reflected on the surface generated by the end of the composite pipe running to a certain sensor sound path can be used 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 starts the work of each adjacent ultrasonic detection channel one by one, the subsequent channels are 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. The detection line is composed of detection points with a fixed step length, namely mechanical scanning points, and each scanning point corresponds to an ultrasonic detection. All detection points on the detection line of each channel form a series of detection waveform data sets throughout the entire length of the composite pipe. Each waveform data corresponds to a mechanical scanning point, namely a detection point, and adjacent waveform data are measured from adjacent position points with a fixed step length on the composite pipe. Each series 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, each detection process in which the composite pipe passes through the coupling cavity will generate n detection lines of the same length. These detection lines of the same length are reasonably aligned, and the waveform data characteristics corresponding to each detection point, namely the maximum value of the reflected signal within the monitoring range, are plotted into a graph, so that a mechanical scanning image of the quality of the extremely thin inner layer bimetallic composite pipe can be realized by using multi-channel ultrasonic detection.

[0073] Preferably, the ultrasonic sound field adopts a point focusing or line focusing method, and the inspected bimetallic composite tube is located in the middle position between the sound source and the focus or line, so as to ensure that the energy of the ultrasonic wave is concentrated on the extremely thin inner layer area of ​​the bimetallic composite tube; wherein,

[0074] Point focusing method, in which the central axis of the point focusing sound field intersects perpendicularly with the radial central axis of the composite tube, so that the sound wave is incident into the interior of the composite tube;

[0075] Line focusing method: the symmetric center plane of the line focusing sound field passes through the radial center axis of the composite tube, and the focal line remains parallel to it, so that the sound wave is 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, the axial spacing x between adjacent detection units is between 30 and 60 mm, the radial spacing y is between 5 and 10 mm, or the central angle between adjacent detection units is 5° to 15°.

[0077] See also Figure 5 The circumference of the composite pipe 100 is divided into a plurality of sectors 101 in the circumferential direction. Corresponding to each sector, a series of jet-coupled ultrasonic detection units 1 and 1' that meet the requirements of circumferential resolution of flaw detection are arranged to implement detection; and the detection of the entire composite pipe including the pipe end parts in all sectors is completed in an axial reciprocating working mode of the composite pipe.

[0078] Taking the detection of composite pipes with an outer diameter of 100mm as an example, the spacing of the mechanical imaging grid of the inner wall of the composite pipe to be detected must not be greater than 1mm to avoid missed detection. If the pipe wall thickness is 10mm and the composite layer thickness is 1mm, then the position of the composite layer is on a circle with a diameter of 80mm, and the inner diameter of the composite steel pipe is 78mm. To ensure that the detection of composite pipes with a composite layer diameter of 80mm is not missed, if 8 reciprocating times are used to complete the detection task of a composite steel pipe, that is, one detection is completed in a sector with a 45-degree angle in the circumference, the detection of a composite steel pipe can be completed by reciprocating the detection of 8 45-degree sectors of the circumference of the steel pipe. Then, the diameter of the circle to be detected is 80mm, and the circumference is about 251.2mm, corresponding to the length of each 45-degree sector of 31.4mm, then 32 channels are used. Using 32 channels is also Figure 3 There are 32 detection points. On the circumference of the composite steel pipe, the 32 channels are evenly distributed in a 45-degree sector, and adjacent channels are numbered in sequence. The detection is carried out when the jet direction of each channel 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 500 mm, then its circumference is 1.57 m, and the length of the 45-degree angle sector of the composite pipe is 196.25 mm. For a 32-channel detection system, the projection spacing between every two adjacent channels on the circumference of the composite pipe is about 6.13 mm, that is, Figure 3 If the diameter of the jet head is 40 mm, then the projection distance between each two adjacent channels in the axial direction of the composite tube can also be 40 mm, that is, Figure 3 x=40mm, and the total length of 32 channels is less than 1.28m. The angle between the detection line formed by all detection points and the axis of the composite pipe can be calculated, which is approximately: arctg(6.13 / 40)=8.7゜.

[0080] The above is a case of completing the detection of a composite steel pipe by reciprocatingly detecting 8 45-degree angle sectors of the circumference of the steel pipe. If you want to reduce the equipment manufacturing cost, or if the detection time is sufficient, the number of channels can be halved, that is, 16 channels. If the diameter of the above circular water circulation cavity is still 500mm, its overall length will be less than 640mm, and so on.

[0081] In the method of the present invention,

[0082] The quality inspection of the extremely thin inner layer of the bimetallic composite pipe is carried out by using ultrasonic sensors with sufficient channels arranged adjacent to each other; the arrangement of adjacent sensors is as follows: Figure 3 to Figure 5 As shown; during detection, the composite pipe only makes axial linear motion, while the multi-channel sensor group arranged on the composite pipe remains stationary while maintaining fixed detection conditions.

[0083] The results of ultrasonic mechanical imaging detection implemented by the above method may still be different from conventional mechanical scanning imaging, which is manifested in that the detection results of each channel are scan lines that are offset from each other by a long distance. The scan lines cannot be aligned according to the specific positions on the composite pipe body, and a two-dimensional image of mechanical scanning cannot be formed, and quality flaw detection can not be achieved through contrast analysis.

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

[0085] To this end, the present invention uses a method in which, during the detection implementation process, the end of the composite pipe reflects the sound wave signal and triggers each adjacent detection channel one by one to start entering the detection mode, so that the scanning lines detected by each adjacent channel can be aligned one by one. The implementation method is that when arranging the adjacent channel sensors, each adjacent sensor has been arranged equidistantly in the axial direction of the composite pipe at a spacing of x. At the beginning of the detection, the ultrasonic sensor group remains stationary in a fixed position of the detection equipment, but the detection system of each channel has entered a detection state in which various conditions have been adjusted. At this time, the end of the composite pipe has not yet entered the channel, and the channel can only detect noise signals. The detection has not actually been performed, and the data has not been acquired and stored. Figure 7 shown.

[0086] When the composite pipe is transported in a straight line by the clamping roller and enters the detection space below each adjacent sensor one by one, the end of the composite pipe enters a certain adjacent channel, and the channel detects the ultrasonic 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 through which the composite pipe passes in the coupling cavity of the detection equipment, this ensures that the transmission distance of the sound waves emitted from each channel to the surface of the composite pipe is also the same. Therefore, the reflected signal of the ultrasonic wave on the surface generated by the end of the composite pipe running to a certain sensor sound path can be used (detection starts from the entry of the pipe end, and the detection is not completed as long as the composite pipe body does not leave the sensor sound path) to trigger the detection program to perform the actual detection task and start the acquisition and storage of the detection signal data, such as Figure 8 shown.

[0087] Since the end of the composite pipe starts the work of each adjacent ultrasonic detection channel one by one, the conditions for subsequent detection and data acquisition in the axial direction of each channel are the same, so that each adjacent channel detects a detection line at its own angle, which is composed of detection points (i.e. mechanical scanning points) with a fixed step spacing, and each scanning point corresponds to an ultrasonic detection. All the detection points on the detection line of each channel form a series of detection waveform data sets that run through the entire length of the composite pipe. Each waveform data corresponds to a mechanical scanning point (detection point), and the adjacent waveform data are measured from adjacent position points with a fixed step length on the composite pipe. Each series of detection line results of each channel starts from the pipe end and is formed by the same number of detection points. In this way, if there are 32 channels, each detection process of the composite pipe passing through the coupling cavity will generate 32 detection lines of the same length. As long as these detection lines of the same length are reasonably aligned and the waveform data characteristics corresponding to each detection point (the maximum value of the reflected signal within the monitoring range) are plotted into a graph, the mechanical scanning image of the quality of the extremely thin inner layer bimetallic composite pipe can be realized by using multi-channel ultrasonic detection.

[0088] The present invention can also adopt the following two methods to present the results of mechanical scanning imaging:

[0089] The first method is to follow the above steps. Since the length of the detection line measured by all channels is the same and is composed of the same number of detection points, each two adjacent detection lines correspond to the detection results of the adjacent channels on the composite pipe at a certain angle and through the head and tail of the composite pipe. Therefore, if the 32 scanning lines of 32 channels are arranged in rows by aligning the heads of each scanning line of the adjacent channels, a mechanical scanning image for detecting the quality of the extremely thin inner bimetallic composite pipe is formed. By changing the circumferential sector angle range of the composite pipe covered by the ultrasonic channel, repeatedly detecting the composite pipe, and redrawing it in the form of a two-dimensional plane according to the above method, ultrasonic mechanical scanning imaging detection of the entire body of the extremely thin inner bimetallic composite pipe is realized.

[0090] When detecting a position without defects in the composite pipe, the physical state near the inner wall of the composite pipe is relatively consistent. Under reasonable conditions, the waveform echo height within the ultrasonic monitoring position is basically consistent, and the contrast color of the mechanical imaging is not much different. However, if a defective position is detected, the waveform echo height within the ultrasonic monitoring position will be significantly different from the signal height at the position without defects. After the obtained detection data is quantified by using gradient colors to define the signal amplitude, that is, different colors are used to identify different signal amplitudes, the image color of the defective position is more contrasted with the color of the non-defective position, thus realizing the ultrasonic mechanical scanning imaging detection of the entire body of the bimetallic composite pipe with an extremely thin inner layer. By using the difference in contrast, the imaging quality detection is performed online, and the interpretation and judgment of the detection results are very clear and convenient.

[0091] The second method is that since the scanning line results of each adjacent channel detection start from the tube end, the detection position results of each channel can be said to be relatively aligned. Since the image is formed by the data of a surface, that is, it is formed by several lines, we can cut the scanning line results of a very long channel into several fixed-length lines, and arrange them in sequence to form a plane diagram. Fig. 9 In the process of detecting the composite pipe of length AB passing through the detection unit, ultrasonic waves are emitted to the inside of the composite pipe at a certain interval y. The detection starts from the time when the composite pipe enters the detection unit and ends when the composite pipe passes through the detection unit. L detection waveform data are evenly spaced along the axial direction of the composite pipe. Each detection waveform data corresponds to a mechanical scanning point. In order to present the detection result as an intuitive image, the data points with a length of L are drawn as a line for every M data points. Then, a detection image with L / M=N lines can be obtained.

[0092] On a composite tube with a length of AB, if there is a defect on the inner wall of the composite tube between the cd segments, after detection by the detection unit, the detection data of length L is obtained. Since the composite tube passes through a certain detection channel at a constant speed and the step length between the detection points is a fixed spacing y, the length of the composite tube is proportional to the length of the data line obtained by detection. The position of the defect in the length direction of the composite tube corresponds to the position in the data queue. On the composite tube, the same continuous defect along the radial direction may have Fig. 9 There are two forms in which the defect is drawn on the same line, and form two is drawn on two adjacent lines.

[0093] exist Fig. 9 The result of a data line measured by a channel at a certain angle, starting from the end A of the composite pipe and ending at the end B of the composite pipe, is formed by a large number of data points, and each adjacent data point corresponds to an adjacent detection position on the composite pipe (the spacing is the step length). For the length of the composite pipe, the system measured a certain length of data line queue A'B' starting from data point A' and ending at data point B'. The waveform echo height within the ultrasonic monitoring position range is basically the same, and the contrast color of the mechanical imaging is not much different. If the segment from data point c' to data point d' in the data line queue corresponds to the position where the defect exists in the cd segment on the composite pipe, then the waveform echo height within the ultrasonic monitoring position range will be significantly different from the signal height at the position without defects. After the obtained detection data is quantified and defined by the signal amplitude with gradient colors (different colors are used to identify different signal amplitudes), the image color of the defective area is greatly contrasted with the color of the non-defective area, so that the ultrasonic mechanical scanning imaging detection of the entire body of the bimetallic composite pipe with an extremely thin inner layer is realized, using the difference in contrast. If the defect can be detected by multiple adjacent channels, then an image reflection of the defect will be obtained at the same position of the ultrasonic mechanical scanning imaging test results of each channel.

[0094] When the entire circumference of the composite pipe is covered and scanned by the detection channel, the ultrasonic mechanical scanning and imaging detection of the entire circumference of the bimetallic composite pipe with an extremely thin inner layer is completed.

[0095] For a certain composite composite pipe, according to the method of the present invention, a complete mechanical scanning imaging result of the inner layer of the extremely thin composite pipe can be obtained after detection, and the composite layer defects and pore defects are displayed very clearly, such as Fig.10 If there are pores or unbonded defects in the composite layer or functional layer, after the amplitude of the defect reflection signal at the detection point is quantified, different echo amplitudes are continuously defined with gradient colors, and the following can be obtained: Fig.10This is an intuitive mechanical scanning imaging result for the inner layer of the extremely thin composite tube. Thus, the present invention overcomes the problem that the spacing between sensors is too large when using multiple channels to perform mechanical imaging flaw detection, resulting in the mechanical scanning line result being unable to form an overall mechanical scanning image.

Claims

1. A mechanical scanning imaging method for an extremely thin inner layer bimetallic composite tube, characterized in that: The steps include: 1) A water coupling circulation system is provided, and a plurality of jet coupling ultrasonic detection units are installed along the circumferential direction of a cylindrical coupling cavity. The central angles of the detection units are the same, forming a fan-shaped distribution, and the detection units 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 unit is adjustable; 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 coincide with each other; 3) Start the water coupling circulation system, drive the composite pipe to pass through each adjacent detection unit in turn at a uniform speed, and use the dynamic water jet to couple the ultrasonic wave into the composite pipe body for imaging detection until the composite pipe passes through all the detection units; when the composite pipe enters the detection space below the sensor of each adjacent detection unit one by one, the end of the composite pipe enters a certain adjacent channel, and the channel detects the ultrasonic 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 through which the composite pipe passes in the coupling cavity of the detection equipment, this ensures that the transmission distance of the sound waves emitted from each channel to the surface of the composite pipe is also the same, so that the ultrasonic wave reflected on the surface generated by the end of the composite pipe running to a certain sensor sound path can be used 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 starts the work of each adjacent ultrasonic detection channel one by one, each subsequent channel detects and acquires in the axial direction The conditions of the data are the same, and each adjacent channel detects a detection line at its own angle. The detection line is composed of detection points with a fixed step length, namely 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 series of detection waveform data sets throughout the entire length of the composite pipe, and each waveform data corresponds to a mechanical scanning point, namely a detection point, and adjacent waveform data are measured from adjacent position points with a fixed step length on the composite pipe; each series 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, each detection process in which the composite pipe passes through the coupling cavity will generate n detection lines of the same length. These detection lines of the same length are reasonably aligned, and the waveform data characteristics corresponding to each detection point, namely the maximum value of the reflected signal within the monitoring range, are plotted into a graph, so that a mechanical scanning image of the quality of the extremely thin inner layer bimetallic composite pipe can be realized by using multi-channel ultrasonic detection.

2. The mechanical scanning imaging method of the inner layer ultra-thin bimetallic composite tube according to claim 1, characterized in that In the step 3), the length of the detection line measured by all channels is the same, and they are composed of the same number of detection points. Each two adjacent detection lines correspond to the detection results of the adjacent channels on the composite pipe at a certain angle and through the head and tail of the composite pipe; if the heads of each scanning line of the adjacent channels are 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 bimetallic composite pipe; the circumferential sector angle range of the composite pipe covered by the ultrasonic channel is changed, the composite pipe is repeatedly detected, and it is re-drawn in the form of a two-dimensional plane diagram according to the above method, so as to realize the ultrasonic mechanical scanning imaging detection of the entire body of the bimetallic composite pipe with an extremely thin inner layer; When inspecting a composite pipe without defective positions, the physical state near the inner wall of the composite pipe is relatively consistent, the waveform echo height within the ultrasonic monitoring range of the position is basically consistent, and the contrast color of the mechanical imaging is not much different; however, if the composite pipe is inspected to a defective position, the waveform echo height within the ultrasonic monitoring range of the position will be significantly different from the signal height at the position without defect. After the obtained inspection data is quantified by using gradient colors to define the signal amplitude, that is, different colors are used to identify different signal amplitudes, the image color at the defective position has a large contrast with the color at the non-defective position. At this point, ultrasonic mechanical scanning imaging inspection of the entire body of the bimetallic composite pipe with an extremely thin inner layer is realized, and the imaging quality detection is performed online using the difference in contrast.

3. The mechanical scanning imaging method of the inner layer ultra-thin bimetallic composite tube according to claim 1, characterized in that In the step 3), since the scanning line results of each adjacent channel detected start from the tube end, the results of the detection position points between the channels are relatively aligned; since the image is formed by the data of a surface, that is, formed by a number of lines, the scanning line results of a very long channel are cut into a number of fixed-length lines, which are arranged in sequence to form a plane diagram.

4. The mechanical scanning imaging method of the inner layer ultra-thin bimetallic composite tube according to claim 1, characterized in that: The ultrasonic sound field adopts point focusing or line focusing. The inspected bimetallic composite tube is located in the middle between the sound source and the focus or line, ensuring that the energy of the ultrasonic wave is concentrated on the extremely thin inner layer of the bimetallic composite tube. Point focusing method, in which the central axis of the point focusing sound field intersects perpendicularly with the radial central axis of the composite tube, so that the sound wave is incident into the interior of the composite tube; Line focusing method: the symmetric center plane of the line focusing sound field passes through the radial center axis of the composite tube, and the focal line remains parallel to it, so that the sound wave is incident into the interior of the composite tube.

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

6. The mechanical scanning imaging method of the inner layer ultra-thin bimetallic composite tube according to claim 1 or 5, characterized in that: In step 1), the ultrasonic waves emitted by adjacent detection units enter the composite pipe through water coupling and reach the composite interface to form adjacent detection points with axial and circumferential spacings a and b of 0.5 to 2 mm respectively.

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