Panoramic annular scanning infrared detection system and method for pipe cracks and application

Abstract

The invention discloses a panoramic annular scanning infrared detection system and method for pipe cracks and application. The panoramic annular scanning infrared detection system comprises a photo-thermal excitation collection system and a reflection scanning system which are arranged in the axis direction in a pipeline. The photo-thermal excitation acquisition system shapes laser into annular light spots through an optical fiber coupler lens cone, the annular light spots are projected to the reflection scanning system, the reflection scanning system reflects the projected annular light spots through a cone reflector, a circle of full-circumferential scanning annular laser is formed on the inner wall of the pipeline curved surface, and dynamic scanning heat flow is formed on the pipeline curved surface structure; by collecting a dynamic temperature field of a full-circumferential curved surface in a detected pipeline, full-circumferential annular laser scanning infrared detection of pipeline curved surface structure defects is realized. According to the invention, through fusion of mechanical movement, laser shaping and conical reflector principles, full-circumferential efficient integrated non-contact on-line detection of the pipeline curved surface structure is realized, the detection capability and efficiency of the pipeline curved surface structure are greatly improved, and the detection applicability of laser infrared detection to heterogenous structures is expanded.

Description

Technical Field

[0001] The present invention relates to the technical field of non-contact photothermal infrared non-destructive testing, and particularly relates to a panoramic circumferential scanning infrared detection system, method and application for pipe cracks. Background Art

[0002] Pipelines are widely used in energy fields such as water supply, oil, and heating, and are an important part of special equipment and infrastructure. They are prone to cracks under complex stress and chemical corrosion environments, which affect mechanical properties and pose a serious threat to safety. Therefore, efficient full-coverage detection and accurate crack defect evaluation are required.

[0003] Currently, automated vision detection based on video probes is widely used in in-pipe detection. It has the advantages of high efficiency, speed, and system miniaturization, but it does not have the ability to detect internal damage to the pipe wall. Existing detection methods such as eddy current and ultrasonic, and corresponding online detection technologies are applied to in-pipe detection. On the one hand, problems such as near-contact detection methods (eddy current and ultrasonic detection) and surface blind spots (ultrasonic detection) pose huge challenges to detection coverage and efficiency in long-distance and large-scale detection requirements. On the other hand, the diverse applications of pipelines with different materials, diameters, and sizes also pose huge challenges to the complexity and cost of the mechanical control systems of the above methods.

[0004] Infrared non-destructive testing technology is widely used in key fields such as aerospace, national defense, ships, and energy due to its non-contact, long-distance, and large-area detection characteristics. Especially in damage and defect assessment, active infrared detection has higher sensitivity and signal-to-noise ratio. However, current technologies are still difficult to achieve full circumferential panoramic high-efficiency online detection of pipelines. Laser infrared detection uses high-energy focusing and dynamically adjustable lasers that can be flexibly shaped and precisely controlled as thermal excitation sources. The laser infrared detection method under spatial modulation is applicable to the detection of circumferentially distributed curved cracks in pipes. In order to achieve efficient and accurate detection of circumferentially distributed damage in pipes, it is necessary to deeply study the heat conduction and heat wave diffusion laws of the curved surface structure of pipes. Especially in laser infrared detection, the quantitative research on curved cracks in pipes is still insufficient. Summary of the Invention

[0005] To solve the above-mentioned defects in the prior art, the purpose of the present invention is to provide a panoramic circumferential scanning infrared detection system, method and application for pipe cracks. The present invention generates a scanning annular laser through the coupled design of mechanical movement and laser shaping, and forms a full circumferential dynamic annular scanning laser thermal excitation mode in the pipe through the reflection of a conical mirror. Similarly, the principle of the conical mirror is used to achieve infrared thermal imaging detection of the full circumferential curved surface of the pipe, and solve the problem of efficient full-coverage detection of surface and subsurface defects of the curved surface structure inside the pipe.

[0006] The present invention is realized through the following technical solutions.

[0007] In one aspect of the present invention, there is provided a panoramic circumferential ring-scanning infrared detection system for pipe cracks, including a photothermal excitation acquisition system and a reflection scanning system arranged along the inner axis direction of the pipeline;

[0008] The photothermal excitation acquisition system is configured with a laser fiber connected to a laser, a fiber coupler barrel connected to the laser fiber, a first axicon lens and a convex lens arranged inside the fiber coupler barrel, and a second axicon lens is located inside the movable lens; it is used to project the annular light spot shaped by the fiber coupler barrel from the laser introduced by the optical fiber onto the reflection scanning system;

[0009] The reflection scanning system is configured with a conical mirror arranged inside the pipe, which is used to reflect the annular light spot projected by the photothermal excitation acquisition system through the conical mirror to form a circumferential scanning annular laser on the inner wall of the pipe curve, and form a dynamic scanning heat flow on the pipe curve structure;

[0010] By collecting the dynamic temperature field of the entire circumferential surface inside the pipeline to be measured, the circumferential ring-scanning infrared detection of the defects of the pipeline curve structure is realized.

[0011] Preferably, the dynamic temperature field of the entire circumferential surface inside the pipeline to be measured is collected by a small infrared thermal imager arranged above the fiber coupler barrel, and the circumferential ring-scanning infrared detection of the defects of the pipeline curve structure is realized.

[0012] Preferably, the movable lens can move back and forth along its own axis direction.

[0013] Preferably, the axicon lens and the convex lens are coaxial inside the fiber coupler barrel.

[0014] Preferably, the cone angle of the conical mirror is at least greater than 90°.

[0015] Preferably, the photothermal excitation acquisition system and the reflection scanning system maintain a fixed distance.

[0016] In another aspect of the present invention, there is provided a detection method for a panoramic circumferential ring-scanning infrared detection system for pipe cracks, including:

[0017] Fix the photothermal excitation acquisition system and the reflection scanning system in the center inside the pipe, and keep the center of the rotatable lens of the photothermal excitation acquisition system and the center of the conical mirror of the reflection scanning system coaxially arranged;

[0018] Control the computer to synchronously start the sampling of the small infrared thermal imager and the generation of laser by the laser to the laser fiber;

[0019] The Bessel beam introduced by laser fiber enters the inner part of the fiber coupler barrel. It passes through the first axicon, convex lens, and second axicon successively, and is reshaped into an annular light spot which is reflected by the conical mirror, generating a stationary annular laser beam along the tube axis direction and irradiating on the inner wall of the pipeline curved surface;

[0020] Adjust the distance d between the convex lens and the second axicon to adjust the diameter R of the annular light spot projected onto the conical mirror;

[0021] Adjust the numerical aperture NA of the second axicon to control the width D of the ring of a circumferential scanning annular laser beam irradiating on the inner wall of the pipeline;

[0022] Control the photothermal excitation acquisition system and the reflection scanning system to move and scan along the pipeline axis direction together, and the circumferential line scanning laser with a precessional motion performs dynamic scanning and thermal excitation heating on the inner wall of the pipeline;

[0023] The small infrared thermal imager acquires the transient temperature field of the inner curved surface structure of the pipe through the infrared reflection optical path of the conical mirror and transmits it back to the control computer, realizing the circumferential annular laser scanning infrared detection of the defects of the overall curved surface structure of the pipeline.

[0024] Preferably, the relationship between the distance d between the convex lens and the second axicon and the diameter R of the annular light spot projected onto the conical mirror satisfies the following conditions:

[0025] Keep the axicon angle α of the first axicon, the axicon angle θ of the conical mirror, and the focal length f of the convex lens unchanged, fix the numerical aperture NA of the second axicon, and the distance d between the convex lens and the second axicon is directly proportional to the diameter R of the annular light spot of the conical mirror; then the width D of the circumferential scanning annular laser beam remains unchanged;

[0026] The relationship between the numerical aperture NA of the second axicon and the width D of the circumferential scanning annular laser beam satisfies the following conditions:

[0027] Keep the axicon angle α of the first axicon, the axicon angle θ of the conical mirror, and the focal length f of the convex lens unchanged, fix the distance d between the convex lens and the second axicon, and the numerical aperture NA of the second axicon is inversely proportional to the width D of the circumferential scanning annular laser beam, then the diameter R of the annular light spot of the conical mirror remains unchanged.

[0028] Preferably, the wavelength of the thermal excitation laser is 980 - 1064 nm, and the acquisition wavelength of the infrared thermal imager is 7 - 14 μm.

[0029] Due to the adoption of the above technical solutions, the present invention has the following beneficial effects:

[0030] 1. Through the annular beam shaping lens group probe (fiber coupler lens barrel, two axicons, convex lens, movable lens), the high-power fiber laser is shaped into an annular scanning light spot, and the annular scanning light spot is coaxially irradiated onto the conical mirror and then split and reflected onto the inner wall curved surface of the pipeline to achieve full circumferential annular scanning thermal excitation.

[0031] 2. The small infrared thermal imager is used to collect the defect temperature detection image signals of the entire circumferential inner wall of the pipeline reflected by the conical mirror, so as to achieve full circumferential detection and collection of the curved surface structure.

[0032] 3. By controlling the photothermal excitation acquisition system and the reflection scanning system to jointly perform centering scanning along the pipeline axis direction, efficient non-contact annular scanning photothermal infrared detection is realized. This detection system can obtain multiple information of the inner wall defects of the pipeline only by one scan inside the pipeline to be inspected.

[0033] The tube crack panoramic ring scan infrared detection system of the present invention has the advantages of being easy to implement, easy to operate, strong practicability, high detection efficiency, low cost, etc., and can be widely used in the detection of defects and damages of water supply, oil, and heating pipelines. Description of the Drawings

[0034] The drawings described herein are used to provide a further understanding of the present invention, form a part of this application, and do not constitute an improper limitation to the present invention. In the drawings:

[0035] Figure 1 It is a schematic diagram of a tube crack panoramic ring scan infrared detection system proposed by the present invention;

[0036] Figure 2(a) is a system diagram of the laser annular scanning probe in the present invention;

[0037] Figure 2(b) is a schematic diagram of the annular scanning laser reflection optical path in the present invention;

[0038] Figure 3 It is a schematic diagram of the tube curved structure model in the present invention;

[0039] Figure 4(a) is a schematic diagram of defect detection from the perspective of the tube axis in the present invention;

[0040] Figure 4(b) is a schematic diagram of partial enlarged defect detection from the perspective of the tube axis in the present invention;

[0041] Figure 5 It is a schematic diagram of the temperature line across the defect in the present invention.

[0042] In the figure: 1. Small infrared thermal imager; 2. Fiber optic coupler barrel; 3. Optical fiber; 4. First axicon; 5. Convex lens; 6. Movable lens; 7. Second axicon; 8. Annular light spot; 9. Cone reflector; 10. Annular laser; 11. In-tube centering scanning mechanism; 12. Photo-thermal excitation acquisition system; 13. Reflection scanning system; 14. Surface defect. Detailed implementation manners

[0043] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Here, the schematic embodiments and descriptions of the present invention are used to explain the present invention, but do not limit the present invention.

[0044] As Figure 1 shown, a panoramic circumferential ring-scanning infrared detection system for pipe cracks provided by an embodiment of the present invention includes a photo-thermal excitation acquisition system 12 and a reflection scanning system 13 arranged along the axial direction A of the pipeline. The photo-thermal excitation acquisition system 12 and the reflection scanning system 13 jointly perform a moving scanning motion along the axial direction A of the pipeline. The circumferential scanning annular laser will form a circumferential scanning annular laser 10 on the inner wall of the pipe, and form a dynamic scanning heat flow on the curved surface structure of the pipe, realizing efficient circumferential infrared non-destructive detection of the curved surface structure defect 14 of the pipe.

[0045] As shown in Fig. 2(a), the photo-thermal excitation acquisition system 12 includes a small infrared thermal imager 1, a fiber optic coupler barrel 2, a laser optical fiber 3, and a movable lens 6. The incident end of the fiber optic coupler barrel 2 is connected to the laser optical fiber 3, and the outgoing end is connected to the movable lens 6. A first axicon 4 and a convex lens 5 are arranged inside the fiber optic coupler barrel 2. The first axicon 4, the convex lens 5, and the fiber optic coupler barrel 2 are coaxial. The second axicon 7 is located inside the movable lens 6. The small infrared thermal imager 1 is arranged above the fiber optic coupler barrel 2.

[0046] As Figure 1 shown, the reflection scanning system 13 includes an in-tube centering scanning mechanism 11 and a cone reflector 9; the cone reflector 9 is arranged inside the pipe through the in-tube centering scanning mechanism 11. The cone reflector 9 is coaxial with the movable lens 6, and the annular light spot 8 emitted by the movable lens 6 is projected onto the conical surface of the cone reflector 9.

[0047] The detection principle of the method of the present invention is as follows: During the in-pipe circumferential scanning detection process, the Bessel beam introduced through the laser optical fiber 3 is reshaped into a two-dimensionally focused annular light spot 8 by the first axicon 4, the convex lens 5, and the second axicon 7. The annular light spot 8 is split and projected onto the inner wall of the pipe curve by the conical mirror 9 to form a full circumferential scanning annular laser 10. Then, in cooperation with the photo-thermal excitation acquisition system 12 and the reflection scanning system 13, a moving scanning motion is carried out along the pipe axis direction A. The full circumferential scanning annular laser will form a full circumferential scanning annular laser 10 on the inner wall of the pipe and form a dynamic scanning heat flow on the pipe curve structure. Defects 14 on the upper surface and subsurface of the curve structure will hinder the diffusion mode of the dynamic scanning heat flow, thereby forming a local temperature rise with defect heat characteristics on the surface. The small infrared thermal imager 1 also acquires the dynamic temperature field of the full circumferential surface inside the measured pipe in a reflection manner through the conical mirror 9; further, by planar unfolding the infrared image of the conical reflection and identifying and quantitatively analyzing the defect heat characteristic signals in the image, the detection of defects in this area is realized; the distance between the photo-thermal excitation acquisition system 12 and the reflection scanning system 13 is fixed and they jointly carry out a moving scanning along the pipe axis direction A, and the video sequences of the infrared detection images of the defects are spliced, that is, the on-line non-destructive detection and full imaging detection of the overall structure of the pipe curve are realized, and the efficient full circumferential infrared non-destructive detection of the defects of the pipe curve structure can be realized.

[0048] The following combines Figures 1 to 3 specific embodiments to further describe the present invention in detail.

[0049] A method for panoramic circumferential scanning infrared detection of pipe cracks provided by an embodiment of the present invention includes the following steps:

[0050] Step 1: As Figure 1 shown, fix the photo-thermal excitation acquisition system 12 and the reflection scanning system 13 of the full circumferential annular laser scanning infrared detection system in the center inside the pipe, and keep the movable lens 6 of the photo-thermal excitation acquisition system and the center of the conical mirror 9 of the reflection scanning system coaxially arranged.

[0051] Step 2: Complete the settings on the control computer to make the synchronous control system synchronously start the sampling of the small infrared thermal imager 1 and the laser to generate laser input into the laser optical fiber 3.

[0052] Step 3: The Bessel beam introduced by the laser fiber 3 enters the inside of the fiber coupler barrel 2 and successively passes through the first axicon 4, the convex lens 5 and the second axicon 7, and finally is reshaped into an annular light spot 8. The reshaped annular light spot 8 is reflected by the conical mirror 9 to generate a stationary annular laser 10 along the tube axis direction and irradiate on the inner wall of the pipeline curve, as shown in Fig. 2(a). The cone angle of the conical mirror 9 should be at least greater than 90°, and its mirror surface can efficiently reflect the laser wavelength and the wavelength collected by the infrared thermal imager to ensure effective infrared imaging optical path angle and laser reflection projection angle.

[0053] Step 4: When adjusting the distance d between the convex lens 5 and the second axicon 7, the diameter R of the annular light spot 8 projected onto the conical mirror 9 can be adjusted. When adjusting the numerical aperture (Numerical Aperture, NA) of the second axicon 7, the width D of the ring of a full circumferential scanning annular laser 10 irradiated on the inner wall of the pipeline can be controlled, thereby controlling the mode of the dynamic excitation heat flux, as shown in Fig. 2(b).

[0054] The relationship between the distance d between the convex lens 5 and the second axicon 7 and the diameter R of the annular light spot 8 satisfies the following conditions:

[0055] On the condition that the axicon angle α of the first axicon 4, the axicon angle θ of the conical mirror 9 and the focal length f of the convex lens 5 remain unchanged, fixing the numerical aperture NA of the second axicon 7, the distance d between the convex lens 5 and the second axicon 7 is in a direct proportional relationship with the annular light spot diameter R of the conical mirror 9; the larger d is, the larger R is; the smaller d is, the smaller R is; then the width D of the ring of the full circumferential scanning annular laser 10 remains unchanged;

[0056] The relationship between the numerical aperture NA of the second axicon 7 and the adjustment of the width D of the ring of the full circumferential scanning annular laser 10 satisfies the following conditions:

[0057] On the condition that the axicon angle α of the first axicon 4, the axicon angle θ of the conical mirror 9 and the focal length f of the convex lens 5 remain unchanged, fixing the distance d between the convex lens 5 and the second axicon 7, the numerical aperture NA of the second axicon 7 is in an inverse proportional relationship with the width D of the ring of the full circumferential scanning annular laser 10, the larger NA is, the smaller D is, the smaller NA is, the larger D is; then the annular light spot diameter R of the conical mirror 9 remains unchanged.

[0058] Step 5: Control the photothermal excitation acquisition system 12 and the reflection scanning system 13 to move and scan along the pipeline axis direction A. The full circumferential scanning annular laser 10 will perform dynamic scanning thermal excitation heating on the inner wall of the pipeline. The dynamic full circumferential scanning annular laser 10 will mainly generate a dynamic heat flux diffusing along the surface. When encountering a crack defect on the curved inner wall, there will be an obvious temperature difference on both sides of the surface crack perpendicular to the surface of the object to be measured. At the same time, the thermal excitation of the dynamic full circumferential scanning annular laser 10 includes a heat flux diffusing along the pipe thickness. When encountering a debonding or thinning defect in the subsurface, a local temperature rise will be formed at the defect.

[0059] Step 6: While the laser performs scanning thermal excitation, the small infrared thermal imager 1 acquires the transient temperature field of the inner curved surface structure of the pipe in a full circumferential manner through the infrared reflection optical path of the conical mirror 9 and transmits it back to the control computer. Since the wavelength of the thermal excitation laser is 980 - 1064 nm, which is completely different from the wavelength of the infrared thermal imager acquisition, which is 7 - 14 μm, and the two reflection optical paths do not interfere with each other, the infrared imaging detection structure will fully reflect the temperature change on the inner wall curved surface of the pipe. By performing planar unfolding, quantitative detection analysis, and detection result image stitching on the circular detection image of the conical surface reflection imaging, full coverage detection of the surface and subsurface defects 14 of the overall curved surface structure of the pipeline is achieved.

[0060] The following combines Figures 3 to 5 and specific embodiments to further describe the present invention in detail.

[0061] Use finite element simulation software to establish a pipe curved structure model as Figure 3 shown. The material of the pipe curved structure is structural steel, with a density of 7850 kg / m 3 , an isotropic thermal conductivity of 60.5 W / m·°C, and a specific heat at constant pressure of 434 J / kg·°C. The size parameters of the pipe curved structure model: the outer radius is 110 mm, the inner radius is 100 mm, and the length is 250 mm. There is 1 axial transverse and longitudinal defect pre-buried in the pipe curved structure, and the specific parameters are shown in Table 1. The purpose of establishing this model is to simulate the heat conduction process of the real pipe curved structure after annular laser excitation, and to prove the application of the present invention in this embodiment.

[0062] Table 1 Axial transverse and longitudinal defect parameters of the pre-buried pipe curved structure

[0063]

[0064] In this embodiment, in order to ensure the authenticity of the numerical simulation, according to the size parameters of the pipe curved structure model, a grid size of 1 mm is selected to divide the model into grids.

[0065] In this embodiment, to meet the requirements of detecting the defects of the pipe curve structure, a laser wavelength of 1064 nm is selected, the laser power is about 25 W, the heat flux density is 2×10 5 W / m, the radius of the laser spot is 6 mm, the axicon angle of the first axicon lens is 140°, the focal length of the convex lens is 50 mm, and the axicon angle of the second axicon lens is 140°. The conical mirror is a single-sided mirror with an axicon angle of 100°. The 6-mm laser spot passes through the first axicon lens, the convex lens, and the second axicon lens in sequence, and finally is reshaped into an annular spot with an annular width of 4 mm. The reshaped annular spot is reflected by the conical mirror to generate a stationary 4-mm-wide annular laser beam along the pipe axis direction and irradiate the inner wall of the pipe curve. Therefore, a 4-mm-wide annular laser is selected for simulating and exciting the pipe curve structure model in the numerical simulation.

[0066] In this embodiment, to meet the requirements that the optothermal excitation acquisition system and the reflection scanning system move along the pipe axis direction for scanning movement, and the continuity of the temperature cloud map during numerical simulation, the present invention selects the advancing speed of the annular laser to be 6 mm / s.

[0067] In this embodiment, the software data acquisition module is directly used to extract the data of the inner surface temperature characteristic numbers of the pipe curve structure, which is used to simulate the data collected by a small infrared thermal imager under real conditions. The dynamic full-circumferential scanning annular laser will mainly generate a dynamic heat flux diffusing along the surface. When encountering the obstacle of the embedded crack defect on the inner wall of the curve, there are obvious temperature differences on both sides of the embedded crack defect perpendicular to the surface of the measured object, as shown in Fig. 4(a). The local enlarged temperature cloud map of the defect is shown in Fig. 4(b), and the temperature line chart across the defect is as Figure 5 shown. The results show that an obvious fault-like difference is formed in the temperature field on both sides of the crack, and the maximum value of the difference is about 20°C. This significant temperature difference can be clearly collected and imaged by a small infrared thermal imager to form clear and definite infrared detection characteristics. It only takes one scan with a duration of 40 seconds to detect the inner surface area of the entire pipe of 157000 mm 2 area.

[0068] As can be seen from the above embodiments, the present invention makes full use of the dynamic heat flux signal and damage characteristics excited by the full circumferential annular scanning laser, adopts the annular shaped scanning laser and the reflective full circumferential thermal excitation and imaging detection, and finally realizes the purpose of full coverage infrared non-destructive testing for the pipe curved surface structure. The method proposed by the present invention is simple, with distinct characteristic technologies and significant detection characteristic signals. It has high detection reliability and efficiency for the pipe curved structure, providing an effective implementation approach for realizing the efficient on-line detection of special equipment such as pipelines. The present invention is not limited to the above embodiments. Based on the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and deformations to some technical features without creative labor according to the disclosed technical content, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. A panoramic scanning infrared detection system for pipe cracks, characterized in that: It includes a photothermal excitation collection system and a reflection scanning system arranged along the inner axis direction of the pipeline; The photothermal excitation collection system is equipped with a laser optical fiber connected to the laser, a fiber coupler lens barrel connected to the laser optical fiber, a first axicon and a convex lens located in the fiber coupler lens barrel, and a second axicon located in the movable lens; It is used to project the annular light spot shaped by the optical fiber laser introduced by the optical fiber through the optical fiber coupler lens barrel onto the reflection scanning system; The reflection scanning system is equipped with a conical reflector installed in the pipe, which is used to reflect the annular light spot projected by the photothermal excitation collection system through the conical reflector, forming a circle of full-circumferential scanning annular laser on the inner wall of the pipe curved surface, forming a dynamic scanning heat flow on the pipe curved surface structure; By collecting the dynamic temperature field of the full circumferential surface inside the tested pipeline, full circumferential annular laser scanning infrared detection of pipeline curved surface structural defects can be achieved.

2. The panoramic scanning infrared detection system for pipe cracks according to claim 1 is characterized in that: The dynamic temperature field of the full-circumferential curved surface inside the tested pipeline is collected by a small infrared thermal imager installed above the optical fiber coupler lens barrel, thereby realizing full-circumferential annular laser scanning infrared detection of structural defects on the pipeline curved surface.

3. The panoramic scanning infrared detection system for pipe cracks according to claim 1 is characterized in that: The movable lens can move back and forth along its own axis.

4. The panoramic scanning infrared detection system for pipe cracks according to claim 1 is characterized in that: The axicon and the convex lens are coaxial inside the optical fiber coupler tube.

5. The panoramic scanning infrared detection system for pipe cracks according to claim 1 is characterized in that: The cone angle of the conical reflector is at least greater than 90°.

6. The panoramic scanning infrared detection system for pipe cracks according to claim 1 is characterized in that: The photothermal excitation collection system and the reflection scanning system maintain a fixed distance.

7. A detection method for a pipe crack panoramic scanning infrared detection system according to any one of claims 1 to 6, characterized in that: include: Fix the photothermal excitation collection system and the reflection scanning system in the center of the tube, and keep the rotatable lens of the photothermal excitation collection system and the center of the conical reflector of the reflection scanning system coaxially arranged; The control computer synchronously starts the small infrared thermal imager sampling and the laser generating laser to the laser optical fiber; The Bessel beam introduced by the laser fiber enters the fiber coupler barrel, passes through the first axis cone mirror, convex lens and second axis cone mirror, and is shaped into an annular light spot, which is reflected by the cone reflector to generate a stationary annular laser beam along the pipe axis direction and irradiate the inner wall of the pipe curved surface. Adjust the distance d between the convex lens and the second axicon mirror, and adjust the diameter R of the annular light spot projected onto the conical reflector; The numerical aperture NA of the second axicon is adjusted to control the ring width D of a full circumferential scanning ring laser irradiated on the inner wall of the pipeline; The photothermal excitation acquisition system and the reflection scanning system are controlled to move and scan along the pipeline axis, and the rotating full-circumferential line scanning laser performs dynamic scanning and thermal excitation heating on the inner wall of the pipeline; The small infrared thermal imager collects the transient temperature field of the curved surface structure inside the pipe in all directions through the infrared reflection light path of the conical reflector, and transmits the image back to the control computer to realize the all-round circular laser scanning infrared detection of the defects of the overall curved surface structure of the pipeline.

8. The method for detecting pipe cracks by panoramic scanning infrared according to claim 7, characterized in that: The relationship between the distance d between the convex lens and the second axis conic mirror and the diameter R of the annular light spot projected onto the conical reflector satisfies the following conditions: Keep the axis cone angle α of the first axicon mirror, the axis cone angle θ of the cone reflector and the focal length f of the convex lens unchanged, fix the numerical aperture NA of the second axicon mirror, and the distance d between the convex lens and the second axicon mirror is proportional to the annular spot diameter R of the cone reflector; then the annular width D of the full circumferential scanning annular laser remains unchanged; The relationship between the numerical aperture NA of the second axis conic mirror and the ring width D of the ring laser for adjusting the full circumferential scanning satisfies the following conditions: Keep the axis cone angle α of the first axicon mirror, the axis cone angle θ of the conical reflector and the focal length f of the convex lens unchanged, fix the distance d between the convex lens and the second axicon mirror, the numerical aperture NA of the second axicon mirror is inversely proportional to the ring width D of the full-circle scanning ring laser, then the annular spot diameter R of the conical reflector remains unchanged.

9. The method for detecting pipe cracks by panoramic scanning infrared according to claim 7, characterized in that: The wavelength of the thermal excitation laser is 980-1064nm, and the infrared thermal imager collection wavelength is 7-14μm.

10. An application of the panoramic scanning infrared detection system for pipe cracks according to any one of claims 1 to 7 in defect damage detection of water supply, petroleum and heating pipelines.

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