A method for eddy current inspection of a pipe

Abstract

The application discloses a kind of pipe eddy flaw detection methods, it is characterized in that, including the following steps: S1, using straightening equipment to the pipe to be detected is straightened, so that the pipe to be detected is less than or equal to 1.5 millimeter / meter bending degree;S2, the guide sleeve specification is selected 2~3 millimeter than the pipe to be detected outer diameter, and the selected probe specification is consistent with guide sleeve specification, and ensure that the filling factor of probe is greater than or equal to 85%;S3, the pipe to be detected is steadily passed through eddy flaw detection equipment, and completes eddy flaw detection.The application has the advantages that the length of pipe two end flaw detection blind area can be shortened, and production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of steel pipe manufacturing technology, and in particular to an eddy current flaw detection method for pipes. Background Technology

[0002] Currently, cold-drawn seamless steel pipe manufacturers require all boiler tubes, including low- and medium-pressure boiler tubes, high-pressure boiler tubes, high-pressure fertilizer tubes, and petroleum cracking tubes, to undergo eddy current testing before leaving the factory. This involves inspecting the surface and subsurface of the pipe to remove substandard products and ensure the quality of the pipes used. For pipes with an outer diameter of 180 mm or less, a through-type coil eddy current testing system is generally used. For pipes with an outer diameter greater than 180 mm, either a rotating point probe / flat coil or a fixed point probe / flat coil eddy current testing system can be used. However, regardless of the eddy current testing system used or the specifications of the pipe being tested, there are always undetectable areas at both ends of each steel pipe, i.e., blind spots. According to the "Comprehensive Performance Test Method for Automatic Eddy Current Testing Systems of Steel Pipes and Bars" (YB / T 4083-2020), the undetectable area at the ends of eddy current testing systems using through-type coils should not exceed 200 mm. According to incomplete statistics, the outer diameter of low- and medium-pressure boiler tubes and high-pressure boiler tubes used is more than 180 mm or less. This means that eddy current testing of low- and medium-pressure and high-pressure boilers uses the through-type coil method, which has a 200 mm blind zone at both ends of the tube.

[0003] Because the pipes in the flaw detection blind zone have not undergone flaw detection, it is necessary to cut off the blind zone to ensure quality. This means that a total length of 400mm needs to be cut off from both ends of each pipe, significantly reducing the yield and thus affecting production costs and revenue. Taking the commonly used 20G material high-pressure boiler tube with a central specification of 51*5*10000 mm as an example, approximately 40 kg more waste is added for every ton of finished product produced. For every 10,000 tons of such high-pressure pipes produced, revenue is reduced by approximately 1.34 million yuan. Therefore, how to shorten the length of the flaw detection blind zone at both ends of the pipe has become an urgent problem to be solved. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to provide a pipe eddy current flaw detection method that can shorten the length of the flaw detection blind zone at both ends of the pipe and help reduce production costs.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] An eddy current testing method for pipes, characterized by comprising the following steps:

[0007] S1. Use straightening equipment to straighten the pipe to be inspected so that the curvature of the pipe to be inspected is less than or equal to 1.5 mm / m.

[0008] S2. The selected guide sleeve specification is 2-3 mm larger than the outer diameter of the pipe to be inspected, and the selected probe specification is consistent with the guide sleeve specification, and the probe's fill factor is greater than or equal to 85%;

[0009] S3. Smoothly pass the pipe to be inspected through the eddy current testing equipment to complete the eddy current testing.

[0010] Furthermore, before flaw detection, an eddy current flaw detection system with the following structure is obtained, including an eddy current flaw detection device and conveyor rollers connected to both ends of the eddy current flaw detection device along the pipe conveying direction. The conveyor rollers include multiple V-shaped conveyor rollers arranged at intervals, and the V-shaped conveyor rollers rotate synchronously through a drive motor connected to them.

[0011] Furthermore, the outer diameter of the eddy current flaw detector is 38-114 mm, the slope angle of the V-shaped conveyor roller is 120°, and the bottom corner radius of the slope is 5 mm.

[0012] Furthermore, the V-shaped conveyor roller is made of 45 steel.

[0013] Furthermore, the input end of the eddy current testing equipment is provided with an auxiliary conveying mechanism. The auxiliary conveying mechanism includes a guide mechanism arranged along the pipe conveying direction and a slide seat slidably arranged on the guide mechanism. The guide mechanism also has a parallel linear drive mechanism. The drive end of the linear drive mechanism is connected to the slide seat and can drive the slide seat to move at a constant speed along the guide mechanism. A retractable baffle is vertically arranged on the slide seat. The height of the baffle in the vertical state matches the height of the pipe to be tested on the V-shaped conveying roller, and the axial projections of the baffle and the pipe to be tested on the V-shaped conveying roller overlap. A retraction drive mechanism for driving the baffle to retract is provided between the slide seat and the baffle. The maximum distance between the baffle and the eddy current testing equipment is greater than the length of the pipe to be tested, and the sum of the minimum distance between the baffle and the eddy current testing equipment and the length of the eddy current testing equipment is less than the length of the pipe to be tested.

[0014] During flaw detection, the baffle on the auxiliary conveying mechanism is first moved away from the eddy current flaw detection equipment, and the baffle is retracted downward by the retraction drive mechanism. The pipe to be tested is conveyed between the baffle and the eddy current flaw detection equipment by the V-shaped conveying roller. The baffle is then changed to a vertical state by the retraction drive mechanism, reducing the conveying speed of the V-shaped conveying roller. The baffle is then driven to move at a constant speed along the guide mechanism by the linear drive mechanism, pushing the pipe to be tested into the eddy current flaw detection equipment at a constant speed. After the baffle has moved to its maximum stroke, the conveying speed of the V-shaped conveying roller is restored until the flaw detection of the pipe to be tested is completed.

[0015] In the above method, since the maximum distance between the baffle and the eddy current testing equipment is greater than the length of the pipe to be tested, when the pipe to be tested is located between the baffle and the eddy current testing equipment, the end of the pipe has not yet entered the eddy current testing equipment. At this time, the linear drive mechanism pushes the pipe to be tested into the eddy current testing equipment at a constant speed through the baffle. Compared with using the synchronous rolling of multiple V-shaped conveying rollers to transport the pipe to be tested into the eddy current testing equipment, the use of the linear drive mechanism can make the transport of the pipe more stable and the control difficulty lower, thereby reducing the length of the blind zone at the end of the pipe.

[0016] Furthermore, each end of the eddy current flaw detection equipment is provided with an auxiliary conveying mechanism, and the baffle is provided with an electromagnet for adsorbing the pipe to be tested.

[0017] During flaw detection, the baffles on both auxiliary conveying mechanisms are first moved towards the direction of the incoming material of the pipe to be tested. The baffle at the input end is retracted downward by the retraction drive mechanism, while the baffle at the output end is kept upright by the retraction drive mechanism. At the input end, the baffle attracts the pipe to be tested by an electromagnet and pushes the pipe into the eddy current flaw detection equipment at a constant speed until the baffle reaches its maximum stroke and the electromagnet is disconnected. The conveying speed of the V-shaped conveying roller is restored, and the pipe to be tested continues to be conveyed through the V-shaped conveying roller for flaw detection of the middle section of the pipe until the pipe to be tested approaches the baffle at the output end. The baffle at the output end attracts the pipe to be tested by an electromagnet and reduces the conveying speed of the V-shaped conveying roller. The baffle pulls the pipe to be tested out of the eddy current flaw detection equipment at a constant speed, completing the flaw detection.

[0018] In this way, the eddy current testing equipment is used for both the end of the pipe to be tested and the end of the pipe, which can ensure that the testing at the end of the pipe is more stable and help reduce the blind zone at the end.

[0019] Furthermore, the guiding mechanism consists of two guide rods arranged along the pipe conveying direction, with the two guide rods facing each other horizontally; the slide has two guide holes corresponding to the guide rods, and the two guide rods pass through the guide holes respectively; the linear drive mechanism includes a lead screw arranged parallel between the two guide rods and a lead screw nut that cooperates with it, the lead screw nut is fixedly installed on the slide, and one end of the lead screw is connected to a stepper motor.

[0020] In this way, the stepper motor drives the lead screw to rotate, and the lead screw nut, which is matched with it, drives the slide to move at a constant speed along the guide rod, making the speed control more stable.

[0021] Furthermore, the slide has a vertically through guide groove, and the bottom of the baffle has a guide post that slides with the guide groove. The retraction drive mechanism is a cylinder vertically arranged below the slide, and the piston rod of the cylinder passes through the slide and is connected to the guide post of the baffle.

[0022] In this way, the retraction and extension of the baffle can be achieved quickly through the cylinder.

[0023] In summary, the present invention has the advantages of shortening the length of the flaw detection blind zone at both ends of the pipe, which is beneficial to reducing production costs. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the eddy current flaw detection system in this embodiment.

[0025] Figure 2 for Figure 1 A schematic diagram of the auxiliary conveying mechanism.

[0026] Figure 3 This is a schematic diagram of the V-shaped conveyor roller. Implementation

[0027] The present invention will be further described in detail below with reference to the embodiments.

[0028] In specific implementation: A pipe eddy current flaw detection method includes the following steps: Before flaw detection, the pipe to be tested is straightened using a straightening device so that the curvature of the pipe to be tested is less than or equal to 1.5 mm / m; for the specifications of the pipe to be tested, the selected guide sleeve is 2-3 mm larger than the outer diameter of the pipe to be tested, and the selected probe is consistent with the guide sleeve, ensuring that the probe's filling coefficient is greater than or equal to 85%; and the pipe to be tested is smoothly passed through the eddy current flaw detection device to complete the eddy current flaw detection.

[0029] To ensure that the pipe to be inspected can pass smoothly through the eddy current testing equipment, this embodiment also employs an eddy current testing system with the following structure: Figure 1 and Figure 2 As shown, the device includes an eddy current testing device 1 and a conveying roller conveyor 2 connected to both ends of the eddy current testing device 1 along the pipe conveying direction. The conveying roller conveyor 2 includes a plurality of V-shaped conveying rollers arranged at intervals. The V-shaped conveying rollers rotate synchronously through a drive motor connected to them.

[0030] The eddy current flaw detection equipment 1 has an auxiliary conveying mechanism 3 at each end. Each auxiliary conveying mechanism 3 includes a guide mechanism 31 arranged along the pipe conveying direction and a slide block 32 slidably mounted on the guide mechanism 31. The guide mechanism 31 also has a parallel linear drive mechanism 33, the drive end of which is connected to the slide block 32 and can drive the slide block 32 to move uniformly along the guide mechanism 31. A downwardly retractable baffle 34 is vertically mounted on the slide block 32. The height of the vertically positioned tube matches the height of the tube to be inspected on the V-shaped conveyor roller, and the axial projections of the baffle 34 and the tube to be inspected on the V-shaped conveyor roller overlap; a shrinkage drive mechanism 35 for driving the baffle 34 to shrink is provided between the slide block 32 and the baffle 34; the maximum distance between the baffle 34 and the eddy current testing device 1 is greater than the length of the tube to be inspected, and the sum of the minimum distance between the baffle 34 and the eddy current testing device 1 and the length of the eddy current testing device 1 is less than the length of the tube to be inspected.

[0031] In order to allow the baffle 34 at the output end to pull the pipe to be tested out of the eddy current testing equipment 1 at a uniform speed, the baffle 34 is provided with an electromagnet for attracting the pipe to be tested, and the electromagnet is located on the side of the baffle 34 away from the eddy current testing equipment 1.

[0032] In this embodiment, the guiding mechanism 31 consists of two guide rods arranged along the pipe conveying direction, with the two guide rods facing each other in the horizontal direction; the slide 32 has two guide holes corresponding to the guide rods, and the two guide rods pass through the guide holes respectively; the linear drive mechanism 33 includes a lead screw arranged parallel between the two guide rods and a lead screw nut that cooperates with it, the lead screw nut is fixedly installed on the slide 32, and one end of the lead screw is connected to a stepper motor.

[0033] The slide block 32 has a vertically extending guide groove, and the bottom of the baffle 34 has a guide post that slides in conjunction with the guide groove. The retraction drive mechanism 35 is a cylinder vertically arranged below the slide block 32. The piston rod of the cylinder passes through the slide block 32 and is connected to the guide post of the baffle 34. In this embodiment, to avoid interference between the lead screw and the guide post, the guide post also has a clearance groove corresponding to the lead screw.

[0034] In addition, in this embodiment, in order to make the speed of the V-shaped conveying rollers conveying the pipe to be inspected more stable, all V-shaped conveying rollers between the two baffles 34 are driven by independent drive motors.

[0035] When using the above-mentioned equipment, the following steps shall be taken during flaw detection:

[0036] 1. First, move the baffles 34 on both auxiliary conveying mechanisms 3 toward the incoming direction of the pipe to be inspected. At the same time, retract the baffle 34 at the input end downward through the retraction drive mechanism 35, and keep the baffle 34 at the output end in an upright state through the retraction drive mechanism 35.

[0037] 2. Flaw detection at the beginning of the pipe to be inspected: At the input end, the pipe to be inspected is conveyed to the space between the baffle 34 and the eddy current testing equipment 1 via a V-shaped conveying roller. The baffle 34 is changed to a vertical position by the shrinking drive mechanism 35, reducing the conveying speed of the V-shaped conveying roller (lower than the moving speed of the baffle). The baffle 34 is driven to move at a constant speed along the guide mechanism 31 by the linear drive mechanism 33. The baffle 34 attracts the pipe to be inspected by an electromagnet and pushes the pipe to be inspected into the eddy current testing equipment 1 at a constant speed.

[0038] 3. Mid-section flaw detection of the pipe to be inspected: After the baffle 34 at the input end moves to the maximum stroke, the electromagnet is disconnected or turned off, the conveying speed of the V-shaped conveying roller is restored, and the pipe to be inspected continues to be conveyed through the V-shaped conveying roller for mid-section flaw detection.

[0039] 4. Flaw detection at the tail end of the pipe to be tested: After the pipe to be tested approaches the baffle 34 at the output end, the electromagnet on the baffle 34 at the output end is turned on. The baffle 34 attracts the pipe to be tested through the electromagnet and reduces the conveying speed of the V-shaped conveying roller (lower than the moving speed of the baffle 34). The pipe to be tested is pulled out of the eddy current flaw detection equipment 1 at a uniform speed through the baffle 34, and the flaw detection is completed.

[0040] In the above method, since the maximum distance between the baffle and the eddy current testing equipment is greater than the length of the pipe to be tested, when the pipe to be tested is located between the baffle and the eddy current testing equipment, the end of the pipe has not yet entered the eddy current testing equipment. At this time, the linear drive mechanism pushes the pipe to be tested into the eddy current testing equipment at a constant speed through the baffle. Compared with using the synchronous rolling of multiple V-shaped conveying rollers to transport the pipe to be tested into the eddy current testing equipment, the use of the linear drive mechanism can make the transport of the pipe more stable and the control difficulty lower, thereby reducing the length of the blind zone at the end of the pipe.

[0041] To verify whether the above-mentioned eddy current flaw detection method can shorten the flaw detection blind zone, the following steps were used for testing:

[0042] 1. Fabrication of the test tube: In accordance with the requirements of GB / T 11260-2017, add two consecutive Φ5 mm through holes (or transverse grooves) at positions 100-200 mm from each end and close to 100 mm from each end on a conventional eddy current test tube. The two through holes are spaced 20 mm apart. This serves as the test tube and must be inspected and certified by a legal metrology institution.

[0043] 2. In accordance with the requirements of the "Comprehensive Performance Test Method of Automatic Eddy Current Testing System for Steel Pipes and Bars" (YB / T 4083-2020), adjust the circumferential sensitivity difference and signal-to-noise ratio of the equipment to the specified range according to the outer diameter of the pipe.

[0044] 3. When the eddy current flaw detection method of this application is used to inspect the sample tube, all flaws within 100-200 mm of the end of the sample tube can be reported, indicating that this method can shorten the original flaw detection blind zone from 200 mm to 100 mm.

[0045] Taking the commonly used 20G material high-pressure boiler tube with a standard diameter of 51*5*10000 mm as an example, if the flaw detection blind zone is 200 mm, the length of each tube before cutting should be 10400 mm, and each tube needs to be cut by 400 mm. However, by using the flaw detection method of this invention, since the flaw detection blind zone is shortened to 100 mm, the length of each tube before cutting should be 10200 mm, and each tube only needs to be cut by 200 mm. For every ton of finished product produced, about 20 kg less waste will be generated compared to the original method (200 mm flaw detection blind zone). For every 10,000 tons of such high-pressure tubes produced, the loss will be reduced by about 670,000 yuan.

[0046] In addition, in this embodiment, the outer diameter of the eddy current flaw detection device 1 is 38-114mm, the slope angle of the V-shaped conveyor roller is 120°, the bottom corner radius of the slope is 5mm, and the material of the V-shaped conveyor roller is 45 steel.

[0047] Considering that V-shaped conveyor rollers will wear down after use, causing them to bounce during the conveying of steel pipes, affecting the accuracy of flaw detection and the length of the flaw detection blind zone, this embodiment further employs a V-shaped conveyor roller with the following structure, such as... Figure 3As shown, the assembly includes two axially symmetrically arranged rollers 21 and an intermediate sleeve 22 coaxially disposed between the two rollers 21. The diameter of each roller 21 gradually decreases towards the intermediate sleeve 22, forming a frustum shape. The diameter of the intermediate sleeve 22 gradually decreases from both ends towards the center, forming a V-shaped conveying groove 23. Both ends of the intermediate sleeve 22 are respectively fitted to the corresponding rollers 21, and the diameters at the connection points of the rollers 21 and the intermediate sleeve 22 are consistent. During installation, the rollers and the intermediate sleeve need to be coaxially connected. Both the rollers 21 and the intermediate sleeve 22 have coaxially through mounting holes 24, and keyways 25 are axially through the mounting holes 24. Simultaneously, the end of each roller 21 facing away from the intermediate sleeve 22 has a radially protruding flange. Considering the inherent characteristics of materials such as round steel, the rollers need to rotate to provide a reverse frictional force to the material, enabling forward or backward movement. The surface of the intermediate sleeve needs to have a certain roughness to allow for material transport through friction, and it also needs to have better wear resistance, corrosion resistance, and fatigue resistance. The requirements for the roller body material are lower; therefore, in implementation, the intermediate sleeve 22 can be made of 45 steel, and the roller body 1 can be made of cast iron. Simultaneously, based on the material size, the included angle of the V-shaped conveying trough 23 is set to 120° to accommodate the material.

[0048] To facilitate the installation or replacement of the roller body and intermediate sleeve, the roller body 21 has a protruding limiting block on the side near the intermediate sleeve 22. The intermediate sleeve 22 has a limiting hole that matches the limiting block, so that the limiting block fits into the limiting hole when the keyways 25 on the roller body 21 and the intermediate sleeve 22 are axially aligned. In this way, with the limiting block and the limiting hole in the correct alignment, the keyways on the roller body and the intermediate sleeve are aligned, which improves the speed of installation or replacement.

[0049] In implementation, the roller body can be die-cast. The roller body 21 has a coaxially arranged annular groove on the side away from the intermediate sleeve 22. The side of the annular groove facing the mounting hole 24 is cylindrical, and the side away from the mounting hole 24 is conical. The diameter of the conical surface gradually decreases along the direction towards the intermediate sleeve 22. This saves materials and reduces costs.

[0050] In the above scheme, the roller is divided into three parts. When the roller is installed on the shaft, the roller body and the intermediate sleeve can be respectively fitted onto the shaft through the mounting holes. At this time, the key on the shaft is inserted into the mounting holes and keyway to achieve coaxial rotation. The round steel or pipe materials are always in the V-shaped conveying trough and the conveying operation is completed through the V-shaped conveying trough on the intermediate sleeve. During the conveying process, the material is in contact with the intermediate sleeve and does not directly contact the roller body. After the intermediate sleeve is worn and affects the use, it can be removed and replaced.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for eddy current testing of pipes, characterized in that, Includes the following steps: S1. Use straightening equipment to straighten the pipe to be inspected so that the curvature of the pipe to be inspected is less than or equal to 1.5 mm / m. S2. The selected guide sleeve specification is 2-3 mm larger than the outer diameter of the pipe to be inspected, and the selected probe specification is consistent with the guide sleeve specification, and the probe's fill factor is greater than or equal to 85%; S3. Smoothly pass the pipe to be tested through the eddy current testing equipment to complete the eddy current testing; Before flaw detection, an eddy current flaw detection system with the following structure is obtained, including an eddy current flaw detection device (1) and a conveying roller conveyor (2) connected to both ends of the eddy current flaw detection device (1) along the pipe conveying direction. The conveying roller conveyor (2) includes a plurality of V-shaped conveying rollers arranged at intervals. The V-shaped conveying rollers rotate synchronously through a drive motor connected to them. The input end of the eddy current flaw detection equipment (1) is provided with an auxiliary conveying mechanism (3). The auxiliary conveying mechanism (3) includes a guide mechanism (31) arranged along the pipe conveying direction and a slide (32) slidably arranged on the guide mechanism (31). The guide mechanism (31) also has a parallel linear drive mechanism (33). The drive end of the linear drive mechanism (33) is connected to the slide (32) and can drive the slide (32) to move at a constant speed along the guide mechanism (31). A retractable baffle (34) is vertically arranged on the slide (32). 34) The height in the vertical state matches the height of the pipe to be inspected on the V-shaped conveyor roller, and the projections of the baffle (34) and the pipe to be inspected on the V-shaped conveyor roller overlap in the axial direction; a shrinkage drive mechanism (35) for driving the baffle (34) to shrink is provided between the slide (32) and the baffle (34); the maximum distance between the baffle (34) and the eddy current testing device (1) is greater than the length of the pipe to be inspected, and the sum of the minimum distance between the baffle (34) and the eddy current testing device (1) and the length of the eddy current testing device (1) is less than the length of the pipe to be inspected; The eddy current flaw detection equipment (1) is provided with an auxiliary conveying mechanism (3) at each end, and the baffle (34) is provided with an electromagnet for adsorbing the pipe to be tested. During flaw detection, the baffles (34) on both auxiliary conveying mechanisms (3) are first moved toward the incoming direction of the pipe to be inspected; the baffle (34) at the input end is retracted downwards by the retraction drive mechanism (35), and the baffle (34) at the output end is kept upright by the retraction drive mechanism (35); at the input end, the baffle (34) attracts the pipe to be inspected by an electromagnet and pushes the pipe to be inspected into the eddy current flaw detection equipment (1) at a uniform speed until the pipe is inspected. When the baffle (34) reaches its maximum stroke, the electromagnet is disconnected; the conveying speed of the V-shaped conveying roller is restored, and the pipe to be inspected continues to be conveyed through the V-shaped conveying roller for inspection of the middle section of the pipe until the pipe to be inspected approaches the baffle (34) at the output end. The baffle (34) at the output end attracts the pipe to be inspected through the electromagnet and reduces the conveying speed of the V-shaped conveying roller. The pipe to be inspected is pulled out of the eddy current inspection equipment (1) at a uniform speed through the baffle (34) to complete the inspection.

2. The eddy current testing method for pipes as described in claim 1, characterized in that, The outer diameter of the eddy current flaw detector (1) is 38-114 mm, the slope angle of the V-shaped conveyor roller is 120°, and the bottom corner radius of the slope is 5 mm.

3. The eddy current testing method for pipes as described in claim 2, characterized in that, The V-shaped conveyor roller is made of 45 steel.

4. The eddy current testing method for pipes as described in claim 1, characterized in that, The guiding mechanism (31) consists of two guide rods arranged along the pipe conveying direction, with the two guide rods facing each other in the horizontal direction; the slide (32) has two guide holes corresponding to the guide rods, with the two guide rods passing through the guide holes respectively; the linear drive mechanism (33) includes a lead screw arranged parallel between the two guide rods and a lead screw nut that is fitted together, the lead screw nut being fixedly installed on the slide (32), and one end of the lead screw being connected to a stepper motor.

5. The eddy current testing method for pipes as described in claim 1, characterized in that, The slide (32) has a vertically through guide groove, and the bottom of the baffle (34) has a guide post that slides with the guide groove. The retraction drive mechanism (35) is a cylinder that is vertically arranged below the slide (32). The piston rod of the cylinder passes through the slide (32) and is connected to the guide post of the baffle (34).

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