A method for manufacturing an ultra-large-diameter thin-walled seamless steel pipe

Abstract

The present application discloses a manufacturing method for an ultra-large diameter thin-walled seamless steel pipe, which belongs to the field of machining. The method includes the following steps: S1: Heat-treat the steel pipe to be processed into a primary steel pipe with an outer diameter of D 初 ; S2: Heat-treat the primary steel pipe to make the strength of the steel pipe reach a certain value ΔS exceeding S 名义 , and satisfy the following relationship: ΔS ≥ [(1 - D_initial / D) × 100 × k] MPa; S3: Then, use an induction heating device to thermally expand the steel pipe to obtain the final finished product. The specifications of the finished product are yield strength ≥ 450 MPa, outer diameter = 813 - 1200 mm, and t / D ≤ 0.03. The beneficial effect of the present application is to provide a manufacturing method for an ultra-large diameter thin-walled seamless steel pipe that avoids the finished product from becoming elliptical or concave.

Description

Technical Field

[0001] This application relates to the field of machining technology, and more specifically, to a method for manufacturing ultra-large diameter thin-walled seamless steel pipes. Background Technology

[0002] For large-diameter, thin-walled steel pipes, welded pipes made from steel plates are generally easier to manufacture, such as large-diameter spiral welded pipes and straight seam welded pipes. However, the weld seam of welded pipes is often the source of failure and cracking. Therefore, for applications with harsh operating environments and high safety requirements, such as the transportation of oil and gas containing hydrogen sulfide, submarine pipelines, and cryogenic pipelines, seamless steel pipes must be used to ensure the safe operation of the pipeline.

[0003] For ultra-large diameter seamless steel pipes with an outer diameter of 813-1200mm, heating, holding, and heat treatment are generally carried out in a bogie hearth furnace. For thin-gauge steel pipes with a t / D (wall thickness to outer diameter) ≤0.03, during austenitization at high temperatures in the bogie hearth furnace, the steel pipe gradually becomes elliptical or even concave due to its lower strength, thinner wall, and larger outer diameter (greater mass). This significantly exceeds the outer diameter tolerance, making it difficult to manufacture seamless steel pipes of this specification. Some manufacturers use the method of adding internal support frames to the pipe ends, but since the middle of long steel pipes remains elliptical, this does not solve the fundamental problem. Summary of the Invention

[0004] The summary section of this application is intended to provide a brief overview of the concepts, which will be described in detail in the detailed description section below. This summary section is not intended to identify key or essential features of the claimed technical solutions, nor is it intended to limit the scope of the claimed technical solutions.

[0005] To address the technical problems mentioned in the background section above, some embodiments of this application provide a method for manufacturing ultra-large diameter thin-walled seamless steel pipes, including the following steps:

[0006] S1: Heat treat the steel pipe to be processed to a diameter of D. 初 Primary steel pipes;

[0007] S2: The primary steel pipe undergoes heat treatment to increase its strength beyond that of S. 名义 A certain value ΔS, satisfying the following relationship: ΔS≥[(1-D_initial / D)×100×k]MPa;

[0008] S3: The steel pipe is then thermally expanded using induction heating equipment to obtain the final product. The specifications of the finished product are: yield strength ≥ 450MPa, outer diameter = 813-1200mm, and t / D ≤ 0.03.

[0009] The induction heating equipment includes a thermal expansion mechanism, a propulsion mechanism, a wall shrinking mechanism, and a PLC control console. The thermal expansion mechanism induction heats the steel pipe during the expansion process. The wall shrinking mechanism is used to control the t / D of the finished steel pipe to be ≤0.03 after thermal expansion. The maximum temperature T of the induction-heated steel pipe is ≤[Ac1-80℃+(1-D)]. 初 / D)×1000℃].

[0010] The pushing speed of the propulsion mechanism on the steel pipe is V≤[100-(1-D]]. 初 / D)×1000]mm / min.

[0011] The heat treatment in S1 is hot rolling or hot expansion, and the resulting D 初 =0.95-0.98D.

[0012] The heat treatment in S2 is either normalizing or quenching and tempering. For normalizing, k is 5, and for quenching and tempering, k is 10. 名义 This is the nominal strength.

[0013] The propulsion mechanism includes a feeding roller, a discharging roller, and multiple pushing cylinders. The thermal expansion mechanism and the wall shrinking mechanism are located between the feeding roller and the discharging roller, and the wall shrinking mechanism is located behind the thermal expansion mechanism. The thermal expansion mechanism includes a thermal expansion rod, a thermal expansion head detachably connected to the end of the thermal expansion rod, and an induction coil. The thermal expansion head passes through the induction coil. The wall shrinking mechanism includes a base and two sets of wall shrinking components on the base. The two sets of wall shrinking components are arranged one in front of the other along the propulsion direction of the steel pipe. After the steel pipe is processed by the two sets of wall shrinking components, the t / D reaches ≤ 0.03.

[0014] The wall-shrinking assembly includes an inner mold, an outer mold, and a bracket for positioning the outer mold. The inner mold is disc-shaped and has a threaded connection. The outer mold has a circular groove, and there is a gap between the outer wall of the inner mold and the circular groove to allow the steel pipe to pass through. During the advancement process of the pushing mechanism, the steel pipe is thermally expanded by the thermal expansion mechanism. After that, the steel pipe passes through the gap and its wall thickness becomes thinner under the extrusion of the inner mold and the outer mold.

[0015] The bracket is provided with multiple connectors, each connector having multiple positioning pins spaced apart. Multiple positioning holes are provided at the four corners of the outer mold, with the spacing between the positioning holes being the same as the spacing between the positioning pins. Two bolts are provided on the upper and lower sides of the bracket, and two threaded holes are provided on the upper and lower sides of the outer mold. The lower part of the bolt can pass through the bracket and be screwed into the threaded hole. In step S3, before heat expansion, the corresponding inner mold and outer mold also need to be assembled. The steps are as follows: According to the inner diameter and wall thickness requirements of the finished product, select the corresponding inner mold and outer mold, screw the inner mold onto the heat expansion head, and then adjust the outer mold to a position where the gap between it and the inner mold is equal to the wall thickness.

[0016] The wall-shrinking mechanism also includes rollers located at the lower part of the support, slide rails on the base that cooperate with the rollers, a fixing frame on the base that cooperates with the support, and an outer mold calibration component. The outer mold calibration component includes a ring on one of the inner molds, a pneumatic clamp inside the ring, and multiple calibration arms on the pneumatic clamp. The side wall of the ring is provided with a strip groove. The operation of adjusting the outer mold to a position where the gap between it and the inner mold is equal to the wall thickness is as follows: After screwing the two inner molds together, screw them onto the hot expansion head with the side with the pneumatic clamp facing outward. Then, put the outer mold over the calibration arm. The pneumatic clamp drives the calibration arm to move and press against the inner wall of the outer mold. Then, move the support so that the positioning pin on the support is inserted into the positioning hole, and then tighten the bolt. Subsequently, the pneumatic clamp drives the calibration arm to move back, and the moving support drives the outer mold to the position of the inner mold. Then, the position of the moving support is fixed by the fixing frame.

[0017] The beneficial effect of this application is that it provides a method for manufacturing ultra-large diameter thin-walled seamless steel pipes with an outer diameter of 813-1200 mm and t / D≤0.03. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of the application and to make other features, objects, and advantages of the application more apparent. The illustrative embodiments and descriptions of this application are used to explain the application and do not constitute an undue limitation of the application.

[0019] Furthermore, throughout the accompanying drawings, the same or similar reference numerals denote the same or similar elements. It should be understood that the drawings are schematic, and the elements are not necessarily drawn to scale.

[0020] In the attached diagram:

[0021] Figure 1 This is an overall schematic diagram based on an embodiment of this application;

[0022] Figure 2 This is a schematic diagram of the thermal expansion mechanism and the wall contraction mechanism in this application;

[0023] Figure 3 yes Figure 2 The front view;

[0024] Figure 4 This is a schematic cross-sectional view of the mating of the outer mold and the bracket in this application;

[0025] Figure 5 This is a schematic diagram of the internal mold in this application;

[0026] Figure 6 This is a schematic diagram of the structure of the outer mold in this application. Detailed Implementation

[0027] Embodiments of this disclosure will now be described in more detail with reference to the accompanying drawings. While some embodiments of this disclosure are shown in the drawings, it should be understood that this disclosure can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this disclosure. It should be understood that the accompanying drawings and embodiments of this disclosure are for illustrative purposes only and are not intended to limit the scope of protection of this disclosure.

[0028] It should also be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings. Unless otherwise specified, the embodiments and features described in this disclosure can be combined with each other.

[0029] It should be noted that the concepts of "first" and "second" mentioned in this disclosure are used only to distinguish different devices, modules or units, and are not used to limit the order of functions performed by these devices, modules or units or their interdependencies.

[0030] It should be noted that the terms "a" and "a plurality of" used in this disclosure are illustrative rather than restrictive, and those skilled in the art should understand that, unless otherwise expressly indicated in the context, they should be understood as "one or more".

[0031] This disclosure will now be described in detail with reference to the accompanying drawings and embodiments.

[0032] A method for manufacturing ultra-large diameter thin-walled seamless steel pipes includes the following steps:

[0033] S1: Hot-roll or hot-expand the steel pipe to be processed to a diameter of D. 初 The primary steel pipe, and the D obtained from processing 初 =0.95-0.98D;

[0034] S2: The primary steel pipe undergoes normalizing or quenching and tempering treatment to achieve a strength exceeding that of S. 名义 Let S be a certain value ΔS, satisfying the following relationship: ΔS ≥ [(1-Dinitial / D) × 100 × k] MPa; where S 名义 For nominal strength, k is 5 during normalizing and 10 during quenching and tempering.

[0035] S3: The steel pipe is then thermally expanded using induction heating equipment to obtain the final product. The specifications of the finished product are: yield strength ≥ 450MPa, outer diameter = 813-1200mm, and t / D ≤ 0.03.

[0036] High-strength and high-toughness seamless steel pipes are produced by processing hot-rolled or hot-expanded primary steel pipes—normalizing or quenching and tempering heat treatment—hot expansion into finished steel pipes. Firstly, the outer diameter of the primary steel pipe has a significant impact on the performance of the final finished steel pipe. A large difference in outer diameter between the primary and finished steel pipes (D...) 初 If the diameter ratio ( / D < 0.95) is too large after heat treatment, it will significantly damage the mechanical properties of the hot-expanded steel pipe, leading to a decrease in strength or toughness. The difference in outer diameter between the primary steel pipe and the finished steel pipe is too small (D... 初 If the diameter (D > 0.98) is too small after heat treatment, the elliptical or concave shape defects in the outer diameter caused by heat treatment cannot be corrected by using a hot expansion mandrel. Therefore, the outer diameter D of the primary steel pipe is... 初 =0.95-0.98D (D is the outer diameter of the finished steel pipe) is most suitable.

[0037] Secondly, for normalizing or quenching and tempering heat treatments, to ensure that the steel pipe's strength still meets the minimum nominal strength requirement after hot expansion, the heat treatment should provide a certain strength margin. For normalized heat-treated steel pipes, subsequent hot expansion has a relatively small impact on their performance, thus the strength margin is relatively small. For quenching and tempering heat-treated steel pipes, subsequent hot expansion has a relatively large impact on their performance, thus the strength margin is relatively large.

[0038] like Figure 1-6 As shown, the induction heating equipment includes a thermal expansion mechanism, a propulsion mechanism, a wall shrinking mechanism, and a PLC control console. The thermal expansion mechanism induction heats the steel pipe during the expansion process. The wall shrinking mechanism is used to control the t / D of the finished steel pipe to be ≤0.03 after thermal expansion. The maximum temperature T of the induction-heated steel pipe is ≤[Ac1-80℃+(1-D]). 初 [ / D)×1000℃]. To ensure that the strength and toughness of the steel pipe are not deteriorated after heat treatment and hot expansion, the hot expansion temperature must be strictly limited. For large expansion diameters, a relatively higher hot expansion temperature is needed to prevent defects during hot expansion; for small expansion diameters, a relatively lower temperature can be used. However, regardless of the expansion diameter, the hot expansion temperature must not exceed Ac1, otherwise the strength and toughness of the steel pipe will deteriorate. The temperature set by the above formula ensures high strength and high toughness of the steel pipe during hot expansion.

[0039] The pushing speed of the propulsion mechanism on the steel pipe is V≤[100-(1-D]). 初[D)×1000]mm / min. To ensure the steel pipe is free of defects during the final hot expansion process, the hot expansion pushing speed must be controlled according to the expansion ratio. Too fast a hot expansion speed will cause wrinkling and deformation of the steel pipe in the high-temperature induction heating section. Too slow a hot expansion speed will affect the hot expansion efficiency. The pushing speed set by the above formula ensures stable hot expansion while preventing wrinkling and deformation of the steel pipe, achieving high quality in the final product. A commercially available PLC controller is used as the PLC control console. The hot expansion mechanism, pushing mechanism, and wall-shrinking mechanism are all electrically connected to this PLC control console. The induction heating temperature and pushing speed are controlled through the PLC control console to ensure that the above data are consistent with the calculated values, guaranteeing the quality of the finished product.

[0040] like Figure 1 As shown, the propulsion mechanism includes a feeding roller 11, a discharging roller 12, and multiple pushing cylinders 13. Specifically, the pushing cylinders 13 are electrically connected to the PLC controller. For the specific working principle, please refer to Chinese Patent CN201676907U, which will not be elaborated here. The thermal expansion mechanism and the wall shrinking mechanism are located between the feeding roller 11 and the discharging roller 12, with the wall shrinking mechanism located behind the thermal expansion mechanism; as shown... Figure 2 As shown, the thermal expansion mechanism includes a thermal expansion rod 21, a thermal expansion head 22 detachably connected to the end of the thermal expansion rod, and an induction coil 23. The thermal expansion head 22 passes through the induction coil 23. The wall shrinking mechanism includes a base 31 and two sets of wall shrinking components on the base 31. The two sets of wall shrinking components are arranged one in front of the other along the pushing direction of the steel pipe. After the steel pipe is processed by the two sets of wall shrinking components, the t / D ≤ 0.03 is achieved.

[0041] Specifically, such as Figure 2 , 5 As shown, each wall-shrinking assembly includes an inner mold 41, an outer mold 42, a support 43, a roller 71, a slide rail 72, a fixing frame 73, and an outer mold calibration component. The inner mold 41 is disc-shaped and has a threaded connection 44. During assembly, the threaded connection 44 of the inner mold of the first wall-shrinking assembly is threaded to the hot expansion head, and the threaded connection 44 of the inner mold of the other wall-shrinking assembly is connected to the previous inner mold. The outer mold has a circular groove 45, and there is a gap between the outer wall of the inner mold and the circular groove 45 to allow the steel pipe to pass through. During the advancement of the pushing mechanism, the steel pipe is hot-expanded by the hot expansion mechanism, and then the steel pipe passes through the gap, and the wall thickness becomes thinner under the extrusion of the inner mold and the outer mold. Preferably, the gap formed by the inner mold and the outer mold of the front wall-shrinking assembly is slightly larger than the gap formed by the inner mold and the outer mold of the rear wall-shrinking assembly, so that the wall-shrinking operation is completed gradually, the operation is more stable, and the steel pipe is less likely to be damaged or have quality problems.

[0042] like Figure 3-4As shown in Figure 6, roller 71 is located at the lower part of the bracket, slide rail 72 is located on the base 31 and cooperates with roller 71, and fixed bracket 73 is located on the base 31 and cooperates with bracket 43. Preferably, the end of slide rail is inclined to facilitate roller entry into slide rail. When the bracket moves, the roller is always located in slide rail, which can limit the position of the bracket. Outer mold 42 is detachable from bracket 43. Both inner mold and outer mold can be detached to realize the processing of steel pipes with various diameters and wall thicknesses. Bracket 43 is used to position outer mold 42. Bracket 43 is provided with multiple connectors 5. In this embodiment, there are four connectors 5, which are triangular steel plates welded to the bracket and respectively located at the four corners of the bracket. Multiple positioning posts 51 are distributed at intervals on each connector 5. Multiple positioning holes 421 are distributed at the four corners of outer mold 42. The distribution interval of positioning holes 421 is the same as the distribution interval of positioning posts 51. The bracket 43 has two bolts 6 distributed on its upper and lower sides, and the outer mold 42 has two threaded holes on its upper and lower sides. The lower part of the bolts 6 can pass through the bracket 43 and be screwed into the threaded holes. In step S3, before heat expansion, the corresponding inner mold 41 and outer mold 42 also need to be assembled. The steps are as follows: According to the inner diameter and wall thickness requirements of the finished product, select the corresponding inner mold 41 and outer mold 42, screw the inner mold 41 to the heat expansion head, and then adjust the outer mold 42 to a position where the gap between it and the inner mold 41 is equal to the wall thickness.

[0043] like Figure 3 As shown, the outer mold calibration component includes a ring 81, a pneumatic clamp 82, and multiple calibration arms 83. The ring 81 is located on the inner mold 41 at its rear side, the pneumatic clamp 82 is located inside the ring 81, and the multiple calibration arms 83 are located on the pneumatic clamp 82. The pneumatic clamp 82 is electrically connected to a PLC controller, which controls the extension length of the calibration arms 83. A strip groove 811 is provided on the side wall of the ring 81. When the pneumatic clamp 82 is placed inside the ring 81, the wires can pass through the strip groove, avoiding the presence of wires from affecting the calibration work. The operation of adjusting the outer mold 42 to a position where the gap between it and the inner mold 41 equals the wall thickness is as follows: After screwing the two inner molds 41 together, screw them onto the heat expansion head 22 with the side with the pneumatic clamp 82 facing outwards. Then, place the outer mold 42 over the calibration arm 83. According to the set gap width, the PLC controller drives the pneumatic clamp 82 to move the calibration arm 83 a specified distance to press against the inner wall of the outer mold 42. Then, move the bracket so that the positioning pin 51 on the bracket 43 is inserted into the positioning hole 421, and then tighten the bolt 6. Subsequently, the pneumatic clamp 82 moves the calibration arm 83 back, and the moving bracket 43 moves the outer mold 42 to the position of the inner mold 41. Then, the position of the moving bracket 43 is fixed by the fixing bracket 73. Specifically, both the fixing bracket 73 and the moving bracket 43 have multiple screw holes on their side walls, and the positions of the two can be fixed by inserting screws.

[0044] This calibration method ensures that the centers of the inner mold 41 and the outer mold 42 are aligned, resulting in a uniform annular gap thickness and ultimately ensuring uniform wall thickness of the processed steel pipe. The pneumatic clamp 82 is only placed on the inner mold during calibration and is removed afterwards, without affecting the wall-shrinking operation of the steel pipe. The overall structure is simple, the calibration operation is convenient, and the alignment of the centers of the inner mold 42 and the outer mold 42 is always guaranteed. The cooperation of multiple positioning pins 51 and positioning holes 421 allows the relative position of the outer mold 42 and the support 43 to be adjusted freely. As long as a positioning pin 51 can be inserted into the positioning hole 421 at that position, the outer mold can be pre-positioned, and then locked with bolts 6. This method first determines the position of the outer mold, and then the support cooperates with the position of the outer mold to position it, further ensuring the alignment of the centers of the outer mold and the inner mold. In this method, simply pushing the bracket allows for the insertion of the positioning column and the positioning hole, making the pre-positioning operation simple and achieving high efficiency and accuracy in the entire calibration operation.

[0045] The above description is merely a selection of preferred embodiments of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in the embodiments of this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in the embodiments of this disclosure.

Claims

1. A method for manufacturing ultra-large diameter thin-walled seamless steel pipes, characterized in that: Includes the following steps: S1: Heat treat the steel pipe to be processed to a diameter of D. 初 Primary steel pipes; S2: The primary steel pipe undergoes heat treatment to increase its strength beyond that of S. 名义 A certain value ΔS, satisfying the following relationship: ΔS≥[(1-D_initial / D) ×100×k] MPa; S3: The steel pipe is then thermally expanded using induction heating equipment to obtain the final product. The specifications of the finished product are: yield strength ≥ 450MPa, outer diameter = 813-1200mm, t / D ≤ 0.03, where t is the wall thickness of the finished steel pipe and D is the outer diameter of the finished steel pipe. The induction heating equipment includes a thermal expansion mechanism, a propulsion mechanism, a wall shrinking mechanism, and a PLC control console. The thermal expansion mechanism induction heats the steel pipe during the expansion process. The wall shrinking mechanism is used to control the t / D of the finished steel pipe to be ≤0.03 after thermal expansion. The maximum temperature T of the induction-heated steel pipe is ≤[Ac1-80℃+(1-D)]. 初 [ / D)×1000℃]; The pushing speed of the propulsion mechanism on the steel pipe is V≤[100-(1-D]]. 初 [ / D)×1000] mm / min; The heat treatment in S1 is hot rolling or hot expansion, and the resulting D 初 =0.95-0.98D; The heat treatment in S2 is either normalizing or quenching and tempering. For normalizing, k is 5, and for quenching and tempering, k is 10. 名义 Nominal strength; The propulsion mechanism includes a feeding roller, a discharging roller, and multiple pushing cylinders. The thermal expansion mechanism and the wall shrinking mechanism are located between the feeding roller and the discharging roller, with the wall shrinking mechanism located behind the thermal expansion mechanism. The thermal expansion mechanism includes a thermal expansion rod, a thermal expansion head detachably connected to the end of the thermal expansion rod, and an induction coil, with the thermal expansion head passing through the induction coil. The wall shrinking mechanism includes a base and two sets of wall shrinking components mounted on the base. The two sets of wall shrinking components are arranged one in front of the other along the propulsion direction of the steel pipe, and the steel pipe achieves a t / D ≤ 0.03 after being processed by the two sets of wall shrinking components. The wall-shrinking assembly includes an inner mold, an outer mold, and a bracket for positioning the outer mold; the inner mold is disc-shaped and has a threaded connection; the outer mold has a circular groove, and there is a gap between the outer wall of the inner mold and the circular groove to allow the steel pipe to pass through; during the pushing process of the pushing mechanism, the steel pipe is thermally expanded by the thermal expansion mechanism, and then the steel pipe passes through the gap, and the wall thickness becomes thinner under the extrusion of the inner mold and the outer mold; The bracket is provided with multiple connectors, each connector having multiple positioning pins spaced apart. Multiple positioning holes are distributed at the four corners of the outer mold, with the spacing between the positioning holes matching the spacing between the positioning pins. Two bolts are distributed on the upper and lower sides of the bracket, and two threaded holes are distributed on the upper and lower sides of the outer mold. The lower part of the bolts can pass through the bracket and be screwed into the threaded holes. In step S3, before heat expansion, the corresponding inner and outer molds need to be assembled. The steps are as follows: Based on the inner diameter and wall thickness requirements of the finished product, select the corresponding inner and outer molds, screw the inner mold onto the heat expansion head, and then adjust the outer mold to a position where the gap between it and the inner mold is equal to the wall thickness. The wall-shrinking mechanism also includes rollers located at the lower part of the support, slide rails on the base that cooperate with the rollers, a fixing frame on the base that cooperates with the support, and an outer mold calibration component. The outer mold calibration component includes a ring on one of the inner molds, a pneumatic clamp inside the ring, and multiple calibration arms on the pneumatic clamp. The side wall of the ring is provided with a strip groove. The operation of adjusting the outer mold to a position where the gap between it and the inner mold is equal to the wall thickness is as follows: After screwing the two inner molds together, screw them onto the hot expansion head with the side with the pneumatic clamp facing outward. Then, put the outer mold over the calibration arm. The pneumatic clamp drives the calibration arm to move and press against the inner wall of the outer mold. Then, move the support so that the positioning pin on the support is inserted into the positioning hole, and then tighten the bolt. Subsequently, the pneumatic clamp drives the calibration arm to move back, and the moving support drives the outer mold to the position of the inner mold. Then, the position of the moving support is fixed by the fixing frame.

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