Super-long girth-welding-free reinforced seamless tube and manufacturing method thereof

Abstract

The invention provides a super-long girth-welding-free reinforced seamless pipe and a manufacturing method thereof, and belongs to the technical field of pipe machining. The method comprises the following steps: firstly, obtaining a pierced billet by utilizing a blank, then carrying out three-pass cold rolling by adopting a common rolling mill to obtain a tube blank, and sequentially carrying out cleaning and heat treatment after each pass of cold rolling; performing four-pass cold rolling on the tube blank by adopting a rotary rolling mill to obtain a semi-finished tube, and sequentially performing cleaning and heat treatment after each pass of rolling; according to the manufacturing method, the semi-finished pipe is subjected to circulating cold drawing-solid solution heat treatment, it is ensured that the steel pipe can still keep a seamless structure and excellent mechanical performance under the ultrahigh length, and the ultra-long girth-welding-free reinforced seamless pipe which is high in strength and toughness, free of welding seams and long in service life is obtained. The integrity of the large-length girth-welding-free reinforced seamless pipe can be guaranteed, the large-length girth-welding-free reinforced seamless pipe with the length larger than 3000 m is manufactured, and the production stability is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of pipe processing technology, and in particular to an ultra-long reinforced seamless pipe without ring welding and its manufacturing method. Background Technology

[0002] Seamless steel pipe (also known as seamless steel tube) is a long strip of steel with a hollow cross-section and no seams around its perimeter. It belongs to the alloy pipe category and is mainly used in the petroleum, natural gas, chemical, boiler manufacturing, and mechanical engineering industries. Seamless steel pipes for oil and gas cables are specifically designed for cable laying or oil and gas transportation in the petroleum industry, featuring high strength, high sealing performance, and good corrosion resistance. Currently, conventional seamless steel pipe products have limited lengths, and there are no ultra-long seamless steel pipe products with high strength, high toughness, and no weld seams. Long seamless steel pipes for oil and gas cables are generally made by butt-jointing pipes to increase the overall length. Because there are multiple butt welds on the entire pipe body, and these welds are weak points, the safety factor is low and the service life is short.

[0003] In existing technologies, improper connection processes during seamless pipe butt welding (such as weak welding or inadequate sealing) can cause the joint to become a weak point in the entire pipeline, affecting its overall strength. In high-pressure, high-temperature, or corrosive environments, the strength issues at the joint may be even more pronounced, increasing the risk of leakage or rupture and significantly shortening its service life. Furthermore, pipe butt welding suffers from uneven weld microstructure and unrelieved stress, among other welding defects. In addition, there are no ultra-long, reinforced seamless pipe products without circumferential welding available on the market. Summary of the Invention

[0004] The purpose of this invention is to provide an ultra-long reinforced seamless pipe without ring welding and its manufacturing method. The method provided by this invention can ensure that the steel pipe can maintain a seamless structure and excellent mechanical properties even at ultra-high lengths, and obtain an ultra-long reinforced seamless pipe without ring welding with high strength, high toughness, no weld seam, and long service life.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for manufacturing an ultra-long, ring-free, reinforced seamless tube, comprising the following steps:

[0007] (1) The billet is subjected to external stripping, internal boring and decontamination treatment in sequence to obtain a rough tube;

[0008] (2) Using a conventional rolling mill, the rough tube obtained in step (1) is cold rolled in three passes to obtain a tube blank, and after each cold rolling pass, it is cleaned and heat treated in sequence;

[0009] (3) Using a rotary rolling mill, the tube blank obtained in step (1) is cold rolled in four passes to obtain a semi-finished tube, and after each rolling pass, it is cleaned and heat-treated in sequence.

[0010] (4) The semi-finished tube obtained in step (3) is subjected to cyclic cold drawing-solution heat treatment to obtain an ultra-long reinforced seamless tube without ring welding.

[0011] Preferably, the chemical composition of the billet in step (1) by mass percentage is: carbon ≤ 0.03%, manganese ≤ 1.20%, phosphorus ≤ 0.03%, sulfur ≤ 0.015%, silicon ≤ 0.8%, nickel 6.0%~8.0%, chromium 24.0%~26.0%, molybdenum 3.0%~5.0%, nitrogen 0.26%~0.34%, copper ≤ 0.5%, and the remainder is iron; the outer diameter of the rough tube is 168mm±0.5mm.

[0012] Preferably, in step (2), the parameters of each of the three cold rolling processes include: rolling speed of 38~65 times / min, feed rate of 0.6mm, and outer diameter of the tube blank of 82mm±0.5mm.

[0013] Preferably, the rotary mill in step (3) includes:

[0014] The pay-off reel feeds the tube blank coiled on it into the rotary mill at a constant speed via the first traction machine;

[0015] In a planetary gear structure, the sun gear is connected to the drive shaft via a belt and provides rotational power to the planet gears;

[0016] The spinning roll and roll support are connected to the planetary gear. The roll pressurization device provides a maximum radial pressure of 25kN, and the pressure difference between the rolls is not greater than 1kN. The spinning roll base is made of 45# steel, with surface nitriding treatment, and PCD polycrystalline diamond is grown on its surface.

[0017] The support and limiting frame serves to support the tube blank between the first and second traction machines; the second and first traction machines work together to control the feed speed of the tube blank.

[0018] The take-up reel winds the finished tube blank around it.

[0019] Preferably, in the four-pass cold rolling process in step (3), the rolling speed of each pass is 100~140 rpm; the outer diameter of the semi-finished tube is 22 mm ± 0.5 mm.

[0020] Preferably, the heat treatment in step (3) includes: heating to 1080~1120℃ at a rate of 110~275℃ / min, holding for 12min, and water cooling to room temperature.

[0021] Preferably, the cyclic cold drawing-solution heat treatment in step (4) includes:

[0022] (S1) The semi-finished tube is subjected to a first cold drawing, a first solution heat treatment, a second cold drawing, and a second solution heat treatment in sequence to obtain a tube body with a diameter of Φ18mm±0.5mm after solution heat treatment;

[0023] (S2) The Φ18mm±0.5mm tube obtained after solution heat treatment in step (S1) is subjected to a third cold drawing, a third solution heat treatment, a fourth cold drawing, and a fourth solution heat treatment in sequence to obtain a Φ14mm±0.5mm tube after solution heat treatment.

[0024] (S3) The Φ14mm±0.5mm tube obtained after solution heat treatment in step (S2) is subjected to a fifth cold drawing, a fifth solution heat treatment, a sixth cold drawing, and a sixth solution heat treatment in sequence to obtain a Φ9.61mm±0.5mm tube after solution heat treatment.

[0025] (S4) The Φ14mm±0.5mm tube body obtained after solution heat treatment in step (S3) is subjected to the seventh cold drawing, the seventh heat treatment, the eighth cold drawing, and the eighth solution heat treatment in sequence to obtain an ultra-long reinforced seamless tube with no ring weld of Φ6.35mm±0.5mm.

[0026] Preferably, the cold drawing speed during the cyclic cold drawing-solution heat treatment process in step (4) is 1.5~3.5m / min.

[0027] Preferably, the solution heat treatment in step (4) during the cyclic cold drawing-solution heat treatment process includes: heating to 1070~1130℃ at a rate of 265~285℃ / min, holding for 5~9min, and then air cooling to room temperature.

[0028] The present invention also provides an ultra-long reinforced seamless tube without ring welding manufactured by the manufacturing method described in the above technical solution.

[0029] This invention provides a method for manufacturing an ultra-long, ring-free, reinforced seamless tube. First, a rough tube is obtained from a billet, and then a tube blank is obtained by three cold rolling passes using a conventional rolling mill. The three cold rolling passes involve plastic deformation of the tube blank under cold conditions using rolls, which alters its microstructure, mechanical properties, dimensional accuracy, and surface quality. Specifically: (1) During the cold rolling process, the internal grains of the tube blank are elongated and broken, and the dislocation density increases significantly, resulting in a significant increase in tensile strength and yield strength; (2) The plastic deformation of the cold rolling transforms the original equiaxed grains into fibrous grains that extend along the rolling direction, and the grain size... Refining the annealed state from 50~80μm to 10~20μm increases the grain boundary area and improves the toughness and fatigue strength of the material; (3) Cold rolling is a precision plastic processing, which can accurately control the outer diameter tolerance (±0.05~0.1mm), wall thickness tolerance (±0.03~0.08mm), and roundness (≤0.1mm) of the tube; (4) The surface roughness of cold-rolled tubes can be reduced to Ra≤0.8μm, and there are no defects such as oxide scale and pitting of hot-rolled tubes. The surface smoothness is high, and subsequent preparation can be carried out without pickling and rust removal. After each cold rolling, cleaning and heat treatment are carried out in sequence to eliminate the processing Hardening also restores the alloy phase equilibrium, avoiding the risk of cracking during subsequent large deformations. Then, a rotary rolling mill is used to perform four passes of cold rolling on the billet to obtain a semi-finished tube. After each rolling pass, the tube is cleaned and heat-treated sequentially. Subsequently, the semi-finished tube undergoes cyclic cold drawing-solution heat treatment. In the cold drawing process, axial tension and radial pressure are applied to the tube through a die, causing plastic deformation and elongating the grains into a fibrous structure. This significantly increases the dislocation density, directly resulting in a significant increase in strength (for example, after cold drawing, the yield strength of 2507 duplex steel can increase from 450 MPa in the annealed state to 650 MPa). The tensile strength is increased to 850-1000 MPa (~800 MPa), while the plasticity is reduced, resulting in an elongation of more than 18%. The work hardening effect is obvious, ensuring that the steel pipe can maintain a seamless structure and excellent mechanical properties even at ultra-high lengths. This results in ultra-long reinforced seamless pipes without ring welds, which are high-strength, high-toughness, weld-free, and have a long service life. Furthermore, the manufacturing method provided by this invention can guarantee the integrity (no surface defects) of long reinforced seamless pipes without ring welds, enabling the production of single long reinforced seamless pipes with ring welds of more than 3000 meters, and ensuring production stability. Attached Figure Description

[0030] Figure 1 This is a photograph of the surface of the rough tube prepared in Example 1 of the present invention;

[0031] Figure 2 A physical diagram of the cross-section of the rough tube prepared in Example 1 of the present invention;

[0032] Figure 3 This is a photograph of the surface of the tube blank prepared in Example 1 of the present invention;

[0033] Figure 4 A physical diagram of the cross-section of the tube blank prepared in Example 1 of the present invention.

[0034] Figure 5 This is a photograph of the surface of the semi-finished tube prepared in Example 1 of the present invention.

[0035] Figure 6 This is a physical diagram of the cross-section of the semi-finished tube prepared in Example 1 of the present invention.

[0036] Figure 7 This is a physical image of the surface of the ultra-long, ring-free, reinforced seamless tube prepared in Example 3 of the present invention;

[0037] Figure 8 This is a physical diagram of the cross-section of the ultra-long, ringless, reinforced seamless tube prepared in Embodiment 3 of the present invention;

[0038] Figure 9 This is a schematic diagram of the structure of the rotary rolling mill in this invention, wherein, Figure 9 In the diagram, 1 is the pay-off reel, 2 is the first traction machine, 3 is the machine housing, 4 is the planetary gear, 5 is the roll pressing device, 6 is the support and limit frame, 7 is the trolley track, 8 is the spinning roll and roll support, 9 is the second traction machine, and 10 is the take-up reel.

[0039] Figure 10 This is a schematic diagram of the internal structure of the rotary rolling mill casing and the planetary gears in this invention, wherein, Figure 10 In the middle, the left picture shows the inside of the machine casing, the right picture shows the planetary gears, 4 is the planetary gear, 5 is the roll pressing device, and 8 is the spinning roll and roll support. Detailed Implementation

[0040] This invention provides a method for manufacturing an ultra-long, ring-free, reinforced seamless tube, comprising the following steps:

[0041] (1) The billet is subjected to external stripping, internal boring and decontamination treatment in sequence to obtain a rough tube;

[0042] (2) Using a conventional rolling mill, the rough tube obtained in step (1) is cold rolled in three passes to obtain a tube blank, and after each cold rolling pass, it is cleaned and heat treated in sequence;

[0043] (3) Using a rotary rolling mill, the tube blank obtained in step (1) is cold rolled in four passes to obtain a semi-finished tube, and after each rolling pass, it is cleaned and heat-treated in sequence.

[0044] (4) The semi-finished tube obtained in step (3) is subjected to cyclic cold drawing-solution heat treatment to obtain an ultra-long reinforced seamless tube without ring welding.

[0045] Unless otherwise specified, all raw materials used in this invention are commercially available products in the art.

[0046] This invention involves sequentially processing the billet through external stripping, internal boring, and decontamination to obtain a rough tube.

[0047] In this invention, the preferred parameters for the external cutter are: feed speed of 45 mm / min, tool rotation speed of 30 mm / min, and cutting depth of 1 mm.

[0048] In this invention, the preferred parameters of the internal boring are: a cutting speed of 260 r / min, a cutting depth of 1.5 mm, and a feed speed of 30 mm / min.

[0049] The present invention does not impose any special limitations on the operation of the decontamination treatment; any technical solution well known in the art can be used. After the decontamination treatment is completed, the surface roughness of the raw tube is tested. If the roughness is less than Ra2, the next process is carried out.

[0050] In this invention, the preferred chemical composition of the billet, by mass percentage, is: carbon ≤ 0.03%, manganese ≤ 1.20%, phosphorus ≤ 0.03%, sulfur ≤ 0.015%, silicon ≤ 0.8%, nickel 6.0%~8.0%, chromium 24.0%~26.0%, molybdenum 3.0%~5.0%, nitrogen 0.26%~0.34%, copper ≤ 0.5%, with the remainder being iron. This invention controls the chemical composition of the billet within the above ranges, strictly controlling the upper limit of silicon content. Silicon is a deoxidizer, but excessive silicon increases the material's resistance to cold deformation, leading to cracking during cold drawing and spinning. The blank you provide has a lower silicon content, resulting in better cold workability and reducing the risk of wear on drawing dies and cracking during spinning. The nitrogen content range in this invention is slightly higher (0.24%~0.32% above the standard). Nitrogen is the core strengthening element of 2507 and also stabilizes the austenite phase. A slightly higher upper limit for nitrogen content can increase the yield strength by 10~20 MPa after solution heat treatment, and the stability of the two-phase ratio (ferrite / austenite ≈ 50:50) is better, making it more suitable for preparing high-pressure-resistant reinforced seamless tubes. In this invention, the outer diameter of the rough tube is preferably 168 mm ± 0.5 mm.

[0051] After obtaining the rough tube, the present invention uses a conventional rolling mill to perform three cold rolling passes on the rough tube to obtain a tube blank, and then performs cleaning and heat treatment sequentially after each cold rolling pass.

[0052] In this invention, the parameters for each of the three-pass cold rolling process preferably include: a rolling speed of 38-65 times / min and a feed rate of 0.6 mm. This invention controls the parameters of each cold rolling pass within the above range to balance deformation uniformity, work hardening degree, and process efficiency, while also adapting to the performance requirements of the subsequent spinning-solution-cold drawing chain, ultimately ensuring the high pressure resistance and corrosion resistance of the reinforced seamless tube. In this invention, the outer diameters of the tube blanks obtained by the three consecutive cold rolling passes are preferably 140 mm ± 0.5 mm, 114 mm ± 0.5 mm, and 82 mm ± 0.5 mm, respectively, and the difference in the outer diameter of the tube blank after each cold rolling pass shall not exceed ± 0.5 mm. In this invention, the outer diameter of the tube blank is preferably 82 mm ± 0.5 mm. In this invention, the cleaning preferably includes: using a 35°C alkaline cleaning agent (such as Mebel) and sponge beads to clean the rolling lubricating oil on the inner wall of the tube blank after each cold rolling pass, until the sponge beads no longer change color. This invention eliminates oil sludge residue between passes, improves the uniformity of subsequent cold rolling deformation, ensures the stability of microstructure and surface quality, extends the life of rolls and subsequent tooling, and reduces production costs by cleaning after each of the three cold rolling passes (35°C temperature, sponge bead colorfastness criterion). Standardized operation for each of the three passes (35°C temperature, sponge bead colorfastness criterion) avoids incomplete cleaning due to human error, ensuring consistent cleanliness of each tube blank. Furthermore, the 35°C cleaning temperature is in the medium temperature range, reducing energy consumption by 30% compared to high-temperature cleaning (>50°C), and does not cause oxidation of the tube surface, balancing cleaning effectiveness and economy. In this invention, the heat treatment preferably includes: heating to 1080~1120°C at a rate of 35~60°C / min, holding at that temperature for 45~110min, and then water cooling to room temperature. This invention controls the parameters of the heat treatment after cleaning in the three-pass cold rolling process within the above-mentioned range, so as to precisely regulate the balance of the two-phase structure, eliminate work hardening, and avoid the precipitation of embrittled phases.

[0053] After obtaining the tube blank, the present invention uses a rotary rolling mill to perform four cold rolling passes on the tube blank to obtain a semi-finished tube, and then performs cleaning and heat treatment sequentially after each rolling pass.

[0054] In this invention, the rotary rolling mill preferably comprises:

[0055] The pay-off reel feeds the tube blank coiled on it into the rotary mill at a constant speed via the first traction machine;

[0056] In a planetary gear structure, the sun gear is connected to the drive shaft via a belt and provides rotational power to the planet gears;

[0057] The spinning roll and roll support are connected to the planetary gear. The roll pressurization device provides a maximum radial pressure of 25kN, and the pressure difference between the rolls is not greater than 1kN. The spinning roll base is made of 45# steel, with surface nitriding treatment, and PCD polycrystalline diamond is grown on its surface.

[0058] The support and limiting frame serves to support the tube blank between the first and second traction machines; the second and first traction machines work together to control the feed speed of the tube blank.

[0059] The take-up reel winds the finished tube blank around it.

[0060] The working process of the rotary rolling mill in this invention is as follows: the rolls revolve synchronously around the axis of the billet, while the rolls themselves rotate and continuously feed along the radial direction of the billet, gradually reducing the distance between the rolls; the deformation of the billet is entirely accomplished by the extrusion force of the rolls and its own metal flow characteristics: firstly, the outer layer of the billet is subjected to the extrusion force of the rolls, undergoing plastic deformation and conforming to the shape of the roll cavity; secondly, as the rolls continue to feed, the extrusion force is gradually transmitted to the inner layer of the billet, and the inner layer of the metal flows towards the axis of the billet or along the axial direction of the billet, gradually forming the required cross-sectional shape; the billet rotates synchronously with the revolution of the rolls, ensuring that the circumference of the billet is uniformly stressed, avoiding uneven wall thickness or deviation in cross-sectional shape.

[0061] In this invention, during the four-pass cold rolling process, the rolling speed of each pass is preferably 100-140 rpm. This invention controls the rolling speed of each pass within this range to ensure uniform deformation, stable dimensional accuracy, and consistent surface quality, while also considering production efficiency, adapting to the billet performance requirements of subsequent process chains, and eliminating the need for additional rounding procedures. In this invention, the outer diameters of the tube blanks obtained through the four consecutive cold rolling passes are preferably 68mm±0.5mm, 47mm±0.5mm, 32mm±0.5mm, and 22mm±0.5mm, respectively, and the difference in outer diameter after each cold rolling pass shall not exceed ±0.5mm. In this invention, the outer diameter of the semi-finished tube is preferably 22mm±0.5mm. In this invention, the cleaning preferably includes: using a 35°C alkaline cleaning agent (such as Mebel) and sponge beads to clean the rolling lubricating oil on the inner wall of the tube blank after each cold rolling pass, until the sponge beads no longer change color. This invention eliminates oil sludge residue between passes by cleaning after each of the four cold rolling passes, improves the uniformity of subsequent cold rolling deformation, ensures the stability of microstructure and surface quality, extends the life of the rolls and subsequent tooling, and reduces production costs. The standardized operation of cleaning for each of the three passes (35°C temperature, sponge bead colorfastness criterion) avoids incomplete cleaning due to human judgment errors, ensuring consistent cleanliness of each tube blank. Furthermore, the 35°C cleaning temperature is in the medium temperature range, reducing energy consumption by 30% compared to high-temperature cleaning (>50°C), and does not cause oxidation of the tube surface, balancing cleaning effectiveness and economy. In this invention, the heat treatment preferably includes: heating to 1080~1120°C at a rate of 110~275°C / min, holding for 12 minutes, and water cooling to room temperature. This invention controls the parameters of the heat treatment after cleaning in the four-pass cold rolling process within the above range, so as to precisely regulate the balance of the two-phase structure, eliminate work hardening, and avoid the precipitation of embrittled phases.

[0062] After obtaining the semi-finished tube, the present invention performs cyclic cold drawing-solution heat treatment on the semi-finished tube to obtain an ultra-long reinforced seamless tube without ring welding.

[0063] In this invention, the cyclic cold drawing-solution heat treatment preferably includes:

[0064] (S1) The semi-finished tube is subjected to a first cold drawing, a first solution heat treatment, a second cold drawing, and a second solution heat treatment in sequence to obtain a tube body with a diameter of Φ18mm±0.5mm after solution heat treatment;

[0065] (S2) The Φ18mm±0.5mm tube obtained after solution heat treatment in step (S1) is subjected to a third cold drawing, a third solution heat treatment, a fourth cold drawing, and a fourth solution heat treatment in sequence to obtain a Φ14mm±0.5mm tube after solution heat treatment.

[0066] (S3) The Φ14mm±0.5mm tube obtained after solution heat treatment in step (S2) is subjected to a fifth cold drawing, a fifth solution heat treatment, a sixth cold drawing, and a sixth solution heat treatment in sequence to obtain a Φ9.61mm±0.5mm tube after solution heat treatment.

[0067] (S4) The Φ14mm±0.5mm tube body obtained after solution heat treatment in step (S3) is subjected to the seventh cold drawing, the seventh solution heat treatment, the eighth cold drawing, and the eighth solution heat treatment in sequence to obtain an ultra-long reinforced seamless tube with no ring weld of Φ6.43mm±0.5mm.

[0068] In this invention, the cold drawing speed during the cyclic cold drawing-solution heat treatment process is preferably 1.5~3.5 m / min, more preferably 2~3 m / min, and even more preferably 2.5 m / min. This invention controls the cold drawing speed within the above range during the cyclic cold drawing-solution heat treatment process, ensuring deformation uniformity, dimensional accuracy stability, and surface quality consistency, while also considering production efficiency and eliminating the need for an additional rounding process. In this invention, the solution heat treatment during the cyclic cold drawing-solution heat treatment process preferably includes: heating to 1070~1130℃ at a rate of 265~285℃ / min, holding at that temperature for 5~9 min, and then air cooling to room temperature. This invention controls the solution heat treatment parameters during the cold drawing process within the above range to precisely control the dual-phase microstructure equilibrium, eliminate work hardening, and avoid the precipitation of embrittled phases.

[0069] The present invention also provides an ultra-long reinforced seamless tube without ring welding manufactured by the manufacturing method described in the above technical solution.

[0070] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0071] Unless otherwise specified, all experiments were repeated three times, and the results are expressed as averages.

[0072] Example 1

[0073] A method for manufacturing an ultra-long, ring-free, reinforced seamless tube, comprising the following steps:

[0074] (1) The 1016kg billet was subjected to external stripping, internal boring and cleaning treatment in sequence to obtain a rough tube of Φ168mm;

[0075] The chemical composition of the billet, by mass percentage, is as follows: carbon ≤ 0.03%, manganese ≤ 1.20%, phosphorus ≤ 0.03%, sulfur ≤ 0.015%, silicon ≤ 0.8%, nickel 6.0%~8.0%, chromium 24.0%~26.0%, molybdenum 3.0%~5.0%, nitrogen 0.26%~0.34%, copper ≤ 0.5%, with the remainder being iron;

[0076] The parameters for the external cutter are: feed speed of 45 mm / min, tool rotation speed of 30 mm / min, and depth of cut of 1 mm; the parameters for the internal boring are: cutting speed of 260 r / min, depth of cut of 1.5 mm, and feed speed of 30 mm / min; after the decontamination treatment is completed, the surface roughness of the rough tube is tested. If the roughness is less than Ra2, the next process is carried out.

[0077] (2) Using a conventional rolling mill, the Φ168mm rough tube obtained in step (1) is cold rolled to a Φ140mm tube blank. The rolling speed is 40 times / min and the feed rate is 0.6mm. The outer diameter of the rolled tube blank is measured and shall not exceed ±0.5mm. After passing the inspection, the rolling lubricating oil on the inner wall of the tube is first cleaned with 35℃ alkaline cleaning agent and sponge beads until the sponge beads do not change color.

[0078] After the first cleaning, the tube blank is subjected to the first heat treatment, which is heated to 1080~1120℃ at a heating rate of 37℃ / min, held for 100min, and then water-cooled to room temperature to obtain an annealed Φ140mm tube blank. Samples of the tube blank are cut and tested, requiring a yield strength ≥550MPa, tensile strength ≥800MPa, elongation ≥15%, and hardness ≤300HV1.

[0079] The annealed Φ140mm tube blank is cold rolled a second time using a conventional rolling mill to obtain a Φ114mm tube blank. The rolling speed is 50 times / min and the feed rate is 0.6mm. The outer diameter of the rolled tube blank must be measured and must not exceed ±0.5mm. After passing the inspection, the rolling lubricating oil on the inner wall of the tube is cleaned a second time using 35℃ alkaline cleaning agent and sponge beads until the sponge beads no longer change color.

[0080] After the second cleaning, a second heat treatment is performed, heating to 1080-1120℃ at a heating rate of 44℃ / min, holding for 70min, and then water-cooled to room temperature to obtain an annealed Φ114mm tube blank; tube blank samples are cut for testing, requiring yield strength ≥550MPa, tensile strength ≥800MPa, elongation ≥15%, and hardness ≤300HV1;

[0081] The annealed Φ114mm tube blank is subjected to a third cold rolling process using a conventional rolling mill to obtain a tube blank with an outer diameter of Φ82mm. The rolling speed is 60 times / min and the feed rate is 0.6mm. The outer diameter of the rolled tube blank must be measured and must not exceed ±0.5mm. After passing the inspection, the rolling lubricating oil on the inner wall of the tube is cleaned for the third time using 35℃ alkaline cleaning agent and sponge beads until the sponge beads no longer change color.

[0082] After the third cleaning, a third heat treatment is performed, heating to 1080-1120℃ at a heating rate of 58℃ / min, holding for 50min, and then water-cooled to room temperature to obtain a Φ82mm tube blank; samples are cut for testing, requiring yield strength ≥550MPa, tensile strength ≥800MPa, elongation ≥15%, and hardness ≤300HV1;

[0083] (3) Use a rotary rolling mill to perform a fourth cold rolling on the Φ82mm tube blank obtained in step (2) to obtain a Φ68mm tube blank. The rolling speed is 100rpm. The outer diameter of the rolled tube blank must be measured and must not exceed ±0.5mm. After passing the inspection, use 35℃ alkaline cleaning agent plus sponge beads to perform a fourth cleaning on the rolling lubricating oil on the inner wall of the tube until the sponge beads no longer change color.

[0084] After the fourth cleaning, a fourth heat treatment is performed, heating to 1080-1120℃ at a heating rate of 110℃ / min, holding for 35min, and then water-cooled to room temperature to obtain an annealed Φ68mm tube blank; samples are cut for testing, requiring yield strength ≥550MPa, tensile strength ≥800MPa, elongation ≥15%, and hardness ≤300HV1;

[0085] The annealed Φ68mm tube blank is cold rolled to Φ47mm using a rotary rolling mill at a rolling speed of 120rpm. The outer diameter of the rolled tube blank must be measured and must not exceed ±0.5mm. After passing the inspection, the rolling lubricating oil on the inner wall of the tube is cleaned for the fifth time using 35℃ alkaline cleaning agent and sponge beads until the sponge beads no longer change color.

[0086] After the fifth cleaning, a fifth heat treatment is performed, heating to 1080-1120℃ at a heating rate of 184℃ / min, holding for 30min, and then water-cooled to room temperature to obtain an annealed Φ47mm tube blank; samples are cut for testing, requiring yield strength ≥550MPa, tensile strength ≥800MPa, elongation ≥15%, and hardness ≤300HV1;

[0087] The annealed Φ47mm tube blank is cold rolled for the sixth time using a rotary rolling mill to obtain a Φ32mm tube blank. The rolling speed is 130rpm. The outer diameter of the rolled tube blank must be measured and must not exceed ±0.5mm. After passing the inspection, the rolling lubricating oil on the inner wall of the tube is cleaned for the sixth time using 35℃ Mebel alkaline cleaning agent with sponge beads until the sponge beads no longer change color.

[0088] After the sixth cleaning, a sixth heat treatment is performed, heating to 1080-1120℃ at a heating rate of 220℃ / min, holding for 25min, and then water-cooled to room temperature to obtain an annealed Φ32mm tube blank; samples are cut for testing, requiring a yield strength ≥550MPa, tensile strength ≥800MPa, elongation ≥15%, and hardness ≤300HV1;

[0089] The annealed Φ32mm tube blank is cold rolled for the seventh time using a rotary rolling mill to obtain a Φ22mm tube blank. The rolling speed is 130rpm. The outer diameter of the rolled tube blank must be measured and must not exceed ±0.5mm. After passing the inspection, the rolling lubricating oil on the inner wall of the tube is cleaned for the seventh time using 35℃ alkaline cleaning agent with sponge beads until the sponge beads no longer change color.

[0090] After the seventh cleaning, the seventh heat treatment is carried out, which involves heating to 1080-1120℃ at a heating rate of 275℃ / min, holding for 12 minutes, and then water cooling to room temperature to obtain a semi-finished pipe with a diameter of 22mm. Samples are cut and tested, requiring a yield strength ≥550MPa, tensile strength ≥800MPa, elongation ≥15%, and hardness ≤300HV1.

[0091] (4) The Φ22mm semi-finished tube obtained in step (3) is subjected to cyclic cold drawing-solution heat treatment to obtain a finished Φ6.35mm ultra-long reinforced seamless tube without ring welding;

[0092] The cyclic cold drawing-solution heat treatment specifically includes:

[0093] (S1) The semi-finished tube is first cold drawn to obtain a Φ20mm tube body, and then the first solution heat treatment, the second cold drawing, and the second solution heat treatment are performed in sequence to obtain a Φ18mm tube body after solution heat treatment.

[0094] (S2) The Φ18mm tube obtained from the solution heat treatment in step (S1) is cold-drawn to obtain a Φ16mm tube, and then the third solution heat treatment, the fourth cold drawing, and the fourth solution heat treatment are performed in sequence to obtain a Φ14mm tube after solution heat treatment.

[0095] (S3) The Φ14mm tube obtained after solution heat treatment in step (S2) is cold-drawn to obtain a Φ12mm tube, and then the fifth solution heat treatment, the sixth cold drawing, and the sixth solution heat treatment are performed in sequence to obtain a Φ9.61mm tube after solution heat treatment.

[0096] (S4) The Φ14mm tube obtained after solution heat treatment in step (S3) is cold-drawn to obtain a Φ7.8mm tube, and then subjected to the seventh solution heat treatment, the eighth cold drawing, and the eighth solution heat treatment in sequence to obtain an ultra-long reinforced seamless tube with no ring weld of Φ6.35mm.

[0097] The cold drawing speed during the cyclic cold drawing-solution heat treatment process is 2.5 m / min; the solution heat treatment during the cyclic cold drawing-solution heat treatment process is specifically as follows: heating to 1070~1130℃ at a rate of 275℃ / min, holding at that temperature for 7 min, and then air cooling to room temperature.

[0098] Examples 2 and 3

[0099] The ultra-long reinforced seamless tube without ring welding was prepared according to the method of Example 1, and the difference between the outer diameter of the tube blank and the corresponding tube blank of Example 1 was controlled to not exceed ±0.5 mm during the preparation process.

[0100] The dimensions and mechanical properties of the ultra-long, ringless reinforced seamless tubes prepared in Examples 1-3, as well as seamless tubes purchased from the market, were tested, and the results are shown in Table 1.

[0101] The above mechanical properties were tested according to ASTM A1016, "General requirements for ferritic alloy steel, austenitic alloy steel and stainless steel pipes". The results of tensile strength (MPa), yield strength (MPa) and elongation (%) are shown in Table 1.

[0102] Table 1. Statistical analysis of the dimensions and performance of the ultra-long, ring-free reinforced seamless tubes prepared in Examples 1-3, and commercially available seamless tubes.

[0103]

[0104] As shown in Table 1, the mechanical properties of the ultra-long, ringless, reinforced seamless tubes prepared in Examples 1-3 using the method provided by this invention are superior to those of commercially available seamless tubes.

[0105] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for manufacturing an ultra-long, ring-free, reinforced seamless tube, characterized in that, Includes the following steps: (1) The billet is subjected to external stripping, internal boring and decontamination treatment in sequence to obtain a rough tube; (2) Using a conventional rolling mill, the rough tube obtained in step (1) is cold rolled in three passes to obtain a tube blank, and after each cold rolling pass, it is cleaned and heat treated in sequence; (3) Using a rotary rolling mill, the tube blank obtained in step (1) is cold rolled in four passes to obtain a semi-finished tube, and after each rolling pass, it is cleaned and heat-treated in sequence. (4) The semi-finished tube obtained in step (3) is subjected to cyclic cold drawing-solution heat treatment to obtain an ultra-long reinforced seamless tube without ring welding.

2. The manufacturing method according to claim 1, characterized in that, The chemical composition of the billet in step (1) by mass percentage is as follows: carbon ≤ 0.03%, manganese ≤ 1.20%, phosphorus ≤ 0.03%, sulfur ≤ 0.015%, silicon ≤ 0.8%, nickel 6.0%~8.0%, chromium 24.0%~26.0%, molybdenum 3.0%~5.0%, nitrogen 0.26%~0.34%, copper ≤ 0.5%, and the remainder is iron; the outer diameter of the rough tube is 168mm±0.5mm.

3. The manufacturing method according to claim 1, characterized in that, In step (2), the parameters for each of the three cold rolling processes are as follows: rolling speed is 38~65 times / min, feed rate is 0.6mm, and the outer diameter of the tube blank is 82mm±0.5mm.

4. The manufacturing method according to claim 1, characterized in that, The rotary mill in step (3) includes: The pay-off reel feeds the tube blank coiled on it into the rotary mill at a constant speed via the first traction machine; In a planetary gear structure, the sun gear is connected to the drive shaft via a belt and provides rotational power to the planet gears; The spinning roll and roll support are connected to the planetary gear. The roll pressurization device provides a maximum radial pressure of 25kN, and the pressure difference between the rolls is not greater than 1kN. The spinning roll base is made of 45# steel, with surface nitriding treatment, and PCD polycrystalline diamond is grown on its surface. The support and limiting frame serves to support the tube blank between the first and second traction machines; the second and first traction machines work together to control the feed speed of the tube blank. The take-up reel winds the finished tube blank around it.

5. The manufacturing method according to claim 1, characterized in that, In step (3), during the four-pass cold rolling process, the rolling speed of each pass is 100~140 rpm; the outer diameter of the semi-finished tube is 22 mm ± 0.5 mm.

6. The manufacturing method according to claim 1, characterized in that, The heat treatment in step (3) includes: heating to 1080~1120℃ at a rate of 110~275℃ / min, holding for 12min, and water cooling to room temperature.

7. The manufacturing method according to claim 1, characterized in that, The cyclic cold drawing-solution heat treatment in step (4) includes: (S1) The semi-finished tube is subjected to a first cold drawing, a first solution heat treatment, a second cold drawing, and a second solution heat treatment in sequence to obtain a tube body with a diameter of Φ18mm±0.5mm after solution heat treatment; (S2) The Φ18mm tube obtained in step (S1) after solution heat treatment is subjected to a third cold drawing, a third solution heat treatment, a fourth cold drawing, and a fourth solution heat treatment in sequence to obtain a Φ14mm±0.5mm tube after solution heat treatment. (S3) The Φ14mm±0.5mm tube obtained after solution heat treatment in step (S2) is subjected to a fifth cold drawing, a fifth solution heat treatment, a sixth cold drawing, and a sixth solution heat treatment in sequence to obtain a Φ9.61mm tube after solution heat treatment; (S4) The Φ14mm±0.5mm tube body obtained after solution heat treatment in step (S3) is subjected to the seventh cold drawing, the seventh heat treatment, the eighth cold drawing, and the eighth solution heat treatment in sequence to obtain an ultra-long reinforced seamless tube with no ring weld of Φ6.35mm±0.5mm.

8. The manufacturing method according to claim 1, characterized in that, In step (4), the cold drawing speed during the cyclic cold drawing-solution heat treatment process is 1.5~3.5m / min.

9. The manufacturing method according to claim 1, characterized in that, In step (4), the solution heat treatment in the cyclic cold drawing-solution heat treatment process includes: heating to 1070~1130℃ at a rate of 265~285℃ / min, holding for 5~9min, and then air cooling to room temperature.

10. An ultra-long, ringless, reinforced seamless tube manufactured by the manufacturing method according to any one of claims 1 to 9.

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