A supercritical carbon dioxide HFW welded pipe, a manufacturing method and application thereof

Abstract

The application discloses a supercritical carbon dioxide HFW welded pipe, a manufacturing method and application thereof, and the welded pipe comprises the following components in percentage by mass: C: 0.04-0.06%, Si: ≤0.32%, P: ≤0.010%, S: ≤0.001%, Mn: 1.0-1.6%, Ni: 0.1-0.2%, Nb: 0.04-0.07%, Cr: 0.1-0.2%, Al: 0.02-0.05%, Zr: 0.03-0.05%, Mg: 0.02-0.04%, Nb+V+Ti: ≤0.15%, the mass ratio of Mn / Si is 5-8, and the rest is iron and inevitable impurities. The microstructure of the welded pipe is polygonal ferrite+pearlite, the ratio of the content of polygonal ferrite to the content of pearlite is 12.5:1-15:1, the fine and numerous polygonal ferrite can ensure the low-temperature toughness of the weld, the average grain size of the weld is 10.5-11, the average corrosion rate is 0.02-0.04 mm / a in the simulated supercritical carbon dioxide working environment, the Charpy impact toughness of the pipe body and the weld is all greater than or equal to 180 J at-80 DEG C, and the Charpy impact toughness of the pipe body and the weld is all greater than or equal to 100 J at-95 DEG C, and the low-temperature performance of the pipe body and the weld is very excellent.

Description

Technical Field

[0001] This invention relates to the field of pipe welding technology, and in particular to a welded pipe for conveying supercritical carbon dioxide (HFW), its manufacturing method, and its application. Background Technology

[0002] High-frequency welded (HFW) steel pipes are manufactured by heating the edges of hot-rolled steel coils to a molten state using the skin effect and proximity effect principles generated by high-frequency current, followed by welding through mechanical extrusion. Currently, the main shortcomings of conventional low-temperature HFW welded pipes are that the Charpy impact energy of the pipe body rapidly decreases to ≤27J below -75℃ or the weld seam below -60℃, failing to meet the requirements for high toughness at ultra-low temperatures, and also exhibiting insufficient corrosion resistance.

[0003] Several technologies have also provided methods for manufacturing high-strength, corrosion-resistant HFW welded pipes. CN111805180A discloses a manufacturing method for antibacterial corrosion X65 HFW welded pipes, employing a small extrusion amount and small opening angle process, combined with aging heat treatment, resulting in welded pipes with low residual stress. The circumferential opening of the pipe body, measured by the ring cutting method, is only -20 to 0 mm, and it is formed with low stress and negative residual stress. CN106906348A discloses a contact welding process for X70M large wall thickness HFW welded pipes, controlling the thickness of the hot-rolled steel coil, the tilt angle of the contact electrode feet, the contact welding foot pressure, the welding V-angle size, the welding extrusion amount, the welding speed, power, and frequency, which can save energy and ensure that the product quality meets the standards. Some technologies also provide HFW welded pipes with toughness at temperatures below -40°C. For example, CN101617062A, CN104220622A, and CN104641014A disclose methods that achieve weld toughness at low temperatures of -40°C to -60°C by finning or controlling oxide inclusions in the weld. However, HFW welded pipes manufactured using these methods lack toughness of the pipe body and weld at ultra-low temperatures (<-78.5°C) and lack evaluation of the pipe body and weld's resistance to supercritical carbon dioxide corrosion.

[0004] Currently, carbon dioxide capture, utilization, and storage (CCUS / CCS) technology has attracted widespread attention as a large-scale greenhouse gas emission reduction technology. For large-scale carbon dioxide storage, pipeline transportation is the most economical option. All existing carbon dioxide pipelines in China transport gases in the gas phase; construction of supercritical carbon dioxide pipelines has not yet begun. The decompression wave velocity during leakage in supercritical carbon dioxide pipelines differs from that of other media, potentially causing long-range brittle fracture propagation. Furthermore, under throttling and rapid decompression conditions, supercritical carbon dioxide pipelines exhibit a high Joule-Thomson coefficient, and the pipe materials may be exposed to temperatures ranging from -50℃ to -90℃ (the temperature at which supercritical carbon dioxide forms dry ice at normal pressure is -78.5℃), placing additional demands on the pipe materials' cryogenic fracture performance. This is particularly true for venting and throttling pipes transporting supercritical carbon dioxide, which require excellent resistance to cryogenic brittle fracture. Additionally, because it is difficult to completely remove impurities such as H2O, NO2, and SO2 from supercritical carbon dioxide using existing technologies, pipeline corrosion is easily induced, requiring steel pipes to possess certain resistance to corrosion under supercritical carbon dioxide operating conditions.

[0005] Therefore, it is necessary to develop an HFW welded pipe that can be used for supercritical carbon dioxide transport. Summary of the Invention

[0006] This invention addresses the problems of low Charpy impact absorption energy and insufficient resistance to supercritical carbon dioxide corrosion in conventional HFW welded pipes, particularly in the pipe body and weld seam. By precisely controlling the raw material composition and microstructure of HFW welded pipes and modifying the pipe-making equipment and processes, a fine polygonal ferrite + pearlite microstructure is achieved in the weld seam area. This results in the manufacture of HFW welded pipes with a Charpy ductile-brittle transition temperature below -95℃ and excellent resistance to supercritical carbon dioxide corrosion.

[0007] To achieve the above objectives, the present invention provides a welded pipe for conveying supercritical carbon dioxide (HFW), the composition of which, by mass percentage, comprises,

[0008] C: 0.04-0.06%, Si: ≤0.32%, P: ≤0.010%, S: ≤0.001%, Mn: 1.0-1.6%, Ni: 0.1-0.2%, Nb: 0.04-0.07%, Cr: 0.1-0.2%, Al: 0.02-0.05%, Zr: 0.03-0.05%, Mg: 0.02-0.04%, Nb+V+Ti: ≤0.15%, Mn / Si mass ratio is 5-8, the remainder is iron and unavoidable impurities.

[0009] Furthermore, the weld microstructure of the welded pipe is polygonal ferrite + pearlite, the ratio of polygonal ferrite content to pearlite content is controlled at 12.5:1-15:1, and the average grain size of the weld is grade 10.5-11.

[0010] This invention also provides a method for manufacturing a welded pipe for conveying supercritical carbon dioxide (HFW), comprising,

[0011] The coil is sequentially uncoiled and welded, planed, shaped, high-frequency contact welded, normalized heat treatment, and thermomechanical hammering of the weld seam to obtain the HFW welded pipe for conveying supercritical carbon dioxide.

[0012] The supercritical carbon dioxide (HFW) welded pipe comprises, by mass percentage: C: 0.04-0.06%, Si: ≤0.32%, P: ≤0.010%, S: ≤0.001%, Mn: 1.0-1.6%, Ni: 0.1-0.2%, Nb: 0.04-0.07%, Cr: 0.1-0.2%, Al: 0.02-0.05%, Zr: 0.03-0.05%, Mg: 0.02-0.04%, Nb+V+Ti: ≤0.15%, with an Mn / Si mass ratio of 5-8, and the remainder being iron and unavoidable impurities.

[0013] Furthermore, the planing includes controlling the plate width to ±0.5mm, and adjusting it according to the wall thickness of the rolled plate.

[0014] When the wall thickness of the rolled sheet is ≤12mm, no beveling is required;

[0015] When the wall thickness of the rolled plate is 12mm-25.4mm, a double-sided U-shaped bevel is welded, with a bevel angle of 10°±2.5°, a bevel radius of 5mm, and a bevel blunt edge of 12mm.

[0016] Furthermore, the forming process includes rough forming and fine forming;

[0017] The rough forming adopts the roller downhill forming method, and an additional pre-bending roller is added according to the pipe diameter design, and the plate width is pre-bent by 20°-30° on both sides.

[0018] The precision forming process involves adding a weld seam guide roller based on the tube curvature and strength design, increasing the extrusion amount to 10mm±2mm and the sizing amount to 4.0mm±0.5mm; the slit length between the convergence point of the coil and the weld point is 12mm-16mm.

[0019] Furthermore, the high-frequency contact welding includes the design of adding a multi-functional weld foot adapter and adding a shielding gas supply in the welding area:

[0020] The length of the molten zone of the coil is >25mm, and the welding opening angle is controlled at 3°-5°; the induction frequency is 425kHz±20kHz; the welding speed is 20m / min±3m / min, the width of the heat-affected zone of the weld is adjusted to 0.9mm-1.2mm, the minimum bright line width at the center of the weld is controlled at 150μm-280μm, and the metal flow line angle is controlled at 40°-50°; a shielding gas is introduced into the pipe directly below the welding area, and high-frequency oxygen-free welding is completed in the welding area under the shielding gas atmosphere.

[0021] Furthermore, the normalizing heat treatment includes,

[0022] Hold the weld at 930℃±20℃ for 10-30 seconds.

[0023] Furthermore, the thermomechanical hammering of the weld includes,

[0024] After normalizing heat treatment, the weld seam on the outside of the steel pipe is forged by a thermomechanical soft hammer at a frequency of 30Hz±5Hz.

[0025] Furthermore, after obtaining the HFW welded pipe for conveying supercritical carbon dioxide, the process also includes finished product dimensional adjustment and finished product inspection.

[0026] The present invention also provides the application of the above-mentioned HFW welded pipe in transporting supercritical carbon dioxide.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. This invention precisely controls the chemical composition of the raw materials for HFW welded pipes used for supercritical carbon dioxide transportation, precisely controls the C, Mn, and Si elements, reduces the P element, especially the S element, and particularly rationally adds the Mn, Ni, Zr, and Al elements, which can significantly reduce the ductile-brittle transition temperature of steel, and supplements appropriate Nb, Cr, and Mg elements to increase the strength, toughness, and resistance to supercritical carbon dioxide corrosion of thick-walled HFW welded pipe plates and welds.

[0029] 2. This invention uses a low-temperature, high-tonnage press to control the reduction amount, reduce billet segregation, and roll out a flat, quasi-polygonal ferrite + pearlite microstructure with a grain size of grade 11. The refined quasi-polygonal ferrite grains have an aspect ratio of ≥4, which avoids crack propagation and ensures the low-temperature toughness of the HFW welded pipe body for supercritical carbon dioxide transportation. At the same time, it improves the pipe body's resistance to corrosion by supercritical carbon dioxide containing impurities.

[0030] 3. This invention adopts a double-sided U-shaped bevel with minimal welding deformation and uses a roller-downhill forming method. A pre-bending roller is added according to the pipe diameter design, and a weld seam guide roller is added according to the pipe curvature and strength design. The extrusion amount is increased to 10mm±2mm to ensure high-precision butt joint of the pipe blank edge. This allows the oxide inclusions in the weld seam area to be fully extruded and squeezed out, keeping the length and number of residual oxide defects in the weld seam as short as possible, and ensuring the geometric dimensional accuracy of the HFW welded pipe.

[0031] 4. This invention employs high-frequency and high-speed welding, which greatly eliminates microscopic inclusions of several micrometers in size distributed in clusters. A multi-functional weld foot adapter is added during high-frequency contact welding to incorporate the advantages of high-frequency induction welding, achieving uniform heating of the neutral layer welding points and opening corner apex of thick-walled pipes. 99.99% pure nitrogen gas produced by an outdoor air nitrogen generator is introduced, and high-frequency welding is completed in the welding area through a copper pipe under nitrogen protection after oxygen isolation, further improving the purity of the weld metal. The addition of a low-frequency thermomechanical soft hammer pressing welding joint area allows for finer weld grains under forging pressure, significantly reducing micro-deformation defects within the weld and achieving micro-deformation strengthening and stress relief in the welding area. This further improves the low-temperature toughness and resistance to supercritical carbon dioxide corrosion of the HFW welded pipe joint.

[0032] 5. The weld microstructure of the welded pipe of the present invention is polygonal ferrite + pearlite, with the ratio of polygonal ferrite content to pearlite content being 12.5:1-15:1. The numerous small polygonal ferrite particles ensure the low-temperature toughness of the weld. The average grain size of the weld is grade 10.5-11. In a simulated supercritical carbon dioxide environment, the average corrosion rate is 0.02mm / a-0.04mm / a. At -80℃, the Charpy impact toughness of both the pipe body and the weld is ≥180J, and at -95℃, the Charpy impact toughness of both the pipe body and the weld is ≥100J. The low-temperature performance of both the pipe body and the weld is excellent.

[0033] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the steps or apparatus pointed out in the description and the drawings. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1The metallographic structure of the weld seam of the HFW welded pipe for conveying supercritical carbon dioxide in an embodiment of the present invention is shown. Detailed Implementation

[0036] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention. In this invention, all materials, instruments, and apparatus are commercially available and equivalent, and experimental methods without specific conditions are conventional methods and conditions well known in the art, or according to the conditions recommended by the instrument manufacturer.

[0037] The HFW welded pipe for conveying supercritical carbon dioxide of the present invention is made of X70 steel. Its composition, by mass percentage, includes: C: 0.04-0.06%, Si: ≤0.32%, P: ≤0.010%, S: ≤0.001%, Mn: 1.0-1.6%, Ni: 0.1-0.2%, Nb: 0.04-0.07%, Cr: 0.1-0.2%, Al: 0.02-0.05%, Zr: 0.03-0.05%, Mg: 0.02-0.04%, Nb+V+Ti: ≤0.15%, and the Mn / Si mass ratio is controlled at 5-8. The remainder is iron and unavoidable impurities. The microstructure of the pipe body consists of flat quasi-polygonal ferrite and pearlite, with an average grain size of grade 11. The microstructure of the weld consists of polygonal ferrite and pearlite, with the ratio of polygonal ferrite content to pearlite content controlled at 12.5:1-15:1, and the average grain size of the weld is grade 10.5-11.

[0038] The composition design principle of the HFW welded pipe for supercritical carbon dioxide transportation in this invention is as follows: In low-carbon microalloyed steel, the C content tends to increase pearlite, increasing the brittleness of the steel. Mn and Ni are both substitutional atoms, which can significantly reduce the ductile-brittle transition temperature of the steel, but excessive Mn can easily cause segregation. Adding a large amount of Zr refines the dendrites and grains in the heat-affected zone of the weld, and can also significantly improve the low-temperature toughness of the heat-affected zone of the HFW welded pipe. Mg reduces the size of inclusions in the steel, and the Zr-Mg composite reduces the number and size of inclusions in the HFW welded pipe weld. Al has a strong affinity for oxygen and nitrogen in steel, and the AlN formed by combining with N can refine the grains, inhibit the aging of low-carbon steel, and improve the toughness of the steel at low temperatures. P and S reduce the surface energy of grain boundaries, reduce fracture stress, and seriously affect the ductile-brittle transition temperature, requiring strict control. Although Si deoxidizes, it tends to increase the oxide content in the resistance weld, which has an adverse effect on toughness. The relative content of Mn and Si in the plate determines the type of composite inclusions. Different Mn / Si composite inclusions have different melting points. When the melting point of the inclusions in the weld is higher than the melting point of the welded part (-1550℃), oxides are difficult to remove and remain in the weld. To facilitate oxide removal, the Mn / Si ratio should be controlled within the range of 5-8. Nb, V, and Al can be precipitation-strengthened and grain-refining, which is beneficial for improving the brittle-ductile transition temperature. Ti has a strong affinity for N, combining to form TiN, achieving grain refinement and effectively improving material toughness. However, excessive Ti, resulting in large TiN particles, can affect the low-temperature toughness of the material. The addition of Cr can improve the hardenability of steel and is relatively economical, ensuring lower pipe costs. Appropriate amounts of Nb, Cr, and Mg all contribute to increasing the strength and toughness of the pipe body and weld of thick-walled HFW welded pipes, and inhibit the formation of coarse polygonal ferrite, thus improving the resistance of HFW welded pipes to supercritical carbon dioxide corrosion.

[0039] The microstructure design of the HFW welded pipe for supercritical carbon dioxide transportation in this invention is as follows: LF and RH co-refining is employed, utilizing electromagnetic stirring and a low-temperature, high-tonnage press to control the reduction, minimize billet segregation, and ensure the homogeneity of the billet. The plate grain size reaches grade 11, refining the polygonal ferrite to prevent crack propagation. The average aspect ratio of the polygonal ferrite grains is ≥4. The flat, quasi-polygonal ferrite + pearlite microstructure of the plate increases the fracture path, ensuring the low-temperature toughness of the HFW welded pipe for supercritical carbon dioxide transportation, while simultaneously improving the pipe's resistance to corrosion from supercritical carbon dioxide containing impurities.

[0040] The manufacturing method of the HFW welded pipe for conveying supercritical carbon dioxide of the present invention includes the following steps:

[0041] The rolled steel sheet undergoes a series of processes including uncoiling and butt welding, edge planing, forming, high-frequency contact welding, normalizing heat treatment, thermomechanical hammering of the weld seam, sizing and flying shearing, straightening, X-ray inspection and ultrasonic inspection, and pipe end beveling to obtain the supercritical carbon dioxide (HFW) welded pipe. After obtaining the HFW welded pipe, the process also includes finished product inspection and dimensional adjustment.

[0042] The uncoiling and welding refers to the flush joining of the head and tail of the coiled sheet.

[0043] The beveling process includes controlling the plate width to ±0.5mm, and adjusting it according to the plate wall thickness. Specifically, when the plate wall thickness is ≤12mm, no beveling is performed; when the plate wall thickness is 12mm-25.4mm, a double-sided U-shaped beveling with minimal welding deformation is performed, with a beveling angle of 10°±2.5°, a beveling radius of 5mm, and a beveling blunt edge of 12mm. This avoids stress concentration in the weld seam at the center of the thick-walled pipe during subsequent welding, and avoids uneven heating in the thickness direction caused by the initial heating and melting of the upper and lower corners of the conventional plate. By precisely controlling the plate width to ±0.5mm through beveling at both ends of the plate, the uniformity of the circumferential dimensions of the tube blank can be ensured.

[0044] The supercritical carbon dioxide HFW welded pipe forming of the present invention is an optimized roller forming process compared to the existing (conventional) HFW welded pipe forming process. It also includes the addition of a pre-bending roller and a weld seam guide roller.

[0045] The forming process includes rough forming and fine forming. The rough forming adopts a roller downhill forming method, and a pre-bending roller is added according to the pipe diameter design, with the plate width pre-bent by 20°-30° on both sides. The fine forming adds a weld seam guide roller according to the pipe curvature and strength design, increasing the extrusion amount to 10mm±2mm and the sizing amount to 4.0mm±0.5mm. The slit length between the convergence point of the coil and the weld point is 12mm-16mm to ensure that impurities in the weld are extruded from the interface and squeezed out of the weld during subsequent welding.

[0046] The rough forming process using a roller-downhill forming method ensures that the longitudinal tensile strain generated by the sheet metal is evenly distributed along the width of the tube blank, with minimal edge extension, significantly reducing uneven deformation at the tube blank edge and thus minimizing wavy bends. An additional pre-bending roller is added according to the tube diameter design, utilizing a pre-bending anti-recovery forming method on the plate edge. A small angle of 20°-30° is pre-bent in a 200mm area on each side to ensure minimal stress and strain at the plate edge during precision forming and welding, ensuring uniform wall thickness in the weld heat-affected zone, reducing residual stress in the weld area, and guaranteeing the welding quality of thick-walled tubes. During precision forming, a weld guide roller is added between the existing two extrusion rollers according to the tube curvature and strength design. A certain amount of pressure is applied in the direction perpendicular to the weld tube, precisely pressing the pre-welded tube blank into a flat ellipse, making the two surfaces to be welded completely parallel, ensuring the stability of the tube blank edge, ensuring the center of the strip steel is aligned with the center of the roll, and increasing the extrusion amount to 1. 0mm±2mm allows more oxide inclusions in the weld area to be squeezed out. By reasonably adjusting the position and spacing of the two side extrusion rollers, a high-frequency dynamic expansion and contraction slit will exist between the convergence point at both ends of the coil and the weld point. This ensures that the slit length between the convergence point of the coil and the weld point is about 12mm-16mm, so that the fine oxide inclusions can be melted and squeezed out more easily. This controls the area ratio of micro-defects with a maximum weld length of less than 20μm to be below 0.04%, ensuring that the HFW weld is in an ultra-low defect rate state. The sizing amount is controlled at 4.0mm±0.5mm to ensure the geometric dimensional accuracy of the HFW welded pipe.

[0047] The high-frequency contact welding includes the design of adding a multi-functional welding foot adapter and introducing shielding gas into the welding area: the length of the molten zone of the coil is >25mm, the welding opening angle is controlled at 3°-5°; the induction frequency is 425kHz±20kHz; the welding speed is 20m / min±3m / min, the width of the heat-affected zone of the weld is adjusted to 0.9mm-1.2mm, the minimum bright line width at the center of the weld is controlled at 150μm-280μm, and the metal flow line angle is controlled at 40°-50°; shielding gas is introduced into the pipe directly below the welding area to complete high-frequency oxygen-free welding of the welding area under the shielding gas atmosphere.

[0048] The high-frequency contact welding of this invention, compared to existing (conventional) methods, adds a multi-functional welding foot adapter to achieve uniform heating of the welding area, while simultaneously achieving the advantages of high-frequency induction welding. This ensures uniform heating of the neutral layer welding point and the apex of the opening angle in thick-walled pipes, improving welding efficiency and preventing arc burns that are common in traditional contact welding. The welding opening angle is controlled at 3°-5°, and the welding speed is 20m / min±3m / min. A fully automatic speed / power control system is used to ensure that the time from the start of heating to the extrusion welding of the plate edge is controlled within 1.0s-1.8s, ensuring uniform heating of the upper and lower ends of the thick-walled pipe without melting and sagging, and maintaining the viscosity and heating depth of the molten metal at the edge of the steel strip. The high-frequency contact welding induction frequency is 425kHz±20kHz, the heat-affected zone width is adjusted from 0.9mm to 1.8mm, the minimum bright line width at the weld center is controlled at 180μm-250μm, and the metal flow line angle is controlled at 40°-50°, ensuring uniform heating during welding. This facilitates the extrusion and removal of fine oxides along the double-sided U-shaped bevel, improving the toughness of the weld and heat-affected zone. Nitrogen gas with a purity of 99.99% produced by an economical air nitrogen generator is introduced into the pipe directly below the welding area. High-frequency welding is then performed on the welding area under the oxygen-free protection of nitrogen gas, further improving the purity of the weld metal.

[0049] The normalizing heat treatment includes holding the weld at 930℃±20℃ for 10-30 seconds, preferably 20 seconds.

[0050] The thermomechanical hammering of the weld seam includes hammering the forged weld seam at a frequency of 30Hz±5Hz in the weld seam area on the outside of the steel pipe after normalizing heat treatment using a thermomechanical soft hammer.

[0051] The normalizing heat treatment and the thermomechanical hammering of the weld are mainly used to refine the weld grains and reduce residual stress in the weld area, thereby further improving the low-temperature toughness and resistance to supercritical carbon dioxide corrosion of the weld metal. Within a 1-meter area after normalizing heat treatment, a low-frequency thermomechanical soft hammer is added to hammer the outer side of the weld, controlling and eliminating welding stress after high-speed welding. This causes slight deformation of the grains in the weld joint area, resulting in grain refinement and strengthening, reducing defects within the weld, and further improving the low-temperature toughness and resistance to supercritical carbon dioxide corrosion of the HFW welded pipe joint.

[0052] After normal production processes, HFW welded pipes for conveying supercritical carbon dioxide undergo further dimensional adjustments and inspections, including sizing with a flying shear, straightening, X-ray and ultrasonic inspections, pipe end beveling, visual dimensional checks, and final weld quality and corrosion resistance testing. This process ensures the performance of the HFW welded pipes for conveying supercritical carbon dioxide and their suitability for further applications.

[0053] The present invention also provides applications of the above-mentioned HFW welded pipe, such as supercritical carbon dioxide transportation and cryogenic transportation.

[0054] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] Example

[0056] A method for manufacturing HFW welded pipe,

[0057] Step 1: Raw material acquisition

[0058] X70 steel grade with a wall thickness of 14mm was used as the raw material for the coil. Its chemical composition is designed as shown in Table 1 (wt.%). After low-temperature high-tonnage rolling, a coil with a flat microstructure and an average length-to-width ratio of 4.3 for quasi-polygonal ferrite micrograins was obtained.

[0059] Table 1. Raw material composition (wt.%) of coiled steel for supercritical carbon dioxide conveying welded pipes

[0060] C Mn Si P S Ni Cr Al Ti V Nb Zr Mg 0.04 1.18 0.19 0.009 0.0008 0.18 0.15 0.03 0.014 0.05 0.05 0.04 0.03

[0061] Step 2, Welded Pipe Manufacturing

[0062] The rolled plate obtained in step 1 is used to produce HFW welded pipes for conveying supercritical carbon dioxide with an outer diameter of Φ323.9mm and a wall thickness of 14mm.

[0063] After uncoiling, leveling, and double-sided U-shaped milling, the strip width is precisely controlled at 1007mm. Rough forming employs a roller-downhill forming method, adding a 27° pre-bending roller to pre-bend the strip to 24° on both sides. A weld seam curvature guide roller is added between the original two side extrusion rollers. The extrusion amount is adjusted to 11mm based on the 14mm wall thickness and X70 steel grade, with a sizing amount of 4.2mm. During high-frequency induction resistance welding, a multi-functional welding foot adapter is added to achieve uniform heating of the welding area. The welding opening angle is controlled at 3.7°. A fully automatic speed / power control system is used, adjusting the high-frequency contact welding induction frequency to 440kHz, the welding speed to 21.3m / min, the width of the heat-affected zone at the weld center to 0.98mm, the minimum bright line width at the weld center to 152μm, and the metal flow line angle to 42°. 99.99% pure nitrogen gas, produced by a nitrogen generator, is introduced into a copper tube directly below the welding area, allowing for high-frequency contact welding under oxygen-free nitrogen protection. The weld was then subjected to normalizing heat treatment at 935℃ for 20 seconds. After heat treatment, the outside of the steel pipe was hammered with a medium-frequency thermomechanical soft hammer at a frequency of 25Hz to strengthen the weld deformation and relieve stress.

[0064] Step 3: Finished Product Inspection

[0065] The HFW welded pipes obtained in step 2 are subjected to sizing, straightening, X-ray inspection, ultrasonic inspection, pipe end beveling, appearance and dimensional inspection, and chemical and corrosion resistance testing of the finished welded pipes according to the design length.

[0066] Figure 1 The metallographic structure of the weld seam of the HFW welded pipe for transporting supercritical carbon dioxide is shown. The weld seam microstructure consists of polygonal ferrite and pearlite, with a polygonal ferrite to pearlite content ratio of 14:1. The average grain size of the weld seam is 10.5, and the area ratio of micro-defects with a maximum weld length of less than 20 μm is 0.02%. The metallographic structure of the HFW welded pipe body shows that the microstructure of the pipe body consists of flattened quasi-polygonal ferrite and pearlite, with an average grain size of grade 11. The fine grains in the pipe body and weld seam, and the significant reduction in pearlite, which is detrimental to the poor performance of supercritical carbon dioxide, indicate that the HFW welded pipe for transporting supercritical carbon dioxide manufactured by this invention has high resistance to supercritical carbon dioxide corrosion.

[0067] The mechanical property test results of the HFW welded pipe for conveying supercritical carbon dioxide according to the embodiments of the present invention are as follows: the yield strength Rt of the HFW welded pipe body 0.5 485MPa-600MPa, tensile strength R of the pipe body b The pipe strength is 575MPa-690MPa, the yield strength ratio is 0.78-0.90, the elongation is 28%-34%, and the weld tensile strength Rm ≥ 575MPa. Flattening tests were conducted at 0° and 90° positions. When the two sides of the welded pipe were pressed together, no cracks or splits were observed in any of the welds. At 0°C, the pipe AkV was 220J-350J, and the weld AkV was 210-325J. Referring to API 5L standard, all mechanical property tests met the standard requirements. Furthermore, at -80°C (the melting point of carbon dioxide at normal pressure is -78.5°C), the pipe AkV was 270J-350J, and the weld AkV was 180-288J. The Charpy impact toughness of the pipe body and weld is ≥180J at -80℃, and AkV of the pipe body and weld is ≥100J at -95℃, indicating excellent low-temperature performance of the weld. These results demonstrate that the mechanical properties of the HFW welded pipe manufactured according to this invention meet the requirements for transporting supercritical carbon dioxide.

[0068] The supercritical carbon dioxide (HFW) welded pipe manufactured according to the embodiments of the present invention was compared with the conventional X70 steel grade high-frequency welded pipe in a supercritical carbon dioxide corrosion comparison test. Table 2 shows the chemical composition of the coiled plate used for the conventional X70 steel grade high-frequency welded pipe. The Mn / Si ratio in the raw material is 9.5, with no Zr and Mg. Other microalloying elements are added arbitrarily. After conventional forming and welding, the weld has relatively more inclusions, relatively coarse weld grains, and a pearlite content of 17% in the weld. There are relatively more micro-defects in the weld, resulting in poor resistance to carbon dioxide corrosion. In a specially made high-temperature and high-pressure autoclave, the composition of the supercritical carbon dioxide medium under a certain conventional working condition was simulated. After 7 days, the corrosion performance test results are shown in Table 3.

[0069] Table 2. Raw material composition of conventional X70 coil (wt.%)

[0070] C Mn Si P S Ni Cr Cu Al Ti V Nb Zr Mg 0.03 1.70 0.18 0.009 0.003 0.15 0.10 0.15 0.04 0.012 0.02 0.04 / /

[0071] Table 3 Corrosion performance test results

[0072]

[0073]

[0074] As shown in Table 3, in a simulated supercritical carbon dioxide environment, the average corrosion rate of the HFW welded pipe manufactured in this embodiment is less than half that of the conventional X70 HFW welded pipe. The HFW welded pipe for supercritical carbon dioxide transportation exhibits an average corrosion rate of 0.02 mm / a-0.04 mm / a, demonstrating stronger resistance to supercritical carbon dioxide corrosion. Mechanical property and corrosion resistance test results indicate that the supercritical carbon dioxide HFW welded pipe manufactured in this invention is defect-free, exhibits excellent low-temperature weld performance, and demonstrates strong resistance to supercritical carbon dioxide corrosion, showing great promise for use as a pipe material for transporting supercritical carbon dioxide.

[0075] In summary, this invention precisely controls the chemical composition of the raw materials for HFW welded pipes used in supercritical carbon dioxide transportation, precisely controls C, Mn, and Si elements, reduces P, especially S elements, and particularly rationally adds Mn, Ni, Zr, and Al elements, which can significantly reduce the ductile-brittle transition temperature of steel, and supplements appropriate Nb, Cr, and Mg elements to increase the strength, toughness, and resistance to supercritical carbon dioxide corrosion of the thick-walled HFW welded pipe plates and welds. The microstructure of the weld in this invention consists of polygonal ferrite and pearlite, with a polygonal ferrite to pearlite ratio of 12.5:1 to 15:1. The numerous fine polygonal ferrite particles ensure the low-temperature toughness of the weld. The average grain size of the weld is grade 10.5 to 11. At -80℃, the Charpy impact toughness of both the pipe and the weld is ≥180J, and at -95℃, the Charpy impact toughness of both the pipe and the weld is ≥100J. The pipe and the weld exhibit excellent low-temperature performance, with an average corrosion rate of 0.02mm / a to 0.04mm / a in a simulated supercritical carbon dioxide environment.

[0076] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A welded pipe for conveying supercritical carbon dioxide (HFW), characterized in that, Its components, by mass percentage, include, C: 0.04-0.06%, Si: ≤0.32%, P: ≤0.010%, S: ≤0.001%, Mn: 1.0-1.6%, Ni: 0.1-0.2%, Nb: 0.04-0.07%, Cr: 0.1-0.2%, Al: 0.02-0.05%, Zr: 0.03-0.05%, Mg: 0.02-0.04%, Nb+V+Ti: ≤0.15%, Mn / Si mass ratio is 5-8, the remainder is iron and unavoidable impurities; The weld microstructure of the welded pipe is polygonal ferrite + pearlite, with the ratio of polygonal ferrite content to pearlite content controlled at 12.5:1-15:1, and the average grain size of the weld is grade 10.5-11.

2. A method for manufacturing a welded pipe for conveying supercritical carbon dioxide (HFW) as described in claim 1, characterized in that, include, The coil is sequentially uncoiled and welded, planed, shaped, high-frequency contact welded, normalized heat treatment, and thermomechanical hammering of the weld seam to obtain the HFW welded pipe for conveying supercritical carbon dioxide. The supercritical carbon dioxide (HFW) welded pipe comprises, by mass percentage: C: 0.04-0.06%, Si: ≤0.32%, P: ≤0.010%, S: ≤0.001%, Mn: 1.0-1.6%, Ni: 0.1-0.2%, Nb: 0.04-0.07%, Cr: 0.1-0.2%, Al: 0.02-0.05%, Zr: 0.03-0.05%, Mg: 0.02-0.04%, Nb+V+Ti: ≤0.15%, with an Mn / Si mass ratio of 5-8, and the remainder being iron and unavoidable impurities.

3. The manufacturing method according to claim 2, characterized in that, The planing process includes controlling the plate width to ±0.5mm, and adjusting it according to the wall thickness of the rolled plate. When the wall thickness of the rolled sheet is less than 12mm, no beveling is required; When the wall thickness of the rolled plate is 12mm-25.4mm, a double-sided U-shaped bevel is welded, with a bevel angle of 10°±2.5°, a bevel radius of 5mm, and a bevel blunt edge of 12mm.

4. The manufacturing method according to claim 2, characterized in that, The forming process includes rough forming and fine forming; The rough forming adopts the roller downhill forming method, and an additional pre-bending roller is added according to the pipe diameter design, and the plate width is pre-bent by 20°-30° on both sides. The precision forming process involves adding a weld seam guide roller based on the tube curvature and strength design, increasing the extrusion amount to 10mm±2mm and the sizing amount to 4.0mm±0.5mm; the slit length between the convergence point of the coil and the weld point is 12mm-16mm.

5. The manufacturing method according to claim 2, characterized in that, The high-frequency contact welding includes the design of adding a multi-functional welding foot adapter and adding a shielding gas supply to the welding area: The length of the molten zone of the coil is >25mm, and the welding opening angle is controlled at 3°-5°; the induction frequency is 425kHz±20kHz; the welding speed is 20m / min±3m / min, the width of the heat-affected zone of the weld is adjusted to 0.9mm-1.2mm, the minimum bright line width at the center of the weld is controlled at 150μm-280μm, and the metal flow line angle is controlled at 40°-50°; a shielding gas is introduced into the pipe directly below the welding area, and high-frequency oxygen-free welding is completed in the welding area under the shielding gas atmosphere.

6. The manufacturing method according to claim 2, characterized in that, The normalizing heat treatment includes, Hold the weld at 930℃±20℃ for 10-30 seconds.

7. The manufacturing method according to claim 2, characterized in that, The thermomechanical hammering of the weld includes, After normalizing heat treatment, the weld seam on the outside of the steel pipe is forged by a thermomechanical soft hammer at a frequency of 30Hz±5Hz.

8. The manufacturing method according to any one of claims 2-7, characterized in that, After obtaining the HFW welded pipe for conveying supercritical carbon dioxide, the process also includes finished product size adjustment and finished product inspection.

9. The application of the HFW welded pipe as described in claim 1 in transporting supercritical carbon dioxide.

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