Low-temperature-resistant coiled tubing as well as preparation method and application thereof

Abstract

The invention provides a low-temperature-resistant coiled tubing and a preparation method and application thereof. Raw materials are prepared from, by weight, 0.03%-0.12% of C, 0.1%-0.3% of Si, 0.8%-1.5% of Mn, 0.1%-0.5% of Ni, 0.1%-0.4% of Mo, 0.1%-0.4% of Cr, 0.05%-0.25% of Cu, 0.005%-0.03% of Ti, 0.01%-0.07% of V, 0.015%-0.12% of Al, 0.03%-0.1% of Nb, 0.001%-0.005% of N, smaller than or equal to 0.0005% of B, smaller than or equal to 0.015% of P, smaller than or equal to 0.002% of S and the balance Fe and inevitable impurity elements. The raw materials are smelted and prepared into a coiled plate, and then the low-temperature-resistant coiled tubing is obtained through a plurality of processes. The obtained low-temperature-resistant coiled tubing has good low-temperature resistance and can meet the application requirements of oil-gas exploration in low-temperature and extremely cold environments.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum and natural gas pipes, and in particular to a low-temperature resistant continuous pipe, a preparation method thereof and applications thereof. Background Art

[0002] Low temperature resistant coiled tubing is called coiled tubing because of its good coilability. It is a new type of oil pipe with a single length of several thousand meters and no threaded connection, made of high-performance metal materials through continuous forming and welding process. The finished product is wound on a reel for transportation and delivery. It can replace conventional oil pipes for a variety of operations. Low temperature resistant coiled tubing operation equipment has the characteristics of pressure operation and continuous lifting and lowering. At the same time, the equipment is small in size, short in operation cycle and low in cost, so it is widely used in oil and gas fields.

[0003] With the rapid development of the economy, the demand for oil and natural gas is also increasing day by day. After a long period of oil and gas development, the world's easily exploitable oil and gas resources have gradually dried up, and the exploitation of oil and gas resources has gradually extended to difficult-to-extract areas such as deserts, frozen soil, oceans, and polar regions. With the continuous development of low-temperature resistant continuous pipe technology in the field of oil and gas resource exploration and development, the areas where low-temperature resistant continuous pipe technology is applied are also constantly expanding to high-latitude and cold regions such as Russia and the polar regions. The low temperature and harsh climate environment in these extremely cold regions has put forward new requirements for the performance of pipes. Russia has extremely rich oil reserves, mainly in the eastern and northern regions. The crude oil reserves in Western Siberia and the Volga-Ural region alone account for about 3 / 4 of the total reserves in Russia, and most of these oil fields are distributed in the cold areas in northern Russia, and some are even in the Arctic region or permafrost. According to the United States Geological Survey, the Arctic contains 13% of the world's undiscovered conventional oil resources and about 30% of conventional natural gas resources. However, parts of the Arctic are covered with ice and snow all year round, with the average temperature in January ranging from -40°C to -10°C, and the lowest temperature in most areas in winter can drop to below -50°C. In history, there have been many pipe breakage accidents caused by low-temperature brittleness, causing great losses. All of the above have seriously restricted the development of oil and gas exploration and development technologies.

[0004] Therefore, there is an urgent need to develop a low-temperature resistant low-temperature coiled pipe in the art to solve the problem that the existing low-temperature resistant coiled pipe has poor low-temperature resistance and is limited in application in oil and gas exploration and production in low-temperature and extremely cold environments. Summary of the invention

[0005] The main purpose of the present invention is to provide a low-temperature resistant coiled pipe, a preparation method and application thereof, so as to solve the problem that the existing low-temperature resistant coiled pipe has poor low-temperature resistance and is limited in application in oil and gas exploration and production in low-temperature and extremely cold environments.

[0006] In order to achieve the above object, the present invention provides a method for preparing a low-temperature resistant coiled tube, comprising:

[0007] The raw materials are prepared according to the following composition: by weight percentage, the components of the low-temperature resistant coiled tube include: C 0.03-0.12%, Si 0.1-0.3%, Mn 0.8-1.5%, Ni 0.1-0.5%, Mo 0.1-0.4%, Cr 0.1-0.4%, Cu 0.05-0.25%, Ti 0.005-0.03%, V 0.01-0.07%, Al 0.015-0.12%, Nb 0.03-0.1%, N 0.001-0.005%, B≤0.0005%, P≤0.015%, S≤0.002%, and the balance is Fe and unavoidable impurity elements;

[0008] The raw materials are smelted and prepared into coils, and then longitudinal shearing, groove processing, butting, forming, longitudinal welding, heat treatment and continuous growth are carried out in sequence to obtain low-temperature resistant continuous pipes.

[0009] Furthermore, in the composition of the above-mentioned low-temperature resistant continuous tube, the weight ratio of Si to Mn elements is 1:(5-8).

[0010] Furthermore, in the composition of the above-mentioned low-temperature resistant continuous tube, the Al element includes Als in the form of acid-soluble aluminum, and the proportion of Als in the low-temperature resistant continuous tube is 0.01-0.07% by weight.

[0011] Furthermore, in the composition of the low-temperature resistant continuous pipe, the content of B element is 0.0002-0.0003% by weight.

[0012] Further, the composition of the low-temperature resistant coiled tube includes, by weight percentage: C 0.06%, Si 0.18%, Mn 1.15%, P 0.005%, S 0.002%, Ni 0.3%, Mo 0.25%, Cr 0.28%, Cu 0.12%, Ti 0.012%, V 0.05%, Al 0.055%, Nb 0.045%, N 0.002%, B 0.0002%, wherein Als is 0.03%, and the balance is Fe and unavoidable impurity elements; or C 0.1%, Si 0.23%, Mn 1.28%, P 0.005%, S 0.002%, Ni 0.45%, Mo 0.35%, Cr 0.35%, Cu 0.22%, Ti 0.025%, V 0.06%, Al 0.095%, Nb 0.055%, N 0.003%, B 0.0003%, of which Als is 0.05%, and the balance is Fe and inevitable impurity elements.

[0013] Furthermore, in the above-mentioned method for preparing the low-temperature resistant continuous tube, the step of smelting and preparing the coiled plate comprises:

[0014] Step S1, refining the raw material and then casting it to obtain a continuous casting billet;

[0015] Step S2, rolling the continuous casting slab into a primary hot-rolled plate at 1000-1050° C., and then rolling the primary hot-rolled plate into a secondary hot-rolled plate at 860-880° C.;

[0016] Step S3, water-cooling and curling the secondary hot-rolled plate to obtain a coil;

[0017] Preferably, the continuous casting billet is a slab with a thickness of 30 to 70 mm; preferably, the thickness of the first hot-rolled plate is 10 to 20 mm; preferably, the thickness of the second hot-rolled plate is 2.3 to 7.65 mm; preferably, the length of the coil is ≥ 250 m.

[0018] Furthermore, in the above-mentioned method for preparing the low-temperature resistant continuous tube, the heat treatment is to perform heat treatment on the entire body of the low-temperature resistant continuous tube; preferably, the heat treatment is isothermal annealing, which is achieved by medium-frequency induction heating; preferably, the heating temperature of the isothermal annealing is 450-700°C, and the cooling temperature is 250-350°C; more preferably, the cooling rate of the isothermal annealing is 8-15°C / s.

[0019] Furthermore, in the above-mentioned method for preparing the low-temperature resistant coiled tube, the butt-jointing step is implemented by a method selected from stir friction welding, CMT welding or TIG welding.

[0020] Another aspect of the present invention provides a low-temperature resistant continuous pipe, which is prepared by the above preparation method, and has a yield strength of ≥620MPa, a tensile strength of ≥689MPa, an elongation of ≥26%, an impact energy of ≥150J at -75°C, an outer diameter range of Φ25.4 to Φ88.9mm, a wall thickness range of 1.9 to 7.6mm, and a length range of 61 to 10000m.

[0021] Another aspect of the present invention provides the use of the above-mentioned low-temperature resistant coiled pipe in the field of oil and gas exploration and production.

[0022] By applying the technical solution of the present invention, the toughness of the obtained low-temperature resistant continuous pipe is improved by adding specific contents of Mn, Ni and Ti elements, the contents of S and P elements are strictly controlled, the grains are refined by microalloying of Nb, V and Al elements, the tough-brittle transition temperature of the obtained low-temperature resistant continuous pipe is improved, the contents of each element are reasonably adjusted, and the contents of each component are coordinated with each manufacturing process parameter to achieve the excellent performance of the obtained low-temperature resistant continuous pipe. The low-temperature resistant continuous pipe prepared by the above method has a yield strength of ≥620MPa, a tensile strength of ≥689MPa, an elongation of ≥26%, an impact energy of ≥150J at -75°C, an outer diameter range of Φ25.4 to Φ88.9mm, a wall thickness range of 1.9 to 7.6mm, and a length range of 61 to 10000m. It has excellent mechanical properties and is resistant to low temperatures, and can be well used in oil and gas exploration and production in low temperature and extremely cold environments. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0024] As described in the background technology, the low-temperature resistant coiled pipe provided by the prior art has poor low-temperature resistance and is limited in application in oil and gas exploration and production in low-temperature and extremely cold environments. In order to solve the above technical problems, the present application provides a method for preparing a low-temperature resistant coiled pipe, comprising:

[0025] The raw materials are prepared according to the following composition: by weight percentage, the components of the low-temperature resistant coiled tube include: C 0.03-0.12%, Si 0.1-0.3%, Mn 0.8-1.5%, Ni 0.1-0.5%, Mo 0.1-0.4%, Cr 0.1-0.4%, Cu 0.05-0.25%, Ti 0.005-0.03%, V 0.01-0.07%, Al 0.015-0.12%, Nb 0.03-0.1%, N 0.001-0.005%, B≤0.0005%, P≤0.015%, S≤0.002%, and the balance is Fe and unavoidable impurity elements;

[0026] The raw materials are smelted and prepared into coils, and then longitudinal shearing, groove processing, butting, forming, longitudinal welding, heat treatment and continuous growth are carried out in sequence to obtain low-temperature resistant continuous pipes.

[0027] In the above preparation method, by adding Mn and Ni elements to the low temperature resistant continuous tube composition, the two elements are replacement atoms, which can be dissolved into the iron alloy material matrix to play a role in solid solution strengthening. The Mn element can form carbides to play a role in dispersion strengthening, and can also promote the obtained low temperature resistant continuous tube to avoid temper brittleness; Ni can produce reversed austenite, reduce the number and size of quasi-polygonal ferrite, and improve the toughness of the material. However, if the content of the two is too high, it may cause organizational segregation and reduce the mechanical properties of the obtained low temperature resistant continuous tube. Therefore, the present invention limits the content of the two to 0.8-1.5% and 0.1-0.5% respectively. The C element can improve the mechanical strength of the obtained low temperature resistant continuous tube through interstitial solid solution strengthening, but its content is too high, which is not conducive to the low temperature toughness of the alloy. At the same time, it is easy to form a more serious hard phase segregation zone, aggravate the organizational inhomogeneity, and is not conducive to the fatigue performance of the obtained low temperature resistant continuous tube. Therefore, the present invention controls it to 0.03-0.12%. Mo element can inhibit the formation of ferrite and pearlite, and its content is controlled at 0.1-0.4% to obtain a low-temperature resistant continuous pipe with strong toughness and plasticity; Cr element also has the effect of solid solution strengthening, and can improve the corrosion resistance of the obtained low-temperature resistant continuous pipe to a certain extent. The present invention controls its content at 0.1-0.4% to better play its strengthening role, and at the same time ensure that the quality of the weld is not deteriorated due to its excessive content; similarly, Cu can also improve its corrosion resistance and weather resistance, and the present invention controls its content at 0.05-0.25% to reduce its hot brittleness. Adding the above-mentioned content of Nb, V, and Al and utilizing their microalloying can refine the grains and improve the tough-to-brittle transition temperature of the obtained low-temperature resistant continuous pipe. Regarding the non-metallic elements N, B, P and S, a trace amount of N element can be combined with other elements in the alloy to play a role in precipitation hardening, while an excessive amount of N element may cause the resulting low-temperature resistant coiled tube to fail due to quenching or deformation, so the present invention controls its content to 0.001-0.005%; boron, as a micro-alloying element, can improve the hardenability of the alloy, and at the same time, an appropriate amount of boron in the ferroalloy can also improve its yield strength, tensile strength, fatigue strength and wear resistance, while an excessive amount of boron may form a brittle compound FeB, thereby causing the alloy toughness to deteriorate, so the present invention limits its content to less than 0.005%; phosphorus is prone to cold brittleness of the alloy, and sulfur is prone to hot brittleness, so the present invention tries to reduce the contents of these two elements as much as possible, limiting them to less than 0.015% and 0.002% respectively.

[0028] At the same time, the present invention does not use Ca, an element commonly used in the conventional knowledge of the art, as one of the components of the low-temperature resistant continuous pipe, because the inventors found that the introduction of Ca element into the above-mentioned specific main component will cause the crystallinity of the obtained alloy, thereby causing the low-temperature toughness of the obtained low-temperature resistant continuous pipe to deteriorate and the overall performance degradation. In short, the present invention uses the above-mentioned raw materials to produce low-temperature resistant continuous pipes, and strictly controls the content of each element, which can exert the synergistic effect between the elements with low energy consumption.

[0029] Based on the above raw material components, the present invention smelts the raw materials and prepares them into coils, and then sequentially performs longitudinal shearing, groove processing, butting, forming, longitudinal welding, heat treatment and continuous growth to obtain a low-temperature resistant continuous pipe with excellent mechanical properties and low temperature resistance.

[0030] The above-mentioned longitudinal shearing, groove processing, butt jointing, forming, longitudinal welding, heat treatment and continuous growth processes can all adopt conventional processes in the production process of low-temperature resistant continuous pipes. Preferably, after longitudinal shearing, a steel strip of 50 to 280 mm is obtained, and the front and rear ends of the longitudinally cut steel strip are processed into 45° and grooved, and the groove can be I-type, V-type or U-type; then the head and tail are butted by stir friction welding, CMT welding, TIG welding and other methods, and the weld is polished and cleaned after the butt joint is completed and cooled; before forming, the side of the steel strip after the butt joint is planed into an I-type groove again, and the UOE forming method is used to control the steel strip forming; the formed steel strip is longitudinally welded by high-frequency induction welding, and after heat treatment, it is wound on a reel with an appropriate core diameter by a coiler for continuous growth to obtain a low-temperature resistant continuous pipe with a length of 61 to 10,000 m.

[0031] The UOE forming method is a forming method that first forms a U shape and then forms an O shape. It uses a double-radius eccentric method to produce an elliptical effect by alternating flat rolls and vertical rolls. Compared with other forming methods, it plays a great role in improving the shape and position tolerance level of steel pipes, overcoming unfavorable factors such as steel strip rebound and distortion, and improving the quality of finished pipes.

[0032] During the smelting process of the above raw materials, there are oxides that enter the molten steel from the slag or furnace lining or are generated by the action of oxygen in the raw materials and the deoxidizer. When the melting point of the oxides is higher than the melting point of the welded part, the oxides are difficult to discharge and remain in the weld, which leads to the quality and performance degradation of the obtained low-temperature resistant continuous pipe. On this basis, since the content of Mn and Si has a significant impact on the melting point of oxygen composite inclusions, in order to make the oxides easy to discharge, in a preferred embodiment, the weight ratio of Si to Mn elements is 1: (5-8).

[0033] In the ferroalloy products including the low-temperature resistant continuous pipe provided by the present invention, Al exists in the form of acid-soluble aluminum in the form of metal solid solution and acid-insoluble aluminum in the form of chemical combination. Acid-insoluble aluminum includes non-metallic inclusions including aluminum oxide. Such non-metallic inclusions will reduce the cleanliness of the alloy and eventually cause the various properties of the obtained low-temperature resistant continuous pipe to deteriorate. In a preferred embodiment, the Al element includes Als in the form of acid-soluble aluminum, and the proportion of Als in the low-temperature resistant continuous pipe is 0.01 to 0.07% by weight. Controlling the proportion of acid-soluble aluminum within the above range is conducive to further improving the overall performance of the low-temperature resistant continuous pipe.

[0034] The existence form of boron in ferroalloys is also divided into solid solution state and chemical state, among which the chemical state is not conducive to improving the hardenability of the alloy and has a certain negative impact on its toughness; although the solid solution state is conducive to strengthening its mechanical properties, the content of solid solution boron in the alloy is limited. Therefore, further, in order to make the boron atoms exist in the form of substitutional or interstitial solid solution in the low-temperature resistant continuous tube provided by the present invention and be evenly distributed on the matrix, and have a certain interaction with defects such as dislocations and vacancies in the internal structure of the low-temperature resistant continuous tube, so as to play a role in solid solution strengthening, in the composition of the above-mentioned low-temperature resistant continuous tube, the content of B element is controlled to be 0.0002-0.0003% by weight.

[0035] In a typical embodiment, the composition of the low-temperature resistant coiled tube includes, by weight percentage: C 0.06%, Si 0.18%, Mn 1.15%, P 0.005%, S 0.002%, Ni 0.3%, Mo 0.25%, Cr 0.28%, Cu 0.12%, Ti 0.012%, V 0.05%, Al 0.055%, Nb 0.045%, N 0.002%, B 0.0002%, wherein Als is 0.03%, and the balance is Fe and unavoidable impurity elements; or C 0.1%, Si 0.23%, Mn 1.28%, P 0.005%, S 0.002%, Ni 0.45%, Mo 0.35%, Cr 0.35%, Cu 0.22%, Ti 0.025%, V0.06%, Al 0.095%, Nb 0.055%, N 0.003%, B0.0003%, wherein Als is 0.05%, and the balance is Fe and inevitable impurity elements. The present invention further optimizes the above range for each component of the low-temperature resistant coiled tube through a large number of experiments, and the use of each component content within this range can obtain a low-temperature resistant coiled tube with better mechanical properties and low-temperature resistance.

[0036] Furthermore, in the above-mentioned method for preparing the low-temperature resistant continuous tube, the step of smelting and preparing the coiled plate comprises:

[0037] Step S1, refining the raw material and then casting it to obtain a continuous casting billet;

[0038] Step S2, rolling the continuous casting slab into a primary hot-rolled plate at 1000-1050° C., and then rolling the primary hot-rolled plate into a secondary hot-rolled plate at 860-880° C.;

[0039] Step S3, water-cooling and curling the secondary hot-rolled plate to obtain a coil.

[0040] In step S1, the molten steel obtained by smelting the raw materials is refined in the same furnace by using an LF refining furnace or an RH refining furnace, and the steel is tapped after the mass percentage of its components reaches the above requirements, and cast into a continuous casting billet, using continuous casting technology, and applying electromagnetic stirring and a low-temperature large-tonnage press to control the casting into a slab with a thickness of 30 to 70 mm, which is more conducive to subsequent processing; in step S2, the thermomechanical rolling (TMPC) technology is applied, and the thickness of the first hot-rolled plate is preferably 10 to 20 mm, and the thickness of the second hot-rolled plate is preferably 2.3 to 7.65 mm; in step S3, the second hot-rolled plate is water-cooled and curled, and the length of the coil is preferably ≥ 250m.

[0041] In order to further improve the mechanical properties of the low-temperature resistant coiled tube and repair the defects in its structure, the above-mentioned low-temperature resistant coiled tube is subjected to full-tube heat treatment. In a preferred embodiment, the heat treatment is isothermal annealing, which is achieved by medium-frequency induction heating; the medium-frequency induction heating method uses the principle of electromagnetic induction to generate eddy currents in the workpiece placed in the induction coil, thereby causing the workpiece to heat up and heat to the required temperature. The equipment uses series resonance or parallel resonance, so the power factor is relatively high. Compared with traditional heating methods, it has the advantages of high efficiency and low pollution.

[0042] The heating temperature of the isothermal annealing is preferably 450-700°C, and the cooling temperature is preferably 250-350°C, so as to improve the processability of the low-temperature resistant coiled tube to a greater extent, so that its subsequent continuous growth is easier to carry out and a low-temperature resistant coiled tube product with a more suitable length is obtained; more preferably, the cooling rate of the isothermal annealing is 8-15°C / s, so as to obtain a more uniform internal structure, thereby improving the low temperature resistance and comprehensive mechanical properties of the obtained low-temperature resistant coiled tube.

[0043] In several typical embodiments, in the preparation method of the above-mentioned low-temperature resistant continuous pipe, the implementation method of the butt joint step is selected from stir friction welding, CMT welding or TIG welding. The butt joint can be implemented by selecting a welding method commonly used in the field, and compared with other welding methods, among the above-mentioned welding methods, stir friction welding is more suitable for the low-temperature resistant continuous pipe provided by the present invention, which can weld materials sensitive to thermal cracks, and at the same time, the microstructure change of the heat-affected zone of the welded joint is small, the residual stress is low, and the obtained low-temperature resistant continuous pipe is not easy to deform and has excellent comprehensive performance; TIG welding is also more suitable for the low-temperature resistant continuous pipe provided by the present invention, and the argon gas used in the process can effectively isolate the air, which is more conducive to protecting the various components in the low-temperature resistant continuous pipe from oxidation or nitridation; the arc of CMT welding is extremely stable, and when applied to the welding of the low-temperature resistant continuous pipe provided by the present invention, it can better avoid spatter in welding and reduce the thermal impact of welding on the low-temperature resistant continuous pipe.

[0044] Another aspect of the present invention provides a low-temperature resistant coiled pipe, which is prepared by the above-mentioned preparation method, and has a yield strength of ≥620MPa, a tensile strength of ≥689MPa, an elongation of ≥26%, an impact energy of ≥150J at -75°C, an outer diameter range of Φ25.4 to Φ88.9mm, a wall thickness range of 1.9 to 7.6mm, and a length range of 61 to 10000m. The obtained low-temperature resistant coiled pipe has excellent comprehensive mechanical properties, has good low-temperature resistance compared to existing low-temperature resistant coiled pipes, and can be well used in oil and gas exploration and production in low-temperature and extremely cold environments.

[0045] Another aspect of the present invention provides the application of the above-mentioned low-temperature resistant coiled tubing in the field of oil and gas exploration and production. The low-temperature resistant coiled tubing provided by the present invention achieves effective improvement of the low-temperature resistance of the low-temperature resistant coiled tubing by comprehensively controlling the content of each element component and accurately controlling the processing technology, thereby meeting its application in oil and gas exploration and production in low-temperature and extremely cold environments, and broadening the development of the oil and gas exploration and production industry.

[0046] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0047] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0048] Example 1

[0049] A method for preparing a low temperature resistant continuous pipe:

[0050] The raw materials are prepared according to the following composition: by weight percentage, C 0.06%, Si 0.18%, Mn 1.15%, P0.005%, S0.002%, Ni 0.3%, Mo 0.25%, Cr 0.28%, Cu 0.12%, Ti 0.012%, V 0.05%, Al 0.055%, Nb 0.045%, N 0.002%, B 0.0002%, wherein Als is 0.03%, and the balance is Fe and unavoidable impurity elements.

[0051] Step 1, prepare the ingredients according to the above chemical composition, smelt and prepare the coil. The process of smelting and preparing the coil is to refine the molten iron in the same furnace using LF and RH, so that the mass percentage of the composition of the molten steel reaches the above requirements, and then cast it into a continuous casting billet, and use the continuous casting technology to apply electromagnetic stirring and a low-temperature large-tonnage press to control the casting into a 50mm thick slab; use TMPC technology at a temperature of 1020°C to roll it into a 10mm thick hot-rolled plate; finally, at 860°C, roll it into a 3.4mm thick hot-rolled plate, then water-cooled and curled, and finally make a coil with a length of 600 meters;

[0052] Step 2: Cut the coiled plate in step 1 into 120 mm steel strips;

[0053] Step 3: Process the front and rear ends of the steel strip cut in step 2 into 45° and perform groove processing, the groove is V-shaped;

[0054] Step 4, the steel strips cut longitudinally in step 3 are joined head to tail, butted by friction stir welding, and the welds are polished and cleaned after cooling;

[0055] Step 5, planing the side of the steel strip after the cleaning in step 4 into an I-shaped groove, and using the UOE forming method to control the steel strip forming;

[0056] Step 6: The steel strip formed in step 5 is longitudinally welded by high-frequency induction welding to form a straight seam low-temperature resistant continuous pipe with a diameter of Φ38.1 mm and a wall thickness of 3.4 mm;

[0057] Step 7, heat treatment is performed on the whole body of the low-temperature resistant continuous pipe welded in step 6, and isothermal annealing is performed by medium frequency induction heating, firstly heated to 550° C., and then cooled to 300° C. at a water cooling rate of 10° C. / s;

[0058] Step 8: Wind the low-temperature resistant continuous pipe after the heat treatment in step 7 onto a reel with an appropriate core diameter through a coiler, and continuously produce a low-temperature resistant continuous pipe with a length of 10,000 m for transportation and use.

[0059] Example 2

[0060] A method for preparing a low temperature resistant continuous pipe:

[0061] The raw materials are prepared according to the following composition: by weight percentage, C 0.1%, Si 0.23%, Mn 1.28%, P0.005%, S 0.002%, Ni 0.45%, Mo 0.35%, Cr 0.35%, Cu 0.22%, Ti 0.025%, V0.06%, Al 0.095%, Nb 0.055, N 0.003%, B 0.0003%, wherein Als is 0.05%, and the balance is Fe and unavoidable impurity elements.

[0062] Step 1, prepare the ingredients according to the above chemical composition, smelt and prepare the coil. The process of smelting and preparing the coil is to refine the molten iron in the same furnace using LF and RH, so that the mass percentage of the composition of the molten steel reaches the above requirements, and then cast it into a continuous casting billet, and use the continuous casting technology to apply electromagnetic stirring and a low-temperature large-tonnage press to control the casting into a 70mm thick slab; use TMPC technology at a temperature of 1040°C to roll it into a 20mm thick hot-rolled plate; finally, at 880°C, roll it into a 5.2mm thick hot-rolled plate, then water-cooled and curled, and finally make a coil with a length of 500 meters;

[0063] Step 2: Cut the coiled plate in step 1 into 280 mm steel strips;

[0064] Step 3: Process the front and rear ends of the steel strip cut in step 2 into 45° and perform groove processing, the groove is U-shaped;

[0065] Step 4: Connect the ends of the steel strips cut longitudinally in step 3 by TIG welding, and grind and clean the welds after cooling;

[0066] Step 5, planing the side of the steel strip after the cleaning in step 4 into an I-shaped groove, and using the UOE forming method to control the steel strip forming;

[0067] Step 6: The steel strip formed in step 5 is longitudinally welded by high-frequency induction welding to form a straight seam low-temperature resistant continuous pipe with a diameter of Φ88.9 mm and a wall thickness of 5.2 mm;

[0068] Step 7, heat treatment is performed on the whole body of the low-temperature resistant continuous pipe welded in step 6, and isothermal annealing is performed by medium frequency induction heating, firstly heated to 600° C., and then cooled to 330° C. at a water cooling rate of 10° C. / s;

[0069] Step 8: Wind the low-temperature resistant continuous pipe that has been heat treated in step 7 onto a reel with an appropriate core diameter through a coiler, and continuously produce a low-temperature resistant continuous pipe with a length of 2500m for transportation and use.

[0070] Example 3

[0071] A method for preparing a low temperature resistant continuous pipe:

[0072] The difference from Example 1 is that in the low-temperature resistant continuous tube alloy composition, Si accounts for 0.16% and Mn accounts for 1.44%.

[0073] Comparative Example 1

[0074] A method for preparing a low temperature resistant continuous pipe:

[0075] The difference from Example 1 is that the B element is not added, and 0.001% of the Ca element is added.

[0076] The performance parameters of the above embodiments and comparative examples are shown in Table 1. The average value of the impact energy at -75°C is used to measure the low-temperature toughness of the obtained low-temperature resistant coiled tube. The higher the value, the better the low-temperature toughness of the obtained low-temperature resistant coiled tube, the lower the tough-brittle transition temperature, and the better the low-temperature resistance of the low-temperature resistant coiled tube.

[0077] Table 1 Mechanical properties of various embodiments and comparative examples

[0078] Yield Strength tensile strength Elongation Average impact energy at -75℃ Example 1 652MPa 702MPa 36％ 238J Example 2 695MPa 748MPa 30％ 215J Example 3 630MPa 729MPa 27％ 206J Comparative Example 1 604MPa 682MPa 23％ 198J

[0079] From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve high mechanical properties and excellent low-temperature resistance, and can meet the application requirements in oil and gas exploration and production in low-temperature and extremely cold environments.

[0080] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those described herein, for example.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a low-temperature resistant coiled tube, characterized in that: The preparation method of the low-temperature resistant coiled tube comprises: The raw materials are prepared according to the following composition: in terms of weight percentage, the components of the low-temperature resistant coiled tube include: C 0.03-0.12%, Si 0.1-0.3%, Mn 0.8-1.5%, Ni 0.1-0.5%, Mo 0.1-0.4%, Cr 0.1-0.4%, Cu 0.05-0.25%, Ti 0.005-0.03%, V 0.01-0.07%, Al 0.015-0.12%, Nb 0.03-0.1%, N 0.001-0.005%, B≤0.0005%, P≤0.015%, S≤0.002%, and the balance is Fe and unavoidable impurity elements; The raw materials are smelted and prepared into coils, and then longitudinal shearing, groove processing, butting, forming, longitudinal welding, heat treatment and continuous growth are carried out in sequence to obtain the low-temperature resistant coiled tube.

2. The preparation method according to claim 1, characterized in that: In the composition of the low-temperature resistant continuous pipe, the weight ratio of the Si to the Mn element is 1:(5-8).

3. The preparation method according to claim 1 or 2, characterized in that: In the components of the low-temperature resistant coiled tube, the Al element includes Als in the form of acid-soluble aluminum, and the Als accounts for 0.01-0.07% of the low-temperature resistant coiled tube by weight.

4. The preparation method according to any one of claims 1 to 3, characterized in that In the composition of the low-temperature resistant continuous pipe, the content of the B element is 0.0002-0.0003% by weight.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In terms of weight percentage, the composition of the low-temperature resistant coiled tube includes: C 0.06%, Si 0.18%, Mn 1.15%, P 0.005%, S 0.002%, Ni 0.3%, Mo 0.25%, Cr 0.28%, Cu 0.12%, Ti 0.012%, V 0.05%, Al 0.055%, Nb 0.045%, N 0.002%, B 0.0002%, wherein Als is 0.03%, and the balance is Fe and unavoidable impurity elements; or C 0.1%, Si 0.23%, Mn 1.28%, P 0.005%, S 0.002%, Ni 0.45%, Mo 0.35%, Cr 0.35%, Cu 0.22%, Ti 0.025%, V 0.06%, Al 0.095%, Nb 0.055%, N 0.003%, B 0.0003%, of which Als is 0.05%, and the balance is Fe and inevitable impurity elements.

6. The preparation method according to any one of claims 1 to 5, characterized in that The steps of smelting and preparing the coils include: Step S1, refining the raw material and then casting it to obtain a continuous casting billet; Step S2, rolling the continuous casting slab into a primary hot-rolled plate at 1000-1050° C., and then rolling the primary hot-rolled plate into a secondary hot-rolled plate at 860-880° C.; Step S3, water-cooling and curling the secondary hot-rolled plate to obtain the coiled plate; Preferably, the continuous casting billet is a slab with a thickness of 30 to 70 mm; Preferably, the thickness of the primary hot-rolled plate is 10 to 20 mm; Preferably, the thickness of the secondary hot-rolled plate is 2.3 to 7.65 mm; Preferably, the length of the rolled plate is ≥ 250m.

7. The preparation method according to any one of claims 1 to 6, characterized in that The heat treatment is to perform heat treatment on the whole body of the low-temperature resistant coiled tube; preferably, the heat treatment is isothermal annealing, which is achieved by medium-frequency induction heating; preferably, the heating temperature of the isothermal annealing is 450-700°C, and the cooling temperature is 250-350°C; more preferably, the cooling rate of the isothermal annealing is 8-15°C / s.

8. The preparation method according to any one of claims 1 to 7, characterized in that The butting step is implemented by a method selected from friction stir welding, CMT welding or TIG welding.

9. A low temperature resistant coiled pipe, characterized in that: The low-temperature resistant continuous pipe is prepared by the preparation method described in any one of claims 1 to 8, and has a yield strength of ≥620MPa, a tensile strength of ≥689MPa, an elongation of ≥26%, an impact energy of ≥150J at -75°C, an outer diameter range of Φ25.4 to Φ88.9mm, a wall thickness range of 1.9 to 7.6mm, and a length range of 61 to 10000m.

10. Use of the low-temperature resistant coiled tubing according to claim 9 in the field of oil and gas exploration and production.