Titanium alloy coiled tubing and method of making same

Abstract

The application provides a titanium alloy coiled tubing and a preparation method thereof. The titanium alloy coiled tubing comprises, in percentage by weight, Al 1.0-1.5%, Fe≤0.30%, C≤0.05%, Mo 0.20-0.40%, N≤0.05%, V 1.00-1.40%, and the balance of Ti and inevitable impurities; titanium alloy materials are obtained according to the component ratio; extension welding is carried out under inert gas protection, and the weld is subjected to first heat treatment; after bending forming, closing welding is carried out; after sizing, second heat treatment is carried out at 650-850 DEG C for 3-5 min to obtain the titanium alloy coiled tubing. The chemical composition of the titanium alloy and the heat treatment process after welding are reasonably designed, so that the coiled tubing has good mechanical properties, high fatigue life, good mechanical damage resistance and excellent corrosion resistance, and is especially suitable for strong corrosion environments with high CO2, H2S and Cl ‑ concentrations.

Description

Technical Field

[0001] This invention relates to the field of tubing technology for onshore and offshore oil and gas wells, and more specifically, to a titanium alloy continuous tubing and its manufacturing method. Background Technology

[0002] Coiled tubing, also known as flexible tubing, is a single, continuous tubing, sometimes thousands of meters long, wound around a drum and capable of being continuously run into and retrieved from a well. In recent years, coiled tubing technology has developed rapidly. Its superior performance characteristics, such as low operating costs, simplicity, time-saving, and safety and reliability, have led to its widespread application in various fields including sand flushing, well washing, logging, well completion, and drilling. However, with the continuous development of oil and gas fields, the number of deep, high-pressure wells and oil wells in complex corrosive environments is increasing, making the operating conditions of coiled tubing increasingly challenging. Conventional low-carbon, low-alloy steel coiled tubing is difficult to apply in high-pressure and high-CO2, H2S corrosive environments, and suffers severe corrosion under acidizing conditions, leading to frequent coiled tubing failures. While stainless steel coiled tubing can adapt to high-CO2, H2S corrosive environments, it is susceptible to corrosion when mixed with Cl... - In environments where corrosive liquids and hydrochloric acid are used as acidifying agents, the corrosion resistance drops sharply, the corrosion rate becomes similar to that of carbon steel, and the advantage disappears.

[0003] Titanium and its alloys are important structural metals developed in modern times. Titanium alloys are widely used in various fields due to their high specific strength, good corrosion resistance, and high heat resistance. Titanium is non-toxic, lightweight, high-strength, and has excellent biocompatibility, making it an ideal metallic material. Its heat resistance, strength, plasticity, toughness, formability, weldability, and corrosion resistance are all good, making it a top-tier alloy in industry. In humid atmospheric and seawater environments, titanium alloys exhibit far superior corrosion resistance compared to stainless steel; they are particularly resistant to pitting corrosion, acid corrosion, and stress corrosion; and they possess excellent resistance to alkalis, chlorides, chlorinated organics, nitric acid, and sulfuric acid.

[0004] Chinese patent CN105598200A discloses a method for manufacturing titanium alloy coiled tubing. First, a strip is passed through four sets of rolling equipment to form the shape of a coiled tubing. After the coiled tubing is accurately positioned using clamping equipment, laser welding is used to weld the seams of the strip into a single unit. The welding speed is only 1.5 m / min. Due to the low speed of laser welding, the weld zone and heat-affected zone become excessively wide, and the metallographic microstructure differs significantly from the base material. After welding and during heat treatment, the oxide film formed by the titanium alloy at high temperatures is not dense and is prone to peeling off, severely affecting the corrosion resistance of the coiled tubing. Chinese patent CN115055534A discloses a production process for high-frequency induction welding of titanium alloy continuous tubing. It uses TA9, TA10, and TA18 strips as raw materials and employs induction heating to achieve the welding and forming of titanium alloy continuous tubing. However, the tubing overlaps after coiling, making it impossible to guarantee the cleaning effect of the entire coil. Similarly, when the entire coil is annealed together with the roller, it will cause deformation of the tubing and the roller, resulting in scratches on the tubing and affecting product quality. Cleaning and annealing the entire coil will also bring significant equipment and transportation costs, and reduce production efficiency. Summary of the Invention

[0005] The main objective of this invention is to provide a titanium alloy coiled tubing and its preparation method, so as to solve the problem that the existing titanium alloy coiled tubing cannot simultaneously achieve good mechanical properties, fatigue properties, resistance to mechanical damage and corrosion resistance.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a titanium alloy coiled tubing is provided. The titanium alloy coiled tubing comprises, by weight percentage, Al 1.0–1.5%, Fe ≤0.30%, C ≤0.05%, Mo 0.20–0.40%, N ≤0.05%, V 1.00–1.40%, with the balance being Ti and unavoidable impurities. The preparation method includes the following steps: Step S1, obtaining a titanium alloy sheet according to the composition ratio of the titanium alloy coiled tubing; Step S2, butt-welding the titanium alloy sheet under a first inert gas protection, and subjecting the weld to a first heat treatment to obtain a titanium alloy strip; Step S3, bending the titanium alloy strip into shape, and then performing straight weld welding under a second inert gas protection to obtain a titanium alloy coiled tubing precursor; Step S4, sizing the titanium alloy coiled tubing precursor, and then holding it at 650–850°C for 3–5 minutes under a third inert gas protection for a second heat treatment to obtain the titanium alloy coiled tubing.

[0007] Furthermore, by weight percentage, the composition of the titanium alloy coiled tubing includes Al 1.42–1.48%, Fe 0.22–0.26%, C 0.045–0.048%, Mo 0.33–0.38%, N 0.039–0.042%, V 1.21–1.31%, with the balance being Ti and unavoidable impurities.

[0008] Furthermore, the first inert gas, the second inert gas, and the third inert gas each independently include argon or a mixture of argon and helium.

[0009] Furthermore, in step S2, the welding method for butt welding is plasma welding or argon arc welding; and / or the welding method for butt welding is 45° butt welding.

[0010] Furthermore, in step S2, the temperature of the first heat treatment is 950–1050°C, and the holding time is 20–30 seconds.

[0011] Furthermore, prior to step S3, the preparation method further includes a step of cleaning the titanium alloy strip; preferably, the cleaning solution contains 400-500 g / L NaOH and 100-150 g / L NaNO2; and / or the cleaning temperature is 100-120°C.

[0012] Furthermore, in step S3, a copper roller unit is used for bending and forming.

[0013] Further, in step S3, the welding method for the straight weld seam is high-frequency induction welding, laser welding, or argon arc welding; preferably, during the straight weld seam welding process, the gap t between the induction coil of the welding machine and the bent titanium alloy strip is ≤9mm, and the welding V-shaped opening angle α is 8~10°; preferably, the power of the welding machine is 100~500KW, and the welding speed is 25~80m / min; more preferably, the power of the welding machine is 130~200KW, and the welding speed is 25~50m / min.

[0014] Furthermore, prior to step S4, the preparation method further includes the following steps: the titanium alloy coiled tubing precursor is subjected to gas-protected cooling in a fourth inert gas atmosphere until the surface temperature of the titanium alloy coiled tubing precursor is 100-150°C, and the oxygen volume concentration of the fourth inert gas atmosphere is ≤5%.

[0015] According to another aspect of the present invention, a titanium alloy continuous tubing is provided, which is obtained by the preparation method described above.

[0016] The technical solution of this invention has three main advantages. First, by designing the chemical composition of the titanium alloy, focusing on controlling the content of Al and V elements based on the α-type titanium microstructure, and combining this with the deformation strengthening effect during the forming process, the mechanical properties of the coiled tubing, such as strength, can be synergistically improved, making it suitable for high-pressure operations. Second, by designing a reasonable heat treatment process after welding, the need for weld solution treatment is eliminated, simplifying the production process and effectively eliminating the stress generated during the forming and welding of the coiled tubing, thus improving its overall performance. Third, by optimizing the gas protection process during the overall fabrication of the coiled tubing, a dense oxide film can be formed on the surface of the coiled tubing, greatly improving its corrosion resistance, especially suitable for high CO2, H2S, and Cl environments. - It is suitable for highly corrosive environments, even harsh conditions such as acidizing operations primarily using hydrochloric acid. The titanium alloy coiled tubing prepared by this invention has a uniform structure, good mechanical properties, long fatigue life, good resistance to mechanical damage, and excellent corrosion resistance, exhibiting superior comprehensive performance and high production efficiency. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0018] Figure 1 A process flow diagram of the preparation according to Embodiment 1 of the present invention is shown;

[0019] Figure 2 A schematic diagram of the induction coil and V-shaped nozzle control for high-frequency induction welding according to Embodiment 1 of the present invention is shown.

[0020] Figure 3 A cross-sectional view of a gas shield tooling according to Embodiment 1 of the present invention is shown; and

[0021] Figure 4 An axial view of the gas protective cover tooling according to Embodiment 1 of the present invention is shown.

[0022] The above figures include the following reference numerals:

[0023] 1. Argon gas detection port; 2. Continuous oil tubing; 3. Argon gas inlet; 4. Air-cooled support. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] As described in the background section of this invention, existing technologies have the problem that titanium alloy coiled tubing cannot simultaneously achieve good mechanical properties, fatigue performance, resistance to mechanical damage, and corrosion resistance. To address the aforementioned problems, in a typical embodiment of the present invention, a method for preparing a titanium alloy coiled tubing is provided. The titanium alloy coiled tubing, by weight percentage, comprises Al 1.0–1.5%, Fe ≤ 0.30%, C ≤ 0.05%, Mo 0.20–0.40%, N ≤ 0.05%, V 1.00–1.40%, with the balance being Ti and unavoidable impurities. The preparation method includes the following steps: Step S1, obtaining a titanium alloy sheet according to the composition ratio of the titanium alloy coiled tubing; Step S2, butt-welding the titanium alloy sheet under a first inert gas protection, and subjecting the weld to a first heat treatment to obtain a titanium alloy strip; Step S3, bending the titanium alloy strip into shape, and then performing straight weld welding under a second inert gas protection to obtain a titanium alloy coiled tubing precursor; Step S4, sizing the titanium alloy coiled tubing precursor, and then holding it at 650–850°C for 3–5 minutes under a third inert gas protection for a second heat treatment to obtain the titanium alloy coiled tubing.

[0026] This invention first obtains titanium alloy sheets using conventional methods according to the composition ratio of titanium alloy coiled tubing. The chemical composition of the titanium alloy is designed, focusing on controlling the content of Al and V elements based on the α-type titanium microstructure. Combined with the deformation strengthening effect during the forming process, this synergistically improves the tensile strength and other mechanical properties of the coiled tubing, making it suitable for high-pressure operations. Furthermore, by controlling the Mo content within a specific range, tensile strength can be further improved, grain refinement can be achieved, and corrosion resistance can be enhanced.

[0027] Titanium alloy sheets are longitudinally slit into strips of varying widths. Then, under a first inert gas atmosphere, these sheets are butt-welded to a target length. The weld seam undergoes a first heat treatment to refine the grains and improve the weld microstructure. This eliminates the need for weld solution treatment, simplifying the production process and effectively eliminating stress generated during coiled tubing forming and welding, thus improving the overall performance of the coiled tubing. The resulting titanium alloy strip is cleaned in a cleaning machine and then transferred to a tubing forming unit. It is gradually bent and shaped by a forming unit, and then, under a second inert gas atmosphere, straight weld seams are performed, with the aid of welding extrusion rollers to prevent the formation of weld inclusions, resulting in the titanium alloy coiled tubing precursor.

[0028] Finally, the titanium alloy coiled tubing precursor is sized to obtain the required outer diameter. Then, under a third inert gas protection environment, it is held at 650–850℃ for 3–5 minutes for a second heat treatment. This full-tube heat treatment eliminates residual stress, improves overall tubing performance, and yields a titanium alloy coiled tubing with uniform microstructure, good mechanical properties, high fatigue life, good resistance to mechanical damage, and excellent corrosion resistance. Simultaneously, by optimizing the gas protection process during the overall fabrication of the coiled tubing, a dense oxide film can be formed on the surface of the coiled tubing, significantly improving its corrosion resistance, especially suitable for high CO2, H2S, and Cl environments. - It is suitable for highly corrosive environments and even harsh conditions such as acidification operations, which are mainly based on hydrochloric acid.

[0029] The titanium alloy strip of this invention exhibits uniform and consistent microstructure in its oblique welds, straight welds throughout the entire tube body, heat-affected zone, and base material. The titanium alloy coiled tubing has a yield strength of 520–680 MPa, preferably 600–680 MPa; a tensile strength of 580–720 MPa; a plastic elongation greater than 15%, preferably greater than 20%; and a hardness of 15–25 HRC, preferably 20–25 HRC. The titanium alloy coiled tubing prepared by this invention possesses advantages such as high strength and good fatigue life. Its bending fatigue life can reach 4.5 times or more of that of conventional coiled tubing of the same specifications (such as CT90), and it can completely resist high CO2 and H2S corrosion. Its hydrochloric acid corrosion resistance is dozens of times that of conventional coiled tubing, while also exhibiting excellent resistance to mechanical damage.

[0030] To further improve the synergistic strengthening effect of the components in the titanium alloy coiled tubing and to further enhance its overall performance, in a preferred embodiment, the titanium alloy coiled tubing comprises, by weight percentage, Al 1.42–1.48%, Fe 0.22–0.26%, C 0.045–0.048%, Mo 0.33–0.38%, N 0.039–0.042%, V 1.21–1.31%, with the balance being Ti and unavoidable impurities.

[0031] In a preferred embodiment, the first inert gas, the second inert gas, and the third inert gas each independently include argon or a mixture of argon and helium, resulting in better protection and a more complete and dense oxide film formed on the surface of the titanium alloy coiled tubing, which can further improve its corrosion resistance.

[0032] To further improve the production efficiency of titanium alloy coiled tubing, in a preferred embodiment, in step S2, the welding method for butt welding is plasma welding or argon arc welding; and / or the welding method for butt welding is 45° butt welding.

[0033] In a preferred embodiment, in step S2, the temperature of the first heat treatment is 950–1050°C, and the holding time is 20–30 seconds, which can better refine the grains, improve the weld structure, and further improve the corrosion resistance of the weld and the mechanical properties of the titanium alloy coiled tubing.

[0034] For the purpose of facilitating continuous tubing welding, in a preferred embodiment, before step S3, the preparation method further includes a step of cleaning the titanium alloy strip; preferably, the cleaning solution contains 400-500 g / L NaOH and 100-150 g / L NaNO2; and / or the cleaning temperature is 100-120°C.

[0035] In a preferred embodiment, in step S3, using a copper roller unit for bending and forming can obtain better surface quality of titanium alloy continuous tubing and improve corrosion resistance.

[0036] Based on the electromagnetic induction characteristics of the coiled tubing material, in a preferred embodiment, in step S3, the welding method for the straight weld seam is high-frequency induction welding, laser welding, or argon arc welding. Preferably, during the straight weld seam welding process, the gap t between the welding machine's induction coil and the bent titanium alloy strip is ≤9mm, and the welding V-shaped bevel angle α is 8-10°. Preferably, the welding machine power is 100-500KW, and the welding speed is 25-80m / min. More preferably, the welding machine power is 130-200KW, and the welding speed is 25-50m / min, thereby obtaining a weld seam with better weld formation and more stable performance. The welding V-shaped bevel angle, welding power, and welding speed can be adjusted according to the specifications of the coiled tubing, which is understandable to those skilled in the art and will not be elaborated further here.

[0037] In a preferred embodiment, before step S4, the preparation method further includes the following steps: gas-protected cooling of the titanium alloy coiled tubing precursor in a fourth inert gas atmosphere until the surface temperature of the titanium alloy coiled tubing precursor is 100-150°C, and the oxygen volume concentration of the fourth inert gas atmosphere is ≤5%, which can further improve the oxide film state formed on the surface of the titanium alloy coiled tubing and further improve its corrosion resistance.

[0038] In another typical embodiment of the present invention, a titanium alloy continuous tubing is also provided, which is obtained by the preparation method of the present invention described above. It has good mechanical properties, high fatigue life, good resistance to mechanical damage, and excellent corrosion resistance, and has excellent comprehensive performance.

[0039] Typical, but not limiting, composition of titanium alloy coiled tubing, by weight percentage, includes Al 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.42%, 1.44%, 1.46%, 1.48%, 1.5%, or any two of these values; Fe 0%, 0.1%, 0.15%, 0.2%, 0.22%, 0.24%, 0.26%, 0.28%, 0.30%, or any two of these values; C 0%, 0.01%, 0.02%, 0.03%, 0.04%, 0.042%, 0.045%, 0.048%, 0.05%, or any two of these values; Mo... 0.20%, 0.25%, 0.30%, 0.33%, 0.35%, 0.38%, 0.40% or any two of these values; N 0%, 0.01%, 0.02%, 0.03%, 0.035%, 0.039%, 0.040%, 0.042%, 0.045%, 0.048%, 0.05% or any two of these values; V 1.00%, 1.05%, 1.10%, 1.15%, 1.21%, 1.25%, 1.31%, 1.35%, 1.40% or any two of these values, with the balance being Ti and unavoidable impurities.

[0040] Typically, but not limitingly, in step S2, the temperature of the first heat treatment is 950℃, 960℃, 970℃, 980℃, 990℃, 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃ or any two of these values, and the holding time is 20s, 22s, 24s, 26s, 28s, 30s or any two of these values.

[0041] Typically, but not limitingly, in step S3, the power of the welding machine is 100KW, 130KW, 155KW, 160KW, 172KW, 200KW, 250KW, 300KW, 350KW, 400KW, 450KW, 500KW or any two of these values, and the welding speed is 25m / min, 30m / min, 32m / min, 35m / min, 38m / min, 40m / min, 50m / min, 60m / min, 70m / min or 80m / min.

[0042] Typically, but not limitingly, in step S4, the temperature of the second heat treatment is 650°C, 680°C, 700°C, 720°C, 750°C, 780°C, 800°C, 820°C, 850°C, or a range of any two of these values.

[0043] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0044] Example 1

[0045] The chemical composition of titanium alloy coiled tubing is shown in Table 1.

[0046] Step S1: Obtain titanium alloy sheet according to the composition ratio of titanium alloy coiled tubing;

[0047] Step S2: Under argon protection, the titanium alloy plate is welded to a fixed length by plasma welding at 45°, and the weld is subjected to the first heat treatment to obtain a titanium alloy strip. The strip is then cleaned at 110°C using a cleaning solution (450g / L NaOH and 120g / L NaNO2).

[0048] Step S3: Transfer the titanium alloy strip to the tube forming unit, continuously pass it through the copper roller forming unit to gradually bend and shape it, and then perform high-frequency induction welding under argon protection, in conjunction with the extrusion of the welding extrusion roller. The gap t between the welding machine's induction coil and the bent titanium alloy strip is 9mm, and the welding V-shaped opening angle α is 9°. Adjust the welding machine power and welding speed to continuously complete the welding of the bent titanium alloy strip and obtain the titanium alloy continuous tubing precursor.

[0049] Step S4: The titanium alloy coiled tubing precursor is fed into a gas protection hood and air-cooled to 120°C with an outlet oxygen volume concentration of 3%. The required outer diameter is obtained by passing it through a sizing unit. Then, a second heat treatment is performed under argon protection to obtain the titanium alloy coiled tubing.

[0050] The specifications, length, first heat treatment, second heat treatment, welding machine power, and welding speed in step S3 of the continuous tubing in Example 1 are shown in Table 2. The process flow chart for the preparation of Example 1 is shown below. Figure 1 The schematic diagram of the induction coil and V-shaped nozzle control for high-frequency induction welding is shown below. Figure 2 See the cross-sectional view of the gas protective cover tooling. Figure 3 See the axial diagram of the gas shield tooling. Figure 4 The continuous tubing 2 is cooled by gas protection under the support of the air-cooled support 4. Argon gas enters from the argon gas inlet 3 and its content is detected at the argon gas detection port 1.

[0051] Examples 2 to 3

[0052] The difference between Examples 2 and 3 and Example 1 is that the chemical composition, specifications, length, first heat treatment, second heat treatment, and process parameters of welding machine power and welding speed in step S3 of the titanium alloy continuous tubing are different, as shown in Tables 1 and 2.

[0053] Example 4

[0054] The difference from Example 1 is that the process parameters of the first heat treatment are different, as shown in Table 2.

[0055] Examples 5 to 6

[0056] The difference from Example 1 is that the process parameters for the second heat treatment are different, as shown in Table 2.

[0057] Examples 7 to 10

[0058] The difference from Example 1 is that the process parameters of welding machine power and welding speed in step S3 are different, as shown in Table 2.

[0059] Example 11

[0060] The chemical composition, specifications, length, first heat treatment, second heat treatment, and process parameters of welding machine power and welding speed in step S3 of the titanium alloy continuous tubing are the same as in Example 1.

[0061] Step S1: Obtain titanium alloy sheet according to the composition ratio of titanium alloy coiled tubing;

[0062] Step S2: Under argon protection, the titanium alloy sheet is welded to a fixed length using argon arc welding at a 45° angle. The weld is then subjected to a first heat treatment to obtain a titanium alloy strip. The strip is then cleaned using a cleaning solution (400 g / L NaOH and 150 g / L NaNO2) at 100°C.

[0063] Step S3: Transfer the titanium alloy strip to the tube forming unit, continuously pass it through the copper roller forming unit to gradually bend and shape it, and then perform laser welding under argon protection, combined with the extrusion of the welding extrusion roller. The gap t between the welding machine's induction coil and the bent titanium alloy strip is 9mm, and the welding V-shaped opening angle α is 9°. Adjust the welding machine power and welding speed to continuously complete the welding of the bent titanium alloy strip and obtain the titanium alloy continuous tubing precursor.

[0064] Step S4: The titanium alloy coiled tubing precursor is fed into a gas protection hood and air-cooled to 100°C with an outlet oxygen volume concentration of 3%. The required outer diameter is obtained by passing it through a sizing unit. Then, a second heat treatment is performed under argon protection to obtain the titanium alloy coiled tubing.

[0065] Example 12

[0066] The chemical composition, specifications, length, first heat treatment, second heat treatment, and process parameters of welding machine power and welding speed in step S3 of the titanium alloy continuous tubing are the same as in Example 1.

[0067] Step S1: Obtain titanium alloy sheet according to the composition ratio of titanium alloy coiled tubing;

[0068] Step S2: Under the protection of a mixture of argon and helium, the titanium alloy sheet is welded to a fixed length by plasma welding at 45°, and the weld is subjected to the first heat treatment to obtain a titanium alloy strip. The strip is then cleaned at 120°C using a cleaning solution (500g / L NaOH and 100g / L NaNO2).

[0069] Step S3: Transfer the titanium alloy strip to the tube forming unit, continuously pass it through the copper roller forming unit to gradually bend and shape it, and then perform argon arc welding under argon protection, in conjunction with the extrusion of the welding extrusion roller. The gap t between the welding machine's induction coil and the bent titanium alloy strip is 9mm, and the welding V-shaped opening angle α is 9°. Adjust the welding machine power and welding speed to continuously complete the welding of the bent titanium alloy strip and obtain the titanium alloy continuous tubing precursor.

[0070] Step S4: The titanium alloy coiled tubing precursor is fed into a gas protection hood and air-cooled to 150°C with an outlet oxygen volume concentration of 3%. The required outer diameter is obtained by passing it through a sizing unit. Then, a second heat treatment is performed under argon protection to obtain the titanium alloy coiled tubing.

[0071] Examples 13 to 18

[0072] The difference from Example 1 is that the chemical composition of the titanium alloy coiled tubing is different, as shown in Table 1.

[0073] Comparative Example 1

[0074] CT90 continuous tubing.

[0075] Comparative Example 2

[0076] 2205 stainless steel continuous tubing.

[0077] Comparative Example 3

[0078] The difference from Example 1 is that argon gas was not used for protection during the preparation process.

[0079] Comparative Example 4

[0080] The difference from Example 1 is that no first heat treatment was performed during the preparation process.

[0081] Comparative Example 5

[0082] The difference from Example 1 is that the temperature of the first heat treatment is 800°C and the time is 15 seconds.

[0083] Comparative Example 6

[0084] The difference from Example 1 is that the temperature of the first heat treatment is 1200°C and the time is 40 seconds.

[0085] Comparative Example 7

[0086] The difference from Example 1 is that no second heat treatment was performed during the preparation process.

[0087] Comparative Example 8

[0088] The difference from Example 1 is that the temperature of the second heat treatment is 550°C and the time is 2 minutes.

[0089] Comparative Example 9

[0090] The difference from Example 1 is that the temperature of the second heat treatment is 950°C and the time is 7 minutes.

[0091] The mechanical properties, bending fatigue life, corrosion performance, and mechanical damage resistance of the coiled tubing in the above embodiments and comparative examples were measured. The test results of mechanical properties are shown in Table 3, the test results of bending fatigue life are shown in Table 4, the test results of corrosion performance are shown in Table 5, and the test results of mechanical damage resistance are shown in Table 6.

[0092] Test method:

[0093] Tensile strength, yield strength, elongation: ASTM A370.

[0094] Hardness: ASTM E18.

[0095] Hydrochloric acid corrosion test: ASTM G111, 170°C, 15% hydrochloric acid.

[0096] CO2 corrosion test: ASTM G111, 5% sodium chloride solution, partial pressure 5 MPa, 120℃.

[0097] H2S stress corrosion test: NACE TM0177-2016, saturated H2S solution, 720h, applied stress of 80% of yield strength.

[0098] Table 1

[0099] / Al Fe C Mo N V Ti Example 1 1.42 0.26 0.048 0.33 0.042 1.28 margin Example 2 1.46 0.24 0.045 0.38 0.041 1.31 margin Example 3 1.48 0.22 0.047 0.35 0.039 1.21 margin Example 13 1.42 0.3 0 0.20 0.05 1.28 margin Example 14 1.42 0 0.05 0.40 0 1.28 margin Example 15 1.0 0.26 0.048 0.33 0.042 1.28 margin Example 16 1.5 0.26 0.048 0.33 0.042 1.28 margin Example 17 1.42 0.26 0.048 0.33 0.042 1.00 margin Example 18 1.42 0.26 0.048 0.33 0.042 1.40 margin

[0100] Table 2

[0101]

[0102]

[0103] Table 3

[0104]

[0105]

[0106] Table 4

[0107]

[0108]

[0109] Table 5

[0110]

[0111]

[0112] Table 6

[0113]

[0114]

[0115] As can be seen from the above, the α-type titanium alloy coiled tubing products prepared by the embodiments of the present invention have uniform microstructure in the weld, heat-affected zone, and base material, and exhibit excellent mechanical properties. Their fatigue performance and resistance to mechanical damage are superior to those of the conventional carbon steel coiled tubing of Comparative Example 1 and the stainless steel coiled tubing of Comparative Example 2 of the same specifications. In the sulfide stress corrosion test, the sample surface showed no significant changes and no cracks were generated; the average rate of CO2 corrosion resistance was 0.0011–0.0016 mm / a, which is thousands of times higher than that of the conventional coiled tubing of Comparative Example 1 (4.36 mm / a); the average rate of hydrochloric acid corrosion resistance was 3.4–4.6 mm / a, which is more than ten times higher than that of the conventional coiled tubing of Comparative Example 1 and the stainless steel tubing of Comparative Example 2, demonstrating excellent corrosion resistance.

[0116] As can be seen from the above, compared with the comparative examples, the embodiments of the present invention design the chemical composition of the titanium alloy. Based on the α-type titanium microstructure, the content of Al and V elements is controlled in a focused manner. Combined with the deformation strengthening effect of the forming process, the mechanical properties such as strength of the coiled tubing can be synergistically improved, making it suitable for high-pressure operations. Secondly, the rationally designed heat treatment process after welding eliminates the need for weld solution treatment, simplifies the production process, and effectively eliminates the stress generated during the forming and welding of the coiled tubing, improving the overall performance of the coiled tubing. Thirdly, the optimized gas protection process during the overall fabrication of the coiled tubing allows for the formation of a dense oxide film on the surface of the coiled tubing, greatly improving its corrosion resistance, especially suitable for highly corrosive environments with high CO2 and H2S, and even for harsh conditions such as acidizing operations mainly using hydrochloric acid. The titanium alloy coiled tubing prepared by the present invention has a uniform microstructure, good mechanical properties, long fatigue life, good resistance to mechanical damage, and excellent corrosion resistance, exhibiting excellent comprehensive performance and high production efficiency. Furthermore, it can be seen that when all process parameters are within the preferred range of this invention, the overall performance of the titanium alloy coiled tubing is better.

[0117] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a titanium alloy continuous tubing, characterized in that, The titanium alloy coiled tubing, by weight percentage, comprises Al 1.42~1.48%, Fe 0.22~0.26%, C 0.045~0.048%, Mo 0.33~0.38%, N 0.039~0.042%, V 1.21~1.31%, with the balance being Ti and unavoidable impurities; the preparation method includes the following steps: Step S1: Obtain titanium alloy sheet according to the composition ratio of titanium alloy coiled tubing; Step S2: Under the protection of a first inert gas, the titanium alloy plate is butt-welded, and the weld is subjected to a first heat treatment to obtain a titanium alloy strip. Step S3: The titanium alloy strip is bent and shaped, and then straight seam welding is performed under the protection of a second inert gas to obtain a titanium alloy continuous tubing precursor. Step S4: The titanium alloy coiled tubing precursor is sized, and then subjected to a second heat treatment at 650~850℃ for 3~5 minutes under a third inert gas protection to obtain the titanium alloy coiled tubing.

2. The preparation method according to claim 1, characterized in that, The first inert gas, the second inert gas, and the third inert gas each independently comprise argon or a mixture of argon and helium.

3. The preparation method according to any one of claims 1 to 2, characterized in that, In step S2, the welding method for the butt weld is plasma welding or argon arc welding; and / or the welding method for the butt weld is 45° butt welding.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In step S2, the temperature of the first heat treatment is 950~1050℃, and the holding time is 20~30s.

5. The preparation method according to any one of claims 1 to 4, characterized in that, Prior to step S3, the preparation method further includes a step of cleaning the titanium alloy strip.

6. The preparation method according to claim 5, characterized in that, The cleaning solution contains 400-500 g / L NaOH and 100-150 g / L NaNO2; and / or the cleaning temperature is 100-120℃.

7. The preparation method according to any one of claims 1 to 6, characterized in that, In step S3, a copper roller unit is used to perform the bending and forming.

8. The preparation method according to any one of claims 1 to 7, characterized in that, In step S3, the welding method for the straight weld seam is high-frequency induction welding, laser welding, or argon arc welding.

9. The preparation method according to claim 8, characterized in that, During the straight weld seam welding process, the gap t between the welding machine's induction coil and the bent titanium alloy strip is ≤9mm, and the welding V-shaped opening angle α is 8~10°.

10. The preparation method according to claim 9, characterized in that, The welding machine has a power of 100~500KW and a welding speed of 25~80m / min.

11. The preparation method according to claim 10, characterized in that, The welding machine has a power of 130~200KW and a welding speed of 25~50m / min.

12. The preparation method according to any one of claims 1 to 11, characterized in that, Before step S4, the preparation method further includes the following steps: the titanium alloy coiled tubing precursor is subjected to gas protection cooling in a fourth inert gas atmosphere until the surface temperature of the titanium alloy coiled tubing precursor is 100~150℃, and the oxygen volume concentration of the fourth inert gas atmosphere is ≤5%.

13. A titanium alloy continuous tubing, characterized in that, It is obtained by the preparation method according to any one of claims 1 to 12.

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