Titanium alloy pipe suitable for geothermal resource exploitation and manufacturing method thereof

Abstract

The invention discloses a titanium alloy pipe suitable for geothermal resource exploitation and a manufacturing method. The titanium alloy pipe comprises the following components in percentage by weight: 3.0-5.0% of Al, 1.5-3.5% of V, 0.5-2.0% of Mo, 1.0-2.0% of Fe, 0.1-0.3% of Nb, 0.05-0.15% of Ru, 0.08-0.15% of O, less than or equal to 0.015% of C, less than or equal to 0.015% of H, less than or equal to 0.02% of N and the balance of Ti and other inevitable impurities. And the contents of the elements must simultaneously meet the following relation: Nb / Ru is greater than or equal to 2 and less than or equal to 5. The room-temperature yield strength of the obtained titanium alloy pipe is larger than or equal to 760 MPa, the yield strength at 450 DEG C is reduced by less than 25% compared with the room-temperature yield strength, the transverse Charpy impact energy at-10 DEG C is larger than or equal to 40 J, and the titanium alloy pipe has good oxygen corrosion resistance and hydrogen sulfide and carbon dioxide corrosion resistance, is at the high temperature of 450 DEG C and is rich in O2, H2S, CO2 and water vapor (so called rich, H2S, CO2 and water vapor). And the corrosion rate is less than 0.25 mm / a under the environment corrosion test condition that the gas volume fraction is not less than 1%.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy tube manufacturing, and particularly relates to a titanium alloy tube suitable for geothermal resource exploitation and a manufacturing method thereof. Background Art

[0002] Titanium alloy is an important structural material and is widely used in fields such as aviation, aerospace, petroleum, chemical industry, and medical treatment due to its excellent mechanical properties, chemical stability, and biocompatibility. Among them, as a typical material with high strength and high toughness, titanium alloy tubes play an extremely important role in the pipeline systems in fields such as petroleum and natural gas.

[0003] Geothermal resources refer to the thermal energy inside the earth, including geothermal water, geothermal steam, geothermal rock, etc. It is a green, clean, and renewable energy source, which has the advantages of being unaffected by seasons and climate changes and having no carbon dioxide emissions. At the same time, geothermal resources can be used for power generation, heating, greenhouse agriculture, water treatment, etc. Geothermal resources for energy supply often come from geothermal rock, etc. Injecting water and then extracting high-energy steam to drive an energy conversion device for power generation is an important field of current geothermal applications. However, the development pipe strings for geothermal rock face huge challenges such as heat loss, high-temperature strength attenuation, and corrosive media containing oxygen, hydrogen sulfide, and carbon dioxide. Titanium alloy, with its low thermal diffusivity, corrosion resistance, and high-temperature resistance characteristics, becomes an optimal solution for the development pipe strings of geothermal rock.

[0004] Currently, the research status of titanium alloy tubes applied in the oil and gas industry is as follows:

[0005] Chinese Patent CN 110983102A discloses a titanium alloy oil pipe and a manufacturing method thereof. The mass percentages of the chemical components of the titanium alloy oil pipe are: Al: 2.30 - 5.80%, V: 1.80 - 5.20%, Nb: 0.80 - 2.50%, Zr: 2.50 - 6.50%, Mo: 1.50 - 6.50%, Pd: 0.15 - 0.60%, rare earth elements 0.10 - 0.50%, C ≤ 0.05%, Fe ≤ 0.20%, N ≤ 0.05%, and the rest is Ti and inevitable impurities. After smelting, forging, piercing rolling, cold rolling, warm drawing, heat treatment, straightening, and non-destructive testing, the pipe ends are processed according to the designed special threads. The mechanical properties of the finally manufactured titanium alloy oil pipe products meet: yield strength Rp 0.2 : 758 MPa - 965 MPa, tensile strength Rm ≥ 862 MPa, elongation at break A50 ≥ 14%, Charpy impact value at -10°C ≥ 45 J, meeting the requirements of the API Spec 5CT standard for the 110 ksi strength level, and having good resistance to CO2, H2S, and Cl -The coexistence of a harsh corrosion environment and stress corrosion performance requirements can meet the development needs of oil and gas fields in deep wells, ultra-deep wells, and harsh corrosion environments. However, the performance of this titanium alloy pipe at high temperatures is not mentioned.

[0006] Chinese Patent CN 110592425 A discloses a titanium alloy with high impact toughness. The chemical composition by weight percentage is: Al 4.0 - 9.0%, Mo 0.5 - 5.0%, Zr 1 - 5%, Nb 1 - 5%, Fe 0.2 - 2.0%, and the balance is Ti and impurities. The method for preparing seamless pipes using this high impact toughness titanium alloy is as follows: Weigh the aluminum-niobium master alloy, molybdenum blocks, pure sponge zirconium, iron nails, and sponge titanium according to the chemical composition requirements and mix them. Press them into electrode rods, and then put them into a vacuum consumable arc furnace for secondary melting to obtain a titanium alloy ingot. Forge the titanium alloy ingot at 1150 °C for blooming, and then forge it at 970 - 1020 °C to obtain a bar blank. Then heat the bar blank to 950 - 1200 °C. Obtain a tube blank by cross-rolling piercing of the bar blank. Use the waste heat after cross-rolling piercing to hot-roll the tube blank, and then perform sizing and reducing to obtain pipes. Heat-treat, straighten, saw-cut, inspect, and store the pipes. The seamless pipes prepared using this titanium alloy in this invention have high strength, high plasticity, high low-temperature impact toughness, and good corrosion resistance, meeting the application requirements of harsh working conditions in oil and gas wells.

[0007] Chinese Patent CN108467969A discloses a highly corrosion-resistant titanium alloy pipe for oil and gas development and its preparation method, mainly solving problems such as insufficient corrosion resistance, high cost, processing complexity, and large performance gaps of existing titanium alloy pipes in a high-corrosion environment. Besides Ti, the titanium alloy pipe mainly consists of the following components by mass percentage: Al: 3.6 - 4.1%, V: 2.1 - 2.6%, Fe: 0.7 - 1.6%, O: 0.15 - 0.26%, Ru: 0.01 - 1.1%, Ni: 0.05 - 1.5%, 0 < C ≤ 0.07%, 0 < N ≤ 0.05%, 0 < H ≤ 0.0155%. At the same time, this invention also provides a method for preparing the above titanium alloy pipe. In the composition design of this titanium alloy pipe material, the usage amounts of precious metals such as Ru and V in the original composition are reduced, and a reasonable ratio of Fe element and O element is used to supplement β-phase stabilizing elements, improving the strength and toughness of the alloy. Utilize the synergistic effect of elements such as Ru, V, Fe, Ni, W, and Mo to maintain the density and stability of the surface oxide film to improve the corrosion resistance.

[0008] Chinese Patent CN108467970A discloses an iron-containing titanium alloy pipe for highly corrosive oil and gas development and its preparation method, which solves the problems of high cost, processing complexity, and large performance gaps in existing titanium alloy pipes. Except for Ti, the iron-containing titanium alloy pipe is mainly composed of the following components by mass percentage: Al: 5.8 - 6.4%, V: 2.4 - 3.0%, Fe: 0.6 - 1.2%, Ru: 0.02 - 0.06%, Ni: 0.05 - 1.3%, O ≤ 0.2%, C ≤ 0.04%, N ≤ 0.04%, H ≤ 0.0135%. At the same time, the present invention also provides a method for preparing the above titanium alloy pipe. In the design of the material composition of the titanium alloy pipe, the usage amounts of precious metals such as Ru and V in the original components are reduced, and a reasonable ratio of Fe element and O element is used to supplement β-phase stabilizing elements, improving the strength and toughness of the alloy. By the synergistic effect of elements such as Ru, V, Fe, Ni, W, and Mo, the cathodic hydrogen evolution reaction rate on the surface of the titanium alloy is increased, and the density and stability of the surface oxide film are maintained to improve the corrosion resistance.

[0009] Chinese Patent CN 111349817 B discloses a titanium alloy drill pipe, its preparation method and application. The titanium alloy drill pipe is composed of the following components by mass percentage: Al 3 - 5%; V 6 - 9%; Cr 2 - 7%; Mo 1.5 - 3.5%; Zr 2.5 - 5%; W 1 - 5%; Fe 1 - 5%; Si 1 - 5%; C ≤ 0.1%; N ≤ 0.05%; H ≤ 0.015%; O ≤ 0.25%; the balance is Ti. The titanium alloy drill pipe has good high-temperature corrosion resistance. The annual corrosion rate of H2S and CO2 at 150°C - 260°C is reduced to less than 0.0006 mm / a, and the density is reduced to 4.4 - 5.8 g / cm 3 and the build-up curvature radius is reduced to 10 - 18 meters.

[0010] Chinese Patent CN111485135A discloses a 930MPa grade Ti - Al - V - Zr - Ru corrosion-resistant titanium alloy pipe and its manufacturing method, belonging to the technical field of manufacturing oil well pipes in the oil and gas industry. By mass fraction, its composition includes Al: 5.8 - 6.5%, V: 2.0 - 3.0%, Zr: 1.0 - 1.7%, Mo: 0.5 - 1.0%, Ru: 0.1 - 0.3%, and the balance is Ti and inevitable impurities. Its preparation method is: smelting, casting, forging, extrusion, rolling, annealing treatment, solution treatment, pre-stretching treatment and aging treatment. The titanium alloy drill pipe obtained through the above process route has a yield strength greater than 930 MPa and good corrosion resistance.

[0011] Chinese Patent CN 111593230A discloses a kind of tubing for 930MPa grade ultra-high strength titanium alloy drill pipe and its manufacturing method, belonging to the technical field of manufacturing oil well pipes in the oil and gas industry. By mass percentage, the composition of this titanium alloy tubing is: Al: 5.8 - 6.5%, V: 2.0 - 3.0%, Zr: 1.0 - 1.7%, Mo: 0.5 - 1.0%, and the balance is Ti and inevitable impurities. Its manufacturing method is: smelting, casting, ingot forging, extrusion, rolling, annealing treatment, multi-stage solution treatment, pre-stretching treatment and aging treatment. The titanium alloy drill pipe obtained by the manufacturing method of this invention has a yield strength greater than 930MPa and an elongation greater than 10%, meeting the mechanical property standard requirements of drill pipes with a strength level of 135Ksi in API-5DP.

[0012] Chinese Patent CN116590572A discloses an oxidation-resistant high-temperature titanium alloy and its preparation method, and the oxidation-resistant high-temperature titanium alloy is composed of the following components by mass percentage: Al 5.5 - 6.5%, Sn 3.0 - 4.0%, Hf 3.5 - 4.5%, Si 0.3 - 0.5%, Ta 0 - 3%, Nb 0 - 3%, and the balance is Ti; and this invention first uses theoretical calculation to screen oxidation-resistant alloying elements and design the alloy composition, then uses the non-consumable vacuum arc melting method to carry out the melting of master alloy and target alloy in sequence, and finally carries out homogenization heat treatment to obtain a high-temperature titanium alloy with excellent oxidation resistance.

[0013] In the prior art, the research on titanium alloy tubes is focused on how to meet the usage environment of oil and gas fields, and there is less research on titanium alloy tubes for geothermal resource development. How to obtain titanium alloy tubes that can meet the exploitation and utilization of geothermal resources at 450°C and above is a technical problem that urgently needs to be solved at present. Summary of the Invention

[0014] The purpose of this invention is to provide a kind of titanium alloy tube applicable to the exploitation of geothermal resources and its manufacturing method. This titanium alloy tube has excellent mechanical properties and corrosion resistance, among which the room temperature yield strength ≥ 760MPa, the reduction amplitude of the yield strength at 450°C compared with the room temperature yield strength < 25%, the -10°C transverse Charpy impact energy ≥ 40J, and has good characteristics of resistance to oxygen corrosion, hydrogen sulfide and carbon dioxide corrosion. Under the environmental corrosion test conditions of 450°C high temperature and rich in O2, H2S, CO2 and water vapor (so-called rich means that the volume fractions of the above gases are not less than 1% respectively), the corrosion rate < 0.25mm / a. At the same time, the skew rolling piercing + hot continuous rolling process is adopted to prepare a titanium alloy seamless tube with good surface quality, and the process flow is simple, and the processing cost is greatly reduced compared with the traditional hot extrusion process of titanium alloy tubing.

[0015] To achieve the above purpose, the technical solution of this invention is:

[0016] A titanium alloy tube suitable for geothermal resource exploitation, the component weight percentages of which are as follows: Al: 3.0 - 5.0%, V: 1.5 - 3.5%, Mo: 0.5 - 2.0%, Fe: 1.0 - 2.0%, Nb: 0.1 - 0.3%, Ru: 0.05 - 0.15%, O: 0.08 - 0.15%, C ≤ 0.015%, H ≤ 0.015%, N ≤ 0.02%, and the balance includes Ti and other inevitable inclusions; and the contents of the above elements must simultaneously satisfy the following relationship:

[0017] 2 ≤ Nb / Ru ≤ 5.

[0018] Furthermore, Al: 3.5 - 4.5%, and / or, V: 2 - 3%, and / or, Mo: 1.0 - 1.5%, and / or, Fe: 1.2 - 1.8%.

[0019] Even further, the balance is Ti and other inevitable inclusions.

[0020] The microstructure of the titanium alloy tube described in the present invention is a basket weave structure.

[0021] The yield strength of the titanium alloy tube described in the present invention ≥ 760 MPa, the reduction amplitude of the yield strength at 450°C compared to the yield strength at room temperature < 25%, the transverse Charpy impact energy at -10°C ≥ 40 J, and the corrosion rate under the corrosion test conditions of a high temperature of 450°C and an environment rich in O2, H2S, CO2, and water vapor < 0.25 mm / a.

[0022] In the component design of the titanium alloy tube suitable for geothermal resource exploitation described in the present invention:

[0023] Al: The Al element is the most widely added alloy element in titanium alloys and belongs to a substitutional α-phase stabilizing element, which has a solid solution strengthening effect on the alloy. For every 1% addition of Al, the tensile strength at room temperature increases by about 50 MPa. If the content of the A1 element is too low, the strengthening effect on the alloy is not obvious. If the content of the A1 element is too high, an ordered phase Ti3Al (α2) superstructure phase appears in the structure, which will cause a significant decrease in the plasticity and impact toughness of the alloy and reduce its workability, making the alloy unable to be used for preparing tubes; for the purpose of achieving high strength, the addition amount of Al in the present invention is 3.0 - 5.0%, preferably 3.5 - 4.5%.

[0024] V: V is a β-phase stabilizing element, which can obtain a stable β-phase at room temperature. Adding V can enable the alloy to obtain a solid solution strengthening effect; at the same time, as the total amount of β-phase stabilizing elements increases, the two-phase region range of the alloy expands, and the proportion of the β-phase (body-centered cubic structure, bcc) is high at a lower temperature in the two-phase region of the alloy, and its forging deformation ability is high, and defects such as deformation cracks are not likely to appear. Therefore, the addition amount of V in the present invention is 1.5 - 3.5%, preferably 2 - 3%.

[0025] Mo: The diffusion rate of Mo element in titanium alloy is relatively slow, which can play the role of fine grain strengthening, and it is not easy to form brittle intermetallic compounds, thus greatly improving the strength of titanium alloy. At the same time, Mo is also a good corrosion-resistant element. Adding Mo can significantly improve the corrosion resistance of titanium alloy, especially in the environment of high temperature containing O2, H2S, CO2 and water vapor. However, when the Mo equivalent is too high, the plasticity and impact toughness of the alloy will be significantly reduced. Therefore, the addition amount of Mo in the present invention is 0.5-2.0%, preferably 1.0-1.5%.

[0026] Fe: Fe is the strongest slow eutectoid type β-stabilizing element and has the strongest strengthening effect among all β-stabilizing elements. Its solution strengthening effect on titanium alloy is the most significant. Therefore, adding an appropriate amount of Fe element can significantly improve the strength of titanium alloy. At the same time, the price of Fe is lower than that of elements such as V, so the production cost of titanium alloy can be reduced to a certain extent. However, when the Fe content in titanium alloy exceeds a certain amount, it will have a significant adverse impact on the impact performance of the alloy. The addition amount of Fe in the present invention is 1.0-2.0%, preferably 1.2-1.8%.

[0027] Nb, Ru: Nb and Ru are both β-phase stabilizing elements. Through research, it is found that the composite addition of Nb and Ru can significantly improve the strength stability of titanium alloy in high temperature environment, especially in the service environment below 450 °C for geothermal resource development and application, and reduce the strength attenuation affected by temperature rise. To achieve this effect, the addition amounts of Nb and Ru need to reach Nb: 0.1-0.3%, Ru: 0.05-0.15%, and at the same time Nb / Ru needs to satisfy 2 ≤ Nb / Ru ≤ 5.

[0028] O: As a low interstitial element, controlling the O content at 0.08-0.15% helps to improve the strength of titanium alloy.

[0029] C, H, N: They are inevitable impurity elements. However, in order to ensure the strength and toughness of the titanium alloy of the present invention, it is necessary to control C ≤ 0.015%, H ≤ 0.015%, and N ≤ 0.02%.

[0030] The manufacturing method of the titanium alloy tube applicable to geothermal resource exploitation described in the present invention includes the following steps:

[0031] 1) Electrode pressing, melting, and casting

[0032] Press, melt, and cast the electrodes into ingots according to the above components;

[0033] 2) Blooming

[0034] The ingot is subjected to upsetting and drawing forging for 2 to 3 heats at 50 to 150 °C above the phase transformation point of the titanium alloy. The forging ratio for each heat is controlled between 1.5 and 2.0, and after each heat of forging, it is air-cooled to the ambient temperature;

[0035] Then, it is subjected to 1 upsetting and drawing forging within the temperature range from the phase transformation point of the titanium alloy to 50 °C above the phase transformation point, and the forging ratio is controlled between 1.5 and 2.5;

[0036] Directly perform recrystallization heat treatment after forging. The recrystallization heat treatment temperature is controlled within the range from the phase transformation point of the titanium alloy to 50 °C above the phase transformation point. The recrystallization heat treatment time is 2 to 5 hours, and it is air-cooled to room temperature after being taken out of the furnace;

[0037] 3) Tube blank preparation

[0038] The obtained forged blank is heated within the range of the phase transformation point of the titanium alloy and 60 °C below the phase transformation point of the titanium alloy, and then subjected to 2 to 3 heats of upsetting and drawing forging. The forging ratio for each heat is controlled between 1.8 and 2.5, and after each heat of forging, it is air-cooled to the ambient temperature;

[0039] The obtained tube blank is finished, and surface defects are removed. A through hole with a diameter of 20 to 60 mm is obtained in the core of the tube blank by machining;

[0040] 4) Rotary piercing

[0041] The tube blank is heated within the range from the phase transformation point of the titanium alloy to 40 °C above the phase transformation point for piercing, and the deformation amount is controlled between 60 and 70%;

[0042] 5) Continuous rolling

[0043] The heating temperature is controlled within the range from the phase transformation point of the titanium alloy to 50 °C below the phase transformation point, and the deformation amount is controlled between 20 and 25%;

[0044] 6) Annealing heat treatment

[0045] The annealing heat treatment temperature is between the phase transformation point and 60 °C below the phase transformation point. The annealing heat treatment time is 0.5 to 3 h, and it is air-cooled to room temperature after being taken out of the furnace after the annealing heat treatment;

[0046] 7) Subsequently, straightening and surface cleaning are carried out to obtain the titanium alloy tube.

[0047] Furthermore, in step 3), before finishing, the obtained tube blank is subjected to 1 heat of rotary swaging at 40 to 60 °C below the phase transformation point of the titanium alloy.

[0048] In the manufacturing method of the present invention:

[0049] Step (1) Electrode pressing, melting, and casting: According to the chemical composition of the titanium alloy, electrode pressing is completed on a hydraulic press, and the electrode is subjected to two or three times of vacuum consumable melting to prepare an ingot with uniform composition.

[0050] To meet the characteristics of fast deformation speed in piercing and hot continuous rolling, improve the hot working performance of the tube blank and reduce the occurrence of surface defects in tube manufacturing, two processes of blooming and billet making are adopted for the ingot.

[0051] Step (2) Ingot blooming: The ingot is subjected to upsetting and drawing forging for 2 - 3 heating times at 50 - 150 °C above the phase transformation point of the titanium alloy. The forging ratio for each heating time is controlled between 1.5 - 2.0, and air cooling is carried out after each forging. Then, upsetting and drawing forging is carried out once within the range of the phase transformation point of the titanium alloy and 50 °C above the phase transformation point of the titanium alloy. The forging ratio is controlled between 1.5 - 2.5, and after forging, it is directly sent back to the furnace for recrystallization heat treatment. The heat treatment heating temperature is within the range of the phase transformation point of the titanium alloy to 50 °C above the phase transformation point. After heat treatment for 2 - 5 hours, it is taken out of the furnace and air cooled to room temperature. During the blooming process, by controlling the forging temperature and forging ratio, the coarsening of the original β-phase grains can be effectively avoided, and large-sized α lamellar clusters are generated subsequently, which has an adverse effect on toughness.

[0052] Step (3) Tube blank preparation: The forged billet obtained in step (2) is heated within the range of the phase transformation point of the alloy and 60 °C below the phase transformation point, and then subjected to upsetting and drawing forging for 2 - 3 heating times. The forging ratio is controlled between 1.8 - 2.5 to obtain a controllable basketweave structure.

[0053] According to the size of the final tube blank, the forged bar billet can also be subjected to one-pass rotary swaging at 40 - 60 °C below the phase transformation point of the titanium alloy to form a tube blank. Then, finishing treatments such as peeling are carried out on the tube blank to remove surface defects.

[0054] Step (4) A through hole with a diameter of 20 - 60 mm is obtained in the center of the tube blank by machining. Machining the through hole can significantly reduce the risk of rolling jamming during cross-rolling piercing and reduce the occurrence of defects.

[0055] Through the above process control, the obtained tube blank maintains good toughness, and then cross-rolling piercing + hot continuous rolling is carried out, strictly controlling the heating temperature and deformation amount, and a titanium alloy seamless tube with good surface quality is prepared.

[0056] Compared with the prior art, the beneficial effects of the present invention are:

[0057] In the composition design of the present invention, by utilizing the strengthening effects of Al, V, and Fe and combining the addition of Mo element, the strength of the titanium alloy is increased. At the same time, by compounding the addition of Nb and Ru elements, the strength stability of the titanium alloy in high-temperature environments is significantly improved, especially in the use environment below 450 °C for geothermal resource development applications, reducing the strength attenuation caused by temperature rise. Most of the existing titanium alloy tubes can meet the strength requirements for use at room temperature, but the strength of titanium alloy tubes still cannot meet the use requirements in the 450 °C high-temperature environment for geothermal resource development.

[0058] The titanium alloy tube obtained by the present invention has a room temperature yield strength ≥ 760 MPa, a yield strength attenuation at 450 °C not exceeding 25%, a -10 °C transverse Charpy impact energy ≥ 40 J, and has good resistance to oxygen corrosion and corrosion by hydrogen sulfide and carbon dioxide. Under the environmental corrosion test conditions of 450 °C and rich in O2, H2S, CO2 and water vapor, the corrosion rate < 0.25 mm / a. By "rich" is meant that the volume fractions of the above gases are all not less than 1%.

[0059] On the basis of composition design, the present invention controls the upsetting and drawing forging deformation temperature and forging ratio, effectively avoiding grain growth, especially avoiding the coarsening of the original β-phase grains, forming a controllable basket weave structure and avoiding adverse effects on toughness. First, a through-hole is processed in the tube blank, significantly reducing the risk of rolling jamming during the subsequent cross-rolling piercing process and reducing the occurrence of defects, providing a basis for obtaining high strength, high toughness, high hot working performance and corrosion resistance. The cross-rolling piercing + hot continuous rolling process is directly used to prepare a titanium alloy seamless tube with good surface quality, achieving the performance objectives of high strength, corrosion resistance and high temperature stability of the titanium alloy tube. The overall preparation process is simpler than the hot extrusion process used in the preparation of traditional titanium alloy tubes, and the processing cost is greatly reduced. Brief Description of the Drawings

[0060] Figure 1 It is a microstructural photograph of the tube blank obtained in Example 3 of the present invention.

[0061] Figure 2 It is a microstructural photograph of the titanium alloy tube obtained in Example 3 of the present invention. Detailed Description of the Invention

[0062] The following further describes the present invention with reference to the embodiments.

[0063] The compositions of the titanium alloy tubes in the examples and comparative examples of the present invention are shown in Table 1, and the manufacturing process parameters of the examples and comparative examples of the present invention are shown in Tables 2 and 3.

[0064] The titanium alloy tubes obtained in the examples and comparative examples of the present invention are subjected to performance tests, and the specific performance is shown in Table 4.

[0065] Room temperature yield strength test: The prepared titanium alloy tube is processed into an API arc-shaped specimen, and the average value is obtained after inspection according to the API standard to obtain the room temperature yield strength.

[0066] 450 °C yield strength test: Specimens are processed according to the ASTM E8 standard and subjected to a tensile test at 450 °C to obtain the yield strength at 450 °C.

[0067] Charpy V-notch impact energy absorption (i.e., impact toughness) test: V-notch impact specimens with dimensions of 7.5 * 10 * 55 (mm) in volume were cut from the titanium alloy tube. After inspection according to the GB / T 229 standard, the average value was taken and converted into full-size specimens of 10 * 10 * 55 (mm) according to the API 5CT standard and listed in Table 3. The test temperature was -10°C.

[0068] Corrosion resistance: The high-temperature corrosion test conditions were a temperature of 450°C, a mixed gas composition of 1% O2, 10% water vapor, 15% CO2, 5% H2S, and the rest nitrogen. The test time was 240 h. By comparing the weights of the specimens before and after the test, the uniform weight gain rate was calculated and the results were listed in Table 4.

[0069] As can be seen from Table 4, the titanium alloy tube obtained in the embodiment of the present invention has a room temperature yield strength ≥ 760 MPa, the yield strength attenuation at 450°C is not more than 25%, the -10°C transverse Charpy impact energy ≥ 40 J, has good impact toughness at -10°C, and has good resistance to oxygen corrosion, hydrogen sulfide and carbon dioxide corrosion characteristics. Under the corrosion test conditions of 450°C high temperature and an environment rich in O2, H2S, CO2 and water vapor, the corrosion rate < 0.25 mm / a.

[0070] In Comparative Example 1, the addition amounts of Al and V were too low, and the addition amount of Nb was too high. The yield strengths at room temperature and 450°C high temperature were both low. The reduction amplitude of the yield strength of the titanium alloy tube at 450°C high temperature was large, the -10°C transverse Charpy impact energy was low, the toughness was poor, and the corrosion rate was high, and the corrosion resistance was poor.

[0071] In Comparative Example 2, the addition amount of Nb was too low, and Nb / Ru = 0.67, and the ratio was too low. Therefore, for the obtained titanium alloy tube, although the strength could meet the requirements, the reduction amplitude of the yield strength of the titanium alloy tube at 450°C high temperature was large, the -10°C transverse Charpy impact energy was low, the toughness was poor, the corrosion rate was high, and the corrosion resistance was poor.

[0072] In Comparative Example 3, Ru was not added. For the obtained titanium alloy tube, although the strength could meet the requirements, the reduction amplitude of the yield strength of the titanium alloy tube at 450°C high temperature was large, the -10°C transverse Charpy impact energy was low, the toughness was poor, the corrosion rate was high, and the corrosion resistance was poor.

[0073] Comparative Examples 4 - 6 used the same composition as in Example 3 of the present invention. However, in Comparative Examples 4 and 5, due to the blooming temperature and forging temperature exceeding the process range, the original β grain was coarse, and the α lamellar cluster size formed during subsequent processing was large. The crack propagation path was straight during the impact process, resulting in the impact energy being lower than the requirement. In Comparative Example 6, the strength was too low due to too high annealing temperature.

[0074] Figure 1This is the microstructural photo of the tube blank obtained in Example 3 of the present invention. It can be seen from the picture that the microstructure of the tube blank at this time is Widmanstätten structure, and the β grain size is < 1 mm. Figure 2 This is the microstructural photo of the titanium alloy tube obtained in Example 3 of the present invention. The microstructure of the final titanium alloy tube is basket weave structure, providing a good combination of strength and toughness.

[0075]

[0076]

[0077]

[0078]

[0079]

Claims

1. A titanium alloy tube suitable for geothermal resource exploitation, with its component weight percentages as follows: Al: 3.0 - 5.0%, V: 1.5 - 3.5%, Mo: 0.5 - 2.0%, Fe: 1.0 - 2.0%, Nb: 0.1 - 0.3%, Ru: 0.05 - 0.15%, O: 0.08 - 0.15%, C ≤ 0.015%, H ≤ 0.015%, N ≤ 0.02%, and the balance includes Ti and other inevitable inclusions; and the contents of the above elements must simultaneously satisfy the following relationship: 2 ≤ Nb / Ru ≤ 5.

2. The titanium alloy pipe applicable to geothermal resource exploitation as described in claim 1, wherein Al: 3.5 - 4.5%, and / or, V: 2 - 3%, and / or, Mo: 1.0 - 1.5%, and / or, Fe: 1.2 - 1.8%.

3. The titanium alloy pipe applicable to geothermal resource exploitation according to claim 1 or 2, wherein The balance is Ti and other inevitable inclusions.

4. The titanium alloy pipe applicable to geothermal resource exploitation according to claim 1 or 2 or 3, characterized in that, The microstructure of the titanium alloy tube is basket weave structure.

5. The titanium alloy pipe applicable to geothermal resource exploitation according to claim 1 or 2 or 3 or 4, characterized in that, The yield strength of the titanium alloy tube ≥ 760 MPa, the reduction amplitude of the yield strength at 450 °C compared with the yield strength at room temperature < 25%, the transverse Charpy impact energy at -10 °C ≥ 40 J, and the corrosion rate under the corrosion test conditions of an environment containing O2, H2S, CO2 and water vapor at 450 °C < 0.25 mm / a.

6. The manufacturing method of the titanium alloy pipe applicable to geothermal resource exploitation according to any one of claims 1 to 5, characterized in that, It includes the following steps; 1) Electrode pressing, melting, casting Press, melt and cast the electrode according to the composition described in Claim 1 or 2 or 3 into an ingot; 2) Blooming Perform upsetting and drawing forging on the ingot at 50 - 150 °C above the titanium alloy phase transformation point for 2 - 3 forging heats, control the forging ratio between 1.5 and 2.0 for each forging heat, and air cool to the ambient temperature after each forging heat; Then perform upsetting and drawing forging once within the temperature range from the titanium alloy phase transformation point to 50 °C above the phase transformation point, and control the forging ratio between 1.5 and 2.5; Directly perform recrystallization heat treatment after forging, control the recrystallization heat treatment temperature within the range from the titanium alloy phase transformation point to 50 °C above the phase transformation point, the recrystallization heat treatment time is 2 - 5 hours, and air cool to room temperature after taking out of the furnace; 3) Tube blank preparation Heat the obtained forged blank within the range of the titanium alloy phase transformation point and 60 °C below the phase transformation point, and then perform upsetting and drawing forging for 2 - 3 forging heats, control the forging ratio between 1.8 and 2.5 for each forging heat, and air cool to the ambient temperature after each forging heat; Perform sizing on the obtained tube blank to remove surface defects, and obtain a through hole with a diameter of 20 - 60 mm in the center of the tube blank by machining; 4) Rotary piercing Heat the tube blank to within the range from the titanium alloy phase transformation point to 40 °C above the phase transformation point for piercing, and control the deformation amount between 60 - 70%; 5) Continuous rolling Control the heating temperature within the range from the titanium alloy phase transformation point to 50 °C below the phase transformation point, and control the deformation amount between 20 - 25%; 6) Annealing heat treatment The annealing heat treatment temperature is within the range from the phase transformation point to 60 °C below the phase transformation point, the annealing heat treatment time is 0.5 - 3 h, and air cool to room temperature after taking out of the furnace after annealing heat treatment; 7) Straightening and surface cleaning, then the titanium alloy tube is obtained.

7. The manufacturing method according to claim 6, characterized in that, In step 3), before sizing, perform one pass of rotary swaging on the obtained tube blank at 40 - 60 °C below the titanium alloy phase transformation point.

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