Improved TA18 titanium alloy strip coil for coiled tubing and preparation method

Abstract

The invention discloses an improved TA18 titanium alloy strip coil for a coiled tubing and a preparation method. The improved TA18 titanium alloy strip coil is controlled to comprise the following components in percentage by weight: 0.12-0.15 wt% of O, 3.0-3.5 wt% of Al, 2.5-3.0 wt% of V and the balance of Ti. According to the method, the element content of TA18 titanium alloy is improved, the Al alloy and the V alloy are located at the upper limit according to the standard requirement, the O element content is increased, the requirement that the longitudinal yield strength of the TA18 titanium strip coil is larger than or equal to 80 ksi is met through the strengthening effect of the elements, the transverse plasticity index A50 of the titanium strip is larger than 15%, and cracking is avoided when the titanium strip is transversely bent by 180 degrees.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy technology, specifically to an improved TA18 titanium alloy strip coil for continuous tubing and its preparation method. Background Technology

[0002] Coiled tubing, also known as flexible tubing or coiled tubing, is a long tubing wound around a disc. It is widely used in various operations such as dewaxing, acidizing, cementing, well killing, well washing, logging, well completion, and well workover. Coiled tubing is formed by bending and welding strip material. During operation, coiled tubing is subjected to bending, tensile, and internal pressure loads, making it prone to fatigue fracture. As the applications of coiled tubing have expanded to deep well operations, increasingly higher requirements are placed on material strength and the length of the welding strip to accommodate high-pressure and high-load operations. Simultaneously, to meet the development needs of oil wells in areas with high H2S and CO2 content, the selection of coiled tubing materials must consider corrosion resistance.

[0003] Titanium materials possess advantages such as high specific strength and strong corrosion resistance. When applied to coiled tubing, they can improve the corrosion resistance of the tubing and reduce its weight, offering unparalleled advantages over alloy steel and nickel-based alloys. TA18 titanium alloy features low alloy element content, easy control of melting uniformity, and easy plastic forming, while also possessing excellent corrosion resistance and comprehensive mechanical properties, making it the preferred material for medium-strength oilfield coiled tubing. This invention proposes a method for preparing TA18 titanium alloy strip coils with a thickness of 4mm–7mm and a width of 1000mm–1500mm. The strips are slit to achieve different width requirements, satisfying the needs of different pipe diameters.

[0004] Patent CN202110906543.X proposes a hot-rolled TA18 titanium alloy coil and its pickling process. The TA18 grade used in the patent is limited to the requirements of GB / T3620.1 standard. The rolling method used is continuous rolling. No specific annealing temperature is given for the rolled titanium alloy strip, and the mechanical properties of the final product are not tested. Patent CNET01610118108.X proposes a method for producing TA18 titanium alloy coils in a conventional hot continuous rolling mill. The composition range of the TA18 titanium alloy used is not specified, and the rolling is also sampled from the hot continuous rolling method. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides an improved TA18 titanium alloy strip coil for coiled tubing and its preparation method.

[0006] The technical solution of the present invention is: an improved TA18 titanium alloy strip coil for coiled tubing, wherein the composition of the improved TA18 titanium alloy strip coil is controlled as follows: O content is 0.12-0.15wt%, Al content is 3.0-3.5wt%, V content is 2.5-3.0wt%, and the balance is Ti.

[0007] Note: According to the composition range of the national standard GB / T3620.1, the yield strength of TA18 titanium alloy materials produced is difficult to reach the requirement of 582MPa. Based on the national standard, this invention controls the Al content to 3.0-3.5%, the V content to 2.5-3.0%, and increases the O content from the standard requirement of ≤0.12% to between 0.12-0.15%. By bringing the reinforcing elements Al and V close to the upper limit of the standard and increasing the O content, a strengthening effect is achieved, laying the foundation for the yield strength of TA18 titanium materials to reach above 582MPa.

[0008] This invention also provides a method for preparing an improved TA18 titanium alloy strip coil for coiled tubing, comprising the following steps:

[0009] S1. Raw material selection and smelting

[0010] According to the composition ratio, sponge titanium, Al-V alloy, Al bean and TiO2 powder are selected as raw materials. After being mixed evenly, they are pressed into electrodes and melted in a vacuum arc furnace twice to obtain TA18 titanium alloy ingots whose composition meets the composition content of the improved TA18 titanium alloy strip. Then, the surface of the TA18 titanium alloy ingot is machined to remove surface oxidation and surface loose layer.

[0011] The parameters for the two vacuum arc furnace melting processes are as follows: for the first vacuum arc furnace melting process, the vacuum degree is <6Pa, the voltage is 32-35V, the current is 22000-25000A, and the time is 8-12h; for the second vacuum arc furnace melting process, the vacuum degree is <4Pa, the voltage is 32-35V, the current is 32000-35000A, and the time is 8-12h.

[0012] S2, Slab Preparation

[0013] TA18 titanium alloy ingots are heated and held at 1100-1150℃ using a natural gas furnace for 10-12 hours. They are then forged into slabs with a thickness of 200-240mm and a width of 1000-1500mm. The forged slabs are then machined to remove the surface oxide layer and to saw off the rounded ends of the slabs. The lowest point of the upper and lower surfaces of the slabs is machined by ≥4mm.

[0014] S3, Slab Rolling

[0015] S3-1, Slab heating: The slab is heated using a walking beam natural gas furnace, with a total furnace time of 240-300 minutes;

[0016] S3-2, Rough rolling: The slab after heating is rough rolled. The rolling is divided into seven passes. The thickness of the intermediate slab after the seven passes of rough rolling is controlled at 35mm to 40mm. The final rolling temperature is controlled at 840℃ to 880℃.

[0017] S3-3, Finish rolling: The slab after rough rolling is finished rolling. The starting temperature of finish rolling is 820℃~850℃. After five passes of reciprocating rolling, the final thickness is 4mm~7mm. The finishing rolling speed is controlled at 1.5~2.5m / s, and the final rolling temperature is ≥700℃.

[0018] S3-4. Winding: The rolled titanium strip is wound up in a winding machine;

[0019] S4, Post-processing of titanium strip coil

[0020] S4-1, Uncoiling and Welding: The titanium strip coil is opened by the uncoiling mechanism, the ends of the titanium strip coil are cut flat, and multiple titanium strip coils are welded to form a continuous TA18 titanium strip.

[0021] S4-2, Annealing: Continuous online annealing is used to anneal the continuous TA18 titanium strip at an annealing temperature of 820℃~840℃ and an annealing time of 9~12min. The speed of continuous online annealing is determined according to the equipment parameters of the annealing furnace. This invention uses a continuous annealing furnace with a length of 97 meters and an online speed of 8~10m / min. Recrystallization of the rolled deformation structure is achieved through continuous online annealing, which improves the plasticity of the material, ensures the bending and forming of the tube, and meets the plasticity requirements of the continuous oil tube.

[0022] S4-3. Mechanical Descaling and Shot Blasting: The annealed TA18 titanium strip is mechanically descaled, and then the surface of the TA18 titanium strip is shot blasted using four shot blasting machines at a speed of 50–70 m / s, a steel shot diameter of 0.8–1.2 mm, and a shot dosage of 8–10 kg / m. 2 The angle between the shot blasting and the TA18 titanium strip is 50-60°, and the running speed of the TA18 titanium strip is 10-12 m / min;

[0023] S4-4 Surface treatment: The TA18 titanium strip is surface treated, and then the surface of the TA18 titanium strip is rinsed with clean water with a metal ion concentration of <0.5g / L.

[0024] S4-5, Drying and winding

[0025] Hot air at 85-95℃ is used in the drying unit to blow on the surface of the TA18 titanium strip to remove water residue. The dried TA18 titanium strip is wound up in the winding mechanism, and the end of the roll is cut off from the continuity of other TA18 titanium strip rolls. Steps S4-1 to S4-5 are repeated 3 to 4 times.

[0026] Furthermore, in S3-1, the heating is divided into a preheating section, a first-stage heating section, a second-stage heating section, and a uniform heating section. The preheating section temperature is 400-500℃ and the holding time is 80-90 minutes; the first-stage heating temperature is 800-850℃ and the holding time is 60-80 minutes; the second-stage heating temperature is 950-1000℃ and the holding time is 60-80 minutes; and the uniform heating section temperature is 950-980℃ and the holding time is 40-50 minutes.

[0027] Note: Using multi-stage heating can avoid excessive temperature difference between the inside and outside of the slab caused by heating it once, which could lead to slab deformation. At the same time, by setting different heating temperature ranges through multi-stage heating, thermal efficiency can be improved and energy consumption can be reduced.

[0028] Furthermore, in S3-2, the reduction amounts for the seven passes are controlled as follows: 18%–20% for the first pass, 20%–24% for the second pass, 25%–30% for the third pass, 25%–30% for the fourth pass, 25%–30% for the fifth pass, 20%–24% for the sixth pass, and 18%–22% for the seventh pass.

[0029] Explanation: After the heated slab exits the furnace, the temperature distribution on the slab will be uneven due to uneven heating. The first pass with a small reduction is used to roll and deform the slab, making the thickness and temperature of the slab more uniform. The reduction is increased in the 2nd to 5th passes. In the sixth and seventh passes, the reduction is reduced to improve the shape of the slab with the middle thickness.

[0030] Furthermore, in S3-3, the reduction amount of the five passes of reciprocating rolling is controlled as follows: 25% to 30% for the first pass, 35% to 40% for the second pass, 35% to 40% for the third pass, 35% to 40% for the fourth pass, and 25% to 30% for the fifth pass.

[0031] Explanation: Similar to the roughing principle, the first pass uses a smaller reduction, followed by large deformation reduction in passes 2-4 to achieve rapid deformation, improve production efficiency, and avoid the decrease in billet temperature and increase in strength caused by slow rolling speed, which would increase rolling difficulty. The fifth pass is the final rolling pass, which focuses on improving billet accuracy, thickness, and shape, so the reduction force is reduced.

[0032] Furthermore, in S4-3, the mechanical descaling is performed using a descaling machine, which consists of three descaling units. The first two descaling units are used for descaling and removing scales, and the last descaling unit is used for straightening. The depressing amount of the first descaling unit is (51-54) ± 2 mm, the depressing amount of the second descaling unit is (50-51) ± 2 mm, and the depressing amount of the third descaling unit is (40-41) ± 1 mm. The thickness of the TA18 titanium strip roll is 4-7 mm, and the depressing amount decreases as the thickness of the TA18 titanium strip roll increases.

[0033] Note: Mechanical descaling is used to remove the oxide scale from titanium strip. By precisely adjusting the pressing amount, the oxide scale can be uniformly broken down, avoiding excessive pressing into the steel plate or residual oxide scale. Excessive pressing amount can lead to high energy consumption and load on the descaling equipment, while insufficient pressing amount may result in incomplete descaling. Therefore, multiple descaling units are used in combination for mechanical descaling of titanium strip.

[0034] Furthermore, in S4-3, a reinforcing agent is added to the shot blasting machine to provide wet blasting conditions for the steel shot. The mixing ratio of the reinforcing agent to the steel shot is 1L:10-20L, wherein the reinforcing agent is composed of 1-2 parts of potassium titanium oxalate, 3-5 parts of glycerol and 20-50 parts of water.

[0035] Explanation: By replacing the water used in the original shot blasting process with a reinforcing agent, the agent can replace the water in the basic conditions for wet shot blasting. Furthermore, the potassium titanium oxalate and glycerol added in the above ratio can effectively improve the shot blasting effect on titanium strips, providing an ideal base for subsequent surface treatment and improving the performance of titanium strips.

[0036] Furthermore, in S4-4, the surface treatment is as follows: TA18 titanium strip is continuously pickled in a two-stage pickling tank. The acid mixture uses HF and HNO3, with HF concentration of 4±1g / L, HNO3 concentration of 50±5g / L, and metal ion concentration of <40g / L. The pickling temperature is controlled at 50±5℃, and the first and second stages of mixed acid use the same acid concentration, metal ion concentration, and temperature control.

[0037] Note: HF is mainly used to clean and remove oxide scale from the surface of the hot-rolled titanium strip. HNO3 mainly acts as a corrosion inhibitor to prevent excessive HF pickling, which can cause uneven pickling in certain areas. By controlling the metal ion concentration to be less than 40 g / L, it is mainly to avoid excessive metal ion concentration in the mixed acid solution, which can deposit on the titanium strip surface, causing pickling spots and poor pickling surface. By controlling the temperature at 50±5℃, the activity of the acid in the acid solution can be fully utilized to improve pickling efficiency. However, if the temperature is too high, a large amount of acid will volatilize, resulting in waste.

[0038] Furthermore, in S4-5, for titanium strip thickness ≤ 5mm, repeat steps S4-1 to S4-5 3 times; for titanium strip thickness ≤ 7mm, repeat steps S4-1 to S4-5 4 times.

[0039] Note: TA18 titanium alloy strip coils require annealing heat treatment after hot rolling. For TA18 titanium alloy annealing, a certain holding time at high temperature is necessary to achieve the desired annealing effect. For thinner titanium strips (below 5mm), the annealing furnace length is approximately 100m. Based on the 97-meter continuous annealing furnace used in this product, each annealing pickling cycle allows for approximately 10 minutes of high-temperature holding time, with three cycles reaching 30 minutes. For thicker titanium strips (above 5mm), a longer holding time is required, so four cycles, totaling 40 minutes, are needed to meet the requirements for 5-7mm thicknesses.

[0040] The beneficial effects of this invention are:

[0041] (1) This invention improves the element content of TA18 titanium alloy, with Al and V alloys at the upper limit required by the standard, and increases the content of O element. Through the strengthening effect of these elements, it ensures that the longitudinal yield strength of TA18 titanium strip coil is ≥80ksi (582MPa). Furthermore, since the strip needs to be bent laterally during the tube manufacturing process to form a tube, the improved TA18 titanium strip provided by this invention meets the transverse plasticity index A. 50 >15%, and no cracking is required when bending laterally (9T elbow) 180°.

[0042] (2) The present invention uses furnace rolling for fine rolling, with 5 passes and the rolling speed of each pass being basically the same, resulting in uniform material deformation. This ensures that the TA18 titanium strip coil after rolling has good consistency in microstructure and properties, meeting the requirements of continuous tubing. It solves the problem that the large difference in rolling speed and uneven deformation of titanium strip lead to poor microstructure consistency of titanium strip after final rolling, making it difficult to guarantee the microstructure consistency requirements of continuous tubing.

[0043] (3) The present invention uses a temperature of 830-850℃, and after 3-4 consecutive annealings, the oxide scale on the surface is treated by shot blasting and pickling. The performance of the titanium strip coil meets the requirements of medium-strength oil coiled tubing. By providing specific parameters for online continuous annealing of rolled TA18, the annealing temperature and the number of annealings are clearly specified, so that the final mechanical properties of the titanium strip can meet the needs of coiled tubing. Detailed Implementation

[0044] The present invention will now be described in more detail with reference to specific embodiments, so as to better demonstrate the advantages of the present invention.

[0045] Example 1: An improved TA18 titanium alloy strip coil for coiled tubing, wherein the composition of the improved TA18 titanium alloy strip coil is controlled as follows: O content 0.13wt%, Al content 3.0wt%, V content 2.8wt%, with the balance being Ti and other elements and unavoidable impurities; wherein, the other elements are unavoidable elements in titanium raw materials, and the content of a single unavoidable element is <0.1wt%, and the total content of unavoidable elements is <0.4wt%; the unavoidable impurities are Fe, C, N, and H, and the Fe content is <0.03%, C, The N and H contents are both <0.01wt%. It should be noted that the unavoidable elements in titanium raw materials refer to those other than the specific Fe, C, N, H and added Al and V elements. There are no special specifications. Generally, the sponge titanium used in titanium alloys contains more than ten elements such as Ni, Cu, Zr, Si, and Sn. The content of these elements is extremely low, but they will be introduced after the titanium alloy is produced. According to GB / T3620.1 Chemical Composition of Titanium and Titanium Alloys, these elements are not specifically specified. It is only required that the content of these elements alone cannot exceed 0.1%, and the total content cannot exceed 0.4%.

[0046] The above-mentioned method for preparing the improved TA18 titanium alloy strip coil for coiled tubing includes the following steps:

[0047] S1. Raw material selection and smelting

[0048] According to the above component content ratio, sponge titanium, Al-V alloy, Al bean and TiO2 powder are selected as raw materials. After being mixed evenly, they are pressed into electrodes and melted in a vacuum arc furnace twice to obtain TA18 titanium alloy ingots whose composition meets the requirements of the improved TA18 titanium alloy strip coil. Then, the surface of the TA18 titanium alloy ingot is machined to remove surface oxidation and surface loose layer.

[0049] The parameters for the two vacuum arc furnace melting processes are as follows: the vacuum degree of the first vacuum arc furnace melting process is 5 Pa, the voltage is 33 V, the current is 24000 A, and the time is 10 h; the vacuum degree of the second vacuum arc furnace melting process is 3 Pa, the voltage is 33 V, the current is 33500 A, and the time is 10 h.

[0050] S2, Slab Preparation

[0051] The TA18 titanium alloy ingot was heated and held at 1130℃ using a natural gas furnace for 11 hours. It was then forged into a slab with a thickness of 220mm and a width of 1200mm. The forged slab was then machined to remove the surface oxide layer and saw off the rounded ends of the slab. The lowest point of the upper and lower surfaces of the slab was required to be machined by ≥4mm.

[0052] S3, Slab Rolling

[0053] S3-1. Slab heating: The slab is heated using a walking beam natural gas furnace. The heating process is divided into a preheating section, a first-stage heating section, a second-stage heating section, and a homogenization section. The preheating section temperature is 480℃ and the holding time is 85 minutes; the first-stage heating temperature is 820℃ and the holding time is 70 minutes; the second-stage heating temperature is 980℃ and the holding time is 70 minutes; the homogenization section temperature is 970℃ and the holding time is 45 minutes. The total furnace time is 270 minutes.

[0054] S3-2, Rough Rolling: The heated slab is rough rolled in seven passes. The reduction for each pass is controlled as follows: 19% for the first pass, 22% for the second pass, 28% for the third pass, 28% for the fourth pass, 28% for the fifth pass, 22% for the sixth pass, and 20% for the seventh pass. The thickness of the slab after the seven passes of rough rolling is controlled at 38mm, and the final rolling temperature is controlled at 850℃.

[0055] S3-3, Finishing Rolling: The rough-rolled slab is fed into the furnace coil mill via a transfer track for finishing rolling. The starting temperature for finishing rolling is 840℃. After five passes of reciprocating rolling, the reduction for each pass is controlled as follows: 28% for the first pass, 38% for the second pass, 38% for the third pass, 38% for the fourth pass, and 28% for the fifth pass. The final thickness of the titanium strip coil is 4mm. The finishing rolling speed is controlled at 2.0m / s, and the final rolling temperature is ≥700℃.

[0056] S3-4. Winding: The rolled titanium strip is wound up in a winding machine;

[0057] S4, Post-processing of titanium strip coil

[0058] S4-1, Uncoiling and Welding: The titanium strip coil is opened by the uncoiling mechanism, the ends of the titanium strip coil are cut flat, and multiple titanium strip coils are welded to form a continuous TA18 titanium strip.

[0059] S4-2, Annealing: The continuous TA18 titanium strip is annealed using an online continuous annealing method. The annealing temperature is 830℃ and the annealing time is 10min. The online continuous annealing speed is determined according to the equipment parameters of the annealing furnace. This patent uses a continuous annealing furnace with a length of 97 meters and an online speed of 9m / min. The recrystallization of the rolled deformation structure is achieved through online continuous annealing, which improves the plasticity of the material and ensures the bending and forming of the tube, as well as the plasticity requirements of the continuous oil tube.

[0060] S4-3. Mechanical Descaling and Shot Blasting: The annealed TA18 titanium strip is mechanically descaled. The mechanical descaling is performed using a descaling machine, which consists of three descaling units. The first two units are used for descaling and removing scale, and the last unit is used for straightening. The thickness of the TA18 titanium strip is 4–7 mm, and the reduction amount decreases as the thickness of the TA18 titanium strip coil increases. The specific reduction amount is selected according to the thickness, as shown in Table 1 below.

[0061] Table 1. Decompression amount of TA18 titanium strip coils with different thicknesses in the descaling unit.

[0062]

[0063]

[0064] The surface of the TA18 titanium strip was then shot blasted using four shot blasting machines at a speed of 60 m / s, a steel shot diameter of 1.0 mm, and a shot blasting amount of 9 kg / m. 2 The angle between the shot blasting and the TA18 titanium strip is 55°, and the running speed of the TA18 titanium strip is 11m / min;

[0065] S4-4 Surface Treatment: The TA18 titanium strip is surface treated as follows: The TA18 titanium strip is continuously pickled in a two-stage pickling tank. The acid mixture uses HF and HNO3, with HF concentration of 4g / L, HNO3 concentration of 50g / L, and metal ion concentration of <40g / L. The pickling temperature is controlled at 50℃, and the same acid concentration, metal ion concentration, and temperature control are used in the first and second stages of the mixed acid. Then, the surface of the TA18 titanium strip is rinsed with clean water with a metal ion concentration of <0.5g / L.

[0066] S4-5, Drying and winding

[0067] Hot air at 90°C is used in the drying unit to blow away water residue on the surface of the TA18 titanium strip. The dried TA18 titanium strip is then wound up in the winding mechanism, and the end of the roll is cut off from the continuity of other TA18 titanium strips. Steps S4-1 to S4-5 are repeated 3 times for titanium strip thicknesses of 4mm ≤ 5mm and 4 times for titanium strip thicknesses of 5mm < 7mm. In this embodiment, the thickness is 4mm, so steps S4-1 to S4-5 are repeated 3 times to obtain the improved TA18 titanium alloy strip coil.

[0068] Example 2: This example differs from Example 1 in that the composition of the improved TA18 titanium alloy strip is controlled as follows: O content is 0.12wt%, Al content is 3.0wt%, and V content is 2.5wt%.

[0069] Example 3: This example differs from Example 1 in that the composition of the improved TA18 titanium alloy strip is controlled as follows: O content is 0.15wt%, Al content is 3.5wt%, and V content is 3.0wt%.

[0070] Example 4: The difference between this example and Example 1 is that the parameters for the two vacuum arc remelting processes are as follows: the vacuum degree of the first vacuum arc remelting process is 5 Pa, the voltage is 32 V, the current is 22000 A, and the time is 8 h; the vacuum degree of the second vacuum arc remelting process is 3 Pa, the voltage is 32 V, the current is 32000 A, and the time is 8 h.

[0071] Example 5: The difference between this example and Example 1 is that the parameters for the two vacuum arc remelting processes are as follows: the vacuum degree of the first vacuum arc remelting process is 5 Pa, the voltage is 35 V, the current is 25000 A, and the time is 12 h; the vacuum degree of the second vacuum arc remelting process is 3 Pa, the voltage is 35 V, the current is 35000 A, and the time is 12 h.

[0072] Example 6: The difference between this example and Example 1 is that a natural gas furnace is used to heat and hold the TA18 titanium alloy ingot at a temperature of 1100°C for 10 hours; then it is forged into a slab with a thickness of 200 mm and a width of 1000 mm.

[0073] Example 7: This example differs from Example 1 in that a natural gas furnace is used to heat and hold the TA18 titanium alloy ingot at a temperature of 1150°C for 12 hours; the ingot is then forged into a slab with a thickness of 240 mm and a width of 1500 mm.

[0074] Example 8: The difference between this example and Example 1 is that the heating is divided into a preheating section, a first heating section, a second heating section, and a uniform heating section. The preheating section temperature is 400℃ and the holding time is 800℃ for 80 minutes; the first heating section temperature is 800℃ and the holding time is 60 minutes; the second heating section temperature is 950℃ and the holding time is 60 minutes; the uniform heating section temperature is 950℃ and the holding time is 40 minutes. The total furnace time is 240 minutes.

[0075] Example 9: This example differs from Example 1 in that the heating is divided into a preheating section, a first-stage heating section, a second-stage heating section, and a uniform heating section. The preheating section temperature is 500℃ and the holding time is 90 minutes; the first-stage heating temperature is 850℃ and the holding time is 80 minutes; the second-stage heating temperature is 1000℃ and the holding time is 80 minutes; the uniform heating section temperature is 980℃ and the holding time is 50 minutes. The total furnace time is 300 minutes.

[0076] Example 10: The difference between this example and Example 1 is that the reduction amount of the seven passes is controlled as follows: 18% for the first pass, 20% for the second pass, 25% for the third pass, 25% for the fourth pass, 25% for the fifth pass, 20% for the sixth pass, and 18% for the seventh pass. The thickness of the slab after the seven passes of initial rolling is controlled at 35mm, and the final rolling temperature is controlled at 840℃.

[0077] Example 11: The difference between this example and Example 1 is that the reduction amount of the seven passes is controlled as follows: 20% for the first pass, 24% for the second pass, 30% for the third pass, 30% for the fourth pass, 30% for the fifth pass, 24% for the sixth pass, and 22% for the seventh pass. The thickness of the slab after the seven passes of initial rolling is controlled at 40mm, and the final rolling temperature is controlled at 880℃.

[0078] Example 12: The difference between this example and Example 1 is that the reduction amount of the five passes of reciprocating rolling is controlled as follows: 25% for the first pass, 35% for the second pass, 35% for the third pass, 35% for the fourth pass, and 25% for the fifth pass. The final thickness of the titanium strip coil is 4mm. The finishing rolling speed is controlled at 1.5m / s, and the final rolling temperature is ≥700℃.

[0079] Example 13: The difference between this example and Example 1 is that the reduction amount of the five passes of rolling is controlled as follows: 30% for the first pass, 40% for the second pass, 40% for the third pass, 40% for the fourth pass, and 30% for the fifth pass. The final thickness of the titanium strip coil is 4mm. The finishing rolling speed is controlled at 2.5m / s, and the final rolling temperature is ≥700℃.

[0080] Example 14: The difference between this example and Example 1 is that the continuous TA18 titanium strip is annealed at a temperature of 820°C for 9 minutes, using a continuous annealing furnace with a length of 97 meters and an online speed of 8 m / min.

[0081] Example 15: The difference between this example and Example 1 is that the continuous TA18 titanium strip is annealed at a temperature of 840°C for 12 minutes using a continuous annealing furnace with a length of 97 meters and an online speed of 10 m / min.

[0082] Example 16: This example differs from Example 1 in that the shot blasting speed is 50 m / s, the steel shot diameter is 0.8 mm, and the shot blasting amount is 8 kg / m. 2 The angle between the shot blasting and the TA18 titanium strip is 50°, and the running speed of the TA18 titanium strip is 10m / min.

[0083] Example 17: This example differs from Example 1 in that the shot blasting speed is 70 m / s, the steel shot diameter is 1.2 mm, and the shot blasting amount is 10 kg / m. 2 The angle between the shot blasting and the TA18 titanium strip is 60°, and the running speed of the TA18 titanium strip is 12m / min.

[0084] Example 18: The difference between this example and Example 1 is that a reinforcing agent is added to the shot blasting machine to provide wet blasting conditions for the steel shot. The mixing ratio of the reinforcing agent to the steel shot is 1L:16L. The reinforcing agent is composed of 1.5 parts potassium titanium oxalate, 4 parts glycerol and 35 parts water.

[0085] Example 19: The difference between this example and Example 18 is that the mixing ratio of the reinforcing agent and steel shot is 1L:10L, wherein the reinforcing agent is composed of 1 part potassium titanium oxalate, 3 parts glycerol and 20 parts water.

[0086] Example 20: This example differs from Example 18 in that the mixing ratio of the reinforcing agent to steel shot is 1L:20L, wherein the reinforcing agent is composed of 2 parts potassium titanium oxalate, 5 parts glycerol and 50 parts water.

[0087] Experimental Example: Taking a 4mm improved TA18 titanium alloy strip coil (Example 1) as an example, the performance of the head and tail samples was tested. The results are shown in Table 2 below:

[0088] Table 2 Performance Test Table for 4mm Improved TA18 Titanium Strip Coil

[0089]

[0090] As can be seen from the table above, the 4mm improved TA18 titanium strip coil produced by the process of this invention meets the transverse plasticity index A. 50 Material performance requirements for 80ksi medium-strength coiled tubing with a strength greater than 15% and no cracking after 180° lateral bending.

[0091] In order to further investigate the effect of the process of this invention on the performance of the improved TA18 titanium strip coil of the same specification, the following experiments were conducted:

[0092] (1) The effect of two melting parameters on the performance of improved TA18 titanium strip coils: The head samples of 4mm improved TA18 titanium alloy strip coils (Examples 4-5) were tested for performance. The results are shown in Table 3 below:

[0093] Table 3 Performance Test Table for 4mm Improved TA18 Titanium Strip Coil

[0094]

[0095] As can be seen from the table above, the 4mm improved TA18 titanium strip coils produced by different slab preparation parameters in the process of this invention all meet the transverse plasticity index A. 50The material performance requirements for 80ksi medium-strength coiled tubing with a strength greater than 15% and no cracking after 180° transverse bending are different for TA18 titanium strip coils. Among them, the improved TA18 titanium alloy strip coil produced in Example 1 has the best performance.

[0096] (2) Effect of slab preparation parameters on the performance of improved TA18 titanium strip coils: The head samples of 4mm improved TA18 titanium alloy strip coils (Examples 6-7) were tested for performance. The results are shown in Table 4 below:

[0097] Table 4 Performance Test Table for 4mm Improved TA18 Titanium Strip Coil

[0098]

[0099] As can be seen from the table above, the 4mm improved TA18 titanium strip coils produced by different slab preparation parameters in the process of this invention all meet the transverse plasticity index A. 50 The material performance requirements for 80ksi medium-strength coiled tubing with a strength greater than 15% and no cracking when bent 180° laterally are different for TA18 titanium strip coils. Among them, the improved TA18 titanium alloy strip coil produced in Example 7 has the best performance, but its performance is not much different from that of the product produced in Example 1. It can be adjusted as needed according to the actual production efficiency requirements.

[0100] (2) Effect of slab heating parameters on the performance of improved TA18 titanium strip coils: Performance tests were conducted on head samples of 4mm improved TA18 titanium alloy strip coils (Examples 8-9), and the results are shown in Table 5 below:

[0101] Table 5 Performance Test Table for 4mm Improved TA18 Titanium Strip Coil

[0102]

[0103] As can be seen from the table above, the 4mm improved TA18 titanium strip coils produced by different slab heating parameters in the process of this invention all meet the transverse plasticity index A. 50 The material performance requirements for 80ksi medium-strength coiled tubing with a strength greater than 15% and no cracking after 180° transverse bending are different for TA18 titanium strip coils. Among them, the improved TA18 titanium alloy strip coil produced in Example 9 has the best performance. Similarly, its performance is similar to that of the product produced in Example 1, and can be adjusted as needed according to actual production efficiency requirements.

[0104] (3) The effect of slab rolling parameters on the performance of improved TA18 titanium strip coils: The head samples of 4mm improved TA18 titanium alloy strip coils (Examples 10-13) were tested for performance. The results are shown in Table 6 below:

[0105] Table 6 Performance Test Table for 4mm Improved TA18 Titanium Strip Coil

[0106]

[0107] As can be seen from the table above, the 4mm improved TA18 titanium strip coils produced by different slab rolling parameters in the process of this invention all meet the transverse plasticity index A. 50 The material performance requirements for 80ksi medium-strength coiled tubing with a strength greater than 15% and no cracking after 180° transverse bending are different for TA18 titanium strip coils. Among them, the improved TA18 titanium alloy strip coil produced in Example 1 has the best performance.

[0108] (4) The effect of annealing parameters on the performance of improved TA18 titanium strip coils: The head samples of 4mm improved TA18 titanium alloy strip coils (Examples 14-15) were tested for performance. The results are shown in Table 7 below:

[0109] Table 7 Performance Test Table for 4mm Improved TA18 Titanium Strip Coil

[0110]

[0111] As can be seen from the table above, the 4mm improved TA18 titanium strip coils produced by different titanium strip coil annealing parameters in the process of this invention meet the transverse plasticity index A. 50 The material performance requirements for 80ksi medium-strength coiled tubing with a strength greater than 15% and no cracking when bent 180° laterally are different for TA18 titanium strip coils. Among them, the improved TA18 titanium alloy strip coil produced in Example 15 has the best performance. Similarly, its performance is relatively similar to that of the product produced in Example 1, and can be adjusted as needed according to actual production efficiency requirements.

[0112] (5) The effect of mechanical descaling and shot blasting parameters on the performance of improved TA18 titanium strip coils: Head sampling performance tests were conducted on 4mm improved TA18 titanium alloy strip coil products (Examples 16-20), and the results are shown in Table 8 below:

[0113] Table 8 Performance Test Table for 4mm Improved TA18 Titanium Strip Coil

[0114]

[0115] As can be seen from the table above, the 4mm improved TA18 titanium strip coils produced by different shot blasting parameters and methods in the process of this invention meet the transverse plasticity index A. 50The performance requirements for 80ksi medium-strength coiled tubing with a strength greater than 15% and no cracking after 180° transverse bending are different for TA18 titanium strip coils. Among them, the performance of the improved TA18 titanium alloy strip coils produced by Examples 18-20 using reinforcing agents is higher than that of titanium strip coils prepared by other shot blasting processes. It can be seen that by using reinforcing agents to replace the water used in the original shot blasting, on the one hand, the basic conditions for wet shot blasting of steel shot can be replaced by replacing the water, and on the other hand, the potassium titanium oxalate and glycerol added in the above ratio can effectively improve the shot blasting effect of titanium strip, providing an ideal base for subsequent surface treatment, thereby improving the performance of titanium strip.

Claims

1. An improved TA18 titanium alloy strip coil for continuous tubing, characterized in that, The composition of the improved TA18 titanium alloy strip is as follows: O content is 0.12-0.15 wt%, Al content is 3.0-3.5 wt%, V content is 2.5-3.0 wt%, and the balance is Ti.

2. The method for preparing an improved TA18 titanium alloy strip coil for coiled tubing according to claim 1, characterized in that, Includes the following steps: S1. Raw material selection and smelting According to the composition ratio, sponge titanium, Al-V alloy, Al bean and TiO2 powder are selected as raw materials. After being mixed evenly, they are pressed into electrodes and melted in a vacuum arc furnace twice to obtain TA18 titanium alloy ingots whose composition meets the composition content of the improved TA18 titanium alloy strip. Then, the surface of the TA18 titanium alloy ingot is machined to remove surface oxidation and surface loose layer. The parameters for the two vacuum arc furnace melting processes are as follows: for the first vacuum arc furnace melting process, the vacuum degree is <6Pa, the voltage is 32-35V, the current is 22000-25000A, and the time is 8-12h; for the second vacuum arc furnace melting process, the vacuum degree is <4Pa, the voltage is 32-35V, the current is 32000-35000A, and the time is 8-12h. S2, Slab Preparation TA18 titanium alloy ingots are heated and held at 1100-1150℃ using a natural gas furnace for 10-12 hours. They are then forged into slabs with a thickness of 200-240mm and a width of 1000-1500mm. The forged slabs are then machined to remove the surface oxide layer and to saw off the rounded ends of the slabs. The lowest point of the upper and lower surfaces of the slabs is machined by ≥4mm. S3, Slab Rolling S3-1, Slab heating: The slab is heated using a walking beam natural gas furnace, with a total furnace time of 240-300 minutes; S3-2, Rough rolling: The slab after heating is rough rolled. The rolling is divided into seven passes. The thickness of the intermediate slab after the seven passes of rough rolling is controlled at 35mm to 40mm. The final rolling temperature is controlled at 840℃ to 880℃. S3-3, Finish rolling: The slab after rough rolling is finished rolling. The starting temperature of finish rolling is 820℃~850℃. After five passes of reciprocating rolling, the final thickness is 4mm~7mm. The finishing rolling speed is controlled at 1.5~2.5m / s, the final rolling temperature is ≥700℃, and the thickness of the rolled titanium strip coil is 4mm~7mm. S3-4. Winding: The rolled titanium strip is wound up in a winding machine; S4, Post-processing of titanium strip coil S4-1, Uncoiling and Welding: The titanium strip coil is opened by the uncoiling mechanism, the ends of the titanium strip coil are cut flat, and multiple titanium strip coils are welded to form a continuous TA18 titanium strip. S4-2, Annealing: The continuous TA18 titanium strip is annealed online at a temperature of 820℃~840℃ for 9~12min. S4-3. Mechanical Descaling and Shot Blasting: The annealed TA18 titanium strip is mechanically descaled, and then the surface of the TA18 titanium strip is shot blasted using four shot blasting machines at a speed of 50–70 m / s, a steel shot diameter of 0.8–1.2 mm, and a shot dosage of 8–10 kg / m. 2 The angle between the shot blasting and the TA18 titanium strip is 50-60°, and the running speed of the TA18 titanium strip is 10-12 m / min; S4-4 Surface treatment: The TA18 titanium strip is surface treated, and then the surface of the TA18 titanium strip is rinsed with clean water with a metal ion concentration of <0.5g / L. S4-5, Drying and winding Hot air at a temperature of 85-95℃ is used to blow on the surface of TA18 titanium strip in the drying unit. The dried TA18 titanium strip is then wound up in the winding mechanism, and the end of the roll is cut off from the continuity of other TA18 titanium strips. Steps S4-1 to S4-5 are repeated 3 to 4 times.

3. The method for preparing an improved TA18 titanium alloy strip coil for coiled tubing according to claim 2, characterized in that, In S3-1, a walking beam natural gas heater is used to heat the slab. The heating process is divided into a preheating section, a first-stage heating section, a second-stage heating section, and a homogenization section. The preheating section temperature is 400-500℃ and the holding time is 80-90 minutes. The first-stage heating temperature is 800-850℃ and the holding time is 60-80 minutes. The second-stage heating temperature is 950-1000℃ and the holding time is 60-80 minutes. The homogenization section temperature is 950-980℃ and the holding time is 40-50 minutes.

4. The method for preparing an improved TA18 titanium alloy strip coil for coiled tubing according to claim 2, characterized in that, In S3-2, the reduction amounts for the seven passes are controlled as follows: 18%–20% for the first pass, 20%–24% for the second pass, 25%–30% for the third pass, 25%–30% for the fourth pass, 25%–30% for the fifth pass, 20%–24% for the sixth pass, and 18%–22% for the seventh pass.

5. The method for preparing an improved TA18 titanium alloy strip coil for coiled tubing according to claim 2, characterized in that, In S3-3, the reduction amount for the five passes of reciprocating rolling is controlled as follows: 25%–30% for the first pass, 35%–40% for the second pass, 35%–40% for the third pass, 35%–40% for the fourth pass, and 25%–30% for the fifth pass.

6. The method for preparing an improved TA18 titanium alloy strip coil for coiled tubing according to claim 2, characterized in that, In S4-3, the mechanical descaling is performed using a descaling machine, which consists of three descaling units. The first two descaling units are used for descaling and removing scales, and the last descaling unit is used for straightening. The depressing amount of the first descaling unit is (51-54) ± 2 mm, the depressing amount of the second descaling unit is (50-51) ± 2 mm, and the depressing amount of the third descaling unit is (40-41) ± 1 mm. The thickness of the TA18 titanium strip roll is 4-7 mm, and the depressing amount decreases as the thickness of the TA18 titanium strip roll increases.

7. The method for preparing an improved TA18 titanium alloy strip coil for coiled tubing according to claim 2, characterized in that, In S4-3, a reinforcing agent is added to the shot blasting machine to provide wet blasting conditions for the steel shot. The mixing ratio of the reinforcing agent to the steel shot is 1L:10-20L. The reinforcing agent is composed of 1-2 parts of potassium titanium oxalate, 3-5 parts of glycerol and 20-50 parts of water.

8. The method for preparing an improved TA18 titanium alloy strip coil for coiled tubing according to claim 2, characterized in that, In S4-4, the surface treatment is as follows: TA18 titanium strip is continuously pickled in a two-stage pickling tank. The acid mixture uses HF and HNO3, with HF concentration of 4±1g / L, HNO3 concentration of 50±5g / L, and metal ion concentration of <40g / L. The pickling temperature is controlled at 50±5℃, and the first and second stages of mixed acid use the same acid concentration, metal ion concentration, and temperature control.

9. The method for preparing an improved TA18 titanium alloy strip coil for coiled tubing according to claim 2, characterized in that, In S4-5, repeat steps S4-1 to S4-5 3 times for titanium strip thickness ≤ 5mm and repeat steps S4-1 to S4-5 4 times for titanium strip thickness ≤ 5mm.

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