Titanium alloy pipe for petroleum drill pipe and its processing method

Abstract

This invention discloses a processing method for titanium alloy tubing for oil drill pipe, comprising the following steps: heating an ingot to 20-30°C below the material phase transformation point and holding it at that temperature for 1-2 hours, then extruding to obtain a titanium alloy tubing blank; performing internal and external surface treatment on the tubing blank; preheating the rolling mill's pass and mandrel using an acetylene torch at a preheating temperature of 450-500°C; preheating the rolled tubing blank at 1000mm from the feed end and heating it at 300mm from the feed end to ensure that the final rolling temperature of the tubing blank is controlled at 400-700°C and the rolling deformation is controlled at 40-45%; degreasing, pickling, and high-temperature vacuum annealing treatment on the rolled tubing blank; and pickling and inspecting the tubing blank to obtain titanium alloy tubing for oil drill pipe of grade 120ksi and above. The processing method for titanium alloy pipes for oil drill pipes provided by this invention solves the problem of large differences in cross-sectional microstructure and uneven radial properties caused by insufficient radial deformation during the cold rolling process of thick-walled, large-diameter titanium alloy pipes.

Description

Technical Field

[0001] This invention relates to the field of new material processing technology, specifically to a titanium alloy pipe for oil drill pipe and its processing method. Background Technology

[0002] Currently, titanium alloy tubing for oil drill pipe is under development. Preliminary processes include skew rolling piercing billet preparation + multi-pass cold rolling, skew rolling piercing billet preparation + hot continuous rolling at a steel mill, and radial forging. The skew rolling piercing billet preparation + multi-pass cold rolling process requires piercing temperatures above the titanium alloy phase transformation point, resulting in coarse micrograins, difficulty in cold rolling deformation, and high requirements for rolling equipment capabilities. The numerous rolling passes lead to low production efficiency and high overall costs. Furthermore, the high strength and thick wall characteristics of titanium alloy tubing for oil drill pipe make it prone to radial microstructure inhomogeneity when produced using a small-deformation, multi-pass cold rolling method. This can lead to continuous torsion and failure during oil drilling and production. The continuous production method using skew rolling piercing followed by hot continuous rolling is suitable for producing single-specification metal pipes with stable processes and lower requirements. However, for the production of high-strength titanium alloy pipes for oil drill pipes, defects in the billet caused by skew rolling piercing cannot be removed in time during hot continuous rolling, resulting in low overall pipe quality. Furthermore, the high temperature during hot continuous rolling also presents difficulties in controlling the final microstructure and properties. The produced titanium alloy pipes suffer from severe oxidation on both the inner and outer surfaces, requiring specialized equipment for internal and external surface treatment. Moreover, the internal surface treatment cannot guarantee uniform wall thickness. Overall, the equipment investment is high, efficiency is low, and the comprehensive cost is high. Radial forging currently has limited production length and faces the same problems as hot continuous rolling: high heating temperature, difficulty in controlling microstructure and properties, and issues with removing defects on the inner and outer surfaces of the finished pipes, as well as uneven wall thickness. Only short samples can be produced.

[0003] Therefore, it is necessary to provide a new process to solve the above-mentioned technical problems. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a processing method for titanium alloy tubing for oil drill pipes. This method combines extrusion at temperatures below the phase transformation point, single-pass hot rolling with large deformation, and vacuum heat treatment. This solves the problem of large differences in cross-sectional microstructure and uneven radial properties caused by insufficient radial deformation during the cold rolling of thick-walled, large-diameter titanium alloy tubing. Simultaneously, the large deformation hot rolling significantly improves the surface quality and overall performance of the tubing, resulting in a uniform microstructure, good impact toughness, high level of non-destructive testing, and excellent surface quality. The prepared oil drill pipe meets the requirements for high-strength, high-toughness, thick-walled, large-diameter titanium alloy tubing.

[0005] The technical solution of the present invention is as follows:

[0006] A method for processing titanium alloy tubing for oil drill pipe includes the following steps:

[0007] Step S1: Heat the billet to 20-30°C below the material phase transformation point and hold for 1-2 hours, then extrude it using a horizontal extrusion press to obtain a titanium alloy tube billet.

[0008] Step S2: Perform internal and external surface treatment on the tube blank prepared in step S1;

[0009] Step S3: The roll pass and mandrel of the billet rolling mill are preheated by air rolling with an acetylene flame gun at a temperature of 450-500℃.

[0010] Specifically, the preheating temperature can be 450℃, 480℃, or 500℃, or other temperatures within this range.

[0011] Step S4: The tube blank to be rolled in Step S2 is loaded onto the preheated rolling mill in Step S3 for rolling deformation. The tube blank is preheated at 1000mm from the feed end and heated at 300mm to ensure that the final tube blank rolling temperature is controlled at 400-700℃ and the rolling deformation is controlled at 40-45%. During rolling, molybdenum disulfide aqueous solution is sprayed onto the roll pass and tube blank surface for surface lubrication and roll temperature control. The rolling temperature can be 400℃, 500℃, 500℃, or 700℃, or other values ​​within this range.

[0012] Step S5: The tube blank rolled in step S4 is subjected to degreasing, pickling, and high-temperature vacuum annealing.

[0013] Step S6: Pickling and inspection of the tube blank to obtain titanium alloy tubes for oil drill pipes with a grade of 120ksi or higher.

[0014] Furthermore, in step S4, the rolling feed rate is ≤5mm / time.

[0015] Preferably, in step S4, the rolling temperature is controlled at 500-550℃, such as 500℃, 510℃, 520℃, 530℃, 540℃ or 550℃, or other temperature values ​​within this range.

[0016] Further, in step S4, the preheating temperature for the rolled tube blank at 1000mm from the feed end is 300-500℃, such as 300℃, 350℃, 400℃, 450℃, or 500℃, or other values ​​within this range; the heating temperature for the rolled tube blank at 300mm from the feed end is 500-700℃, such as 500℃, 550℃, 600℃, 650℃, or 700℃, or other values ​​within this range. The setting of the preheating temperature at 1000mm from the feed end and the heating temperature at 300mm from the feed end controls the final rolling temperature of the tube blank.

[0017] Furthermore, in step S5, the high-temperature vacuum annealing temperature is 700-950℃, such as 700℃, 750℃, 800℃, 820℃, 850℃, 900℃ or 950℃, or other temperature values ​​within this range.

[0018] Furthermore, in step S2, the internal and external surface treatments of the tube blank include:

[0019] First, mechanical repair is carried out on the inner and outer surfaces of the tube blank to remove defects caused by extrusion on the inner and outer surfaces;

[0020] Then, the inner and outer surfaces of the tube blank are pickled and inspected.

[0021] Next, apply graphite emulsion to both the inner and outer surfaces and let it air dry.

[0022] The present invention also provides a titanium alloy pipe for oil drill pipe, which is processed by the above method.

[0023] Compared with existing technologies, the titanium alloy pipe for oil drill pipe and its processing method provided by this invention have the following advantages:

[0024] I. The processing method for titanium alloy tubing for oil drill pipe provided by this invention employs an extrusion process below the phase transformation point, followed by a single hot rolling and vacuum annealing. The extrusion temperature is controlled 20-30°C below the phase transformation point. The deformed microstructure of the extruded billet is a typical equiaxed structure, with equiaxed α phases distributed on the transformed β matrix. In contrast, existing technologies heat the material above the phase transformation point, resulting in a lamellar microstructure in the extruded billet. This is characterized by the breakage of the original β grains, with lamellar α phases interspersed within the β grains, forming a lamellar structure. Equiaxed materials have lower strength and better plasticity compared to lamellar materials, which is beneficial for plastic deformation and improves dimensional accuracy, surface quality control, and microstructure uniformity of the tubing. In the hot rolling process, the mill pass and mandrel are first preheated, followed by preheating at 1000mm from the feed end of the billet and heating at 300mm (the preheating and heating positions are before the rolling deformation zone). Because titanium alloy has a thermal conductivity λ = 15.24 W / (mK), approximately 1 / 4 that of nickel, 1 / 5 that of iron, and 1 / 14 that of aluminum, its poor thermal conductivity means that direct high-temperature heating would result in uneven heating along the billet wall thickness, easily causing excessive internal stress and uneven deformation during rolling, which could lead to defects such as internal cracks in the tube. Therefore, this invention employs a preheating process... The process allows the billet to quickly reach the required rolling temperature within a short time while maintaining a uniform temperature field along the wall thickness. Employing a large-deformation, one-pass hot rolling method maximizes the utilization of existing rolling equipment and metal deformation capabilities, completely solving the problem of large differences in cross-sectional microstructure and uneven radial properties caused by insufficient radial deformation in the cold rolling of thick-walled, large-size titanium alloy tubes. Simultaneously, the large-deformation hot rolling significantly improves the internal and external surface quality and overall performance of the tube. The rolled titanium alloy tube exhibits uniform microstructure, good impact toughness, high non-destructive testing capability, and excellent surface quality. Vacuum annealing after rolling prevents surface oxidation, thus preventing microcracks and brittle fracture, further enhancing tube performance. Therefore, the processing technology of this invention, by preparing a two-phase (α+β) microstructure billet, refining the microstructure through rolling, and adjusting the microstructure morphology and quantity of the two phases through vacuum heat treatment, achieves the goal of improving material properties and obtaining high-strength, high-toughness, thick-walled, large-size titanium alloy tubes.

[0025] II. The processing method for titanium alloy tubing for oil drill pipe provided by this invention involves rolling at a temperature below the phase transformation point of titanium alloy. This allows for convenient control of the microstructure and properties of the produced titanium alloy tubing. During hot rolling, graphite emulsion lubrication is used on both the inner and outer surfaces to prevent oxidation during continuous hot rolling, resulting in high-quality inner and outer surfaces. Simultaneously, the deformation capacity of the heated titanium alloy is maximized, allowing for large deformation per pass and more complete radial deformation, leading to good consistency in radial properties. This processing method can achieve the production of high-strength, high-toughness, large-diameter, thick-walled titanium alloy tubing for oil drill pipe with a yield strength greater than 827 MPa.

[0026] Third, the processing method for titanium alloy pipes for oil drill pipes provided by this invention has a simple production process, fewer rolling passes, high production efficiency, and low overall cost, making it suitable for large-scale industrial promotion. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 These are longitudinal and transverse micrographs of the titanium alloy tubing after heat treatment in Examples 1 and 2.

[0029] Figure 2 This is a schematic diagram of the dimensional test points for the titanium alloy pipes in Examples 1 and 2. Detailed Implementation

[0030] To enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, and to make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be further described below.

[0031] It should be noted that the descriptions of these embodiments are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] Example 1

[0033] Oil drill pipe The processing method for titanium alloy tubing includes the following steps:

[0034] Step S1: The extrusion billet is heated to 950°C using a 6300-ton horizontal extrusion press and extruded. TC4 titanium alloy tube blank;

[0035] Step S2: After pickling the inner and outer surfaces of the titanium alloy tube blank obtained in step S1, the extrusion defects on the inner and outer surfaces are machined and cleaned. After strong pickling and chemical coating, the inner and outer surfaces are brushed with graphite emulsion coating and dried for rolling.

[0036] Step S3: Preheat the rolling pass and mandrel to 400-450°C using an acetylene flame;

[0037] Step S4: The tube blank to be rolled in step S2 is loaded into the preheated rolling mill in step S3 for rolling deformation. A special heating system is used to preheat and heat the tube blank at 1000mm and 300mm from the feed end of the rolling mill. By adjusting the flow rate of the torch in the preheating zone and the feed speed of the tube blank, the temperature of the final tube blank during rolling is controlled at 500-550℃, the rolling deformation is controlled at 40-45%, and the feed rate is ≤5mm / time. During rolling, molybdenum disulfide water is sprayed on the pass and the surface of the tube blank for surface lubrication and roll temperature control to ensure good rolling lubrication and avoid surface adhesion caused by overheating of the pass.

[0038] Step S5: The titanium alloy pipe obtained in step S4 is subjected to degreasing and pickling treatment, and then annealing treatment.

[0039] Step S6: The titanium alloy tube obtained in step S5 is subjected to vacuum heat treatment at 820℃ for 1.5 hours. After annealing, the locally bent area is subjected to three-point compressive stress temperature straightening.

[0040] Step S7: The titanium alloy pipe obtained in step S6 is subjected to longitudinal and transverse wave flaw detection using water immersion ultrasonic testing. Qualified pipes are then pickled and subjected to dimensional, surface, and performance inspections to obtain oil drill pipe. Titanium alloy hot-rolled pipe.

[0041] Example 2

[0042] Oil drill pipe The processing method for titanium alloy tubing includes the following steps:

[0043] Step S1: The extrusion billet is heated to 950°C using a 6300-ton horizontal extrusion press and extruded. TC4 titanium alloy tube blank;

[0044] Step S2: After pickling the inner and outer surfaces of the titanium alloy tube blank obtained in step S1, the extrusion defects on the inner and outer surfaces are machined and cleaned. After strong pickling and chemical coating, the inner and outer surfaces are brushed with graphite emulsion coating and dried for rolling.

[0045] Step S3: Preheat the rolling pass and mandrel to 400-450°C using an acetylene flame;

[0046] Step S4: The tube blank to be rolled in step S2 is loaded onto the preheated rolling mill in step S3 for rolling deformation. A proprietary propane heating torch device is used to preheat and heat the tube blank at 1000mm and 300mm from the feed end of the rolling mill. By adjusting the flow rate of the torch in the preheating zone and the feed speed of the tube blank, the temperature of the final tube blank during rolling is controlled at 500-550℃, the rolling deformation is controlled at 40-45%, and the feed rate is ≤5mm / time. During rolling, molybdenum disulfide aqueous solution is sprayed onto the pass and the surface of the tube blank for surface lubrication and roll temperature control to ensure good rolling lubrication and avoid surface adhesion caused by overheating of the pass.

[0047] Step S5: The titanium alloy pipe obtained in step S4 is subjected to degreasing and pickling treatment, and then annealing treatment.

[0048] Step S6: The titanium alloy tube obtained in step S5 is subjected to vacuum heat treatment at 900℃ for 1 hour. After annealing, the local bending area is subjected to three-point compressive stress temperature straightening.

[0049] Step S7: The titanium alloy pipe obtained in step S6 is subjected to longitudinal and transverse wave flaw detection using water immersion ultrasonic testing. Qualified pipes are then pickled and subjected to dimensional, surface, and performance inspections to obtain oil drill pipe. Titanium alloy hot-rolled pipe.

[0050] Please see Figure 1 The images show the longitudinal and transverse microstructures of the titanium alloy tubing after heat treatment in Examples 1 and 2. Figure 1 It can be seen that after heat treatment, the titanium alloy tube exhibits a typical α+β two-phase titanium alloy structure. The original β grain boundaries are completely broken, and the β grains contain initial α phase and secondary acicular α phase. The morphology and quantity of each structure are adjusted through heat treatment to ensure that its comprehensive mechanical properties meet the standard requirements.

[0051] The mechanical and technological properties of the pipes processed in Examples 1-2 were tested, and their dimensions were inspected. The test results are as follows:

[0052] Table 1: Room temperature mechanical properties of Φ88.9×9.35×10000mm

[0053]

[0054] Table 2: Room temperature mechanical properties of Φ101.6×9.7×9700mm

[0055]

[0056]

[0057] Table 3: Room temperature impact test of Φ88.9×9.35×10000mm

[0058]

[0059] Table 4: Room temperature impact test of Φ101.6×9.7×9700mm

[0060]

[0061]

[0062] Dimensional checks were performed at various test points on the pipe, such as... Figure 2 As shown, the cross-section of the pipe is symmetrically divided into 6 equal parts from both ends, and a line is drawn along the axial direction of the pipe for each part (e.g., ...). Figure 2 Points 1-6 in the diagram are marked with circles every 1 meter along the pipe axis, starting from one end of the pipe. Figure 2 In the grid, lines a, b, c, d, etc., are arranged vertically and horizontally to form a grid. At each grid intersection, one wall thickness value and two outer diameter values ​​are measured. Dimensional accuracy measurement data are shown in Table 5-8.

[0063] Table 5: Outer Diameter Dimensions of Φ88.9×9.35×10000mm Pipes (Unit: mm)

[0064]

[0065] Table 6: Wall thickness dimensions of Φ88.9×9.35×10000mm pipes (unit: mm)

[0066]

[0067] Table 7: Outer Diameter Dimensions of Φ101.6×9.7×9700mm Pipes (Unit: mm)

[0068]

[0069] Table 8: Wall thickness dimensions of Φ101.6×9.7×9700mm pipe (unit: mm)

[0070]

[0071] As shown in Table 5-8, the pipes processed by the method of the present invention have good dimensional accuracy and can meet the index requirements.

[0072] Meanwhile, each pipe processed in Examples 1-2 was subjected to ultrasonic longitudinal and transverse inspection, and all met the requirements of the ultrasonic testing standard in Part 3 of NB / T47013.3 "Non-destructive Testing of Pressure Equipment".

[0073] The processing method of the present invention enables continuous production of pipes to produce ultra-long pipes.

[0074] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations made to these embodiments without departing from the principles and spirit of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for processing titanium alloy tubing for oil drill pipe, characterized in that, The titanium alloy is TC4 titanium alloy, and the processing method includes the following steps: Step S1: Heat the billet to 20-30°C below the material phase transformation point and hold for 1-2 hours, then extrude it using a horizontal extrusion press to obtain a titanium alloy tube billet. Step S2: Perform internal and external surface treatment on the tube blank prepared in step S1; Step S3: The roll pass and mandrel of the billet rolling mill are preheated by air rolling with an acetylene flame gun at a temperature of 450-500℃. Step S4: The tube blank to be rolled in Step S2 is loaded onto the preheated rolling mill in Step S3 for rolling deformation. The tube blank is preheated at 1000mm from the feed end and heated at 300mm to ensure that the final tube blank rolling temperature is controlled at 500-550℃ and the rolling deformation is controlled at 40-45%. During rolling, molybdenum disulfide water is sprayed onto the pass and the surface of the tube blank for surface lubrication and roll temperature control. The rolling temperature is below the phase transformation point of titanium alloy. The rolling is a single hot rolling process. The preheating temperature for preheating the rolled tube blank at 1000mm from the feed end is 300-500℃, and the heating temperature for heating the rolled tube blank at 300mm from the feed end is 500-700℃. Step S5 involves degreasing, pickling, and high-temperature vacuum annealing of the tube blank rolled in step S4; the high-temperature vacuum annealing temperature is 700-950℃. Step S6 involves pickling and inspecting the tube blank to obtain thick-walled, large-diameter, high-strength titanium alloy tubes for oil drill pipes with a yield strength greater than 827 MPa, and a grade of 120 ksi or higher.

2. The processing method for titanium alloy tubing for oil drill pipe according to claim 1, characterized in that, In step S4, the rolling feed rate is ≤5mm / time.

3. The processing method for titanium alloy tubing for oil drill pipe according to claim 1, characterized in that, Step S2, the internal and external surface treatment of the tube blank includes: First, mechanical repair is carried out on the inner and outer surfaces of the tube blank to remove defects caused by extrusion on the inner and outer surfaces; Then, the inner and outer surfaces of the tube blank are inspected by pickling. Next, apply graphite emulsion to both the inner and outer surfaces and let it air dry.

4. A titanium alloy pipe for oil drill pipe, characterized in that, It is obtained by the method according to any one of claims 1-3.

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