High strength high toughness coiled tubing and method of making same

Abstract

This invention discloses a high-strength, high-toughness coiled tubing, comprising the following components by mass percentage: 0.5%≤C≤0.8%; 0.8%≤Mn≤1.4%; 0.2%≤Si≤0.4%; 0.11%≤Cr≤0.25%; 0.08%≤Ni≤0.20%; 0.10%≤Cu≤0.30%; S≤0.03%; P≤0.03%, with the balance being Fe and unavoidable impurities. This invention also discloses a method for preparing the high-strength, high-toughness coiled tubing. First, alloy powder is melted, rolled into coils, the coils are slid and lengthened with steel strips, and then welded into shape. Finally, a quenching and lead bath heat treatment process optimizes the microstructure of the coiled tubing, resulting in a good strength-toughness ratio and improving the fatigue life and load-bearing capacity of the coiled tubing.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas pipeline technology, specifically relating to high-strength and high-toughness continuous tubing, and also to a method for preparing high-strength and high-toughness continuous tubing. Background Technology

[0002] Coiled tubing is a high-strength, high-ductility, threadless flexible tubing material, with single strands reaching lengths of several kilometers. It is widely used in logging, well workover, drilling, well completion, and oil and gas transportation. Over the past decade, newly discovered oil and gas reservoirs globally have shifted from mid- to shallow layers to deep and ultra-deep layers, with these deep and ultra-deep areas becoming crucial for future global reserve and production increases. With continuously improving oil and gas operations, the intensity of deep and high-pressure well production is increasing, placing higher demands on coiled tubing applications. Conventional coiled tubing may struggle to meet the required run-in depth; therefore, high strength and high toughness are key research directions for coiled tubing. A conventional solution for extending run-in depth is to butt-joint two coiled tubing coils, but this often results in reduced strength in the weld heat-affected zone or decreased fatigue life, impacting operational efficiency and safety.

[0003] To solve this problem, a high-strength and high-toughness coiled tubing is needed that can meet the required insertion depth, possess high strength and toughness, and improve the efficiency and safety of oil and gas development. Summary of the Invention

[0004] The purpose of this invention is to provide high-strength and high-toughness continuous tubing.

[0005] The purpose of this invention is to provide a method for preparing high-strength and high-toughness coiled tubing, which solves the problem of poor toughness in existing coiled tubing; it effectively increases the insertion depth of the coiled tubing, thereby improving the efficiency and safety of oil and gas development.

[0006] The first technical solution adopted in this invention is: a high-strength, high-toughness continuous tubing, comprising the following components by mass percentage: 0.5%≤C≤0.8%; 0.8%≤Mn≤1.4%; 0.2%≤Si≤0.4%; 0.11%≤Cr≤0.25%; 0.08%≤Ni≤0.20%; 0.10%≤Cu≤0.30%; S≤0.03%; P≤0.03%, with the balance being Fe and unavoidable impurities.

[0007] The high-strength and high-toughness continuous tube has a yield strength ≥1000MPa, tensile strength ≥1150MPa, elongation ≥17.5%, outer diameter range of Φ25.4~Φ88.9mm, and wall thickness range of 1.9~6.4mm.

[0008] The second technical solution adopted in this invention is: a method for preparing high-strength and high-toughness coiled tubing, the specific operation steps of which are as follows: Step 1: Weigh the raw materials according to the following mass percentages: 0.5%≤C≤0.8%; 0.8%≤Mn≤1.4%; 0.2%≤Si≤0.4%; 0.11≤Cr≤0.25%; 0.08≤Ni≤0.20%; 0.10≤Cu≤0.30%, with the balance being Fe and unavoidable impurities; Step 2: Add the prepared metal powders to the smelting furnace for smelting, and then refine them in a static furnace; after that, cast them, and then process them by hot rolling, cold rolling and finishing to make coils; Step 3: Cut the prepared coil into steel strips of 50-300mm using a slitting machine according to the specifications of continuous pipe. After processing the ends of the two steel strips at 45°, process a V-shaped bevel. Butt weld the steel strips using laser welding. After welding, water cooling or air cooling is performed. After the weld has cooled, grind and clean the weld surface. Step 4: The steel strip is milled into a V-shaped bevel on the side, and the UOE roller forming method is used to control the forming of the steel strip; the formed steel strip is longitudinally welded using laser technology to form a continuous tube; Step 5: Heat the prepared continuous tube to 830-930℃ for quenching, then temper it. After heat treatment, the continuous tube is precisely sized and then wound onto a drum with an appropriate core diameter using a coiler to produce a high-strength and high-toughness continuous tube.

[0009] The invention is further characterized in that, Furthermore, in step 2, the melting temperature is 1520±20℃, the refining temperature is 1430±20℃, and the refining time is 60-120min; casting is carried out at a temperature of 1320±30℃.

[0010] Furthermore, the thickness of the rolled plate in step 2 is 1.9 to 6.35 mm, and the length is greater than 300 meters.

[0011] Furthermore, in step 3, the laser welding speed is 100~500mm / min, and the welding wire used is ER120S.

[0012] Furthermore, in step 4, the V-groove gap on the side of the steel strip is controlled to be ≤0.8mm, the welding speed is 100~500mm / min, the laser power is 5500-6000kw, and the downward pressure is 0.1~0.3mm.

[0013] Furthermore, the continuous tube produced in step 4 has a diameter of Φ25.4~Φ88.9mm and a wall thickness of 1.9~6.4mm.

[0014] Furthermore, in step 5, tempering is carried out in a lead bath furnace at 350-450℃.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a method for manufacturing high-strength, high-toughness coiled tubing. Its key feature is the self-designed composition of the coiled tubing, allowing for material design tailored to various working conditions and depth requirements, thus fully utilizing material properties. Compared to existing heat treatment methods, this invention employs lead bath heat treatment, achieving a perfect match between materials and processes, resulting in coiled tubing with superior performance and meeting the required depth for coiled tubing deployment. During manufacturing, the base material composition of the coiled tubing is self-designed, and subsequent heat treatment utilizes quenching followed by lead bath tempering. This treatment method endows the manufactured coiled tubing with high strength and toughness, effectively increasing the deployment depth and improving the efficiency and safety of oil and gas development. Detailed Implementation

[0016] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1 The high-strength, high-toughness coiled tubing of the present invention comprises the following components by mass percentage: 0.5%≤C≤0.8%; 0.8%≤Mn≤1.4%; 0.2%≤Si≤0.4%; 0.11%≤Cr≤0.25%; 0.08%≤Ni≤0.20%; 0.10%≤Cu≤0.30%; S≤0.03%; P≤0.03%, with the balance being Fe and unavoidable impurities.

[0018] The high-strength and high-toughness continuous tube has a yield strength ≥1000MPa, tensile strength ≥1150MPa, elongation ≥17.5%, outer diameter range of Φ25.4~Φ88.9mm, and wall thickness range of 1.9~6.4mm.

[0019] Example 2 The specific steps for preparing high-strength, high-toughness coiled tubing are as follows: Step 1: Weigh the raw materials according to the following mass percentages: 0.5%≤C≤0.8%; 0.8%≤Mn≤1.4%; 0.2%≤Si≤0.4%; 0.11≤Cr≤0.25%; 0.08≤Ni≤0.20%; 0.10≤Cu≤0.30%, with the balance being Fe and unavoidable impurities.

[0020] Step 2: Add the prepared metal powders to the smelting furnace for smelting, and then refine them in a static furnace; after that, cast them, and then process them by hot rolling, cold rolling and finishing to make coils; Step 3: Cut the prepared coil into steel strips of 50-300mm using a slitting machine according to the specifications of continuous pipe. After processing the ends of the two steel strips at 45°, process a V-shaped bevel. Butt weld the steel strips using laser welding. After welding, water cooling or air cooling is performed. After the weld has cooled, grind and clean the weld surface. Step 4: The steel strip is milled into a V-shaped bevel on the side, and the UOE roller forming method is used to control the forming of the steel strip; the formed steel strip is longitudinally welded using laser technology to form a continuous tube; Step 5: Heat the prepared continuous tube to 830-930℃ for quenching, then temper it. After heat treatment, the continuous tube is precisely sized and then wound onto a drum with an appropriate core diameter using a coiler to produce a high-strength and high-toughness continuous tube.

[0021] Example 3 Based on Example 2, In step 2, the melting temperature is 1520±20℃, the refining temperature is 1430±20℃, and the refining time is 60-120min; casting is carried out at a temperature of 1320±30℃.

[0022] The thickness of the rolled plate in step 2 is 1.9 to 6.35 mm, and the length is greater than 300 meters.

[0023] In step 3, the laser welding speed is 100~500mm / min.

[0024] In step 4, the V-groove gap on the side of the steel strip is controlled to be ≤0.8mm, the welding speed is 100~500mm / min, the laser power is 5500-6000kw, and the downward pressure is 0.1~0.3mm.

[0025] The continuous tube produced in step 4 has a diameter of Φ25.4~Φ88.9mm and a wall thickness of 1.9~6.4mm.

[0026] In step 5, tempering is performed in a lead bath furnace at 350-450℃.

[0027] Example 4 The specific steps of the method for preparing the high-strength, high-toughness coiled tubing of the present invention are as follows: 1. Coil rolling 1) Weigh the raw materials according to the following mass percentages: C: 0.5%; Mn: 1.0%; Si: 0.4%; Cr: 0.23%; Ni: 0.20%; Cu: 0.18%; P≤0.03%; S≤0.03%, with the balance being Fe and unavoidable impurities. Prepare various alloy components according to the raw material ratio of the plate. Add the prepared alloy components to a melting furnace for melting at 1530℃. Then, refine them in a static furnace at 1430℃ for 85 minutes. Cast the plate at 1350℃. Finally, hot-roll, cold-roll, and finishing processes are performed to form a coil approximately 500m long and 3.0mm thick.

[0028] 2. Slitting of rolled steel sheets and splicing of steel strips: This pipe production involved a length of 1000 meters and an outer diameter of 50.8 mm. The prepared coils were cut into 159.59 mm steel strips using a slitting machine according to continuous pipe specifications. The ends of the two steel strips were then machined at a 45° angle. Laser welding was then used for butt welding of the steel strips, with a V-shaped bevel. The welding speed was 400 mm / min, and the pressure was 0.12 mm. After welding, the strips were water-cooled. Once cooled, the weld surface was ground and cleaned. 3. Welding and forming: Based on the final continuous tube outer diameter and wall thickness requirements, the steel strip is milled into a V-shaped bevel on the side using a milling method. The width of the steel strip and the perpendicularity of the plate edge are precisely controlled. The UOE roller forming method is used to control the forming of the steel strip. Laser technology is used to precisely control parameters such as rotation speed, welding speed, and tilt angle, controlling the forming bevel gap to ≤0.8mm, welding speed to 430mm / min, laser power to 5600kw, and downward pressure to 0.15mm. The formed steel strip is then longitudinally welded using ER120S welding wire. This produces a high-toughness, high-strength continuous tube with a diameter of Φ60.3mm and a wall thickness of 4.0mm. 4. Heat treatment and curling The prepared high-strength, high-toughness continuous tube with a diameter of Φ60.3mm and a wall thickness of 4.0mm is first quenched at 860±20℃, and then tempered in a lead bath furnace at 380±20℃. This heat treatment process optimizes the microstructure of the continuous tube, resulting in a good strength-toughness ratio and improving its fatigue life and load-bearing capacity. The high-strength, high-toughness continuous tube with a diameter of Φ60.3mm and a wall thickness of 4.0mm is then wound onto a drum of appropriate core diameter using a coiler, continuously producing continuous tubes with a length of 1000m.

[0029] Example 5 The specific steps of the method for preparing the high-strength, high-toughness coiled tubing of the present invention are as follows: 1. Coil rolling 1) The chemical element composition of the coil, by weight percentage, is: C: 0.75%; Mn: 1.35%; Si: 0.28%; Cr: 0.26%; Ni: 0.20%; Cu: 0.18%; P≤0.03%; S≤0.03%, with the balance being Fe and unavoidable impurities. Various alloy components are prepared according to the raw material ratio of the plate. These alloy components are then added to a melting furnace for melting at 1540℃. Refining is then carried out in a static furnace at 1440℃ for 85 minutes. Casting is performed at 1320℃. Finally, hot rolling, cold rolling, and finishing processes are performed to form a coil approximately 500m long and 4.0mm thick.

[0030] 2. Slitting of rolled steel sheets and splicing of steel strips: This pipe production involved a length of 1000 meters and an outer diameter of 50.8 mm. The prepared coils were cut into 159.59 mm steel strips using a slitting machine according to continuous pipe specifications. The ends of the two steel strips were then machined at a 45° angle. Laser welding was then used for butt welding of the steel strips, with a V-shaped bevel. The welding speed was 400 mm / min, and the pressure was 0.12 mm. After welding, the strips were water-cooled. Once cooled, the weld surface was ground and cleaned. 3. Welding and forming: Based on the final continuous tube outer diameter and wall thickness requirements, the steel strip is milled into a V-shaped bevel on the side to precisely control the steel strip width and edge perpendicularity. The UOE roller forming method is used to control the steel strip forming. Laser technology is employed to precisely control parameters such as rotation speed, welding speed, and tilt angle, ensuring the forming bevel gap is ≤0.8mm, the welding speed is 430mm / min, the laser power is 5600kw, and the downward pressure is 0.15mm. The formed steel strip is then longitudinally welded using ER120S welding wire. This produces a high-toughness, high-strength continuous tube with a diameter of Φ50.8mm and a wall thickness of 4.0mm. 4. Heat treatment and curling The prepared high-strength, high-toughness continuous tube with a diameter of Φ50.8mm and a wall thickness of 4.0mm is first quenched at 860±20℃, and then tempered in a lead bath furnace at 380±20℃. This heat treatment process optimizes the microstructure of the continuous tube, resulting in a good strength-toughness ratio and improving its fatigue life and load-bearing capacity. The high-strength, high-toughness continuous tube with a diameter of Φ50.8mm and a wall thickness of 4.0mm is then wound onto a drum of appropriate core diameter using a coiler, continuously producing continuous tubes with a length of 1000m.

[0031] Example 6 The high-strength, high-toughness continuous pipe prepared using the method in Example 5 above achieves a yield strength exceeding 1034 MPa, a steel grade of CT130, and a microstructure dominated by tempered sorbite. The actual performance test results are shown in Table 1. Table 1 demonstrates that the high-strength, high-toughness continuous pipe produced by this method meets API standard requirements. This significantly improves the service life and operational safety of the continuous pipe during operation.

[0032]

[0033] One of the main innovations of this invention lies in the alloy composition and its corresponding proportions. The specific design concept is as follows: Carbon (C) is a traditional strengthening element in steel, significantly improving its strength through solid solution strengthening and precipitation strengthening. However, low carbon content does not significantly increase steel strength. Excessive carbon content, however, negatively impacts the toughness, plasticity, and weldability of the pipe. Therefore, the design range for C in this invention is 0.5-0.8%.

[0034] Manganese (Mn) can be infinitely dissolved in Fe and effectively increases the hardenability of steel, thus playing a role in solid solution strengthening and improving the strength of steel. Simultaneously, Mn promotes the formation of retained austenite phase in steel plates by stabilizing austenite, thereby improving the plasticity of the steel plates. However, with increasing Mn content, the tendency of the steel billet to crack during quenching increases, and it also reduces the weldability of the steel. Therefore, the design range of Mn in this invention is 0.8-1.4%.

[0035] Silicon (Si) is a ferrite solid solution strengthening element. While improving strength, it can significantly enhance the mechanical stability of retained austenite, helping steel plates achieve a good strength / plasticity balance, improving elongation, ensuring good edge mechanical properties, and thus reducing the probability of cracking. However, when the Si content is too high, the surface iron oxide scale formed by Si in the heating furnace is difficult to remove, increasing descaling difficulty and resulting in poor surface finish. Therefore, the Si content in this invention is designed to be in the range of 0.2-0.4%.

[0036] Chromium (Cr) has a significant solid solution strengthening effect, which can significantly improve tensile strength. However, when the content is high, it is easy to produce defects such as inclusions and gray plating during welding, as well as hardened structures that are difficult to eliminate. Therefore, the design range of Cr in this invention is 0.11-0.25%.

[0037] Nickel (Ni) effectively improves the hardenability of steel, but its effect on increasing steel strength is relatively small. However, Ni is a precious metal element and is expensive. Therefore, the design range of Ni in this invention is 0.08-0.20%.

[0038] Copper (Cu) enhances the strength, hardenability, and high-temperature stability of steel through solid solution strengthening, and also improves weather resistance and corrosion resistance. However, excessive addition is detrimental to the low-temperature toughness and hot workability of steel. Therefore, the design range of Cu in this invention is 0.10-0.30%.

[0039] P and S: Phosphorus (P) and sulfur (S) are both harmful elements that easily produce inclusions such as FeS and MnS, which can lead to hydrogen-induced cracking and sulfide stress corrosion, causing crack initiation and affecting the bending fatigue performance of continuous tubes. Therefore, it is necessary to strictly control the content of phosphorus and sulfur in steel. Thus, the P content in this invention is controlled below 0.03%, and the target S content is controlled below 0.03%.

[0040] In the process of preparing continuous tubing, this invention employs quenching followed by lead bath heat treatment. Lead bath tempering can transform the hard and brittle martensite formed during quenching into a softer and tougher structure, such as troostite or sorbite, thereby improving the toughness of the material. Lead bath tempering can also provide better surface quality and reduce the risk of surface oxidation and decarburization.

[0041] The above content is a further detailed description of the present invention in conjunction with specific implementation examples. It should not be considered that the specific implementation examples of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the patent protection scope defined by the claims submitted by the present invention.

Claims

1. A high-strength, high-toughness coiled tubing, characterized in that, The composition by mass percentage includes the following components: 0.5%≤C≤0.8%; 0.8%≤Mn≤1.4%; 0.2%≤Si≤0.4%; 0.11%≤Cr≤0.25%; 0.08%≤Ni≤0.20%; 0.10%≤Cu≤0.30%; S≤0.03%; P≤0.03%, with the balance being Fe and unavoidable impurities.

2. The method for preparing high-strength, high-toughness coiled tubing according to claim 1, characterized in that, The specific operating steps are as follows: Step 1: Weigh the raw materials according to the following mass percentages: 0.5%≤C≤0.8%; 0.8%≤Mn≤1.4%; 0.2%≤Si≤0.4%; 0.11≤Cr≤0.25%; 0.08≤Ni≤0.20%; 0.10≤Cu≤0.30%; the balance is Fe and unavoidable impurities; Step 2: Add the prepared metal powders to the smelting furnace for smelting, and then refine them in a static furnace; after that, cast them, and then process them by hot rolling, cold rolling and finishing to make coils; Step 3: Cut the prepared coil into steel strips of 50-300mm using a slitting machine according to the specifications of continuous pipe. After processing the ends of the two steel strips at 45°, process a V-shaped bevel. Butt weld the steel strips using laser welding. After welding, water cooling or air cooling is performed. After the weld has cooled, grind and clean the weld surface. Step 4: The steel strip is milled into a V-shaped bevel on the side, and the UOE roller forming method is used to control the forming of the steel strip; the formed steel strip is longitudinally welded using laser technology to form a continuous tube; Step 5: Heat the prepared continuous tube to 830-930℃ for quenching, then temper it. After heat treatment, the continuous tube is precisely sized and then wound onto a drum with an appropriate core diameter using a coiler to produce a high-strength and high-toughness continuous tube.

3. The method for preparing high-strength, high-toughness coiled tubing according to claim 2, characterized in that: In step 2, the melting temperature is 1520±20℃, the refining temperature is 1430±20℃, and the refining time is 60-120min; casting is carried out at a temperature of 1320±30℃.

4. The method for preparing high-strength, high-toughness coiled tubing according to claim 2, characterized in that: The thickness of the rolled plate in step 2 is 1.9 to 6.35 mm, and the length is greater than 300 meters.

5. The method for preparing high-strength, high-toughness coiled tubing according to claim 2, characterized in that: In step 3, the laser welding speed is 100~500mm / min, and the welding wire used is ER120S.

6. The method for preparing high-strength, high-toughness coiled tubing according to claim 2, characterized in that: In step 4, the V-groove gap on the side of the steel strip is controlled to be ≤0.8mm, the welding speed is 100~500mm / min, the laser power is 5500-6000kw, and the downward pressure is 0.1~0.3mm.

7. The method for preparing a high-strength, high-toughness coiled tubing according to claim 2, characterized in that, The continuous tube produced in step 4 has a diameter of Φ25.4~Φ88.9mm and a wall thickness of 1.9~6.4mm.

8. The method for preparing high-strength, high-toughness coiled tubing according to claim 2, characterized in that, In step 5, tempering is performed in a lead bath furnace at 350-450℃.

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