Production method of martensitic stainless steel coiled tubing

Abstract

The invention provides a production method of a martensitic stainless steel coiled tubing, and relates to the technical field of coiled tubing. The production method of the martensitic stainless steel coiled tubing comprises the steps of surface cleaning and oil removal, forming and welding, polishing and cleaning, solid solution heat treatment, cooling treatment and the like. The temperature of the solid solution heat treatment is 940-960 DEG C, and the heat preservation time is 70 seconds. According to the invention, the problems of poor long-term stability and short service life of a coating in an additional anticorrosive coating method are avoided, the defects of high manufacturing cost and complex process of a double-layer continuous oil pipe are also avoided, and an economic, efficient and excellent-performance continuous oil pipe production and manufacturing method is provided, is suitable for high-pressure, corrosive and low-temperature well conditions, and has wide application prospects. The application range of the coiled tubing is greatly expanded, and a more reliable and economical solution is provided for complex well conditions.

Description

Technical Field

[0001] This invention relates to the field of coiled tubing technology, and more particularly to a method for producing martensitic stainless steel coiled tubing. Background Technology

[0002] Coiled tubing, as a crucial tool in oil and gas field operations, plays an irreplaceable role in drilling, completion, workover, and production enhancement. With the expansion of oil and gas exploration into deeper, ultra-deep, and unconventional reservoirs, coiled tubing needs to operate under increasingly complex and demanding well conditions. These complex conditions typically involve high pressure, high temperature, highly corrosive media, the presence of solid particles, and low temperatures, placing extremely high demands on the comprehensive performance of coiled tubing. Traditional coiled tubing materials often struggle to simultaneously meet the performance requirements of high strength, high wear resistance, excellent corrosion resistance, and good low-temperature toughness under these extreme environments.

[0003] Currently, the coiled tubing widely used in the oil and gas industry is mainly made of medium-carbon or low-carbon alloy steel, such as CT80 grade coiled tubing. This type of coiled tubing exhibits good mechanical properties under normal operating conditions, possessing high strength and wear resistance, and can withstand large axial loads and bending stresses. However, when this type of coiled tubing is applied to well conditions containing corrosive media such as hydrogen sulfide, carbon dioxide, and chloride ions, its corrosion resistance is significantly insufficient, making it prone to corrosion failures such as uniform corrosion, pitting, stress corrosion cracking, and hydrogen-induced cracking. Furthermore, in low-temperature environments, the toughness of medium-carbon or low-carbon alloy steel coiled tubing decreases significantly, easily leading to low-temperature brittleness, increasing the risk of fracture failure during operation. These problems severely limit the application of traditional alloy steel coiled tubing in corrosive and low-temperature well conditions.

[0004] To improve the corrosion resistance of coiled tubing, the industry has attempted to use external or internal anti-corrosion coatings. This method involves coating the surface of the coiled tubing with a polymer material to form a protective layer, isolating the corrosive medium from contact with the base metal. While coating methods can provide corrosion protection to some extent, the long-term stability of the coating has always been a key issue hindering the application of this technology. In actual operation, coiled tubing needs to withstand repeated bending, stretching, and torsion loads, as well as the combined effects of high temperature, high pressure, and corrosive media. The coating is prone to cracking, peeling, and failure, leading to localized exposure of the base metal and subsequent corrosion. Furthermore, the repair and maintenance of the coating are also difficult, making it difficult to meet the service life and reliability requirements of this method for long-term operation.

[0005] In recent years, to balance strength and corrosion resistance, some researchers have developed double-layer composite coiled tubing composed of corrosion-resistant alloys and low-carbon alloy steel. This double-layer structure typically uses austenitic stainless steel or duplex stainless steel as the inner layer to provide corrosion resistance, while the outer layer uses low-carbon alloy steel to provide mechanical strength. Double-layer coiled tubing has demonstrated good overall performance and stability in field applications, meeting the operational requirements of corrosive well conditions to a certain extent. However, the manufacturing process of double-layer coiled tubing is extremely complex, requiring explosive bonding, rolling bonding, or other special metallurgical bonding methods to combine the two materials, resulting in significantly higher manufacturing costs than traditional single-layer coiled tubing. Furthermore, the quality of the interfacial bonding between the two layers is crucial to product performance; interfacial defects can lead to delamination failure. In addition, while duplex stainless steel possesses good corrosion resistance and strength, its toughness at low temperatures is poor, posing a risk of low-temperature brittleness. The high manufacturing cost and complex process limit the large-scale application of double-layer coiled tubing.

[0006] In summary, existing coiled tubing technologies all have limitations when dealing with complex well conditions containing solid particles, corrosive media, high pressure, and low temperatures. While traditional medium-carbon or low-carbon alloy steel coiled tubing possesses good mechanical properties, its corrosion resistance and low-temperature toughness are insufficient. Adding external anti-corrosion coatings results in poor long-term coating stability and short service life. Although double-layer composite coiled tubing offers excellent performance, its manufacturing cost is high, the process is complex, and its toughness in low-temperature environments still needs improvement.

[0007] Therefore, there is an urgent need to develop a new type of coiled tubing material and production method that can guarantee high strength and high wear resistance, as well as excellent corrosion resistance and low-temperature toughness, while also having reasonable manufacturing costs and process feasibility, so as to meet the actual needs of oil and gas field operations under complex well conditions. Summary of the Invention

[0008] In view of this, the present invention provides a method for producing martensitic stainless steel coiled tubing. This invention avoids the problems of poor long-term stability and short service life of external anti-corrosion coating methods, and also avoids the drawbacks of high manufacturing costs and complex processes associated with double-layer coiled tubing. It provides an economical, efficient, and high-performance method for producing coiled tubing, suitable for high-pressure, corrosive, and low-temperature well conditions, greatly expanding the application range of coiled tubing and providing a more reliable and economical solution for complex well conditions.

[0009] The method for producing martensitic stainless steel continuous tubing of the present invention includes the following steps: S1. Surface cleaning and degreasing: Remove impurities and oil stains from the surface of the steel strip; S2. Forming and Welding: The steel strip cleaned in S1 is formed into a continuous tubing using a forming mold, and the seam is welded using laser welding. S3. Grinding and cleaning: Grinding and cleaning the welded continuous tubing. S4. Solution heat treatment: The coiled tubing after step S3 is subjected to solution heat treatment to dissolve the carbides in the steel and form a single austenitic phase. S5. Cooling treatment: After solution heat treatment, spray cooling is performed immediately to obtain martensitic stainless steel continuous tubing.

[0010] Preferably, in step S1, the steel strip is a 2Cr13 martensitic steel strip; the surface cleaning adopts an ultrasonic degreasing and organic solvent mixed degreasing method; the organic solvent is a mixture of trichloroethylene and acetone, and the mass ratio of trichloroethylene to acetone is 8:2.

[0011] Preferably, in step S2, the laser welding is a fillerless welding, the laser welding is performed in an argon atmosphere, the welding speed is 2±0.2 m / min, the welding power is adjusted in the range of 7500-9500 W according to different outer diameters and wall thicknesses, and the focal length is 300 mm.

[0012] Preferably, in step S4, the solution heat treatment temperature is 940℃-960℃, and the holding time is 70 s. More preferably, the solution heat treatment temperature is 940℃ or 960℃.

[0013] Preferably, in step S5, the spray cooling is performed by a dual-circulation cooling device; after the spray cooling, the continuous oil pipe temperature is 15℃-35℃.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention utilizes a specific solution heat treatment process to produce coiled tubing that possesses both high strength and excellent corrosion resistance.

[0015] The martensitic stainless steel coiled tubing produced by this invention exhibits excellent corrosion resistance under high temperature and high pressure corrosive environments, significantly improving the service life of coiled tubing in corrosive media environments.

[0016] The martensitic stainless steel continuous tubing produced by this invention has excellent low-temperature toughness, avoiding the problem of low-temperature brittleness.

[0017] This invention employs laser welding technology, a fillerless welding method, which is carried out under an argon protective atmosphere. It features fast welding speed, high welding quality, and stable weld performance, avoiding the problems of component segregation and performance inhomogeneity that may occur with traditional filler welding.

[0018] This invention employs a dual-circulation cooling device for rapid spray cooling, which ensures that the coiled tubing is rapidly cooled to 15-35°C after solution heat treatment. This effectively fixes the transformation of austenite to martensite, resulting in an ideal microstructure and thus ensuring that the coiled tubing has excellent comprehensive mechanical properties. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings.

[0020] Figure 1 This is a metallographic diagram of the 2Cr13 martensitic stainless steel continuous tubing of Embodiment 1 of the present invention. Figure 2 This is a scanning electron microscope (SEM) image of the 2Cr13 martensitic stainless steel continuous tubing of Embodiment 1 of the present invention. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise specified, all experiments were repeated three times. Results are expressed as mean ± standard deviation, and P < 0.05 indicates a significant difference.

[0023] The production method of 2Cr13 martensitic stainless steel continuous oil tubing includes the following steps: S1. Surface cleaning: The 2Cr13 martensitic steel strip is cleaned by a combination of ultrasonic degreasing and organic solvent degreasing to remove surface impurities and oil stains; the organic solvent is a mixture of trichloroethylene and acetone, with a mass ratio of trichloroethylene to acetone of 8:2. S2. Forming and Welding: The cleaned steel strip is formed into a continuous tubing using a forming mold, and the seam is welded using laser welding. The laser welding is a fillerless welding method, performed in an argon atmosphere, with a welding speed of 2±0.2 m / min, a welding power of 7800 W, and a focal length of 300 mm. S3. Grinding and cleaning: Grinding and cleaning the welded continuous tubing. S4. Solution heat treatment: The coiled tubing after step S3 is subjected to solution heat treatment. S5. Cooling treatment: After solution heat treatment, spray cooling is performed immediately. A double-circulation cooling device is used to cool the continuous tubing to room temperature (25℃) to obtain 2Cr13 martensitic stainless steel continuous tubing with specifications of 38.1 mm × 3.4 mm.

[0024] The solution heat treatment parameters for Examples 1-2 and Comparative Examples 1-13 are shown in Table 1.

[0025] Table 1

[0026] The mechanical properties and fatigue life of the coiled tubing in Examples 1-2 and Comparative Examples 1-13 are shown in Table 2.

[0027] Table 2

[0028] Note: "Qualified" means meeting the industry's recognized requirements.

[0029] Comparative Example 14: Production method of CT90 stainless steel continuous tubing, the steps are as follows: S1. Surface cleaning: The CT90 steel strip is cleaned by a combination of ultrasonic degreasing and organic solvent degreasing to remove surface impurities and oil stains; the organic solvent is a mixture of trichloroethylene and acetone, with a mass ratio of trichloroethylene to acetone of 8:2. S2. Forming and Welding: The cleaned steel strip is formed into a continuous tubing using a forming mold, and the seam is welded using laser welding. The laser welding is a fillerless welding method, performed in an argon atmosphere, with a welding speed of 2.4±0.2 m / min, a welding power of 8000 W, and a focal length of 300 mm. S3. Grinding and cleaning: Grinding and cleaning the welded continuous tubing. S4. Solution heat treatment: The continuous tubing treated in step S3 is subjected to weld normalizing and tempering heat treatment. S5. Cooling treatment: After normalizing at 910℃, air cooling for 40 s is performed, and then the continuous tubing is cooled to room temperature (25℃) using a dual-circulation cooling device. Subsequently, it is tempered at 600℃ to obtain CT90 continuous tubing.

[0030] The high-temperature and high-pressure corrosion performance testing methods for the 2Cr13 coiled tubing of Example 1 and the CT90 coiled tubing of Comparative Example 14 are as follows: The test standard was ASTM G111-1997 (2013), the test temperature was 120℃, the test period was 96 h, the test solution was a 5% sodium chloride solution, the test pressure was 500 psi, and the gas was CO2. The results are shown in Table 3.

[0031] Table 3

[0032] The low-temperature impact performance of the 2Cr13 coiled tubing of Example 1 and the CT90 coiled tubing of Comparative Example 14 was tested, and the results are shown in Table 4.

[0033] Table 4

[0034] It can be seen that the 2Cr13 martensitic stainless steel coiled tubing of the present invention has significantly improved high-temperature and high-pressure corrosion resistance and low-temperature impact resistance compared with conventional carbon steel (CT90) coiled tubing.

[0035] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for producing a martensitic stainless steel continuous tubing, characterized in that, Includes the following steps: S1. Surface cleaning and degreasing: Remove impurities and oil stains from the surface of the steel strip; S2. Forming and Welding: The steel strip cleaned in S1 is formed into a continuous tubing using a forming mold, and the seam is welded using laser welding. S3. Grinding and cleaning: Grinding and cleaning the welded continuous tubing. S4. Solution heat treatment: The coiled tubing after step S3 is subjected to solution heat treatment. S5. Cooling treatment: After solution heat treatment, spray cooling is immediately applied to obtain martensitic stainless steel continuous tubing. The solution heat treatment temperature is 940℃-960℃, and the holding time is 70 s.

2. The method for producing a martensitic stainless steel continuous tubing according to claim 1, characterized in that, In step S1, the steel strip is a 2Cr13 martensitic steel strip.

3. The method for producing a martensitic stainless steel continuous tubing according to claim 1, characterized in that, In step S1, the surface cleaning adopts a method of degreasing by a mixture of ultrasonic degreasing and organic solvent degreasing.

4. The method for producing a martensitic stainless steel continuous tubing according to claim 3, characterized in that, The organic solvent is a mixture of trichloroethylene and acetone, wherein the mass ratio of trichloroethylene to acetone is 8:

2.

5. The method for producing a martensitic stainless steel continuous tubing according to claim 1, characterized in that, In step S2, the laser welding is a fillerless welding.

6. The method for producing a martensitic stainless steel continuous tubing according to claim 5, characterized in that, The laser welding was performed in an argon atmosphere.

7. The method for producing a martensitic stainless steel continuous tubing according to claim 5, characterized in that, The welding speed is 2±0.2 m / min, the welding power is 7500-9500 W, and the focal length is 300 mm.

8. The method for producing a martensitic stainless steel continuous tubing according to claim 1, characterized in that, In step S4, the temperature of the solution heat treatment is 940°C or 960°C.

9. The method for producing a martensitic stainless steel continuous tubing according to claim 1, characterized in that, In step S5, the spray cooling is carried out through a dual-circulation cooling device.

10. The method for producing a martensitic stainless steel continuous tubing according to claim 1, characterized in that, In step S5, the temperature of the continuous oil pipe after spray cooling is 15℃-35℃.

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