Steel for high-strength corrosion-resistant composite sucker rod and preparation process of steel

Abstract

The invention relates to steel for a high-strength corrosion-resistant composite sucker rod, and belongs to the technical field of oil exploitation equipment. An oil well environment has the characteristics of high temperature and strong corrosivity, the improvement of the corrosion resistance of a sucker rod is generally realized by adopting a corrosion-resistant material coating mode in the prior art, and the coating material and a matrix in the mode are not tightly combined before, so that the use strength is still insufficient. In order to overcome the defects in the prior art, the high-strength corrosion-resistant composite steel for the sucker rod is provided, low-structure alloy steel serves as a base material, stainless steel serves as a coating layer, the low-structure alloy steel and the stainless steel are subjected to warm rolling compounding and subsequent heat treatment, good metallurgical bonding is formed between the low-structure alloy steel and the stainless steel, and the bonding strength of the base material and the coating material is improved; and the service life of the product is prolonged, and the steel for the sucker rod, which has high strength and corrosion resistance, is finally provided.

Description

Technical Field

[0001] The present invention relates to the technical field of oil extraction, and particularly relates to a steel for high-strength corrosion-resistant composite sucker rods and a preparation process thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and it is not necessarily regarded as an admission or any form of implication that this information constitutes prior art already known to those of ordinary skill in the art.

[0003] The oil well environment is usually relatively harsh, containing corrosive media and high-temperature environments. Therefore, the steel for sucker rods needs to have good corrosion resistance and high-temperature resistance. In addition, the sucker rod needs to be connected to the pump head, oil pump or other mechanical equipment, and there are high-strength requirements. Therefore, the steel for sucker rods needs to have high strength, wear resistance, good corrosion resistance, adapt to high-temperature environments, good connectivity and sealing performance. According to the different depths and load conditions of the oil well, there are different grade requirements for the steel of sucker rods. For example, K-class and D-class sucker rods need to have good corrosion resistance and mechanical properties, while H-class sucker rods are used in heavy and overweight load oil wells.

[0004] With the continuous exploitation of oil, various harsh environments have new requirements for sucker rods. Brine environment: The sucker rod is often in a brine environment during oilfield operations. Therefore, it needs to have excellent corrosion resistance and be able to resist the corrosion and oxidation of brine for a long time. Acidic reservoir environment: The sucker rod will also be exposed to acidic reservoirs, which requires the steel to not only have high strength and toughness, but also have good corrosion resistance to cope with the corrosion and oxidation in the acidic environment. High load and complex working conditions: The sucker rod needs to withstand high-intensity tensile and compressive forces and operate in a tortuous wellbore. Therefore, the steel must have good strength and toughness and be able to withstand high loads and complex working conditions. H2S corrosion environment: In a corrosion environment containing H2S, the sucker rod needs to have the ability to resist H2S corrosion.

[0005] In order to reduce the degree of corrosion damage of sucker rods and extend the service life of sucker rods, the field usually adopts the method of coating sucker rods with corrosion-resistant steel materials. For example, in Patent CN116696247A, a layer of 304 stainless steel is coated on the solid sucker rod body and annularly sealed by argon arc welding; Patent CN216446861U also provides a corrosion-resistant and fatigue-resistant sucker rod with a stainless steel coating, in which an anti-corrosion layer and a wear-resistant layer are provided on the outer surface of the polished rod and fixed on the surface of the sucker rod by means of threaded socket connection. In view of the above research status, the inventor believes that: 304 stainless steel is a common stainless steel material containing a relatively high content of chromium and nickel, which endows it with excellent corrosion resistance and can resist the erosion of most chemical media, including acids, alkalis, and salts, etc.; it can withstand high temperatures of 800 °C and is suitable for use in high-temperature environments; it is easy to be processed into various shapes, including plates, pipes, profiles, etc., and can be formed by methods such as cold working and hot working, and is easy to be welded, cut, and processed into shape; it has relatively high strength and toughness at room temperature and can withstand certain tensile, bending, and impact loads; a dense oxide film is formed on the surface in the air, which has good oxidation resistance and can effectively prevent metal oxidation and rusting, thus extending the service life. In summary, stainless steel is suitable for use in steel under harsh environments due to its excellent corrosion resistance, high-temperature resistance, and good processing performance. However, stainless steel has many alloying elements and is expensive. When used in large quantities, it brings very high costs. Moreover, stainless steel is easy to process but has low strength and is not suitable for directly preparing sucker rods. When used as a coating material, the thickness is often small, resulting in insufficient strength of the coating layer, and the fixing methods of welding or socket connection also reduce the bonding strength between the coating material and the substrate, making it difficult to serve for a long time. Summary of the Invention

[0006] Aiming at the deficiencies existing in the above-mentioned prior art, the purpose of the present invention is to provide a steel for sucker rods, which can achieve an anti-corrosion effect while having relatively high strength. In order to achieve the above technical purpose, the present invention provides the following technical solutions: In the first aspect of the present invention, there is provided a high-strength corrosion-resistant composite steel for sucker rods, including a substrate and a coating layer. Among them, the substrate is a low-alloy structural steel, and the coating layer is stainless steel and metallurgically bonded to the substrate.

[0007] Low alloy structural steel, whose main components include carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), chromium (Cr) and molybdenum (Mo), is a material with high strength and high toughness. Compared with ordinary carbon steel, low alloy structural steel has higher strength and hardness, and at the same time has better weldability and processing performance. In addition, its fatigue resistance and corrosion resistance are also better than ordinary steel, especially excellent in non-corrosive environments. It is often used to manufacture gears, shafts, automotive engines, high-pressure pipe fittings, etc. However, its corrosion resistance is poor in the weak acidic environment of crude oil co-produced water. Therefore, low alloy structural steel and stainless steel are hot-rolled and compounded. Using low alloy structural steel bars as the base material and stainless steel pipes as the clad material, through the hot-rolled compounding process, a layer of stainless steel clad material is concentrically coated on the low alloy structural steel, and then heat treatment is carried out to form a good metallurgical bond between them, improve the bonding strength between the base material and the clad material, and extend the service life of the product. Through this composite bar of stainless steel and low alloy structural steel and its production method, the process is easy to implement, the production cost is reduced, the use performance of the product is guaranteed, and the sucker rod has the excellent characteristics of two different materials at the same time. It has both the corrosion resistance of stainless steel and the advantages of low alloy structural steel such as low price, good stiffness and strength, and is an ideal material for preparing sucker rod steel with high strength, wear resistance and corrosion resistance.

[0008] The sucker rod steel described in the first aspect above is rod-shaped, with a diameter of 15 - 50 mm. The base is a low alloy structural steel bar, and the surface is combined with a stainless steel clad layer with uniform thickness. Among them, the ratio of the diameter of the base to the thickness of the clad layer is 20:1 - 6, preferably 20:2 - 4, and specific examples are 20:2, 20:3, 20:4.

[0009] Among them, the low alloy structural steel is preferably of a type with good weldability and high strength, preferably chromium molybdenum steel, and further preferably 40CrMo low alloy structural steel, 30CrMo low alloy structural steel or 25CrMo low alloy structural steel.

[0010] The stainless steel of the clad layer is preferably of a type with good non-magnetic, high-temperature resistance and corrosion resistance, including but not limited to 201, 202, 301, 304, 316, 309 or 321.

[0011] In an implementation manner verified by the present invention, the base is a 40CrMo low alloy structural steel bar with a diameter of 20 mm, and the clad layer is a 304 stainless steel pipe with a thickness of 4 mm.

[0012] In another implementation manner, the base is a 30CrMo low alloy structural steel bar with a diameter of 20 mm, and the clad layer is a 304 stainless steel pipe with a thickness of 4 mm.

[0013] In another embodiment, the substrate is a 25CrMo low-alloy structural steel bar with a diameter of 20 mm, and the cladding layer is a 304 stainless steel pipe with a thickness of 4 mm.

[0014] In another embodiment, the substrate is a 25CrMo low-alloy structural steel bar with a diameter of 20 mm, and the cladding layer is a 301 stainless steel pipe with a thickness of 4 mm.

[0015] For the steel used in the sucker rod in the above specific embodiments, its yield strength averages over 800 MPa, its tensile strength averages over 900 MPa, and its service life can average reach over 2.6 million times. The tensile strength of the current D-class alloy steel sucker rod is in the range of 793 - 965 MPa, and the lower yield strength is greater than 586 MPa. The strength and corrosion resistance of the sucker rod are significantly improved, and the metallurgically bonded rod body can better resist wear during construction, greatly reducing the maintenance probability and extending the service time of the sucker rod.

[0016] In the second aspect of the present invention, there is provided a preparation process for the steel used in the sucker rod described in the first aspect, including the following steps: Surface grinding is performed on the low-alloy structural steel bar serving as the substrate, and pickling treatment is performed on the stainless steel pipe serving as the cladding layer; after loading the treated low-alloy structural steel bar into the stainless steel pipe, warm rolling composite and heat treatment are successively carried out to achieve metallurgical bonding, and then finish rolling and surface treatment are performed to obtain the product.

[0017] Further, the surface grinding is carried out by shot peening. Ceramic balls are used, the shot peening intensity is 0.3 - 0.5 MPa, and the shot peening time is 2 - 3 min.

[0018] Further, the pickling acid pickling solution is a mixed aqueous solution of nitric acid and hydrofluoric acid. In one embodiment, the composition and ratio of the acid pickling solution are as follows: nitric acid: hydrofluoric acid: water = 1: 0.5 - 1.5: 4 - 6.

[0019] Further, the parameters of the warm rolling composite are as follows: the temperature is 400°C - 500°C, rolling is carried out under the protection of inert gas, and the rolling speed is 1 - 1.5 m / min.

[0020] Further, the heat treatment temperature is 700 - 750°C, and the time is 0.5 - 1.5 h.

[0021] Further, the rolling friction coefficient of the finish rolling is between 0.1 - 0.3, and the rolling speed is 5 - 6 m / s.

[0022] Further, the surface roughness after the surface treatment is between 0.2 - 0.8 μm.

[0023] Compared with the prior art, the beneficial effects of the present invention are: Compared with the existing steel for sucker rods, the unique feature of the present invention lies in: using low-alloy high-strength steel as the matrix, which has high strength and low price, and using stainless steel as the cladding layer, which has very good corrosion resistance and adaptability to high-temperature environments, is inexpensive and of good quality, and for the discarded steel for sucker rods, the outer layer wear is easy to repair, improving the service life and secondary utilization rate of the sucker rods. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The schematic diagrams of the accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0025] Figure 1 It is a schematic structural diagram of the steel for sucker rods described in Embodiment 1; Wherein, 1 is the matrix and 2 is the cladding layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] It should be noted that the following detailed description is illustrative and is intended to provide a further description of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0027] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0028] As introduced in the background art, in order to improve the service life of sucker rods, the prior art usually coats the sucker rods with corrosion-resistant materials. However, the coating material and the matrix are not closely combined. As the sucker rods reciprocate continuously in the oil pipe, the coating material is prone to deformation and detachment. Therefore, relatively frequent maintenance is still required. To solve the above technical problems, the present invention proposes a steel for sucker rods, using low-alloy structural steel bars as the base material and stainless steel as the cladding layer, and the two are metallurgically combined. It has been verified that the composite steel provided by the present invention has good corrosion resistance and adaptability to high-temperature environments, and is cost-effective, effectively extending the service life of the sucker rods.

[0029] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with specific embodiments.

[0030] Embodiment 1 In this embodiment, a steel for sucker rods is provided, and its structure is as shown in the attachedFigure 1 As shown, the steel is rod-shaped, using a 30CrMo low-alloy structural steel bar with a diameter of 20 mm as the substrate 1 and a 304 stainless steel pipe with a thickness of 4 mm as the cladding layer 2. The composition of alloying elements in the 304 stainless steel pipe is shown in Table 1.

[0031] Table 1 Content of alloying elements in stainless steel For the steel used in the sucker rod above, the substrate 1 and the cladding layer 2 are metallurgically bonded, and the preparation process includes the following steps: (1) Pretreatment: The surface of the 40CrMo low-alloy structural steel bar is ground and shot-peened. Ceramic balls are used, the shot-peening intensity is 0.4 MPa, and the shot-peening time is 2 - 3 min. A mixed solution of nitric acid and hydrofluoric acid is used as the pickling solution, where the ratio of nitric acid to hydrofluoric acid is approximately nitric acid:hydrofluoric acid:water = 1:1:5 to pickle the surface of the 304 stainless steel pipe to remove impurities on the contact surface between the cladding layer and the substrate.

[0032] (2) Warm rolling composite: The warm rolling composite process is carried out at 400 °C - 500 °C, the protective atmosphere is argon, and the rolling speed is 1.22 m / min.

[0033] (3) Heat treatment: Degradation treatment is carried out, the annealing temperature is 700 - 750 °C, and the annealing time is 0.5 - 1.5 h.

[0034] (4) Finish rolling: Use a Y-type three-high KOCKS tangent pass mill, control the rolling friction coefficient to be between 0.1 - 0.3, and the rolling speed is about 5.8 m / s.

[0035] (5) Surface treatment: Through grinding and shot-peening strengthening treatment, surface impurities are removed, and the surface roughness is between 0.2 - 0.8 μm.

[0036] Mechanical tests are carried out in accordance with GB / T228.1, and its yield strength is 841 MPa and the tensile strength is 983 MPa. The neutral salt spray experiment is carried out in accordance with ISO 9227∶2017. Control the pH of the NaCl droplet to be 6.5 - 7.2. The test environment temperature is maintained at (35 ± 1) °C, and a 500-hour neutral salt spray test is carried out. Shallow rust spots appear on the stainless steel surface, and its corrosion rate is calculated through the mass change, and the calculated corrosion rate is 0.0024 mm / a. Take a sine wave with a frequency f = 10 Hz and a stress ratio R = 0.1, and the number of cycles is greater than 1*10 6 times, and the corrosion fatigue test is carried out at room temperature. Through the fatigue test results at different stroke frequencies, it is predicted that its service life can reach 2.6 million times.

[0037] Example 2 In this embodiment, another kind of steel for sucker rods is provided. The difference from Embodiment 1 is that a 30CrMo low-alloy structural steel bar with a diameter of 20 mm is used as the base material, and a 304 stainless steel pipe with a thickness of 4 mm is used as the clad material. The composition of alloying elements in the stainless steel pipe is shown in Table 2.

[0038] Table 2 Content of alloying elements in stainless steel Its yield strength is tested to be 793 MPa, and the tensile strength is 951 MPa. A neutral salt spray test is carried out for 500 hours, and relatively light rust spots appear on the stainless steel surface. The corrosion rate is calculated through the mass change, and the calculated corrosion rate is 0.002 mm / a. Through the fatigue test results at different strokes, its service life is predicted to reach 2.65 million times.

[0039] Embodiment 3 In this embodiment, another kind of steel for sucker rods is provided. The difference from Embodiment 1 is that a 25CrMo low-alloy structural steel bar with a diameter of 20 mm is used as the base material, and a 304 stainless steel pipe with a thickness of 4 mm is used as the clad material. The composition of alloying elements in the 304 stainless steel pipe is shown in Table 3.

[0040] Table 3 Content of alloying elements in stainless steel Its yield strength is tested to be 877 MPa, and the tensile strength is 1067 MPa. A neutral salt spray test is carried out for 500 hours, and relatively light rust spots appear on the stainless steel surface. The corrosion rate is calculated through the mass change, and the calculated corrosion rate is 0.0018 mm / a. Through the fatigue test results at different strokes, its service life is predicted to reach 2.71 million times.

[0041] Embodiment 4 In this embodiment, another kind of steel for sucker rods is provided. The difference from Embodiment 1 is that a 25CrMo low-alloy structural steel bar with a diameter of 20 mm is used as the base material, and a 301 stainless steel pipe with a thickness of 4 mm is used as the clad material. The composition of alloying elements in the stainless steel pipe is shown in Table 4.

[0042] Table 4 Content of alloying elements in stainless steel Its yield strength is tested to be 877 MPa, and the tensile strength is 1067 MPa. A neutral salt spray test is carried out for 500 hours, and relatively light rust spots appear on the stainless steel surface. The corrosion rate is calculated through the mass change, and the calculated corrosion rate is 0.001 mm / a. Through the fatigue test results at different strokes, its service life is predicted to reach 2.8 million times.

[0043] Example 5 In this example, another kind of steel for sucker rod is provided. The difference from Example 1 is that a 25CrMo low-alloy structural steel bar with a diameter of 20 mm is used as the base material, and a 301 stainless steel pipe with a thickness of 4 mm is used as the clad material. The composition of alloy elements in the stainless steel pipe is shown in Table 5.

[0044] Table 5 Alloy element content in stainless steel Its yield strength is tested to be 880 MPa, and the tensile strength is 1055 MPa. A neutral salt spray test is carried out for 500 hours, and relatively light rust spots appear on the surface of the stainless steel. The corrosion rate is calculated through the mass change, and the calculated corrosion rate is 0.0011 mm / a. Through the fatigue test results at different strokes, its service life is predicted to reach 2.83 million times.

[0045] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high-strength, corrosion-resistant composite steel for sucker rods, characterized in that: The sucker rod steel is in a rod shape, and comprises a matrix and a cladding layer, wherein the matrix is ​​low alloy structural steel, and the cladding layer is stainless steel and metallurgically bonded to the matrix.

2. The steel for sucker rod according to claim 1, characterized in that: The diameter is 15~50mm.

3. The steel for sucker rod according to claim 1, characterized in that: The ratio of the diameter of the substrate to the thickness of the coating layer is 20:1-4, preferably 20:2-4, and specific examples are 20:2, 20:3, and 20:

4.

4. The steel for sucker rod according to claim 1, characterized in that: The low alloy structural steel is chromium-molybdenum steel, preferably 40CrMo low alloy structural steel, 30CrMo low alloy structural steel or 25CrMo low alloy structural steel.

5. The steel for sucker rod according to claim 1, characterized in that: The stainless steel of the coating layer is preferably non-magnetic, high temperature resistant and corrosion resistant, including but not limited to 201, 202, 301, 304, 316, 309 or 321.

6. The steel for sucker rod according to claim 5 or 6, characterized in that: The substrate is a 40CrMo low alloy structural steel bar with a diameter of 20 mm, and the coating layer is a 304 stainless steel pipe with a thickness of 4 mm; Or, the substrate is a 30CrMo low alloy structural steel bar with a diameter of 20 mm, and the coating layer is a 304 stainless steel pipe with a thickness of 4 mm; Or, the substrate is a 25CrMo low alloy structural steel bar with a diameter of 20 mm, and the coating layer is a 304 stainless steel pipe with a thickness of 4 mm; Alternatively, the substrate is a 25CrMo low alloy structural steel bar with a diameter of 20 mm, and the coating layer is a 301 stainless steel pipe with a thickness of 4 mm.

7. The process for preparing steel for sucker rod according to any one of claims 1 to 6, characterized in that: The steps include: The low alloy structural steel rod as the substrate is surface-grinded, and the stainless steel pipe as the cladding layer is pickled; the low alloy structural steel rod after the above treatment is loaded into the stainless steel pipe, and then warm rolling and heat treatment are performed in sequence to achieve metallurgical bonding, and then fine rolling and surface treatment are performed to obtain the product.

8. The process for preparing steel for sucker rod according to claim 7, characterized in that: The surface grinding is performed by shot blasting, using ceramic balls, the shot blasting intensity is 0.3~0.5MPa, and the shot blasting time is 2~3min; Alternatively, the pickling solution is a mixed aqueous solution of nitric acid and hydrofluoric acid, and the composition and proportion of the pickling solution are as follows: nitric acid: hydrofluoric acid: water = 1: 0.5~1.5: 4~6.

9. The process for preparing steel for sucker rod according to claim 7, characterized in that: The parameters of the warm rolling composite are as follows: the temperature is 400°C-500°C, the rolling is carried out under the protection of inert gas, and the rolling speed is 1-1.5 m / min; Alternatively, the heat treatment temperature is 700-750° C. and the time is 0.5-1.5 h.

10. The process for preparing steel for sucker rod according to claim 7, characterized in that: The finishing rolling friction coefficient is between 0.1 and 0.3, and the rolling speed is between 5 and 6 m / s; Alternatively, the surface roughness after the surface treatment is between 0.2-0.8 μm.

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