High-strength heat-resistant welded bushing against secondary corrosion and processing method thereof

Abstract

This invention relates to the field of oil and gas pipeline technology, and particularly to a high-strength, heat-resistant welded sleeve resistant to secondary corrosion and its processing method. The high-strength, heat-resistant welded sleeve resistant to secondary corrosion has the following chemical element composition by weight percentage: C: 0.15~0.25%, Si: 0.15~0.30%, Mn: 1.0~1.3%, Cr: 0.30~0.50%, Mo: 0.4~0.6%, Nb: 0.02~0.05%, Ti: 0.01~0.025%, V: 0.05~0.09%, Ni: 0.1~0.3%, B: 0.006~0.012%, W: 0.05~0.15%, S≤0.005%, P≤0.010%, with the balance being Fe and unavoidable impurities. This invention utilizes processes such as steelmaking, continuous casting of slabs, TMCP, welding, weld heat treatment, quenching and tempering of the entire pipe, and thread machining to produce casing with a yield strength ≥800MPa at 350℃ and a decay rate of less than 12%. In the secondary H2S / CO2 corrosion environment generated during thermal recovery well production, with a system pressure of 15MPa, CO2 partial pressure of 0.2MPa, and H2S partial pressure of 0.0023MPa, the corrosion rate is 0.04~0.09mm / a, meeting the requirements for secondary corrosion caused by crude oil cracking and steam injection during thermal recovery.

Description

Technical Field

[0001] This invention relates to the field of oil and gas pipeline technology, and in particular to a high-strength, heat-resistant welded sleeve resistant to secondary corrosion and its processing method. Background Technology

[0002] Currently, the most widely used and efficient method for heavy oil extraction both domestically and internationally is the steam injection single-well huff and puff process. This is a high-temperature, high-pressure extraction process with an average temperature of around 320℃, reaching over 350℃ in some cases, and a pressure typically between 10MPa and 15MPa. Research indicates that one of the main causes of casing deformation in thermal recovery wells is the alternating load generated during steam injection and well shut-in. In addition to internal pressure and external extrusion loads, the casing is also subjected to tensile and compressive loads caused by thermal stress. This alternating load ultimately leads to casing structural failure. Furthermore, because the steam injection process for heavy oil thermal recovery is a high-temperature process and contains water, it triggers hydrothermal decomposition reactions of different forms of sulfides in the crude oil, producing hydrogen sulfide. Simultaneously, the CO2 contained in the injected high-temperature, high-pressure steam, as well as the associated CO2 in the wellbore, pose a serious corrosion risk to the wellbore. All of these factors severely impact the production safety of heavy oil thermal recovery wells, requiring the threaded joints of the casing to withstand cyclic high-temperature conditions without leakage or failure.

[0003] Currently, most casing for heavy oil thermal recovery wells uses seamless steel pipes. Application No. 202011007623.3 describes a high-strength, heat-resistant seamless oil casing that uses a Cr-Mo system with the addition of appropriate amounts of Zr. The weight percentage composition of the casing material is: C 0.25~0.30%, Si 0.15~0.35%, Mn 0.9~1.1%, Cr 0.9~1.1%, V 0.04~0.08%, Ti 0.01~0.03%, Al≤0.01%, Zr 0.01~0.03%. Application No. 201310409200.8 describes a special oil casing for heavy oil thermal recovery wells that uses a Cr-Mo-V system with the addition of appropriate amounts of rare earth elements to improve the morphology of non-metallic inclusions and increase grain boundary activation energy. The material's composition by weight percentage is as follows: C 0.23~0.28%, Si 0.08~0.28%, Mn 0.35~0.65%, P≤0.015%, S≤0.006%, Cr 1.15~1.35%, Mo 0.20~0.30%, V 0.05~0.07%, B 0.002~0.004%, and rare earth element RE 0.0005~0.01%. Compared with seamless pipes, welded pipes have advantages such as higher geometric dimensional accuracy and better roundness, thus possessing a natural advantage in resisting external pressure crushing, which can further enhance the safety of the wellbore. At the same time, due to the good uniformity of the rolled plate wall thickness, compared with seamless pipes, under the same wall thickness conditions, the weight of a single well casing can be reduced by about 3%.

[0004] Regarding welded pipes, application number 201810882941.0 relates to a high-temperature resistant oil casing for steam-injected heavy oil thermal recovery wells. This invention only considers H2S corrosion performance, failing to consider the secondary H2S / CO2 corrosion performance during the production process of steam-injected thermal recovery wells. Furthermore, its threaded joints do not consider the failure problem caused by periodic temperature changes during steam-injected thermal recovery well production. Application number 201110148660.0 relates to a high-strength oil casing steel for heavy oil thermal recovery wells; this invention does not consider corrosion performance and threaded joint failure issues. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a high-strength, heat-resistant welded casing resistant to secondary corrosion and its processing method. This welded casing possesses excellent high-temperature resistance and resistance to secondary corrosion, preventing secondary H2S / CO2 corrosion caused by crude oil cracking and steam injection during thermal recovery. The strength of this welded casing can adapt to the alternating loads generated by thermal stress during thermal recovery, and it can meet the requirements for casing use in steam-injected heavy oil thermal recovery wells.

[0006] The technical solution of the present invention is: a high-strength, heat-resistant welded sleeve resistant to secondary corrosion, wherein the chemical element composition of the sleeve by weight percentage is: C: 0.15~0.25%, Si: 0.15~0.30%, Mn: 1.0~1.3%, Cr: 0.30~0.50%, Mo: 0.4~0.6%, Nb: 0.02~0.05%, Ti: 0.01~0.025%, V: 0.05~0.09%, Ni: 0.1~0.3%, B: 0.006~0.012%, W: 0.05~0.15%, S≤0.005%, P≤0.010%, with the balance being Fe and unavoidable impurities.

[0007] The above-mentioned processing method for a high-strength, heat-resistant welded sleeve resistant to secondary corrosion includes the following steps:

[0008] S1: Steelmaking: Melting steelmaking raw materials into molten iron. The chemical composition of the molten iron by weight percentage is: C: 0.15~0.25%, Si: 0.15~0.30%, Mn: 1.0~1.3%, Cr: 0.30~0.50%, Mo: 0.4~0.6%, Nb: 0.02~0.05%, Ti: 0.01~0.025%, V: 0.05~0.09%, Ni: 0.1~0.3%, B: 0.006~0.012%, W: 0.05~0.15%, S≤0.005%, P≤0.010%, with the balance being Fe and unavoidable impurities.

[0009] S2: Coil preparation: The molten iron obtained in S1 is smelted in a converter, refined in a ladle and treated with VD vacuum, and then continuously cast into slabs by electromagnetic stirring. The continuously cast slabs are rolled and coiled into hot-rolled coils by TMCP process.

[0010] S3: Tube making: The rolled plate obtained in S2 is longitudinally cut and milled, then bent and shaped by FFX and high-frequency welded to make a welded pipe;

[0011] S4: Weld annealing: The weld is annealed using medium frequency induction heating at a temperature of 600~800℃.

[0012] S5: Thermal tension reduction: After heating the welded pipe to 900℃~980℃ using medium frequency induction heating, thermal tension reduction is performed to the target specification, so that the weld structure is consistent with the base material structure. Then, air cooling is performed using water ring spray to control the cooling rate of the high-temperature section of the tube blank.

[0013] S6: Perform overall heat treatment on the welded pipe after thermal tension reduction: The heat treatment process is quenching and tempering, with a quenching temperature of 890~920℃ and a furnace time of 40~60min, a tempering temperature of 500~590℃ and a furnace time of 80~120min, followed by water cooling.

[0014] S7: Hot straightening, flaw detection and thread processing: After the tube blank is heat-treated, it passes hot straightening, magnetic flux leakage and ultrasonic flaw detection. Then, it undergoes special thread processing at the tube end, coupling screwing, hydrostatic pressure test, and finally the finished tube is made.

[0015] The curling temperature in S2 is 500℃~600℃.

[0016] In S3, the high-frequency welding speed is 12~20m / min, the heat input is 200~300kw, and the extrusion amount is 6~8mm.

[0017] In S3, the height of the inner and outer flash is adjusted after high-frequency welding, and the height of both the inner and outer flash is ≤0.15mm.

[0018] The S6 heat treatment process employs an external spray + internal spray + rotating water cooling method. The external spray flow rate is 1000~2000 m³ / h, and the external spray time is 8~12s. The internal spray flow rate is 400~800 m³ / h, the internal spray time is 12~16s, the internal spray water pressure is 0.6~0.8MPa, and the cooling rate is 20~100℃ / s.

[0019] The thermal straightening temperature in S7 is ≥480℃.

[0020] The high-strength heat-resistant welded casing resistant to secondary corrosion has a yield strength ≥800MPa at 350℃ and a decay rate of less than 12%. In the secondary H2S / CO2 corrosion environment generated during the production process of thermal recovery wells, the system pressure is 15MPa, the CO2 partial pressure is 0.2MPa, the H2S partial pressure is 0.0023MPa, and the corrosion rate is 0.04~0.09mm / a.

[0021] The VD vacuum treatment used in this invention is a technology for improving metal quality. For example, before casting ingots, molten steel is held in a vacuum for a certain period to remove most of the gases and non-metallic inclusions, thereby improving metal quality. The TMCP, or Thermo Mechanical Control Process, used in this invention, is a general term for technologies that, in hot rolling, control the heating temperature, rolling temperature, and reduction amount, further implement air cooling or controlled cooling. The FFX bending forming, or Flexible Forming Excellent, used in this invention, organically combines the involute roll shape with the roll bending method, achieving full compatibility of roughing rolls. It effectively utilizes the strengths of both horizontal and vertical roll forming, rationally distributing the forming amount in the steel pipe forming process to create a high-strength, high-rigidity mechanical structure and a stable forming process.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. This invention improves the hardenability and strength of materials by adding elements such as Cr and Mn; enhances toughness and high-temperature performance by adding elements such as Mo, V, and W; and refines grain size, improves toughness and corrosion resistance, and ensures the overall mechanical properties of the material by adding alloying elements such as Nb, Ti, Al, and B. 2. This invention reduces raw material costs by optimizing the chemical composition of conventional steel pipes, which is beneficial for large-scale industrial production. 3. This invention, through processes such as steelmaking, continuous casting slab production, TMCP, high-frequency welding, weld heat treatment, quenching and tempering full-pipe heat treatment, and thread machining, enables the manufactured casing to achieve a yield strength ≥800MPa at 350℃, and its mechanical properties meet API standards. The 5CT standard specifies the mechanical properties of P110 steel grade, with a decay rate of less than 12%. In the secondary H2S / CO2 corrosion environment generated during thermal recovery well production, the system pressure is 15 MPa, CO2 partial pressure is 0.2 MPa, H2S partial pressure is 0.0023 MPa, and the corrosion rate is 0.04~0.09 mm / a, which meets the requirements for secondary H2S / CO2 corrosion generated by crude oil cracking and steam injection during thermal recovery. 4. This invention employs an external spray + internal spray + rotating water cooling method, which can effectively reduce the precipitation of undesirable structures in low-carbon high-alloy steel. Simultaneously, it controls the cooling rate of the high-temperature section of the tube blank. After high-temperature thermal tension reduction deformation treatment, the welded pipe can reduce structural segregation and anisotropy, significantly improving the uniformity of the weld and base material structures. 5. This invention performs overall tube tempering heat treatment on the quenched tube blank, significantly reducing residual stress in the pipe body and improving the pipe's resistance to external pressure crushing.

[0024] The following will provide further explanation in conjunction with the accompanying drawings. Attached Figure Description

[0025] Figure 1 This is a load curve diagram of a high-strength, heat-resistant welded sleeve threaded joint resistant to secondary corrosion, as described in an embodiment of the present invention, for physical evaluation on a composite load test platform. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to embodiments:

[0027] Example 1

[0028] A high-strength, heat-resistant welded sleeve resistant to secondary corrosion, wherein the chemical element composition of the sleeve by weight percentage is as follows: C: 0.15~0.25%, Si: 0.15~0.30%, Mn: 1.0~1.3%, Cr: 0.30~0.50%, Mo: 0.4~0.6%, Nb: 0.02~0.05%, Ti: 0.01~0.025%, V: 0.05~0.09%, Ni: 0.1~0.3%, B: 0.006~0.012%, W: 0.05~0.15%, S≤0.005%, P≤0.010%, with the balance being Fe and unavoidable impurities;

[0029] This invention improves the hardenability and strength of materials by adding elements such as Cr and Mn; improves the toughness and high-temperature performance of materials by adding elements such as Mo, V, and W; and refines the grains, improves the toughness and corrosion resistance, and ensures the comprehensive mechanical properties of the materials by adding alloying elements such as Nb, Ti, Al, and B.

[0030] Example 2

[0031] A method for processing a high-strength, heat-resistant welded sleeve resistant to secondary corrosion includes the following steps:

[0032] S1: Steelmaking: Melting steelmaking raw materials into molten iron. The chemical composition of the molten iron by weight percentage is: C: 0.15~0.25%, Si: 0.15~0.30%, Mn: 1.0~1.3%, Cr: 0.30~0.50%, Mo: 0.4~0.6%, Nb: 0.02~0.05%, Ti: 0.01~0.025%, V: 0.05~0.09%, Ni: 0.1~0.3%, B: 0.006~0.012%, W: 0.05~0.15%, S≤0.005%, P≤0.010%, with the balance being Fe and unavoidable impurities.

[0033] S2: Coil preparation: The molten iron obtained in S1 is smelted in a converter, refined in a ladle and treated with VD vacuum, and then continuously cast into slabs by electromagnetic stirring. The continuously cast slabs are rolled and coiled into hot-rolled coils by TMCP process.

[0034] S3: Tube making: The rolled plate obtained in S2 is longitudinally cut and milled, then bent and shaped by FFX and high-frequency welded to make a welded pipe;

[0035] S4: Weld annealing: The weld is annealed using medium frequency induction heating at a temperature of 600~800℃.

[0036] S5: Thermal tension reduction: After heating the welded pipe to 900℃~980℃ using medium frequency induction heating, thermal tension reduction is performed to the target specification, so that the weld structure is consistent with the base material structure. Then, air cooling is performed using water ring spray to control the cooling rate of the high-temperature section of the tube blank.

[0037] S6: Perform overall heat treatment on the welded pipe after thermal tension reduction: The heat treatment process is quenching and tempering, with a quenching temperature of 890~920℃ and a furnace time of 40~60min, a tempering temperature of 500~590℃ and a furnace time of 80~120min, followed by water cooling.

[0038] S7: Hot straightening, flaw detection and thread processing: After the tube blank is heat-treated, it passes hot straightening, magnetic flux leakage and ultrasonic flaw detection. Then, it undergoes special thread processing at the tube end, coupling screwing, hydrostatic pressure test, and finally the finished tube is made.

[0039] The molten iron obtained from S1 is smelted in a converter, refined in a ladle, and treated with vacuum distillation (VD) before being continuously cast into slabs by electromagnetic stirring. The high-cleanliness steelmaking technology of ladle refining and VD treatment helps to reduce the content of inclusions in the molten iron and reduce the impact of inclusions on corrosion performance.

[0040] The curling temperature in S2 is 500℃~600℃. A high curling temperature can reduce the strength of the coil and is beneficial for bending and forming the coil.

[0041] In S3, the high-frequency welding speed is 12~20m / min, the heat input is 200~300kw, and the extrusion amount is 6~8mm.

[0042] With an extrusion amount of 6~8mm, using a large extrusion amount can increase the amount of molten metal extruded during the welding process, which is beneficial for the removal of impurities such as oxide scale and reduces the impact of weld inclusions on mechanical properties and corrosion.

[0043] In S3, the height of the inner and outer flash is adjusted after high-frequency welding, and the height of both the inner and outer flash is ≤0.15mm.

[0044] The annealing temperature in the S4 weld is 600~800℃. After annealing, the poor weld structure can be reduced or eliminated, and the weld stress can be reduced.

[0045] The S6 tube, after heat treatment, employs an external spray + internal spray + rotating water cooling method. The external spray flow rate is 1000~2000 m³ / h, and the external spray time is 8~12 s; the internal spray flow rate is 400~800 m³ / h, and the internal spray time is 12~16 s. The internal spray water pressure is 0.6~0.8 MPa, and the cooling rate is 20~100℃ / s. The cooling rate can be controlled through a water ring spray system, effectively reducing the precipitation of undesirable microstructures in low-carbon high-alloy steel. This mitigates or eliminates the impact of segregation and undesirable microstructures on corrosion resistance. Simultaneously, the cooling rate of the high-temperature section of the tube blank is controlled. After high-temperature hot tension diameter reduction deformation treatment, the welded pipe exhibits reduced microstructure segregation and anisotropy, significantly improving the uniformity of the weld and base metal microstructure.

[0046] The thermal straightening temperature in S7 is ≥480℃.

[0047] The high-strength heat-resistant welded casing resistant to secondary corrosion has a yield strength ≥800MPa at 350℃ and a decay rate of less than 12%. In the secondary H2S / CO2 corrosion environment generated during the production process of thermal recovery wells, the system pressure is 15MPa, the CO2 partial pressure is 0.2MPa, the H2S partial pressure is 0.0023MPa, and the corrosion rate is 0.04~0.09mm / a.

[0048] According to the high-strength heat-resistant welded sleeve with secondary corrosion resistance described in Example 1 above, the high-strength heat-resistant welded sleeve is processed using the processing method of the high-strength heat-resistant welded sleeve with secondary corrosion resistance described in Example 2. The specific details are as described in Examples 3, 4, and 5, and the comparisons are as described in Comparative Examples 1, 2, and 3.

[0049] The chemical composition of the casings in Examples 3-5 and Comparative Examples 1-3 is shown in Table 1, with the balance being iron and unavoidable impurities.

[0050]

[0051] Table 2 shows the mechanical properties of the bushings at room temperature and high temperature, measured according to GB / T 228-2010 standard for Examples 3-5 and Comparative Examples 1-3.

[0052] Table 3 shows the corrosion rates of Examples 3-5 and Comparative Examples 1-3 in a high-temperature and high-pressure autoclave, measured by the weight loss method.

[0053]

[0054] This invention achieves steel purification through converter smelting and ladle refining, thereby reducing the content of sulfur (S) and phosphorus (P). It also improves the hardenability and strength of the material by adding elements such as Cr and Mn; enhances the toughness and high-temperature performance of the material by adding elements such as Mo, V, and W; and refines the grain size, improves the toughness and corrosion resistance, and ensures the overall mechanical properties of the material by adding alloying elements such as Nb, Ti, Al, and B.

[0055] As shown in Table 1, the weight percentage of certain chemical elements in the plates of Comparative Examples 1-4 exceeds the scope covered by the technical solution of this invention. For example, in Comparative Example 1, the weight percentages of Mo and W are lower than those in the pipe of this invention. Tables 2 and 3 show that in the steel pipes of Comparative Examples 1-3, at least one of the performance indicators is lower than the design requirements. For example, the yield strength at 350℃ in Comparative Example 1 does not meet the design requirements, and the corrosion rate in Comparative Example 2 does not meet the design requirements. Therefore, the performance of the casing in Comparative Examples 1-3 is not suitable for the complex operating conditions of oil and gas field development, such as steam-injected heavy oil thermal recovery wells.

[0056] As can be seen from Tables 2 and 3, the welded pipe produced using the chemical composition and process described in this invention has a good match between room temperature strength and toughness, excellent high-temperature mechanical properties at 350℃, and good resistance to secondary corrosion.

[0057] Figure 1 Load curves for welded casing threaded joints were evaluated on a composite load testing platform according to ISO 13679-2019 "Test Procedures for Casing and Tubing Threaded Connections" and in conjunction with the actual operating conditions of thermal recovery wells. From... Figure 1 It can be seen that, using the special threaded joint of the present invention, under constant displacement, internal pressure, and bending conditions, after 10 thermal cycles, the internal pressure of the tubing remains stable and no gas leakage occurs.

[0058] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-strength, heat-resistant welded sleeve resistant to secondary corrosion, characterized in that: The chemical element composition of the sleeve, by weight percentage, is as follows: C: 0.15~0.25%, Si: 0.15~0.30%, Mn: 1.0~1.3%, Cr: 0.30~0.50%, Mo: 0.4~0.6%, Nb: 0.02~0.05%, Ti: 0.01~0.025%, V: 0.05~0.09%, Ni: 0.1~0.3%, B: 0.006~0.012%, W: 0.05~0.15%, S≤0.005%, P≤0.010%, with the balance being Fe and unavoidable impurities. The processing of the high-strength, heat-resistant welded sleeve resistant to secondary corrosion includes the following steps: S1: Steelmaking: Melting steelmaking raw materials into molten iron. The chemical composition of the molten iron by weight percentage is: C: 0.15~0.25%, Si: 0.15~0.30%, Mn: 1.0~1.3%, Cr: 0.30~0.50%, Mo: 0.4~0.6%, Nb: 0.02~0.05%, Ti: 0.01~0.025%, V: 0.05~0.09%, Ni: 0.1~0.3%, B: 0.006~0.012%, W: 0.05~0.15%, S≤0.005%, P≤0.010%, with the balance being Fe and unavoidable impurities. S2: Coil preparation: The molten iron obtained in S1 is smelted in a converter, refined in a ladle and treated with VD vacuum, and then continuously cast into slabs by electromagnetic stirring. The continuously cast slabs are rolled and coiled into hot-rolled coils by TMCP process. S3: Tube making: The rolled plate obtained in S2 is longitudinally cut and milled, then bent and shaped by FFX and high-frequency welded to make a welded pipe; S4: Weld annealing: The weld is annealed using medium frequency induction heating at a temperature of 600~800℃. S5: Thermal tension reduction: After heating the welded pipe to 900℃~980℃ using medium frequency induction heating, thermal tension reduction is performed to the target specification, so that the weld structure is consistent with the base material structure. Then, air cooling is performed using water ring spray to control the cooling rate of the high-temperature section of the tube blank. S6: Perform overall heat treatment on the welded pipe after thermal tension reduction: The heat treatment process is quenching and tempering, with a quenching temperature of 890~920℃ and a furnace time of 40~60min, a tempering temperature of 500~590℃ and a furnace time of 80~120min, followed by water cooling. S7: Hot straightening, flaw detection and thread processing: After the tube blank is heat-treated, it passes hot straightening, magnetic flux leakage and ultrasonic flaw detection. Then, it undergoes special thread processing at the tube end, coupling screwing, hydrostatic pressure test, and finally the finished tube is made.

2. The high-strength, heat-resistant welded sleeve resistant to secondary corrosion according to claim 1, characterized in that: The curling temperature in S2 is 500℃~600℃.

3. The high-strength, heat-resistant welded sleeve resistant to secondary corrosion according to claim 1, characterized in that: In S3, the high-frequency welding speed is 12~20m / min, the heat input is 200~300kw, and the extrusion amount is 6~8mm.

4. The high-strength, heat-resistant welded sleeve resistant to secondary corrosion according to claim 1, characterized in that: In the S3 high-frequency welding process, the height of the inner and outer flash is adjusted after welding, and both the inner and outer flash heights are ≤0.15mm.

5. The high-strength, heat-resistant welded sleeve resistant to secondary corrosion according to claim 1, characterized in that: The S6 heat treatment process employs an external spray + internal spray + rotating water cooling method, with an external spray flow rate of 1000~2000 m³ / h. 3 / h, external spraying time 8~12s; internal spraying flow rate 400~800m³ / h. 3 / h, internal spray time 12~16s, internal spray water pressure 0.6~0.8MPa, cooling rate 20~100℃ / s.

6. The high-strength, heat-resistant welded sleeve resistant to secondary corrosion according to claim 1, characterized in that: The thermal straightening temperature in S7 is ≥480℃.

7. The high-strength, heat-resistant welded sleeve resistant to secondary corrosion according to claim 1, characterized in that: The high-strength heat-resistant welded casing resistant to secondary corrosion has a yield strength ≥800MPa at 350℃ and a decay rate of less than 12%. In the secondary H2S / CO2 corrosion environment generated during the production process of thermal recovery wells, the system pressure is 15MPa, the CO2 partial pressure is 0.2MPa, the H2S partial pressure is 0.0023MPa, and the corrosion rate is 0.04~0.09mm / a.

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