Expansion sleeve with low expansion pressure and high external extrusion resistance after expansion

Abstract

The invention discloses an expansion sleeve with low expansion pressure and high external extrusion resistance after expansion. The expansion sleeve comprises chemical components in percentage by weight as follows: 0.04%-0.25% of C, 0.1%-1.0% of Si, 0.5%-1.8% of Mn, 0.02%-0.10% of Nb and Plt. Slt, 150 ppm, Slt; 80 ppm, with the balance being Fe and unavoidable impurities. The production method comprises the following steps: smelting and continuously casting molten steel to obtain a proper casting blank; a pipe blank is produced through hot rolling, and it is ensured that the proper size and a good-plasticity organization structure are achieved; pretreating the hot-rolled pipe blank, wherein the pretreatment comprises acid pickling, cleaning, neutralizing, phosphating and saponifying; cold rolling is conducted to achieve the needed size specification, and high size precision is achieved; heat treatment is carried out, and methods such as annealing or hardening and tempering can be selected to optimize the material performance; and the inner surface is subjected to sand blasting or polishing treatment, and anti-rust measures are taken.

Description

Technical Field

[0001] The present invention relates to the technical field of expandable casing, and more particularly, to an expandable casing with low expansion pressure and high external extrusion resistance after expansion. Background Art

[0002] The (solid) expandable casing in oil and gas development engineering is a metal round tube, which can be an aluminum alloy tube, a titanium alloy tube, etc., but currently the most mature and widely used one is a steel tube. Due to its good plasticity, its diameter can be increased by mechanical or hydraulic means underground, while improving its own rigidity, so as to obtain a good bonding force with the underground structure and play a role in resisting internal and external pressures. The solid expandable casing is mainly used for plugging lost circulation zones and high-pressure water zones, sealing fractured zones, repairing damaged casings and plugging perforated casings, replacing conventional liner hangers and liner hanger packers, and as an alternative product to conventional casings. Existing expandable casings have many problems such as too high expansion pressure, unstable expansion pressure, and low level of resistance to internal and external pressures after expansion due to deficiencies in the comprehensive design of strength - plasticity - toughness and dimensional accuracy control.

[0003] Therefore, it is necessary to design the chemical composition of the expandable casing and adopt a more reasonable process route to improve the product performance and enhance the product quality to meet the engineering application requirements. Summary of the Invention

[0004] The present invention provides an expandable casing with low expansion pressure and high external extrusion resistance after expansion to overcome at least one technical problem existing in the prior art.

[0005] An embodiment of the present invention provides an expandable casing with low expansion pressure and high external extrusion resistance after expansion, including: The chemical composition by weight percentage is C: 0.04% - 0.25%, Si: 0.1% - 1.0%, Mn: 0.5% - 1.8%, Nb: 0.02% - 0.10%, P < 150 ppm, S < 80 ppm, and the balance is Fe and unavoidable impurities; The production method of the expandable casing with low expansion pressure and high external extrusion resistance after expansion specifically includes: Step S1: Smelt molten steel using a converter or an electric furnace according to the composition, and produce a billet by continuous casting; Step S2: Produce a tube blank by hot rolling, the heating temperature of the steel billet is 1150 - 1250 o °C, keep warm for 1 - 4 hours, the starting rolling temperature is above 1100 o °C, the final rolling temperature is 850 - 950 o °C, and after rolling, it is naturally cooled in the air; the size of the hot-rolled tube blank has a diameter of 105% - 120% of the final product diameter and a wall thickness of 100% - 120% of the final product diameter; the microstructure of the tube blank is ferrite + a small amount of pearlite; Step S3: Pickle, clean, neutralize, phosphatize, and saponify the hot-rolled tube billet, and then continuously roll the steel tube billet using a cold rolling mill to achieve the final required dimensions, with dimensional tolerance requirements as follows: wall thickness tolerance < ±3%, outer diameter tolerance < ±0.3%; Step S4: Heat-treat the steel tube obtained after cold rolling. The heat treatment method selected is annealing, using a gas furnace, resistance furnace, or induction heating furnace. The annealing temperature is controlled at 400 o °C ~ 750 o °C, for a time of 0.5 h ~ 4 h, and air-cool to room temperature. The final microstructure is ferrite plus a small amount of carbide; or adopt the heat treatment method of quenching and tempering, using a gas furnace, resistance furnace, or induction heating furnace, heat to 800 o °C ~ 950 o °C, quench to obtain a lower bainite structure, and then heat to 400 o °C ~ 750 o °C, for a time of 0.5 h ~ 4 h, and air-cool to room temperature. The final microstructure is tempered bainite; Step S5: Straighten the heat-treated steel tube using a multi-roll straightening machine. After straightening, the dimensional accuracy reaches a wall thickness tolerance < ±4%, an outer diameter tolerance < ±0.4%, and a straightness < 0.2 mm / m; Step S6: Sandblast the inner wall of the heat-treated steel tube, or polish it with an iron brush to remove the scale on the inner surface of the steel tube. Under the condition of keeping it dry, add pipe plugs to both ends of the steel tube for protection; spray paint on the outer wall of the steel tube for protection to prevent corrosion during storage.

[0006] Preferably, it also includes Cr: 0.1% ~ 1.5%, Ni: 0.1% ~ 3.0%.

[0007] Preferably, it also includes: Cu: 0.1% ~ 1.0%, Ti: 0.01 ~ 0.02%, and V: 0.01 ~ 0.2%.

[0008] Preferably, the content of Cu does not exceed 40% of the content of Ni.

[0009] One embodiment of this specification can at least achieve the following beneficial effects: It is designed to solve the problems encountered in the use of expandable casing, especially to meet the requirements of low expansion pressure and high external extrusion resistance after expansion. The technical solution of this application improves the overall performance of the expandable casing by optimizing the material composition and production process, such as improving dimensional accuracy and maintaining appropriate strength, so as to better meet the actual application requirements. The product produced by this expandable tube production technology has a final structure of refined ferrite + a small amount of carbide, with a strength generally in the range of 300 - 500 MPa, and the control method is simple with extremely small performance fluctuations. In this way, the strength before expansion can be maintained above 300 MPa, and the pressure during the expansion process will not be too high; more importantly, by adopting the method of hot rolling + cold rolling + heat treatment, compared with existing products, the dimensional accuracy is greatly improved, the wall thickness tolerance < ±4%, the outer diameter tolerance < ±0.4%, and the straightness < 0.2 mm / m (for hot rolled tubes, the standard wall thickness tolerance < ±8%, the outer diameter tolerance < ±1%, and the straightness < 0.5 mm / m). The improvement of the dimensional accuracy of the steel tube before expansion can effectively improve the dimensional accuracy of the steel tube after expansion, and the improvement of dimensional accuracy is the key to improving the ability of the tube to resist higher internal and external pressures. Therefore, the technical solution of this application uses low-alloy addition (low-cost) materials and achieves an excellent match between material properties and product quality under the condition of limited increase in the production cost of the steel tube to meet the technical requirements of low expansion pressure and high external extrusion resistance of the expandable casing. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0011] Figure 1 It is a flowchart of the production method of an expandable casing with low expansion pressure and high external extrusion resistance after expansion according to the embodiments of this application; Figure 2 Based on Figure 1 The schematic diagram of the microstructure of the expandable tube produced by the annealing process using the method in - ferrite + carbide; Figure 3 Based on Figure 1 The schematic diagram of the microstructure of the expandable tube produced by the quenching and tempering process using the method in - tempered bainite. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0012] To make the objectives, technical solutions, and advantages of one or more embodiments of this specification clearer, the following will clearly and completely describe the technical solutions of one or more embodiments of this specification in conjunction with specific embodiments of this specification and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this specification, rather than all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by one or more embodiments of this specification.

[0013] The performance requirements of the expandable casing are mainly as follows: 1. Maintain a certain strength (above 300 MPa) and have good plasticity before expansion; 2. The expansion pressure during expansion should not be too high (generally not higher than 30 MPa, preferably within 25 MPa); 3. After expansion, it can resist relatively high internal and external pressures. Generally, the internal pressure resistance is required to be 60 MPa and the external pressure resistance is 20 MPa.

[0014] To achieve the above technical objectives, the present invention provides an expandable casing with low expansion pressure and high external extrusion resistance after expansion. The chemical composition by weight percentage is C: 0.04% - 0.25%, Si: 0.1% - 1.0%, Mn: 0.5% - 1.8%, Nb: 0.02% - 0.10%, P < 150 ppm, S < 80 ppm, and the balance is Fe and inevitable impurities; The production method of the expandable casing with low expansion pressure and high external extrusion resistance after expansion specifically includes: Step S1: Smelt molten steel using a converter or an electric furnace according to the above chemical composition, and produce a continuous casting billet by continuous casting. Step S2: Produce a tube blank by hot rolling, specifically including heating the steel billet to 1150 - 1250 o °C and holding for 1 - 4 hours. Subsequently, start rolling when the starting rolling temperature is maintained above 1100 o °C until the final rolling temperature reaches 850 - 950 o °C. After rolling is completed, let the tube blank cool naturally in the air. During this process, the size diameter of the hot-rolled tube blank should be 105% - 120% of the final product diameter, and the wall thickness should be 100% - 120% of the final product diameter. In addition, the microstructure of the tube blank after the above treatment is ferrite plus a small amount of pearlite to obtain good plasticity and provide conditions for subsequent cold rolling.

[0015] Step S3: Pickle, clean, neutralize, phosphatize, and saponify the hot-rolled tube blank, and then continuously roll the steel tube blank using a cold rolling mill to reach the final required size, with the dimensional tolerance requirements reaching: wall thickness tolerance < ±3%, outer diameter tolerance < ±0.3%.

[0016] In this step, the hot-rolled billet is pickled to remove the surface oxides; then it is cleaned, rinsed, neutralized, and phosphated to ensure that the surface of the billet is clean and free of impurities. This is a necessary treatment step before the cold rolling process. After that, saponification treatment is carried out. Saponification refers to a chemical treatment method for the surface of materials during the production process. Through saponification treatment, a soapy substance can be formed on the surface of the material, which can play a lubricating role, help reduce the friction during the subsequent cold rolling process, thereby protecting the surface of the material and improving the processing quality.

[0017] Subsequently, a cold rolling mill is used to continuously roll the processed steel pipe billet, and the precise dimensions required for the final product are achieved by controlling the cold rolling process parameters. Specifically, during the cold rolling process, by precisely controlling process parameters such as the reduction and rolling speed of the cold rolling mill, precise control of the steel pipe dimensions is realized. Since permanent plastic deformation occurs to the material during cold rolling, higher dimensional accuracy can be obtained. In this step, the dimensional tolerance after cold rolling is required to reach: wall thickness tolerance < ±3%, outer diameter tolerance < ±0.3%. This high-precision dimensional control enables the expandable casing to better meet the engineering requirements during subsequent use. Especially during the expansion process, it can more stably maintain dimensional accuracy, thereby improving the ability to resist internal and external pressures. In this step, the cold rolling processing method can not only change the dimensions of the steel pipe, but also increase the dislocation density and interface distortion energy in the material through plastic deformation, increase the nucleation point density of recrystallization or austenitization during the subsequent heat treatment process, and is conducive to grain refinement of the heat treatment structure, thereby obtaining better mechanical properties.

[0018] Step S4: Heat-treat the steel pipe obtained after cold rolling. The annealing method is selected for heat treatment, and a gas furnace, resistance furnace, or induction heating furnace is used. The annealing temperature is controlled at 400 o °C to 750 o °C, the time is 0.5 h to 4 h, and it is air-cooled to room temperature. The final microstructure is ferrite plus a small amount of carbide; or the quenching and tempering heat treatment method is adopted, using a gas furnace, resistance furnace, or induction heating furnace, heating to 800 o °C to 950 o °C, quenching to obtain a lower bainite structure, and then reheating to 400 o °C to 750 o °C, the time is 0.5 h to 4 h, and it is air-cooled to room temperature. The final microstructure is tempered bainite.

[0019] In this step, heat treatment is performed on the steel pipe obtained after cold rolling. Specifically, there are two methods to choose from. The first is the annealing method. The steel pipe is heated to 400°C - 750°C using a gas furnace, resistance furnace or induction heating furnace and maintained for between 0.5 hours and 4 hours. Then, the steel pipe is allowed to cool naturally in the air to room temperature. The final microstructure of the steel pipe after this treatment is ferrite and a small amount of carbide. Producing an expandable casing using the annealing method can achieve the desired strength - plasticity - toughness, and the production cost is relatively low.

[0020] The second method is quenching and tempering treatment. Similarly, any of the heating devices mentioned above is used to heat the steel pipe to 800°C - 950°C for quenching, then reheated to 400°C - 750°C and held for 0.5 hours to 4 hours. Finally, it is also cooled to room temperature by natural air cooling. After this process, the microstructure of the steel pipe will transform into tempered bainite. Although the cost of producing an expandable casing using the quenching and tempering method is slightly higher, the process stability is better. Also, while achieving the desired strength - plasticity - toughness matching, the toughness is better than that of the annealing process. As Figure 2 and Figure 3 shown, Figure 2 Figure Figure 3 shows the microstructure of the expandable pipe produced by the annealing process - a schematic diagram of ferrite + carbide,

[0021] Figure

[0022] shows the microstructure of the expandable pipe produced by the quenching and tempering process - a schematic diagram of tempered bainite. Step S5: Sandblast the inner wall of the heat - treated steel pipe or use an iron brush to polish it to remove the scale on the inner surface of the steel pipe. Under the condition of keeping it dry, pipe plugs are added to both ends of the steel pipe for protection; the outer wall of the steel pipe is spray - painted for protection to prevent corrosion during storage. Good inner surface quality can effectively guarantee the stability of pressure during the expansion construction.

[0022] In the above solution, the chemical composition weight percentage of C (carbon) is set between 0.04% and 0.25% to ensure that the expansion casing has appropriate strength, while matching good plasticity and toughness, so that the expansion pressure will not be too high and the stability of the expansion process can be ensured. The carbon content within this range helps to form a microstructure mainly composed of ferrite in the required microstructure, with a small amount of carbide strengthening, thus meeting the expected performance requirements of the material. The chemical composition weight percentage of Si (silicon) is set at 0.1% - 1.0% because within this range, it can effectively improve the strength and hardness of the material, while inhibiting the growth of ferrite and carbide during annealing / tempering, so as to maintain good plasticity and toughness after heat treatment, which helps to optimize the overall performance of the expansion casing. The chemical composition weight percentage of Mn (manganese) is set at 0.5% - 1.8% because within this range, Mn can effectively improve the strength of the material and help to increase the hardenability. Therefore, when using the quenching and tempering process for thick-walled expansion pipes, more Mn can be appropriately added. The chemical composition weight percentage of Nb (niobium) is set at 0.02% - 0.10% because within this range, Nb can effectively refine the grains of the steel, form dispersion precipitation to improve the strength of the material, and will not have an adverse impact on other properties. P (phosphorus) and S (sulfur) are both impurity elements in steel, and their presence will reduce the performance of the steel. In this solution, to ensure that the expansion casing has good mechanical properties and processing properties, it is necessary to strictly control the contents of phosphorus (P) and sulfur (S), that is, P < 150 ppm and S < 80 ppm. Specifically, phosphorus will make the material brittle, especially under low-temperature conditions, which is not conducive to improving the toughness of the material; while sulfur will form low-melting-point sulfide inclusions, which are prone to distribute along the grain boundaries during hot processing, resulting in hot brittleness, reducing the plasticity and toughness of the material, and thus affecting the mechanical properties and processing properties of the final product. Therefore, to ensure that the expansion casing has good mechanical properties and processing properties, it is necessary to strictly control the contents of P and S. In actual production, it is better to have P < 100 ppm and S < 50 ppm.

[0023] In an alternative embodiment technical solution, it further includes Cr: 0.1% - 1.5%, Ni: 0.1% - 3.0%. In this solution, the chemical composition weight percentage of Cr is 0.1% - 1.5%, and the chemical composition weight percentage of Ni is 0.1% - 3.0%. Adding Cr has a certain strengthening effect and can greatly improve the corrosion resistance of the expansion pipe and improve the surface quality. Adding the Ni element can improve the plasticity and toughness of the material and can also improve its corrosion resistance to a certain extent, making it perform better under specific application conditions.

[0024] In an alternative embodiment of the technical solution, it further includes: Cu: 0.1% - 1.0%, Ti: 0.01 - 0.02, and V: 0.01% - 0.2%. In this solution, for low expansion pressure and high external extrusion resistance expansion casing after expansion, the weight percentage of the chemical composition of copper (Cu) is set to 0.1% - 1.0%, the chemical composition percentage of titanium (Ti) is set to 0.01% - 0.02%, and the weight percentage of the chemical composition of vanadium (V) is set to 0.01% - 0.2%, mainly to optimize the material properties. Specifically: Copper (Cu), as an alloying element, can improve the corrosion resistance of the material in steel and also has a certain effect on improving the strength and toughness of the material. However, if the content is too high, it is easy to form a copper-rich phase with a lower melting point at the interface, resulting in the deterioration of hot working performance. Generally, Cu and Ni are added in combination, and the addition amount of Cu is half of that of Ni. The technical solution of this application puts forward more stringent requirements, and the Cu content is less than 40% of the Ni content. Titanium (Ti) is added to the steel as a microalloying element, mainly in the form of binding with C and N to form precipitates, inhibiting the growth of austenite at high temperature stages, so as to obtain a finer austenite structure and improve the performance of hot-rolled pipes. Vanadium (V) is added to the steel as a microalloying element, mainly playing a role in precipitation strengthening. At the same time, V can refine the grains to a certain extent, so that while improving the strength of the material, its toughness will not be severely damaged. To sum up, by reasonably controlling the addition amounts of copper, titanium, and vanadium, the key performance indicators of the expansion casing can be effectively adjusted without significantly increasing the cost.

[0025] In summary, in the technical solution of the present invention, by controlling the chemical components within a specific range (such as C: 0.04% - 0.25%, Si: 0.1% - 1.0%, Mn: 0.5% - 1.8%, Nb: 0.02% - 0.10%, etc.), the basic properties of the material are ensured. During the production process, the method of hot rolling + cold rolling + heat treatment is adopted, which not only improves the dimensional accuracy (wall thickness tolerance < ±4%, outer diameter tolerance < ±0.4%, straightness < 0.2 mm / m), but also ensures that the material has good mechanical properties. The dimensional accuracy of the expandable casing is the key factor to ensure the stability of its expansion pressure. At the same time, the high dimensional accuracy of the steel pipe before expansion can also inhibit the further deterioration of the dimensional accuracy during the expansion process, so that good dimensional accuracy can also be obtained after expansion, which is the most effective measure to improve the anti-internal and external pressure failure ability of the steel pipe after expansion in addition to strength. In the heat treatment step, annealing can be selected to obtain a final microstructure composed of refined ferrite and a small amount of carbides, with good strength, toughness and plasticity matching; or quenching and tempering treatment can be selected to obtain tempered bainite, whose essence is also ferrite and a small amount of carbides, only the distribution form is different. Although the cost is slightly higher, the impact toughness is better. By adopting the two processes, the yield strength of the expandable pipe can be controlled between 300 - 500 MPa, which can fully ensure the reliability of thread processing, while the expansion pressure will not be too high, and the high strength requirements after expansion can be ensured. Example 1

[0026] The weight percentage of chemical components is C: 0.08%, Si: 0.3%, Mn: 1.0%, Nb: 0.03%, Ni: 0.5%, P < 120 ppm, S < 60 ppm, and the balance is Fe and inevitable impurities; the molten steel is smelted in a converter, and the billet is produced by continuous casting; the tube blank is produced by hot rolling, and the heating temperature of the steel billet is 1200 o °C, keep warm for 2 hours, and the starting rolling temperature is 1140 o °C, and the final rolling temperature is 900 o °C, and it is naturally cooled in the air after rolling; the size of the hot-rolled tube blank is the final product Φ245 mm × 13.5 mm; the microstructure of the hot-rolled tube blank is ferrite + a small amount of pearlite; pickling, cleaning, neutralization, phosphating and saponification are carried out, and then the steel pipe blank is continuously rolled by a cold rolling mill. The size after cold rolling is Φ219 mm × 12.4 mm, the wall thickness tolerance < ±2.5%, and the outer diameter tolerance < ±0.2%; the heat treatment selects 680 oAnnealed at C for 1 h and air-cooled to room temperature, the final microstructure is ferrite plus a small amount of carbide. The heat-treated steel pipe is straightened by a multi-roll straightening machine, and after straightening, the dimensional accuracy reaches a wall thickness tolerance of <±3%, an outer diameter tolerance of <±0.3%, and a straightness of <0.15 mm / m. The inner wall of the heat-treated steel pipe is sandblasted to remove the scale on the inner surface of the steel pipe. Under the condition of keeping dry, pipe plugs are added to both ends of the steel pipe for protection. The outer wall of the steel pipe is sprayed with paint for protection to prevent corrosion during storage.

[0027] The feature of Example 1 is that it can provide good comprehensive mechanical properties. Specifically, the yield strength of the steel pipe in this example is 330 MPa, the tensile strength is 460 MPa, the uniform elongation is 18%, the elongation after fracture is 40%, and the Charpy impact energy reaches 220 J. In addition, the expansion pressure at a 15% expansion rate is 20 - 21 MPa, the impact energy after expansion is greater than 150 J, the external pressure resistance is not less than 20 MPa, and the internal pressure resistance is not less than 50 MPa. These data indicate that through hot rolling, cold rolling, and annealing processes, expansion casing materials that meet specific performance requirements can be produced. Example 2

[0028] The chemical composition by weight percentage is C: 0.10%, Si: 0.3%, Mn: 1.4%, Nb: 0.02%, Cr: 0.4%, P < 100 ppm, S < 50 ppm, and the balance is Fe and inevitable impurities. The molten steel is smelted in a converter and the billet is produced by continuous casting. The tube blank is produced by hot rolling, and the heating temperature of the steel billet is 1220 o °C, held for 2 hours, the starting rolling temperature is 1150 o °C, the final rolling temperature is at 910 o °C, and it is naturally cooled in the air after rolling. The size of the hot-rolled tube blank is the final product Φ219 mm × 12.5 mm. The microstructure of the hot-rolled tube blank is ferrite + a small amount of pearlite. Pickling, cleaning, neutralizing, phosphating, and saponifying are carried out, and then the steel pipe blank is continuously rolled by a cold rolling mill. After cold rolling, the size is Φ194 mm × 11.4 mm, the wall thickness tolerance is <±2%, and the outer diameter tolerance is <±0.2%. The heat treatment selects the quenching and tempering process, quenched at 900 o °C, tempered at 690 o °C for 1 h and air-cooled to room temperature, the final microstructure is tempered bainite (as Figure 3 shown); the heat-treated steel pipe is straightened by a multi-roll straightening machine, and after straightening, the dimensional accuracy reaches a wall thickness tolerance of <±3%, an outer diameter tolerance of <±0.3%, and a straightness of <0.15 mm / m. The inner wall of the heat-treated steel pipe is sandblasted to remove the scale on the inner surface of the steel pipe. Under the condition of keeping dry, pipe plugs are added to both ends of the steel pipe for protection. The outer wall of the steel pipe is sprayed with paint for protection to prevent corrosion during storage.

[0029] Compared with Example 1, the steel pipe in Example 2 has higher strength, with a yield strength reaching 420 MPa, a tensile strength of 550 MPa, a uniform elongation of 16%, an elongation after fracture of 44%, a Charpy impact energy reaching 310 J, an expansion pressure of 24 - 25 MPa at a 15% expansion rate, an impact energy after expansion greater than 200 J, an external pressure resistance of 24 MPa, and an internal pressure resistance not less than 60 MPa.

[0030] Compared with Example 1, in this embodiment, higher strength is obtained by adding more C and Mn. Both the yield strength (420 MPa) and the tensile strength (550 MPa) are increased by nearly 100 MPa, and at the same time, the plasticity of the steel pipe does not decrease; adding 0.4% of Cr element increases the corrosion resistance of the product and obtains better surface quality; heat treatment is carried out by using the quenching and tempering treatment method, and the toughness is increased by 90 J. Due to the increase in strength, the expansion pressure during the expansion process is also increased, but the process is still stable, and the impact toughness, internal pressure resistance, and external extrusion resistance after expansion are all correspondingly improved.

[0031] The technical solution of this application is designed to solve the problems encountered during the use of expansion casing, especially to meet the requirements of low expansion pressure and high external extrusion resistance after expansion. The technical solution of this application improves the overall performance of the expansion casing by optimizing the material composition and production process, such as improving dimensional accuracy, maintaining appropriate strength, etc., so as to better meet the actual application requirements. The product produced by this expansion pipe production technology has a final structure of refined ferrite + a small amount of carbides, with a strength generally in the range of 300 - 500 MPa, and the control method is simple, and the performance fluctuation is extremely small. In this way, it can not only maintain the strength before expansion above 300 MPa, but also prevent the pressure during the expansion process from being too high; more importantly, by adopting the method of hot rolling + cold rolling + heat treatment, compared with existing products, the dimensional accuracy is greatly improved, the wall thickness tolerance < ±4%, the outer diameter tolerance < ±0.4%, and the straightness < 0.2 mm / m (for hot-rolled pipes, the standard wall thickness tolerance < ±8%, the outer diameter tolerance < ±1%, and the straightness < 0.5 mm / m). The improvement of the dimensional accuracy of the steel pipe before expansion can effectively improve the dimensional accuracy of the steel pipe after expansion, and the improvement of dimensional accuracy is the key to improving the pipe's ability to resist higher internal and external pressures. Therefore, the technical solution of this application uses low-alloy addition (low-cost) materials and achieves an excellent match between material properties and product quality under the condition of limited increase in the production cost of the steel pipe to meet the technical requirements of low expansion pressure and high external extrusion resistance after expansion of the expansion casing.

[0032] Those of ordinary skill in the art can understand that the drawings are only schematic diagrams of an embodiment, and the modules or processes in the drawings are not necessarily essential for implementing the present invention.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An expansion casing with low expansion pressure and high resistance to external collapse after expansion, characterized in that: The chemical composition weight percentage is C: 0.04%~0.25%, Si: 0.1%~1.0%, Mn: 0.5%~1.8%, Nb: 0.02%~0.10%, P<150ppm, S<80ppm, the balance is Fe and unavoidable impurities; The production method of the low expansion pressure and high anti-external collapse expansion casing after expansion specifically comprises: Step S1: using a converter or an electric furnace to smelt molten steel according to the composition, and using a continuous casting method to produce ingots; Step S2: hot rolling is used to produce tube billets, and the billet heating temperature is 1150~1250 o C, keep warm for 1~4 hours, start rolling at 1100 o C or above, the final rolling temperature is 850~950 o C, naturally cooled in the air after rolling; the diameter of the hot rolled tube billet is 105%~120% of the diameter of the final product, and the wall thickness is 100%~120% of the diameter of the final product; the microstructure of the tube billet is ferrite + a small amount of pearlite; Step S3: pickling, cleaning, neutralizing, phosphating and saponifying the hot-rolled tube blank, and then continuously rolling the steel tube blank using a cold rolling mill to achieve the final required size. The dimensional tolerance requirements are: wall thickness tolerance <±3%, outer diameter tolerance <±0.3%; Step S4: heat treatment is performed on the steel pipe obtained after cold rolling. The heat treatment is performed by annealing method, using a gas furnace, a resistance furnace or an induction heating furnace. The annealing temperature is controlled at 400 o C ~750 o C, time 0.5h~4h, air cooling to room temperature, the final microstructure is ferrite plus a small amount of carbide; or adopt the heat treatment method of quenching and tempering, using a gas furnace, resistance furnace or induction heating furnace, heating to 800 o C ~950 o C, quench to obtain lower bainite structure, and then heat to 400 o C~750 o C, time 0.5h~4h, air cooling to room temperature, the final microstructure is tempered bainite; Step S5: straightening the heat-treated steel pipe using a multi-roll straightening machine, and the dimensional accuracy after straightening reaches a wall thickness tolerance of <±4%, an outer diameter tolerance of <±0.4%, and a straightness of <0.2 mm / m; Step S6: The inner wall of the heat-treated steel pipe is sandblasted or polished with an iron brush to remove the oxide scale on the inner surface of the steel pipe. While keeping it dry, pipe plugs are added to both ends of the steel pipe for protection; the outer wall of the steel pipe is sprayed with paint for protection to prevent corrosion during storage.

2. The low expansion pressure and high anti-external collapse expansion casing according to claim 1 is characterized in that: It also includes Cr: 0.1%~1.5%, Ni: 0.1%~3.0%.

3. The low expansion pressure and high anti-external collapse expansion casing according to claim 2 is characterized in that: Also includes: Cu: 0.1%~1.0%, Ti: 0.01~0.02%, and V: 0.01~0.2%.

4. The low expansion pressure and high anti-external collapse expansion casing according to claim 3 is characterized in that: The Cu content does not exceed 40% of the Ni content.

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