A steel for velocity tubing and its preparation method

Abstract

This application relates to a steel for velocity tube columns and a method for preparing the same. The chemical composition of the steel for velocity tube columns includes: C, Si, Mn, P, S, Ti, Al, N, and Fe; wherein, by mass fraction, the content of C is 0.07%–0.12%, the content of Si is ≤0.10%, the content of Mn is 0.71%–1.52%, the content of P is ≤0.019%, the content of S is ≤0.0028%, the content of Ti is 0.011%–0.049%, the content of Al is 0.019%–0.038%, and the content of N is ≤0.0052%. This application, through the rational design of the chemical composition and reduction of alloy additives, achieves low cost and can balance economic efficiency with ensuring the operational safety and efficiency of the steel tube.

Description

Technical Field

[0001] This application relates to the field of steel manufacturing technology, and in particular to a steel for velocity tubing and a method for preparing the same. Background Technology

[0002] In oil and gas field operations, for low-pressure, low-production wells or wells in the late stages of production, the low gas output, low flow rate, and limited drainage capacity lead to fluid backflow and bottom-hole fluid accumulation, resulting in reduced production. To increase gas production, a new production string (i.e., a velocity string) with a smaller diameter is typically installed inside the well. This increases the gas velocity due to the reduced cross-sectional area, thereby improving drainage capacity and increasing production.

[0003] Existing velocity tubing mainly falls into two categories: one is conventional tubing, with a single length of about 10m, which needs to be connected to the required length via threads. However, a large number of threaded connections pose risks to connection safety and airtightness, and also result in low operational efficiency. The other is coiled tubing, which generally contains high levels of alloys such as Cu, Ni, Mo, Cr, and Nb, and has excellent corrosion resistance and fatigue resistance. However, for oil wells that require almost one-time installation and are non-corrosive or only mildly corrosive, its weight is excessive, its cost is too high, and it lacks economic efficiency. Summary of the Invention

[0004] This application provides a steel for velocity tubing and a method for preparing the same, in order to solve the technical problem of high production cost of existing velocity tubing steel.

[0005] In a first aspect, this application provides a steel for velocity tubing, the chemical composition of which includes:

[0006] C, Si, Mn, P, S, Ti, Al, N, and Fe; wherein, by mass fraction,

[0007] The C content is 0.07%–0.12%, the Si content is ≤0.10%, the Mn content is 0.71%–1.52%, the P content is ≤0.019%, the S content is ≤0.0028%, the Ti content is 0.011%–0.049%, the Al content is 0.019%–0.038%, and the N content is ≤0.0052%.

[0008] Optionally, the chemical composition of the steel used for the velocity column further includes Cu and Ni; wherein, by mass fraction, the content of Cu is ≤0.30% and the content of Ni is ≤0.20%.

[0009] Optionally, the chemical composition of the steel used for the velocity column further includes: Nb; the Nb content, by mass fraction, is ≤0.025%.

[0010] Optionally, the microstructure of the steel used for the velocity column is ferrite and nanoscale Ti-containing precipitates; wherein the grain size of the ferrite is grade 12 or higher.

[0011] Optionally, the steel used for the velocity column has an average Charpy impact performance of ≥37J at -20℃.

[0012] Secondly, this application provides a method for preparing steel for velocity tubing, used to prepare the steel for velocity tubing as described in any embodiment of the first aspect, the method comprising:

[0013] The slab is heated and then rolled to obtain a hot-rolled plate;

[0014] The hot-rolled plate is cooled in stages and then coiled to obtain steel for speed tube columns; wherein, the staged cooling includes: performing a first cooling on the hot-rolled plate and controlling the cooling rate and the end temperature of the first cooling, followed by a second cooling.

[0015] Optionally, the cooling rate of the first cooling is >100℃ / s.

[0016] Optionally, the endpoint temperature of the first cooling is 620°C to 670°C.

[0017] Optionally, the second cooling method is air cooling, and the air cooling time is 8s to 15s.

[0018] Optionally, the winding temperature is 580℃~630℃.

[0019] The technical solutions provided in this application have the following advantages compared with the prior art:

[0020] The steel for the speed pipe column provided in this application embodiment has a low cost by rationally designing the chemical composition and reducing the amount of alloy additives. It can ensure the safety and efficiency of the steel pipe operation while taking into account economy. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1A microstructure diagram of a velocity column steel provided in an embodiment of this application;

[0024] Figure 2 This is a schematic flowchart illustrating a method for preparing steel for velocity tubing, as provided in an embodiment of this application. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0027] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0028] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0029] In a first aspect, this application provides a steel for velocity tubing, the chemical composition of which includes:

[0030] C, Si, Mn, P, S, Ti, Al, N, and Fe; wherein, by mass fraction,

[0031] The C content is 0.07%–0.12%, the Si content is ≤0.10%, the Mn content is 0.71%–1.52%, the P content is ≤0.019%, the S content is ≤0.0028%, the Ti content is 0.011%–0.049%, the Al content is 0.019%–0.038%, and the N content is ≤0.0052%.

[0032] In this embodiment, by rationally designing the chemical composition and reducing the amount of alloy added, the cost is low, ensuring both the safety and efficiency of steel pipe operation while also considering economic efficiency. The reasons for controlling the above chemical composition are as follows:

[0033] By controlling the carbon (C) content, carbon (C) becomes the most economical interstitial solid solution strengthening element. It also refines the grain size and provides precipitation strengthening by combining with microalloying elements Nb and Ti to form nano-sized precipitates. However, if the C content is too low, the yield strength ratio of the designed material will be too low, resulting in insufficient material deformation capacity; if the C content is too high, C segregation in the material will be too severe, leading to excessively serious problems such as lightweight cracking during service. Specifically, the C content can be 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, etc.

[0034] Controlling the Si content is crucial, as silicon (Si) primarily functions as a solid solution strengthener and aids in desulfurization during the smelting process. However, excessive Si content can lead to segregation at the half-thickness position of the plate, resulting in surface tiger-skin defects, uneven material microstructure, and deteriorated surface roughness of the finished product. Specifically, the Si content can be 0.10%, 0.09%, 0.08%, etc.

[0035] Controlling the Mn content can improve the hardenability of steel and significantly enhance its yield and tensile strength. However, Mn is a segregating element, which increases the stability of austenite in segregated areas. During phase transformation, it further intensifies the diffusion of carbon to segregated areas, ultimately forming a brittle and hard martensite phase, which is detrimental to the material's toughness. Severe segregation, especially in the center of the plate thickness, is often a major cause of fracture separation. Specifically, the Mn content can be 0.71%, 0.90%, 1.1%, 1.2%, 1.3%, 1.5%, 1.52%, etc.

[0036] The content of phosphorus (P), sulfur (S), and nitrogen (N) should be controlled, as these are all harmful elements in pipeline steel and their content should be minimized. Specifically, the content of P can be 0.019%, 0.018%, 0.017%, 0.016%, etc.; the content of S can be 0.0028%, 0.0027%, 0.0026%, 0.0025%, etc.; and the content of N can be 0.0052%, 0.0051%, 0.0050%, 0.0049%, etc.

[0037] Controlling the Ti content, titanium (Ti) microalloying element, can significantly refine grains and exert precipitation strengthening effects. Simultaneously, it can significantly increase the austenite recrystallization temperature of steel, expand the non-recrystallized region, and facilitate increased cumulative strain in the non-recrystallized region, promoting the acicular ferrite phase transformation during controlled cooling. Furthermore, Ti is inexpensive. Specifically, the Ti content can be 0.011%, 0.021%, 0.031%, 0.041%, 0.049%, etc.

[0038] The content of Al is controlled as a deoxidizing element in steel. Specifically, the content of Al can be 0.019%, 0.022%, 0.025%, 0.027%, 0.029%, 0.031%, 0.033%, 0.035%, 0.037%, 0.038%, etc.

[0039] In some embodiments, the chemical composition of the steel used for the velocity column further includes Cu and Ni; wherein, by mass fraction, the content of Cu is ≤0.30% and the content of Ni is ≤0.20%.

[0040] In this embodiment, the contents of Cu and Ni are controlled. Copper (Cu) has a certain solid solution strengthening effect and improves the corrosion resistance of steel, but Cu should not be added alone. Nickel (Ni) can improve the low-temperature toughness of the material and improve the surface brittleness caused by Cu. When it is necessary to improve corrosion resistance, Cu and Ni can be added appropriately; when there is no need to improve corrosion resistance, they can be omitted. Specifically, the content of Cu can be 0.30%, 0.29%, 0.28%, 0.27%, etc.; the content of Ni can be 0.20%, 0.18%, 0.19%, 0.17%, etc.

[0041] In some embodiments, the chemical composition of the steel used for the velocity column further includes Nb; the Nb content, by mass fraction, is ≤0.025%.

[0042] In this embodiment, the Nb content is controlled. Niobium (Nb) is a microalloying element that can significantly refine grains and provide precipitation strengthening. It can also significantly increase the austenite recrystallization temperature of steel, expand the non-recrystallized region, and facilitate increased cumulative strain in the non-recrystallized region, promoting the acicular ferrite phase transformation during controlled cooling. Since Nb is relatively expensive, a smaller amount is added to control costs, making it economical. Specifically, the Nb content can be 0.025%, 0.024%, 0.023%, 0.022%, etc.

[0043] In some embodiments, the microstructure of the velocity column steel consists of ferrite and nanoscale Ti-containing precipitates; images of the microstructure of this velocity column steel can be found in [reference needed]. Figure 1 The microstructure is uniformly distributed and has ultrafine grains; wherein the grain size of the ferrite is grade 12 or higher.

[0044] In this embodiment, the microstructure of the steel used for the velocity column consists of ferrite and nanoscale Ti-containing precipitates. The positive effects are: the ultra-fine single-phase structure reduces electrode potential difference and micro-stress concentration, improving corrosion resistance, strength, and fatigue performance. Simultaneously, the solidification effect of Ti reduces C segregation in the steel, further enhancing corrosion resistance. Furthermore, Ti-containing precipitates at a scale below 20 nm further strengthen the material. The ferrite is ultrafine-grained ferrite. Controlling the ferrite grain size to level 12 or higher has the following positive effects: by controlling the ferrite grain size to level 12 or higher, the material's corrosion resistance, fatigue performance, and toughness can meet the product performance requirements. Specifically, the ferrite grain size can be level 12, 13, 14, etc.

[0045] In some embodiments, the steel used for the velocity column has an average Charpy impact strength of ≥37J at -20°C.

[0046] In this embodiment, the alloy cost of the aforementioned velocity column steel is controlled, achieving low-cost production of the velocity column steel. Simultaneously, the average Charpy impact strength of this velocity column steel at -20℃ is ≥37J (for a 3.3×10×55mm specimen), exhibiting excellent low-temperature toughness. Furthermore, the yield strength of this velocity column steel reaches 450MPa~550MPa.

[0047] Secondly, this application provides a method for preparing steel for velocity tubing, please refer to [link to relevant documentation]. Figure 2 The method for preparing the steel for the velocity column as described in any embodiment of the first aspect comprises:

[0048] S1. The slab is heated and then rolled to obtain a hot-rolled plate;

[0049] Before step S1, the process also includes: smelting and casting: smelting, refining, and continuous casting according to the above composition, with a slab thickness of 230 mm. Heating in step S1: the heating temperature should not be lower than 1230℃, and the slab tapping temperature should be 1230℃~1320℃.

[0050] The aforementioned rolling process includes finishing and roughing. The roughing process parameters include: 5-6 rolling passes, a final rolling temperature of 1050℃-1150℃, and a total reduction of not less than 70%. Finishing uses a lower temperature final rolling, between 820℃ and 870℃, with a final stand rolling speed ≥7m / s. This ensures sufficient hardening of the austenite, providing favorable conditions for ferrite phase transformation and precipitation during cooling. High-speed finishing increases the strain rate of each finishing pass and controls the recovery of hardened austenite during the finishing process, thereby promoting the uniform nucleation of single-phase ferrite and nanoscale TiC.

[0051] S2. The hot-rolled plate is cooled in stages and then coiled to obtain steel for speed tube columns; wherein, the staged cooling includes: performing a first cooling on the hot-rolled plate and controlling the cooling rate and the end temperature of the first cooling, and then performing a second cooling.

[0052] In the embodiments of this application, the positive effects of staged cooling are as follows: since single-phase ferrite and nano-TiC precipitation have different temperatures, staged cooling optimizes the control of single-phase ferrite phase transformation and TiC precipitation.

[0053] In some embodiments, the cooling rate of the first cooling is >100°C / s.

[0054] In this embodiment, the cooling rate of the first cooling step is controlled. Through ultra-rapid cooling, the austenite is sufficiently undercooled, resulting in more favorable thermodynamic conditions for phase transformation. This promotes the extensive nucleation of ferrite, leading to homogenization and ultrafine refinement of the transformed ferrite, while simultaneously suppressing the formation of pearlite. If the cooling rate of the first cooling step is too low, it can lead to a decrease in the uniformity of the microstructure. Specifically, the cooling rate of the first cooling step can be 105℃ / s, 106℃ / s, 107℃ / s, 108℃ / s, 109℃ / s, etc.

[0055] In some embodiments, the endpoint temperature of the first cooling is 620°C to 670°C.

[0056] In this embodiment, the endpoint temperature of the first cooling is controlled within this temperature range, allowing for sufficient phase transformation of single-phase ferrite. If the endpoint temperature of the first cooling is too high, it can lead to insufficient undercooling of austenite, resulting in poor uniformity of ferrite phase deformation nuclei and a less uniform microstructure. Additionally, the presence of more pearlite in the microstructure is detrimental to corrosion resistance. Conversely, if the endpoint temperature of the first cooling is too low, it can lead to the formation of bainite, which, while improving material strength, results in poor microstructure / phase uniformity and a decrease in the proportion of large-angle grain boundaries. After heat treatment in tube manufacturing, this portion of the microstructure exhibits significant degradation, affecting the overall uniformity of the material's properties. Specifically, the endpoint temperature of the first cooling can be 620℃, 625℃, 630℃, 635℃, 640℃, 645℃, 650℃, 655℃, 660℃, 665℃, 670℃, etc.

[0057] In some embodiments, the second cooling method is air cooling, and the air cooling time is 8s to 15s.

[0058] In this embodiment, the positive effects of air cooling are: providing sufficient time for single-phase ferrite to undergo phase transformation, thus meeting the requirements of phase transformation kinetics. If the air cooling time is too short, the ferrite phase transformation will be insufficient, and some bainite may remain in the microstructure after secondary cooling, leading to uneven microstructure after tube heat treatment; if the air cooling time is too long, a large amount of TiC will precipitate and grow, inhibiting the precipitation strengthening effect. Specifically, the air cooling time can be 8s, 9s, 10s, 11s, 12s, 13s, 14s, 15s, etc.

[0059] In some embodiments, the winding temperature is 580°C to 630°C.

[0060] In this embodiment, the winding temperature is controlled to ensure the precipitation effect of the obtained ultrafine ferrite and nano-TiC. If the winding temperature is too high, it will lead to the growth of ferrite grains and nano-TiC particles to a certain extent, weakening the beneficial effect obtained; if the winding temperature is too low, it will lead to insufficient TiC precipitation to a certain extent, resulting in insufficient utilization of Ti. Specifically, the winding temperature can be 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, etc.

[0061] The preparation method of the velocity column steel is based on the above-mentioned velocity column steel. The specific chemical composition of the velocity column steel can be referred to the above embodiments. Since the preparation method of the velocity column steel adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0062] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0063] This application provides steels for velocity tubing in Examples 1 to 6, the specific chemical composition (wt%) of which can be found in Table 1.

[0064] Table 1 Chemical composition (wt%) of steel used for velocity tubing

[0065]

[0066] The ferrite grain size level of the microstructure of the speed tubing steel in Examples 1-6 is grade 12 or higher. In Table 1, "residual" indicates trace amounts or none.

[0067] This application provides a method for preparing steel for velocity tubing, the method comprising:

[0068] S11. The slab is heated and then rolled to obtain a hot-rolled plate;

[0069] S21. The hot-rolled plate is cooled in stages and then coiled to obtain steel for speed tube columns; wherein the hot-rolled plate is subjected to a first cooling, and the cooling rate and the end temperature of the first cooling are controlled, and then a second cooling is performed.

[0070] Please refer to Table 2 for the specific process parameters of the steel used for the velocity tubing in Examples 1 to 6.

[0071] Table 2 Process parameters for steel used in velocity tubing

[0072]

[0073] The mechanical properties of the steel used for the velocity tubing in Examples 1 to 6 were tested, and the test results are shown in Table 3.

[0074] Table 3 Mechanical properties of steel used for velocity tubing

[0075]

[0076] Comparative Examples 1 and 2 are embodiments disclosed in patent applications 201610313230.2 and 202110869006.2, respectively. By comparison, it can be seen that the steel used for the velocity tubing in Examples 1 to 6 of this application has a lower alloy design, contains no or less precious alloys such as Nb, Mo, and Cr, and has better economic efficiency.

[0077] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A type of steel for velocity tubing, characterized in that, The chemical composition of the steel used for the velocity tubing includes: C, Si, Mn, P, S, Ti, Al, N, and Fe; wherein, by mass fraction, The C content is 0.07%–0.12%, the Si content is ≤0.10%, the Mn content is 0.71%–1.52%, the P content is ≤0.019%, the S content is ≤0.0028%, the Ti content is 0.011%–0.049%, the Al content is 0.019%–0.038%, the N content is ≤0.0052%, and the balance is Fe and unavoidable impurities; The microstructure of the steel used for the velocity column is ferrite and nano-sized Ti-containing precipitates; the grain size of the ferrite is grade 12 or higher; the average Charpy impact strength of the steel used for the velocity column at -20℃ is ≥37J; and the yield strength is 450MPa~550MPa. The method for preparing the steel for the speed tube column includes: heating a slab and then rolling it to obtain a hot-rolled plate; cooling the hot-rolled plate in stages and then coiling it to obtain the steel for the speed tube column; wherein, the staged cooling includes: performing a first cooling on the hot-rolled plate, controlling the cooling rate of the first cooling to be >100℃ / s and the final temperature of the first cooling to be 620℃~670℃, followed by a second cooling, the second cooling method being air cooling, the air cooling time being 8s~15s; the coiling temperature being 580℃~630℃; the rolling includes finishing rolling and roughing rolling, the process parameters of roughing rolling include: 5~6 rolling passes, the final rolling temperature of roughing rolling should be 1050℃~1150℃, the total reduction rate not less than 70%, finishing rolling using a lower temperature final rolling, the temperature being 820℃~870℃, and the rolling speed of the last stand of finishing rolling ≥7m / s.

2. The steel for the velocity tube column according to claim 1, characterized in that, The chemical composition of the steel used for the velocity tubing also includes: Cu and Ni; wherein, by mass fraction, The content of Cu is ≤0.30%, and the content of Ni is ≤0.20%.

3. The steel for the velocity tubing according to claim 1 or 2, characterized in that, The chemical composition of the steel used for the velocity column also includes Nb; the Nb content is ≤0.025% by mass fraction.

4. A method for preparing steel for a velocity tube column, characterized in that, Used to prepare any one of claims 1 to 3 The steel for the velocity tubing described in the item, the method comprising: The slab is heated and then rolled to obtain a hot-rolled plate; The hot-rolled plate is cooled in stages and then coiled to obtain steel for speed tubes. The staged cooling includes: a first cooling of the hot-rolled plate, with the cooling rate controlled to be >100℃ / s and the final temperature of the first cooling being 620℃~670℃; followed by a second cooling, which is air cooling for 8s~15s, and the coiling temperature being 580℃~630℃. The rolling process includes finishing rolling and roughing rolling. The roughing rolling process parameters include: 5~6 rolling passes, a final rolling temperature of 1050℃~1150℃, and a total reduction rate of not less than 70%. The finishing rolling uses a lower temperature final rolling, with a temperature of 820℃~870℃, and a final stand rolling speed of ≥7m / s.

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