A low-cost, ultra-high-strength seamless steel pipe for oil drilling and production perforating guns and its manufacturing method

Abstract

This invention relates to a low-cost, ultra-high-strength seamless steel pipe for oil drilling perforating guns and its production method. The chemical composition by weight percentage is: C: 0.15%–0.20%, Si: 0.15%–0.40%, Mn: 1.00%–1.60%, P≤0.015%, S≤0.010%, Cr: 0.60%–1.00%, Nb: 0.015%–0.040%, V: 0.020%–0.050%, Ti: 0.010%–0.030%, B: 0.0006%–0.0020%, Als: 0.020%–0.050%, N<0.0060%, with the balance being Fe and unavoidable impurities. The advantages are: avoiding the addition of expensive alloys, using a C / Mn steel base with the addition of Cr, and the addition of small amounts of micro-alloying and B to achieve strengthening, thus reducing steel costs.

Description

Technical Field

[0001] This invention belongs to the field of low-alloy high-strength seamless steel pipe manufacturing, and particularly relates to a low-cost ultra-high-strength seamless steel pipe for oil drilling and production perforating guns and its production method. Background Technology

[0002] In oilfield development, to improve oil and gas well productivity and reservoir recovery, it is necessary to further penetrate the passage between the oil and gas layer and the casing, i.e., well completion. Perforation completion is the most widely used completion method in oil exploration and development both domestically and internationally, and the quality of the perforation determines the recovery rate of the oil and gas well. As one of the important components of perforation, the perforation gun not only plays a role in positioning the perforation direction and protecting the oil layer casing during the perforation process, but also withstands the high temperature, high pressure, and strong impact of the perforation projectile generated during the explosion. Its performance directly affects the perforation quality.

[0003] In the early stages of perforation technology development in China, due to differences between industries, perforation gun designers in the petroleum industry typically used readily available low-grade steel casing material as the perforation gun body material, which to some extent affected the perforation completion effect. With the development of the petroleum extraction industry, to adapt to the efficient development of oil and gas reservoirs and the development of complex oil and gas blocks, and to solve the perforation problems of deep wells and ultra-deep wells with high bottom-hole flowing pressure, high-density, deep-penetration perforators are needed. This places new demands on the seamless steel pipe materials used to manufacture perforation gun barrels, from P110 grade to the currently required high-grade V140 and V150 grades, requiring not only high strength but also good impact toughness. Currently, perforation gun barrels are all made of seamless steel pipes, using medium-carbon Cr / Mo series steel that has been quenched and tempered to achieve P110, V140, and V150 grades. Seamless steel pipes for V150 grade oil drilling perforation guns generally use a composition with a Cr content of about 1% and a Mo content of about 0.7%. Due to the addition of a high content of Cr and Mo alloys, the cost of the steel is relatively high.

[0004] In the prior art, patent application number CN200910069758.X discloses a 150Ksi grade high-strength and high-toughness steel pipe for downhole operations in oil and gas wells and its production method. The main components of this steel pipe are: C: 0.22%~0.26%, Si: 0.15%~0.35%, Mn: 0.40%~0.60%, P: ≤0.010%, S: ≤0.005%, Cr: 0.90%~1.10%, Mo: 0.70%~0.80%, V: 0.10~0.15%, with the balance being iron and residual elements. The addition of Mo alloy and the relatively high amounts of Cr and V significantly increase the cost of the steel.

[0005] Patent application CN201710673405.5 discloses a seamless steel pipe for drill pipe bodies. The steel pipe has a yield strength of 1034–1138 MPa, a tensile strength ≥1102 MPa, an elongation A ≥14%, and a longitudinal average impact energy of ≥85 J at room temperature and ≥80 J at -20℃ for a 3 / 4 size specimen, meeting the performance requirements of V150 grade drill pipe bodies. Its main components are: C: 0.24–0.30%, Si: 0.20–0.30%, Mn: 0.60–0.75%, P: ≤0.015%, S: ≤0.005%, Cr: 1.10–1.25%, Mo: 0.45–0.65%, Al: ≤0.040%, with the balance being iron and residual elements. The addition of Mo alloy and a relatively high amount of Cr significantly increases the cost of the steel.

[0006] The article "Performance Study of Seamless Steel Tubes for V150 Grade Drill Pipes" published in the August 2021 issue (Volume 47, Issue 4) of *Baogang Technology* magazine used the following steel composition: C: 0.28%, Si: 0.27%, Mn: 0.66%, P: 0.008%, S: 0.003%, Cr: 1.15%, Mo: 0.52%, with the balance being iron and residual elements. Subsequent quenching and tempering heat treatment was used to meet product performance requirements. The inclusion of Mo and a relatively high Cr content in the composition design of this 150 grade steel increased the cost of the steel.

[0007] The article "Ultra-Deep Wells" published in the February 2021 issue (Volume 50, Issue 1) of the journal *Steel Pipe* The research and application of high torsion drill pipes also incorporates Mo and higher contents of Cr and V into the steel composition, which increases the cost of the steel.

[0008] While ensuring that product quality meets requirements, the composition design should consider reducing the amount of alloying elements added to steel products in order to reduce production costs and conserve alloy resources. Summary of the Invention

[0009] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a low-cost, ultra-high-strength seamless steel pipe for V150 grade oil drilling perforation guns and its production method. This method can manufacture ultra-high-strength seamless steel pipes for oil drilling perforation guns with a yield strength of 1034–1240 MPa, tensile strength ≥1137 MPa, elongation A ≥13%, and longitudinal full-size impact energy ≥60 J at 0℃. Based on C and Mn steels, through economical alloy composition design and a heat treatment process of controlled cooling after rolling followed by quenching and low-temperature tempering, the microstructure of the steel pipe is controlled to obtain a seamless steel pipe with ultra-high strength and good toughness, thereby reducing steel costs.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A low-cost, ultra-high-strength seamless steel pipe for an oil drilling perforation gun, wherein the chemical composition of the seamless steel pipe by weight percentage is:

[0012] C: 0.15%–0.20%, Si: 0.15%–0.40%, Mn: 1.00%–1.60%, P≤0.015%, S≤0.010%, Cr: 0.60%–1.00%, Nb: 0.015%–0.040%, V: 0.020%–0.050%, Ti: 0.010%–0.030%, B: 0.0006%–0.0020%, Als: 0.020%–0.050%, N<0.0060%, with the balance being Fe and unavoidable impurities.

[0013] The yield strength R of the seamless steel pipe p0.2 1034~1240MPa; tensile strength R m ≥1137MPa; Elongation: A≥13%; Longitudinal full-size impact energy at 0℃≥60J.

[0014] The microstructure of the seamless steel pipe is tempered martensite + tempered bainite, and a trace amount of ferrite. The volume percentage of tempered martensite is 70% to 95%, the volume percentage of tempered bainite is 5% to 30%, and the total volume percentage of the two phases is not less than 95%.

[0015] The rationale behind the composition design of this seamless steel pipe is as follows:

[0016] Carbon (C): Its main function is solid solution strengthening, and it is an important element to ensure the strength of seamless steel pipes. To improve hardenability and achieve the requirement of a yield strength greater than 1034 MPa, C must be above 0.15%. However, if C exceeds 0.20%, the plasticity and toughness of the steel will decrease. Therefore, the range of C is 0.15% to 0.20%, with a preferred range of 0.16% to 0.19%.

[0017] Si is an effective deoxidizing element. Too low a content will reduce the deoxidation effect of the material, while too high a content will reduce the toughness of the steel. Therefore, 0.15% to 0.40% is selected as the alloy content range of Si.

[0018] Mn is an austenite stabilizing element and an effective element for improving the toughness of steel. Its influence on the mechanical properties of quenched and tempered steel is mainly achieved by improving the hardenability of the steel. If the Mn content is too low, the expected strengthening effect will not be achieved; if the Mn content is too high, it will cause severe segregation in the continuously cast billet, resulting in a decrease in the toughness of the steel. Therefore, the upper limit of Mn is controlled at 1.60%, and the lower limit is controlled at 1.00%.

[0019] Cr can improve the hardenability and strength of steel, and it can also promote the precipitation of carbides during tempering, thus playing a role in precipitation strengthening. However, the addition of too much Cr alloy tends to increase the temper brittleness of steel, so its content should be controlled below 1.00%. At the same time, the effect is not obvious when the Cr content is low, so the preferred range of Cr is 0.60% to 0.80%.

[0020] In low-alloy steels, vanadium (V) primarily functions as precipitation strengthening and grain refinement, increasing the steel's strength and inhibiting aging. In this invention, the addition of V serves two purposes: firstly, it utilizes the VN (VN) effect for grain refinement; secondly, the combination of V and N effectively reduces the formation of boron nuclei (BN), thus lowering the material's crack susceptibility. A V content of 0.02% or higher is effective, therefore the preferred V range is 0.020%–0.050%.

[0021] Al is a major deoxidizing element in steel and also an inexpensive grain-refining element. In this invention, the main purpose of adding Al is to refine the grains and fix nitrogen (N) in the steel, thereby significantly improving the impact toughness of the steel. If the Al content exceeds 0.050%, it easily leads to an increase in non-metallic inclusions in the steel, resulting in poor toughness; therefore, its upper limit is set below 0.050%. The preferred range is 0.010% to 0.04%.

[0022] Ti has a strong affinity for N, O, and C. This invention incorporates ferrotitanium into steel for micro-titanium treatment, utilizing Ti to form TiN with N in the steel. Simultaneously, controlling the titanium content in the steel controls the amount of titanium oxides and carbonitrides. This method allows the Ti(CN) and Ti oxides precipitated during the solidification process of the cast billet to act as grain boundary pinning agents, preventing grain growth. At the same time, the titanium precipitates within the grains act as new nucleation sites, increasing the number of grains and reducing their volume, effectively refining the grains and improving the plasticity and toughness of the steel pipe. However, excessive Ti addition can easily form TiN inclusions, worsening the toughness of the steel pipe; therefore, its upper limit is set at 0.030%, with a preferred range of 0.010% to 0.020%. The main functions of Nb are precipitation strengthening and preventing grain growth during austenitization by forming nano-precipitates that pin interface migration. The addition of Nb in this invention primarily prevents austenite grain growth during quenching and heating, and simultaneously improves the material's strength through precipitation strengthening during tempering. When the Nb content is too low, the precipitation strengthening and grain refinement effects are not significant; therefore, the lower limit of the Nb content is set at 0.015%, with a preferred range of 0.020% to 0.030%.

[0023] The main function of boron (B) is to improve the hardenability of steel. A B content of 0.0005% or higher is effective, but above 0.002%, B tends to segregate at grain boundaries and form carbonitrides, reducing the toughness of the steel pipe. Therefore, the optimal B content is 0.0006%–0.0020%, with a preferred range of 0.0010%–0.0015%.

[0024] P tends to segregate at grain boundaries, which can increase the ductile-brittle transition temperature and reduce the toughness of steel. If the content is too high, it will reduce the impact toughness, so it must be limited to below 0.015%.

[0025] S readily forms non-hard inclusions with manganese and other materials. An increase in S content leads to an increase in the number of inclusions, which extend and deform along the rolling direction during processing, disrupting the continuity of the material matrix and reducing the low-temperature impact toughness of seamless steel pipes. Therefore, its content must be limited to below 0.010%.

[0026] The effect of nitrogen (N) on steel properties is similar to that of carbon and phosphorus. Increased nitrogen content significantly improves steel strength but significantly reduces toughness. In steels microalloyed with Nb, V, Ti, and Al, excessively high N content leads to the formation of excessive nitrides. This increases the difficulty of control during continuous casting, increasing the likelihood of surface cracks in the cast billet and ultimately causing cracks on the outer surface of the steel pipe, thus increasing the failure rate of the pipe's flaw detection. Therefore, its content must be limited to below 0.0060%, and more preferably below 0.0050%.

[0027] A method for producing a seamless steel pipe for a low-cost, ultra-high-strength oil drilling perforation gun includes the following steps;

[0028] 1) The hot-rolled round tube billet is heated to 1240-1270℃, and then passes through the piercing mill → continuous rolling mill → tension reduction mill in sequence to form steel pipes. The steel pipes coming out of the tension reduction mill are cooled to 600-650℃ by a tunnel cooling device at a cooling rate of not less than 10℃ / s, and then air-cooled to room temperature.

[0029] 2) After hot rolling, the steel pipe is heated in a walking beam furnace at 890-910℃ and held for 30-60 minutes, and then subjected to external quenching and internal spraying water quenching treatment with a cooling rate of not less than 20℃ / s.

[0030] 3) After water quenching, the steel pipe is heated in a walking beam furnace at 450℃~480℃ and held for 45~90 minutes before being air cooled.

[0031] Step 3) The outer diameter of the hollow-cooled steel pipe is The wall thickness is 5-13 mm.

[0032] The outer diameter of the hot-rolled round tube blank in step 1) is 210±5mm.

[0033] The reasons for employing post-rolling controlled cooling + quenching + low-temperature tempering heat treatment in this invention are as follows:

[0034] 1. Controlled cooling after rolling: The steel pipes coming out of the tensioning mill are cooled to 600-650°C at a cooling rate of 10°C / s by a tunnel cooling device, and then air-cooled to room temperature. The purpose is to avoid grain growth in the high-temperature section of the steel pipe and to provide a good basic structure for the subsequent quenching and tempering treatment.

[0035] 2. Quenching heat treatment: Quenching temperature 890~910℃.

[0036] The main purpose of quenching is to transform the austenitized steel pipe into martensite with a small amount of bainite, so that it can obtain good microstructure and mechanical properties after tempering at an appropriate temperature. To ensure that the steel pipe achieves a balance of high strength and high toughness, sufficient cooling intensity must be achieved during water quenching. Based on the CCT curve of the seamless steel pipe composition, the average cooling rate during water quenching of the steel pipe is designed to be above 20℃ / s.

[0037] 3. Tempering temperature is 450~480℃

[0038] The main purpose of tempering is to eliminate the residual stress after quenching of steel pipes, improve the plasticity and toughness of steel, and obtain the precipitation of carbides such as VC, so as to obtain steel pipes with high strength and good toughness.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] (1) From a low-cost and economical perspective, this invention avoids the addition of expensive alloys such as Mo and Ni in its composition design. Instead, it uses a C / Mn steel base with the addition of a small amount of Cr, and achieves strengthening through micro-alloying with small amounts of Nb, V, Ti, and the effect of B, thus significantly reducing steel costs. The addition of Ti is particularly noteworthy, as it aims to prevent the growth of austenite grains under high-temperature hot rolling conditions, thereby refining the grain size from the source. Under this composition, the seamless steel pipe's strength and toughness are ensured to meet requirements through a quenching and tempering heat treatment process.

[0041] (2) The heat treatment process of controlled cooling after rolling followed by quenching and low-temperature tempering in this invention regulates the microstructure of the steel pipe, resulting in a seamless steel pipe with ultra-high strength and good toughness. After exiting the tensioning mill, the steel pipe is cooled to 600-650°C at a cooling rate of not less than 10°C / s by a tunnel cooling device, and then air-cooled to room temperature. The purpose is to avoid grain growth in the high-temperature section of the steel pipe and to provide a good basic microstructure for the subsequent quenching and tempering treatment.

[0042] (3) Seamless steel pipes treated with quenching at 890~910℃ + low-temperature tempering at 450~480℃ have a microstructure of tempered martensite + tempered bainite, and possess high strength and high toughness.

[0043] (4) The ultra-high strength seamless steel pipe for oil drilling perforating guns manufactured using the process of this invention meets the following performance requirements: yield strength 1034~1240MPa, tensile strength ≥1137MPa, elongation A ≥13%, and longitudinal full-size impact energy ≥60J at 0℃. This invention can meet the production requirements of seamless steel pipes for V150 grade perforating guns and can also be applied to V150 grade oil casing and various high-strength structural components. Attached Figure Description

[0044] Figure 1 This is an SEM image of the seamless steel pipe used in low-cost, ultra-high-strength oil drilling perforation guns.

[0045] Figure 2 This is a metallographic diagram of the seamless steel pipe used in low-cost, ultra-high-strength oil drilling perforation guns. Detailed Implementation

[0046] The seamless steel pipe for V150 grade perforating guns with a yield strength of 1034-1240 MPa, tensile strength ≥1137 MPa, elongation A ≥13%, and longitudinal full-size impact energy ≥60 J at 0℃ will be further described below with reference to specific embodiments. However, the specific embodiments and related descriptions do not constitute an improper limitation on the technical solution of the present invention.

[0047] See Figure 1 , Figure 2 The composition of the steels in the embodiments and comparative examples of the present invention (the comparative example is a steel containing Mo) is shown in Table 1.

[0048] Table 1. Composition (wt%) of the steels used in the embodiments and comparative examples of the present invention.

[0049]

[0050] The production process route for seamless steel pipes used in low-cost, ultra-high-strength oil drilling perforation guns is as follows: molten iron pretreatment → converter smelting → LF+VD ladle refining → cast square billet → hot-rolled round tube billet → hot-rolled steel pipe → online controlled cooling → quenching + low-temperature tempering heat treatment → inspection. The production process parameters for the embodiments and comparative examples of this invention are shown in Table 2.

[0051] Table 2 Production process parameters for seamless steel pipes

[0052]

[0053] The main performance indicators of the embodiments and comparative examples of the present invention under heat treatment are shown in Table 3.

[0054] Table 3 Mechanical properties of the product of this invention

[0055]

[0056]

Claims

1. A seamless steel pipe for a low-cost, ultra-high-strength oil drilling perforation gun, characterized in that, The chemical composition of the seamless steel pipe, by weight percentage, is as follows: C: 0.15%~0.20%, Si: 0.15%~0.40%, Mn: 1.00%~1.60%, P≤0.015%, S≤0.010%, Cr: 0.60%~1.00%, Nb: 0.015%~0.040%, V: 0.020%~0.050%, Ti: 0.010%~0.030%, B: 0.0006%~0.0020%, Als: 0.020%~0.050%, N<0.0060%, balance being Fe and unavoidable impurities; The yield strength R of the seamless steel pipe p0.2 1034~1240MPa; tensile strength R m ≥1137MPa; Elongation: A≥13%; Longitudinal full-size impact energy at 0℃≥60J; The microstructure of the seamless steel pipe is tempered martensite + tempered bainite, and a trace amount of ferrite. The volume percentage of tempered martensite is 70%~95%, the volume percentage of tempered bainite is 5%~30%, and the total volume percentage of the two phases is not less than 95%. The method for producing the seamless steel pipe for the low-cost, ultra-high-strength oil drilling perforation gun includes the following steps: 1) The hot-rolled round tube billet is heated to 1240-1270℃, and then passes through the piercing mill → continuous rolling mill → tension reduction mill in sequence to form steel pipe. The steel pipe coming out of the tension reduction mill is cooled to 600-650℃ by a tunnel cooling device at a cooling rate of not less than 10℃ / s, and then air-cooled to room temperature. 2) After hot rolling, the steel pipe is heated in a walking beam furnace at 890~910℃ and held for 30~60 minutes, and then subjected to external quenching and internal spraying water quenching treatment with a cooling rate of not less than 20℃ / s. 3) After water quenching, the steel pipe is heated in a walking beam furnace at 450℃~480℃ and held for 45~90 minutes before being air cooled.

2. A method for producing a seamless steel pipe for a low-cost, ultra-high-strength oil drilling perforation gun as described in claim 1, characterized in that, Includes the following steps; 1) The hot-rolled round tube billet is heated to 1240-1270℃, and then passes through the piercing mill → continuous rolling mill → tension reduction mill in sequence to form steel pipe. The steel pipe coming out of the tension reduction mill is cooled to 600-650℃ by a tunnel cooling device at a cooling rate of not less than 10℃ / s, and then air-cooled to room temperature. 2) After hot rolling, the steel pipe is heated in a walking beam furnace at 890~910℃ and held for 30~60 minutes, and then subjected to external quenching and internal spraying water quenching treatment with a cooling rate of not less than 20℃ / s. 3) After water quenching, the steel pipe is heated in a walking beam furnace at 450℃~480℃ and held for 45~90 minutes before being air cooled.

3. The method for producing a seamless steel pipe for a low-cost, ultra-high-strength oil drilling perforation gun according to claim 2, characterized in that, Step 3) The outer diameter of the hollow-cooled steel pipe is φ60.32~φ177.8mm, and the wall thickness is 5~13mm.

4. The method for producing a seamless steel pipe for a low-cost, ultra-high-strength oil drilling perforation gun according to claim 2, characterized in that, The outer diameter of the hot-rolled round tube blank in step 1) is 210±5mm.

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