Method for manufacturing a stainless steel rod for a perforating gun

Abstract

The application provides a manufacturing method of a stainless steel rod for a perforating gun, and comprises the following steps: S1, smelting a steel ingot with a target chemical composition; S2, forming the steel ingot to obtain a rod; S3, performing austenitizing heat treatment on the rod; S4, after the water quenching of the austenitized rod, performing air cooling, self-rotating straightening during the water quenching process, performing hot straightening after the first tempering, and then performing the second tempering to obtain the stainless steel rod for the perforating gun; the method controls the content of chemical elements and the corrosion resistance equivalent, ensures the pitting corrosion resistance, can obtain a steel grade material with a strength of 110KSI-140KSI through heat treatment, and obtains the stainless steel rod which has the strength and toughness matching, good corrosion resistance, and good uniformity of the whole cross-section structure and mechanical properties, and meets the performance requirements of the perforating gun in the machining and use.

Description

Technical Field

[0001] This invention relates to the field of stainless steel material manufacturing technology, specifically to a method for manufacturing stainless steel bars for perforating guns. Background Technology

[0002] In the harsh environments of oil and gas development, the corrosion prevention of steel materials used in the manufacture of oil and gas drilling, production, and transportation equipment is attracting increasing attention. Due to the unique geographical conditions, the equipment is exposed to high CO2 partial pressures and high Cl- concentrations. - In corrosive environments with high H2S concentrations, stress corrosion is often the main cause of equipment failure, making the replacement of alloy structural steel with stainless steel an inevitable trend.

[0003] Perforation is a primary completion method for oil and gas wells in oilfields, playing a crucial role in oil extraction. The purpose of perforation is to establish fluid pathways between the wellbore and the formation, ensuring that oil and gas wells achieve their intended production capacity. Perforation guns are currently made of alloy steel and withstand the enormous impact of explosive detonations during the perforation process. Therefore, perforation guns require not only suitable strength but also sufficient toughness.

[0004] Stainless steel, as a material for perforating guns, meets the strength and toughness requirements of such guns. Furthermore, its corrosion resistance allows for long-term service in harsh mining environments. Analysis of the well media composition, particularly CO2 partial pressure, H2S content / partial pressure, chloride ion concentration, temperature, and pH, is crucial. S13Cr is particularly suitable for corrosive environments with high CO2 but no or only trace amounts of H2S. However, stainless steel is not currently included in domestic perforating gun specifications, primarily due to the following technical bottlenecks: 1. The difficulty of controlling the uniformity of texture and hardness has increased dramatically. Compared to hollow tubing, large-section solid bars exhibit significant differences in cooling rates between the core and surface during forging, rolling, and heat treatment. This easily leads to uneven distribution of microstructure (such as the degree of martensite transformation and retained austenite content) and carbides across the entire cross-section. The core structure may suffer from insufficient transformation, resulting in lower hardness and toughness, or the formation of abnormal structures. This directly causes inconsistent distribution of core properties such as impact toughness and strength across the cross-section, failing to meet the stringent requirements of perforation guns for overall performance consistency.

[0005] 2. Internal quality and defect control

[0006] The main challenge in bar stock production lies in avoiding internal defects such as central porosity, shrinkage cavities, and cracks. These defects can become crack initiation points under high pressure after being processed into a perforating gun, leading to premature gun failure. The tubing in the comparative document, due to its hollow structure, requires different levels of central quality control during the perforation and other tube-making processes compared to solid bars. Ensuring the dense core quality of large-diameter bars is the primary prerequisite for guaranteeing the safety of the perforating gun.

[0007] 3. Residual stress and work hardening

[0008] After rolling or forging, the distribution and magnitude of residual stress in solid bars are more complex than those in tubes. If not eliminated through precisely controlled heat treatment, this high residual stress will be released during machining (especially deep hole machining with a perforating gun), causing workpiece deformation or even cracking. Simultaneously, the inherent work hardening tendency of stainless steel is more pronounced during the roughing stage of the bar stock, placing higher demands on tool selection and cutting parameters, increasing manufacturing costs and time.

[0009] Based on the manufacturing requirements of the perforating gun, a stainless steel with suitable strength and toughness and good corrosion resistance needs to be selected, while also meeting the practical application requirements in terms of cost and feasibility. The coaxiality tolerance of the inner and outer circles of the perforating gun body should not exceed 1.2mm, and the uniformity of the microstructure and mechanical properties of the material after heat treatment must be considered.

[0010] After heat treatment, the straightness of the perforation gun body should not exceed 1 mm per meter and 2.5 mm over its entire length. Material curvature must be considered.

[0011] Therefore, it is necessary to provide a method for manufacturing stainless steel bars for perforating guns to meet the application requirements of the above-mentioned perforating guns. Summary of the Invention

[0012] This invention proposes a method for manufacturing stainless steel bars for perforating guns, which meets the performance requirements when used in the processing and application of perforating guns.

[0013] The technical solution of this invention is implemented as follows: This invention proposes a method for manufacturing stainless steel bars for perforating guns, comprising: S1. Smelting to obtain die-cast steel ingots with the target chemical composition; S2. Form the steel ingot into bars; S3. Perform austenitizing heat treatment on the bar stock; S4. After austenitization, the bar is water-quenched and then air-cooled. During the water quenching process, it is straightened by rotation. After one tempering, it is hot-straightened and then tempered a second time to obtain stainless steel bar for perforating guns. The stainless steel bar has the following chemical composition by mass percentage: C: 0-0.03%, Si: 0-1.00%, Mn: 0-1.00%, P: 0-0.02%, S: 0-0.002%, Ni: 4.0-7.0%, Cr: 11.0-14.0%, Mo: 1.5-3.0%, Ti: 0-0.01%, V: 0-0.50%, Cu: 0-0.50%, N: 0.07-0.11%, and the balance Fe; the stainless steel bar has a pitting corrosion resistance PREN ≥ 19.

[0014] Furthermore, in step S4, the transfer time of the austenitized bar into the quenching process is ≤1 min; and / or, the water temperature of the bar after water quenching is ≤50℃.

[0015] Further, in step S4, the temperature of the first tempering is 500-590℃, and the holding time is (3h / 100mm) D)-(4h / 100mm) (D+5h), the temperature of the second tempering is 10-50℃ lower than the temperature of the first tempering, and the holding time is (3h / 100mm). D)-(4h / 100mm) (D+5h), where h represents hours and D is the diameter value in millimeters.

[0016] Furthermore, in step S4, the straightness of the generatrix of the stainless steel bar used for the perforating gun is ≤1mm per meter and ≤2.5mm over the entire length.

[0017] Furthermore, in step S3, the austenitizing heat treatment temperature is 920-960℃, and the holding time is (2h / 100mm) D) - (2h / 100mm) (D+5h), where h represents hours and D represents the diameter value in millimeters.

[0018] Further, in step S2, the steel ingot is heated to 1150-1230℃ during the forming process, and / or the forming compression ratio is ≥5:1, and / or the forming endpoint temperature is ≥850℃.

[0019] Preferably, the forming process is selected from forging or rolling.

[0020] Furthermore, in step S1, the smelting process is as follows: first, electric furnace smelting is carried out, then oxygen blowing decarburization is carried out in sequence, followed by secondary refining and vacuum degassing before casting.

[0021] Preferably, the oxygen blowing decarburization uses argon-oxygen decarburization or vacuum oxygen decarburization; and / or, the casting temperature is 40-65°C above the liquidus line.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: The manufacturing method of stainless steel bars for perforating guns described in this invention controls the chemical composition and corrosion resistance equivalent to ensure resistance to pitting corrosion. After heat treatment, steel grade materials of 110KSI to 140KSI can be obtained, resulting in stainless steel bars with a good balance of strength and toughness, good corrosion resistance, and uniform microstructure and mechanical properties throughout the cross section, thus meeting the performance requirements of perforating gun processing and use. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The image shows the annular hardness distribution of the stainless steel bar for the perforating gun obtained in Example 1 of this invention.

[0025] Figure 2 The grain size test results of the stainless steel bar for the perforating gun obtained in Example 1 of this invention are shown.

[0026] Figure 3 The image shows the annular hardness distribution of the stainless steel bar for the perforating gun obtained in Example 2 of this invention.

[0027] Figure 4 The grain size test results of the stainless steel bar for the perforating gun obtained in Example 2 of the present invention are shown.

[0028] Figure 5 The corrosion results of the stainless steel bar for the perforating gun obtained in Example 1 of this invention under 3% H2S SSC for 720h.

[0029] Figure 6 The corrosion results of the stainless steel bar for the perforating gun obtained in Example 2 of this invention under 3% H2S SSC for 720h.

[0030] Figure 7 The corrosion results of the stainless steel bar for the perforating gun obtained in Example 1 of this invention under a total pressure of 3 kPa H2S and 3 MPa SCC for 720 h are shown.

[0031] Figure 8 The corrosion results of the stainless steel bar for the perforating gun obtained in Example 2 of this invention under a total pressure of 3 kPa H2S and 3 MPa SCC for 720 h are shown. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] This invention proposes a method for manufacturing stainless steel bars for perforating guns, comprising: S1. Smelting to obtain steel ingots with the target chemical composition; S2. Form the steel ingot into bars; S3. Perform austenitizing heat treatment on the bar stock; S4. After austenitization, the bar is water-quenched and then air-cooled. During the water quenching process, it is straightened by rotation. After one tempering, it is hot-straightened and then tempered a second time to obtain stainless steel bar for perforating guns. The chemical composition of the stainless steel bars by mass percentage is shown in Table 1.

[0034] Table 1:

[0035] Table 1 shows the basic composition of Super 13Cr. By controlling the corrosion equivalent of the material, strong resistance to pitting corrosion is ensured during use, satisfying PREN = Cr% + 3.3×Mo% + 16×N% ≥ 19. Under this composition, steel grade materials of 110KSI~140KSI can be obtained after heat treatment. These materials can be used in the manufacture of perforating guns, resulting in stainless steel bars with a good balance of strength and toughness, excellent corrosion resistance, and uniform microstructure and mechanical properties across the entire cross-section, meeting the performance requirements for perforating gun processing and use.

[0036] In a preferred embodiment, the smelting process utilizes electric furnace smelting + AOD / VOD + LF + VD technology. During VD, vacuum evacuation reduces the oxygen content to 25 ppm and the hydrogen content to 2 ppm. Nitrogen is then purged into the VD furnace to achieve a nitrogen content of at least 0.07% in the steel. The casting process controls the casting temperature, using low superheat casting, with the casting temperature 40-65°C above the liquidus. This ensures uniform solidification of the steel ingot, reduces segregation, and suppresses columnar crystals. Argon gas protection during casting prevents secondary oxidation of the molten steel, promotes the flotation of inclusions, and ensures the purity of the molten steel.

[0037] In a preferred embodiment, the forming process can be either forging or rolling. The heating temperature of the formed steel ingot is controlled at 1150-1230℃, and the homogenization time of the steel ingot is sufficient to ensure complete heating. The overall compression ratio of the material should be ≥5:1, and the final forming temperature should be ≥850℃. This ensures uniform microstructure and prepares for uniform hardness after heat treatment.

[0038] In a preferred embodiment, the austenitizing temperature is 920-960℃, and the austenitizing holding time is 2h / 100mm. D) - (2h / 100mm) (D+5h), where h represents hours and D represents diameter in mm. Stainless steel bars are immersed in a continuously flowing coolant for quenching. The transfer time from austenitization to entering the quenching tank is ≤1 min, and the water temperature of the stainless steel bars is ≤50℃.

[0039] In a preferred embodiment, the tempering temperature is selected according to the steel grade of the delivered material, and the holding temperature for the first tempering is 500~590℃, with a holding time of 3h / 100mm. D)-(4h / 100mm) (D+5h), where h represents hours and D represents diameter in mm. If the straightness does not meet the delivery requirements after the first tempering, straightening is performed. After straightening, the holding temperature for the second tempering is 10-50℃ lower than the holding temperature for the first tempering, and the holding time is (3h / 100mm). D)-(4h / 100mm) (D+5h), where h represents hour and D represents diameter in mm. Secondary tempering helps stabilize material properties and release straightening and quenching stresses.

[0040] In a preferred embodiment, the straightened stainless steel bar has a generatrix straightness of ≤1mm per meter and ≤2.5mm over its entire length, meeting the bending requirements. The stainless steel bar has a maximum outer diameter of 250mm, which can cover the outer diameter of existing perforating guns.

[0041] Example 1

[0042] Taking the 110KSI as an example, the 95mm specification is produced for manufacturing the 89 specification perforating gun.

[0043] The ingredients are designed as follows:

[0044] The steps are as follows: 1) Electric furnace smelting + VOD + LF + VD, ingot casting of 3t steel ingots. Casting temperature is 40℃ above the liquidus. PREN=19.362; 2) The product is rolled into 97mm diameter sections. The heating temperature is controlled at 1220℃, and the final rolling temperature is 942℃. 3) Heat treatment is carried out in a continuous furnace at an austenitizing temperature of 960℃ and a holding time of 2 hours before being removed from the furnace; 4) Select water quenching, immersion time 45s, water quench to 36℃, then air cool. Use self-rotation straightening during water quenching, first tempering temperature 580℃, holding time 4h, then select hot straightening to further optimize flatness and air cool to 20℃, then perform second tempering at 550℃, holding time 4h.

[0045] 5) The material is machined to further optimize the curvature, and the actual straightness is 1mm per meter.

[0046] 6) After flaw detection, the product is finished and put into storage to ensure that it leaves the factory without defects.

[0047] Example 2

[0048] Taking the 125KSI as an example, the 135mm specification is produced for manufacturing the 127 specification perforating gun.

[0049] The ingredients are designed as follows:

[0050] The steps are as follows: 1) Electric furnace smelting + AOD + LF + VD, ingot casting of 5t steel ingots. Casting temperature is 45℃ above the liquidus. PREN=20.521; 2) The product is forged into a 135mm diameter section. The heating temperature is controlled at 1180℃, and the final forging temperature is 883℃. 3) Heat treatment in a continuous furnace, austenitizing temperature 980℃, holding time 3h, then remove from the furnace; 4) Select water quenching, immersion time 52s, water quench to 25℃, then air cool. Use self-rotation straightening during water quenching, first tempering temperature 575℃, holding time 46h, then select hot straightening to further optimize straightness and air cool to 23℃, then perform second tempering at 540℃, holding time 6h.

[0051] 5) The material is machined to further optimize the curvature, and the actual straightness is 1mm per meter.

[0052] 6) After flaw detection, the product is finished and put into storage to ensure that it leaves the factory without defects.

[0053] Performance testing

[0054] 1) The annular hardness and distribution of the stainless steel bars prepared in Examples 1 and 2 were tested, and the results are as follows: Figure 1 ,、 Figure 3 As shown, it is easy to see that the ring hardness of Example 1 is 30.3~31.6, and the hardness distribution is uniform; the ring hardness of Example 2 is 30.6~31.5, and the hardness distribution is uniform.

[0055] 2) The grain size of the stainless steel bars prepared in Examples 1 and 2 was detected, and the results of the four-quadrant detection are as follows: Figure 2 , Figure 4 As shown; the results were all at level 6, with no ferrite observed, indicating a uniform tempered martensite structure.

[0056] 3) The H2S corrosion resistance and pitting corrosion resistance of the stainless steel bars obtained in Examples 1 and 2 were tested, and the results are as follows: Figure 5-8 As shown, the corrosion results (100X) of Examples 1 and 2 under 3% H2S SSC for 720h are respectively as follows. Figure 5 , Figure 6 As shown; the corrosion results (100X) of Examples 1 and 2 under 175℃, 3 kPa H2S total pressure 3 MPa SCC for 720 h are respectively as shown. Figure 7 , Figure 8 As shown, the stainless steel bars produced by the method of this invention exhibit excellent resistance to H2S corrosion and pitting corrosion, enabling them to serve in deep-sea environments for extended periods.

[0057] 4) Mechanical property testing

[0058] The mechanical properties of the bars obtained in Examples 1-2 above were tested and compared with those in Example 1 (Comparative Example 1) and Example 2 (Comparative Example 2) of patent document CN103614631A. The results are shown in Table 2.

[0059] Table 2:

[0060] As can be seen from Table 2, the performance of the stainless steel bar obtained by the manufacturing method of the present invention fully meets the design requirements of the perforation gun, and its performance is superior to that of the prior art.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for manufacturing a stainless steel bar for a perforating gun, characterized in that, include: S1. Smelting to obtain steel ingots with the target chemical composition; S2. Form the steel ingot into bars; S3. Perform austenitizing heat treatment on the bar stock; S4. After austenitization, the bar is water-quenched and then air-cooled. During the water quenching process, it is straightened by rotation. After one tempering, it is hot-straightened and then tempered a second time to obtain stainless steel bar for perforating guns. The stainless steel bar has the following chemical composition by mass percentage: C: 0-0.03%, Si: 0-1.00%, Mn: 0-1.00%, P: 0-0.02%, S: 0-0.002%, Ni: 4.0-7.0%, Cr: 11.0-14.0%, Mo: 1.5-3.0%, Ti: 0-0.01%, V: 0-0.50%, Cu: 0-0.50%, N: 0.07-0.11%, and the balance Fe; the stainless steel bar has a pitting corrosion resistance PREN ≥ 19.

2. The manufacturing method as described in claim 1, characterized in that, In step S4, the transfer time of the austenitized bar into the quenching process is ≤1 min; and / or, the water temperature of the bar after water quenching is ≤50℃.

3. The manufacturing method as described in claim 1, characterized in that, In step S4, the temperature of the first tempering is 500-590℃, and the holding time is (3h / 100mm) D)-(4h / 100mm) (D+5h), the temperature of the second tempering is 10-50℃ lower than the temperature of the first tempering, and the holding time is (4h / 100mm). D) - (3h / 100mm) (D+5h), where h represents hours and D is the diameter value in millimeters.

4. The manufacturing method as described in claim 1, characterized in that, In step S4, the straightness of the generatrix of the stainless steel bar used for the perforating gun is ≤1mm per meter and ≤2.5mm over the entire length.

5. The manufacturing method as described in claim 1, characterized in that, In step S3, the austenitizing heat treatment temperature is 920-960℃, and the holding time is (2h / 100mm) D) - (2h / 100mm) (D+5h), where h represents hours and D represents the diameter value in millimeters.

6. The manufacturing method as described in claim 1, characterized in that, In step S2, the steel ingot is heated to 1150-1230℃ during the forming process, and / or the forming compression ratio is ≥5:1, and / or the forming endpoint temperature is ≥850℃.

7. The manufacturing method as described in claim 6, characterized in that, The forming process can be either forging or rolling.

8. The manufacturing method as described in claim 1, characterized in that, In step S1, the smelting process is as follows: first, electric furnace smelting is carried out, then oxygen blowing decarburization is carried out in sequence, followed by secondary refining and vacuum degassing before casting.

9. The manufacturing method as claimed in claim 8, characterized in that, The oxygen blowing decarburization uses argon-oxygen decarburization or vacuum oxygen decarburization; and / or, the casting temperature is 40-65°C above the liquidus line.

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