Hydrogen sulfide corrosion resistant gas cylinder steel pipe and preparation process thereof

Abstract

The invention relates to the technical field of metal materials, and discloses a hydrogen sulfide corrosion resistant gas cylinder steel pipe and a preparation process thereof. The hydrogen sulfide corrosion resistant gas cylinder steel pipe comprises the following components in percentage by mass: 0.32 to 0.36 percent of C, 0.20 to 0.35 percent of Si, 0.70 to 0.85 percent of Mn, 0.80 to 1.10 percent of Cr, 0.15 to 0.25 percent of Mo, less than or equal to 0.010 percent of P, less than or equal to 0.0050 percent of S, 0.020 to 0.045 percent of Al, 0.02 to 0.04 percent of V and 0.0005 to 0.0015 percent of B. And the balance of Fe and inevitable impurities. The steel pipe has high sulfide stress corrosion resistance.

Description

Technical Field

[0001] The invention relates to the technical field of metal materials, in particular to a hydrogen sulfide corrosion resistant gas cylinder steel pipe and a preparation process thereof. Background Art

[0002] With the development of the national economy and the formulation and implementation of low-carbon environmental protection by the country, a new development trend has been formed in the field of automobile energy, that is, using liquefied natural gas instead of traditional gasoline and diesel as a power source. Liquefied natural gas (LNG), whose main component is methane, is recognized as the cleanest fossil energy on the earth. It is colorless, odorless, non-toxic and non-corrosive. Its volume is about 1 / 625 of the volume of the same amount of gaseous natural gas, and the mass of liquefied natural gas is only about 45% of the same volume of water. Its manufacturing process is to purify the natural gas produced by the gas field first, and then transport it by liquefied natural gas ship after a series of ultra-low temperature liquefaction. After burning, liquefied natural gas causes very little air pollution and releases a lot of heat, so liquefied natural gas is a relatively advanced energy source.

[0003] Natural gas is a general term for a mixture of hydrocarbons that exists in underground rock reservoirs, of which methane accounts for the vast majority, with a small amount of ethane, propane and butane. Its specific gravity is about 0.65, which is lighter than air and has the characteristics of being colorless, odorless and non-toxic. Natural gas is one of the safer fuels. It does not contain carbon monoxide and is lighter than air. Once leaked, it will immediately spread upwards and is not easy to accumulate to form explosive gas. It is relatively safe. Using natural gas as an energy source can reduce the use of coal and oil, thus greatly improving environmental pollution problems; as a clean energy source, natural gas does not produce dust and solid particles, can reduce sulfur dioxide and dust emissions by nearly 100%, reduce carbon dioxide emissions by 60% and nitrogen oxide emissions by 50%, and help reduce acid rain formation, alleviate the global greenhouse effect, and fundamentally improve environmental quality. It is also the only energy source that can replace oil and coal in power generation, heating, and civil use.

[0004] There is a small amount of hydrogen sulfide, i.e. water, remaining in liquefied natural gas. Under the filling pressure (20MPa) or bearing pressure, the gas cylinder may form sulfide stress corrosion cracking, causing safety accidents. Figure 1 Therefore, it is necessary to develop a gas cylinder tube resistant to hydrogen sulfide stress corrosion for use in vehicle-mounted gas cylinders.

[0005] The wall thickness of gas cylinders made of existing steel grades 4130X and 30CrMo often exceeds 20mm, which seriously affects the loading capacity of gas cylinders; and because sulfides are not effectively controlled, the corrosion resistance is poor. This requires the development of a high-strength, high-toughness, high-purity steel for hydrogen sulfide corrosion resistance. The material's resistance to hydrogen sulfide stress fracture is mainly related to the material's grain boundary strength, so alloy elements such as Cr, Mo, Nb, Ti, and Cu are often added to refine the original austenite grain size. After quenching, the ultrafine-grained original austenite forms ultrafine-grained ferrite and well-distributed ultrafine carbide structure, which is the most effective way to develop high-strength steel resistant to sulfide stress corrosion. Use pure steel with very low content of harmful elements H, O, N, As, Sn, Pb, Sb, and Bi; design good hardenability and uniform and fine tempering structure, and minimize performance fluctuations; reduce the S content in the steel as much as possible, reduce sulfide inclusions, and prevent stress corrosion.

[0006] Ordinary gas cylinder tubes have the following problems:

[0007] 1. Conventional gas cylinder pipe steel does not have the ability to resist hydrogen sulfide stress corrosion;

[0008] 2. For steel cylinders with tensile strength greater than 880MPa after quenching and tempering heat treatment, sulfide stress corrosion test shall be carried out in accordance with Appendix A of GB / T17258 "Compressed Natural Gas Cylinders for Automobiles". Only stress corrosion test under tensile stress of 60% of the designed minimum yield strength of the steel cylinder can be passed.

[0009] Therefore, it is necessary to develop a hydrogen sulfide stress corrosion resistant gas cylinder tube for the production of compressed natural gas cylinders for automobiles. Summary of the invention

[0010] The object of the present invention is to provide a hydrogen sulfide corrosion resistant gas cylinder steel pipe and a preparation process thereof, so as to solve the problems raised in the above background technology.

[0011] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0012] A hydrogen sulfide corrosion resistant gas cylinder steel pipe, the components of the hydrogen sulfide corrosion resistant gas cylinder steel pipe include, by mass percentage, C: 0.32-0.36%, Si: 0.20-0.35%, Mn: 0.70-0.85%, Cr: 0.80-1.10%, Mo: 0.15-0.25%, P≤0.010%, S≤0.0050%, Al: 0.020-0.045%, V: 0.02-0.04%, B: 0.0005-0.0015%, and the balance is Fe and unavoidable impurities.

[0013] Furthermore, the components of the hydrogen sulfide corrosion-resistant gas cylinder steel pipe include, by mass percentage, C: 0.32-0.36%, Si: 0.20-0.35%, Mn: 0.70-0.85%, Cr: 0.80-1.10%, Mo: 0.15-0.25%, P≤0.008%, S≤0.0012%, Al: 0.020-0.045%, V: 0.02-0.04%, B: 0.0005-0.0015%, As≤0.005%, Sn≤0.005%, Sb≤0.005%, Pb≤0.005%, Bi≤0.005%, and the sum of the mass percentages of As, Sn, Sb, Pb, and Bi is ≤0.020%, and the balance is Fe and unavoidable impurities.

[0014] Control the composition range and function of each element;

[0015] C: 0.32-0.36%. The reason is that C ensures the strength of the steel, improves the hardenability and thus increases the percentage of martensitic transformation. In addition, increasing the C content can increase the number of carbides precipitated during tempering, and these carbides are good H traps. However, too high a C content will not only cause segregation itself, but will also greatly increase the segregation of Mn and P, thereby reducing the SSC resistance.

[0016] Si: 0.20-0.35%. The reason is that Si is an effective deoxidizer and improves tempering resistance. However, Si is an element that strongly promotes graphitization, which is not conducive to the organization that hopes to obtain a large amount of carbide precipitation. Therefore, Si should be kept as small as possible.

[0017] Mn: 0.70~0.85%. The reason is that Mn improves the strength and hardenability of steel, but Mn is an element that is easy to segregate. When Mn is greater than 1.0%, it is easy to segregate with S and P at the grain boundary, so it is not good for anti-SSC performance.

[0018] S: ≤0.0012%, because S is easy to segregate elements at the grain boundaries, causing intergranular cracking; in addition, MnS inclusions are formed, which is not good for SSC, so the less the better.

[0019] P: ≤0.008%, because it is easy to segregate elements at the grain boundary and cause cold cracking, the less the better. In addition, it is reported that P is a hydrogen absorption promoter, which can block hydrogen atoms from synthesizing molecules, thereby increasing the degree of hydrogen permeation.

[0020] Cr: 0.80-1.10%, because Cr is a strong element that prevents bainite transformation during quenching, and can effectively improve the hardenability of steel. It has resistance to temper softening, can improve the mechanical strength of steel, and reduce the corrosion rate of steel. However, excessive Cr content can lead to the formation of coarse chromium carbide precipitation at the grain boundary, reducing SSC resistance and toughness.

[0021] Mo: 0.15-0.25%, because Mo has better hydrogen resistance than Cr, and it can also reduce the absorption and penetration of hydrogen in steel, and improve the hardenability of steel; in addition, Mo can also reduce the segregation of P at the grain boundary by reducing the diffusion coefficient of P. However, when Mo is too much, larger M2C carbides are likely to appear, which is not conducive to the anti-SSC performance.

[0022] V: 0.02-0.04%, because a small amount of V element can refine the grains of steel, increase the impact toughness, and improve the tempering strength of steel. On the other hand, if the content is too high, the aggregated carbides will precipitate, which will reduce the strength and room temperature impact toughness, causing large fluctuations in mechanical properties.

[0023] B: 0.0005~0.0015%. The reason is that a trace amount of B can significantly improve the hardenability of steel without increasing the quenching crack sensitivity of steel (i.e., without reducing the Ms point of steel), which is very beneficial for thick-walled steel pipes. However, too high B content will promote the production of coarse Fe2B and Mo2B, which will damage the steel's anti-SSC performance.

[0024] Five harmful elements (As≤0.005%, Sn≤0.005%, Sb≤0.005%, Pb≤0.005%, Bi≤0.005%, and the sum of the five ≤0.020%). Reducing the content of the five harmful elements can significantly improve the steel's resistance to sulfide stress corrosion.

[0025] Furthermore, the production specification range of the hydrogen sulfide corrosion resistant gas cylinder steel pipe is 114-279mm in outer diameter and 4.5-16mm in wall thickness.

[0026] Furthermore, the hydrogen sulfide corrosion resistant gas cylinder steel pipe adopts CrMo series steel, and the metallographic structure is tempered troostite after modulated heat treatment.

[0027] Furthermore, the tensile strength of the hydrogen sulfide corrosion-resistant gas cylinder steel pipe after heat treatment is greater than 880MPa, the yield strength is greater than or equal to 735MPa, and the elongation is greater than or equal to 15%.

[0028] A preparation process for a hydrogen sulfide corrosion-resistant gas cylinder steel pipe comprises the following steps:

[0029] S1: Billet smelting: KR desulfurization, basic oxygen converter smelting, LF refining, vacuum degassing, CCM continuous casting operations are carried out in sequence to obtain billets;

[0030] S2: Steel pipe rolling: The billet is sawed, heated in a ring furnace, punched, continuously rolled, sizing, flaw detection, manual inspection, ultrasonic flaw detection, spray marking and packaging are carried out in sequence to obtain a hydrogen sulfide corrosion resistant gas cylinder steel pipe.

[0031] Furthermore, the specific steps of KR desulfurization include stirring molten iron in a ladle to form a vortex, adding a homemade desulfurizer into the vortex to allow the desulfurizer to fully react with the sulfur in the molten iron, and then removing the desulfurization product by thoroughly skimming off the slag to reduce the S content of the molten iron, thereby ensuring that the S content of the molten iron after desulfurization is ≤0.0015%.

[0032] Furthermore, the specific steps of the converter smelting include smelting in a top and bottom double-blown converter, using molten iron and high-quality scrap steel as raw materials for primary smelting to achieve pre-P removal, adding lime, synthetic refined slag and a variety of high-purity alloys for pre-deoxidation and initial adjustment of composition before steelmaking, and using slag cones and slide plates for composite slag blocking to ensure slag-free steelmaking and prevent P return.

[0033] Furthermore, the specific steps of the LF refining outside the furnace include: deep deoxidation and alloying of molten steel in the LF furnace to produce basicity refining slag; controlling the ratio of lime to refining slag, stirring the whole refining process, large stirring in the early stage of refining, strengthening desulfurization and removing inclusions through slag reaction; and using weak stirring in the later stage of refining to prevent secondary oxidation of molten steel.

[0034] Furthermore, the specific steps of vacuum degassing include: after LF refining, using RH cycle degassing equipment to perform vacuum degassing and remove inclusions, maintaining it under a high vacuum of <100Pa for 30-35 minutes, ensuring that H≤0.000012%, O≤0.0008%, N≤0.0030%, and all components are within the required internal control range.

[0035] Furthermore, the specific steps of the CCM continuous casting include: using a large round billet continuous casting machine, using a protective slag automatic baking and automatic adding device to ensure uniform and timely addition, and implementing full-process full-protection casting to produce continuous casting round billets; using a M-EMS+S-EMS+F-EMS three-stage electromagnetic stirring device to fully and evenly organize the structure.

[0036] Furthermore, the specific steps of the billet sawing include: calculating the billet length according to the billet outer diameter, head and tail cutting rate, finished steel pipe specifications, dimensional tolerance and hot rolling multiples, and sawing the billet into corresponding lengths. Using equipment with an automatic centering device to perform tail heat centering to improve the uniformity of the wall thickness of the tail of the gas cylinder tube.

[0037] Furthermore, the specific steps of ring furnace heating include: formulating a scientific heating system based on the chemical composition of the steel type, using circulating pulse burners and automatic temperature measurement and control systems in the heating section and soaking section to accurately control the heating temperature of the billet in each zone.

[0038] Furthermore, the specific steps of perforation, rolling and sizing include: optimizing the distribution of perforation and rolling deformation to avoid defects such as internal and external folds and iron ears during the perforation process. It is equipped with advanced continuous rolling process monitoring system (PSS), continuous rolling automatic roll gap control system (HGS), and sizing machine process auxiliary design (CARTA-SM). After continuous rolling and sizing processes, the steel pipe obtains the optimal outer diameter and wall thickness, and the wall thickness tolerance of steel pipes of specific specifications can be close to ±8%

[0039] Furthermore, the preparation process of the hydrogen sulfide corrosion resistant gas cylinder steel pipe further comprises the following steps:

[0040] S1: Billet smelting: KR desulfurization, basic oxygen converter smelting, LF refining, vacuum degassing, CCM continuous casting operations are carried out in sequence to obtain billets;

[0041] S2: Steel pipe rolling: billet sawing, ring furnace heating, perforation, continuous rolling, sizing, low-temperature oxynitriding, micro-arc oxidation, flaw detection, manual inspection, ultrasonic flaw detection, spray marking and packaging are carried out in sequence to obtain hydrogen sulfide corrosion resistant gas cylinder steel pipe.

[0042] Furthermore, the specific steps of the low-temperature oxynitriding include preheating the mixed inorganic salt to 430-440°C, grinding the surface of the sized steel pipe with sandpaper, washing, and drying, immersing it in the molten mixed inorganic salt for 8-8.5 hours, taking it out, cooling it to room temperature, washing, and drying; the components of the mixed inorganic salt include, by mass percentage, 5-55% sodium cyanate, 10-55% potassium cyanate, 5-15% potassium carbonate, 5-15% sodium carbonate, 1-15% lithium carbonate, 3-20% sodium chloride, and 3-20% potassium chloride.

[0043] Furthermore, the specific steps of the micro-arc oxidation include embedding an aluminum impregnant on the surface of a steel pipe that has completed low-temperature oxynitridation, heating to 530-540°C to encapsulate a FeAl coating on the surface, and connecting a micro-arc oxidation device with a FeAl coated steel pipe using a copper wire to prepare a ceramic coating; the components of the aluminum impregnant include, by mass percentage, 8-10% aluminum powder, 1% aluminum chloride, and 89-91% aluminum oxide; the micro-arc oxidation parameters include, an anode current of 0.5-4.6A / cm 2 , the pulse frequency is 980-1000Hz, the reaction time is 10-12min, and the electrolyte is composed of 10g / L sodium aluminate, 1.5g / L sodium dihydrogen phosphate, and 1.5g / L sodium tungstate.

[0044] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0045] ① The unique chemical composition design of the present invention and the low S and P composition design significantly improve the sulfide stress corrosion resistance of the steel.

[0046] ② The present invention designs a new type of steel. After the steel pipe of this type of steel is subjected to modulated heat treatment, the tensile strength is greater than 880MPa, and the steel has high resistance to sulfide stress corrosion.

[0047] ③ The loading ratio of the sulfide stress corrosion resistance evaluation test of the steel pipe prepared by the present invention is increased from the minimum yield strength*60% of the designed minimum yield strength of the steel cylinder to the minimum yield strength*80%.

[0048] ④ Based on the unique chemical composition design, the present invention uses low-temperature oxynitriding technology to modify the surface of the steel pipe through carbonate, cyanate and chloride, and from the outside to the inside, it is dense ferroferric oxide and nitrogen-rich S phase. The low-temperature nitrogen oxidation does not precipitate nitrides at a low temperature, which prevents nitrogen atoms from being corroded during contact with hydrogen sulfide. At the same time, the continuous and dense ferroferric oxide film prevents sulfur-containing corrosive media (H 2 S,HS - ,S 2- ) is in direct contact with the substrate, slowing down the diffusion rate of the corrosive ion phase matrix and improving the corrosion resistance; the low-temperature oxynitriding technology infiltrates interstitial atoms into the metal surface to form a supersaturated solid solution. When these vacancies are filled with interstitial atoms and huge residual compressive stress is established on the surface, the transmission vacancies of free ions / atoms are reduced. Therefore, the movement of ions / atoms through the low-temperature oxynitriding surface film is restricted, thereby improving the corrosion resistance of the material. The S phase is continuously consumed by the corrosive medium. The active nitrogen atoms in the layer, a single NH 4 + The formation of S phase reduces the nitrogen concentration near the surface, but does not destroy the integrity of the device. The reason is that the S phase contains a large amount of nitrogen-supersaturated dissolved solids, dislocations, stacking faults and twins, which further improves the corrosion resistance.

[0049] ⑤ Based on low-temperature oxynitriding, the present invention utilizes the outer layer of ferroferric oxide film to jointly treat low-temperature aluminizing and micro-arc oxidation to prepare a corrosion-resistant FeAl / aluminum oxide double coating. Compared with the traditional hydrogen sulfide corrosion-resistant inorganic coating, it coexists with the low-temperature oxynitriding coating, and the two are closely combined at the fingertips, further enhancing the hydrogen sulfide corrosion resistance of the steel pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0051] Figure 1 This is a tensile specimen diagram of the sulfide stress corrosion test of the present invention;

[0052] Figure 2 This is a diagram after the sulfide stress corrosion test of the present invention. DETAILED DESCRIPTION

[0053] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] In the following examples, all raw materials are commercially available.

[0055] Example 1: A process for preparing a steel tube for a gas cylinder resistant to hydrogen sulfide corrosion: S1: steel billet smelting: sequentially performing KR desulfurization, basic oxygen converter smelting, LF refining outside the furnace, vacuum degassing, and CCM continuous casting operations to obtain a steel billet;

[0056] S2: Steel pipe rolling: The billet is sawed, heated in a ring furnace, punched, continuously rolled, sizing, flaw detection, manual inspection, ultrasonic flaw detection, spray marking and packaging are carried out in sequence to obtain a hydrogen sulfide corrosion resistant gas cylinder steel pipe.

[0057] Example 2: A process for preparing a steel tube for a gas cylinder resistant to hydrogen sulfide corrosion: S1: steel billet smelting: sequentially performing KR desulfurization, basic oxygen converter smelting, LF refining outside the furnace, vacuum degassing, and CCM continuous casting operations to obtain a steel billet;

[0058] S2: Steel pipe rolling: billet sawing, ring furnace heating, perforation, continuous rolling, sizing, low-temperature oxynitriding, micro-arc oxidation, flaw detection, manual inspection, ultrasonic flaw detection, spray marking and packaging are carried out in sequence to obtain hydrogen sulfide corrosion resistant gas cylinder steel pipe.

[0059] The specific steps of the low-temperature oxynitriding include preheating the mixed inorganic salt to 430° C., grinding the surface of the sized steel pipe with sandpaper, washing, and drying, immersing it in the molten mixed inorganic salt for 8 hours, taking it out, cooling it to room temperature, washing, and drying; the components of the mixed inorganic salt include, by mass percentage, 27% sodium cyanate, 28% potassium cyanate, 5% potassium carbonate, 10% sodium carbonate, 10% lithium carbonate, 10% sodium chloride, and 10% potassium chloride.

[0060] The specific steps of the micro-arc oxidation include embedding an aluminum impregnant on the surface of a steel pipe that has been subjected to low-temperature oxynitridation, heating to 530°C to encapsulate a FeAl coating on the surface, and connecting a micro-arc oxidation device with a FeAl coated steel pipe using a copper wire to prepare a ceramic coating; the components of the aluminum impregnant include, by mass percentage, 8% aluminum powder, 1% aluminum chloride, and 91% aluminum oxide; the micro-arc oxidation parameters include an anode current of 2.0 A / cm 2 , the pulse frequency is 1000 Hz, the reaction time is 10 min, and the electrolyte consists of 10 g / L sodium aluminate, 1.5 g / L sodium dihydrogen phosphate, and 1.5 g / L sodium tungstate.

[0061] Comparative Example 1: A process for preparing a steel tube for gas cylinders resistant to hydrogen sulfide corrosion: S1: Steel billet smelting: KR desulfurization, basic oxygen converter smelting, LF refining outside the furnace, vacuum degassing, and CCM continuous casting are sequentially performed to obtain a steel billet;

[0062] S2: Steel pipe rolling: The billet is sawed, heated in a ring furnace, punched, continuously rolled, sizing, flaw detection, manual inspection, ultrasonic flaw detection, spray marking and packaging are carried out in sequence to obtain a hydrogen sulfide corrosion resistant gas cylinder steel pipe.

[0063] Comparative Example 2: A process for preparing a steel tube for gas cylinders resistant to hydrogen sulfide corrosion: S1: steel billet smelting: sequentially performing KR desulfurization, basic oxygen converter smelting, LF refining outside the furnace, vacuum degassing, and CCM continuous casting operations to obtain a steel billet;

[0064] S2: Steel pipe rolling: The billet is sawed, heated in a ring furnace, punched, continuously rolled, sizing, flaw detection, manual inspection, ultrasonic flaw detection, spray marking and packaging are carried out in sequence to obtain a hydrogen sulfide corrosion resistant gas cylinder steel pipe.

[0065] Comparative Example 3: A process for preparing a steel tube for gas cylinders resistant to hydrogen sulfide corrosion: S1: steel billet smelting: sequentially performing KR desulfurization, basic oxygen converter smelting, LF refining outside the furnace, vacuum degassing, and CCM continuous casting operations to obtain a steel billet;

[0066] S2: Steel pipe rolling: billet sawing, ring furnace heating, perforation, continuous rolling, sizing, micro-arc oxidation, low-temperature oxynitriding, flaw detection, manual inspection, ultrasonic flaw detection, spray marking and packaging are carried out in sequence to obtain hydrogen sulfide corrosion resistant gas cylinder steel pipe.

[0067] The remaining steps are the same as those in Example 2.

[0068] Experiment: Sulfide stress corrosion evaluation test was carried out according to Appendix A of GB / T 17258 "Vehicle-mounted compressed natural gas cylinders". Test solution: 0.5% (mass fraction) sodium acetate trihydrate (CH 3 COONa•3H 2 O), use acetic acid to adjust the initial pH of the acidic buffer solution to 4.0. The test solution should be continuously saturated with hydrogen sulfide test gas (mixed with nitrogen) at a partial pressure of 0.414MPa at room temperature. The evaluation test loading ratio is the minimum yield strength of the gas cylinder design * 80% (stricter than the 60% required by the steel cylinder design standard). The evaluation test cycle is 144h. The experimental data are shown in Table 2.

[0069] The wt% of each element composition of Examples 1-2 and Comparative Examples 1-3 are shown in Table 1.

[0070] Table 1 Element composition of experimental part

[0071] element C Si Mn P≤ S≤ (P+S)≤ Cr Mo Al Comparative Example 1 0.28 0.25 0.60 0.015 0.010 0.020 1.0 0.09 0.04 Comparative Example 2 0.36 0.25 0.85 0.010 0.005 0.020 0.8 0.20 0.04 Example 1 0.35 0.28 0.8 0.008 0.0012 0.020 1.0 0.25 0.04 Example 2 0.36 0.30 0.8 0.008 0.0010 0.020 1.1 0.22 0.03 Comparative Example 3 0.36 0.30 0.8 0.008 0.0010 0.020 1.1 0.22 0.03 element V B Comparative Example 1 / / Comparative Example 2 0.03 / Example 1 0.04 0.001 Example 2 0.02 0.0015 Comparative Example 3 0.02 0.0015 Table 2 Steel pipe corrosion resistance data

[0072] Conclusion: The steel pipe prepared by the present invention has excellent resistance to hydrogen sulfide corrosion.

[0073] The P and S elements in Comparative Examples 1 and 2 are not as unique as those in the most preferred design of the present invention, and their excessive contents reduce the corrosion resistance. In Comparative Example 3, the low-temperature oxynitridation and micro-arc oxidation steps are exchanged, the coating is easy to fall off, and the corrosion resistance is reduced.

[0074] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation process for a hydrogen sulfide corrosion resistant gas cylinder steel pipe, characterized in that: The following steps are involved: S1: Billet smelting: KR desulfurization, basic oxygen converter smelting, LF refining, vacuum degassing, CCM continuous casting operations are carried out in sequence to obtain billets; S2: Steel pipe rolling: billet sawing, ring furnace heating, perforation, continuous rolling, sizing, low-temperature oxynitriding, micro-arc oxidation, flaw detection, manual inspection, ultrasonic flaw detection, spray marking and packaging are carried out in sequence to obtain hydrogen sulfide corrosion resistant gas cylinder steel pipe.

2. The process for preparing a hydrogen sulfide corrosion resistant gas cylinder steel pipe according to claim 1, characterized in that: The specific steps of the KR desulfurization include stirring molten iron in a ladle to form a vortex, adding a desulfurizer into the vortex to allow the desulfurizer to fully react with sulfur in the molten iron, and then removing the desulfurization product by thoroughly skimming off the slag; The specific steps of converter smelting include: smelting in a top and bottom double-blown converter, using molten iron and scrap steel as raw materials for primary smelting, adding lime, synthetic refining slag and high-purity alloy to the steel for pre-deoxidation and initial adjustment of composition; the specific steps of LF off-furnace refining include: deep deoxidation and alloying of molten steel in an LF furnace to make basicity refining slag; stirring throughout the refining process to control the ratio of lime to refining slag; the specific steps of vacuum degassing include: after LF refining, using RH circulating degassing equipment for vacuum degassing and inclusion removal treatment, maintaining at a high vacuum of <100Pa for 30-35 minutes, ensuring that H≤0.000012%, O≤0.0008%, and N≤0.0030%.

3. The process for preparing a hydrogen sulfide corrosion resistant gas cylinder steel pipe according to claim 1, characterized in that: The specific steps of the low-temperature oxynitriding include preheating the mixed inorganic salt to 430-440° C., grinding the surface of the sized steel pipe with sandpaper, washing, and drying, immersing it in the molten mixed inorganic salt for 8-8.5 hours, taking it out, cooling it to room temperature, washing, and drying; the components of the mixed inorganic salt include, by mass percentage, 5-55% sodium cyanate, 10-55% potassium cyanate, 5-15% potassium carbonate, 5-15% sodium carbonate, 1-15% lithium carbonate, 3-20% sodium chloride, and 3-20% potassium chloride.

4. The process for preparing a hydrogen sulfide corrosion resistant gas cylinder steel pipe according to claim 1, characterized in that: The specific steps of the micro-arc oxidation include embedding an aluminum penetrant on the surface of a steel pipe that has undergone low-temperature oxynitriding, heating to 530-540° C. to encapsulate a FeAl coating on the surface, and connecting a micro-arc oxidation device with the FeAl coated steel pipe using a copper wire to prepare a ceramic coating; the components of the aluminum penetrant include, by mass percentage, 8-10% aluminum powder, 1% aluminum chloride, and 89-91% aluminum oxide.

5. The process for preparing a hydrogen sulfide corrosion resistant gas cylinder steel pipe according to claim 4, characterized in that: The micro-arc oxidation parameters include: anode current 0.5-4.6A / cm 2 , the pulse frequency is 980-1000Hz, the reaction time is 10-12min, and the electrolyte is composed of 10g / L sodium aluminate, 1.5g / L sodium dihydrogen phosphate, and 1.5g / L sodium tungstate.

6. The hydrogen sulfide corrosion resistant gas cylinder steel pipe prepared by the preparation process of the hydrogen sulfide corrosion resistant gas cylinder steel pipe according to claims 1-5 is characterized in that: The components of the hydrogen sulfide corrosion resistant gas cylinder steel pipe include, by mass percentage, C: 0.32-0.36%, Si: 0.20-0.35%, Mn: 0.70-0.85%, Cr: 0.80-1.10%, Mo: 0.15-0.25%, P≤0.010%, S≤0.0050%, Al: 0.020-0.045%, V: 0.02-0.04%, B: 0.0005-0.0015%, and the balance is Fe and unavoidable impurities.

7. The hydrogen sulfide corrosion resistant gas cylinder steel pipe according to claim 6, characterized in that: The components of the hydrogen sulfide corrosion resistant gas cylinder steel pipe include, by mass percentage, C: 0.32-0.36%, Si: 0.20-0.35%, Mn: 0.70-0.85%, Cr: 0.80-1.10%, Mo: 0.15-0.25%, P≤0.008%, S≤0.0012%, Al: 0.020-0.045%, V: 0.02-0.04%, B: 0.0005-0.0015%, As≤0.005%, Sn≤0.005%, Sb≤0.005%, Pb≤0.005%, Bi≤0.005%, and the sum of the mass percentages of As, Sn, Sb, Pb and Bi is ≤0.020%, and the balance is Fe and unavoidable impurities.

8. The hydrogen sulfide corrosion resistant gas cylinder steel pipe according to claim 6, characterized in that: The production specification range of the hydrogen sulfide corrosion resistant gas cylinder steel pipe is 114-279mm in outer diameter and 4.5-16mm in wall thickness.

9. The hydrogen sulfide corrosion resistant gas cylinder steel pipe according to claim 6, characterized in that: The hydrogen sulfide corrosion resistant gas cylinder steel pipe adopts CrMo series steel, and the metallographic structure is tempered troostite after modulated heat treatment.

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