X65 hydrogen transmission pipeline steel low-hydrogen embrittlement sensitivity welding joint and control method

Abstract

The invention discloses an X65 hydrogen transmission pipeline steel low-hydrogen embrittlement sensitivity welded joint which comprises the following chemical components of base metal in percentage by mass: 0.02-0.045% of C, 0.12-0.20% of Si, 0.70-1.30% of Mn, less than or equal to 0.010% of P, less than or equal to 0.0008% of S, 0.10-0.30% of Ni, 0.20-0.35% of Cr, 0.10-0.20% of Cu, 0.03-0.05% of Nb, 0.010-0.10% of Mo, 0.035-0.06% of V, 0.01-0.02% of Ti and the balance of Fe and inevitable impurities, meanwhile, through regulation and control of microalloy elements of the base metal and matching of a straight seam double-face submerged arc welding process, the welded joint has high strength and high toughness, and the welded joint has high hydrogen The X65-grade pipeline steel has the outstanding advantage of low hydrogen embrittlement sensitivity while the mechanical property requirement of the X65-grade pipeline steel is met, and the technical problems in the research and development process of materials for the hydrogen transmission pipeline steel are solved.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and relates to a low-hydrogen embrittlement sensitive welded joint for X65 hydrogen pipeline steel and a control method thereof. Background Technology

[0002] Hydrogen, with its clean, zero-carbon, high energy density, and cross-scenario adaptability, has become a key link connecting renewable energy and end-use energy. However, in its "production-storage-transmission-use" chain, long-distance, large-scale storage and transportation have always been a bottleneck in terms of cost and efficiency. Pipeline hydrogen transportation, with its advantages of low cost, low loss, and high stability, precisely meets the demand for large-scale hydrogen energy transportation. The combination of the two allows "green hydrogen" produced from renewable energy sources such as photovoltaics and wind power to overcome geographical limitations and be efficiently transported through pipelines to large users such as hydrogen steel mills and hydrogen refueling station clusters thousands of miles away. At the same time, the low-cost operation characteristics of pipelines can reduce the cost of hydrogen energy end-use applications. Pipeline hydrogen transportation promotes the popularization of hydrogen energy in transportation, industry, and other fields. This synergistic model of "hydrogen energy providing zero-carbon energy value and pipeline hydrogen transportation ensuring large-scale implementation" ultimately builds a complete zero-carbon chain of "renewable energy hydrogen production - pipeline hydrogen transportation - multi-scenario hydrogen use," becoming a core force supporting the "dual carbon" goal and reconstructing the energy system.

[0003] However, under pressure and flow, hydrogen in hydrogen pipelines dissociates into H atoms through adsorption and desorption processes on the pipeline steel surface. Due to their unique property of having the smallest atomic radius, hydrogen atoms can penetrate micron- to submicron-level defects on the steel surface and be captured by crystal defects such as dislocations and vacancies. The captured hydrogen undergoes thermodynamic desorption and migrates directionally along defect channels such as grain boundaries / phase boundaries. In this situation, under the presence of external stresses—which may originate from residual stress, localized plastic deformation, micropore accumulation, and microcrack propagation—microstructures can form within the steel. Hydrogen permeation-induced material property degradation manifests as deterioration of key mechanical properties in the pipeline steel, leading to a significant reduction in service life. However, in practical engineering applications, hydrogen pipeline steel still requires welded pipe fabrication. During welding, the material is subjected to different thermal cycles, resulting in significant inhomogeneity in the microstructure of the weld joint. Especially in hydrogen-rich environments, the weld joint becomes the most susceptible location for hydrogen embrittlement.

[0004] Existing technologies cannot adequately solve the aforementioned technical problems. For example, invention CN117900693A discloses a welding wire, manufacturing method, and welding process for submerged arc welding of hydrogen-resistant pipeline steel; however, this invention does not involve a method for controlling the welded joints of hydrogen-resistant pipeline steel. Invention CN118848331A discloses a welding structure and method for circumferential welds in hydrogen transmission pipelines; this invention does not mention a method for controlling the submerged arc welding of hydrogen transmission pipeline welds. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a low hydrogen embrittlement sensitive welded joint for X65 hydrogen pipeline steel and a control method thereof.

[0006] To solve the above technical problems, the technical solution of the present invention is as follows: A low-hydrogen embrittlement-sensitive welded joint of X65 hydrogen pipeline steel, with the following base metal chemical composition by mass percentage: C: 0.02~0.045%, Si: 0.12~0.20%, Mn: 0.70~1.30%, P≤0.010%, S≤0.0008%, Ni: 0.10~0.30%, Cr: 0.20~0.35%, Cu: 0.10~0.20%, Nb: 0.03~0.05%, Mo: 0.010~0.10%, V: 0.035~0.06%, Ti: 0.01~0.02%, with the balance being Fe and unavoidable impurities.

[0007] The specific principles behind the addition of the above chemical elements are as follows: Carbon (C): The main element affecting the toughness, hardness, strength and weldability of pipeline steel. It can improve the tensile strength and yield strength of steel through solid solution strengthening. As the C content increases, the toughness, ductility and weldability of steel decrease, and the resistance to HIC and SSCC decreases. Therefore, the C content in this invention is 0.02 to 0.045%.

[0008] Manganese (Mn) is an important solid solution strengthening element in steel, which can significantly improve the strength of steel and reduce the phase transformation temperature of steel, thus balancing strength and toughness. However, excessive Mn will increase the "strain aging sensitivity" of steel, so it is limited to 0.7 to 1.3% in this invention.

[0009] Silicon (Si) is a key "pre-deoxidizer" in the smelting of hydrogen pipeline steel. It reacts with O in the steel to generate stable SiO2. It enhances the strength of steel through the "solid solution strengthening" mechanism. It can also indirectly refine the microstructure by affecting the phase transformation process of steel. However, excessive Si will significantly increase the hydrogen embrittlement sensitivity of steel and deteriorate the weldability and joint quality. Therefore, in this invention, Si is controlled at 0.12-0.20%.

[0010] Phosphorus (P) and sulfur (S): S combines with Mn to form MnS inclusions, which can also reduce the low-temperature impact toughness of pipeline steel. S is a major element affecting the HIC and SSCC properties of pipeline steel. P easily forms segregations in steel, worsening weldability, reducing the low-temperature impact toughness, and increasing the ductile-brittle transition temperature. Therefore, in this invention, P ≤ 0.010% and S ≤ 0.0008% are specified in the composition.

[0011] Niobium (Nb), vanadium (V), and titanium (Ti): ① Form fine carbonitrides that "pin" grain boundaries during steel rolling, preventing grain growth and achieving "fine-grain strengthening"; ② Delay recrystallization, allowing the steel to maintain a fine-grained structure after high-temperature rolling, reducing subsequent heat treatment costs, and improving the fatigue resistance of the steel. In this embodiment, the amount of niobium added is 0.03-0.05%, the amount of titanium added is 0.010-0.020%, and the amount of vanadium added is 0.035-0.060%.

[0012] Chromium (Cr): It can form fine carbides with carbon in steel. These carbides are highly stable and can avoid "hydrogen traps" caused by carbide precipitation, thereby reducing the risk of hydrogen-induced cracking (HIC) and stress-directed hydrogen-induced cracking (SOHIC). It can improve the pitting corrosion resistance of steel and avoid pipe wall thinning or perforation caused by local corrosion. In this invention, Cr is controlled in the range of 0.20% to 0.35%.

[0013] Molybdenum (Mo) is a key element in resisting hydrogen embrittlement. Its core functions are: ① to inhibit the coarsening of cementite (Fe3C) in steel and promote the formation of a more stable microstructure; ② to reduce the diffusion coefficient of hydrogen in steel, slow down the migration rate of hydrogen to stress concentration areas, and avoid the initiation and propagation of hydrogen embrittlement cracks. Therefore, the range of Mo should be controlled between 0.010 and 0.10%.

[0014] Nickel (Ni): It can improve the low-temperature toughness of steel and refine the grains through "solid solution strengthening" to reduce the number of hydrogen traps. Ni can increase the "hydrogen embrittlement threshold" of steel - that is, hydrogen embrittlement will only occur when the hydrogen concentration reaches a higher level, thereby broadening the safe service range of pipeline steel. The Ni content of this invention is 0.10 to 0.30%.

[0015] Copper (Cu): It can form a Cu enrichment layer on the steel surface. This enrichment layer can hinder the penetration of corrosive media and improve the stability of the passivation film. In addition, Cu can improve the steel's resistance to soil corrosion, making it especially suitable for hydrogen pipelines laid in humid, high-salt soil environments. Therefore, the Cu content is controlled in the range of 0.10~0.20%.

[0016] In a further preferred embodiment of the present invention, the non-metallic inclusions in the welded joint satisfy the following conditions: the grades of non-metallic inclusions of types A, B, C and D are all ≤1.0, and the sum of the grades of the above four types of non-metallic inclusions is ≤2.0.

[0017] In a further preferred embodiment of the present invention, the metallographic structure of the welded joint includes a weld structure, a coarse-grained heat-affected zone structure, and a fine-grained heat-affected zone structure; wherein the weld structure is composed of acicular ferrite, the coarse-grained heat-affected zone structure is composed of ferrite and granular bainite, and the fine-grained heat-affected zone structure is composed of ferrite and bainite; the grain size of the ferrite is ≥12.

[0018] In a further preferred embodiment of the present invention, the mechanical properties of the welded joint are: yield strength 460~470MPa, tensile strength 570~580MPa, and Charpy impact energy of the weld area at -20℃ 150~170J.

[0019] In a further preferred embodiment of the present invention, the hydrogen embrittlement index of the low hydrogen embrittlement sensitivity welded joint in the slow strain rate tensile test is <30% under a test pressure of 7.2 MPa.

[0020] In a further preferred embodiment of the present invention, the rolling process employs a controlled rolling and controlled cooling process, specifically: Heating stage: furnace exit temperature 1160~1200℃; Rough rolling stage: final rolling temperature ≥1000℃; Finish rolling stage: initial rolling temperature 890~910℃, final rolling temperature 810~820℃; Cooling stage: initial cooling temperature 770~790℃, cooling rate 15~20℃ / s (laminar cooling), reheating temperature 530~570℃ and prohibited from falling below 530℃. In a further preferred embodiment of the present invention, the welding process for the low hydrogen embrittlement sensitive welded joint adopts a straight seam double-sided submerged arc welding process, wherein the inner welding current is 550~1000A, the voltage is 36~42V, and the welding speed is 1.0~1.6m / min; the outer welding current is 500~1100A, the voltage is 36~42V, and the welding speed is 1.0~1.6m / min; the welding materials used are: submerged arc welding wire H65MH(II), flux SJ101MH-2, and gas shielded welding wire HSGX-6H.

[0021] The beneficial effects of this invention are: This invention ensures that the hydrogen embrittlement index of the welded joint section of the hydrogen pipeline is <30% (under a test pressure of 7.2 MPa) by strictly controlling the content of elements such as P and S and adding alloying elements such as Ni, Cr, Cu, and Nb. It also employs Ca and Mg inclusion modification technology to fully spheroidize, fine and uniform inclusions in the steel, reducing their adverse effects. In this invention, the grade of non-metallic inclusions does not exceed level 1.0, and the total grade of all inclusions does not exceed level 2.0, which significantly improves the uniformity and fatigue resistance of the material, reduces stress concentration sources, and ensures its long-term service safety in the service environment. Attached Figure Description

[0022] Figure 1 This is a microstructure diagram of the welded steel joint of the hydrogen pipeline in Example 1; Figure 2 This is a microstructure diagram of the welded steel joint of the hydrogen pipeline in Example 2; Figure 3 This is a microstructure diagram of the welded joint of pipeline steel in Comparative Example 1. Figure 4 The fracture surface morphology of the welded joint under slow strain rate tension in a nitrogen and hydrogen environment of Example 1 is shown. Figure 5 This is the fracture morphology of the welded joint under slow strain rate tension in an environment of nitrogen and hydrogen at 7.2 MPa, as described in Example 2. Figure 6 This is the fracture morphology of the welded joint under slow strain rate tension in a nitrogen and hydrogen environment, as shown in Comparative Example 1. Detailed Implementation

[0023] To make the content of this invention easier to understand, the invention will be further described in detail below based on specific embodiments.

[0024] A low-hydrogen embrittlement-sensitive welded joint of X65 hydrogen pipeline steel, with the following base metal chemical composition by mass percentage: C: 0.02~0.045%, Si: 0.12~0.20%, Mn: 0.70~1.30%, P≤0.010%, S≤0.0008%, Ni: 0.10~0.30%, Cr: 0.20~0.35%, Cu: 0.10~0.20%, Nb: 0.03~0.05%, Mo: 0.010~0.10%, V: 0.035~0.06%, Ti: 0.01~0.02%, with the balance being Fe and unavoidable impurities.

[0025] The non-metallic inclusions in the above-mentioned welded joints meet the following requirements: the grades of non-metallic inclusions of types A, B, C and D are all ≤1.0, and the sum of the grades of the above four types of non-metallic inclusions is ≤2.0.

[0026] The metallographic structure of the above-mentioned welded joint includes weld structure, coarse-grained heat-affected zone structure and fine-grained heat-affected zone structure; wherein, the weld structure is composed of acicular ferrite, the coarse-grained heat-affected zone structure is composed of ferrite and granular bainite, and the fine-grained heat-affected zone structure is composed of ferrite and bainite; the grain size of the ferrite is ≥12.

[0027] The rolling process of the above-mentioned welded joint adopts a controlled rolling and controlled cooling process, specifically as follows: Heating stage: furnace exit temperature is 1160~1200℃; Rough rolling stage: final rolling temperature ≥1000℃; Finish rolling stage: initial rolling temperature is 890~910℃, final rolling temperature is 810~820℃; Cooling stage: initial cooling temperature is 770~790℃, cooling rate is 15~20℃ / s (laminar cooling), and the reddening temperature is 530~570℃ and must not be lower than 530℃.

[0028] The welding process for the above-mentioned welded joint adopts the straight seam double-sided submerged arc welding process, wherein the inner welding current is 550~1000A, the voltage is 36~42V, and the welding speed is 1.0~1.6m / min; the outer welding current is 500~1100A, the voltage is 36~42V, and the welding speed is 1.0~1.6m / min.

[0029] Two examples and one comparative example were prepared according to the above chemical element composition and mass percentage, namely Example 1, Example 2 and the comparative example. The specific composition is shown in Table 1, the welding material and welding process parameters are shown in Table 2, the microstructure purity is shown in Table 3, and the mechanical properties are shown in Table 4.

[0030] Table 1 serial number C Si Mn Cu Ni Cr Mo Nb V Ti Example 1 0.04 0.20 1.25 0.20 0.1 0.20 0.01 0.04 0.04 0.01 Example 2 0.04 0.20 1.25 0.20 0.1 0.20 0.01 0.04 0.04 0.01 Comparative Example 1 0.06 0.20 1.55 0.02 0.01 0.17 0.001 0.04 0.004 0.01 Table 2 serial number Submerged arc welding wire flux Gas shielded welding wire Internal welding current Internal welding voltage Internal welding speed External welding current External welding voltage External welding speed Example 1 H65MH (Ⅱ) SJ101MH-2 HSGX-6H 1000 / 650 / 550 / 550A 36 / 38 / 40 / 42V 1.55 m / min 1100 / 650 / 550 / 500A 36 / 38 / 40 / 42V 1.55 m / min Example 2 H65MH (Ⅱ) SJ101MH-2 HSGX-6H 1000 / 650 / 550 / 550A 36 / 38 / 40 / 42V 1.30 m / min 1100 / 650 / 550 / 500A 36 / 38 / 40 / 42V 1.30 m / min Comparative Example 1 H65MH SJ101MH HSGX-6H 1000 / 650 / 550 / 550A 36 / 38 / 40 / 42V 1.55 m / min 1100 / 650 / 550 / 500A 36 / 38 / 40 / 42V 1.55 m / min Table 3 Table 4 As can be seen from Tables 1-4, the level of non-metallic inclusion control in Example 1 is extremely high. The sum of the fine and coarse levels of various inclusions is far below the standard upper limit. The tensile properties are excellent, with a yield strength of 470 MPa, a tensile strength of 572 MPa, an average Charpy impact energy of 157 J for the weld at -20℃, and an average Charpy impact energy of 414 J for the heat-affected zone at -20℃, demonstrating excellent low-temperature toughness. The reduction of area (RIA) of the welded joint under slow strain rate tension in a nitrogen atmosphere was 89.3%, while that under slow strain rate tension in a hydrogen atmosphere was 62.9%. According to the formula: (1) In the formula, RRA is the reduction of area and hydrogen embrittlement index, and RA is the reduction of area and hydrogen embrittlement index. N2 RA represents the reduction of area under nitrogen atmosphere. H2 The section reduction ratio is the section reduction ratio under hydrogen environment, and the hydrogen embrittlement index of the section reduction ratio is 29.6% (under a test pressure of 7.2 MPa).

[0031] The welded joint in Example 2 has a yield strength of 465 MPa and a tensile strength of 570 MPa. The average Charpy impact energy of the weld at -20℃ is 160 J, and the average Charpy impact energy of the heat-affected zone at -20℃ reaches 420 J. The reduction of area of ​​the welded joint under slow strain rate tension in a nitrogen environment was 88.7%, and the reduction of area of ​​the welded joint under slow strain rate tension in a hydrogen environment was 63.2%. According to Formula 1, the hydrogen embrittlement index of the reduction of area was 28.7% (under a test pressure of 7.2 MPa).

[0032] The welded joint in Comparative Example 1 has a yield strength of 479 MPa and a tensile strength of 598 MPa. The average Charpy impact energy of the weld at -20℃ is 144 J, and the average Charpy impact energy of the heat-affected zone at -20℃ reaches 368 J. The reduction of area of ​​the welded joint under slow strain rate tension in a nitrogen environment was 82.7%, and the reduction of area of ​​the welded joint under slow strain rate tension in a hydrogen environment was 46.2%. According to Formula 1, the hydrogen embrittlement index of the reduction of area was 44.1% (under a test pressure of 7.2 MPa).

[0033] In addition to the above embodiments, the present invention may have other implementation methods; all technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A low-hydrogen-embrittlement-sensitive welded joint made of X65 hydrogen pipeline steel, characterized in that, The chemical composition of the base material, by mass percentage, is as follows: C: 0.02~0.045%, Si: 0.12~0.20%, Mn: 0.70~1.30%, P≤0.010%, S≤0.0008%, Ni: 0.10~0.30%, Cr: 0.20~0.35%, Cu: 0.10~0.20%, Nb: 0.03~0.05%, Mo: 0.010~0.10%, V: 0.035~0.06%, Ti: 0.01~0.02%, with the balance being Fe and unavoidable impurities.

2. The low-hydrogen-embrittlement-sensitive welded joint for X65 hydrogen pipeline steel according to claim 1, characterized in that: The non-metallic inclusions in the welded joint meet the following requirements: the grades of non-metallic inclusions of types A, B, C, and D are all ≤1.0, and the sum of the grades of the above four types of non-metallic inclusions is ≤2.

0.

3. The low-hydrogen-embrittlement-sensitive welded joint of X65 hydrogen pipeline steel according to claim 1, characterized in that: The metallographic structure of the welded joint includes weld structure, coarse-grained heat-affected zone structure, and fine-grained heat-affected zone structure; wherein, the weld structure is composed of acicular ferrite, the coarse-grained heat-affected zone structure is composed of ferrite and granular bainite, and the fine-grained heat-affected zone structure is composed of ferrite and bainite; the grain size of the ferrite is ≥12.

4. A low-hydrogen-embrittlement-sensitive welded joint for X65 hydrogen pipeline steel according to claim 1, characterized in that: The mechanical properties of the welded joint are as follows: yield strength 460~470MPa, tensile strength 570~580MPa, and Charpy impact energy of the weld area at -20℃ 150~170J.

5. A low-hydrogen-embrittlement-sensitive welded joint for X65 hydrogen pipeline steel according to claim 1, characterized in that: The hydrogen embrittlement index of the low hydrogen embrittlement sensitivity welded joint under a test pressure of 7.2 MPa and a slow strain rate tensile test is <30%.

6. A method for controlling low-hydrogen embrittlement-sensitive welded joints of X65 hydrogen pipeline steel according to any one of claims 1-5, characterized in that: Specifically, it includes: The rolling process adopts controlled rolling and controlled cooling, specifically: Heating stage: furnace exit temperature is 1160~1200℃; Rough rolling stage: final rolling temperature ≥1000℃; Finish rolling stage: initial rolling temperature is 890~910℃, final rolling temperature is 810~820℃; Cooling stage: initial cooling temperature is 770~790℃, cooling rate is 15~20℃ / s (laminar cooling), and the reheating temperature is 530~570℃ and must not be lower than 530℃; The welding process adopts straight seam double-sided submerged arc welding, with the inner welding current being 550~1000A, the voltage being 36~42V, and the welding speed being 1.0~1.6m / min; the outer welding current being 500~1100A, the voltage being 36~42V, and the welding speed being 1.0~1.6m / min; the welding materials used are: submerged arc welding wire H65MH(Ⅱ), flux SJ101MH-2, and gas shielded welding wire HSGX-6H.

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