A welding method for arc-submerged pipe hetero-multiple wire in-situ metallurgy of hydrogen transmission pipeline

Abstract

A welding method for heterogeneous multi-wire in-situ metallurgy of submerged arc welding (SAW) pipes in hydrogen transportation pipelines is disclosed. This invention aims to address the hydrogen-induced failure problems caused by traditional SAW methods, such as coarse weld microstructure, secondary phase particle aggregation, and reduced low-temperature impact toughness. The welding method includes: 1. Grinding and cleaning the surface of the hydrogen transportation pipeline to be welded; 2. Welding the cleaned hydrogen transportation pipeline using three-wire SAW. The first welding wire is H08MnMoTiB, the second is BH60GX-III, and the third is H08Mn2NiA. The composition of the three welding wires is optimized, and the wire feed speed, current, and voltage are adjusted accordingly. This invention integrates the concept of in-situ metallurgy with SAW, changing the wire feed speed of different welding wires to achieve a certain alloy composition ratio in the weld pool transition metal. Combined with different welding process parameters, this allows for quantitative adjustment of the weld cladding metallurgical properties, thereby improving resistance to hydrogen corrosion.

Description

Technical Field

[0001] This invention belongs to the field of general welding technology and falls within the scope of high-quality manufacturing of large-diameter hydrogen transmission pipelines. Specifically, it relates to a welding method for in-situ metallurgical welding of heterogeneous multi-wire submerged arc pipes in hydrogen transmission pipelines. Background Technology

[0002] Hydrogen energy is a high-quality secondary energy source with the advantages of being clean, zero-carbon, and renewable, simultaneously meeting the requirements of resource conservation, environmental protection, and sustainable development. However, hydrogen energy distribution exhibits a typical pattern of "rich in the west and poor in the east, abundant in the north and scarce in the south," with extremely uneven distribution on both the demand and supply sides. Therefore, the core issue in my country's hydrogen energy development lies in transportation. To further reduce the cost of hydrogen transportation, the current approach involves using existing pipelines for natural gas-blended hydrogen transportation and constructing new pure hydrogen pipelines in parallel. However, hydrogen can degrade the mechanical properties of pipelines and equipment, such as strength, toughness, and plasticity. Therefore, it is necessary to improve the plasticity and toughness reserves of welds. The existing pipeline steel welding technology is the traditional multi-wire submerged arc welding method, with a maximum current exceeding 3000A. Consequently, defects such as weld coarsening, secondary phase particle aggregation, reduced low-temperature impact toughness, and microcracks in the weld area are unavoidable. These welding defects typically have a higher hydrogen binding energy than the crystal lattice, causing H atoms to accumulate locally at the defect sites, creating "hydrogen traps." This leads to hydrogen embrittlement, hydrogen cracking, and other hydrogen-induced defects during hydrogen transportation, reducing the service life of the pipeline. To ensure efficient manufacturing and batch supply of steel pipes, seamless steel pipes cannot be used. Therefore, a welding method for in-situ metallurgical welding of dissimilar multi-wire submerged arc pipes in hydrogen transmission pipelines is proposed. This method not only ensures welding efficiency but also solves the hydrogen-induced failure problem from a metallurgical perspective, which is of great significance for improving the construction capacity and service life of hydrogen transmission pipelines. Summary of the Invention

[0003] The purpose of this invention is to solve the hydrogen-induced failure problem caused by the coarse weld structure, secondary phase particle aggregation, and reduced low-temperature impact toughness of traditional multi-wire submerged arc welding methods, thereby providing a welding method for hydrogen pipelines based on heterogeneous multi-wire in-situ metallurgy.

[0004] The welding method of the present invention for in-situ metallurgical welding of dissimilar multi-wire submerged arc pipes in hydrogen transportation pipelines is implemented according to the following steps:

[0005] 1. A bevel is machined on the surface of the hydrogen pipeline to be welded. The surface of the hydrogen pipeline to be welded is then ground and cleaned to obtain a cleaned hydrogen pipeline to be welded.

[0006] 2. The cleaned hydrogen pipeline to be welded is welded using three-wire submerged arc welding. The first welding wire is H08MnMoTiB, and the mass percentage of the chemical composition of the first welding wire is: C 0.09%, Si 0.2%, Mn 1.4%~1.6%, S 0.015%, P 0.01%, Mo 0.04%~0.07%, Ti 0.3%~0.5%, Cr 0.06%, Cu 0.09%, Ni 0.008%, and the balance Fe.

[0007] The second welding wire is BH60GX-III, and the chemical composition of the second welding wire is as follows (mass percentage): C 0.06%, Si 0.16%, Mn 1.2%, S 0.002%, P 0.007%, Ti 0.3%, Cr 0.0812%, Ni 0.01%, and the balance Fe.

[0008] The third welding wire is H08Mn2NiA, and its chemical composition by mass percentage is: C 0.08%, Si 0.05%, Mn 1.72%, S 0.004%, P 0.011%, Mo 0.08%, Ti 0.009%, Cu 0.016%, Ni 0.35%, and the balance Fe;

[0009] The first welding wire uses DC positive polarity, with a wire feed speed of 2.46 m / min, a welding current of 1100–1300 A, and a welding voltage of 34–38 V. The second welding wire uses AC polarity, with a wire feed speed of 2.35 m / min, a welding current of 900–1000 A, and a welding voltage of 36–40 V. The third welding wire uses AC polarity, with a wire feed speed of 1.9 m / min, a welding current of 750–850 A, and a welding voltage of 38–44 V. The welding speed of the first, second, and third welding wires is controlled at 1.5 m / min.

[0010] By controlling the composition of alloying elements entering the weld pool through different wire feeding speeds of the first, second, and third welding wires, a welding method for heterogeneous multi-wire in-situ metallurgy of submerged arc pipes for hydrogen transportation pipelines is completed.

[0011] This invention introduces the concept of in-situ metallurgy into multi-wire submerged arc welding. First, different commonly used welding wires are used as the base material for the first, second, and third welding wires, respectively. Each welding wire has a different chemical composition. By controlling the wire feeding speed of each welding wire, the content of alloying elements entering the molten pool is adjusted to achieve the designed alloying element content. However, due to the matching relationship between wire feeding speed and process requirements, simply adjusting the wire feeding speed cannot meet the requirements. Therefore, in order to adapt to the process requirements, this invention further optimizes (micro-adjusts) the composition of the base material of each welding wire, finally forming a quantitative welding wire composition. Then, the adjusted welding wire is used for welding.

[0012] The welding method for hydrogen pipelines based on heterogeneous multi-wire in-situ metallurgy described in this invention mainly addresses the problem of hydrogen-induced failure caused by the local enrichment of hydrogen atoms in the weld area of ​​welded steel pipes under long-distance hydrogen transportation environments due to factors such as inclusions, microcracks, and coarse weld grain structure. By integrating the concept of in-situ metallurgy with multi-wire submerged arc welding, the alloy element composition of different welding wires is optimized through theoretical calculations. The alloy composition ratio of the transition metal in the weld pool is achieved by changing the wire feeding speed of different welding wires. With the assistance of different welding process parameters, the metallurgical properties of the weld cladding are quantitatively adjusted, thereby improving the resistance to hydrogen-induced corrosion. Attached Figure Description

[0013] Figure 1 This is a flowchart illustrating the design of a welding method for heterogeneous multi-wire in-situ metallurgy of submerged arc pipes in hydrogen transportation pipelines, as shown in the embodiment.

[0014] Figure 2 This is a topographic image of the bevel weld seam on the front side of the hydrogen transport pipeline obtained in the embodiment;

[0015] Figure 3 This is a topographic image of the reverse bevel weld seam of the hydrogen transport pipeline obtained in the embodiment;

[0016] Figure 4 This is a cross-sectional view of the hydrogen pipeline weld obtained in the embodiment;

[0017] Figure 5 The image shows the microstructure of the weld zone in the hydrogen transport pipeline obtained in the example. Detailed Implementation

[0018] Specific Implementation Method 1: This implementation method for welding heterogeneous multi-wire in-situ metallurgical submerged arc pipes in hydrogen transportation pipelines is carried out according to the following steps:

[0019] 1. A bevel is machined on the surface of the hydrogen pipeline to be welded. The surface of the hydrogen pipeline to be welded is then ground and cleaned to obtain a cleaned hydrogen pipeline to be welded.

[0020] 2. The cleaned hydrogen pipeline to be welded is welded using three-wire submerged arc welding. The first welding wire is H08MnMoTiB, and the mass percentage of the chemical composition of the first welding wire is: C 0.09%, Si 0.2%, Mn 1.4%~1.6%, S 0.015%, P 0.01%, Mo 0.04%~0.07%, Ti 0.3%~0.5%, Cr 0.06%, Cu 0.09%, Ni 0.008%, and the balance Fe.

[0021] The second welding wire is BH60GX-III, and the chemical composition of the second welding wire is as follows (mass percentage): C 0.06%, Si 0.16%, Mn 1.2%, S 0.002%, P 0.007%, Ti 0.3%, Cr 0.0812%, Ni 0.01%, and the balance Fe.

[0022] The third welding wire is H08Mn2NiA, and its chemical composition by mass percentage is: C 0.08%, Si 0.05%, Mn 1.72%, S 0.004%, P 0.011%, Mo 0.08%, Ti 0.009%, Cu 0.016%, Ni 0.35%, and the balance Fe;

[0023] The first welding wire uses DC positive polarity, with a wire feed speed of 2.46 m / min, a welding current of 1100–1300 A, and a welding voltage of 34–38 V. The second welding wire uses AC polarity, with a wire feed speed of 2.35 m / min, a welding current of 900–1000 A, and a welding voltage of 36–40 V. The third welding wire uses AC polarity, with a wire feed speed of 1.9 m / min, a welding current of 750–850 A, and a welding voltage of 38–44 V. The welding speed of the first, second, and third welding wires is controlled at 1.5 m / min.

[0024] By controlling the composition of alloying elements entering the weld pool through different wire feeding speeds of the first, second, and third welding wires, a welding method for heterogeneous multi-wire in-situ metallurgy of submerged arc pipes for hydrogen transportation pipelines is completed.

[0025] In this embodiment, the positive electrode of each welding power source is connected to the welding torch, and the negative electrode is fixed to the welding platform (the workpiece is placed on the platform). Each welding wire forms an independent arc, and the last three wires are coupled to all the arcs to form a molten pool on the workpiece. The alloy composition of each welding wire is different.

[0026] Specific Implementation Method Two: The difference between this implementation method and Specific Implementation Method One is that the hydrogen transportation pipeline in step one is an X65 steel pipe.

[0027] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that a V-shaped bevel is machined at the welding surface of the hydrogen pipeline in step 1.

[0028] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that in step two, the positive terminal of the submerged arc welding power source is connected to the welding torch, and the negative terminal of the submerged arc welding power source is fixed to the welding platform (the workpiece is placed on the platform).

[0029] Specific Implementation Method 5: This implementation method differs from Specific Implementation Methods 1 to 4 in that the first welding wire in step 2 is H08MnMoTiB. The mass percentage of the chemical composition of the first welding wire is: C 0.09%, Si 0.2%, Mn 1.45%, S 0.015%, P 0.01%, Mo 0.05%, Ti 0.3%, Cr 0.06%, Cu 0.09%, Ni 0.008%, and the balance Fe.

[0030] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the diameters of the first welding wire, the second welding wire, and the third welding wire in step two are all 4mm.

[0031] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that in step two, the wire extension of the first welding wire is controlled to be 29mm, the wire extension of the second welding wire is controlled to be 26mm, and the wire extension of the third welding wire is controlled to be 27mm.

[0032] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the first welding wire in step two adopts the DC positive polarity method, and the wire feeding speed is controlled at 2.46m / min, the welding current is 1200A and the welding voltage is 36V.

[0033] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the second welding wire in step two uses an AC method, with the wire feeding speed controlled at 2.35m / min, the welding current at 950A, and the welding voltage at 38V.

[0034] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 1 to 9 in that the third welding wire in step 2 uses an AC method, with the wire feeding speed controlled at 1.9 m / min, the welding current at 800 A, and the welding voltage at 40 V.

[0035] Example: This example describes a welding method for dissimilar multi-wire in-situ metallurgical welding of submerged arc welding pipes in hydrogen transportation pipelines, implemented according to the following steps:

[0036] This embodiment analyzes the function and characteristics of each welding wire to determine the type of welding wire to be selected (i.e., the selection of the substrate):

[0037] The first welding wire is the main wire for in-situ metallurgy of heterogeneous multi-wire submerged arc welding. It uses a large current to ensure that the penetration depth meets the requirements. This wire has a large welding current and parameters, and adopts the DC positive polarity method. The welding wire melts quickly, penetrates deeply, and reacts violently with the base material. In order to ensure grain refinement, the welding wire containing Ti and Ni, H08MnMoTiB, is selected.

[0038] Chemical composition and basic parameters of the first welding wire (wt%)

[0039]

[0040] The second welding wire is a filler wire for in-situ metallurgy of dissimilar multi-wire submerged arc welding. It meets the requirements of weld filling with a large cladding volume. The alternating current method is used, and BH60GX-III welding wire is selected as the second welding wire.

[0041] Chemical composition and basic parameters (wt%) of the second welding wire

[0042]

[0043] The third welding wire is a filler wire for in-situ metallurgical submerged arc welding with heterogeneous multi-wires. It meets the requirements for weld filling with a large cladding amount. It adopts the alternating current method and selects H08Mn2NiA submerged arc welding wire as the third welding wire.

[0044] Chemical composition and basic parameters (wt%) of the third welding wire

[0045]

[0046] By matching welding process parameters and adjusting different wire feeding speeds, the alloy element content of the molten pool metal can be achieved. In order to ensure that the welding process performance and metallurgical performance are matched, the wire feeding speed cannot be changed indefinitely. Therefore, it is necessary to add appropriate alloy elements to each welding wire. Then, by matching welding process parameters and wire feeding speed, precise control can be achieved. Since alloy elements will be burned off during the welding process, a general alloy loss coefficient of 0.94 (Ti is more reactive, and its loss coefficient is 0.88) is used as the calculation basis.

[0047] Based on the analysis of the cladding metal using electrochemical hydrogen charging experiments, the optimal composition was obtained as 1.1-1.7% (wt%) Ti, 0.5-0.7% Ni, 0.1% Cu, and 0.06% Cr.

[0048] To achieve the alloy element content and proportion of the deposited metal as described above, the following welding process parameters are used:

[0049]

[0050] Theoretical calculations show that the above wire feeding speed can meet the design requirements for different alloy element contents in the ideal weld metal. However, the overall mechanical properties are poor, which is largely related to process adaptability. Because the wire feeding speed and welding current are positively correlated under constant voltage mode, modifying the wire feeding speed will change the welding current. This results in a deterioration in performance due to a disguised change in the welding process, solely to meet element design requirements. Therefore, this embodiment specifically refines the second welding wire BH60GX-III, increasing the Ni content to 0.01 and the Ti content to 0.3; the Cu content of the first wire is increased to 0.09; and the Cr content is increased to 0.06. In other words, the redesigned welding wire's alloy element composition is as follows:

[0051] Chemical composition and basic parameters (wt%) of each fiber after remelting

[0052]

[0053]

[0054] This embodiment of in-situ metallurgical technology for electric arc pools is a method that simultaneously performs the cladding process and material transport based on a directional direct energy deposition system. A molten pool is formed under the action of an electric arc heat source, and in-situ reactions occur within the pool. Through analysis of the theory of in-situ metallurgical technology, the principles of in-situ metallurgy are introduced into multi-wire submerged arc welding. The original uniform wire feeding in multi-wire submerged arc welding is replaced with variable-speed wire feeding for each welding wire, meaning each welding wire has a different feeding speed. This allows the cladding process and material transport to be separated in principle, controlling the composition of alloying elements entering the molten pool, thereby increasing the content of beneficial elements and suppressing hydrogen-induced failure.

[0055] The main approaches to suppressing hydrogen-induced failure are to inhibit hydrogen diffusion, avoid concentrated hydrogen distribution, regulate dislocation multiplication, and increase the number of beneficial "hydrogen traps." The core objectives are to: refine grains by adding austenite-forming elements to the welding wire; and control the morphology of inclusions through in-situ metallurgical process optimization and alloying element addition to obtain fine, uniformly distributed spherical oxides and reduce the formation of irregularly shaped carbides and sulfides.

[0056] The microstructure after in-situ metallurgy shows that a large number of chain-like polygonal ferrite structures and short rod-shaped or independent block-shaped ferrite structures are generated in the weld zone, which can effectively inhibit crack propagation. In the weld heat-affected zone, some supersaturated austenite transforms into lath bainite, and there are needle-like MA components between the lath bundles, which can give the heat-affected zone good strength and toughness.

[0057] Focusing on the two core points mentioned above, alloying elements were selected from two directions: refining grain size and controlling the morphology of inclusions. A (V-shaped) bevel was pre-machined on the welding surface of the hydrogen pipeline. The effects of welding wires containing different alloying elements on the microstructure and properties of X65 pipeline steel weld metal were obtained through experiments. The role of different alloying elements in resisting hydrogen-induced damage was analyzed. First, the elements to be added were determined, then the type of welding wire base material was selected, and finally, the amount of addition was determined.

[0058] Specifically, this is reflected in the following ways:

[0059] (1) Ni element improves the toughness of cladding metal. Intermetallic compounds containing Ni element have lower crack sensitivity, and the microstructure of intermetallic compounds containing Ni is mostly irregular large-area blocky with rounded edges and no sharp corners, thus improving toughness.

[0060] (2) Ti element refines grains by restricting grain growth, causing the grains to transform from columnar to equiaxed and increasing the proportion of low-angle grain boundaries. It can reduce alloy density and increase lattice distortion.

[0061] (3) Cu can eliminate thermal stress and structural stress formed during in-situ metallurgical reactions.

[0062] (4) Cr and Nb (trace alloying elements) do not change the alloy phase, but increase the tensile strength of the alloy without affecting its plasticity.

[0063] Experimental analysis showed that nanoscale vanadium carbide particles, acting as effective hydrogen traps, can reduce the number of diffusing atoms in steel. Appropriately increasing the vanadium content can improve the material's resistance to hydrogen corrosion. With increasing vanadium content, the susceptibility to hydrogen-induced cracking exhibits a trend of first decreasing and then increasing, with the best hydrogen corrosion resistance observed at a vanadium content of 0.12%.

[0064] This embodiment conducted multiple sets of experimental analyses and found that, under the aforementioned wire feeding speed and welding process matching parameters, the quality of the welded joint was verified through an electrochemical hydrogen charging experiment. The electrochemical hydrogen charging experiment utilizes hydrogen ions in the electrolyte solution to reduce the metal loaded on the electrode surface. The specific process is as follows:

[0065] a. After welding, the weld is perpendicular to the weld direction. Using a saw, milling machine and grinding machine, it is processed into a metal strip sample with a length × width × height of 50mm × 10mm × 10mm, and the center of the weld is located in the center area of ​​the length. It is then polished with sandpaper, rinsed with alcohol and dried for later use.

[0066] b. Prepare 1000ml of electrolyte in a circular electrolytic cell. The electrolyte contains water, sulfuric acid and sodium chloride, and a small amount of thiourea is added as a corrosion inhibitor.

[0067] c. Connect the electrodes. Set the power supply to 24V and 1.5A. Connect the sample to the cathode of the electrode and the carbon rod to the anode of the electrode. Place both in the extraction solution at the same time and turn on the power to form an electrochemical circuit.

[0068] d. After energizing and charging with hydrogen for 30 minutes, remove the sample and rinse it with water to remove the electrolyte and residue on the surface.

[0069] e. Subsequently, tensile, impact, and drop weight tests are performed within one hour, and the experimental data are compared.

[0070] The obtained welded joint exhibited the best resistance to hydrogen-induced damage; its comprehensive mechanical properties also met the standard requirements. Table 1 below shows the comparative data of the mechanical properties of experimental blocks prepared using the above in-situ metallurgical method and those prepared using conventional welding methods.

[0071] Welding methods -10°C impact toughness (J) Tensile strength (MPa) Hardness (HRC) Falling weight experiment (J) Conventional submerged arc welding 42 478 178 84 In-situ metallurgical submerged arc welding 77.2 490 186 100

[0072] In Table 1, the three welding wires used in conventional submerged arc welding are all H08MnMoTiB. The three welding wires are used in AC-AC-AC or DC-AC-AC mode. The process parameters of each welding wire are the same, and the process parameters of each welding wire are shown in Table 2 below.

[0073] Table 2

[0074]

Claims

1. A welding method for in-situ metallurgical welding of dissimilar multi-wire submerged arc pipes in hydrogen transportation pipelines, characterized in that... This welding method is implemented according to the following steps:

1. A bevel is machined on the surface of the hydrogen pipeline to be welded. The surface of the hydrogen pipeline to be welded is then ground and cleaned to obtain a cleaned hydrogen pipeline to be welded.

2. The cleaned hydrogen pipeline to be welded is welded using three-wire submerged arc welding. The first welding wire is H08MnMoTiB, and the mass percentage of the chemical composition of the first welding wire is: C 0.09%, Si 0.2%, Mn 1.4%~1.6%, S 0.015%, P 0.01%, Mo 0.04%~0.07%, Ti 0.3%~0.5%, Cr 0.06%, Cu 0.09%, Ni 0.008%, and the balance Fe. The second welding wire is BH60GX-III, and the chemical composition of the second welding wire is as follows (mass percentage): C 0.06%, Si 0.16%, Mn 1.2%, S 0.002%, P 0.007%, Ti 0.3%, Cr 0.0812%, Ni 0.01%, and the balance Fe. The third welding wire is H08Mn2NiA, and its chemical composition by mass percentage is: C 0.08%, Si 0.05%, Mn 1.72%, S 0.004%, P 0.011%, Mo 0.08%, Ti 0.009%, Cu 0.016%, Ni 0.35%, and the balance Fe; The first welding wire uses DC positive polarity, with a wire feed speed of 2.46 m / min, a welding current of 1100–1300 A, and a welding voltage of 34–38 V. The second welding wire uses AC polarity, with a wire feed speed of 2.35 m / min, a welding current of 900–1000 A, and a welding voltage of 36–40 V. The third welding wire uses AC polarity, with a wire feed speed of 1.9 m / min, a welding current of 750–850 A, and a welding voltage of 38–44 V. The welding speed of the first, second, and third welding wires is controlled at 1.5 m / min. By controlling the composition of alloying elements entering the weld pool through different wire feeding speeds of the first, second, and third welding wires, a welding method for heterogeneous multi-wire in-situ metallurgy of submerged arc pipes for hydrogen transportation pipelines is completed.

2. The welding method for heterogeneous multi-wire in-situ metallurgy of submerged arc pipes for hydrogen transportation pipelines according to claim 1, characterized in that... In step one, the hydrogen transport pipeline is an X65 steel pipe.

3. The welding method for heterogeneous multi-wire in-situ metallurgy of submerged arc pipes for hydrogen transportation pipelines according to claim 1, characterized in that... In step one, a V-shaped bevel is machined on the surface of the hydrogen pipeline to be welded.

4. The welding method for in-situ metallurgical welding of dissimilar multi-wire submerged arc pipes in hydrogen transportation pipelines according to claim 1, characterized in that... In step two, the positive terminal of the submerged arc welding power source is connected to the welding torch, and the negative terminal of the submerged arc welding power source is fixed to the welding platform.

5. The welding method for heterogeneous multi-wire in-situ metallurgy of submerged arc pipes for hydrogen transportation pipelines according to claim 1, characterized in that... In step two, the first welding wire used is H08MnMoTiB. The chemical composition of the first welding wire is as follows (mass percentage): C 0.09%, Si 0.2%, Mn 1.45%, S 0.015%, P 0.01%, Mo 0.05%, Ti 0.3%, Cr 0.06%, Cu 0.09%, Ni 0.008%, and the balance Fe.

6. The welding method for heterogeneous multi-wire in-situ metallurgy of submerged arc pipes for hydrogen transportation pipelines according to claim 1, characterized in that... In step two, the diameters of the first, second, and third welding wires are all 4mm.

7. The welding method for heterogeneous multi-wire in-situ metallurgy of submerged arc pipes for hydrogen transportation pipelines according to claim 1, characterized in that... In step two, the wire extension of the first welding wire is controlled to be 29mm, the wire extension of the second welding wire is 26mm, and the wire extension of the third welding wire is 27mm.

8. The welding method for in-situ metallurgical welding of dissimilar multi-wire submerged arc pipes in hydrogen transportation pipelines according to claim 1, characterized in that... In step two, the first welding wire uses the DC positive polarity method, with the wire feeding speed controlled at 2.46 m / min, the welding current at 1200 A, and the welding voltage at 36 V.

9. The welding method for heterogeneous multi-wire in-situ metallurgy of submerged arc pipes for hydrogen transportation pipelines according to claim 8, characterized in that... In step two, the second welding wire is fed using an AC method, with the wire feeding speed controlled at 2.35 m / min, the welding current at 950 A, and the welding voltage at 38 V.

10. The welding method for in-situ metallurgical welding of dissimilar multi-wire submerged arc pipes in hydrogen transportation pipelines according to claim 8, characterized in that... In step two, the third welding wire is fed using an AC method, with the wire feeding speed controlled at 1.9 m / min, the welding current at 800 A, and the welding voltage at 40 V.

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