Welding method for hydrogen conveying pipeline submerged arc pipe heterogeneous multi-wire in-situ metallurgy

Abstract

The invention discloses a welding method for heterogeneous multi-wire in-situ metallurgy of a submerged arc pipe of a hydrogen conveying pipeline, and aims to solve the problem of hydrogen-induced failure caused by the problems of coarse weld structure, secondary phase particle aggregation, low-temperature impact toughness and the like caused by a traditional multi-wire submerged arc welding method. The welding method comprises the steps that firstly, the to-be-welded face of the hydrogen conveying pipeline is polished and cleaned; and secondly, the cleaned hydrogen conveying pipeline to be welded is welded through three-wire submerged arc welding, H08MnMoTiB is adopted as a first welding wire, BH60GX-III is adopted as a second welding wire, H08Mn2NiA is adopted as a third welding wire, the components of the three welding wires are optimized, and the technological parameters such as the wire feeding speed, the current and the voltage of the three welding wires are optimized and adjusted. According to the method, the idea of in-situ metallurgy and multi-wire submerged arc welding are fused, the alloy component proportion of transition metal of a welding pool is achieved by changing the wire feeding speed of different welding wires, and different welding process parameters are supplemented, so that quantitative adjustment of the cladding metallurgy performance of a welding seam is achieved, and the hydrogen-induced corrosion resistance is improved.

Description

Technical Field

[0001] The invention belongs to the field of general welding technology and the scope of high-quality manufacturing of large-diameter hydrogen pipelines, and specifically relates to a welding method for heterogeneous multi-wire in-situ metallurgy of submerged arc tubes of hydrogen pipelines. Background Art

[0002] Hydrogen energy is a high-quality secondary energy source with the advantages of clean, zero-carbon and renewable. It can meet the requirements of resources, environment and sustainable development at the same time. However, the distribution of hydrogen energy shows a typical "rich in the west and poor in the east, more in the north and less in the south". The demand and supply sides are extremely unevenly distributed. Therefore, the core problem of my country's hydrogen energy development lies in transportation. In order to further reduce the cost of hydrogen energy transportation, the existing pipeline is currently used to transport hydrogen with natural gas and build new pure hydrogen pipelines in parallel. However, hydrogen will cause the mechanical properties of pipelines and equipment such as strength, toughness and plasticity to deteriorate. Therefore, it is necessary to improve the plastic toughness reserve of welds. The existing pipeline steel welding technology is the traditional multi-wire submerged arc welding method, and the maximum current can reach more than 3000A. Therefore, the defects such as weld organization coarsening, secondary phase particle aggregation, low-temperature impact toughness reduction and micro-cracks in the weld area are inevitable. These welding defects usually have higher hydrogen binding energy than the lattice lattice, so that H atoms are locally aggregated at the defects, forming "hydrogen traps", and then in the process of hydrogen transportation, hydrogen-induced defects such as hydrogen embrittlement and hydrogen cracks are generated, reducing the service life of the pipeline. In order to ensure efficient manufacturing of steel pipes and batch supply capacity, seamless steel pipes cannot be used. Therefore, a heterogeneous multi-wire in-situ metallurgical welding method for submerged arc tubes of hydrogen pipelines is proposed. While ensuring welding efficiency, the problem of hydrogen-induced failure is solved from the metallurgical principle, which is of great significance for improving the construction capacity and service life of hydrogen pipelines. Summary of the invention

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

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

[0005] 1. Processing a groove on the surface to be welded of the hydrogen pipeline, grinding and cleaning the surface to be welded of the hydrogen pipeline, and obtaining the cleaned hydrogen pipeline to be welded;

[0006] Second, three-wire submerged arc welding is used to weld the cleaned hydrogen pipeline to be welded. 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%, Cu0.09%, Ni 0.008% and the balance Fe;

[0007] The second welding wire adopts BH60GX-III, and the mass percentage of the chemical composition of the second welding wire is: 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 adopts H08Mn2NiA, and the mass percentage of the chemical composition of the third welding wire 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 adopts the direct current positive connection method, and the wire feeding speed is controlled to be 2.46m / min, the welding current is 1100-1300A, and the welding voltage is 34-38V; the second welding wire adopts the alternating current method, and the wire feeding speed is controlled to be 2.35m / min, the welding current is 900-1000A, and the welding voltage is 36-40V; the third welding wire adopts the alternating current method, and the wire feeding speed is controlled to be 1.9m / min, the welding current is 750-850A, and the welding voltage is 38-44V; the welding speeds of the first welding wire, the second welding wire, and the third welding wire are all controlled to be 1.5m / min;

[0010] Based on the different wire feeding speeds of the first welding wire, the second welding wire and the third welding wire, the composition of the alloy elements entering the welding molten pool is controlled, thereby completing the heterogeneous multi-wire in-situ metallurgical welding method for the submerged arc tube of the hydrogen transmission pipeline.

[0011] The present invention introduces the concept of in-situ metallurgy into multi-wire submerged arc welding. First, different existing common welding wires are used as base materials of the first welding wire, the second welding wire and the third welding wire respectively. The chemical composition of each welding wire is different. The content of alloy elements entering the molten pool is adjusted by controlling the wire feeding speed of each welding wire, so as to achieve the designed alloy element content; however, due to the matching relationship between the wire feeding speed and processability, simply adjusting the wire feeding speed cannot meet the requirements. Therefore, in order to adapt to the processability requirements, the present invention optimizes (micro) adjustments to the composition of the base material of each welding wire, and finally forms a quantitative welding wire composition, and then uses the adjusted welding wire for welding.

[0012] The welding method of the submerged arc welding hydrogen pipeline based on heterogeneous multi-wire in-situ metallurgy described in the present invention mainly solves the problem of hydrogen-induced failure caused by local enrichment of hydrogen atoms in the weld area of ​​the welded steel pipe due to factors such as inclusions, microcracks and coarse weld grain structure in a long-distance hydrogen transmission environment. By integrating the concept of in-situ metallurgy with multi-wire submerged arc welding, optimizing the alloy element composition of different welding wires through theoretical calculation, changing the wire feeding speed of different welding wires to achieve the alloy composition ratio of transition metals in the welding molten pool, and assisted by different welding process parameters, quantitative adjustment of the metallurgical properties of the weld cladding is achieved, thereby improving the resistance to hydrogen-induced corrosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A flow chart of the design of a welding method for heterogeneous multi-wire in-situ metallurgy of a submerged arc tube of a hydrogen transmission pipeline in an embodiment;

[0014] Figure 2 This is a morphology diagram of the front groove weld of the hydrogen pipeline obtained in the embodiment;

[0015] Figure 3 This is a morphology image of the back groove weld of the hydrogen pipeline obtained in the embodiment;

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

[0017] Figure 5 : is the microstructure diagram of the weld area of ​​the hydrogen pipeline obtained in the embodiment. DETAILED DESCRIPTION

[0018] Specific implementation method 1: The heterogeneous multi-wire in-situ metallurgical welding method for submerged arc tubes of hydrogen pipelines in this implementation method is implemented according to the following steps:

[0019] 1. Processing a groove on the surface to be welded of the hydrogen pipeline, grinding and cleaning the surface to be welded of the hydrogen pipeline, and obtaining the cleaned hydrogen pipeline to be welded;

[0020] Second, three-wire submerged arc welding is used to weld the cleaned hydrogen pipeline to be welded. 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%, Cu0.09%, Ni 0.008% and the balance Fe;

[0021] The second welding wire adopts BH60GX-III, and the mass percentage of the chemical composition of the second welding wire is: 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 adopts H08Mn2NiA, and the mass percentage of the chemical composition of the third welding wire 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 adopts the direct current positive connection method, and the wire feeding speed is controlled to be 2.46m / min, the welding current is 1100-1300A, and the welding voltage is 34-38V; the second welding wire adopts the alternating current method, and the wire feeding speed is controlled to be 2.35m / min, the welding current is 900-1000A, and the welding voltage is 36-40V; the third welding wire adopts the alternating current method, and the wire feeding speed is controlled to be 1.9m / min, the welding current is 750-850A, and the welding voltage is 38-44V; the welding speeds of the first welding wire, the second welding wire, and the third welding wire are all controlled to be 1.5m / min;

[0024] Based on the different wire feeding speeds of the first welding wire, the second welding wire and the third welding wire, the composition of the alloy elements entering the welding molten pool is controlled, thereby completing the heterogeneous multi-wire in-situ metallurgical welding method for the submerged arc tube of the hydrogen transmission pipeline.

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

[0026] Specific implementation method 2: The difference between this implementation method and specific implementation method 1 is that the hydrogen transmission pipeline in step 1 is an X65 steel pipe.

[0027] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that in step one, a V-shaped groove is processed at the surface to be welded of the hydrogen transmission pipeline.

[0028] Specific implementation method 4: This implementation method is different from specific implementation methods 1 to 3 in that in step 2, the positive electrode of the submerged arc welding power supply is connected to the welding gun, and the negative electrode of the submerged arc welding power supply is fixed to the welding platform (the workpiece is placed on the platform).

[0029] Specific embodiment five: This embodiment differs from any one of specific embodiments one to four in that the first welding wire in step two adopts H08MnMoTiB, and the mass percentage of the chemical composition of the first welding wire is: C 0.09%, Si 0.2%, Mn1.45%, S 0.015%, P 0.01%, Mo 0.05%, Ti 0.3%, Cr 0.06%, Cu 0.09%, Ni 0.008% and the remainder Fe.

[0030] Specific implementation method 6: The difference between this implementation method and specific implementation methods 1 to 5 is that the diameters of the first welding wire, the second welding wire and the third welding wire in step 2 are all 4 mm.

[0031] Specific implementation method seven: The difference between this implementation method and any one of specific implementation methods one to six is ​​that in step two, the welding wire elongation length of the first welding wire is controlled to be 29 mm, the welding wire elongation length of the second welding wire is controlled to be 26 mm, and the welding wire elongation length of the third welding wire is controlled to be 27 mm.

[0032] Specific implementation eight: This implementation differs from specific implementations one to seven in that in step two, the first welding wire is connected by direct current, the wire feeding speed is controlled to be 2.46 m / min, the welding current is 1200 A and the welding voltage is 36 V.

[0033] Specific implementation method 9: The difference between this implementation method and specific implementation methods 1 to 8 is that the second welding wire in step 2 adopts the AC method, the wire feeding speed is controlled to be 2.35m / min, the welding current is 950A and the welding voltage is 38V.

[0034] Specific implementation method ten: This implementation method is different from specific implementation methods one to nine in that the third welding wire in step two adopts the AC method, the wire feeding speed is controlled to be 1.9m / min, the welding current is 800A and the welding voltage is 40V.

[0035] Embodiment: The heterogeneous multi-wire in-situ metallurgical welding method for submerged arc tubes of hydrogen pipelines in this embodiment is implemented according to the following steps:

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

[0037] The first welding wire: It is the main wire for heterogeneous multi-wire submerged arc welding in-situ metallurgy. It uses large current to ensure that the penetration depth meets the requirements. This wire has a large welding current and large parameters. It adopts the DC positive connection method. The welding wire melts quickly, has a large penetration depth, and reacts violently with the base material. In order to ensure grain refinement, the welding wire H08MnMoTiB containing Ti and Ni 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 heterogeneous multi-wire submerged arc welding in-situ metallurgy. It meets the requirements of weld filling with a large amount of cladding. The AC method is adopted and BH60GX-III welding wire is selected as the second welding wire.

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

[0042]

[0043] The third welding wire: It is a filling wire for heterogeneous multi-wire submerged arc welding in-situ metallurgy. It meets the requirements of weld filling with a large amount of cladding. The AC method is adopted, and H08Mn2NiA submerged arc welding wire is selected as the third welding wire.

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

[0045]

[0046] By matching the 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 properties match, the wire feeding speed cannot be changed indefinitely. Therefore, it is necessary to add appropriate alloy elements to each welding wire, and then achieve precise control by matching the welding process parameters and wire feeding speed. Since the alloy elements will be burned during the welding process, the general alloy loss coefficient of 0.94 (Ti element is more active, and its loss coefficient is 0.88) is used as the basis for calculation.

[0047] Based on the electrochemical hydrogen charging experiment, the cladding metal was analyzed and optimized to 1.1-1.7% (wt%) Ti, 0.5-0.7% Ni, 0.1% Cu and 0.06% Cr.

[0048] In order to achieve the above alloy element content and proportion of the deposited metal, the following welding process parameters are used:

[0049]

[0050] Through theoretical calculation, the above wire feeding speed can meet the design requirements of different alloy element contents in the ideal deposited metal, but the comprehensive mechanical properties are not good, which has a lot to do with process adaptability. Because the wire feeding speed and welding current in the constant pressure mode are positively correlated, modifying the wire feeding speed will change the welding current, resulting in poor performance of the welding process that is changed in disguise just to meet the element design requirements. Therefore, this embodiment is targeted at smelting the second welding wire BH60GX-III, and its Ni element content is increased to 0.01, and the Ti element content is increased to 0.3; the Cu element of 1 wire is increased to 0.09; the Cr element is increased to 0.06; that is, the alloy element composition of the redesigned welding wire is:

[0051] Chemical composition and basic parameters of each wire after re-smelting (wt%)

[0052]

[0053]

[0054] The arc molten pool in-situ metallurgy technology of the present embodiment is a method of synchronously carrying out a cladding process and material transportation based on a directional direct energy deposition system. A molten pool is formed under the action of an arc heat source and through an in-situ reaction in the molten pool, the principle of in-situ metallurgy is introduced into multi-wire submerged arc welding through the analysis of the in-situ metallurgical technology theory. The original same-speed wire feeding of the multi-wire submerged arc is changed to variable-speed wire feeding of each welding wire, that is, the wire feeding speed of each welding wire is different. In this way, the cladding process and material transportation can be separated in principle, and the composition of the alloy elements entering the molten pool can be controlled, so as to increase the content of beneficial elements and thus suppress the problem of hydrogen-induced failure.

[0055] The direction of inhibiting hydrogen-induced failure mainly starts from inhibiting hydrogen diffusion, avoiding concentrated distribution of hydrogen, regulating dislocation proliferation, increasing the number of beneficial "hydrogen traps", etc. The core goal is to: refine the grains by adding elements that promote austenite formation to the welding wire; control the morphology of inclusions through in-situ metallurgical process optimization and alloying element addition, obtain fine and evenly distributed spherical oxides, and reduce the formation of irregularly shaped carbides and sulfides.

[0056] The microstructure after in-situ metallurgy shows that a large amount of chain-like polygonal ferrite structure and short rod-shaped or independent block-shaped ferrite structure are generated in the weld area, which can effectively inhibit the crack propagation; part of the supersaturated austenite in the welding heat affected zone is transformed into lath-shaped bainite, and there are needle-shaped MA components between the lath bundles, which can make the heat affected zone obtain good strength and toughness.

[0057] Focusing on the above two core points, alloy elements are selected in two directions: one is grain refinement, and the other is to control the morphology of inclusions; a (V-shaped) groove is pre-processed on the welded surface of the hydrogen pipeline, and the influence of welding wires containing different alloy elements on the metal structure and properties of the X65 pipeline steel weld is obtained through experiments. The role of different alloy elements in resisting hydrogen-induced damage is analyzed, and the added elements are determined first, then the base material of the welding wire is decided, and then the addition amount is determined.

[0058] The specific manifestations are as follows:

[0059] (1) The Ni element improves the toughness of the cladding metal. The crack sensitivity of the intermetallic compound containing the Ni element is low, and the microstructure of the intermetallic compound containing the Ni element is mostly irregular and large-area blocks with rounded edges and no edges, thereby improving the toughness.

[0060] (2) Ti element achieves refinement by limiting the growth of grains, promoting the transformation of grains from columnar to equiaxed and increasing the proportion of low-angle grain boundaries. It can reduce alloy density and increase lattice distortion.

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

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

[0063] Experimental analysis shows that nano-scale vanadium carbide particles can act as effective hydrogen traps to reduce the number of diffused atoms in steel. Properly increasing the vanadium content can improve the material's resistance to hydrogen corrosion. With the increase of vanadium content, the sensitivity to hydrogen-induced cracking shows a trend of first decreasing and then increasing. The best resistance to hydrogen corrosion is achieved when the vanadium content is 0.12%.

[0064] This embodiment conducted multiple sets of experimental analysis and found that under the above wire feeding speed and welding process matching parameters, the quality of the welded joint was verified by electrochemical hydrogen charging experiment. The electrochemical hydrogen charging experiment is a process in which the metal loaded on the electrode surface is reduced by hydrogen ions in the electrolyte solution. The specific process is as follows:

[0065] a. Make the weld perpendicular to the weld direction, and use sawing machine, milling machine and grinder to process it into a metal strip sample with length × width × height of 50mm × 10mm × 10mm, and make the center of the weld in the center of the length; polish it with sandpaper, rinse with alcohol and blow dry it for later use;

[0066] b. 1000 ml of electrolyte is placed in a circular electrolytic cell, wherein 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, connect the carbon rod to the anode of the electrode, place both in the extraction solution, and turn on the power supply to form an electrochemical circuit;

[0068] d. Power on and charge with hydrogen. Keep the charge for 30 minutes, then take out the sample and rinse it with water to remove the electrolyte and residue on the surface.

[0069] e. Then perform tensile, impact, and drop hammer tests within one hour and compare the experimental data

[0070] The obtained welded joint has the best resistance to hydrogen damage; the comprehensive mechanical properties also meet the standard requirements. The mechanical properties of the experimental test block made by the above in-situ metallurgical method are compared with the conventional welding method, and the comparison data is shown in Table 1 below:

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

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

[0073] Table 2

[0074] .

Claims

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

1. Processing a groove on the surface to be welded of the hydrogen pipeline, grinding and cleaning the surface to be welded of the hydrogen pipeline, and obtaining the cleaned hydrogen pipeline to be welded; Second, three-wire submerged arc welding is used to weld the cleaned hydrogen pipeline to be welded. 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 adopts BH60GX-III, and the mass percentage of the chemical composition of the second welding wire is: 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 adopts H08Mn2NiA, and the mass percentage of the chemical composition of the third welding wire 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 adopts the direct current positive connection method, and the wire feeding speed is controlled to be 2.46m / min, the welding current is 1100-1300A, and the welding voltage is 34-38V; the second welding wire adopts the alternating current method, and the wire feeding speed is controlled to be 2.35m / min, the welding current is 900-1000A, and the welding voltage is 36-40V; the third welding wire adopts the alternating current method, and the wire feeding speed is controlled to be 1.9m / min, the welding current is 750-850A, and the welding voltage is 38-44V; the welding speeds of the first welding wire, the second welding wire, and the third welding wire are all controlled to be 1.5m / min; Based on the different wire feeding speeds of the first welding wire, the second welding wire and the third welding wire, the composition of the alloy elements entering the welding molten pool is controlled, thereby completing the heterogeneous multi-wire in-situ metallurgical welding method for the submerged arc tube of the hydrogen transmission pipeline.

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

3. The heterogeneous multi-wire in-situ metallurgical welding method for submerged arc tubes of hydrogen pipelines according to claim 1 is characterized in that In step 1, a V-shaped groove is processed on the surface to be welded of the hydrogen transmission pipeline.

4. The method for in-situ metallurgy of heterogeneous multi-wire welding of submerged arc tubes of hydrogen pipelines according to claim 1, characterized in that In step 2, the positive electrode of the submerged arc welding power source is connected to the welding gun, and the negative electrode of the submerged arc welding power source is fixed to the welding platform.

5. The heterogeneous multi-wire in-situ metallurgical welding method for submerged arc tubes of hydrogen pipelines according to claim 1 is characterized in that In step 2, the first welding wire adopts H08MnMoTiB, and 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.

6. The heterogeneous multi-wire in-situ metallurgical welding method for submerged arc tubes of hydrogen pipelines according to claim 1, characterized in that In step 2, the diameters of the first welding wire, the second welding wire and the third welding wire are all 4 mm.

7. The heterogeneous multi-wire in-situ metallurgical welding method for submerged arc tubes of hydrogen pipelines according to claim 1 is characterized in that In step 2, the wire extension length of the first welding wire is controlled to be 29 mm, the wire extension length of the second welding wire is controlled to be 26 mm, and the wire extension length of the third welding wire is controlled to be 27 mm.

8. The heterogeneous multi-wire in-situ metallurgical welding method for submerged arc tubes of hydrogen pipelines according to claim 1, characterized in that In step 2, the first welding wire adopts the direct current positive connection method, and the wire feeding speed is controlled to be 2.46m / min, the welding current is 1200A and the welding voltage is 36V.

9. The heterogeneous multi-wire in-situ metallurgical welding method for submerged arc tubes of hydrogen pipelines according to claim 8, characterized in that In step 2, the second welding wire adopts the AC method, and the wire feeding speed is controlled to be 2.35m / min, the welding current is 950A and the welding voltage is 38V.

10. The heterogeneous multi-wire in-situ metallurgical welding method for submerged arc tubes of hydrogen pipelines according to claim 8, characterized in that In step 2, the third welding wire adopts the AC method, and the wire feeding speed is controlled to be 1.9m / min, the welding current is 800A and the welding voltage is 40V.

Images