A welding method for hydrogen transport steel pipes based on stirring with an external fixed magnetic field.

Abstract

A welding method for hydrogen transport steel pipes based on external fixed magnetic field stirring is disclosed, relating to the field of welding. This invention solves the problem that existing manufacturing methods for hydrogen transport steel pipes are prone to hydrogen-induced failure, which reduces the service life of hydrogen transport pipelines. The invention comprises three steps: Step 1: Constructing a submerged arc welding test bench; Step 2: Adding an auxiliary magnetic field; an external fixed magnetic field stirring device is added directly below the test plate to generate a stable external fixed magnetic field, acting on the weld pool area; Step 3: Welding two adjacent test plates; the magnetic field is applied through the external fixed magnetic field stirring device, and the magnetic field is applied in the following way: first, a symmetrical fixed magnetic field is applied, and then the position of the N / S poles of the magnetic field is changed to achieve directional control of the external fixed magnetic field; after the welding arc is generated, the mass and heat transfer processes are changed through electromagnetic stirring; until the welding of the test plates is completed. This invention is used for welding hydrogen transport steel pipes.

Description

Technical Field

[0001] This invention relates to the field of general welding technology, specifically to a welding method for hydrogen transport steel pipes based on stirring with an external fixed magnetic field, which falls within the scope of high-quality welding manufacturing of hydrogen transport pipelines. Background Technology

[0002] Currently, the manufacturing method for hydrogen transportation steel pipes uses low-grade X42 and X52 pipeline steel as the base material and employs double-wire or multi-wire submerged arc welding. Although the traditional submerged arc welding method has advantages such as high production efficiency and stable weld quality, it also suffers from high welding heat input and slow welding speed. This results in coarse grains in the weld area during the non-equilibrium transformation process, which easily leads to metallurgical curves such as micro-segregation and inclusions. Consequently, it increases the sensitivity to hydrogen embrittlement, making hydrogen-induced failure more likely and affecting the service life of hydrogen transportation pipelines.

[0003] In summary, existing manufacturing methods for hydrogen transport steel pipes are prone to hydrogen-induced failure, which reduces the service life of hydrogen transport pipelines. Summary of the Invention

[0004] The purpose of this invention is to solve the problem that existing manufacturing methods for hydrogen transport steel pipes are prone to hydrogen-induced failure, which reduces the service life of hydrogen transport pipelines. Therefore, this invention provides a welding method for hydrogen transport steel pipes based on stirring with an external fixed magnetic field.

[0005] The technical solution of this invention is:

[0006] A welding method for hydrogen transport steel pipes based on stirring with an external fixed magnetic field includes the following steps:

[0007] Step 1: Set up the submerged arc welding test bench;

[0008] Step 2: Add an auxiliary magnetic field;

[0009] Based on the submerged arc welding equipment, an external fixed magnetic field stirring device was added directly below the test plate to generate a stable external fixed magnetic field, which acts on the weld pool area.

[0010] Step 3: Initiate the arc for welding, while simultaneously applying a magnetic field;

[0011] Welding is performed on two adjacent test plates. At this time, a magnetic field is applied by an external fixed magnetic field stirring device. The magnetic field is applied in the following way: first, a symmetrical fixed magnetic field is selected, and then the position of the N / S poles of the magnetic field is changed to achieve directional control of the external fixed magnetic field.

[0012] After the welding arc is generated, an external fixed magnetic field is applied to the molten metal in the welding pool, and the mass transfer and heat transfer processes are changed through electromagnetic stirring until the welding of the test plate is completed.

[0013] Furthermore, the construction of the submerged arc welding experimental platform in step one includes the following steps:

[0014] Step 11: Use 3 welding wires installed on a continuous automatic feeder and the same number of welding power sources. The positive terminal of each welding power source is connected to the welding torch, and the negative terminal of each welding power source is fixed to the welding platform. Each welding wire forms an independent arc.

[0015] Steps 1 and 2: The electric arcs of the three welding wires are coupled onto the workpiece and together form a molten pool;

[0016] Step 13: Number the welding wires according to the welding direction, namely wire 1, wire 2, and wire 3.

[0017] Furthermore, the grade of filament 1, filament 2, and filament 3 in steps one and three is H08MnMoTiB.

[0018] Furthermore, in step three, the method of applying a fixed magnetic field symmetrically is as follows: place a magnetic field generating device with the same magnetic field strength and direction on the left and right sides of the weld, respectively.

[0019] Furthermore, in step three, the position of the N / S poles of the magnetic field is changed to achieve the direction control method of the external fixed magnetic field:

[0020] The N pole of the magnetic field generator of the external fixed magnetic field stirring device on the left side of the weld is facing the welding end direction;

[0021] The N pole of the magnetic field generator of the external fixed magnetic field stirring device on the right side of the weld is facing the welding start direction, and the entire magnetic field direction is perpendicular to the weld direction.

[0022] Furthermore, the parameters for arc initiation and welding in step three are as follows:

[0023] The welding current for 1 wire is 900A-1000A, the welding voltage is 32-36V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 0°.

[0024] The welding current for 2 wires is 700A-850A, the welding voltage is 36-40V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 90°.

[0025] The welding current for 3 wires is 650A-750A, the welding voltage is 32-36V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 180°.

[0026] Preferably, the parameters for arc initiation and welding in step three are:

[0027] The welding current for 1 wire is 950A, the welding voltage is 34V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 0°.

[0028] The welding current for 2 wires is 800A, the welding voltage is 38V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 90°.

[0029] The welding current for the 3-wire welding is 700A, the welding voltage is 40V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 180°.

[0030] Preferably, the welding speed of wires 1, 2 and 3 in step three is 1.2 m / min.

[0031] Furthermore, in step three, the welding extension length of wire 1 is 29mm; the welding extension length of wire 2 is 26mm; and the welding extension length of wire 3 is 28mm.

[0032] Preferably, the welding diameter of wire 1, wire 2 and wire 3 in step three is 4mm.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] 1. The principle of this invention is as follows: In the early hydrogen-filled slow tensile test of the welded parts of the hydrogen transport steel pipe, it was found that the weld joint with higher low-temperature impact performance had better results in the hydrogen-filled slow tensile test and better resistance to hydrogen-induced damage failure. Therefore, this invention starts from the perspective of refining grains and improving low-temperature impact toughness, and invents a submerged arc welding method for hydrogen transport steel pipe based on external magnetic field stirring. By stirring the weld pool with an external magnetic field, the flow of the weld pool is promoted, and the energy of the external magnetic field is used to break the generated columnar crystals, which plays a role in refining grains and thus improving its resistance to hydrogen-induced damage failure.

[0035] 2. A fixed magnetic field causes magnetic blow of the electric arc, while a uniformly distributed magnetic field on both sides of the arc counteracts the interference of magnetic blow. In this invention, the externally applied fixed magnetic field accelerates the flow velocity of plasma in the arc, thereby compressing the arc, increasing weld penetration, and improving weld morphology. Furthermore, by controlling the different intensities of the magnetic field in the high-temperature and liquefaction zones of the molten pool, and matching the application position with the welding process, the microstructure of the weld is improved, grain growth is controlled, and the weld's resistance to hydrogen embrittlement and low-temperature toughness are enhanced, thus meeting the high requirements of the hydrogen energy industry for welding technology.

[0036] The magnetic field strength is generally classified according to intensity levels: <50mT is a weak magnetic field: the arc is slightly compressed, the penetration depth increases by about 5%-10%, the weld width narrows slightly, the arc stability is improved, and spatter is reduced. 50-150mT is a medium magnetic field: the Lorentz force dominates the molten pool flow, the penetration depth is significantly increased (15%-30%), the weld width tends to be uniform, the molten pool cooling rate is accelerated, and the grains are refined (therefore, we generally choose the medium magnetic field range). >150mT is a strong magnetic field: the arc is excessively compressed, resulting in excessively high energy density, the penetration depth increase slows down or even decreases, the weld width fluctuation intensifies (±0.5mm), the spatter rate increases by 2-3 times, and undercut defects are prone to appear at the weld edge. The magnetic field is uniformly applied, so each welding wire theoretically experiences the same magnetic field.

[0037] In addition, the application position refers to the distance between the magnetic field application point and the weld seam, as well as the direction of the magnetic field. Therefore, the position does not need to be moved, as it is preset in advance, only differing in distance and direction. Generally, there are three types of magnetic fields: longitudinal magnetic field (along the weld seam direction); transverse magnetic field (perpendicular to the weld seam direction); and vertical magnetic field (perpendicular to the workpiece surface). Different magnetic field distances will change the magnitude of the magnetic field strength, so the appropriate magnetic field strength must be achieved by adjusting the distance. Different magnetic field directions also have a significant impact. For example, a longitudinal magnetic field is better, as it can balance the convection of the molten pool and achieve the best uniformity of weld width (≤0.1mm). Furthermore, process matching refers to matching the welding current, voltage, and welding speed with the applied magnetic field strength.

[0038] 3. This invention achieves precise control of mass and heat transfer during the crystallization of the molten metal in the weld pool by introducing an external fixed magnetic field stirring technology and controlling the process parameters of multi-wire submerged arc welding. Specifically, after applying a fixed magnetic field, the welding arc and the conductive fluid in the weld pool are subjected to Lorentz force in the magnetic field, forming directional eddies (circulation velocity reaches 0.8-1.2 m / s). By adjusting the magnetic field strength (50-200 mT) and direction (longitudinal / transverse / vertical), the flow pattern of the weld pool can be precisely controlled. The longitudinal magnetic field induces the weld pool to form a symmetrical double-vortex structure along the weld direction, promoting the uniform distribution of solute elements (such as Mn and Si) and suppressing dendrite segregation; the transverse magnetic field excites transverse shear flow, shortens the solute diffusion path, compresses the solute boundary layer thickness, and improves the reaction kinetic efficiency of the weld pool; the vertical magnetic field forms vertical rotational stirring of the weld pool, eliminating local overheating and refining the equiaxed crystal ratio. In terms of heat and mass transfer: the magnetic field compresses the arc plasma (the arc diameter is reduced by 30%), and the energy density is increased to 2×10⁻⁶. 4 W / cm 2 (Conventional process 1.2×10) 4 W / cm 2The magnetic field induces the formation of a molten pool with an optimal match between the temperature gradient and the solidification rate (G / R), promoting the transformation of columnar crystals to equiaxed crystals, thereby improving its low-temperature impact toughness and resistance to hydrogen damage, and significantly extending the service life of hydrogen transport steel pipes. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the fixed magnetic field stirring device of the present invention installed on the lower end face of the test plate;

[0040] Figure 2 This is a photograph of the actual object during the embedding welding process of this invention. At this time, there are 5 welding wires.

[0041] Figure 3 These are metallographic images of the weld zone. The image on the left is the metallographic image without a magnetic field applied, and the image on the right is the metallographic image with a magnetic field applied.

[0042] Figure 4 These are metallographic images of the fusion zone structure. The image on the left is the metallographic image without an applied magnetic field, and the image on the right is the metallographic image with an applied magnetic field.

[0043] Figure 5 These are EBSD images taken during the welding process without a magnetic field. Observation shows that the grains are relatively coarse at this time.

[0044] Figure 6 The image shows an EBSD image after adding a fixed magnetic field stirring device using the welding method of this invention, where the grains are finer. Detailed Implementation

[0045] Specific implementation method one: Combining Figures 1 to 6 This embodiment describes the following steps:

[0046] Step 1: Set up the submerged arc welding test bench;

[0047] Step 2: Add an auxiliary magnetic field;

[0048] Based on the submerged arc welding equipment, an external fixed magnetic field stirring device was added directly below the test plate to generate a stable external fixed magnetic field, which acts on the weld pool area.

[0049] Step 3: Initiate the arc for welding, while simultaneously applying a magnetic field;

[0050] Welding is performed on two adjacent test plates. At this time, a magnetic field is applied by an external fixed magnetic field stirring device. The magnetic field is applied in the following way: first, a symmetrical fixed magnetic field is selected, and then the position of the N / S poles of the magnetic field is changed to achieve directional control of the external fixed magnetic field.

[0051] After the welding arc is generated, an external fixed magnetic field is applied to the molten metal in the welding pool, and the mass transfer and heat transfer processes are changed through electromagnetic stirring until the welding of the test plate is completed.

[0052] The fixed magnetic field stirring device described in this embodiment includes multiple elongated magnets. By changing the number, size, distribution distance, and direction of the magnets, the strength of the magnetic field can be altered. Currently, the best-performing data from testing shows a distance of 20mm and a size of 50*12*5mm, which effectively achieves the desired grain growth. The strength of the applied fixed magnetic field is controlled by changing the number and size of the magnets; the preferred magnetic field strength is 0.5T.

[0053] This invention utilizes an external fixed magnetic field to induce high-speed spiral motion in charged particles within the welding arc, thereby altering the arc's shape and static characteristics and improving welding stability. The stirring effect of the external fixed magnetic field also changes the microstructure of the weld metal, refining the grains and improving the mechanical properties of the weld joint, while simultaneously reducing welding defects such as porosity and cracks.

[0054] In addition, in step three of the present invention, an external fixed magnetic field stirring device works in conjunction with the submerged arc welding equipment during the welding process.

[0055] Specific Implementation Method Two: Combining Figure 2 This embodiment describes the following steps for setting up the submerged arc welding experimental platform in step one:

[0056] Step 11: Use 3 welding wires installed on a continuous automatic feeder and the same number of welding power sources. The positive terminal of each welding power source is connected to the welding torch, and the negative terminal of each welding power source is fixed to the welding platform. Each welding wire forms an independent arc.

[0057] Steps 1 and 2: The electric arcs of the three welding wires are coupled onto the workpiece and together form a molten pool;

[0058] Step 13: Number the welding wires according to the welding direction, namely wire 1, wire 2, and wire 3.

[0059] This setup facilitates optimization of wire spacing, ensuring that all welding wires remain within the weld bevel. When the welding wires are arranged longitudinally, the combined action of each arc on the molten pool can achieve a stirring effect, reducing the gas concentration in the molten pool and decreasing the probability of porosity. Furthermore, by adjusting the distance and angle between the welding wires, the shape and size of the weld can be flexibly adjusted. Other components and connection relationships are the same as in Specific Implementation Method 1.

[0060] Specific implementation method three: Combining Figure 2 In this embodiment, the grade of filament 1, filament 2, and filament 3 in steps one and three of this embodiment is H08MnMoTiB.

[0061] Other components and connections are the same as in specific embodiments one or two. The specific composition of the welding wire is shown in the table below:

[0062]

[0063] Specific implementation method four: Combination Figure 2 To explain this embodiment, in step three of this embodiment, the method of applying a fixed magnetic field symmetrically is as follows: a magnetic field generating device with the same magnetic field strength and direction is placed on the left and right sides of the weld, respectively.

[0064] In this configuration, since the molten pool formed between each welding wire in multi-wire submerged arc welding acts as an electromagnetic source, the electromagnetic interference between each arc is relatively balanced by controlling the position of the conductive copper busbar and the arc phase angle. If an external magnetic field is introduced at this point, it may interfere with the originally stable welding process. Therefore, there are currently no publicly reported applications of external fixed magnetic field stirring technology to submerged arc welding of hydrogen transport steel pipes. To solve this technical problem, this embodiment selects symmetrical application of a fixed magnetic field to avoid disrupting the static balance of the original magnetic field. Other components and connections are the same as in specific embodiments one, two, or three.

[0065] Specific Implementation Method Five: Combining Figures 1 to 2 This embodiment describes a method for controlling the direction of the applied fixed magnetic field by changing the position of the N / S poles in step three.

[0066] The N pole of the magnetic field generator of the external fixed magnetic field stirring device on the left side of the weld is facing the welding end direction;

[0067] The N pole of the magnetic field generator of the external fixed magnetic field stirring device on the right side of the weld is facing the welding start direction, and the entire magnetic field direction is perpendicular to the weld direction.

[0068] Other components and connections are the same as in specific implementation methods one, two, three, or four.

[0069] Specific Implementation Method Six: Combination Figures 1 to 2 This embodiment describes the parameters for arc initiation and welding in step three of this embodiment:

[0070] The welding current for 1 wire is 900A-1000A, the welding voltage is 32-36V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 0°.

[0071] The welding current for 2 wires is 700A-850A, the welding voltage is 36-40V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 90°.

[0072] The welding current for 3 wires is 650A-750A, the welding voltage is 32-36V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 180°.

[0073] This configuration, by adjusting these parameters, makes the welding process more stable, improves weld formation, and enhances the weld's resistance to hydrogen embrittlement and low-temperature toughness. Other components and connection relationships are the same as in any of the specific embodiments one through five.

[0074] Specific implementation method seven: Combining Figures 1 to 2 This embodiment describes the parameters for arc initiation and welding in step three of this embodiment:

[0075] The welding current for 1 wire is 950A, the welding voltage is 34V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 0°.

[0076] The welding current for 2 wires is 800A, the welding voltage is 38V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 90°.

[0077] The welding current for the 3-wire welding is 700A, the welding voltage is 40V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 180°.

[0078] This configuration, with its uneven distribution of welding wire parameters, maximizes the utilization of the characteristics of the first welding wire (DC for maximum penetration) and the subsequent two wires (AC for maximum cladding), ensuring both penetration and filler volume while preventing excessive arc heat input that could lead to severe weld metal coarsening. Other components and connections are the same as in any of the specific implementation methods one through six.

[0079] Specific implementation method eight: Combination Figures 1 to 3 In this embodiment, the welding speed of wires 1, 2, and 3 in step three is 1.2 m / min.

[0080] This setup ensures a moderate welding speed and guarantees welding quality. Excessive welding speed results in poor weld formation and an unstable arc, while excessively slow speed increases heat input, leading to a decline in the weld's mechanical properties. Other components and connections are the same as in any of the specific embodiments one through seven.

[0081] Specific Implementation Method Nine: Combining Figures 1 to 3In this embodiment, the welding extension length of wire 1 in step three is 29 mm; the welding extension length of wire 2 is 26 mm; and the welding extension length of wire 3 is 28 mm. This arrangement controls the proportion of resistance heat input by adjusting the extension length. Furthermore, considering the distribution of each welding wire, wire 2 is perpendicular to the test plate, while the others are angled. To ensure the ends of the welding wires are on the same plane, the wire lengths are different. Other components and connections are the same as in any of the specific embodiments one through eight.

[0082] Specific Implementation Method Ten: Combining Figures 1 to 3 In this embodiment, the welding diameter of wires 1, 2, and 3 in step three is 4mm.

[0083] With this setup, the diameter of the welding wire determines the current carrying capacity. To meet the requirement of approximately 800A, a 4mm diameter welding wire is necessary; otherwise, the wire will overheat and soften. Other components and connections are the same as in any of the specific implementation methods one through nine.

[0084] This invention achieves effective control over the microstructure of the weld metal through precise control of welding parameters and accurate adjustment of the applied magnetic field stirring, refining the grain size (according to backscattered electron microscopy, the average grain size was reduced by approximately 15% in this experiment), and improving the mechanical properties of the weld joint. Grain refinement reduces segregation in the weld metal, improving its plasticity and toughness. It effectively suppresses welding defects such as porosity and cracks, improving the safety and service life of the weld joint and enhancing its impact resistance.

[0085] Compared with existing technologies, the submerged arc welding method for hydrogen transport steel pipes based on external fixed magnetic field stirring proposed in this invention significantly improves the mechanical properties and reliability of the welded joint. A comparison with traditional submerged arc welding reveals that the microstructure of the weld zone, fusion zone, and heat-affected zone is significantly refined; EBSD images show significantly refined grains and an increased number of small-angle grain boundaries; and hydrogen-charged slow tensile tests show that the welded joint with the applied fixed magnetic field has higher tensile strength.

[0086] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A welding method for hydrogen transport steel pipes based on stirring with an externally applied fixed magnetic field, characterized in that: It includes the following steps: Step 1: Set up the submerged arc welding test bench, including the following steps: Step 11: Use 3 welding wires installed on a continuous automatic feeder and the same number of welding power sources. The positive terminal of each welding power source is connected to the welding torch, and the negative terminal of each welding power source is fixed to the welding platform. Each welding wire forms an independent arc. Steps 1 and 2: The electric arcs of the three welding wires are coupled to the workpiece and together form a molten pool; Step 13: Number the welding wires according to the welding direction, namely wire 1, wire 2, and wire 3; Step 2: Add an auxiliary magnetic field; Based on the submerged arc welding equipment, an external fixed magnetic field stirring device was added directly below the hydrogen transport steel pipe to generate a stable external fixed magnetic field, which acts on the weld pool area. Step 3: Initiate the arc for welding, while simultaneously applying a magnetic field; Welding is performed on two adjacent hydrogen transport steel pipes. At this time, a magnetic field is applied by an external fixed magnetic field stirring device. The magnetic field is applied in the following way: first, a fixed magnetic field is applied symmetrically, and then the position of the N / S poles of the magnetic field is changed to achieve directional control of the external fixed magnetic field. Among them, the method of applying a fixed magnetic field symmetrically is to place a magnetic field generating device with the same magnetic field strength and direction on the left and right sides of the weld, respectively. The method of controlling the direction of an external fixed magnetic field by changing the position of the N / S poles of the magnetic field is as follows: The N pole of the magnetic field generator of the external fixed magnetic field stirring device on the left side of the weld is facing the welding end direction; The N pole of the magnetic field generator of the external fixed magnetic field stirring device on the right side of the weld is facing the welding start direction, and the entire magnetic field direction is perpendicular to the weld direction. After the welding arc is generated, an external fixed magnetic field is applied to the molten metal in the weld pool, and the mass transfer and heat transfer processes are changed through electromagnetic stirring until the welding of the steel pipe for hydrogen transportation is completed. The parameters for arc initiation and welding are as follows: The welding current for 1 wire is 900A-1000A, the welding voltage is 32-36V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 0°. The welding current for 2 wires is 700A-850A, the welding voltage is 36-40V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 90°. The welding current for 3 wires is 650A-750A, the welding voltage is 32-36V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 180°.

2. The welding method for hydrogen transport steel pipes based on stirring with an external fixed magnetic field according to claim 1, characterized in that: The grade of filament 1, filament 2, and filament 3 in steps one and three is H08MnMoTiB.

3. The welding method for hydrogen transport steel pipes based on stirring with an external fixed magnetic field according to claim 2, characterized in that: The parameters for arc initiation and welding in step three are as follows: The welding current for 1 wire is 950A, the welding voltage is 34V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 0°. The welding current for 2 wires is 800A, the welding voltage is 38V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 90°. The welding current for the 3-wire welding is 700A, the welding voltage is 40V, the welding speed is 1-1.5m / min, the wire spacing is 10mm, and the phase is 180°.

4. The welding method for hydrogen transport steel pipes based on stirring with an external fixed magnetic field according to claim 3, characterized in that: In step three, the welding speed for wires 1, 2, and 3 is 1.2 m / min.

5. The welding method for hydrogen transport steel pipes based on stirring with an external fixed magnetic field according to claim 4, characterized in that: In step three, the welding extension length of wire 1 is 29mm; the welding extension length of wire 2 is 26mm; and the welding extension length of wire 3 is 28mm.

6. The welding method for hydrogen transport steel pipes based on stirring with an external fixed magnetic field according to claim 1, characterized in that: The diameter of welding wires 1, 2 and 3 in step 3 is 4mm.

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