Welding method for improving quality of 316L stainless steel hydrogen conveying pipeline joint

Abstract

The invention provides a welding method for improving the quality of a 316L stainless steel hydrogen conveying pipeline joint, and relates to the technical field of hydrogen conveying pipeline welding and manufacturing. The welding method for improving the quality of the connector of the 316L stainless steel hydrogen conveying pipeline comprises the steps that a pipe fitting groove is machined, specifically, the appearance of the pipe fitting of the 316L stainless steel hydrogen conveying pipeline is machined, cleaned and ground; pre-welding treatment is conducted on the pipe fitting, specifically, the pre-welding treatment is conducted on the machined stainless steel hydrogen conveying pipeline; welding treatment is conducted, specifically, the grooves in the ends of the two sections of 316L stainless steel hydrogen conveying pipelines subjected to pre-welding treatment are in butt joint, and then the grooves are welded through high-frequency pulse argon arc welding; and joint quality detection: carrying out quality detection on the welded joint subjected to welding treatment. According to the method, the high-quality 316L pipe fitting welding joint is obtained through reasonable pipe fitting groove design and machining, pre-welding treatment and welding treatment; the method is simple and easy to operate, green and environment-friendly, low in cost, short in process, high in efficiency and beneficial to industrial large-scale production and popularization.

Description

Technical Field

[0001] This invention relates to the technical field of welding and manufacturing of hydrogen pipelines, and in particular to a welding method for improving the quality of 316L stainless steel hydrogen pipeline joints. Background Technology

[0002] With the increasing global demand for clean energy, the construction of hydrogen transportation infrastructure has become crucial as hydrogen is a highly efficient and clean energy carrier. Hydrogen pipelines, as the core mode of large-scale hydrogen transportation, place stringent requirements on material properties and welding processes. 316L stainless steel, due to its austenitic structure, excellent corrosion resistance, and plasticity, has become the mainstream material for medium- and low-pressure hydrogen pipelines.

[0003] During the welding process of 316L stainless steel hydrogen pipelines, it is crucial to pay close attention to the impact of joint performance on the overall pipeline quality. Conventional commercial 316L welded joints typically exhibit higher hydrogen embrittlement susceptibility than the base metal. Hydrogen easily penetrates to micro-defects in the weld joint, reacting with the metal to form hydrides, leading to delayed fracture. Furthermore, grain coarsening in the weld heat-affected zone (HAZ) of 316L stainless steel hydrogen pipelines reduces the joint's toughness and strength, lowers local corrosion resistance, and impacts the safe operation of the pipeline. Simultaneously, traditional welding methods result in excessive spatter and poor weld formation, reducing welding efficiency and quality.

[0004] Chinese patent CN112475532A discloses a welding process for austenitic stainless steel 316L in high-pressure hydrogen environments. The method includes the following steps: A) beveling the weld joint of the workpiece and grinding the bevel and surrounding area to a metallic luster; B) welding in layers sequentially, including: 1) locating welding; 2) performing root pass welding; 3) performing filler pass welding; 4) performing front cover pass welding; controlling the interpass temperature of the weld to not exceed 150℃. However, this technology has technical defects such as high single-layer heat input (e.g., root pass welding current 120-150A) when using conventional TIG welding, insufficient interpass temperature of 150℃ to prevent grain growth, large grain size in the heat-affected zone leading to decreased low-temperature impact toughness of the joint, and severe oxidation on the back of the weld (generating Cr2O3 inclusions, etc.) during root pass welding due to the lack of argon purging on the inner wall of the pipe, which significantly increases hydrogen diffusion channels and reduces pipeline safety.

[0005] Chinese patent CN115922037A discloses a high-frequency pulsed argon arc welding method for 15-5PH stainless steel. This method uses machining to process the part's shape and welding bevel; first, the part is demagnetized, and then acetone or alcohol is used to clean the welding bevel and the area on both sides of it, removing oil, dust, and other impurities; high-frequency pulsed argon arc welding is performed in the solution-treated state, and the design adopts layered welding, followed by aging treatment and welding quality inspection. Obviously, this technology has the disadvantage of not adding filler wire during the root pass, which easily leads to insufficient root penetration (<0.5mm), forming a lack of fusion defect. Moreover, compared with filler wire welding, the shrinkage stress of the weld is greater and more concentrated during the welding process without filler wire, and the inherent hot cracking tendency of 15-5PH steel is superimposed, greatly increasing the risk of weld cracking.

[0006] Chinese patent CN117943666A discloses a method for welding high-temperature sodium stainless steel pipes. This method also requires machining the bevel of the pipe to be welded, cleaning and fixing it, then installing a water cooling device on the bevel, and using tungsten inert gas (TIG) welding for the root pass, fill pass, and cap pass. The welding uses a small current and low heat input. After welding, the ferrite on the weld surface is measured, and liquid penetration and radiographic testing are performed on the welded area. Obviously, this technology has technical defects such as the installation of a water cooling device around the bevel during welding, forced cooling, an increase in the proportion of columnar crystals in the weld, rapid cooling leading to σ phase precipitation, martensitic structure in the heat-affected zone (HAZ), increased brittleness, and reduced joint performance; and the root pass current is only 85-90A, resulting in shallow penetration, which may lead to poor fusion of the base metal and an increased defect rate.

[0007] Chinese patent CN114192935A discloses a method for welding ultra-low temperature high-pressure stainless steel pipes in a confined space, including beveling, pipe degreasing and cleaning, pipe inflation, alignment, plug fabrication, setting welding parameters, and welding. Clearly, this technology uses a sponge + non-woven fabric plug, which decomposes at the high welding temperature, producing organic residue and causing root welding defects. Furthermore, the plug is more than 300mm from the weld, requiring argon gas to diffuse 300mm to reach the back of the bevel, leading to excessive oxygen content, oxidation of the weld back, and increased welding defect rate. Moreover, the patent does not specify the interpass temperature, only requiring the plug to be removed after cooling, which in practice easily leads to chromium depletion in the weld and heat-affected zone, reducing joint performance.

[0008] Chinese patent CN108453349A discloses a welding method for stainless steel pipes, using stainless steel flux-cored welding wire to weld along the circumference of the pipe. The welding process includes root pass welding, filler pass welding, and capping pass welding. The root pass welding uses argon arc welding combined with internal filler wire, while the filler pass welding and capping pass welding both use CO2 gas shielded welding. Clearly, this technology uses CO2 gas shielded welding, and CO2 is a strong oxidizing gas that directly reacts with alloying elements such as Cr and Ni in stainless steel. The carbon produced by decomposition enters the weld, increasing the carbon content of the weld and forming Cr at the grain boundaries. 23 C6 precipitates cause intergranular corrosion; and when flux-cored wire is used with CO2 protection, the slag-forming agent in the stainless steel flux core cannot form stable slag in the oxidizing environment of CO2, which easily leads to technical defects such as slag breakage, porosity and lack of fusion.

[0009] Therefore, developing a welding method suitable for 316L stainless steel hydrogen pipelines to improve the quality of hydrogen pipeline joints is an urgent technical problem to be solved. Summary of the Invention

[0010] To address the technical problems inherent in existing welding methods, such as high heat input, high interpass temperatures leading to grain growth in the weld and base metal heat-affected zone, decreased low-temperature impact toughness of the joint, and welding defects like slag inclusions, porosity, and lack of fusion, this invention proposes a welding method for improving the quality of 316L stainless steel hydrogen pipeline joints. The technical solution is as follows:

[0011] A welding method for improving the quality of 316L stainless steel hydrogen pipeline joints, comprising the following steps:

[0012] S1. Pipe fitting beveling: The pipe fittings of the 316L stainless steel hydrogen pipeline are processed, cleaned and ground to obtain a 316L stainless steel hydrogen pipeline with pipe fitting welding bevel.

[0013] S2. Pre-welding treatment of pipe fittings: Pre-welding treatment is performed on the 316L stainless steel hydrogen pipeline with pipe fitting welding bevel in S1 to obtain a 316L stainless steel hydrogen pipeline with a clean and burr-free bevel surface.

[0014] S3. Welding process: The bevels of the two 316L stainless steel hydrogen pipeline ends with clean and burr-free bevel surfaces from S2 are joined together, and then the bevels are welded using high-frequency pulse argon arc welding to obtain a welded 316L stainless steel hydrogen pipeline product with welded joint.

[0015] S4. Joint Quality Inspection: Conduct quality inspection on the welded joints of the 316L stainless steel hydrogen pipeline products with welded joints that have been welded in S3.

[0016] Optionally, the welding groove in S1 adopts a V-shaped butt groove with a groove angle of 50°±5°, a blunt edge of 0.5-1mm, and a groove gap of 0.5-1mm.

[0017] Optionally, in S1, the pipe fitting shape and welding bevel are machined by turning, milling and / or grinding. Cleaning is to clean the end face and grind it with a half-round file / sandpaper.

[0018] Optionally, in S2, the pre-welding treatment involves cleaning the welding bevel and an area of ​​at least 20mm on both sides with a clean gauze soaked in acetone or alcohol to remove oil, dust, and impurities until no oil or particles are visible on the gauze. The end face is then dried with a hot air gun to prevent liquid residue.

[0019] Optionally, in S3, the high-frequency pulsed argon arc welding groove is a fixed welding process, and layered, multi-pass welding is used.

[0020] Optionally, the welding equipment used for high-frequency pulsed argon arc welding in S3 is an automatic filler wire manual argon arc welding equipment. The high-frequency pulsed argon arc welding current adopts DC positive polarity. The tungsten electrode used in high-frequency pulsed argon arc welding is a cerium tungsten electrode or a lanthanum tungsten electrode with a diameter of 2.0-3.0 mm. The end of the tungsten electrode is ground into a flat truncated cone shape with an included angle of 40-60°. The diameter of the truncated cone is 1 / 4-1 / 3 of the diameter of the tungsten electrode. The horizontal distance between the center of the tungsten electrode end and the welding wire in high-frequency pulsed argon arc welding is 3.0-4.0 mm. The filler wire used in high-frequency pulsed argon arc welding is a welding wire with a chemical composition similar to that of the base metal and a diameter of 0.8-1.0 mm.

[0021] Optionally, in S3, the pre-feeding and delayed feeding of shielding gas before welding is 3-8s, the tungsten electrode travel delay is 2-5s when welding arc ends, the current slow-down delay is 5s, and the interpass temperature control is ≤100℃ when multi-layer and multi-pass welding is performed.

[0022] Optionally, the shielding gas used in S3 high-frequency pulsed argon arc welding is argon gas with a purity of not less than 99.99%. The shielding gas is supplied to the welding torch before welding and is supplied after welding.

[0023] Optionally, the parameters for the first root pass welding in S3 are: pulse frequency 15-20kHz, peak current 130-150A, base current 80-100A, pulse current amplitude 60-80A, pulse current duty cycle 30-50%, arc voltage 9-10V, welding speed 22-24cm / min, wire feed speed 800-1000mm / min, welding torch shielding gas 11-13L / min, and back shielding gas 8-10L / min; the parameters for the fill and cover passes welding are: pulse frequency 15-20kHz, peak current 170-190A, base current 90-110A, pulse current amplitude 80-100A, pulse current duty cycle 30-50%, arc voltage 10-11V, welding speed 20-22cm / min, wire feed speed 1000-1200mm / min, and welding torch shielding gas 11-14L / min.

[0024] Optionally, the interpass temperature of high-frequency pulsed argon arc welding in S3 is strictly controlled below 100℃.

[0025] Optionally, quality inspection in S4 includes visual inspection, gauge inspection, X-ray inspection, vacuum helium leak detection, penetrant testing, and mechanical property testing of the welded joint after welding is completed.

[0026] Optionally, the 316L stainless steel hydrogen pipeline joints were subjected to visual inspection, gauge inspection, X-ray inspection, vacuum helium leak detection, and penetrant testing. No welding defects were found, and all were qualified.

[0027] Optionally, the weld metal of the 316L stainless steel hydrogen pipeline joint at room temperature has the following properties: tensile strength not less than 600 MPa, yield strength not less than 300 MPa, yield ratio of 0.49-0.51, elongation not less than 35%, and low-temperature impact toughness of -40℃ not less than 80 J.

[0028] Technical principle of the invention:

[0029] A V-shaped butt joint bevel (angle 50°±5°, blunt edge 0.5-1mm, gap 0.5-1mm) is used. The matching bevel angle and gap ensure that the arc energy is concentrated at the root of the bevel, achieving full penetration (avoiding incomplete fusion defects; traditional small-angle bevels are prone to root incomplete penetration. The blunt edge control of 0.5-1mm prevents burn-through and allows for metallurgical bonding through a small amount of base metal melting and filler wire, reducing welding stress concentration). Pre-welding treatment (acetone / alcohol cleaning + hot air drying) removes oil, oxide film, and moisture from the bevel and surrounding 20mm area, ensuring cleanliness. High-frequency pulsed TIG welding, based on the synergistic effect of its pulsed current (thermal-mechanical-metallurgical), specifically addresses the challenges of grain coarsening and hydrogen embrittlement sensitivity in 316L stainless steel welding. A 15-20kHz high-frequency pulsed current (peak value 130-190A / base value 80-110A alternating) is used, causing the molten pool to undergo rapid heating and instantaneous cooling. Cyclic operation; penetration is achieved during the peak current stage (high energy), and rapid cooling occurs during the base current stage (low energy), reducing the solidification time of the molten pool to 1 / 3 of that of traditional TIG welding (from 50ms to 15ms). Rapid cooling inhibits austenite grain growth, significantly increases grain boundary area, and significantly improves joint strength and toughness. The "molten pool stirring effect" generated by the high-frequency pulsed arc (resonance between the pulse frequency and the molten pool oscillation frequency) can promote the escape of gas in the molten pool and form refined grains, generating a large number of "hydrogen traps" (grain boundaries, dislocations), reducing the concentration of hydrogen accumulation at grain boundaries, inhibiting the formation of hydrides (such as CrH), and significantly reducing the risk of hydrogen embrittlement.

[0030] This invention achieves performance assurance through layered welding, strict temperature control, and full-process argon protection. Layered welding (root pass + filler pass + cap pass) disperses the heat input (single-layer heat input ≤12kJ / cm), avoiding grain coarsening in the heat-affected zone (HAZ) caused by single high-energy welding. An interpass temperature ≤100℃ inhibits the precipitation of the σ phase (brittle-hard phase), ensuring uniform Cr distribution in the weld and improving resistance to intergranular corrosion. The welding torch shielding gas (11-14L / min) and the back shielding gas (8-10L / min) form a "three-dimensional protection," effectively reducing the oxygen content in the bevel area and preventing oxidation of alloying elements such as Cr and Ni. The back shielding gas prevents oxidation of the pipeline's inner wall, ensuring no corrosive media accelerates hydrogen embrittlement during hydrogen transport. The filler wire is selected with a composition similar to the base metal, ensuring metallurgical compatibility between the weld and the base metal and avoiding electrochemical corrosion caused by compositional differences. The design employs tungsten electrode delayed travel and current slow-descent during arc termination, which avoids the "arc crater cracks" of traditional arc termination, reduces stress concentration at the arc crater, and ensures joint integrity.

[0031] The above technical solution has at least the following advantages compared with the existing technology:

[0032] The above-mentioned solution proposes a welding method for improving the quality of 316L stainless steel hydrogen pipeline joints. This method can solve the technical problems existing in the conventional welding method, such as high heat input and high interpass temperature, which lead to grain growth in the weld and the heat-affected zone of the base metal, decreased low-temperature impact toughness of the joint, and welding defects such as slag inclusion, porosity, and lack of fusion during the welding process. Ultimately, the 316L hydrogen pipeline joint has a room temperature tensile strength ≥600MPa, an impact toughness of -40℃ ≥80J, and a hydrogen embrittlement sensitivity ≤5%, meeting the requirements for long-term safe service under high-pressure hydrogen environment.

[0033] This invention employs high-frequency pulsed tungsten inert gas welding (TIG) to weld the weld bevel of 316L pipe fittings. The welding process features a stable arc, no spatter, and low heat input, reducing welding deformation and effectively improving weld penetration and forming performance. It also refines the grain structure of the weld joint, enhancing weld quality. The resulting weld joint exhibits excellent strength, toughness, and resistance to hydrogen embrittlement. The joint performance at both room temperature and high temperature can reach over 90% of the base material's performance, meeting the welding performance requirements for 316L pipe fittings.

[0034] The present invention optimizes the parameters of the V-shaped butt bevel (angle 50°±5°, blunt edge 0.5-1mm, gap 0.5-1mm) for pipe fitting beveling, which can achieve matching of bevel angle and gap, making the arc energy more concentrated at the root of the bevel, ensuring sufficient penetration during root pass welding, and avoiding root incomplete fusion defects caused by traditional small-angle bevels; the blunt edge is controlled at 0.5-1mm, which can prevent burn-through caused by excessive gap during welding, and can also form a uniform fusion line through the melting of a small amount of base material and filler wire, reducing stress concentration at the root.

[0035] This invention effectively removes moisture and oil from the bevel surface through pre-welding treatment of pipe fittings, avoiding the risk of weld porosity and hydrogen-induced delayed fracture caused by the decomposition of CO, H2 and other gases at high welding temperatures (≥1500℃). The burr-free, clean surface after cleaning and grinding can remove the passivation film (Cr2O3) on the bevel surface: the passivation film hinders the fusion of the base material and the welding wire, and cleaning can improve the uniformity of the fusion line and avoid incomplete fusion defects.

[0036] This invention addresses the challenges of grain coarsening and hydrogen embrittlement in 316L stainless steel welding by employing high-frequency pulsed TIG welding, leveraging the synergistic effect of its pulsed current's "thermal-mechanical-metallurgical" properties. It utilizes a 15-20kHz high-frequency pulsed current (alternating between peak 130-190A and base 80-110A), causing the molten pool to undergo a cycle of "rapid heating-instantaneous cooling." The peak current phase (high energy) achieves penetration, while the base current phase (low energy) enables rapid cooling, reducing the solidification time to one-third that of traditional TIG welding (from 50ms to 15ms). This rapid cooling inhibits austenite grain growth, significantly increases grain boundary area, and substantially improves joint strength and toughness. The "molten pool stirring effect" generated by the high-frequency pulsed arc (resonance between the pulse frequency and the molten pool oscillation frequency) promotes gas escape from the molten pool and forms refined grains, generating numerous "hydrogen traps" (grain boundaries, dislocations). This reduces the concentration of hydrogen at grain boundaries, inhibits the formation of hydrides (such as CrH), and significantly reduces the risk of hydrogen embrittlement. Performance is guaranteed through layered, multi-pass welding, strict temperature control, and full-process argon protection. Layered welding (root pass + filler pass + cap pass) disperses the heat input (single-layer heat input ≤12kJ / cm), avoiding grain coarsening in the heat-affected zone (HAZ) caused by single high-energy welding. Interpass temperature ≤100℃ inhibits the precipitation of σ phase (brittle hard phase), ensuring uniform Cr element distribution in the weld and improving resistance to intergranular corrosion. The welding torch shielding gas (11-14L / min) and back shielding gas (8-10L / min) form a "three-dimensional protection," effectively reducing the oxygen content in the bevel area and preventing the oxidation of alloying elements such as Cr and Ni. The back shielding gas prevents oxidation of the inner wall of the pipeline, ensuring that there is no corrosive medium on the inner wall during hydrogen transportation, thus accelerating hydrogen embrittlement. The filler wire is selected with a composition similar to that of the base metal, ensuring metallurgical compatibility between the weld and the base metal and avoiding electrochemical corrosion caused by compositional differences. The design employs tungsten electrode delayed travel and current slow-descent during arc termination, which avoids the "arc crater cracks" of traditional arc termination, reduces stress concentration at the arc crater, and ensures joint integrity.

[0037] This invention enables a multi-dimensional, end-to-end joint quality inspection system (covering six dimensions: visual inspection, dimensions, non-destructive testing, sealing, mechanical testing, and hydrogen embrittlement) through joint quality inspection. Combined with automated inspection technology, it ensures the safety of welded joints for the hydrogen environment service characteristics of 316L stainless steel hydrogen pipelines.

[0038] The welding method of the present invention is easy to implement and has the characteristics of high flexibility and strong adaptability. It can be applied to welding in various positions and can provide a solution to the problems of welding deformation and insufficient resistance to hydrogen embrittlement at various 316L pipe joints.

[0039] The austenitic stainless steel welding wire for hydrogen transportation pipelines prepared by this invention has a tensile strength ≥600MPa, a yield strength ≥300MPa, a hydrogen embrittlement sensitivity of 5-8%, and an elongation after fracture ≥35%.

[0040] The weld joint formed by welding a hydrogen transport pipeline to a gas turbine using austenitic stainless steel welding wire prepared in this invention has a hardness of 180-220 HV. 10 Tensile strength ≥600MPa, yield strength ≥300MPa, elongation after fracture ≥35%, hydrogen embrittlement sensitivity 5-8%, and weld impact absorption energy at -40℃ ≥80J.

[0041] In summary, compared with other traditional methods, the method of the present invention obtains high-quality 316L pipe fitting welded joints through reasonable pipe fitting beveling design and processing, pre-welding treatment, and welding treatment. The method is simple to operate, environmentally friendly, low in cost, short in process, and high in efficiency, which is conducive to large-scale industrial production and promotion. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of the welding bevel in a welding method for improving the quality of 316L stainless steel hydrogen pipeline joints according to Embodiment 1 of the present invention.

[0044] Figure 2 This is a schematic diagram of a high-frequency pulse square wave current waveform in a welding method for improving the quality of 316L stainless steel hydrogen pipeline joints according to Embodiment 1 of the present invention. Detailed Implementation

[0045] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0046] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0047] In the embodiments of the present invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that when the distinction is not emphasized, their intended meanings are consistent.

[0048] In this embodiment of the invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0049] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0050] A welding method for improving the quality of 316L stainless steel hydrogen pipeline joints, comprising the following steps:

[0051] S1. Pipe fitting beveling: The pipe fittings of the 316L stainless steel hydrogen pipeline are processed, cleaned and ground to obtain a 316L stainless steel hydrogen pipeline with pipe fitting welding bevel.

[0052] S2. Pre-welding treatment of pipe fittings: Pre-welding treatment is performed on the 316L stainless steel hydrogen pipeline with pipe fitting welding bevel in S1 to obtain a 316L stainless steel hydrogen pipeline with a clean and burr-free bevel surface.

[0053] S3. Welding process: The bevels of the two 316L stainless steel hydrogen pipeline ends with clean and burr-free bevel surfaces from S2 are joined together, and then the bevels are welded using high-frequency pulse argon arc welding to obtain a welded 316L stainless steel hydrogen pipeline product with welded joint.

[0054] S4. Joint Quality Inspection: Conduct quality inspection on the welded joints of the 316L stainless steel hydrogen pipeline products with welded joints that have been welded in S3.

[0055] Optionally, the welding groove in S1 adopts a V-shaped butt groove with a groove angle of 50°±5°, a blunt edge of 0.5-1mm, and a groove gap of 0.5-1mm.

[0056] Specifically, in S1, turning, milling, and / or grinding processes are used to process the pipe fitting shape and weld bevel. Cleaning involves cleaning the end face and polishing it with a half-round file / sandpaper.

[0057] Specifically, in S2, the pre-welding treatment involves cleaning the welding bevel and an area of ​​at least 20mm on both sides with a clean gauze soaked in acetone or alcohol to remove oil, dust, and impurities until no oil or particles are visible on the gauze. The end face is then dried with a hot air gun to prevent liquid residue.

[0058] In particular, the groove welded by high-frequency pulsed argon arc welding in S3 is a fixed weld, and it adopts layered and multi-pass welding.

[0059] Specifically, the welding equipment used for high-frequency pulsed argon arc welding in S3 is an automatic filler wire manual argon arc welding equipment. The high-frequency pulsed argon arc welding current uses DC positive polarity. The tungsten electrode used in high-frequency pulsed argon arc welding is a cerium tungsten electrode or a lanthanum tungsten electrode with a diameter of 2.0-3.0 mm. The end of the tungsten electrode is ground into a flat truncated cone shape with an included angle of 40-60°. The diameter of the truncated cone is 1 / 4-1 / 3 of the diameter of the tungsten electrode. The horizontal distance between the center of the tungsten electrode end and the welding wire in high-frequency pulsed argon arc welding is 3.0-4.0 mm. The filler wire used in high-frequency pulsed argon arc welding is a welding wire with a chemical composition similar to the base metal and a diameter of 0.8-1.0 mm.

[0060] Specifically, in S3, the pre-feeding and delayed feeding of shielding gas before welding is 3-8s, the tungsten electrode travel delay is 2-5s when welding arc ends, the current slow-descent delay is 5s, and the interpass temperature control is ≤100℃ when multiple layers and multiple passes are used.

[0061] Specifically, the shielding gas used in S3 high-frequency pulsed argon arc welding is argon gas with a purity of not less than 99.99%. The shielding gas is supplied to the welding torch before welding and is supplied after welding.

[0062] Specifically, the parameters for the first root pass welding in S3 are: pulse frequency 15-20kHz, peak current 130-150A, base current 80-100A, pulse current amplitude 60-80A, pulse current duty cycle 30-50%, arc voltage 9-10V, welding speed 22-24cm / min, wire feed speed 800-1000mm / min, welding torch shielding gas 11-13L / min, and back shielding gas 8-10L / min; the parameters for the fill and cover passes welding are: pulse frequency 15-20kHz, peak current 170-190A, base current 90-110A, pulse current amplitude 80-100A, pulse current duty cycle 30-50%, arc voltage 10-11V, welding speed 20-22cm / min, wire feed speed 1000-1200mm / min, and welding torch shielding gas 11-14L / min.

[0063] In particular, the interpass temperature of high-frequency pulsed argon arc welding in S3 is strictly controlled below 100℃.

[0064] Specifically, quality inspection in S4 includes visual inspection, gauge inspection, X-ray inspection, vacuum helium leak detection, penetrant testing, and mechanical property testing of the welded joint after welding is completed.

[0065] In particular, visual inspection, gauge inspection, X-ray inspection, vacuum helium leak detection, and penetrant testing were conducted on the 316L stainless steel hydrogen pipeline joints, and no welding defects were found, all of which were qualified.

[0066] Specifically, the weld metal of 316L stainless steel hydrogen pipeline joints at room temperature has the following properties: tensile strength not less than 600MPa, yield strength not less than 300MPa, yield-to-tensile ratio of 0.49-0.51, elongation not less than 35%, and low-temperature impact toughness of -40℃ not less than 80J.

[0067] Example 1

[0068] A welding method for improving the quality of 316L stainless steel hydrogen pipeline joints, wherein the 316L stainless steel hydrogen pipeline is a GH4099 316L pipe fitting, and the welding method for improving the quality of 316L stainless steel hydrogen pipeline joints comprises the following steps:

[0069] S1. Pipe Fitting Beveling: The pipe fittings of two 10mm thick 316L stainless steel hydrogen pipelines are machined, cleaned, and ground. Machining is performed using turning, milling, and / or grinding processes to shape the fittings and weld beveling. The weld beveling uses a V-shaped butt beveling with a beveling angle of 50°±5°, a blunt edge of 0.5-1mm, and a beveling gap of 0.5-1mm. Cleaning involves cleaning the end faces and grinding with a half-round file / sandpaper to obtain a clean, burr-free 316L stainless steel hydrogen pipeline with weld beveling. The prepared pipe fitting weld beveling is as follows: Figure 1 As shown;

[0070] S2. Pre-welding treatment of pipe fittings: The 316L stainless steel hydrogen pipeline with pipe fitting welding bevel in S1 is subjected to pre-welding treatment. The pre-welding treatment is to use a clean gauze soaked in acetone or alcohol to clean the oil, dust and impurities in the welding bevel and an area of ​​not less than 20mm on both sides until no oil or particles are visible on the gauze. The end face is then dried with a hot air gun to prevent liquid residue, resulting in a 316L stainless steel hydrogen pipeline with a clean and burr-free bevel surface.

[0071] S3. Welding Process: The bevels of the two 316L stainless steel hydrogen pipeline ends with clean and burr-free bevel surfaces from section S2 are butted together, followed by high-frequency pulsed argon arc welding (HFAT). HFAT beveling is a fixed welding process using layered, multi-pass welding. The welding equipment used is an automatic wire-filling manual argon arc welding machine. The HFAT welding current is DC positive polarity. The tungsten electrode used in HFAT welding is a 2.4mm diameter cerium tungsten electrode or lanthanum tungsten electrode, with the tungsten electrode tip ground into a flat truncated cone shape with an included angle of 50° and a cone diameter of 1 / 4 of the tungsten electrode diameter. The horizontal distance between the center of the tungsten electrode tip and the welding wire is 3.5mm. The filler wire used in HFAT welding is a welding wire with a chemical composition similar to the base metal, and a diameter of 0.8mm. The shielding gas used in HFAT welding is argon with a purity of not less than 99.99%, with a pre-feeding and delayed shielding gas feeding time of 7 seconds. The waveform of the high-frequency pulsed square wave current is as follows: Figure 2 As shown;

[0072] The parameters for the first root pass welding are: pulse frequency 17kHz, peak current 145A, base current 87A, pulse current amplitude 72A, pulse current duty cycle 42%, arc voltage 9.5V, welding speed 23cm / min, wire feed speed 900mm / min, welding torch shielding gas 12L / min, and back shielding gas 9L / min. The parameters for the fill and cover passes welding are: pulse frequency 19kHz, peak current 180A, base current 100A, pulse current amplitude 90A, pulse current duty cycle 40%, arc voltage 10.5V, welding speed 21cm / min, wire feed speed 1100mm / min, and welding torch shielding gas 13L / min. The tungsten electrode travel delay is 2.5s when the arc is extinguished, and the current descent delay is 10s. For multi-pass welding, the interpass temperature is controlled to be ≤100℃.

[0073] A welded 316L stainless steel hydrogen pipeline product with welded joints was obtained.

[0074] S4. Joint Quality Inspection: The welded joints of the 316L stainless steel hydrogen pipeline products with welded joints (S3) are inspected for quality. The quality inspection includes visual inspection, gauge inspection, X-ray inspection, vacuum helium leak detection, penetrant testing, and mechanical property testing of the welded joints after welding.

[0075] In this embodiment, the 316L stainless steel hydrogen pipeline joints were visually inspected, inspected by gauges, X-rayed, vacuum helium leak-detected, and penetrant tested. No welding defects were found, and all were qualified.

[0076] The weld metal of the 316L stainless steel hydrogen pipeline joint in this embodiment has the following characteristics at room temperature: tensile strength of 685 MPa, yield strength of 315 MPa, yield ratio of 0.5, elongation of 36.5%, and low-temperature impact toughness of 102 J at -40℃.

[0077] Example 2

[0078] A welding method for improving the quality of 316L stainless steel hydrogen pipeline joints, wherein the 316L stainless steel hydrogen pipeline is a pipe fitting with a wall thickness of 8mm, the steps of which are as follows:

[0079] S1. Pipe fitting beveling: The V-shaped butt bevel is machined by milling, with a bevel angle of 45°, a blunt edge of 0.5mm, and a bevel gap of 1mm; the end face is sanded until there are no burrs.

[0080] S2. Pre-welding treatment of pipe fittings: Clean the bevel and the 25mm area on both sides with gauze soaked in alcohol, and dry with a hot air gun (temperature 60℃).

[0081] S3. Welding Process: An automatic wire-filling manual TIG welding system is used. The tungsten electrode is a 2.0mm diameter lanthanum tungsten electrode with a 40° end angle and a 0.5mm diameter truncated cone. The welding wire diameter is 1.0mm. The shielding gas is 99.99% argon, with a pre-gas and delayed gas supply time of 5 seconds. Root pass welding parameters: Pulse frequency 15kHz, peak current 130A, base current 80A, pulse amplitude 60A, duty cycle 30%, arc voltage 9V, welding speed 24cm / min, wire feed speed 800mm / min, shielding gas 11L / min, back pass shielding gas 8L / min. Fill / cover pass welding parameters: Pulse frequency 15kHz, peak current 170A, base current 90A, pulse amplitude 80A, duty cycle 30%, arc voltage 10V, welding speed 22cm / min, wire feed speed 1000mm / min, shielding gas 11L / min. Arc termination parameters: tungsten electrode travel delay 2s, current descent delay 5s, inter-channel temperature ≤80℃.

[0082] S4. Connector quality inspection:

[0083] Non-destructive testing: No porosity or cracks, helium leak rate ≤1×10 -9 Pa·m³ / s.

[0084] Mechanical properties: tensile strength 630MPa, yield strength 320MPa, yield ratio 0.51, elongation 37%, impact toughness at -40℃ 95J.

[0085] Example 3

[0086] A welding method for improving the quality of 316L stainless steel hydrogen pipeline joints, wherein the 316L stainless steel hydrogen pipeline is a 12mm thick pipe fitting, and the steps are as follows:

[0087] S1. Pipe fitting beveling: V-shaped butt beveling is processed by grinding, with a beveling angle of 55°, a blunt edge of 1mm, and a beveling gap of 0.5mm; the end face is ground with a semi-circular file.

[0088] S2. Pre-welding treatment of pipe fittings: Clean the bevel and the 30mm area on both sides with gauze soaked in acetone, and dry with a hot air gun (temperature 50℃).

[0089] S3. Welding process: The tungsten electrode used is a 3.0mm diameter cerium tungsten electrode with an included angle of 60° at the end and a truncated cone diameter of 1.0mm; the welding wire diameter is 0.9mm; the shielding gas is 99.995% argon, and the pre-gas supply and delayed gas supply time is 10s.

[0090] Root pass welding parameters: pulse frequency 20kHz, peak current 150A, base current 100A, pulse amplitude 80A, duty cycle 50%, arc voltage 10V, welding speed 22cm / min, wire feed speed 1000mm / min, welding torch shielding gas 13L / min, back shielding gas 10L / min.

[0091] Filler / cover weld parameters: Pulse frequency 20kHz, peak current 190A, base current 110A, pulse amplitude 100A, duty cycle 50%, arc voltage 11V, welding speed 20cm / min, wire feed speed 1200mm / min, welding torch shielding gas 14L / min.

[0092] Arc termination parameters: tungsten electrode travel delay 5s, current descent delay 5s, inter-channel temperature ≤90℃.

[0093] S4. Connector quality inspection:

[0094] Non-destructive testing: The weld formation is good, and the X-ray inspection is qualified at Level I.

[0095] Mechanical properties: tensile strength 655MPa, yield strength 325MPa, yield ratio 0.50, elongation 38%, impact toughness at -40℃ 101J.

[0096] Example 4:

[0097] A welding method for improving the quality of 316L stainless steel hydrogen pipeline joints, wherein the 316L stainless steel hydrogen pipeline is a 9mm thick pipe fitting, and the steps are as follows:

[0098] S1. Pipe fitting beveling: V-shaped butt beveling is machined by turning, with a beveling angle of 50°, a blunt edge of 0.7mm, and a beveling gap of 0.8mm; sandpaper is used to polish to a mirror finish.

[0099] S2. Pre-welding treatment of pipe fittings: alcohol cleaning + hot air gun drying (temperature 55℃).

[0100] S3. Welding process: 2.4mm diameter cerium tungsten electrode, 45° end angle, 0.6mm diameter truncated cone; 0.8mm diameter welding wire; 8s shielding gas pre-feed / delay time.

[0101] Root pass welding parameters: pulse frequency 16kHz, peak current 135A, base current 85A, pulse amplitude 65A, duty cycle 35%, arc voltage 9.2V, welding speed 23.5cm / min, wire feed speed 850mm / min, welding torch shielding gas 12L / min, back shielding gas 8.5L / min.

[0102] Filler / cover weld parameters: pulse frequency 17kHz, peak current 175A, base current 95A, pulse amplitude 85A, duty cycle 35%, arc voltage 10.2V, welding speed 21.5cm / min, wire feed speed 1050mm / min, welding torch shielding gas 12L / min.

[0103] Arc closing parameters: delay 3.2s, descent 3s, inter-track temperature ≤85℃.

[0104] S4. Connector quality inspection:

[0105] Non-destructive testing: No unfused material found; penetrant testing passed.

[0106] Mechanical properties: tensile strength 660MPa, yield strength 330MPa, yield ratio 0.50, elongation 39%, impact toughness at -40℃ 98J.

[0107] Example 5

[0108] A welding method for improving the quality of 316L stainless steel hydrogen pipeline joints, wherein the 316L stainless steel hydrogen pipeline is a pipe fitting with a wall thickness of 11mm, the steps of which are as follows:

[0109] S1. Pipe fitting beveling: Milling + grinding composite process, beveling angle 52°, blunt edge 0.8mm, beveling gap 0.7mm; semi-circular file grinding.

[0110] S2. Pre-welding treatment of pipe fittings: Acetone cleaning + hot air gun drying (temperature 65℃).

[0111] S3. Welding process: 2.8mm diameter lanthanum tungsten electrode, 55° end angle, 0.8mm diameter truncated cone; 1.0mm diameter welding wire; 9s shielding gas pre-feed / delay time.

[0112] Root pass welding parameters: pulse frequency 19kHz, peak current 145A, base current 95A, pulse amplitude 75A, duty cycle 45%, arc voltage 9.8V, welding speed 22.5cm / min, wire feed speed 950mm / min, welding torch shielding gas 12.5L / min, back shielding gas 9.5L / min.

[0113] Filler / cover weld parameters: pulse frequency 18kHz, peak current 185A, base current 105A, pulse amplitude 95A, duty cycle 45%, arc voltage 10.8V, welding speed 20.5cm / min, wire feed speed 1150mm / min, welding torch shielding gas 13.5L / min.

[0114] Arc closing parameters: delay 2.8s, descent 4s, inter-track temperature ≤95℃.

[0115] S4. Connector quality inspection:

[0116] Non-destructive testing: Vacuum helium test passed, no leakage.

[0117] Mechanical properties: tensile strength 690MPa, yield strength 340MPa, yield ratio 0.49, elongation 37%, impact toughness at -40℃ 92J.

[0118] Example 6:

[0119] A welding method for improving the quality of 316L stainless steel hydrogen pipeline joints, wherein the 316L stainless steel hydrogen pipeline is a 10mm thick pipe, and the steps are as follows:

[0120] S1. Pipe fitting beveling: turning process, beveling angle 48°, blunt edge 0.6mm, beveling gap 0.9mm; sandpaper grinding.

[0121] S2. Pre-welding treatment of pipe fittings: Alcohol + acetone are used for alternating cleaning, followed by drying with a hot air gun (temperature 58℃).

[0122] S3. Welding process: 2.5mm diameter cerium tungsten electrode, 50° end angle, 0.7mm diameter truncated cone; 0.9mm diameter welding wire; 7s shielding gas pre-feed / delay time.

[0123] Root pass welding parameters: pulse frequency 18kHz, peak current 140A, base current 90A, pulse amplitude 70A, duty cycle 40%, arc voltage 9.5V, welding speed 23cm / min, wire feed speed 900mm / min, welding torch shielding gas 12L / min, back shielding gas 9L / min.

[0124] Filler / cover weld parameters: Pulse frequency 19kHz, peak current 180A, base current 100A, pulse amplitude 90A, duty cycle 40%, arc voltage 10.5V, welding speed 21cm / min, wire feed speed 1100mm / min, welding torch shielding gas 13L / min.

[0125] Arc closing parameters: delay 2.5s, descent 4s, inter-track temperature ≤88℃.

[0126] S4. Connector quality inspection:

[0127] Non-destructive testing: No defects detected by X-ray inspection, and qualified by gauge inspection.

[0128] Mechanical properties: tensile strength 675MPa, yield strength 335MPa, yield ratio 0.496, elongation 36%, impact toughness at -40℃ 86J.

[0129] The above-mentioned solution proposes a welding method for improving the quality of 316L stainless steel hydrogen pipeline joints. This method can solve the technical problems existing in the conventional welding method, such as high heat input and high interpass temperature, which lead to grain growth in the weld and the heat-affected zone of the base metal, decreased low-temperature impact toughness of the joint, and welding defects such as slag inclusion, porosity, and lack of fusion during the welding process. Ultimately, the 316L hydrogen pipeline joint has a room temperature tensile strength ≥600MPa, an impact toughness of -40℃ ≥80J, and a hydrogen embrittlement sensitivity ≤5%, meeting the requirements for long-term safe service under high-pressure hydrogen environment.

[0130] This invention employs high-frequency pulsed tungsten inert gas welding (TIG) to weld the weld bevel of 316L pipe fittings. The welding process features a stable arc, no spatter, and low heat input, reducing welding deformation and effectively improving weld penetration and forming performance. It also refines the grain structure of the weld joint, enhancing weld quality. The resulting weld joint exhibits excellent strength, toughness, and resistance to hydrogen embrittlement. The joint performance at both room temperature and high temperature can reach over 90% of the base material's performance, meeting the welding performance requirements for 316L pipe fittings.

[0131] The present invention optimizes the parameters of the V-shaped butt bevel (angle 50°±5°, blunt edge 0.5-1mm, gap 0.5-1mm) for pipe fitting beveling, which can achieve matching of bevel angle and gap, making the arc energy more concentrated at the root of the bevel, ensuring sufficient penetration during root pass welding, and avoiding root incomplete fusion defects caused by traditional small-angle bevels; the blunt edge is controlled at 0.5-1mm, which can prevent burn-through caused by excessive gap during welding, and can also form a uniform fusion line through the melting of a small amount of base material and filler wire, reducing stress concentration at the root.

[0132] This invention effectively removes moisture and oil from the bevel surface through pre-welding treatment of pipe fittings, avoiding the risk of weld porosity and hydrogen-induced delayed fracture caused by the decomposition of CO, H2 and other gases at high welding temperatures (≥1500℃). The burr-free, clean surface after cleaning and grinding can remove the passivation film (Cr2O3) on the bevel surface: the passivation film hinders the fusion of the base material and the welding wire, and cleaning can improve the uniformity of the fusion line and avoid incomplete fusion defects.

[0133] This invention addresses the challenges of grain coarsening and hydrogen embrittlement in 316L stainless steel welding by employing high-frequency pulsed TIG welding, leveraging the synergistic effect of its pulsed current's "thermal-mechanical-metallurgical" properties. It utilizes a 15-20kHz high-frequency pulsed current (alternating between peak 130-190A and base 80-110A), causing the molten pool to undergo a cycle of "rapid heating-instantaneous cooling." The peak current phase (high energy) achieves penetration, while the base current phase (low energy) enables rapid cooling, reducing the solidification time to one-third that of traditional TIG welding (from 50ms to 15ms). This rapid cooling inhibits austenite grain growth, significantly increases grain boundary area, and substantially improves joint strength and toughness. The "molten pool stirring effect" generated by the high-frequency pulsed arc (resonance between the pulse frequency and the molten pool oscillation frequency) promotes gas escape from the molten pool and forms refined grains, generating numerous "hydrogen traps" (grain boundaries, dislocations). This reduces the concentration of hydrogen at grain boundaries, inhibits the formation of hydrides (such as CrH), and significantly reduces the risk of hydrogen embrittlement. Performance is guaranteed through layered, multi-pass welding, strict temperature control, and full-process argon protection. Layered welding (root pass + filler pass + cap pass) disperses the heat input (single-layer heat input ≤12kJ / cm), avoiding grain coarsening in the heat-affected zone (HAZ) caused by single high-energy welding. Interpass temperature ≤100℃ inhibits the precipitation of σ phase (brittle hard phase), ensuring uniform Cr element distribution in the weld and improving resistance to intergranular corrosion. The welding torch shielding gas (11-14L / min) and back shielding gas (8-10L / min) form a "three-dimensional protection," effectively reducing the oxygen content in the bevel area and preventing the oxidation of alloying elements such as Cr and Ni. The back shielding gas prevents oxidation of the inner wall of the pipeline, ensuring that there is no corrosive medium on the inner wall during hydrogen transportation, thus accelerating hydrogen embrittlement. The filler wire is selected with a composition similar to that of the base metal, ensuring metallurgical compatibility between the weld and the base metal and avoiding electrochemical corrosion caused by compositional differences. The design employs tungsten electrode delayed travel and current slow-descent during arc termination, which avoids the "arc crater cracks" of traditional arc termination, reduces stress concentration at the arc crater, and ensures joint integrity.

[0134] This invention enables a multi-dimensional, end-to-end joint quality inspection system (covering six dimensions: visual inspection, dimensions, non-destructive testing, sealing, mechanical testing, and hydrogen embrittlement) through joint quality inspection. Combined with automated inspection technology, it ensures the safety of welded joints for the hydrogen environment service characteristics of 316L stainless steel hydrogen pipelines.

[0135] The welding method of the present invention is easy to implement and has the characteristics of high flexibility and strong adaptability. It can be applied to welding in various positions and can provide a solution to the problems of welding deformation and insufficient resistance to hydrogen embrittlement at various 316L pipe joints.

[0136] The austenitic stainless steel welding wire for hydrogen transportation pipelines prepared by this invention has a tensile strength ≥600MPa, a yield strength ≥300MPa, a hydrogen embrittlement sensitivity of 5-8%, and an elongation after fracture ≥35%.

[0137] The weld joint formed by welding a hydrogen transport pipeline to a gas turbine using austenitic stainless steel welding wire prepared in this invention has a hardness of 180-220 HV. 10 Tensile strength ≥600MPa, yield strength ≥300MPa, elongation after fracture ≥35%, hydrogen embrittlement sensitivity 5-8%, and weld impact absorption energy at -40℃ ≥80J.

[0138] In summary, compared with other traditional methods, the method of the present invention obtains high-quality 316L pipe fitting welded joints through reasonable pipe fitting beveling design and processing, pre-welding treatment, and welding treatment. The method is simple to operate, environmentally friendly, low in cost, short in process, and high in efficiency, which is conducive to large-scale industrial production and promotion.

[0139] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it can also represent an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0140] In this invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be a single item or multiple items.

[0141] It should be understood that, in various embodiments of the present invention, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0142] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A welding method for improving the quality of a 316L stainless steel hydrogen delivery pipe joint, characterized by, The welding method for improving the quality of the joint of the 316L stainless steel hydrogen conveying pipe is as follows: S1, pipe fitting bevel processing: the appearance of the pipe fitting of the 316L stainless steel hydrogen conveying pipe is processed, cleaned and ground to obtain the 316L stainless steel hydrogen conveying pipe with a pipe fitting welding bevel; S2, pipe fitting welding before treatment: the 316L stainless steel hydrogen conveying pipe with a pipe fitting welding bevel in S1 is subjected to welding before treatment to obtain the 316L stainless steel hydrogen conveying pipe with a clean and burr-free bevel surface; S3, welding treatment: the bevels at the ends of the two 316L stainless steel hydrogen conveying pipes with a clean and burr-free bevel surface in S2 are butt-jointed, and then the bevels are welded by high-frequency pulse argon arc to obtain the 316L stainless steel hydrogen conveying pipe product with welded joints; S4, joint quality detection: the welded joints of the 316L stainless steel hydrogen conveying pipe product with welded joints in S3 are subjected to quality detection.

2. The welding method for improving the quality of the joint of the 316L stainless steel hydrogen pipeline according to claim 1, characterized in that, In S1, the welding bevel adopts a V-shaped butt joint bevel, the bevel angle is 50°±5°, the land is 0.5-1mm, and the bevel gap is 0.5-1mm.

3. The welding method for improving the quality of the joint of the 316L stainless steel hydrogen pipeline according to claim 1, characterized in that, In S1, the appearance of the pipe fitting and the welding bevel are processed by turning, milling or / and grinding process, and the end face is cleaned and ground with a half-round file / sandpaper.

4. The welding method for improving the quality of the joint of the 316L stainless steel hydrogen transport pipe according to claim 1, characterized in that, In S2, the welding before treatment is to clean the welding bevel and the area of not less than 20mm on both sides of the welding bevel with clean gauze dipped in acetone or alcohol to remove oil stains, dust and impurities until no oil stains and particles are seen on the gauze, and the end face is dried with a hot air gun to prevent liquid residue.

5. The welding method for improving the quality of the joint of the 316L stainless steel hydrogen transport pipe according to claim 1, characterized in that, In S3, the high-frequency pulse argon arc welding of the bevel belongs to fixed welding, and adopts layered and channelized welding.

6. The welding method for improving the quality of the joint of the 316L stainless steel hydrogen transport pipe according to claim 1, characterized in that, In S3, the welding equipment used for high-frequency pulse argon arc welding is automatic wire filling manual argon arc welding equipment, the welding current of high-frequency pulse argon arc welding adopts direct current positive connection, the tungsten electrode of high-frequency pulse argon arc welding adopts cerium tungsten electrode or lanthanum tungsten electrode with a diameter of 2.0-3.0mm, the end of the tungsten electrode is ground into a truncated cone, the end angle is 40-60°, and the truncated cone diameter is 1 / 4-1 / 3 of the diameter of the tungsten electrode; the horizontal distance between the center of the end of the tungsten electrode and the welding wire is 3.0-4.0mm; the filling wire welding material used for high-frequency pulse argon arc welding is a welding wire with chemical composition similar to that of the base material, and the diameter of the welding wire is 0.8-1.0mm.

7. The welding method for improving the quality of the joint of the 316L stainless steel hydrogen transport pipe according to claim 1, characterized in that, In S3, the protective gas used for high-frequency pulse argon arc welding is argon with a purity of not less than 99.99%, the welding gun protective gas is pre-delivered before welding, and the protective gas delivery is maintained after welding.

8. The welding method for improving the quality of the joint of the 316L stainless steel hydrogen transport pipe according to claim 5, characterized in that, The first layer of S3 is prepared by using the welding parameters as follows: pulse frequency 15-20 kHz, peak current 130-150 A, base current 80-100 A, pulse current amplitude 60-80 A, pulse current duty cycle 30-50%, arc voltage 9-10 V, welding speed 22-24 cm / min, wire feeding speed 800-1000 mm / min, welding gun shielding gas 11-13 L / min, back shielding gas 8-10 L / min; the filling and covering layer is prepared by using the welding parameters as follows: pulse frequency 15-20 kHz, peak current 170-190 A, base current 90-110 A, pulse current amplitude 80-100 A, pulse current duty cycle 30-50%, arc voltage 10-11 V, welding speed 20-22 cm / min, wire feeding speed 1000-1200 mm / min, welding gun shielding gas 11-14 L / min.

9. The welding method for improving the quality of the joint of the 316L stainless steel hydrogen transport pipe according to claim 1, characterized in that, The temperature between the welding tracks in S3 is strictly controlled below 100℃.

10. The welding method for improving the quality of the joint of the 316L stainless steel hydrogen transport pipe according to claim 1, characterized in that, The quality detection in S4 includes visual detection, gauge detection, X-ray detection, vacuum helium leak detection, penetration detection and mechanical property test.

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