A welding method based on low spatter outside root welding and melting electrode double pulse filling welding

Abstract

The application discloses a welding method based on low-splashing outer root welding and fusion electrode double-pulse covering welding, relates to the technical field of pipeline welding, and comprises the following steps: S1, welding preparation: adopting a beveling machine to process a U-shaped groove on a pipeline to-be-welded end and performing groove assembly; S2, outer root welding, hot welding, filling welding and covering welding processes: adopting 100% CO2 as a protective gas and low-splashing welding mode to perform welding, adopting a mixed gas of 80% Ar and 20% CO2 as a protective gas and double-pulse mode to perform welding, and adjusting swing, heat input and walking speed according to the flat welding, vertical welding and overhead welding positions; and S3, post-welding inspection: detecting the appearance, defects and size of the weld.The application realizes full-position automatic stable continuous welding of the pipeline, the welding spatter is small during the whole welding process, the arc combustion is stable, the interlayer fusion is reliable, the overall appearance of the finally obtained weld is beautiful and regular, the internal density of the weld is excellent, and the defect occurrence rate is low.

Description

Technical Field

[0001] This invention relates to the field of pipeline welding technology, and more specifically, to a welding method based on low-spatter external root welding and consumable electrode double-pulse filler welding. Background Technology

[0002] Oil and natural gas are key strategic resources for the nation, vital to many sectors of production and daily life. However, most oil and gas resources are concentrated in sparsely populated, remote areas, and transportation from production sites to densely populated areas mainly relies on oil and gas pipelines. In actual industrial production and engineering applications, due to limitations in processing, transportation, and installation conditions, the length of prefabricated pipelines in factories is often insufficient to meet on-site laying requirements. Therefore, multiple pipeline sections need to be joined together on-site through circumferential welding to achieve a continuous and sealed connection of the pipeline.

[0003] However, during pipeline construction, the circumferential welding operations span a wide area, making molten pool control challenging. From root welding and hot welding to filler and capping welding, appropriate welding processes must be selected to simultaneously ensure weld quality and construction efficiency. Traditional manual welding for the root pass and filler pass is inefficient, prone to defects such as incomplete fusion, undercut, and porosity, and requires highly skilled welders, making it commonly used only in scenarios requiring more flexible welding methods. Internal welding machine root pass welding followed by external welding machine filler pass welding produces high-quality welds with easier defect control, offering higher levels of automation and efficiency, but is more difficult to operate and incurs higher equipment and maintenance costs. The fully automated external welding machine root pass welding and filler pass strategy requires only one automated welding carriage to complete the entire process, offering high speed, high efficiency, and lower cost, making it a promising solution.

[0004] In existing processes, root weld layers typically employ non-consumable electrode gas shielded root welds, CO2 gas shielded root welds, or low-spatter root welds. Among these, TIG welding suffers from low welding speed, a wide heat-affected zone, stringent on-site wind protection requirements, and significant challenges in automation integration, making it difficult to meet the demands of oil and gas pipeline construction for welding efficiency, automation levels, and environmental conditions. While CO2 gas shielded root welds offer high deposition efficiency, fast welding speed, strong arc penetration, and deep penetration, they also suffer from significant spatter, a softer arc, and higher heat input, resulting in poor adaptability to all-position welding and limitations in oil and gas pipeline welding. Low-spatter root welds, while achieving penetration depth comparable to CO2 gas shielded root welds, effectively reduce large-particle spatter during welding, lower heat input, and improve the stability of the weld pool in all positions, making them more suitable for automation integration requirements.

[0005] On the other hand, the filler and capping layers commonly employ gas metal arc welding (GMAW). Compared to DC constant current welding, this process significantly improves arc stability and droplet transfer uniformity, while also making the heat input more gentle and concentrated. However, conventional GMAW processes lack sufficient precision in heat input control, making it difficult to balance droplet transfer and weld pool stability across all welding directions and locations on the pipeline. This can easily lead to problems such as low welding efficiency, high weld repair rates, and poor consistency in joint mechanical properties, making it difficult to meet the stringent service requirements of high pressure, long service life, and high reliability for long-distance oil and gas pipelines.

[0006] Therefore, for field circumferential welding technology, there is an urgent need for a welding method that can achieve low spatter at the root, uniform and stable back-side formation, fine-grained control of heat input zones, and consistent and controllable molten pool morphology. Summary of the Invention

[0007] To address the shortcomings of existing all-position pipeline welding processes, such as low precision in heat input control, numerous welding defects, and inconsistent weld formation due to the traditional CO2 gas shielded root welding followed by conventional consumable electrode pulse (MAP) filler welding, and considering the complex conditions of all-position and multi-position welding of circumferential seams in long-distance oil and gas pipelines, this invention provides a welding method based on low-spatter external root welding and MAP double-pulse filler welding. Taking into account the differences in gravity, heat dissipation conditions, and molten pool stress characteristics in different regions of the pipeline, this invention sets general operating parameters such as wire feed speed, oscillation frequency, oscillation amplitude, welding torch dwell time, and carriage travel speed, as well as specific parameters such as double-pulse frequency and duty cycle, for different zones and sections. This achieves precise and zoned control of welding heat input, effectively balancing arc energy output under different welding postures. It ensures continuous and stable droplet transition in flat, vertical, and overhead welding positions, with controllable and stable molten pool morphology. This avoids problems such as molten pool flow, sagging, and poor weld formation caused by gravity and uneven heat input, significantly improving the engineering practicality of automated all-position pipeline welding.

[0008] To achieve the objective of this invention, the technical solution adopted is as follows: a welding method based on low-spatter outer root welding and consumable electrode double-pulse filler welding, comprising the following steps: S1. Pre-welding preparation: Strictly standardize the beveling form and dimensional accuracy. Use a special beveling machine to uniformly process the two pipe sections to be welded into U-shaped beveles suitable for low spatter root welding and double pulse filler welding. At the same time, use a high-precision alignment machine to complete the pipe end assembly. Strictly control the pipe end misalignment and alignment gap to reduce poor fusion and forming defects caused by misalignment and uneven gap. S2. External root welding, hot welding, filler welding, and cover welding processes: External root welding uses 100% CO2 as the shielding gas and is performed using a low-spatter welding mode; Hot welding, filler welding, and cover welding use a mixed gas of 80% Ar and 20% CO2 as the shielding gas and are performed using a high-speed pulse double-pulse mode, with the oscillation, heat input, and travel speed adjusted according to the flat welding, vertical welding, and overhead welding positions respectively; By combining Ar's excellent arc stabilization performance with CO2's superior deoxidation ability, stable arc combustion throughout the process and good deoxidation effect of the molten pool are ensured, reducing internal oxidation defects in the weld and further improving the density and mechanical uniformity of the weld structure. S3. Post-weld inspection: Inspect the appearance, defects, and dimensions of the weld. That is, after welding is completed, a systematic post-weld inspection is carried out in accordance with the requirements of pipeline engineering acceptance specifications. The surface formation, appearance defects, weld dimensional accuracy and surface continuity of the weld are comprehensively inspected and investigated in sequence. Appearance problems such as undercut, surface porosity, cracks and local lack of fusion are promptly investigated to ensure that the overall appearance quality and internal quality of the weld meet the construction and acceptance standards of long-distance oil and gas pipelines.

[0009] Furthermore, before beveling, a standardized pre-welding cleaning process is strictly implemented to thoroughly clean the inner wall of the pipe bevel, the outer wall of the bevel, and the surface of the pipe base material within the specified range on both sides of the bevel. This process thoroughly removes attached oil, rust oxide, surface moisture, and various impurities and contaminants to prevent internal defects such as porosity, slag inclusions, and oxide inclusions caused by residual impurities during welding.

[0010] Furthermore, the U-shaped bevel has a bevel angle of 3–5°, a blunt edge of 1.0–1.5 mm, an arc radius of 3.0–3.2 mm, a butt joint gap of 0–0.5 mm, and a half-bevel width of 3.5–4.5 mm. This U-shaped bevel design is compatible with low-spatter root welding and MIG double-pulse filler welding, which can reduce the filler volume, improve the fusion effect, and reduce the incidence of incomplete penetration and incomplete fusion defects.

[0011] Furthermore, in step S2, the flow rate of the shielding gas is 15-20 L / min to ensure arc stability and good deoxidation of the weld. This not only avoids porosity caused by insufficient gas flow and poor protection, but also avoids porosity caused by excessive gas flow and turbulence that can entangle air. The welding wire is a solid wire, and ER70S-G or ER80S-G welding wire is selected. The wire diameter is 1.0 mm and the wire extension length is 8-15 mm.

[0012] Furthermore, in step S2, the flat welding position is -20° to 45°, the vertical welding position is 45° to 135°, and the overhead welding position is 135° to 225°. In the flat welding position, the direction of gravity of the molten pool is consistent with the direction of arc pressure, which allows for an appropriate increase in welding travel speed. This avoids excessive force on the molten pool during root welding, preventing burn-through, and also improves overall construction efficiency. In the vertical welding position, the welding torch oscillation amplitude can be appropriately reduced to decrease heat input per unit area and slow down the flow of molten pool metal. In the overhead welding position, the arc length can be reasonably shortened, and the overall volume of the molten pool can be compressed to reduce the risk of the high-temperature molten pool falling due to gravity. In the actual welding process, based on the corresponding weld layer and welding angle, the automatic welding system can perform welding sequentially according to the corresponding process. Through zoned differential control, the width of the entire circumferential weld is uniform, the reinforcement height is consistent, and the formation is uniform. At the same time, the process parameters of the corresponding weld layer and welding angle are input into the control program, allowing the automatic welding system to perform welding sequentially according to the corresponding process.

[0013] Furthermore, the welding path in step S2 is: arc initiation at the vertex → half-side welding → return to the vertex → welding the other half-side.

[0014] Furthermore, the welding parameters for the external root welding are as follows: wire feed speed of 3.5–5 m / min, travel speed of 30–45 cm / min, swing width of 0.7–0.9 mm, oscillation frequency of 140–170 times / min, welding torch tilt angle of 3–8°, dwell time after welding torch oscillation of 30–200 ms, and extension length of 10 mm. This ensures root penetration in low-splash mode, resulting in uniform weld formation on the back side without incomplete penetration, concavity, or burn-through.

[0015] Furthermore, the welding parameters for hot welding are as follows: wire feed speed is 7.7–11.9 m / min, wire feed speed variation is 0.5–1.5 m / min, travel speed is 36–52 cm / min, swing width is 1.4–2.0 mm, oscillation frequency is 150–210 times / min, double pulse frequency is 1.5–3 Hz, and duty cycle is 40–50%.

[0016] Furthermore, the welding parameters for filler welding are as follows: wire feed speed is 8.5–11.3 m / min, wire feed speed variation is 1.5–2.5 m / min, welding voltage is 21.0–22.5 V, travel speed is 32–50 cm / min, swing width is 1.6–2.9 mm, oscillation frequency is 120–190 times / min, double pulse frequency is 2–3 Hz, duty cycle is 40%–50%, and interpass temperature is 80–150 °C.

[0017] Furthermore, the welding parameters for the cover weld are as follows: wire feed speed is 5.1–6.7 m / min, wire feed speed variation is 1.5–3 m / min, welding voltage is 21.0–22.5 V, travel speed is 38–56 cm / min, swing width is 0.3–0.7 mm, oscillation frequency is 120–160 times / min, double pulse frequency is 3–6 Hz, and duty cycle is 50%.

[0018] Furthermore, the swinging mode in step S2 is either an angular swing or a horizontal swing.

[0019] The beneficial effects of this invention are: The external root welding process in this invention employs a low-spatter welding mode, which effectively suppresses root spatter and precisely controls the root heat input while ensuring a reasonable penetration depth. This results in a smooth root weld surface, free of spatter adhesion, and with uniform back weld height. Compared to the rough surface and large-particle spatter produced by traditional CO2 gas shielded root welding, the substrate formed by the low-spatter welding mode provides a stable physical arc environment and uniform conductive distance for the hot weld layer. This eliminates arc disturbances caused by irregular weld surface morphology, greatly improving welding stability and forming quality. Furthermore, compared to internal welding machine root pass, single-sided welding with double-sided forming can be achieved without changing equipment or root cleaning throughout the entire process.

[0020] In this invention, the hot-welding, filler welding, and capping welding processes utilize a high-speed pulse dual-pulse mode. This allows for independent matching of dedicated heat input ranges and welding process parameters for each layer based on the fusion requirements, filler volume, and interlayer heat dissipation conditions. This ensures thorough fusion and smooth transitions in each weld bead. Simultaneously, the hot-welding layer process incorporates a smaller variation in wire feed speed. Compared to ordinary high-speed pulses, this invention leverages the advantage of a gentler and more concentrated dual-pulse heat input, guaranteeing root penetration while avoiding excessive heat input that could cause back-side burn-through. Furthermore, it prevents uneven heating on the back side due to excessive wire feed speed variations, thus avoiding defects such as incomplete penetration and undercut. In the filler welding process, a lower arc stiffness and voltage are used simultaneously, along with a higher pulse frequency, resulting in a short and wide arc shape. Compared to ordinary pulsed consumable electrode filler welding, this improves the fusion of the molten pool to the sidewalls. Furthermore, utilizing the dual-pulse process's ability to switch between large and small wire speeds, a wider arc can be obtained under lower heat input conditions. This reduces the risk of the high-temperature molten pool sagging due to gravity during overhead welding and further enhances the fusion of the molten pool to the sidewalls. In the cap welding process, by increasing the voltage and using appropriate dual-pulse frequency and wire feed speed variations, this invention increases the molten pool width compared to ordinary pulsed consumable electrode cap welding, making it easier to obtain a uniform, continuous, and smooth surface. Simultaneously, the alternating molten pool size formed within the dual-pulse large and small wire speed cycles results in a clear, regular, and aesthetically pleasing fish-scale pattern after solidification.

[0021] This invention enables automated, stable, and continuous welding of pipelines in all positions, with minimal welding spatter, stable arc combustion, and reliable interlayer fusion throughout the process. The resulting weld has a beautiful and regular overall shape, excellent internal density, and a low defect rate. Furthermore, the welding method provided by this invention is highly adaptable and can be adapted to automated pipeline welding construction in complex field conditions such as mountains and plateaus, making it suitable for large-scale, mass application in long-distance oil and gas pipeline welding projects. Attached Figure Description

[0022] The accompanying drawings illustrate exemplary embodiments of the present invention and, together with the description thereof, serve to explain the principles of the present invention. These drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification.

[0023] Figure 1 This is a schematic diagram showing the direction of movement of the welding trolley on the pipeline during the external root welding, hot welding, filler welding, and cover welding processes in this invention. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the present invention are shown in the accompanying drawings.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] The following are the basic parameters that will serve as welding reference parameters for subsequent embodiments: Pipe selection: Pipe diameter 1219mm, wall thickness 18mm, steel grade ≥X70; Beveling: U-shaped beveling, with a beveling angle of 3-5°, a blunt edge of 1.0-1.5mm, a root radius of 3.0-3.2mm, a gap of 0-0.5mm, and a half-beveling width of 3.5-4.5mm; Shielding gas: 100% CO2 is used for external root welding, and a mixture of 80% Ar and 20% CO2 is used for hot welding, fill welding and cover welding. The gas flow rate is 15-20 L / min. Welding wire: Model ER70S-G or ER80S–G, diameter 1.0mm; Pre-welding preparation: Use a beveling machine to process a U-shaped bevel on the pipe end to be welded, and remove oil, rust, moisture and oxide scale from the inner wall, outer wall and 20mm range on both sides of the bevel. After the bevel is dried, use a high-precision beveling machine to perform gapless beveling. The beveling gap is 0-0.5mm and the misalignment is less than 1.5mm, which ensures that both sides of the bevel can be easily and uniformly fused, the blunt edge can be easily completely melted, and the back forming can easily meet the specifications. Welding equipment: A track-type fully automatic welding system is adopted. Before welding, the track of the track-type fully automatic welding system is installed and fixed outside the pipe, about 70cm away from the edge of the bevel, parallel to the edge of the bevel. This distance ensures that the center of the welding torch of the welding carriage in the track-type fully automatic welding system can be aligned with the center of the weld. At the same time, the welding carriage is installed and fixed above the track. It is confirmed that the welding torch has sufficient lateral movement margin, and the position of the welding torch is adjusted to align with the center of the weld. The welding carriage is moved to the top of the pipe. A suitable nozzle and contact tip are used, and the dry extension is set to 8-15mm to ensure that the contact tip can be smoothly inserted into the bevel and will not contact the edge of the bevel during the swing. Post-welding inspection: visual inspection, non-destructive testing, mechanical property testing, spatter measurement.

[0027] Example 1 In the welding method provided in this embodiment 1, the steps of external root welding, hot welding, filler welding, and capping welding are as follows: External root welding process: 100% CO2 is used as the shielding gas and low spatter welding mode is used for welding. The wire feed speed is 3.5-5m / min, the travel speed is 30-45cm / min, the welding gun swing mode is angular swing or flat swing, the swing width is 0.7-0.9mm, the swing frequency is 140-170 times / min, the welding gun tilt angle is 3-8°, and the dwell time after the welding gun swing is 30-200ms.

[0028] Specifically, during the external root welding process, such as Figure 1 As shown, first operate the welding carriage from the top of the pipe to the bottom of the pipe to complete half-side welding, then move the welding carriage to the top of the pipe and weld to the bottom position with the same welding parameters to complete the outer root welding.

[0029] During welding, it is necessary to appropriately reduce the swing width, welding voltage, and dwell time after the welding torch swings in the vertical welding position, and appropriately increase the wire feeding speed and travel speed to prevent the molten pool from falling due to gravity, and to ensure that the weld is uniform in shape, without undercut, falling, or burn-through. In the overhead welding position, it is necessary to appropriately reduce the welding voltage, reduce the dwell time after the welding torch swings, and increase the travel speed and swing width to shorten the arc and control the volume of the molten pool.

[0030] In terms of arc condition, the arc should maintain stable combustion throughout the welding process, with a crisp and continuous arc sound and a uniform droplet transfer frequency. Regarding weld formation, without the use of a ceramic backing, these welding parameters effectively achieve single-sided welding with double-sided forming, resulting in a smooth, spatter-free internal surface of the weld, and the weld back forming is no lower than the base metal, thus avoiding additional root cleaning operations.

[0031] Hot welding process: A mixture of 80% Ar and 20% CO2 is used as the shielding gas, and welding is performed in a high-speed pulse double-pulse mode. The wire feed speed is 7.7-11.9 m / min, the wire feed speed variation is 0.5-1.5 m / min, the travel speed is 36-52 cm / min, the welding gun oscillation mode is angular oscillation or horizontal oscillation, the oscillation width is 1.4-2.0 mm, the oscillation frequency is 150-210 times / min, the double pulse frequency is 1.5-3 Hz, the duty cycle is 40-50% for horizontal and vertical welding, and 40% for overhead welding.

[0032] Specifically, during the hot welding process, such as Figure 1 As shown, first operate the welding trolley from the top of the pipe to the bottom of the pipe to complete half-side welding, then move the welding trolley to the top of the pipe and weld to the bottom position with the same welding parameters to complete the hot welding.

[0033] During the welding process, it is important to ensure that the wire feed speed does not change too much during hot welding to avoid uneven remelting at the root.

[0034] From the perspective of arc condition, the arc should maintain a relatively wide arc surface and a relatively short arc length during the hot welding process. When the strong and weak pulses alternate, the arc length should not fluctuate drastically. The sound frequency should be regular, and there should be no arc breakage or set screw phenomenon. This is due to the stable arc environment provided by the weld formed by the outer root weld. The parameter settings in this hot welding process can enhance the remelting of the root weld, eliminate defects such as incomplete penetration and interlayer incomplete fusion, stabilize the back reinforcement of the weld, and at the same time prevent concavity, weld beads, and local overheating burn-through.

[0035] Filler welding process: A mixture of 80% Ar and 20% CO2 is used as the shielding gas, and welding is performed in a high-speed pulse double-pulse mode. The wire feed speed is 8.5-11.3 m / min, the wire feed variation is 1.5-2.5 m / min, the welding voltage is 21.0-22.5 V, the travel speed is 32-50 cm / min, the welding torch oscillation mode is angular or horizontal, the oscillation width is 1.6-2.9 mm, the oscillation frequency is 120-190 times / min, the double pulse frequency is 2-3 Hz, the duty cycle is 40% for overhead welding, the duty cycle is 40-50% for horizontal and vertical welding, the duty cycle is 40% for overhead welding, and the interpass temperature is 80-150℃.

[0036] Specifically, during the filler welding process, such as Figure 1 As shown, first operate the welding carriage from the top of the pipe to the bottom of the pipe to complete half-side welding. Then move the welding carriage to the top of the pipe and weld to the bottom position with the same welding parameters to complete single-layer filler welding. Then repeat the above operation until the height difference between the weld surface and the outer surface of the pipe is 1.5mm, then stop, which completes all filler welding.

[0037] During the formation of each layer of weld, each layer of weld should be kept flat, with good fusion between the two sides of the weld and the groove wall, and free from defects such as slag inclusions, lack of fusion, and undercut, so as to provide sufficient space for subsequent cover welding.

[0038] During welding, the interpass temperature needs to be strictly controlled within the range of 80 to 150 degrees Celsius, and the duty cycle should be flexibly reduced in the overhead welding position to avoid severe heat accumulation, which could cause the molten pool to drop.

[0039] Cover welding process: A mixture of 80% Ar and 20% CO2 is used as the shielding gas, and welding is performed in a high-speed pulse double-pulse mode. The wire feed speed is 5.1-6.7 m / min, the wire feed variation is 1.5-3 m / min, the welding voltage is 21.0-22.5 V, the travel speed is 38-56 cm / min, the welding torch oscillation mode is angular oscillation or horizontal oscillation, the oscillation width is 0.3-0.7 mm, the oscillation frequency is 120-160 times / min, the double pulse frequency is 3-6 Hz, and the duty cycle is 50%.

[0040] Specifically, during the cover welding process, such as Figure 1 As shown, first operate the welding trolley from the top of the pipe to the bottom of the pipe to complete half-side welding. Then move the welding trolley to the top of the pipe and weld to the bottom position with the same welding parameters to complete the cover weld.

[0041] By using the above parameters for cover welding, the weld formation is uniform, the fish scale pattern is clear, and the excess height is moderate.

[0042] By adopting the welding method provided in this embodiment 1, not only is the systemic contradiction between root welding quality and all-position filling and forming resolved, but also multiple technical goals are achieved, including low spatter at the root (no need for slag removal), uniform and stable back-side forming, controllable molten pool in all positions, aesthetically pleasing weld appearance, and uniform mechanical properties.

[0043] Comparative Example 1 In the welding method provided in Comparative Example 1, the steps of external root welding, hot welding, filler welding, and capping welding are as follows: External root welding process: Welding is carried out using CO2 short-circuit transfer mode, with wire feed speed of 3.5-5m / min, travel speed of 30-45cm / min, welding torch oscillation mode of angular swing or flat swing, swing width of 0.7-0.9mm, oscillation frequency of 140-170 times / min, welding torch tilt angle of 3-8°, and welding torch dwell time after swing of 30-200ms; Under the same parameters, when using CO2 short-circuit transfer mode for external root welding, the arc impact force is larger, the spatter is also larger, the weld back formation is a state of bulging in the middle and concave on both sides, and there are obvious large particles of spatter on both sides of the bevel and the weld bead.

[0044] Hot welding process: Welding is performed using a high-speed pulse mode, with a wire feed speed of 7.7–11.9 m / min, a wire feed variation of 1.5–2.5 m / min, a welding voltage of 21.0–22.5 V, a travel speed of 36–52 cm / min, and a welding torch oscillation mode of angular or horizontal swing with a swing width of 1.4–2.0 mm and an oscillation frequency of 150–210 times / min. Due to the presence of large particles of spatter on the surface of the outer root weld layer, the arc stability will be affected when the hot weld layer is welded to this area, increasing the risk of defects. On the other hand, the heat input of ordinary high-speed pulse is relatively large. Under the same parameters, the phenomenon of molten pool sagging is prone to occur in the overhead welding position, causing the weld center to bulge outward.

[0045] Filler welding process: High-speed pulse mode is used for welding, with wire feed speed of 8.5-11.3 m / min, wire feed variation of 1.5-2.5 m / min, welding voltage of 21.0-22.5 V, travel speed of 32-50 cm / min, welding torch oscillation mode of angular swing or flat swing, swing width of 1.6-2.9 mm, oscillation frequency of 120-190 times / min, and interpass temperature of 80-150℃. Because the previous weld layer is convex from the center outward and lower on both sides, incomplete fusion is likely to occur on both sides of the bevel when in the overhead welding position during filler welding. As the number of weld layers increases, the height difference will gradually accumulate, and the probability of incomplete fusion will also increase.

[0046] Cover welding process: High-speed pulse mode is used for welding, with wire feed speed of 5.1-6.7 m / min, wire feed variation of 1.5-3 m / min, welding voltage of 21.0-22.5 V, travel speed of 38-56 cm / min, welding torch oscillation mode of angular swing or flat swing, swing width of 0.3-0.7 mm, and oscillation frequency of 120-160 times / min. Due to the lack of variation in wire feed speed, it is difficult to form clear fish scale pattern in high-speed pulse mode. At the same time, the heat input is too large, and the molten pool is more likely to fall in the overhead welding position due to gravity, and more likely to flow downward in the vertical welding position, resulting in low uniformity of formation.

[0047] Comparative Example 2 In the welding method provided in Comparative Example 2, the steps of external root welding, hot welding, filler welding, and capping welding are as follows: External root welding process: CO2 short-circuit transfer mode is used for welding, wire feed speed is 3.5-5m / min, travel speed is 30-45cm / min, welding torch oscillation mode is angular oscillation or flat oscillation, oscillation width is 0.7-0.9mm, oscillation frequency is 140-170 times / min, welding torch tilt angle is 3-8°, and the dwell time after welding torch oscillation is 30-200ms. Under the same parameters, the arc impact force of ordinary CO2 external root welding is larger, the amount of spatter is more, a large number of large particles of spatter are attached to the bevel sidewall and weld surface, the weld back formation is uneven with a bulge in the middle and a depression on both sides, the root surface roughness is high, and an additional slag removal process is required before subsequent welding can be carried out.

[0048] Hot welding process: High-speed pulse double-pulse mode is used for welding. The wire feed speed is 7.7-11.9 m / min, the wire feed variation is 0.5-1.5 m / min, the welding voltage is 21.0-22.5 V, the travel speed is 36-52 cm / min, the welding torch oscillation mode is angular oscillation or horizontal oscillation, the oscillation width is 1.4-2.0 mm, the oscillation frequency is 150-210 times / min, the double pulse frequency is 1.5-2 Hz, the duty cycle is 40% for overhead welding, 40-50% for horizontal and vertical welding, the duty cycle is 40% for overhead welding, and the interpass temperature is 80-150℃. Hot welding in high-speed double-pulse mode has better heat input control accuracy than ordinary pulse mode and the stability of the molten pool in all positions is improved. However, due to the interference of large particles of spatter remaining on the surface of the outer root weld layer, the arc is prone to drift and sudden changes in arc distance when the welding torch passes through the spatter protrusions. The uniformity of root remelting is affected, and the risk of incomplete interpass fusion is still relatively high.

[0049] Filler welding process: High-speed pulse double-pulse mode is used for welding, with wire feed speed of 8.5-11.3m / min, wire feed variation of 1.5-2.5m / min, welding voltage of 21.0-22.5V, travel speed of 32-50cm / min, welding torch oscillation mode of angular swing or horizontal swing, swing width of 1.6-2.9mm, oscillation frequency of 120-190 times / min, double pulse frequency of 2-3Hz, duty cycle of 40% for overhead welding, and duty cycle of 40-50% for horizontal and vertical welding, and interpass temperature of 80-150℃. In high-speed double-pulse mode, the heat input can be dynamically adjusted by switching between large and small wire speeds. The sag of the molten pool in the overhead welding position is reduced compared with ordinary pulse filler welding, and the sidewall fusion effect is improved to a certain extent. However, the initial forming defects caused by the outer root weld layer will gradually accumulate with the accumulation of weld layers, and the uniformity of fusion depth on both sides of the bevel is still constrained. Although the flow tendency of the molten pool in the vertical welding position is reduced, it is not completely eliminated.

[0050] Cover welding process: High-speed pulse double pulse mode is used for welding, with wire feed speed of 5.1-6.7 m / min, wire feed variation of 1.5-3 m / min, welding voltage of 21.0-22.5 V, travel speed of 38-56 cm / min, welding torch oscillation mode of angular swing or flat swing, swing width of 0.3-0.7 mm, oscillation frequency of 120-160 times / min, double pulse frequency of 3-6 Hz, and duty cycle of 50%. The resulting weld has a certain fish scale pattern morphology, and the appearance quality is better than that of ordinary pulse filler welding. However, the uneven formation of the outer root weld has a significant transmission effect, the weld reinforcement height fluctuation is still obvious, the width consistency across all positions is insufficient, and there is still a slight tendency to droop when welding overhead. It is impossible to achieve the comprehensive forming quality of low spatter root welding combined with double pulse filler welding.

[0051] Comparative Example 3 In the welding method provided in Comparative Example 3, the steps of external root welding, hot welding, filler welding, and capping welding are as follows: External root welding process: Welding is carried out using a low-spatter welding mode, with a wire feed speed of 3.5-5 m / min, a travel speed of 30-45 cm / min, and the welding torch oscillation mode is either angular or horizontal, with an oscillation width of 0.7-0.9 mm, an oscillation frequency of 140-170 times / min, a welding torch tilt angle of 3-8°, and a dwell time of 30-200 ms after the welding torch oscillates. In this external root welding process, the arc combustion is stable, the molten droplet transition is uniform and continuous, the weld surface is flat without large particles of spatter, the back side is uniformly and fully formed, and there are no concave or burn-through defects. It can achieve single-sided welding with double-sided forming without slag removal, providing a flat and stable arc-burning base for subsequent weld layers.

[0052] Hot welding process: Welding is performed using a high-speed pulse mode, with a wire feed speed of 7.7–11.9 m / min, a wire feed variation of 1.5–2.5 m / min, a welding voltage of 21.0–22.5 V, and a welding torch oscillation mode of angular or horizontal swing, a travel speed of 36–52 cm / min, a swing width of 1.4–2.0 mm, and an oscillation frequency of 150–210 times / min. Due to the flat base formed by the outer root weld, the basic stability of the arc combustion is good during the hot welding stage, and the root remelting is uniform overall. However, the heat input control precision of ordinary high-speed pulse is insufficient, and it is impossible to finely adjust the energy output according to the force difference in all positions. When the heat input is relatively high in the vertical welding position, the molten pool tends to flow downwards. In the overhead welding position, the molten pool tends to sag and the center of the weld bead tends to bulge. The uniformity of the back reinforcement height of the root is easily affected.

[0053] Filler welding process: High-speed pulse mode is used for welding, with wire feed speed of 8.5-11.3 m / min, wire feed variation of 1.5-2.5 m / min, welding voltage of 21.0-22.5 V, travel speed of 32-50 cm / min, welding torch oscillation mode of angular swing or flat swing, swing width of 1.6-2.9 mm, oscillation frequency of 120-190 times / min, and interpass temperature of 80-150℃. When using high-speed pulse mode for filler welding, the arc stiffness is too high, the spread of the molten pool to the sidewall is insufficient, the fusion depth of the bevel sidewall is limited, and the heat input matching in all positions is poor. In the overhead welding position, the high temperature molten pool sinks significantly under the influence of gravity, and the weld cross-section is prone to be high in the middle and low on both sides. As the number of filler layers increases, the risk of incomplete fusion of the bevel sidewall gradually increases, and the consistency of interpass formation gradually decreases.

[0054] Cover welding process: High-speed pulse mode is used for welding, with wire feed speed of 5.1-6.7 m / min, wire feed variation of 1.5-3 m / min, welding voltage of 21.0-22.5 V, travel speed of 38-56 cm / min, welding torch oscillation mode of angular oscillation or horizontal oscillation, oscillation width of 0.3-0.7 mm, and oscillation frequency of 120-160 times / min. The resulting weld has no obvious spatter defects, but due to the lack of periodic wire feed speed variation in high-speed pulse, it is impossible to form a regular and clear fish scale pattern appearance, and the all-position molten pool control capability is insufficient. Undercut and weld bead descent are prone to occur in vertical welding section, and excessive reinforcement and uneven weld width are common in overhead welding section. The overall appearance has poor consistency, and the rework rate is higher than that of high-speed pulse dual-pulse mode process.

[0055] Comparing the welding processes of Example 1 with Comparative Examples 1, 2, and 3, the welding method provided in Example 1 exhibits the least spatter, minimal nozzle clogging, and minimal slag removal. After welding Example 1 with Comparative Examples 1, 2, and 3, the weld seam formed in Example 1 shows clear fish-scale patterns, consistent width, uniform reinforcement height, and no undercut; the weld seam formed in Comparative Example 1 has poor formation and is prone to sagging during vertical and overhead welding; the overall consistency of the weld seams formed in Comparative Examples 2 and 3 is not as good as that of the weld seam in Example 1. After welding Example 1 with Comparative Examples 1, 2, and 3, the weld seam formed in Example 1 has the least porosity, slag inclusions, and lack of fusion, and the highest first-pass yield rate for both radiographic and ultrasonic testing; the weld seam formed in Comparative Example 2 has the lowest first-pass yield rate for both radiographic and ultrasonic testing. After welding Example 1 with Comparative Examples 1, 2, and 3, the weld seam formed in Example 1 exhibits the least dispersion in tensile, impact, and hardness, and the most stable performance of the all-position joint.

[0056] The welding method based on low-spatter root welding and metal electrode double-pulse filler welding provided by this invention has the following advantages: (1) Low spatter, no root cleaning required, single-sided welding with double-sided forming; (2) The weld pool is stable in all positions, and there is no sagging or undercut during vertical and overhead welding; (3) The shape is beautiful, the fish scale pattern is clear, and the weld is highly consistent; (4) The joints have uniform mechanical properties, high pass rate and low rework rate; (5) A single external welding trolley can complete the entire process, which is low in cost and easy to promote.

[0057] Those skilled in the art should understand that the above embodiments are merely for illustrating the present invention and are not intended to limit the scope of the invention. Those skilled in the art can make other changes or modifications based on the above disclosure, and these changes or modifications still fall within the scope of the present invention.

Claims

1. A welding method based on low-spatter root welding and metal electrode double-pulse filler welding, characterized in that, Includes the following steps: S1. Pre-welding preparation: Use a beveling machine to process U-shaped bevels on the pipe ends to be welded, and then assemble the bevels. S2. External root welding, hot welding, filler welding, and cover welding processes: External root welding uses 100% CO2 as the shielding gas and is performed using a low-spatter welding mode; Hot welding, filler welding, and cover welding use a mixed gas of 80% Ar and 20% CO2 as the shielding gas and are performed using a dual-pulse mode, with the oscillation, heat input, and travel speed adjusted according to the flat, vertical, and overhead welding positions respectively; The welding parameters for hot welding are as follows: wire feed speed is 7.7–11.9 m / min, wire feed speed variation is 0.5–1.5 m / min, travel speed is 36–52 cm / min, swing width is 1.4–2.0 mm, oscillation frequency is 150–210 times / min, double pulse frequency is 1.5–3 Hz, duty cycle is 40–50% for flat and vertical welding, and 40% for overhead welding; The welding parameters for filler welding are as follows: wire feed speed is 8.5–11.3 m / min, wire feed speed variation is 1.5–2.5 m / min, welding voltage is 21.0–22.5 V, travel speed is 32–50 cm / min, swing width is 1.6–2.9 mm, oscillation frequency is 120–190 times / min, double pulse frequency is 2–3 Hz, duty cycle is 40%–50%, and interpass temperature is 80–150 °C. The welding parameters for the cover weld are as follows: wire feed speed 5.1–6.7 m / min, wire feed speed variation 1.5–3 m / min, welding voltage 21.0–22.5 V, travel speed 38–56 cm / min, swing width 0.3–0.7 mm, oscillation frequency 120–160 times / min, double pulse frequency 3–6 Hz, and duty cycle 50%. S3. Post-weld inspection: Inspect the appearance, defects, and dimensions of the weld.

2. The welding method based on low-spatter root welding and consumable electrode double-pulse filler welding according to claim 1, characterized in that, Before beveling, remove oil, rust and moisture from the inner wall, outer wall and 20mm area on both sides of the bevel.

3. The welding method based on low-spatter root welding and consumable electrode double-pulse filler welding according to claim 1, characterized in that, The bevel angle of the U-shaped bevel is 3-5°, the blunt edge is 1.0-1.5mm, the radius of the arc is 3.0-3.2mm, the gap between the two ends is 0-0.5mm, and the width of the half-bevel is 3.5-4.5mm.

4. The welding method based on low-spatter root welding and consumable electrode double-pulse filler welding according to claim 1, characterized in that, In step S2, the flow rate of the protective gas is 15-20 L / min, and the welding wire is a solid welding wire with a diameter of 1.0 mm and a wire extension length of 8-15 mm.

5. The welding method based on low-spatter root welding and consumable electrode double-pulse filler welding according to claim 1, characterized in that, The welding parameters for external root welding are as follows: wire feed speed is 3.5-5 m / min, travel speed is 30-45 cm / min, swing width is 0.7-0.9 mm, oscillation frequency is 140-170 times / min, welding torch tilt angle is 3-8°, welding torch dwell time after oscillation is 30-200 ms, and dry extension length is 8-15 mm.

6. The welding method based on low-spatter root welding and consumable electrode double-pulse filler welding according to claim 1, characterized in that, The swing mode in step S2 is either angular swing or horizontal swing.

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