Pipeline assembly welding construction process

Abstract

The invention discloses a pipeline assembly welding construction process, and relates to the technical field of pipeline welding construction, and the pipeline assembly welding construction process comprises the following steps: S1, pipe orifice pretreatment: finishing a to-be-welded pipe orifice of a large-thickness dissimilar metal pipeline, and removing oil stains, rust and impurities on the surface of the pipe orifice; through ultrasonic-laser composite film removing treatment, a compact oxidation film on the surface of the aluminum alloy pipe opening can be thoroughly broken, the surface activity of the dissimilar metal pipe opening can be improved through laser micro-melting, the problem that fusion is hindered by the oxidation film is effectively solved, full combination of base metal and welding materials is guaranteed, and the welding quality is improved through collaborative operation of the double welding torches. The main welding torch completes main body welding, the auxiliary welding torch regulates and controls the adding proportion of alloy elements in real time, a gradient component transition layer is formed, generation of brittle intermetallic compounds is effectively restrained, firm combination of large-thickness dissimilar metal pipeline welding seams is achieved, the strength and toughness of a connector are remarkably improved, and the defects of incomplete fusion, slag inclusion and the like are avoided. And the welding quality of the large-thickness dissimilar metal pipeline is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of pipeline welding construction technology, specifically a pipeline butt welding construction process. Background Technology

[0002] Pipelines are indispensable core transport carriers in industrial production, energy transmission, and municipal construction. They are primarily used to transport fluids, gases, slurries, and other media. With advantages such as high transport efficiency, low loss, and small footprint, they are widely used in industries such as petrochemicals, natural gas transmission, urban water supply and drainage, and power engineering. They play an irreplaceable role in ensuring continuous industrial production, stable energy supply, and the normal operation of urban infrastructure. Pipeline butt welding is a crucial process for connecting two or more independent pipe sections to form a complete and continuous transport system. Essentially, it involves metallurgically bonding the welding material and the pipe end material by melting them at high temperatures. The welding quality of this process directly determines the sealing performance, pressure resistance, corrosion resistance, and overall service life of the pipeline system. It is a core and critical link in pipeline engineering construction, and its construction effect directly affects the operational safety and stability of the pipeline system.

[0003] In practical engineering applications, the demand for welding thick dissimilar metal pipelines is increasing. However, existing welding processes still have certain technical defects. Aluminum alloy surfaces are prone to forming dense and stable oxide films. These oxide films have high melting points and strong chemical stability, and existing single-film removal methods are difficult to completely remove them. During welding, they hinder the effective fusion of the base material and the welding material, leading to defects such as incomplete fusion and slag inclusions in the weld. Dissimilar metals have significant differences in physical and chemical properties, and brittle intermetallic compounds are easily generated during welding. Existing processes cannot precisely control the weld composition, resulting in low joint strength and insufficient toughness. This makes it difficult to meet the service requirements of thick dissimilar metal pipelines under complex working conditions such as high pressure and heavy load, seriously affecting the operational reliability of the pipeline system. Therefore, developing a pipeline assembly welding construction process is of great significance. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a pipeline butt welding construction process. This process can completely remove the dense oxide film on the surface of aluminum alloy pipe ends through ultrasonic-laser composite film removal treatment, and enhance the surface activity of dissimilar metal pipe ends through laser micro-melting. This effectively solves the problem of oxide film hindering fusion, ensuring full bonding between the base material and the welding material. Through the coordinated operation of dual welding torches, the main welding torch completes the main welding, while the auxiliary welding torch controls the alloy element addition ratio in real time to form a gradual transition layer, achieving a firm bond of thick dissimilar metal pipe welds, significantly improving the strength and toughness of the joint, and avoiding defects such as incomplete fusion and slag inclusions.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a pipeline butt welding construction process, the process comprising the following steps: S1. Pipe end pretreatment: The pipe ends of thick dissimilar metal pipes to be welded are repaired to remove oil, rust and impurities from the pipe end surface, laying a clean and orderly foundation for subsequent film removal and welding processes, and reducing the adverse effects of impurities on welding quality. S2. Ultrasonic-Laser Composite Film Removal: High-frequency ultrasonic vibration is used to treat the aluminum alloy pipe opening in the dissimilar metal pipe to break the dense oxide film on its surface. A laser beam is used to perform micro-melting treatment on the pipe opening of another parent material. The two treatment methods work together to greatly improve the compatibility of dissimilar metal pipe openings and clear obstacles for subsequent metallurgical bonding. S3. Pipeline alignment and positioning: Place the two pipe sections that have undergone the film removal treatment in the alignment fixture, adjust the position to center the pipes, control the alignment gap, and ensure that the molten pool is formed evenly during the welding process to avoid weld defects caused by alignment deviation or uneven gap. S4. Dual-torch collaborative welding: The main welding torch delivers basic welding materials for root pass and filler welding, while the auxiliary welding torch adjusts the alloy element addition ratio to form a gradual transition layer from the two base materials to the joint in the weld, allowing the weld composition to be smoothly connected with the base material, reducing stress concentration at the joint, and improving the mechanical stability of the overall structure. S5. Post-weld treatment: After the welded joint has cooled to room temperature, perform appearance repair and internal quality inspection, promptly identify and eliminate potential welding hazards, and ensure that the pipe joint meets the stringent standards for industrial applications.

[0006] Furthermore, in step S1, the pipe end trimming is carried out by mechanical cutting using a CNC lathe or a special cutting tool. The perpendicularity tolerance of the pipe end face is ≤0.05mm and the flatness tolerance is ≤0.03mm. For oil stain removal, anhydrous ethanol or acetone is used as the organic solvent, and the operation is carried out by a combination of wiping and ultrasonic cleaning. After cleaning, 120-180 grit sandpaper is used to evenly polish along the circumference of the pipe end, covering the pipe end face and edge area of ​​5-10mm, to remove residual impurities and oxide scale, accurately control the geometric accuracy of the pipe end, and avoid assembly deviation caused by irregular end face. At the same time, a thoroughly cleaned surface can improve the effect of subsequent film removal process.

[0007] Furthermore, in step S2, the high-frequency ultrasonic vibration uses a piezoelectric ultrasonic probe with a vibration frequency of 20-40kHz, a vibration power of 300-500W, a processing time of 30-60s, and the distance between the ultrasonic probe and the surface of the aluminum alloy tube opening is controlled at 1-3mm. The pressure applied by the probe is 0.1-0.3MPa, and it moves uniformly along the circumference of the tube opening at a speed of 5-10mm / s. By precisely controlling the ultrasonic processing parameters, the oxide film can be completely removed without damaging the tube opening material, ensuring the smoothness and activity of the surface after processing.

[0008] Furthermore, in step S2, the laser beam is output from a fiber laser with a wavelength of 1064nm, an output power of 800-1500W, a spot diameter of 0.8-1.5mm, a scanning speed of 10-20mm / s, a spot overlap rate of 50%-70%, and a micro-melting depth controlled at 0.3-0.8mm. The laser scanning path is a continuous circular scan along the end face of the pipe opening, with 2-3 scans. After micro-melting, the pipe opening is naturally cooled. The precise matching of laser parameters makes the micro-melting effect uniform and controllable, improves the metallurgical activity of the base material surface, and creates favorable conditions for the fusion of dissimilar metals.

[0009] Furthermore, in step S3, the assembly fixture uses a servo motor-driven three-jaw centering mechanism, with centering accuracy controlled to ≤0.1mm. The assembly gap is set to 0.2-0.8mm according to the pipe thickness. The gap is adjusted by the fine-tuning knob of the fixture to ensure uniform distribution, with a gap fluctuation value ≤0.1mm. During the assembly process, a dial indicator is used to detect the misalignment of the pipe ends at 8-12 evenly distributed detection points around the circumference, with the misalignment value ≤0.2mm. After the assembly is completed, temporary fixing pins are used for pre-fixation. The combination of servo drive and multi-point detection achieves precise control of assembly accuracy. The pre-fixing design prevents pipe displacement during welding and ensures welding stability.

[0010] Furthermore, in step S4, the main welding torch uses gas metal arc welding (GMAW), with a welding wire diameter of 1.2-1.6 mm, a welding current of 180-280 A, a welding voltage of 22-30 V, a welding speed of 3-8 mm / s, and a shielding gas of a mixture of argon and carbon dioxide in a ratio of 85:15-90:10. The argon purity is ≥99.99%, the carbon dioxide purity is ≥99.5%, and the gas flow rate is 15-25 L / min. During welding, the angle between the welding torch and the nozzle is 15°-30°. This optimized combination of welding parameters ensures the quality of the root pass and fill pass, and the mixed shielding gas effectively isolates air, reduces molten pool oxidation, and improves the weld formation quality.

[0011] Furthermore, in step S4, the alloying elements fed by the auxiliary welding torch include at least two of chromium, nickel, and titanium, with a chromium content of 15%-25%, a nickel content of 8%-15%, and a titanium content of 0.5%-2%. The alloying elements are fed in the form of flux-cored welding wire with a diameter of 1.2-1.6 mm and a core filling rate of 30%-40%. The auxiliary welding torch detects the temperature of the molten pool using an infrared thermometer, with the measuring point located 1-2 mm from the edge of the molten pool. The wire feeding speed is adjusted based on the temperature feedback, with a range of 3-10 m / min. The alloying element content in the transition layer changes linearly from the base material side to the joint center. The dynamic matching of the alloying element ratio and the wire feeding speed makes the composition gradient of the transition layer precisely controllable, maximizing the suppression of brittle phase formation.

[0012] Furthermore, in step S5, the appearance finishing is performed using an angle grinder with a rotation speed of 8000-12000 r / min and a 180-240 mesh flap wheel to remove welding spatter, weld beads, and incomplete penetration protrusions. After finishing, the weld reinforcement is controlled at 0-3 mm. Internal quality inspection is carried out using a combination of ultrasonic testing and radiographic testing. The ultrasonic testing uses a combination of straight and angle probes with a testing frequency of 2.25-5 MHz. The radiographic testing focal length is 600-1000 mm, covering the entire length of the weld and the heat-affected zone. The combination of appearance finishing and dual non-destructive testing comprehensively ensures the appearance quality and internal integrity of the weld, meeting the requirements for use under complex working conditions.

[0013] Furthermore, the thickness of the thick dissimilar metal pipe is 20-80mm, the pipe diameter range is DN50-DN500, and the dissimilar metal combination is one of aluminum alloy and stainless steel, or nickel-based alloy and carbon steel. The thickness of the gradient transition layer in step S4 is 2-5mm. The chromium content of the transition layer gradually increases from 5%-10% on the aluminum alloy side to 20%-25% at the joint center, and the nickel content gradually increases from 3%-5% to 12%-15%. The brittle intermetallic compounds are Fe-Al and Ni-Al compounds with a volume fraction ≤5%. The clear parameter range allows the process to be adapted to dissimilar metal pipes of different specifications, strictly controls the content of brittle compounds, and ensures the reliability of the joint in long-term service.

[0014] Compared with existing technologies, this pipeline offers the following advantages to the assembly welding construction process: This invention utilizes an ultrasonic-laser composite descaling process to thoroughly remove the dense oxide film on the surface of aluminum alloy pipe joints. Simultaneously, laser micro-melting enhances the surface activity of dissimilar metal pipe joints, effectively solving the problem of oxide film hindering fusion and ensuring full bonding between the base material and welding material. Through the coordinated operation of two welding torches, the main torch completes the main welding, while the auxiliary torch dynamically adjusts the alloy element addition ratio to form a gradient transition layer. This effectively inhibits the formation of brittle intermetallic compounds, achieving a strong bond in thick dissimilar metal pipe welds. It significantly improves the joint's strength and toughness, avoids defects such as incomplete fusion and slag inclusions, and ensures the welding quality of thick dissimilar metal pipes, enabling them to meet service requirements under complex operating conditions and extending the service life of the pipeline system.

[0015] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0017] Figure 1 A flowchart of a pipeline butt welding construction process; Figure 2 This is a flowchart of a pipeline butt welding construction process. Detailed Implementation

[0018] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0019] This invention provides a pipe butt welding construction process applicable to the combination of dissimilar metal pipes such as aluminum alloy and stainless steel, or nickel-based alloy and carbon steel, with a thickness of 20-80mm and a pipe diameter of DN50-DN500. The process includes five key steps, see [link to details]. Figure 1 and Figure 2 The specific details are as follows: For pipe end pretreatment, CNC lathes or special cutting tools are used to trim the pipe ends to ensure that the perpendicularity tolerance of the end face is ≤0.05mm and the flatness tolerance is ≤0.03mm. Anhydrous ethanol or acetone is used as a solvent to remove oil stains by wiping and ultrasonic cleaning. Then, 120-180 grit sandpaper is used to polish the pipe end face and the edge area of ​​5-10mm to remove impurities and oxide scale.

[0020] Ultrasonic-laser composite film removal involves using a 20-40kHz, 300-500W piezoelectric ultrasonic probe to treat the aluminum alloy tube opening. The probe is 1-3mm away from the surface, with a pressure of 0.1-0.3MPa, and is moved circumferentially at 5-10mm / s for 30-60s. Simultaneously, a 1064nm wavelength fiber laser is used with a power of 800-1500W and a spot size of 0.8-1.5mm to perform a circular scan on the tube opening of another base material for 2-3 circles, achieving a micro-melting depth of 0.3-0.8mm.

[0021] Pipe alignment is performed using a servo motor-driven three-jaw centering mechanism with an accuracy of ≤0.1mm. A uniform gap of 0.2-0.8mm is set according to the pipe thickness, with a fluctuation value of ≤0.1mm. The misalignment is checked at 8-12 points in the circumference and is ≤0.2mm. The pipe is then temporarily fixed after completion.

[0022] Dual-torch welding is used. The main torch employs gas metal arc welding (GMAW) with 1.2-1.6mm welding wire, 180-280A current, and 22-30V voltage, welding at a speed of 3-8mm / s. An argon-carbon dioxide mixed gas with a ratio of 85:15-90:10 is introduced for protection. The auxiliary torch feeds flux-cored welding wire containing 15%-25% chromium, 8%-15% nickel, and 0.5%-2% titanium. The wire feed speed is adjusted to 3-10m / min according to the molten pool temperature to form a 2-5mm thick gradient transition layer.

[0023] Post-weld treatment involves using an 8000-12000 rpm angle grinder with a 180-240 mesh flap wheel to trim the weld, resulting in a weld reinforcement of 0-3 mm. Ultrasonic testing with a 2.25-5 MHz probe and a 600-1000 mm focal length is then employed to cover the entire weld length and the heat-affected zone. This approach inhibits the formation of brittle intermetallic compounds, ensuring weld quality.

[0024] Example 1 This embodiment is applicable to the welding of dissimilar metal pipes (40mm thick, DN200 diameter) of aluminum alloy and stainless steel in the petrochemical industry. It employs a medium-parameter combination of ultrasonic-laser composite delamination and dual-torch synergistic welding process to ensure weld formation and joint mechanical properties, meeting the requirements of conventional high-pressure operating conditions. (See also...) Figure 1 and Figure 2 The specific content of this embodiment is as follows: Pipe end pretreatment: The pipe end to be welded is mechanically cut using a CNC lathe to control the perpendicularity tolerance of the pipe end face to 0.04mm and the flatness tolerance to 0.02mm. Anhydrous ethanol is used as an organic solvent to remove oil stains by wiping and ultrasonic cleaning. After cleaning, 150-grit sandpaper is used to evenly grind along the circumference of the pipe end, covering the pipe end face and an 8mm edge area to remove residual impurities and oxide scale.

[0025] Ultrasonic-laser composite film removal: A piezoelectric ultrasonic probe is used to perform high-frequency ultrasonic vibration treatment on the aluminum alloy tube opening. The vibration frequency is 25kHz, the vibration power is 350W, and the treatment time is 40s. The distance between the ultrasonic probe and the surface of the aluminum alloy tube opening is 2mm. The probe applies a pressure of 0.2MPa and moves uniformly at a speed of 8mm / s along the circumference of the tube opening. A fiber laser is used to perform micro-melting treatment on the stainless steel tube opening. The wavelength is 1064nm, the output power is 1000W, the spot diameter is 1.0mm, the scanning speed is 15mm / s, the spot overlap rate is 60%, and the micro-melting treatment depth is 0.5mm. The laser continuously scans the tube opening end face in a ring for 2 circles. After treatment, the tube opening is allowed to cool naturally.

[0026] Pipe alignment and positioning: Place the two sections of pipe after membrane removal in the three-jaw centering mechanism alignment fixture driven by the servo motor, adjust the position to center the pipe, with an alignment accuracy of 0.08mm, set the alignment gap to 0.5mm, and use the fine adjustment knob to make the gap evenly distributed, with a gap fluctuation value of 0.08mm; during the alignment process, use a dial indicator to evenly distribute 10 detection points around the circumference to detect the misalignment of the pipe ends, with a misalignment of 0.15mm. After the alignment is completed, use temporary fixing pins for pre-fixing.

[0027] Dual-torch synergistic welding: The main torch uses gas metal arc welding (GMAW), with a welding wire diameter of 1.4mm, a welding current of 220A, a welding voltage of 25V, and a welding speed of 5mm / s. The shielding gas is a mixture of argon and carbon dioxide in a ratio of 88:12, with argon purity of 99.99% and carbon dioxide purity of 99.6%, and a gas flow rate of 20L / min. During welding, the angle between the welding torch and the nozzle is 20°. The auxiliary torch feeds flux-cored welding wire containing 20% ​​chromium and 12% nickel, with a wire diameter of 1.4mm and a core filling rate of 35%. The temperature at the edge of the molten pool is detected by an infrared thermometer, and the wire feed speed is adjusted to 6m / min based on the temperature feedback. A 3mm thick gradient transition layer is formed in the weld, with the chromium content gradually increasing from 8% and nickel content from the aluminum alloy side to 22% and 13% at the joint center.

[0028] Post-weld treatment: After the welded joint has cooled to room temperature, an angle grinder with a speed of 10000r / min and a 200-mesh flap wheel is used for appearance finishing to remove welding spatter, weld beads and incomplete penetration protrusions. After finishing, the weld reinforcement is 2mm. Internal quality inspection is carried out by a combination of ultrasonic testing and radiographic testing. The ultrasonic testing uses a combination of straight and angle probes with a testing frequency of 3MHz. The radiographic testing focal length is 800mm, and the testing covers the entire length of the weld and the heat-affected zone.

[0029] In summary, this embodiment achieves complete removal of the oxide film on the aluminum alloy pipe ends and significant improvement in the surface activity of the stainless steel pipe ends through precise matching of process parameters. The pipe assembly accuracy meets the requirements, and the gradient transition layer formed by the dual welding torches effectively suppresses the formation of Fe-Al brittle intermetallic compounds, with a volume fraction of 3%. The weld is free of defects such as incomplete fusion and slag inclusions, and the joint has good strength and toughness, meeting the service requirements under conventional high-pressure conditions in the petrochemical industry.

[0030] Example 2 This embodiment focuses on the welding of nickel-based alloy and carbon steel dissimilar metal pipes with a thickness of 60mm and a diameter of DN300 in power engineering. It employs high-power ultrasonic-laser processing and a high-parameter dual-torch welding process, primarily improving the crack resistance and load-bearing capacity of the thick-walled pipe joint. (See [link to previous document]). Figure 1 and Figure 2 The specific content of this embodiment is as follows: Pipe end pretreatment: The pipe end is mechanically cut using a special cutting tool to control the perpendicularity tolerance of the pipe end face to 0.03mm and the flatness tolerance to 0.02mm; Acetone is used as an organic solvent to remove oil stains by wiping and ultrasonic cleaning. After cleaning, 180-grit sandpaper is used to evenly polish along the circumference of the pipe end, covering the pipe end face and a 10mm edge area to remove residual impurities and oxide scale.

[0031] Ultrasonic-laser composite film removal: A piezoelectric ultrasonic probe is used to perform high-frequency ultrasonic vibration treatment on the aluminum alloy side of the tube opening (with auxiliary treatment on the nickel-based alloy side). The vibration frequency is 35kHz, the vibration power is 450W, the treatment time is 50s, the distance between the ultrasonic probe and the tube opening surface is 2.5mm, the probe applies a pressure of 0.25MPa, and moves at a uniform speed of 9mm / s along the circumference of the tube opening; A fiber laser is used to perform micro-melting treatment on the carbon steel tube opening. The wavelength is 1064nm, the output power is 1300W, the spot diameter is 1.2mm, the scanning speed is 18mm / s, the spot overlap rate is 65%, the micro-melting treatment depth is 0.7mm, and the laser continuously scans three circles around the tube opening end face. After treatment, the tube opening is allowed to cool naturally.

[0032] Pipe alignment and positioning: Place the two pipe sections in the alignment fixture driven by the servo motor and the three-jaw centering mechanism. Adjust the alignment accuracy to 0.09mm and set the alignment gap to 0.7mm. Use the fine-tuning knob to make the gap evenly distributed with a gap fluctuation of 0.09mm. Use a dial indicator to evenly distribute 12 detection points around the circumference to detect the misalignment of the pipe ends. The misalignment is 0.18mm. After alignment, use temporary fixing pins for pre-fixing.

[0033] Dual-torch synergistic welding: The main torch uses gas metal arc welding (GMAW), with a wire diameter of 1.6 mm, a welding current of 260 A, a welding voltage of 28 V, and a welding speed of 6 mm / s. The shielding gas is a mixture of argon and carbon dioxide in a ratio of 85:15, with argon purity of 99.99% and carbon dioxide purity of 99.5%, and a gas flow rate of 23 L / min. During welding, the angle between the welding torch and the nozzle is 25°. The auxiliary torch feeds flux-cored wire containing 23% chromium and 1.5% titanium, with a wire diameter of 1.6 mm and a core filling rate of 38%. The temperature at the edge of the molten pool is detected by an infrared thermometer at 1.8 mm, and the wire feed speed is adjusted to 8 m / min to form a 4 mm thick gradient transition layer. The chromium content of the transition layer gradually increases from 9% on the nickel-based alloy side to 24% at the joint center.

[0034] Post-weld treatment: After the joint has cooled to room temperature, an angle grinder with a speed of 12000r / min and a 240 mesh flap wheel is used for external finishing. After finishing, the weld reinforcement is 2.5mm. Internal quality inspection is carried out by a combination of ultrasonic testing and radiographic testing. The ultrasonic testing frequency is 5MHz and the radiographic testing focal length is 900mm, which fully covers the weld and heat-affected zone.

[0035] In summary, this embodiment addresses the welding requirements of thick-walled nickel-based alloys and carbon steel pipes. By increasing ultrasonic power, laser output power, and welding parameters, it enhances the film removal effect and weld filling quality. The gradient transition layer effectively alleviates stress concentration caused by the difference in properties between dissimilar metals. With a brittle intermetallic compound volume fraction of 2.5%, the joint exhibits high strength and excellent crack resistance, enabling it to withstand long-term testing under heavy loads and high temperatures in power engineering.

[0036] Example 3 This embodiment is applied to the welding of dissimilar metal pipes (25mm thick, DN100 diameter) made of aluminum alloy and stainless steel in municipal water supply and drainage. It employs a combination of low-power, low-speed process parameters, balancing welding efficiency and construction costs, while meeting the requirements of conventional low-pressure operating conditions. (See [link to relevant documentation]). Figure 1 and Figure 2 The specific content of this embodiment is as follows: Pipe end pretreatment: The pipe end is mechanically cut using a CNC lathe to control the perpendicularity tolerance of the pipe end face to 0.05mm and the flatness tolerance to 0.03mm. Anhydrous ethanol is used as the organic solvent to remove oil stains by wiping and ultrasonic cleaning. After cleaning, 120-grit sandpaper is used to evenly polish along the circumference of the pipe end, covering the pipe end face and edge area within 5mm to remove residual impurities and oxide scale.

[0037] Ultrasonic-laser composite film removal: A piezoelectric ultrasonic probe is used to perform high-frequency ultrasonic vibration treatment on the aluminum alloy tube opening. The vibration frequency is 20kHz, the vibration power is 300W, the treatment time is 30s, the distance between the ultrasonic probe and the tube opening surface is 1mm, the probe applies a pressure of 0.1MPa, and moves uniformly at a speed of 5mm / s along the circumference of the tube opening; A fiber laser is used to perform micro-melting treatment on the stainless steel tube opening. The wavelength is 1064nm, the output power is 800W, the spot diameter is 0.8mm, the scanning speed is 10mm / s, the spot overlap rate is 50%, and the micro-melting treatment depth is 0.3mm. The laser continuously scans in a ring around the tube opening end face for 2 circles. After treatment, the tube opening is allowed to cool naturally.

[0038] Pipe alignment and positioning: Place the two pipe sections in the alignment fixture driven by the servo motor and the three-jaw centering mechanism. Adjust the alignment accuracy to 0.1mm and set the alignment gap to 0.3mm. Use the fine-tuning knob to make the gap evenly distributed with a gap fluctuation of 0.1mm. Use a dial indicator to evenly distribute 8 detection points around the circumference to detect the misalignment of the pipe ends. The misalignment is 0.2mm. After alignment, use temporary fixing pins for pre-fixing.

[0039] Dual-torch synergistic welding: The main torch uses gas metal arc welding (GMAW) with a wire diameter of 1.2 mm, a welding current of 190 A, a welding voltage of 23 V, and a welding speed of 4 mm / s. The shielding gas is a mixture of argon and carbon dioxide in a 90:10 ratio, with argon purity of 99.99% and carbon dioxide purity of 99.7%, and a gas flow rate of 18 L / min. During welding, the angle between the welding torch and the nozzle is 15°. The auxiliary torch feeds flux-cored wire containing 10% nickel and 0.8% titanium, with a wire diameter of 1.2 mm and a core filling rate of 32%. The temperature at the edge of the molten pool is detected by an infrared thermometer, and the wire feed speed is adjusted to 4 m / min to form a 2 mm thick gradient transition layer. The nickel content of the transition layer gradually increases from 3% on the aluminum alloy side to 11% at the joint center.

[0040] Post-weld treatment: After the joint has cooled to room temperature, an angle grinder with a speed of 8000 r / min and a 180 mesh flap wheel is used for external finishing. After finishing, the weld reinforcement is 1.5 mm. Internal quality inspection is carried out by a combination of ultrasonic testing and radiographic testing. The ultrasonic testing frequency is 2.25 MHz and the radiographic testing focal length is 700 mm, covering the entire length of the weld and the heat-affected zone.

[0041] In summary, this embodiment employs low-power and low-speed process parameters, achieving high-quality welding of aluminum alloy and stainless steel thin-walled pipes while controlling construction costs. The oxide film is thoroughly removed, the assembly accuracy meets the standards, the transition layer effectively inhibits the formation of brittle compounds (volume fraction 4%), the weld has no obvious defects, the joint performance meets the requirements of conventional low-pressure conditions in the municipal water supply and drainage field, and the welding efficiency is high.

[0042] Comparative Example This comparative example uses existing conventional welding processes to weld aluminum alloy and stainless steel dissimilar metal pipes with a thickness of 40mm and a diameter of DN200, which are the same as those in Example 1. Ultrasonic-laser composite film removal and dual-torch synergistic welding technology were not used to compare the advantages of the process of this invention.

[0043] Pipe end pretreatment: The pipe ends were finished by ordinary grinding wheel without the use of CNC lathes or special cutting tools. The perpendicularity tolerance of the pipe end face was 0.08mm and the flatness tolerance was 0.05mm, which did not meet the requirements for precise geometric accuracy. Anhydrous ethanol was used to remove oil stains by manual wiping without ultrasonic-assisted cleaning. After cleaning, 100-grit sandpaper was used to simply grind the surface of the pipe ends. The grinding range and intensity were not strictly controlled, and only obvious impurities were removed, leaving some oxide scale and fine rust.

[0044] Film removal treatment: The oxide film on the surface of the aluminum alloy pipe is scraped off by mechanical grinding tools without any ultrasonic or laser-assisted treatment. Because the oxide film on the surface of the aluminum alloy is dense and has strong adhesion, it is difficult to completely remove it by mechanical grinding. Some areas still have residual oxide film. At the same time, no micro-melting treatment is performed on the stainless steel pipe opening, and the surface activity of the pipe opening is low.

[0045] Pipe alignment and positioning: Ordinary manual alignment fixtures are used without a servo motor driven centering mechanism. The alignment accuracy is 0.2mm when adjusted manually, resulting in poor alignment. The alignment gap is set at 0.6mm, and the gap distribution is adjusted by visual observation. The gap fluctuation value is 0.2mm, which is not uniform. A dial indicator is used to detect the misalignment of the pipe ends at only 6 detection points around the circumference. The misalignment is 0.3mm, which does not meet the precision alignment standard. After alignment, the pipes are simply fixed by binding with wire without the use of special temporary fixing pins. This makes the pipes prone to displacement during welding.

[0046] Welding: Single-torch gas metal arc welding was used without an auxiliary torch. The welding wire diameter was 1.4 mm, the welding current was 220 A, the welding voltage was 25 V, and the welding speed was 5 mm / s. Pure argon was used as the shielding gas with a flow rate of 20 L / min. No alloying elements such as chromium, nickel, and titanium were added. There was no gradient transition layer in the weld. The fusion of the base metal and the welding material was achieved solely by a single welding material. It was impossible to control the weld composition to adapt to the differences in the properties of dissimilar metals.

[0047] Post-weld treatment: After the welded joint cooled to room temperature, a regular low-speed angle grinder was used for surface finishing. No special flap wheel was used. After finishing, the weld height was 4mm, and there were obvious welding spatter and weld beads on the surface. Internal quality inspection was carried out using only ultrasonic testing, without radiographic testing. The testing frequency was 3MHz, which could only preliminarily identify some internal defects and could not fully cover the entire length of the weld and the heat-affected zone, making it easy to miss hidden defects.

[0048] In summary, the conventional welding process used in this comparative example has multiple technical shortcomings. The oxide film on the aluminum alloy pipe ends is not completely removed, and the residual oxide film hinders effective fusion between the base metal and the welding material during welding. Furthermore, the pipe assembly precision is low, the gap uniformity is poor, and no composition control is performed during welding, resulting in a high volume fraction of Fe-Al brittle intermetallic compounds in the weld, reaching 12%. Ultimately, the weld exhibits obvious defects such as incomplete fusion and slag inclusions, with poor joint strength and toughness, making it unable to withstand the loads under high-pressure conditions. It can only be used temporarily in low-pressure, simple operating conditions, and there are safety hazards such as leakage and fracture during service. The welding quality and reliability are far lower than the process of this invention, fully highlighting the technical advantages of this invention in welding thick dissimilar metal pipes.

[0049]

[0050] The comparison in the table above shows that all three embodiments of the present invention employ an ultrasonic-laser composite oxide removal and dual-torch synergistic welding process, which significantly outperforms the comparative example using conventional processes in terms of oxide film removal effect, suppression of brittle intermetallic compounds, joint mechanical properties, and weld quality. Embodiment 1 has balanced parameters and excellent overall performance, suitable for conventional high-pressure conditions; Embodiment 2 optimizes parameters for thick-walled pipes, achieving optimal joint strength and crack resistance, suitable for heavy-load, high-temperature conditions; Embodiment 3 uses low-power parameters, controlling costs while ensuring welding quality, suitable for low-pressure conditions. The comparative example, lacking composite oxide removal and composition control methods, suffers from incomplete oxide film removal, excessive formation of brittle compounds, numerous weld defects, and poor joint performance, failing to meet the requirements of complex operating conditions. In summary, the process of the present invention, through multi-process synergistic optimization, effectively solves the technical challenges of welding thick dissimilar metal pipes, adapts to different specifications and operating conditions, and significantly improves welding quality and reliability.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A pipe butt welding construction process, characterized in that, The process includes the following steps: S1. Pipe end pretreatment: Repair the pipe ends of thick dissimilar metal pipes to be welded, and remove oil, rust and impurities from the pipe end surface; S2. Ultrasonic-laser composite film removal: High-frequency ultrasonic vibration is used to treat the aluminum alloy pipe opening in the dissimilar metal pipe to break the dense oxide film on its surface, and a laser beam is used to micro-melt the pipe opening of another parent material. S3. Pipeline alignment and positioning: Place the two pipe sections that have undergone membrane removal treatment in the alignment fixture, adjust their positions to center the pipes, and control the alignment gap. S4. Dual-torch collaborative welding: The main welding torch delivers the base welding material for root pass and filler welding, while the auxiliary welding torch adjusts the alloy element addition ratio to form a gradual transition layer from the two base materials to the joint in the weld. S5. Post-weld treatment: After the welded joint has cooled to room temperature, perform appearance repair and internal quality inspection.

2. The pipeline butt welding construction process according to claim 1, characterized in that, In step S1, the pipe end trimming is carried out by mechanical cutting using a CNC lathe or special cutting tools. The perpendicularity tolerance of the pipe end face is ≤0.05mm and the flatness tolerance is ≤0.03mm. For oil stain removal, anhydrous ethanol or acetone is used as the organic solvent. The operation is carried out by a combination of wiping and ultrasonic cleaning. After cleaning, 120-180 grit sandpaper is used to evenly polish along the circumference of the pipe end, covering the pipe end face and edge area of ​​5-10mm to remove residual impurities and oxide scale.

3. The pipeline butt welding construction process according to claim 1, characterized in that, In step S2, the high-frequency ultrasonic vibration uses a piezoelectric ultrasonic probe with a vibration frequency of 20-40kHz, a vibration power of 300-500W, a processing time of 30-60s, a distance of 1-3mm between the ultrasonic probe and the surface of the aluminum alloy tube opening, a pressure of 0.1-0.3MPa applied by the probe, and a uniform speed of 5-10mm / s along the circumference of the tube opening.

4. The pipeline butt welding construction process according to claim 1, characterized in that, In step S2, the laser beam is output from a fiber laser with a wavelength of 1064nm, an output power of 800-1500W, a spot diameter of 0.8-1.5mm, a scanning speed of 10-20mm / s, a spot overlap rate of 50%-70%, a micro-melting depth controlled at 0.3-0.8mm, and a continuous circular scan along the end face of the tube opening with 2-3 scans. After the micro-melting process, the tube opening is allowed to cool naturally.

5. The pipeline butt welding construction process according to claim 1, characterized in that, In step S3, the assembly tooling uses a servo motor-driven three-jaw centering mechanism, with centering accuracy controlled to ≤0.1mm. The assembly gap is set to 0.2-0.8mm according to the pipe thickness. The gap is adjusted by the fine-tuning knob of the tooling to make the gap evenly distributed, with a gap fluctuation value ≤0.1mm. During the assembly process, a dial indicator is used to detect the misalignment of the pipe ends at 8-12 evenly distributed detection points around the circumference, with the misalignment value ≤0.2mm. After the assembly is completed, temporary fixing pins are used for pre-fixing.

6. The pipeline butt welding construction process according to claim 1, characterized in that, In step S4, the main welding torch uses gas metal arc welding (GMAW), with a welding wire diameter of 1.2-1.6 mm, a welding current of 180-280 A, a welding voltage of 22-30 V, a welding speed of 3-8 mm / s, and a shielding gas mixture of argon and carbon dioxide in a ratio of 85:15-90:

10. The argon purity is ≥99.99%, the carbon dioxide purity is ≥99.5%, and the gas flow rate is 15-25 L / min. During welding, the angle between the welding torch and the nozzle is 15°-30°.

7. The pipeline butt welding construction process according to claim 1, characterized in that, In step S4, the alloying elements fed by the auxiliary welding torch include at least two of chromium, nickel, and titanium, with a chromium content of 15%-25%, a nickel content of 8%-15%, and a titanium content of 0.5%-2%. The alloying elements are fed in the form of flux-cored welding wire with a diameter of 1.2-1.6 mm and a core filling rate of 30%-40%. The auxiliary welding torch detects the temperature of the molten pool using an infrared thermometer, with the measuring point located 1-2 mm from the edge of the molten pool. The wire feeding speed is adjusted according to the temperature feedback, with a wire feeding speed range of 3-10 m / min. The alloying element content in the transition layer changes linearly from the base material side to the joint center.

8. The pipeline butt welding construction process according to claim 1, characterized in that, In step S5, the appearance finishing is carried out using an angle grinder with a speed of 8000-12000 r / min and a 180-240 mesh flap wheel to remove welding spatter, weld beads, and incomplete penetration protrusions. After finishing, the weld reinforcement is controlled at 0-3 mm. The internal quality inspection is carried out using a combination of ultrasonic testing and radiographic testing. The ultrasonic testing uses a combination of straight and angle probes with a testing frequency of 2.25-5 MHz. The radiographic testing focal length is 600-1000 mm, and the inspection covers the entire length of the weld and the heat-affected zone.

9. The pipeline butt welding construction process according to claim 1, characterized in that, The thickness of the thick dissimilar metal pipe is 20-80mm, the pipe diameter range is DN50-DN500, and the dissimilar metal combination is one of aluminum alloy and stainless steel, or nickel-based alloy and carbon steel. The thickness of the gradual transition layer in step S4 is 2-5mm. The chromium content of the transition layer gradually increases from 5%-10% on the aluminum alloy side to 20%-25% at the joint center, and the nickel content gradually increases from 3%-5% to 12%-15%.

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