Boiler tube butt welding method

Abstract

The present invention relates to the technical field of boiler tube welding, and in particular to a method for butt welding of boiler tubes, comprising the following steps: S1, pre-treating the ends and outer surfaces of the boiler tubes to be welded by a dry-wet alternating cleaning method, wherein the process includes first dry brushing, then wiping with acetone, then polishing with sandpaper, and finally cleaning with a chamois cloth; S2, processing a zigzag composite groove; S3, positioning the boiler tube group; S4, preheating the boiler tubes by surrounding them with a spiral flame; S5, performing a base welding and a filler welding by a double-arc alternating interrupted arc welding method during welding; S6, after the filler welding is completed, performing a cover welding; S7, after the cover welding is completed, completing interlayer cleaning of the weld layer by knocking and vibrating; S8, wrapping the final weld with multiple layers of wet towels for insulation and slow cooling, and inspecting the welds after cooling. The method is compatible with conventional equipment, does not require special tooling, can meet the needs of small-space operations with multiple rows of boiler tubes, and has a low threshold for welding, low difficulty, and is suitable for welders to quickly master.

Description

Technical Field

[0001] The invention relates to the technical field of boiler tube welding, in particular to a boiler tube butt welding method. Background Art

[0002] Boiler tubes are core components of the pressure-bearing heating surface, and their welding quality directly determines the safety and operational reliability of boiler equipment. Currently, pipe butt welding mainly uses two methods: manual arc welding and automated welding equipment.

[0003] Although there are some rotary mechanical welding equipment in the prior art that can achieve circumferential welding, their applicability in the welding scenario of multiple rows of boiler tubes is extremely poor.

[0004] For example, the automatic welding equipment disclosed in the Chinese patent application number CN202220287111.5 uses a multi-axis robotic arm to realize the motion control of the welding gun. However, in the welding of multiple rows of boiler tubes, the welding gun transmission mechanism and the rotating bracket structure of such rotating mechanical welding equipment are complex, and the turnover space required during operation is large. The multiple rows of boiler tubes are usually arranged in parallel and spaced apart, and the actual tube spacing is small. The above-mentioned mechanical equipment is difficult to flexibly move and position between the dense tube rows, and cannot effectively avoid interference between the tubes. The welding process frequently causes problems such as welding gun collision and arc offset. Therefore, manual welding is still the main method for butt welding of boiler tubes.

[0005] While existing manual welding methods offer a certain degree of flexibility, they often suffer from serious quality issues. When welding multiple rows of boiler tubes, welders face difficulties in precisely controlling the torch angle and welding speed due to blind spots in their field of view, body posture, and fatigue. This leads to large fluctuations in weld penetration and weld height, and can easily lead to defects such as lack of fusion and porosity. Furthermore, significant differences in welder skill levels can result in a high degree of weld quality dispersion, making it difficult to achieve uniform quality.

[0006] Therefore, it is of great practical significance to develop a control method for improving the quality of manual welding of multi-row boiler tubes. Summary of the Invention

[0007] The present invention solves one of the above technical problems, and the technical solution adopted is: a boiler tube butt welding method, comprising the following steps:

[0008] S1. Pre-treat the ends and outer surfaces of the boiler tubes to be welded using a wet-dry alternating cleaning method. First, dry brush, then wipe with acetone, then sand with sandpaper and finally clean with a suede cloth.

[0009] S2, processing zigzag composite groove.

[0010] S3, positioning of boiler tube group.

[0011] S4, after positioning, the boiler tubes are preheated by spiral flame encircling.

[0012] S5, when welding, double arc alternating broken arc welding is used to complete the base welding, and then filler welding is performed.

[0013] S6: After the filling welding is completed, the cover welding is carried out.

[0014] S7, after the cover welding is completed, the interlayer cleaning of the welding layer is completed by knocking and vibrating.

[0015] S8. After the final welding is completed, wrap it with multiple layers of wet towels to keep it warm and cool slowly, and check the weld after cooling.

[0016] Based on any of the above technical solutions, further optimization is: during the sanding process, the sanding direction is along the circumferential direction of the boiler tube end, so that a uniform brushed texture is formed on the surface.

[0017] On the basis of any of the above technical solutions, further optimized is: the forming method of the zigzag composite groove is as follows: first, a V-shaped groove with a groove angle of 60°-70° is processed.

[0018] A serrated structure is processed on both side walls of the V-shaped groove. During the operation, use a file to file along the side walls of the groove with relatively uniform force and rhythm, starting on one side of the groove wall; file out the serrations in sequence according to the set spacing and depth. After completing the operation on one side, process the other side of the groove wall in the same way; during the filing process, continuously measure the spacing and depth of the serrations with a caliper.

[0019] Based on any of the above technical solutions, further optimization is that the spacing between each sawtooth is 2-3mm, the depth is controlled at 0.5-1mm, the sawtooth shape is a right-angled trapezoid, its hypotenuse faces the center of the groove, and the right-angled side is perpendicular to the side wall of the groove.

[0020] Based on any of the above technical solutions, further optimization is as follows: the specific method of preheating the boiler tube by spiral flame encirclement is as follows: the acetylene-oxygen flame is adjusted to a neutral flame to ensure stable flame combustion and moderate temperature, and avoid local overheating or oxidation of the boiler tube due to improper flame properties.

[0021] Start heating from one end of the boiler tube to be welded, and move the flame in a spiral trajectory from the outside to the inside around the tube body, with the spiral spacing maintained at 10-15mm.

[0022] During the heating process, the distance between the flame nozzle and the tube end is controlled at 5-10mm to ensure that the flame heat is effectively transferred to the boiler tube surface.

[0023] Based on any of the above technical solutions, further optimization is: during the preheating process, the color change of the tube wall of the boiler tube is observed. When the tube wall appears dark red, it indicates that the temperature is close to or reaches the preheating target temperature of 150℃-200℃.

[0024] At the same time, during the surrounding heating process, a relatively uniform movement speed of about 1-2 cm per second is maintained to ensure uniform heating in the circumferential direction of the boiler tube.

[0025] After completing each spiral heating cycle, the heating process needs to be repeated 1-2 times to further ensure the temperature uniformity and preheating adequacy of the entire welded area, reduce welding stress, and reduce the probability of welding crack defects.

[0026] On the basis of any of the above technical solutions, further optimization is as follows: the specific steps of using double arc alternating arc breaking welding are as follows: Step 1, differentiated pretreatment of welding rods: select two welding rods with a diameter of 2.5 mm, marked as welding rod A and welding rod B.

[0027] Step 2. Start arcs with electrodes A and B in steps: Start arc with electrode A: Start arc at the positioning welding point with a current of 70A, using the two-point positioning method of starting with the groove side and then the root.

[0028] Arc striking with electrode B: After electrode A extinguishes its arc, strike an arc at the junction of the edge of the molten pool and the groove when the molten pool is in a semi-solid state. Use a 75A welding current to ignite electrode B, and quickly send the arc to the molten pool that has not been completely solidified, so that the new arc and the old molten pool are fully fused to form a molten hole again.

[0029] In the third step, during the welding process, both electrodes are moved by a composite swing method combining spiral motion and zigzag swing.

[0030] Step 4: The two electrodes perform welding operations alternately at the specified frequency.

[0031] Step 5: When approaching the end of the weld, use the current decay method to extinguish the arc.

[0032] Based on any of the above technical solutions, the following are further optimized: the steps of filling welding are as follows: welding preparation: after the base welding is completed, use a wire brush to clean the slag on the weld surface and a flat shovel to remove spatter; select a welding rod with a diameter of 3.2mm that matches the boiler tube; adjust the welding current to 90-100A and the arc voltage to 22-24V.

[0033] Starting welding: At one end of the weld, align the welding rod with the weld, with the tip 2-3mm away from the bottom, scratch or strike the arc, pull it to the bottom and stay for 0.8-1.2 seconds to form a molten pool; the welding rod is at 90° to the pipe axis and 70°-80° to the welding direction, and maintain a short arc operation.

[0034] Step-by-step swing operation: The electrode swings in steps, staying on both sides for 1-1.5 seconds to ensure fusion, and moving quickly in the middle to prevent the weld from being too high. Move forward 2-3mm after each swing; observe the molten pool during welding. If it collapses, reduce the current or shorten the dwell time; if fusion is poor, increase the dwell time and adjust the electrode angle.

[0035] Filling and finishing: Continue filling until it is 1-2mm below the surface of the base material; when approaching the end, reduce the current in stages 3-5cm in advance, reducing it by 5A-10A each time, and stay in the molten pool for 1-2 seconds to fill the arc pit. Remove the electrode and clean the welding slag.

[0036] On the basis of any of the above technical solutions, further optimization is as follows: the specific steps of completing the interlayer cleaning of the welding layer by tapping and vibration are as follows: After welding is completed, wait for the weld to cool to 60-80℃.

[0037] The small hammer strikes both sides of the weld at a frequency of 2-3 times per second, with a spacing of 5-8 mm between the striking points.

[0038] Move and strike in a spiral shape along the direction of the weld, with a spiral diameter of about 20mm.

[0039] After knocking, use a wire brush to brush away loose slag in one direction along the weld.

[0040] After stubborn slag is found, it is baked with flame until dark red and then rapidly cooled, and peeled off by utilizing thermal expansion and contraction.

[0041] On the basis of any of the above technical solutions, further optimization is as follows: the specific steps of cover welding are as follows: after filling welding and cleaning, select 3.2mm low-hydrogen welding rod, and adjust the current to 85-95A according to the state of the filling weld.

[0042] Strike the arc at the base material 10-15mm in front of the starting end of the weld, pull it to the starting point after it stabilizes, and keep the welding rod at 75°-85° to the welding direction, perpendicular to the pipe axis, and start welding with a short arc to ensure fusion.

[0043] When welding with welding rod, move the center of the weld quickly, press down on both sides and pause for 0.5-1 second, then lift up, and control the weld width to exceed the groove by 1-2mm on each side, and the excess height to 0-3mm.

[0044] When changing the welding rod, grind a gentle slope of 10-15mm at the end of the arc, strike the arc with the new welding rod 5-8mm in front of the joint, pull it until the joint stops and fuses, then continue welding.

[0045] At the end, the current is reduced to 70%-80%, and the arc is extinguished after circular swing to fill the arc pit.

[0046] Based on any of the above technical solutions, further optimization is as follows: the specific steps of wrapping with multiple layers of wet towels to keep warm and slow down cooling are as follows: prepare enough pure cotton towels with good water absorption; prepare warm water, and control the water temperature at 40-50℃ to ensure that the temperature of the towels is appropriate after being soaked.

[0047] After the final welding is completed, soak the towel with warm water and wring it until it stops dripping. With the weld as the center, tightly wrap the first layer of towel from one end to ensure that the weld is completely covered and each layer of towel fits tightly together without leaving any gaps.

[0048] When the temperature of the first layer of towel drops to close to the ambient temperature, quickly wrap the second layer and repeat the operation until 3-4 layers of towels are wrapped.

[0049] Finally, wrap the towel with plastic film to seal it to prevent water from evaporating too quickly and slow down the rate of heat loss.

[0050] During the insulation and slow cooling process, use an infrared thermometer to intermittently measure the weld temperature, record the temperature changes, and control the weld cooling rate by adding or reducing the number of towel layers or adjusting the ambient temperature.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] 1. The present invention uses multi-stage pretreatment to thoroughly remove surface impurities and form directional lines, which can guide the deposited metal to spread evenly, reduce pores and slag inclusions, and improve the fusion quality of the initial section of the weld.

[0053] 2. The present invention adopts a zigzag composite groove to enhance the bonding between the deposited metal and the base material by increasing the surface area and geometric diversion effect, optimize the flow of the molten pool, and reduce defects such as undercuts, weld bumps, pores and cracks.

[0054] 3. The present invention uses spiral flame preheating to achieve uniform heating to the target temperature in the circumferential direction, reduce welding stress and hardening tendency, and reduce the risk of cold cracks.

[0055] 4. The present invention adopts double-arc alternating interrupted arc welding to promote molten pool deoxidation, refine grains, control molten pool continuity and thermal cycle, improve weld strength and toughness, and reduce defects such as lack of fusion and porosity.

[0056] 5. The present invention uses multiple layers of wet towels to keep warm and cool slowly, slowing down the cooling rate, promoting the transformation of austenite into tough structure, avoiding hardened structure and stress concentration; combined with tapping vibration and hot and cold cycle interlayer cleaning, it can efficiently remove slag and ensure the quality of interlayer fusion.

[0057] 6. The process method of the present invention is compatible with conventional equipment, does not require special tooling, and can meet the needs of small-space operations for multiple rows of boiler tubes. The welding process has a low threshold and low difficulty, making it suitable for welders to master quickly. DETAILED DESCRIPTION

[0058] The following embodiments of the technical solution of the present invention are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and are therefore only used as examples and are not intended to limit the scope of protection of the present invention.

[0059] The present invention discloses a boiler tube butt welding method, which can significantly improve the welding quality of boiler tubes through overall process improvements including pretreatment, groove processing, preheating, innovative welding process design, interlayer cleaning, and heat preservation and slow cooling.

[0060] Among them, the serrated groove enhances the bonding strength between the deposited metal and the base material, the spiral flame preheating realizes uniform temperature rise, the double arc alternating interrupted arc welding refines the grains and optimizes the metallurgical reaction of the molten pool, the interlayer knocking and vibration removes the slag and releases the stress, and the multi-layer wet towel insulation and slow cooling control the cooling rate, ultimately reducing welding cracks, pores and other defects, ensuring the beautiful formation of the weld, which is suitable for the welding needs of boiler tubes under high pressure and high temperature conditions.

[0061] Embodiment: A method for butt welding a boiler tube comprises the following steps:

[0062] S1. Pre-treat the ends and outer surfaces of the boiler tubes to be welded using a wet-dry alternating cleaning method. First, dry brush, then wipe with acetone, then sand with sandpaper and finally clean with a suede cloth.

[0063] Based on any of the above technical solutions, further optimization is: during the sanding process, the sanding direction is along the circumferential direction of the boiler tube end, so that a uniform brushed texture is formed on the surface.

[0064] Dry brushing is used to remove large impurities, acetone wiping is used to dissolve grease, sandpaper is used to create a uniform brushed pattern along the circumference to increase surface roughness, and a suede cloth is used to remove fine dust. The overall multi-stage cleaning combines mechanical cleaning with chemical cleaning to thoroughly remove oxides, oil stains, and impurities from the weld area. This ensures the cleanliness of the weld area and reduces the probability of defects such as porosity and slag inclusions during the welding process.

[0065] The circumferential wire drawing pattern guides the deposited metal to spread evenly around the tube. The directional pattern design actively controls the flow direction of the deposited metal and improves the fusion quality of the initial section of the weld.

[0066] S2, processing zigzag composite groove.

[0067] On the basis of any of the above technical solutions, further optimized is: the forming method of the zigzag composite groove is as follows: first, a V-shaped groove with a groove angle of 60°-70° is processed.

[0068] During the specific operation, a V-shaped groove with a groove angle of 60°-70° is first formed at the end of the boiler tube through mechanical processing to determine the welding basic angle and penetration range; then a file is used to perform secondary processing on the two side walls of the V-shaped groove, and a serrated structure is filed along the side wall with uniform force.

[0069] Based on any of the above technical solutions, further optimization is that the spacing between each sawtooth is 2-3mm, the depth is controlled at 0.5-1mm, the sawtooth shape is a right-angled trapezoid, its hypotenuse faces the center of the groove, and the right-angled side is perpendicular to the side wall of the groove.

[0070] During operation, the serrations on one side are machined sequentially according to the set spacing (2-3mm) and depth (0.5-1mm). Upon completion, the other side is treated using the same process. Caliper measurements are used during the process to ensure dimensional accuracy. The serrations are in the shape of a right-angled trapezoid, with the hypotenuse facing the center of the groove and the right-angled sides perpendicular to the groove sidewalls. This geometric structure increases the contact area between the deposited metal and the base metal during welding by increasing the unevenness of the groove's inner wall. This serrated structure increases the surface area of ​​the groove, ensuring more complete contact between the deposited metal and the base metal, enhancing weld adhesion, and also has the following benefits:

[0071] Enhanced metallurgical bonding: The serrated structure significantly increases the surface area of ​​the groove compared to the traditional V-shaped groove. The contact interface between the deposited metal and the base material is expanded during filling, and the diffusion reaction between the liquid metal and the solid base material is more complete, thereby improving the bonding strength of the weld fusion line and reducing the risk of fracture of the weld joint.

[0072] Optimizing Molten Pool Flow: The beveled guiding action of the right-angled trapezoidal serrations can guide the molten pool metal toward the center of the groove, reducing the tendency of liquid metal to flow downward due to gravity. This is particularly suitable for all-position welding scenarios for horizontal fixed pipes, improving weld uniformity and reducing the probability of undercuts and weld bead defects. Furthermore, the expanded contact area slows the solidification rate of the molten pool metal, providing more time for the slag and gas to float up and discharge, reducing volumetric defects such as porosity and slag inclusions. Furthermore, the mechanical bite effect formed by the serrations disperses stress concentration through the microstructure under the action of welding thermal stress, reducing the probability of cracks.

[0073] S3, boiler tube group positioning, the specific operation is as follows:

[0074] Positioning reference setting: Use a stone pencil to evenly mark four positioning points along the circumference at the ends of the two boiler tubes to be welded. They are located at 0°, 90°, 180°, and 270° respectively. The marking points are 10-15mm away from the edge of the tube mouth as a reference for assembly.

[0075] At the same time, draw a straight line along the axial direction on the outer wall of the pipeline to assist in determining the verticality and coaxiality of the pipeline.

[0076] Then use the external pipe pliers to position the pipe, and adjust the external pipe pliers at a distance of 50-80mm from the pipe mouth to initially align the pipe.

[0077] Coarse alignment: Align the ends of the two boiler tubes so that the marked positioning points on the tube openings correspond to each other. Use a steel ruler to measure the gap between the tube openings and adjust the pipe position to ensure a uniform gap within a range of 2-2.5mm. If the pipes are misaligned, use a manual jack to push against the outer wall of the pipe to gradually correct the misalignment, ensuring that the misalignment does not exceed 10% of the pipe wall thickness and is no greater than 1mm.

[0078] Coaxiality calibration.

[0079] Temporary Fixing: Use spot welding to temporarily secure the aligned pipes. Place spot welds evenly around the circumference at 4-6 locations. Each spot weld should be 15-20 mm long and no more than half the pipe wall thickness. Use a low current (20%-30% lower than regular welding) to prevent pipe deformation due to concentrated heat. After spot welding, recheck the coaxiality and pipe end clearance, and adjust any deviations promptly.

[0080] S4, after positioning, the boiler tubes are preheated by spiral flame encircling.

[0081] Based on any of the above technical solutions, further optimization is as follows: the specific method of preheating the boiler tube by spiral flame encirclement is as follows: the acetylene-oxygen flame is adjusted to a neutral flame to ensure stable flame combustion and moderate temperature, and avoid local overheating or oxidation of the boiler tube due to improper flame properties.

[0082] Start heating from one end of the boiler tube to be welded, and move the flame in a spiral trajectory from the outside to the inside around the tube body, with the spiral spacing maintained at 10-15mm.

[0083] During the heating process, the distance between the flame nozzle and the tube end is controlled at 5-10mm to ensure that the flame heat is effectively transferred to the boiler tube surface.

[0084] The use of spiral flame heating provides a more even distribution of heat around the pipe's circumference and axis than traditional linear reciprocating heating. The spiral pitch is controlled at 10-15mm, ensuring appropriate overlap between adjacent heating areas, avoiding partial underheating and effectively reducing the risk of weld deformation and cracking caused by uneven preheating.

[0085] S5, when welding, double arc alternating broken arc welding is used to complete the base welding, and then filler welding is performed.

[0086] On the basis of any of the above technical solutions, further optimization is as follows: the specific steps of using double arc alternating arc breaking welding are as follows: Step 1, differentiated pretreatment of welding rods: select two welding rods with a diameter of 2.5 mm, marked as welding rod A and welding rod B.

[0087] Welding rod A was kept at 50°C and then treated in a 0.3T constant magnetic field for 30 seconds, while welding rod B was stored at room temperature;

[0088] Welding rod A was placed in a constant temperature drying oven at 50°C for 1 hour to allow the moisture inside the welding rod to evaporate fully and enhance its stability. After the insulation was completed, welding rod A was placed in a constant magnetic field device with a magnetic field strength of 0.3T for 30 seconds. The magnetic field treatment changed the distribution of alloying elements in the welding rod coating, promoted molten pool deoxidation, and refined weld grains during welding.

[0089] Welding rod B is kept at room temperature and used as a reference for comparison, forming a differentiated effect with welding rod A during the welding process.

[0090] Grain refinement and deoxidation during welding: After magnetic field treatment, electrode A promotes deoxidation of the weld pool during welding, effectively reducing the oxygen content in the weld and the probability of oxide inclusion defects. Furthermore, the magnetic field promotes grain refinement in the weld, which significantly improves the strength, toughness, and fatigue resistance of the weld metal, enhancing the overall mechanical properties of the weld and meeting the high-quality weld requirements of boiler tube welding.

[0091] Furthermore, it has a defect suppression effect: the pretreatment process of electrode A reduces the moisture content, thereby reducing the source of hydrogen and suppressing the formation of hydrogen pores during welding. During double-arc alternating interrupted arc welding, the alternating use of different electrodes adjusts the solidification rate of the molten pool and the metallurgical reaction process, helping to prevent welding defects such as lack of fusion and incomplete penetration, further improving weld quality.

[0092] Step 2. Start arcs with electrodes A and B in steps: Start arc with electrode A: Start arc at the positioning welding point with a current of 70A, using the two-point positioning method of starting with the groove side and then the root.

[0093] During the specific operation, use a welding current of 70A and ignite electrode A on the positioning welding point;

[0094] Use the two-point positioning method to strike the arc. First, lightly touch the tip of the electrode to the edge of one side of the groove, and then quickly scratch it to ignite the arc.

[0095] Then quickly move the arc to the root of the groove, pause for 1-2 seconds, and use the high temperature of the arc to penetrate the root of the groove to form a molten hole;

[0096] During the arc striking process, maintain short arc operation and strictly control the arc length to not exceed the electrode diameter to ensure that the arc is stable and the heat is concentrated.

[0097] Arc striking with electrode B: After electrode A extinguishes its arc, strike an arc at the junction of the edge of the molten pool and the groove when the molten pool is in a semi-solid state. Use a 75A welding current to ignite electrode B, and quickly send the arc to the molten pool that has not been completely solidified, so that the new arc and the old molten pool are fully fused to form a molten hole again.

[0098] The reference for striking an arc at the junction of the edge of the molten pool and the groove is as follows: visual judgment, this position shows a transition state between metallic luster and dark red molten pool. The metallic luster part shows that it has solidified but still has good fusion properties, while the dark red molten pool part maintains a certain liquid fluidity; tactile judgment: lightly touch this position with the welding rod, there will be a slight sense of resistance. It is neither as easy for the welding rod to sink into the completely liquid molten pool, nor as unresponsive as solid metal.

[0099] This step-by-step arc ignition method, using electrodes A and B at two points, effectively controls the location and size of the initial molten pool. Striking the arc first on the groove side allows the arc to quickly heat the groove edge, reducing the difficulty of subsequent root penetration. The arc is then moved to the root and paused to form a molten hole, ensuring complete root penetration and avoiding incomplete penetration defects. Maintaining a short arc allows the arc heat to be highly concentrated in the weld area, reducing the extent of the heat-affected zone, increasing the temperature gradient in the molten pool, promoting rapid solidification, and promoting weld grain refinement.

[0100] During relay arc striking with electrode B, after electrode A extinguishes its arc, electrode B strikes an arc at the intersection of the molten pool edge and the groove while the molten pool is semi-solid. This utilizes the residual heat of the molten pool to rapidly fuse the new and old arcs. This complete fusion of the new arc and the old molten pool ensures a persistent molten hole, maintaining the continuity of the molten pool during welding and providing a stable foundation for subsequent welding.

[0101] Welding rod A uses a current of 70A. The lower current at the initial arc ignition stage prevents the risk of spattering and burn-through caused by excessive current, allowing the welder to precisely control the arc and weld pool. Welding rod B uses a slightly higher current of 75A, which helps quickly melt the electrode and base metal, ensuring the complete fusion of the new and old weld pools while maintaining stable arc combustion. This differentiated current setting adapts to the arc energy requirements of different welding stages, improving the stability and controllability of the welding process.

[0102] Both electrodes emphasize short arc operation when striking the arc, which can effectively reduce arc swing, reduce the probability of air intrusion into the molten pool, and prevent the formation of porosity in the weld.

[0103] In the third step, during the welding process, both electrodes are moved by a composite swing method combining spiral motion and zigzag swing.

[0104] During the spiral motion, the electrode moves in a circle with a spiral diameter of 2 mm with the electrode axis as the center. After completing one spiral motion, the electrode moves forward 1-1.5 mm in the welding direction.

[0105] The spiral motion can stir the molten pool in three dimensions, promoting the discharge of slag and gas.

[0106] During the zigzag motion, the welding rod simultaneously makes a small zigzag motion based on the spiral motion, with the swing amplitude controlled at 3-5mm. On both sides of the groove, the welding rod stays for 0.8 seconds and performs a small vibration motion at a frequency of 2Hz.

[0107] The dwelling and vibration help the molten pool to fully fuse with the groove wall, ensuring the forming quality of the weld edge.

[0108] The continuous stirring of the molten pool through spiral motion increases the contact area and time between the liquid metal in the molten pool and the decomposition products of the electrode coating and the base material, promotes more complete metallurgical reactions such as deoxidation and desulfurization, effectively reduces the content of harmful impurities in the weld, and improves the purity and mechanical properties of the weld metal.

[0109] Step 4: The two electrodes perform welding operations alternately at the specified frequency.

[0110] During the entire double arc alternating arc interruption welding process, the number of times that electrodes A and B alternately strike and extinguish the arc remains in the range of 45 to 55 times within one minute.

[0111] Each time the welding rods are replaced, the heat input of the new arc and the rapid cooling of the old molten pool alternate, which helps to refine the weld grains; rapid cooling and periodic changes in heat input can break the growth trend of coarse grains, form a finer and denser weld structure, and improve the strength, toughness and fatigue resistance of the weld.

[0112] Furthermore, high-frequency alternating welding allows the molten pool to undergo multiple metallurgical reactions, such as deoxidation and desulfurization, in a relatively short period of time, facilitating the effective removal of harmful gases and impurities. Furthermore, the molten pool's state is constantly adjusted during the alternating process, preventing problems such as element segregation and slag inclusions caused by prolonged exposure to a single heat source, and reducing the probability of defects such as porosity and cracks.

[0113] Step 5: As the weld nears its end, the arc is extinguished using a current decay method. This gradual current decay prevents the rapid solidification of the molten pool caused by the sudden loss of heat during arc interruption, thus preventing defects such as deep arc craters and shrinkage cavities. The current decay process causes the molten pool to cool slowly, helping the weld metal form a more uniform and dense microstructure during solidification.

[0114] During specific operation, reduce the welding current to 80% of the normal welding current and continue welding for 2 to 3 seconds.

[0115] Continue to reduce the current to 60% of the normal welding current and weld for 1 to 2 seconds.

[0116] Reduce the current to 40% of the normal welding current, perform three circular fusions at the arc crater, each fusion for 0.5 seconds, then quickly extinguish the arc and remove the electrode, and cover the weld with insulation cotton to keep it warm for at least 5 minutes to prevent arc crater cracks.

[0117] The circular fusion operation remelts and evenly distributes the metal in the arc crater, eliminating the localized stress concentration caused by the rapid reduction of current. Multiple fusions further promote the discharge of gases and impurities from the molten pool, reducing the risk of defects such as porosity and slag inclusions remaining in the arc crater, and ensuring the structural integrity of the weld at the end.

[0118] Based on any of the above technical solutions, the following are further optimized: the steps of filling welding are as follows: welding preparation: after the base welding is completed, use a wire brush to clean the slag on the weld surface and a flat shovel to remove spatter; select a welding rod with a diameter of 3.2mm that matches the boiler tube; adjust the welding current to 90-100A and the arc voltage to 22-24V.

[0119] Starting welding: At one end of the weld, align the welding rod with the weld, with the tip 2-3mm away from the bottom, scratch or strike the arc, pull it to the bottom and stay for 0.8-1.2 seconds to form a molten pool; the welding rod is at 90° to the pipe axis and 70°-80° to the welding direction, and maintain a short arc operation.

[0120] Step-by-step swing operation: The electrode swings in steps, staying on both sides for 1-1.5 seconds to ensure fusion, and moving quickly in the middle to prevent the weld from being too high. Move forward 2-3mm after each swing; observe the molten pool during welding. If it collapses, reduce the current or shorten the dwell time; if fusion is poor, increase the dwell time and adjust the electrode angle.

[0121] When the electrode is swung in steps, it stays on both sides for 1-1.5 seconds, which allows enough filler metal to accumulate on both sides of the groove, ensuring full fusion of the weld and the base material and avoiding undercut defects; rapid movement in the middle can prevent excessive accumulation of weld metal, effectively control the weld height, and make the weld surface smooth.

[0122] Filling and finishing: Continue filling until it is 1-2mm below the surface of the base material; when approaching the end, reduce the current in stages 3-5cm in advance, reducing it by 5A-10A each time, and stay in the molten pool for 1-2 seconds to fill the arc pit. Remove the electrode and clean the welding slag.

[0123] S6: After the filling welding is completed, the cover welding is carried out.

[0124] On the basis of any of the above technical solutions, further optimization is as follows: the specific steps of cover welding are as follows: after filling welding and cleaning, select 3.2mm low-hydrogen welding rod, and adjust the current to 85-95A according to the state of the filling weld.

[0125] Strike the arc at the base material 10-15mm in front of the starting end of the weld, pull it to the starting point after it stabilizes, and keep the welding rod at 75°-85° to the welding direction, perpendicular to the pipe axis, and start welding with a short arc to ensure fusion.

[0126] When welding with welding rod, move the center of the weld quickly, press down on both sides and pause for 0.5-1 second, then lift up, and control the weld width to exceed the groove by 1-2mm on each side, and the excess height to 0-3mm.

[0127] When changing the welding rod, grind a gentle slope of 10-15mm at the end of the arc, strike the arc with the new welding rod 5-8mm in front of the joint, pull it until the joint stops and fuses, then continue welding.

[0128] At the end, the current is reduced to 70%-80%, and the arc is extinguished after circular swing to fill the arc pit.

[0129] Strike the arc 10-15mm in front of the starting point of the weld, and then pull it back to the starting point after the arc stabilizes. This can avoid defects such as porosity and lack of fusion caused by unstable arc striking at the starting point.

[0130] S7, after the cover welding is completed, the interlayer cleaning of the welding layer is completed by knocking and vibrating.

[0131] On the basis of any of the above technical solutions, further optimization is as follows: the specific steps of completing the interlayer cleaning of the welding layer by tapping and vibration are as follows: After welding is completed, wait for the weld to cool to 60-80℃.

[0132] The small hammer strikes both sides of the weld at a frequency of 2-3 times per second, with a spacing of 5-8 mm between the striking points.

[0133] Move and strike in a spiral shape along the direction of the weld, with a spiral diameter of about 20mm.

[0134] After knocking, use a wire brush to brush away loose slag in one direction along the weld.

[0135] When stubborn slag is found, it is baked with flame until dark red and then rapidly cooled, and peeled off by utilizing thermal expansion and contraction.

[0136] This method can effectively remove slag that is difficult to remove by conventional cleaning, ensuring that there are no impurities between layers, ensuring tight fusion between multi-layer welds, and improving the overall quality of the welds.

[0137] S8. After the final welding is completed, wrap it with multiple layers of wet towels to keep it warm and cool slowly, and check the weld after cooling.

[0138] Based on any of the above technical solutions, further optimization is as follows: the specific steps of wrapping with multiple layers of wet towels to keep warm and slow down cooling are as follows: prepare enough pure cotton towels with good water absorption; prepare warm water, and control the water temperature at 40-50℃ to ensure that the temperature of the towels is appropriate after being soaked.

[0139] After the final welding is completed, soak the towel with warm water and wring it until it stops dripping. With the weld as the center, tightly wrap the first layer of towel from one end to ensure that the weld is completely covered and each layer of towel fits tightly together without leaving any gaps.

[0140] When the temperature of the first layer of towel drops to close to the ambient temperature, quickly wrap the second layer and repeat the operation until 3-4 layers of towels are wrapped.

[0141] Finally, wrap the towel with plastic film to seal it to prevent water from evaporating too quickly and slow down the rate of heat loss.

[0142] Multi-layer wrapping and adding layer by layer according to temperature changes, combined with plastic film sealing, effectively slows down the rate of heat loss and avoids excessive temperature gradients in welds due to rapid cooling.

[0143] During the insulation and slow cooling process, use an infrared thermometer to intermittently measure the weld temperature, record the temperature changes, and control the weld cooling rate by adding or reducing the number of towel layers or adjusting the ambient temperature.

[0144] Based on any of the above technical solutions, further optimization is: during the preheating process, the color change of the tube wall of the boiler tube is observed. When the tube wall appears dark red, it indicates that the temperature is close to or reaches the preheating target temperature of 150℃-200℃.

[0145] At the same time, during the surrounding heating process, a relatively uniform movement speed of about 1-2 cm per second is maintained to ensure uniform heating in the circumferential direction of the boiler tube.

[0146] After completing each spiral heating cycle, the heating process needs to be repeated 1-2 times to further ensure the temperature uniformity and preheating adequacy of the entire welded area, reduce welding stress, and reduce the probability of welding crack defects.

[0147] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some or all of the technical features therein can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention. For those skilled in the art, any replacement improvements or changes made to the implementation methods of the present invention fall within the scope of protection of the present invention.

[0148] Any matters not described in detail in the present invention are well-known technologies to those skilled in the art.

Claims

1. A boiler tube butt welding method, characterized in that: The steps include: S1, pre-treat the ends and outer surfaces of the boiler tubes to be welded using a dry-wet alternating cleaning method, first dry-brushing, then wiping with acetone, then sanding with sandpaper and finally cleaning with a chamois cloth; S2, processing zigzag composite groove; S3, positioning of boiler tube group; S4, after positioning, the boiler tubes are preheated by spiral flame encircling; S5, when welding, double arc alternating broken arc welding is used to complete the base welding, and then filler welding is performed; S6, after the filling welding is completed, the cover welding is carried out; S7, after the cover welding is completed, the welding layer is cleaned between layers by knocking and vibrating; S8, after the final welding is completed, wrap it with multiple layers of wet towels to keep it warm and cool slowly, and check the weld after cooling; The specific steps of using double arc alternating arc interruption welding are as follows: Step 1: Differentiated pretreatment of welding rods: Select two 2.5mm diameter welding rods, marked as welding rod A and welding rod B; Step 2: Strike the arc with electrodes A and B step by step: Arc striking with electrode A: 70A current strikes the arc at the positioning welding point, using the two-point positioning method of striking the arc first at the groove side and then at the root; Ignite the arc with electrode B: After electrode A extinguishes its arc, when the molten pool is in a semi-solid state, strike the arc at the junction of the edge of the molten pool and the groove. Use a welding current of 75A to ignite electrode B, and quickly send the arc to the molten pool that has not yet fully solidified, so that the new arc and the old molten pool are fully fused to form a molten hole again. Step 3: During the welding process, both electrodes are moved by a composite swing method combining spiral motion and zigzag swing; Step 4: The two electrodes perform welding operations alternately at the specified frequency; Step 5: When approaching the end of the weld, use the current decay method to extinguish the arc.

2. The boiler tube butt welding method according to claim 1, characterized in that: During the sanding process, the sanding direction is along the circumferential direction of the boiler tube end to form a uniform brushed texture on the surface.

3. The boiler tube butt welding method according to claim 2, characterized in that: The forming method of the zigzag composite groove is as follows: first, a V-shaped groove with a groove angle of 60°-70° is processed; A serrated structure is processed on both side walls of the V-shaped groove. During the operation, use a file to file along the side walls of the groove with relatively uniform force and rhythm, starting on one side of the groove wall; file out the serrations in sequence according to the set spacing and depth. After completing the operation on one side, process the other side of the groove wall in the same way; during the filing process, continuously measure the spacing and depth of the serrations with a caliper.

4. The boiler tube butt welding method according to claim 3, characterized in that: The spacing between each sawtooth is 2-3mm, the depth is controlled at 0.5-1mm, and the sawtooth shape is a right-angled trapezoid, with its hypotenuse facing the center of the groove and the right-angled side perpendicular to the side wall of the groove.

5. The boiler tube butt welding method according to claim 4, characterized in that: The specific method of preheating the boiler tubes by spiral flame encirclement is as follows: adjust the acetylene-oxygen flame to a neutral flame to ensure stable flame combustion and moderate temperature, and avoid local overheating or oxidation of the boiler tubes due to improper flame properties; Start heating from one end of the boiler tube to be welded, and move the flame in a spiral path from the outside to the inside around the tube body, with the spiral spacing maintained at 10-15mm; During the heating process, the distance between the flame nozzle and the tube end is controlled at 5-10mm to ensure that the flame heat is effectively transferred to the boiler tube surface.

6. The boiler tube butt welding method according to claim 5, characterized in that: The steps of filler welding are as follows: Welding preparation: After the base welding is completed, use a wire brush to clean the slag on the weld surface and a flat shovel to remove spatter; select a welding rod with a diameter of 3.2mm that matches the boiler tube; adjust the welding current to 90-100A and the arc voltage to 22-24V; Initial welding: At one end of the weld, align the welding rod with the weld seam, with the tip 2-3mm away from the bottom, scratch or strike the arc, pull it to the bottom and hold it for 0.8-1.2 seconds to form a molten pool; the welding rod should be at 90° to the pipe axis and 70°-80° to the welding direction, and maintain a short arc operation; Step-by-step oscillation operation: The electrode swings in steps, pausing for 1-1.5 seconds on both sides to ensure fusion, and moving quickly in the middle to prevent the weld from being too high. Move forward 2-3mm after each swing. Observe the molten pool during welding. If it collapses, reduce the current or shorten the dwell time. If fusion is poor, increase the dwell time and adjust the electrode angle. Filling and finishing: Continue filling until it is 1-2mm below the surface of the base material; when approaching the end, reduce the current in stages 3-5cm in advance, reducing it by 5A-10A each time, and stay in the molten pool for 1-2 seconds to fill the arc pit. Remove the electrode and clean the welding slag.

7. The boiler tube butt welding method according to claim 6, characterized in that: The specific steps for completing interlayer cleaning of welding layers by tapping and vibration are as follows: After welding is completed, wait for the weld to cool to 60-80℃; The hammer strikes both sides of the weld at a frequency of 2-3 times per second, with a strike distance of 5-8 mm. Move and strike in a spiral shape along the direction of the weld, with a spiral diameter of about 20mm; After knocking, use a wire brush to remove loose slag in the direction of the weld; When stubborn slag is found, it is baked with flame until dark red and then rapidly cooled, and peeled off by utilizing thermal expansion and contraction.

8. The boiler tube butt welding method according to claim 7, characterized in that: The specific steps of wrapping with multiple layers of wet towels to keep warm and slow down cooling are as follows: Prepare enough absorbent cotton towels; prepare warm water, the water temperature should be controlled at 40-50℃, and ensure the towels are at the right temperature after being soaked; After the final welding is completed, soak the towel with warm water and twist it until it stops dripping. With the weld as the center, wrap the first layer of towel tightly from one end to ensure that the weld is completely covered and each layer of towel fits tightly together without leaving any gaps. When the temperature of the first layer of towels drops to close to the ambient temperature, quickly wrap the second layer, and repeat the process until 3-4 layers of towels are wrapped; Finally, wrap the towel with plastic film to seal it to prevent water from evaporating too quickly and slow down the heat loss. During the insulation and slow cooling process, use an infrared thermometer to intermittently measure the weld temperature, record the temperature changes, and control the weld cooling rate by adding or reducing the number of towel layers or adjusting the ambient temperature.