Welding method of pipe-pipe butt joint vertical circumferential weld

Abstract

The invention discloses a welding method for a pipe-pipe butt joint vertical circumferential weld. The welding method comprises the steps that the pipe ends of two pipes to be welded are straightened; the two pipe ends are subjected to groove machining, so that a V-shaped groove is formed during assembly; the groove is polished and cleaned; the two pipe ends are assembled and positioned; first-layer backing welding is carried out on the V-shaped groove, and second-layer filling welding is carried out on a welding bead of backing welding; third-layer cosmetic welding is carried out on a welding bead of filling welding; welding bead flash and burrs are polished; and inspecting after welding. By means of layered welding, namely first-layer backing welding, second-layer filling welding and third-layer cosmetic welding, the root penetration performance of backing welding is good, and the welding penetration risk is reduced; the penetration depth of filling welding is increased by 20%-30% compared with that of a traditional method, and the grinding time can be saved; cover surface welding forming is smooth and free of undercut, the requirements for strength and sealing performance of pipeline welding are met, and welding defects can be reduced and welding efficiency can be improved through constant-speed welding and reasonable heat input control.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, and in particular relates to a welding method for vertical circumferential welds between pipes. Background Technology

[0002] Pipeline transportation is an efficient, convenient, and environmentally friendly method for transporting oil and gas. my country has over 80,000 kilometers of long-distance pipelines, bringing immense convenience to modern life. Pipelines are special pressure vessels. During the operation of long-distance oil and gas pipelines, corrosion, stress, and other factors can lead to defects, reducing the safety of pipeline operations. Therefore, pipelines require inspection during use. When defects are detected, such as wall thinning due to corrosion or incomplete fusion at the joints of circumferential welds, repair is necessary. There are two main methods for repairing defects at circumferential welds: pipe replacement or reinforcement using a type B sleeve.

[0003] Pipe replacement is a primary means of completely eliminating pipeline hazards, but it requires shutting down pipeline operations, affecting the production of downstream oil and gas users. The welds after pipeline repair using type B sleeves include two lateral longitudinal welds and two end fillet welds, which are prone to welding defects and present significant welding challenges. Summary of the Invention

[0004] This invention provides a welding method for vertical circumferential welds between pipes. During the welding process, layered welding is used to reduce welding defects and improve welding quality.

[0005] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a welding method for a vertical circumferential weld between pipes, comprising the following steps: Step 1: Straighten the ends of the two pipes to be welded, so that the straightness of the ends of the two pipes reaches 0.5~7‰ within the preset length range, and ensure that the axes of the two pipes coincide during assembly; Step 2: Beveling the two pipe ends to form a V-shaped bevel when they are assembled; grinding and cleaning the bevels of the two pipe ends to expose the metallic luster on the outer wall. Step 3: Assemble and position the two pipe ends, and perform tack welding; Step 4: Perform the first layer of root pass welding on the V-shaped groove, then perform the second layer of fill pass welding on the root pass weld; and finally perform the third layer of cover pass welding on the fill pass weld. Step 5: After welding is completed, grind off the weld burrs and flash; Step 6: Post-weld inspection. Check the surface and interior of the weld for cracks, voids, or other defects. If no defects are detected, the weld is considered to be in good condition.

[0006] In some embodiments of this application, the first layer of root pass welding is performed by controlling the welding current to be 80~120A, the arc voltage to be 18~22V, and the welding speed to be maintained at a uniform advance of 50~80mm / min, with a short arc operation and an arc length of 2~3mm.

[0007] In some embodiments of this application, the second layer of filler welding is performed by controlling the welding current to be 140~160A, the arc voltage to be 23~25V, and the angle of the welding torch to be 75°~80°.

[0008] In some embodiments of this application, the third layer cover welding is performed using an arc-extinguishing welding method, with the arc extinguishing frequency controlled to be once every 5-10 mm, and the single arc ignition welding time controlled to be 1-2 seconds.

[0009] In some embodiments of this application, the third cover weld is performed with a welding current of 130-150A and an arc voltage of 22-24V.

[0010] In some embodiments of this application, the third cover weld includes: Step 1: Create the first capping arc at one end of the V-shaped bevel; Step 2: Perform the first cover arc extinguishing at the other end of the V-shaped bevel; Step 3: Create a second cover arc at one end of the V-shaped bevel; Step 4: Next, form a second capping arc at the other end of the V-shaped bevel, and repeat S41~S44 until the entire V-shaped bevel is formed.

[0011] In some embodiments of this application, the point where the first cover surface begins to arc is called the first cover surface arc starting point, the point where the second cover surface begins to arc is called the second cover surface arc starting point, and the distance between the first cover surface arc starting point and the second cover surface arc starting point is 1 / 2 of the weld width.

[0012] In some embodiments of this application, the angle of the welding torch is controlled to be 75°~80° during the cover welding process.

[0013] Compared with the prior art, the advantages and positive effects of the present invention are as follows: The method of the present invention is applicable to pipe diameters of 50~200mm. Through layered welding, namely, the first layer is the root pass weld, the second layer is the fill pass weld, and the third layer is the cover pass weld, the root pass weld has good penetration at the root, reducing the risk of burn-through; the fill pass weld has a penetration depth that is 20%~30% higher than that of the traditional method, which helps to save subsequent grinding time; the cover pass weld is smooth and without undercut, meeting the strength and sealing requirements of pipe welding. Through uniform welding and reasonable heat input control, welding defects are reduced, and welding efficiency and welding quality are improved. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 One of the schematic diagrams of a circumferential welding structure for connecting two pipes provided by the present invention; Figure 2 A second schematic diagram of a circumferential welding structure for connecting two pipes provided by the present invention; Figure 3 The third schematic diagram of the structure for the circumferential welding of two pipes provided by the present invention.

[0016] Explanation of reference numerals in the attached figures: 1. V-shaped bevel; 2. The first starting point of the arc; 3. First corner point; 4. The second starting point of the arc; 5. Second corner point; 6. The starting point of the first cover surface; 7. The first point where the arc is extinguished on the cover surface; 8. The starting point of the second cover surface; 9. The second cover surface arc extinguishing point. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] It should be noted that in the description of this invention, the terms "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," which indicate directional or positional relationships, are based on the directional or positional relationships shown in the accompanying drawings. These are merely for ease of description and do not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0019] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0020] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0021] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0022] In a first aspect, embodiments of this disclosure provide a welding method for a vertical circumferential weld between pipes, the welding method comprising the following steps: S1: Straighten the ends of the two pipes to be welded so that the straightness of the ends of the two pipes reaches 0.5~7‰ within the preset length range, ensuring that the axes of the two pipes coincide during assembly.

[0023] By straightening the ends of the two pipes to be welded, bending and twisting of the welding wire can be eliminated, ensuring that the welding wire enters the welding area smoothly, reducing welding defects, helping to improve the quality of the welded joint, ensuring the strength and sealing of the welded part, avoiding damage to the pipeline due to stress concentration during use, and improving the reliability of the entire pipeline system.

[0024] For example, the straightness of the pipe end within 350~550mm reaches 0.5~7‰.

[0025] Specifically, the preset lengths are 350mm, 400mm, 450mm, 500mm, or 550mm.

[0026] S2: Beveling is performed on the two pipe ends, forming an inclined surface on each pipe end, so that the two pipe ends form a V-shaped bevel 1 when assembled; the bevels of the two pipe ends are polished and cleaned to expose the metallic luster on the outer wall.

[0027] Specifically, by beveling the two pipe ends to form an inclined surface on each pipe end, a V-shaped bevel is formed when the two pipe ends are assembled, which can increase the weld penetration and filling space, thereby improving the joint strength and sealing performance.

[0028] S3: Use tooling to assemble and position the two pipe ends, and then perform tack welding.

[0029] Specifically, tack welding can accurately fix the two pipe ends of the assembly, maintain the stability of the root gap of the V-groove, and help ensure the penetration of the root weld and the overall weld quality.

[0030] S4: Perform the first layer of root pass welding on V-groove 1; The first layer of root pass welding uses a low-current, stable arc. The workpiece is connected to the negative terminal of the power supply, and the welding torch is connected to the positive terminal. DC reverse polarity directs electrons from the workpiece to the tip of the welding wire, concentrating heat at the wire tip, resulting in shallow penetration and high cladding efficiency. A welding current of 80-120A and an arc voltage of 18-22V are used to ensure root penetration and prevent burn-through. Maintain a uniform welding speed of 50-80mm / min, combined with a short arc of 2-3mm.

[0031] A second filler weld is performed on the root pass using a serrated welding method.

[0032] Second layer filler weld: control the zigzag oscillation amplitude to 1 / 2 to 2 / 3 of the width of the V-groove 1, the oscillation frequency to 1 time / s, and pause at the corner for 0.5 to 1s to ensure weld fusion; welding current 140 to 160A, arc voltage 23 to 25V.

[0033] Specifically, by using a sawtooth oscillation to increase the heat input coverage area, the melting depth is increased by 20% to 30% compared to traditional methods.

[0034] The arc-extinguishing welding method is used to perform a third cover weld on the filler weld.

[0035] Third layer cover welding: Set the arc extinguishing interval according to the circumference of the pipe, control the arc extinguishing frequency to extinguish once every 5~10mm, and control the single arc ignition welding time to 1~2s, which helps to avoid local overheating; use medium current, control the welding current to 130~150A and the arc voltage to 22~24V, to ensure smooth surface formation without undercut.

[0036] Specifically, by adopting an arc-extinguishing welding method that uses the "arc ignition-burning-arc extinguishing" cycle of the arc to achieve periodic solidification of the molten pool, the capping welding is achieved. This reduces the requirements for equipment, quantifies the arc extinguishing interval and arc ignition time, reduces excessive reliance on operator experience, and facilitates standardized operations.

[0037] S5: After welding, grind off the weld burrs and flash.

[0038] Specifically, burrs and flash can form sharp edges. Grinding burrs and flash on welds can prevent operators from being scratched during assembly and transportation. At the same time, burrs and flash are prone to stress concentration points when under stress. Grinding can reduce the stress concentration coefficient, thereby reducing the risk of fatigue fracture.

[0039] S6: Post-weld inspection, checking for cracks and voids on the surface and inside of the weld. If no defects are detected, the weld is in good condition.

[0040] Specifically, the method according to the embodiments of this disclosure is applicable to pipe diameters of 50-200mm. Through layered welding, namely, a first root pass weld, a second filler pass weld, and a third cap pass weld, the root pass weld has good penetration at the root, reducing the risk of burn-through; the filler pass weld has a penetration depth that is 20%-30% greater than that of traditional methods, which helps to save subsequent grinding time; the cap pass weld is smooth and without undercut, meeting the strength and sealing requirements of pipe welding. Through uniform welding speed and reasonable heat input control, it is beneficial to reduce welding defects and improve welding efficiency.

[0041] In some embodiments of this application, in step S4, the step of performing filler welding on the root pass using a serrated welding method includes: S41: Make the first arc at one end of the V-shaped bevel 1; S42: The first corner is formed at the other end of the V-shaped bevel 1; S43: Make a second arc at one end of the V-shaped bevel 1; S44: Form a second corner at the other end of V-shaped bevel 1, and repeat S41~S44 until the entire V-shaped bevel 1 is completed.

[0042] Specifically, the second layer of filler welding adopts a sawtooth welding method. The welding rod is oscillated laterally in a sawtooth shape, pausing at the corner for 0.5 to 1 second, and then quickly passing through the middle. This creates a heat input rhythm that is slow on both sides and fast in the middle. This can avoid incomplete fusion at the edge of the bevel, make the heat distribution of the molten pool more uniform, and reduce undercut defects caused by local overheating. At the same time, the weld width is controlled by the oscillation amplitude, and the reinforcement height is adjusted in conjunction with the forward speed to make the weld transition smoothly and form a smooth weld transition surface.

[0043] In some embodiments of this application, the angle of the welding torch is controlled to be 75°~80° during the filler welding process.

[0044] Specifically, by controlling the angle of the welding torch at 75°~80° during the filler welding process, the heating efficiency of the electric arc on the molten pool can be maximized, while ensuring a smooth transition of molten droplets without spattering, resulting in a more uniform weld formation.

[0045] At the same time, it allows the heat of the electric arc to be more concentrated on the base material and the molten pool, avoiding insufficient penetration caused by heat dispersion; the tilt angle can also guide the molten droplets to fall smoothly into the molten pool along the direction of the electric arc, reducing spatter and porosity problems caused by improper angle.

[0046] In some embodiments of this application, the distance between the first arc starting point 2 and the bottom end of the V-shaped bevel 1 is 1 / 3 of the width of the V-shaped bevel 1.

[0047] Specifically, if the arc starting point is too concentrated at the bottom of the groove, it is easy to burn through; if the arc starting point is too concentrated at the edge of the groove, it is easy to cause poor fusion. By setting the distance between the first arc starting point 2 and the bottom of the V-groove 1 to 1 / 3 of the width of the V-groove 1, the arc starting point can be avoided from being too concentrated at the bottom or edge of the groove, so that the heat distribution of the initial molten pool is more even, reducing the situation of incomplete root penetration and reducing the probability of porosity.

[0048] In some embodiments of this application, the line connecting the first arc starting point 2 and the first corner point 3 is parallel to the line connecting the second arc starting point 4 and the second corner point 5; the angle between the line connecting the first arc starting point 2 and the first corner point 3 and the tangent direction of the V-shaped bevel 1 is an acute angle.

[0049] Specifically, by setting the line connecting the first arc starting point 2 and the first corner point 3 to be parallel to the line connecting the second arc starting point 4 and the second corner point 5, the symmetry of the arc trajectory can be ensured, so that the degree of fusion and the amount of cladding metal filling on both sides of the weld can be kept consistent, avoiding the weld being too thick / thin on one side, which is beneficial to improving the mechanical properties of the joint such as tensile strength and deformation resistance.

[0050] Specifically, by making the angle between the line connecting the first arc initiation point 2 and the first corner point 3 and the tangent direction of the V-shaped groove 1 acute, the arc direction can be made to better fit the welding direction of the groove, reducing the instability of the molten pool caused by arc "offset". At the same time, it is easier for the welder to observe the state of the molten pool and reduce problems such as slag inclusion and irregular weld formation.

[0051] For example, the angle between the line connecting the first starting point 2 and the first corner point 3 and the tangent direction of the V-shaped bevel 1 is 30°, 32°, 35°, 38° or 40°.

[0052] In some embodiments of this application, in step S4, the capping weld on the filler weld using the arc-extinguishing welding method includes: S45: The first cover arc is made at one end of the V-shaped bevel 1; S46: Perform the first cover arc extinguishing at the other end of the V-shaped bevel 1; S47: Perform a second cover arc at one end of the V-shaped bevel 1; S48: Form a second capping arc at the other end of the V-shaped bevel 1, and repeat S45~S48 until the entire V-shaped bevel 1 is completed.

[0053] Specifically, by performing a cover weld, the overall tensile strength of the weld can be improved, and the smooth transition surface formed by the cover weld can reduce stress concentration and reduce the risk of fatigue fracture.

[0054] In some embodiments of this application, the angle of the welding torch is controlled to be 75°~80° during the cover welding process.

[0055] Specifically, it can maximize the heating efficiency of the electric arc on the molten pool, while ensuring a smooth transition of molten droplets without splashing, resulting in a more uniform weld formation.

[0056] At the same time, it allows the heat of the electric arc to be more concentrated on the base material and the molten pool, avoiding insufficient penetration caused by heat dispersion; the tilt angle can also guide the molten droplets to fall smoothly into the molten pool along the direction of the electric arc, reducing spatter and porosity problems caused by improper angle.

[0057] In some embodiments of this application, the distance between the first arc-starting point 6 and the second arc-starting point 8 of the cover surface is 1 / 2 of the weld width. In practice, the weld width is basically the same as the width of the V-groove.

[0058] Specifically, by setting the distance between the first arc-starting point 6 and the second arc-starting point 8 of the cover surface to half the weld width, the stress distribution of the cover surface weld can be made more uniform, avoiding defects at weld overlaps; as follows: It can disperse stress concentration: The arc starting point of the cover is a relatively concentrated area of ​​stress in the weld. By setting the distance between the first arc starting point 6 and the second arc starting point 8 of the cover to 1 / 2 of the weld width, the staggered arrangement can avoid the superposition of multiple arc starting stresses and reduce the risk of weld cracking in the later stage.

[0059] It can improve the flatness of the weld: the staggered arrangement of adjacent arc starting points can make the cladding metal of each layer fill more evenly, reduce the occurrence of height differences and local accumulation on the weld surface, and make the appearance more regular.

[0060] It can reduce welding defects: When the arc starting points are concentrated in the same area, porosity and slag inclusions are prone to occur during welding. By staggering the arc starting points, the arc starting points can be avoided from being concentrated in the same area. At the same time, it makes the fusion area more dispersed and reduces the problems of grain coarsening and performance degradation caused by repeated heating.

[0061] refer to Figures 1-3 The following description, in conjunction with specific embodiments, provides further details.

[0062] Two weathering steel pipes with a diameter of 120mm, a wall thickness of 10mm, and material SMA490BW were selected as the base material. The pipe ends of the two steel pipes were straightened within a range of 400mm to achieve a straightness of 5‰.

[0063] The ends of the two steel pipes are beveled, combined with Figure 1 As shown, when two steel pipes are assembled, a V-shaped bevel 1 is formed. The bevel ends of the two steel pipes are ground and cleaned to expose the metallic luster on the outer wall. The angle of the V-shaped bevel 1 is 30°~35°, the root gap is 2~2.5mm, and the blunt edge is 1.0~1.5mm. After preparation, tack welding is performed.

[0064] The welding process uses MAG welding, and the matching welding wire model is CHW-55CNH. First, the first layer of root pass welding is performed. The welding current is 80~120A, the arc voltage is 18~22V, and the welding speed is kept at a uniform advance speed of 50~80mm / min. The arc length is 2~3mm when operating with a short arc.

[0065] Secondly, a serrated welding method is used for the second layer of filler welding, controlling the angle of the welding torch to 75°~80°; combined with Figure 2 As shown, a first arc is started at one end of the V-shaped groove 1, and the point of the first arc is the first arc starting point 2. A first corner is formed at the other end of the V-shaped groove 1, and the point of the first corner is the first corner point 3. Then, a second arc is started at one end of the V-shaped groove 1, and the point of the second arc is the second arc starting point 4. A second corner is formed at the other end of the V-shaped groove 1, and the point of the second corner is the second corner point 5. Filling welds are then performed sequentially until the entire V-shaped groove 1 is completed.

[0066] The distance a between the first arc starting point 2 and the bottom of the V-shaped bevel 1 is 1 / 3 of the width b of the V-shaped bevel 1; the line connecting the first arc starting point 2 and the first corner point 3 is parallel to the line connecting the second arc starting point 4 and the second corner point 5.

[0067] The angle α between the line connecting the first arc starting point 2 and the first corner point 3 and the tangent direction of the V-shaped bevel 1 is an acute angle.

[0068] The zigzag oscillation amplitude is controlled to be 1 / 2 to 2 / 3 of the width of the V-shaped groove 1, the oscillation frequency is 1 time / s, and the dwell time at the corner is 0.5 to 1s; the welding current is 140 to 160A and the arc voltage is 23 to 25V.

[0069] Next, the arc-extinguishing welding method is used for the third layer of cover welding. During the cover welding process, the angle of the welding torch is controlled at 75°~80°.

[0070] At one end of the V-groove 1, a first capping arc is initiated, with the starting point being the first capping arc point 6. At the other end of the V-groove 1, a first capping arc is extinguished, with the starting point being the first capping arc point 7. Then, at one end of the V-groove 1, a second capping arc is initiated, with the starting point being the second capping arc point 8. At the other end of the V-groove 1, a second capping arc is extinguished, with the starting point being the second capping arc point 9. This capping welding is performed sequentially until the entire V-groove 1 is completed.

[0071] The distance between the first arc-starting point 6 and the second arc-starting point 8 on the cover surface is 1 / 2 of the weld width; the arc-extinguishing frequency is controlled to be once every 5~10mm, and the single arc-starting welding time is controlled to be 1~2s; the welding current is 130~150A and the arc voltage is 22~24V; after welding, the weld bead flash and burrs are ground off.

[0072] After welding, the weld quality was inspected from multiple dimensions. The inspection results are as follows: Appearance quality: The weld surface is smooth and regular, without surface defects such as porosity, cracks, and undercut, and the weld is in good condition.

[0073] Non-destructive testing: 100% magnetic particle testing was performed according to ISO 17638 standard, and no surface or near-surface defects were detected. 100% radiographic testing was performed according to ISO 17636 standard, and no welding defects such as slag inclusions or lack of fusion were found inside the weld.

[0074] Sealing performance test: The water pressure sealing performance of the steel pipe was tested according to GB / T 8163 standard. The test pressure was set to 2.5MPa and the pressure holding time was 10s. After inspection, there was no leakage at the weld and pipe connection, and no structural deformation. The sealing performance was confirmed to meet the requirements.

[0075] In summary, the method of this invention, through layered welding—namely, a first root pass weld, a second filler pass weld, and a third cap pass weld—ensures good penetration at the root of the root pass weld, reducing the risk of burn-through. The filler pass weld has a penetration depth 20% to 30% greater than traditional methods, saving subsequent grinding time. The cap pass weld is smooth and free of undercut, meeting the strength and sealing requirements of pipeline welding. Uniform welding speed and reasonable heat input control help reduce welding defects and improve welding efficiency.

[0076] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions claimed by the present invention.

Claims

1. A welding method of a pipe-to-pipe butt girth weld, characterized by, It comprises the following steps: The first step: straighten the pipe ends of the two pipes to be welded, so that the straightness of the pipe ends of the two pipes within a preset length range reaches 0.5-7‰, and the axes of the two pipes coincide when they are assembled; The second step: bevel the two pipe ends to form a V-shaped groove when they are assembled; polish the bevels of the two pipe ends to expose the metal luster on the outer wall; The third step: assemble and position the two pipe ends and perform positioning welding; The fourth step: perform first layer backing welding on the V-shaped groove, second layer filling welding on the weld of the backing welding, and third layer covering welding on the weld of the filling welding; The fifth step: polish the weld flash and burrs after welding; The sixth step: perform post-welding inspection to detect whether there are cracks and cavities in the weld surface and interior, and if no defects are detected, the weld is good.

2. The pipe-to-pipe butt girth welding method according to claim 1, characterized by, The first layer backing welding: control the welding current at 80-120 A, the arc voltage at 18-22 V, and the welding speed at a uniform speed of 50-80 mm / min, and cooperate with short arc operation with an arc length of 2-3 mm.

3. The pipe-to-pipe butt girth welding method according to claim 1, characterized by, The second layer filling welding: control the welding current at 140-160 A, the arc voltage at 23-25 V, and the angle of the welding gun at 75°-80°.

4. The pipe-to-pipe butt girth weld welding method according to claim 1, characterized by, The third layer covering welding: adopt arc extinguishing welding method, control the arc extinguishing frequency at 1-2 s per 5-10 mm, and control the single arc welding time at 1-2 s.

5. The pipe-to-pipe butt girth welding method according to claim 4, characterized by, The third layer covering welding: control the welding current at 130-150 A and the arc voltage at 22-24 V.

6. The pipe-to-pipe butt girth weld welding method according to claim 4, characterized by, The third layer covering welding comprises: The first step: perform first covering arc starting at one end of the V-shaped groove; The second step: perform first covering arc extinguishing at the other end of the V-shaped groove; The third step: perform second covering arc starting at one end of the V-shaped groove; The fourth step: then perform second covering arc extinguishing at the other end of the V-shaped groove, and repeat S41-S44 until the entire V-shaped groove is covered.

7. The pipe-to-pipe butt girth welding method according to claim 6, characterized by, The first covering arc starting point is the first covering arc starting point, and the second covering arc starting point is the second covering arc starting point, and the distance between the first covering arc starting point and the second covering arc starting point is 1 / 2 of the weld width.

8. The pipe-to-pipe butt girth weld welding method according to claim 6, characterized by, During the covering welding process, the angle of the welding gun is controlled at 75°-80°.

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