A welding method for a bimetallic composite pipe used in an acidic environment

Abstract

The present invention discloses a welding method for a bimetallic composite pipe used in an acidic environment, which relates to the technical field of pipeline welding and specifically includes the following steps: (1) machining a stepped notch; (2) preparing a cladding powder; (3) cleaning and preheating the composite pipe; (4) laser cladding surfacing; (5) groove design and machining; (6) groove cleaning and preheating; (7) adding an isolation layer to the groove; (8) groove cleaning and assembly; (9) welding the base layer filling; (10) welding the base layer covering. The present invention divides the welding of the composite pipe into two parts: pre-welding treatment in the factory and post-welding treatment on site. Among them, the pre-welding treatment in the factory uses advanced equipment and technologies such as laser cladding for groove pretreatment, which facilitates subsequent post-welding treatment of the composite pipe directly on site using mature technologies such as tungsten inert gas welding and shielded metal arc welding, saving the process cost of on-site welding and improving the welding quality and efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline welding, and more specifically to a welding method for bimetallic composite pipes used in acidic environments. Background Art

[0002] As oil and gas exploitation gradually turns to high-sulfur and other acidic gas fields, conventional anti-corrosion technologies and pipe materials are difficult to ensure the safe transportation of oil and gas. Bimetallic composite pipes are widely used in the petrochemical industry because they combine the mechanical properties of the base pipe (usually carbon steel) and the corrosion resistance of the lining pipe (usually corrosion-resistant alloy steel). However, due to the special manufacturing process of bimetallic composite pipes, the welding process is an important factor affecting the development of bimetallic composite pipes.

[0003] At present, the welding technologies for bimetallic composite pipes include pipe-end sealing welding and surfacing welding. Although sealing welding has the advantage of low cost, it is easy to generate cracks, which affects the welding quality. Surfacing welding can effectively reduce the generation of weld cracks by using the principle of metallurgical bonding. However, since the surfacing welding process is prone to induce element migration at the joint between the base pipe and the lining pipe during welding, the corrosion resistance at the weld is affected, which is not conducive to the long-term operation of the composite pipe. At the same time, the surfacing welding process is prone to cause large deformation at the pipe end, which is not conducive to subsequent welding and alignment. In addition, the equipment required for the surfacing welding process is complex and difficult to handle at the construction site.

[0004] Laser cladding is a process that uses the instantaneous energy generated by a high-energy laser beam to quickly melt and solidify the material surface and the powder on it to form a low dilution rate cladding layer, and it belongs to a kind of additive manufacturing technology. Compared with the surfacing welding process, laser cladding has a small heat input, will not cause thermal deformation of the cladding layer, and the obtained cladding layer has a dense structure and a low dilution rate. However, at present, the welding of bimetallic composite pipes using laser cladding is still in the development stage, and directly using laser cladding for welding faces problems such as high cost, expensive equipment, and difficult on-site construction.

[0005] Therefore, how to give full play to the advantages of laser cladding while avoiding the above defects is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a welding method for bimetallic composite pipes used in acidic environments, so as to solve the problems such as the decline in corrosion resistance and thermal deformation at the pipe end caused by element migration during the welding process of composite pipes in the prior art, and the difficulties in on-site implementation of laser cladding technology.

[0007] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0008] A welding method for bimetallic composite pipes used in acidic environments specifically includes the following steps:

[0009] (1)Machining a stepped notch

[0010] First, prepare 1 finished bimetallic composite pipe formed by hydroforming, clean its surface and end faces, and then cut off a certain range near the lining pipe at the pipe end to form a stepped notch;

[0011] (2)Preparing the cladding powder

[0012] Mix carbon powder, chromium powder, niobium powder, silicon powder, molybdenum powder, manganese powder, iron powder and nickel powder evenly to obtain the surfacing layer powder and the isolation layer powder respectively;

[0013] (3)Cleaning and preheating the composite pipe

[0014] Clean and preheat the bimetallic composite pipe with the stepped notch machined in step (1);

[0015] (4)Laser cladding surfacing

[0016] Load the surfacing layer powder in step (2) into the powder feeder of the laser cladding equipment. Keep the composite pipe rotating, and use the synchronous laser cladding process to clad the surfacing layer powder in the stepped notch in step (1). The cladding direction is from inside to outside. After forming the surfacing layer, pause the laser cladding equipment. The roundness deviation range of the inner wall surface of the surfacing layer is 0.5% - 1%. Grind the end face of the surfacing layer to make the end face of the surfacing layer flush with the end face of the composite pipe;

[0017] (5)Groove design and machining

[0018] Machine a V-shaped groove on the end face of the composite pipe after surfacing in step (4);

[0019] (6)Cleaning and preheating the groove

[0020] Clean and preheat the V-shaped groove on the end face of the composite pipe in step (5);

[0021] (7)Applying an isolation layer to the groove

[0022] Load the isolation layer powder in step (2) into the powder feeder of the laser cladding equipment. Keep the composite pipe rotating, and use the synchronous laser cladding process to clad the isolation layer powder on the inclined surface of the V-shaped groove in step (5). The cladding direction is from inside to outside. After forming the isolation layer, stop the laser cladding equipment;

[0023] (8)Cleaning and assembling the groove

[0024] Inspect the quality and clean the grooves of the two composite pipes to be welded that have been processed. After ensuring that the grooves and the nearby areas are intact, bright and clean, perform groove assembly;

[0025] (9)Welding the base layer filling

[0026] Under the protection of inert gas, the base layer of the groove bottom is welded by tungsten inert gas welding to form a base weld layer. Subsequently, tungsten inert gas welding is used to perform filling welding on the base weld layer to form a first filling layer, a second filling layer, and a third filling layer.

[0027] (10)Welding the cover layer of the base layer

[0028] The cover layer of the base layer is welded by manual arc welding to form a cover layer.

[0029] In the present invention, steps (1) to (7) are pre-welding treatments in the factory, and steps (8) to (10) are post-welding treatments on-site.

[0030] Furthermore, in the above step (1), the height a of the stepped notch is 2.5 - 4 mm, the depth b is 8 - 12 mm, and the wall thickness L of the inner lining pipe 2 < notch height a < 25% of the wall thickness of the bimetal composite pipe (L 1 + L 2 ).

[0031] Furthermore, in the above step (2), by mass percentage, the surfacing layer powder and the isolation layer powder include 0.01% - 0.03% carbon powder, 21% - 22% chromium powder, 3% - 3.5% niobium powder, 0.01% - 0.1% silicon powder, 8% - 10% molybdenum powder, 0.1% - 0.3% manganese powder, and 1% - 5% iron powder, and the balance is nickel powder.

[0032] Furthermore, in the above step (2), the particle size of the surfacing layer powder and the isolation layer powder is 5 - 50 μm, and the sphericity is 0.7 - 0.9.

[0033] Furthermore, in the above steps (3) and (6), the temperature of the preheating treatment is 80 - 250 °C.

[0034] Furthermore, in the above steps (4) and (7), the parameters of the synchronous laser cladding process are: laser power is 2000 - 4500 W, powder feeding speed is 5 - 15 g / min, spot diameter is 0.1 - 0.5 mm, scanning speed is 90 - 450 mm / min, and the shielding gas is argon.

[0035] Furthermore, in the above step (5), the root face length c of the V-groove is 3 - 6 mm, the root face thickness d is 2 - 2.5 mm, and the single-bevel groove angle β is 30° ± 3°.

[0036] Furthermore, in the above step (7), the height of the isolation layer is uniform and the single-bevel groove angle β is maintained at 30° ± 3°, and the thickness e is 2 - 5 mm.

[0037] Furthermore, in the above step (8), the gap of the groove alignment is 2 - 3 mm.

[0038] Further, in the above step (9), the welding consumables for the root pass welding are welding wires with compositions similar to those of the inner lining pipe, where the mass ratio of Cr to Ni is not less than 1:3, the welding current is 90 - 110 A, and the welding speed is 3 - 4 cm / min.

[0039] Further, in the above step (9), the welding consumables for the filler pass welding are welding wires with compositions similar to those of the inner lining pipe, where the mass ratio of Cr to Ni is not less than 1:3, the welding current is 90 - 110 A, and the welding speed is 4 - 6 cm / min.

[0040] Further, in the above step (10), the welding consumables for the cap pass welding are welding wires with compositions similar to those of the inner lining pipe, where the mass ratio of Cr to Ni is not less than 1:3, the welding current is 50 - 70 A, and the welding speed is 7 - 9 cm / min.

[0041] As can be seen from the above technical solutions, compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] 1. The laser cladding technology is adopted to achieve metallurgical bonding between the base pipe and the inner lining pipe at the end of the composite pipe. While improving the bonding strength, it reduces the dilution rate at the bonding part, ensures the corrosion resistance of the weld seam, and at the same time, the formed precision of the surfacing layer by laser cladding is high, reducing the cost of subsequent grinding and processing.

[0043] 2. A layer of isolation layer is cladded on the inclined surface of the groove, which avoids the migration of carbon elements in the base pipe to the weld seam during groove welding. At the same time, the isolation layer can ensure the excellent anti-corrosion performance of the end face, avoiding the problem of groove corrosion before butt welding of the on-site composite pipe.

[0044] 3. The welding of the composite pipe is divided into two parts: pre-welding treatment in the factory and post-welding treatment on-site. Among them, the pre-welding treatment in the factory uses advanced equipment and technologies such as laser cladding for groove pre-treatment, which facilitates subsequent post-welding treatment of the composite pipe directly using mature technologies such as tungsten inert gas welding and manual arc welding on-site, saving the process cost of on-site welding and improving the welding quality and efficiency. Brief Description of the Drawings

[0045] Figure 1 It is a schematic flow chart of the welding method of the present invention;

[0046] Figure 2 It is a schematic flow chart of the groove machining design in the welding method of the present invention;

[0047] Figure 3 It is a schematic diagram of the machining direction of the laser cladding surfacing layer in the welding method of the present invention;

[0048] Figure 4 It is a schematic diagram of the machining direction of the laser cladding isolation layer in the welding method of the present invention;

[0049] Figure 5 Schematic diagram of the groove structure in the welding method of the present invention;

[0050] Figure 6 Schematic diagram of the structure of the welded layer after groove welding in the welding method of the present invention;

[0051] Wherein, 1 - base pipe, 2 - lining pipe, 3 - stepped notch, 4 - surfacing layer, 5 - V-shaped groove slope, 6 - isolation layer, 7 - base welding layer, 8 - first filling layer, 9 - second filling layer, 10 - third filling layer, 11 - capping layer. Specific embodiments

[0052] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0053] Embodiment 1

[0054] Welding method for bimetal composite pipe used in acidic environment, as Figure 1-6 shown, specifically includes the following steps:

[0055] (1) Machining the stepped notch

[0056] First, prepare 1 finished bimetal composite pipe Φ219 formed by hydroforming. The material of the base pipe 1 is L360QS, and the wall thickness L 1 is 13 mm. The material of the lining pipe 2 is 825, and the wall thickness L 2 is 2 mm. Clean the surface and end face, and then cut off a certain range near the lining pipe 2 at the pipe end to form a stepped notch 3 with a height a of 3.5 mm and a depth b of 9 mm. The wall thickness L 2 (2 mm) of the lining pipe 2 < notch height a (3.5 mm) < 25% of the wall thickness of the bimetal composite pipe (15 mm);

[0057] (2) Preparing the cladding powder

[0058] Weigh 0.15 g of carbon powder, 105.7 g of chromium powder, 16.5 g of niobium powder, 0.49 g of silicon powder, 42.2 g of molybdenum powder, 1.5 g of manganese powder, 19.4 g of iron powder and 299.06 g of nickel powder, mix them evenly to obtain the surfacing layer powder and the isolation layer powder respectively, with a particle size of 20 μm and a sphericity of 0.8;

[0059] (3) Cleaning and preheating the composite pipe

[0060] Clean and preheat the bimetal composite pipe with the stepped notch 3 processed in step (1) at 100 °C;

[0061] (4)Laser cladding surfacing

[0062] Load the surfacing layer powder in step (2) into the powder feeder of the laser cladding equipment, keep the composite pipe rotating, and use the synchronous laser cladding process to clad the surfacing layer powder in the step (1) step groove 3. The cladding direction is from inside to outside. After forming the surfacing layer 4, pause the laser cladding equipment. The roundness deviation range of the inner wall surface of the surfacing layer 4 is 0.7%. Grind the end face of the surfacing layer 4 to make the end face of the surfacing layer 4 flush with the end face of the composite pipe;

[0063] Among them, the parameters of the synchronous laser cladding process are: laser power is 2100W, powder feeding speed is 10g / min, spot diameter is 0.2mm, scanning speed is 100mm / min, and the shielding gas is argon;

[0064] (5)Groove design and machining

[0065] Machine a V-shaped groove on the end face of the composite pipe after surfacing in step (4). The length c of the root face is 5mm, the thickness d of the root face is 2mm, and the single-side groove angle β is 30°;

[0066] (6)Groove cleaning and preheating

[0067] Clean and preheat the V-shaped groove on the end face of the composite pipe in step (5) at 100°C;

[0068] (7)Adding an isolation layer to the groove

[0069] Load the isolation layer powder in step (2) into the powder feeder of the laser cladding equipment, keep the composite pipe rotating, and use the synchronous laser cladding process to clad the isolation layer powder on the inclined surface 5 of the V-shaped groove in step (5). The cladding direction is from inside to outside. After forming the isolation layer 6, stop the laser cladding equipment. The height of the isolation layer 6 is uniform and the single-side groove angle β is maintained at 30°, and the thickness e is 3mm;

[0070] Among them, the parameters of the synchronous laser cladding process are: laser power is 2100W, powder feeding speed is 10g / min, spot diameter is 0.2mm, scanning speed is 100mm / min, and the shielding gas is argon;

[0071] (8)Groove cleaning and alignment

[0072] Inspect and clean the grooves of the two composite pipes to be welded that have been processed. After ensuring that the grooves and the surrounding areas are intact and bright and clean, perform groove alignment with a gap of 3mm;

[0073] (9)Welding the base layer filling

[0074] Under the protection of inert gas, the base layer of the groove bottom is welded by tungsten inert gas welding to form the base weld layer 7. Subsequently, the filling weld is carried out on the base weld layer 7 by tungsten inert gas welding to form the first filling layer 8, the second filling layer 9 and the third filling layer 10;

[0075] Among them, the welding consumables for the base layer welding are welding wires with similar compositions to the inner lining pipe 2, in which the mass ratio of Cr to Ni is 1:3, the welding current is 100A, and the welding speed is 3.5cm / min;

[0076] The welding consumables for the filling weld are welding wires with similar compositions to the inner lining pipe 2, in which the mass ratio of Cr to Ni is 1:3, the welding current is 100A, and the welding speed is 5cm / min;

[0077] (10)Welding the cover layer of the base layer

[0078] The cover layer of the base layer is welded by manual arc welding to form the cover layer 11;

[0079] Among them, the welding consumables for the cover layer welding are welding wires with similar compositions to the inner lining pipe 2, in which the mass ratio of Cr to Ni is 1:3, the welding current is 60A, and the welding speed is 7cm / min.

[0080] Example 2

[0081] The welding method of the bimetal composite pipe for acidic environment is as Figure 1-6 shown, and specifically includes the following steps:

[0082] (1)Processing the stepped notch

[0083] First, prepare 1 finished bimetal composite pipe Φ273 by hydroforming. The material of the base pipe 1 is X60, and the wall thickness L 1 is 15mm, the material of the inner lining pipe 2 is 625, and the wall thickness L 2 is 2mm. Clean the surface and end face, and then cut off a certain range near the inner lining pipe 2 at the pipe end to form a stepped notch 3 with a height a of 3.75mm and a depth b of 10mm. The wall thickness L 2 of the inner lining pipe 2 (2mm) < notch height a (3.75mm) < 25% of the wall thickness of the bimetal composite pipe (17mm);

[0084] (2)Preparing the clad powder

[0085] Weigh 0.23g of carbon powder, 164.11g of chromium powder, 25.6g of niobium powder, 0.75g of silicon powder, 65.5g of molybdenum powder, 2.26g of manganese powder, 30.11g of iron powder and 299.06g of nickel powder, mix them evenly to obtain the surfacing layer powder and the isolation layer powder respectively, with a particle size of 20μm and a sphericity of 0.8;

[0086] (3)Cleaning and preheating the composite pipe

[0087] Clean and preheat the bimetal composite pipe with the stepped notch 3 processed in step (1) at 110°C;

[0088] (4) Laser cladding surfacing

[0089] Load the surfacing layer powder in step (2) into the powder feeder of the laser cladding equipment. Keep the composite pipe rotating, and use the synchronous laser cladding process to clad the surfacing layer powder in the stepped notch 3 in step (1). The cladding direction is from inside to outside. After forming the surfacing layer 4, pause the laser cladding equipment. The roundness deviation range of the inner wall surface of the surfacing layer 4 is 0.7%. Grind the end face of the surfacing layer 4 to make the end face of the surfacing layer 4 flush with the end face of the composite pipe;

[0090] Among them, the parameters of the synchronous laser cladding process are: laser power is 2200W, powder feeding speed is 10g / min, spot diameter is 0.2mm, scanning speed is 100mm / min, and the shielding gas is argon;

[0091] (5) Groove design and machining

[0092] Machine a V-shaped groove on the end face of the composite pipe after surfacing in step (4). The length of the root face c is 5.5mm, the thickness of the root face d is 2.2mm, and the single-side groove angle β is 30°;

[0093] (6) Groove cleaning and preheating

[0094] Clean and preheat the V-shaped groove on the end face of the composite pipe in step (5) at 110°C;

[0095] (7) Adding an isolation layer to the groove

[0096] Load the isolation layer powder in step (2) into the powder feeder of the laser cladding equipment. Keep the composite pipe rotating, and use the synchronous laser cladding process to clad the isolation layer powder on the inclined surface 5 of the V-shaped groove in step (5). The cladding direction is from inside to outside. After forming the isolation layer 6, stop the laser cladding equipment. The height of the isolation layer 6 is uniform and the single-side groove angle β is maintained at 30°, and the thickness e is 4mm;

[0097] Among them, the parameters of the synchronous laser cladding process are: laser power is 2200W, powder feeding speed is 10g / min, spot diameter is 0.2mm, scanning speed is 100mm / min, and the shielding gas is argon;

[0098] (8) Groove cleaning and alignment

[0099] Inspect and clean the grooves of the two composite pipes to be welded that have been processed. After ensuring that the grooves and the nearby areas are intact and bright and clean, perform groove alignment with a gap of 3mm;

[0100] (9) Welding the base layer filling

[0101] Under the protection of inert gas, the base layer of the groove bottom is welded by tungsten inert gas welding to form the base weld layer 7. Subsequently, the filling weld is carried out on the base weld layer 7 by tungsten inert gas welding to form the first filling layer 8, the second filling layer 9 and the third filling layer 10;

[0102] Among them, the welding consumables for the base layer welding are welding wires with similar compositions to the inner lining pipe 2, in which the mass ratio of Cr to Ni is 1:3, the welding current is 100A, and the welding speed is 4cm / min;

[0103] The welding consumables for the filling weld are welding wires with similar compositions to the inner lining pipe 2, in which the mass ratio of Cr to Ni is 1:3, the welding current is 100A, and the welding speed is 5.5cm / min;

[0104] (10) Welding the cover layer of the base layer

[0105] The cover layer welding of the base layer is carried out by manual arc welding to form the cover layer 11;

[0106] Among them, the welding consumables for the cover layer welding are welding wires with similar compositions to the inner lining pipe 2, in which the mass ratio of Cr to Ni is 1:3, the welding current is 60A, and the welding speed is 7.5cm / min.

[0107] Performance test

[0108] 1. Element detection

[0109] Samples are taken from the root welding area of the base layer welding of the composite pipe in Example 1 for element detection. Among them, the mass percentage of Cr element is 21.8%, the mass percentage of Ni element is 60%, and the mass percentage of C element is 0.01%.

[0110] Samples are taken from the root welding area of the base layer welding of the composite pipe in Example 2 for element detection. Among them, the mass percentage of Cr element is 22.3%, the mass percentage of Ni element is 62%, and the mass percentage of C element is 0.02%.

[0111] The above tests show that the composite pipe formed by the welding method of the present invention has a relatively high tensile strength, and the gap with the end surfacing technology is not large, and it has a high promotion value.

[0112] 2. Corrosion resistance test

[0113] The corrosion resistance verification tests of the composite pipes in Example 1 and Example 2 are carried out under the acidic gas field respectively. The specific steps are as follows:

[0114] (1) Using wire cutting technology to take samples at the root of the composite pipe weld. The sample is an arc sample (height 30mm, thickness 2mm, arc central angle 22.5°), and at the same time, ensure that the weld is located at the symmetric center;

[0115] (2) The surface of the specimen was polished step by step with 400#, 800#, 1000#, 1500# and 2000# silicon carbide sandpapers, and then the specimen was cleaned successively with acetone and ethanol. After cleaning, the specimen was dried with cold air and then weighed for use.

[0116] (3) The prepared specimens (3 pieces) were placed in a high-temperature and high-pressure autoclave, and the prepared acidic 3% wt NaCl solution (pH = 3, fully deoxygenated) was added. Then the high-temperature and high-pressure autoclave was sealed and nitrogen was introduced for deoxygenation. After the temperature was raised to 50 °C, 3 MPa CO 2 / 2 MPa H 2 S was introduced, and the test time was 168 h.

[0117] (4) After the test was completed, the specimens were taken out and cleaned successively with the film-removing solution, deionized water and ethanol. After drying with cold air, the weight was measured to calculate the corrosion rate, and then a stereomicroscope was used to observe whether there were holes and cracks on the surface of the specimens.

[0118] The results are shown in Table 1 and Table 2.

[0119] Table 1 Corrosion rate, surface state, and hole and crack conditions of the composite pipe specimens in Example 1

[0120] Specimen number Corrosion rate (mm / y) Surface condition Whether there are holes and cracks 1# 0.0004 Specimen is bright No 2# 0.0005 Specimen is bright No 3# 0.0005 Specimen is bright No

[0121] Table 2 Corrosion rate, surface state, and hole and crack conditions of the composite pipe specimens in Example 2

[0122] Specimen number Corrosion rate (mm / y) Surface condition Whether there are holes and cracks 1# 0.0003 Specimen is bright No 2# 0.0005 Specimen is bright No 3# 0.0006 Specimen is bright No

[0123] As can be seen from Table 1 and Table 2, the average corrosion rates of the composite pipe specimens in Example 1 and Example 2 are much lower than the mild corrosion standard (0.005 mm / y), and at the same time, no holes and cracks are observed on the surface of the specimens.

[0124] The above tests show that the composite pipe formed by the welding method of the present invention has excellent corrosion resistance in acidic gas fields and can meet the application conditions.

[0125] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A bimetallic composite pipe welding method for acidic environment, characterized in that: The specific steps include: (1) Processing step notches First, prepare a finished bimetallic composite pipe formed by hydraulic pressure and clean the surface and end face, then cut off a certain range on the side of the pipe end close to the liner pipe to form a step notch; The height a of the step notch is 2.5-4 mm, the depth b is 8-12 mm, and the wall thickness of the liner pipe L2 is less than the notch height a and less than 25% of the wall thickness of the bimetallic composite pipe (L1+L2); (2) Preparation of cladding powder Mix carbon powder, chromium powder, niobium powder, silicon powder, molybdenum powder, manganese powder, iron powder and nickel powder evenly to obtain cladding layer powder and insulating layer powder respectively; In terms of mass percentage, the cladding layer powder and the insulating layer powder include 0.01% to 0.03% carbon powder, 21% to 22% chromium powder, 3% to 3.5% niobium powder, 0.01% to 0.1% silicon powder, 8% to 10% molybdenum powder, 0.1% to 0.3% manganese powder and 1% to 5% iron powder, and the balance is nickel powder; The granularity of the surfacing layer powder and the insulating layer powder is 5-50 μm, and the sphericity is 0.7-0.9; (3) Composite pipe cleaning and preheating Cleaning and preheating the bimetallic composite tube after the step groove is processed in step (1); (4) Laser cladding welding The cladding layer powder in step (2) is loaded into the powder feeder of the laser cladding equipment, the composite tube is kept rotating, and the cladding layer powder is clad in the step notch of step (1) by a synchronous laser cladding process, the cladding direction is from inside to outside, and the laser cladding equipment is paused after the cladding layer is formed. The roundness deviation range of the inner wall of the cladding layer is 0.5% to 1%, and the end face of the cladding layer is polished to make the end face of the cladding layer flush with the end face of the composite tube; (5) Groove design and processing In step (4), a V-shaped groove is machined on the end face of the composite pipe after cladding. The blunt edge length c of the V-shaped groove is 3-6 mm, the blunt edge thickness d is 2-2.5 mm, and the single-side groove angle β is 30°±3°; (6) Bevel cleaning and preheating Cleaning and preheating the V-groove on the end face of the composite pipe in step (5); (7) Adding an insulating layer to the groove Load the insulating layer powder in step (2) into the powder feeder of the laser cladding equipment, keep the composite tube rotating, and use a synchronous laser cladding process to clad the insulating layer powder on the V-shaped groove slope in step (5), with the cladding direction from inside to outside, and stop the laser cladding equipment after the insulating layer is formed; The height of the insulating layer is uniform and the single-side bevel angle β is maintained at 30°±3°, and the thickness e is 2~5mm; (8) Slope cleaning group The grooves of the two processed composite pipes to be welded are inspected and cleaned to ensure that the grooves and the surrounding areas are intact, bright and clean before the grooves are assembled; (9) Welding base filling Under the protection of inert gas, the bottom of the groove is welded by tungsten inert gas welding to form a base welding layer, and then the base welding layer is filled by tungsten inert gas welding to form a first filling layer, a second filling layer and a third filling layer; (10) Welding base cover Manual arc welding is used to perform cover welding on the base layer to form a cover layer.

2. The method for welding a bimetallic composite pipe for an acidic environment according to claim 1, characterized in that: In step (3) and step (6), the temperature of the preheating treatment is 80-250°C.

3. The bimetallic composite pipe welding method for acidic environment according to claim 1, characterized in that: In step (4) and step (7), the parameters of the synchronous laser cladding process are: laser power of 2000-4500 W, powder feeding speed of 5-15 g / min, spot diameter of 0.1-0.5 mm, scanning speed of 90-450 mm / min, and shielding gas of argon.

4. The bimetallic composite pipe welding method for acidic environment according to claim 1, characterized in that: In step (8), the gap between the groove pairs is 2-3 mm.

5. The bimetallic composite pipe welding method for acidic environment according to claim 1, characterized in that: In step (9), the welding current of the base layer welding is 90-110A, and the welding speed is 3-4cm / min; The welding current of the filling welding is 90-110A, and the welding speed is 4-6cm / min.

6. The bimetallic composite pipe welding method for acidic environment according to claim 1, characterized in that: In step (10), the welding current of the cap welding is 50-70A, and the welding speed is 7-9cm / min.

Images