Bimetal composite pipe welding method for acid environment

Abstract

The invention discloses a bimetal composite pipe welding method for an acid environment, and relates to the technical field of pipeline welding, and the bimetal composite pipe welding method specifically comprises the following steps that (1) a step notch is machined; (2) preparing cladding powder; (3) cleaning and preheating the composite pipe; (4) laser cladding surfacing; (5) designing and processing a groove; (6) cleaning and preheating the groove; (7) adding an isolation layer to the groove; (8) cleaning and assembling the grooves; (9) filling a welding base layer; and (10) welding a base layer cover surface. According to the method, welding of the composite pipe is divided into two parts including factory welding pretreatment and on-site welding aftertreatment, and in the factory welding pretreatment, groove pretreatment is carried out by means of advanced equipment and technologies such as laser cladding and the like; the welding post-treatment of the composite pipe can be directly carried out on the site by applying mature argon tungsten-arc welding, manual arc welding and other technologies subsequently, the process cost of site welding is saved, and the welding quality and efficiency are improved.

Description

Technical Field

[0001] The invention relates to the technical field of pipeline welding, and more particularly to a bimetallic composite pipe welding method for an acidic environment. Background Art

[0002] As oil and gas production gradually shifts to high-sulfur and other acidic gas fields, conventional anti-corrosion technology and pipes 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 liner pipe (usually corrosion-resistant alloy steel). However, due to the special manufacturing process of bimetallic composite pipes, welding process is an important factor affecting the development of bimetallic composite pipes.

[0003] At present, the welding technologies of bimetallic composite pipes include pipe end sealing and cladding. Although sealing has the advantage of low cost, it is easy to produce cracks in sealing, which affects the welding quality. The cladding adopts the principle of metallurgical bonding to effectively reduce the generation of weld cracks. However, since the cladding process is easy to induce element migration at the junction of the base pipe and the liner pipe during the welding process, it affects the corrosion resistance of the weld and is not conducive to the long-term operation of the composite pipe. At the same time, the cladding process is easy to cause large deformation of the pipe end, which is not conducive to subsequent welding assembly. In addition, the equipment required for the cladding 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 surface of the material and the powder on it to form a low-dilution cladding layer. It is a type of additive manufacturing technology. Compared with the cladding process, laser cladding has a small heat input and will not cause thermal deformation of the cladding layer. The resulting cladding layer has a dense structure and a low dilution rate. However, the use of laser cladding for welding of bimetallic composite pipes is still in the development stage. Direct use of laser cladding for welding faces the problems of 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 that technicians in this field need to solve. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a bimetallic composite pipe welding method for an acidic environment, so as to solve the shortcomings of the prior art such as decreased corrosion resistance and thermal deformation of the pipe end caused by element migration during the composite pipe welding process, as well as the difficulty in implementing laser cladding technology on site.

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

[0008] A bimetallic composite pipe welding method for an acidic environment comprises the following steps:

[0009] (1) Processing step notches

[0010] 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;

[0011] (2) Preparation of cladding powder

[0012] Mix carbon powder, chromium powder, niobium powder, silicon powder, molybdenum powder, manganese powder, iron powder and nickel powder uniformly to obtain cladding layer powder and insulating layer powder respectively;

[0013] (3) Composite pipe cleaning and preheating

[0014] Cleaning and preheating the bimetallic composite tube after the step groove is processed in step (1);

[0015] (4) Laser cladding welding

[0016] 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;

[0017] (5) Groove design and processing

[0018] In step (4), a V-shaped groove is machined on the end face of the composite pipe after cladding.

[0019] (6) Bevel cleaning and preheating

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

[0021] (7) Adding an insulation layer to the groove

[0022] 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;

[0023] (8) Slope cleaning group

[0024] 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;

[0025] (9) Welding base filling

[0026] 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;

[0027] (10) Welding base cover

[0028] Manual arc welding is used to perform cover welding on the base layer to form a cover layer.

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

[0030] Furthermore, in the above step (1), 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).

[0031] Furthermore, in the above step (2), the cladding layer powder and the insulating layer powder include, by mass percentage, 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, with the remainder being nickel powder.

[0032] Furthermore, in the above step (2), the particle size of the cladding layer powder and the insulating 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 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.

[0035] Furthermore, in the above step (5), 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°.

[0036] Furthermore, in the above step (7), the height of the insulating layer is uniform and the single-side 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 between the groove pairs is 2-3 mm.

[0038] Furthermore, in the above step (9), the welding material for the base layer welding is a welding wire with a composition similar to that of the inner liner pipe, wherein the mass ratio of Cr to Ni is not less than 1:3, the welding current is 90~110A, and the welding speed is 3~4cm / min.

[0039] Furthermore, in the above step (9), the welding material for the filling welding is a welding wire with a composition similar to that of the inner liner pipe, wherein the mass ratio of Cr to Ni is not less than 1:3, the welding current is 90~110A, and the welding speed is 4~6cm / min.

[0040] Furthermore, in the above step (10), the welding material for the cap welding is a welding wire with a composition similar to that of the liner pipe, wherein the mass ratio of Cr to Ni is not less than 1:3, the welding current is 50~70A, and the welding speed is 7~9cm / min.

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

[0042] 1. The laser cladding technology is used to achieve metallurgical bonding between the base pipe and the liner pipe at the end of the composite pipe, which improves the bonding strength while reducing the dilution rate of the bonding part, ensuring the corrosion resistance of the weld. At the same time, the laser cladding weld layer has high forming accuracy, reducing the cost of subsequent grinding processing.

[0043] 2. A layer of insulation layer is clad on the groove slope to prevent the carbon element in the base pipe from migrating to the weld during groove welding. At the same time, the insulation layer can ensure the excellent anti-corrosion performance of the end face and avoid the problem of groove corrosion before welding of the composite pipe on site.

[0044] 3. The welding of composite pipes is divided into two parts: factory welding pre-treatment and on-site welding post-treatment. Among them, the factory welding pre-treatment uses advanced equipment and technologies such as laser cladding to perform groove pre-treatment, which is convenient for the subsequent on-site use of mature tungsten inert gas welding and manual arc welding technologies to directly carry out the welding post-treatment of composite pipes, saving the process cost of on-site welding and improving the quality and efficiency of welding. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0046] Figure 2 A schematic diagram of the process flow of groove processing design in the welding method of the present invention;

[0047] Figure 3 A schematic diagram of the processing direction of the laser cladding welding layer in the welding method of the present invention;

[0048] Figure 4 A schematic diagram of the processing direction of the laser cladding insulation layer in the welding method of the present invention;

[0049] Figure 5 It is a structural schematic diagram of the groove in the welding method of the present invention;

[0050] Figure 6 It is a schematic diagram of the structure of the weld layer after groove welding in the welding method of the present invention;

[0051] Among them, 1-base pipe, 2-inner lining pipe, 3-step notch, 4-surfacing layer, 5-V-shaped groove slope, 6-insulating layer, 7-base welding layer, 8-first filling layer, 9-second filling layer, 10-third filling layer, 11-covering layer. DETAILED DESCRIPTION

[0052] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] Example 1

[0054] Bimetallic clad pipe welding method for acidic environment, such as Figure 1-6 As shown, the specific steps include:

[0055] (1) Processing step notches

[0056] First, prepare a finished bimetallic composite pipe Φ219 by hydraulic forming. The material of base pipe 1 is L360QS, the wall thickness L1 is 13mm, the material of liner pipe 2 is 825, the wall thickness L2 is 2mm, clean the surface and end face, and then cut off a certain range on the side of the pipe end close to the liner pipe 2 to form a step notch 3, the height a is 3.5mm, the depth b is 9mm, the wall thickness L2 of liner pipe 2 (2mm) < notch height a (3.5mm) < 25% of the bimetallic composite pipe wall thickness (15mm);

[0057] (2) Preparation of 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 cladding layer powder and insulation layer powder respectively, with a particle size of 20 μm and a sphericity of 0.8;

[0059] (3) Composite pipe cleaning and preheating

[0060] The bimetallic composite tube after the step groove 3 is processed in step (1) is cleaned and preheated at 100°C;

[0061] (4) Laser cladding welding

[0062] 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 3 in 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 4 is formed, the roundness deviation range of the inner wall surface of the cladding layer 4 is 0.7%, and the end face of the cladding layer 4 is polished to make the end face of the cladding layer 4 flush with the end face of the composite tube;

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

[0064] (5) Groove design and processing

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

[0066] (6) Bevel cleaning and preheating

[0067] The V-groove on the end face of the composite pipe in step (5) is cleaned and preheated at 100°C;

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

[0069] The insulating layer powder in step (2) is loaded into the powder feeder of the laser cladding equipment, the composite tube is kept rotating, and the insulating layer powder is clad on the V-shaped groove inclined surface 5 in step (5) by a synchronous laser cladding process, the cladding direction is from inside to outside, and the laser cladding equipment is stopped after the insulating layer 6 is formed. The height of the insulating layer 6 is uniform and the single-side groove angle β is maintained at 30°, and the thickness e is 3 mm;

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

[0071] (8) Slope cleaning group

[0072] 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, and then the grooves are assembled with a gap of 3mm;

[0073] (9) Welding base filling

[0074] Under the protection of inert gas, the bottom of the groove is welded by tungsten inert gas welding to form a base welding layer 7, and then the base welding layer 7 is filled with tungsten inert gas welding to form a first filling layer 8, a second filling layer 9 and a third filling layer 10;

[0075] Among them, the welding material for the base welding is a welding wire with a composition similar to that of the inner liner 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 material for the filling welding is a welding wire with a composition similar to that of the inner liner pipe 2, wherein 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 base cover

[0078] Using manual arc welding to perform cap welding on the base layer to form a cap layer 11;

[0079] Among them, the welding material for the cap welding is a welding wire with a composition similar to that of the inner liner 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] Bimetallic clad pipe welding method for acidic environment, such as Figure 1-6 As shown, the specific steps include:

[0082] (1) Processing step notches

[0083] First, prepare a finished bimetallic composite pipe Φ273 by hydraulic forming. The base pipe 1 is made of X60 with a wall thickness L1 of 15mm. The liner pipe 2 is made of 625 with a wall thickness L2 of 2mm. Clean the surface and end face. Then, cut off a certain range on the side of the pipe end close to the liner pipe 2 to form a step notch 3. The height a is 3.75mm and the depth b is 10mm. The wall thickness L2 (2mm) of the liner pipe 2 is less than the notch height a (3.75mm) and less than 25% of the wall thickness of the bimetallic composite pipe (17mm).

[0084] (2) Preparation of cladding powder

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

[0086] (3) Composite pipe cleaning and preheating

[0087] The bimetallic composite tube after the step groove 3 is processed in step (1) is cleaned and preheated at 110°C;

[0088] (4) Laser cladding welding

[0089] 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 3 in 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 4 is formed, the roundness deviation range of the inner wall surface of the cladding layer 4 is 0.7%, and the end face of the cladding layer 4 is polished to make the end face of the cladding layer 4 flush with the end face of the composite tube;

[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 protective gas is argon;

[0091] (5) Groove design and processing

[0092] In step (4), a V-shaped groove is machined on the end face of the composite pipe after surfacing, with a blunt edge length c of 5.5 mm, a blunt edge thickness d of 2.2 mm, and a single-side groove angle β of 30°;

[0093] (6) Bevel cleaning and preheating

[0094] The V-groove on the end face of the composite pipe in step (5) is cleaned and preheated at 110°C;

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

[0096] The insulating layer powder in step (2) is loaded into the powder feeder of the laser cladding equipment, the composite tube is kept rotating, and the insulating layer powder is clad on the V-shaped groove inclined surface 5 in step (5) by a synchronous laser cladding process, the cladding direction is from inside to outside, and the laser cladding equipment is stopped after the insulating layer 6 is formed. The height of the insulating layer 6 is uniform and the single-side groove angle β is maintained at 30°, and the thickness e is 4 mm;

[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 protective gas is argon;

[0098] (8) Slope cleaning group

[0099] 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, and then the grooves are assembled with a gap of 3mm;

[0100] (9) Welding base filling

[0101] Under the protection of inert gas, the bottom of the groove is welded by tungsten inert gas welding to form a base welding layer 7, and then the base welding layer 7 is filled with tungsten inert gas welding to form a first filling layer 8, a second filling layer 9 and a third filling layer 10;

[0102] Among them, the welding material for the base welding is a welding wire with a composition similar to that of the inner liner 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 material for the filling welding is a welding wire with a composition similar to that of the inner liner 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 base cover

[0105] Using manual arc welding to perform cap welding on the base layer to form a cap layer 11;

[0106] Among them, the welding material for the cap welding is a welding wire with a composition similar to that of the inner liner 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 Testing

[0108] 1. Element detection

[0109] The root weld zone of the composite tube base weld in Example 1 was sampled for element detection, wherein the mass percentage of Cr element was 21.8%, the mass percentage of Ni element was 60%, and the mass percentage of C element was 0.01%.

[0110] The root weld zone of the composite tube base weld in Example 2 was sampled for element detection, wherein the mass percentage of Cr element was 22.3%, the mass percentage of Ni element was 62%, and the mass percentage of C element was 0.02%.

[0111] The above tests show that the composite pipe formed by the welding method of the present invention has high tensile strength, which is not much different from the end cladding technology and has high promotion value.

[0112] 2. Corrosion resistance test

[0113] The corrosion resistance verification test in the acid gas field was carried out on the composite pipes of Example 1 and Example 2 respectively, and the specific steps are as follows:

[0114] (1) Wire cutting technology is used to sample the root of the weld of the composite pipe. The sample is a circular arc sample (height 30 mm, thickness 2 mm, arc center angle 22.5°), and the weld is ensured to be located at the symmetric center;

[0115] (2) Use 400#, 800#, 1000#, 1500# and 2000# silicon carbide sandpaper to polish the surface of the sample step by step, then use acetone and ethanol to clean the sample in turn. After cleaning, dry the sample with cold air and then weigh it for later use;

[0116] (3) Put the prepared samples (3 pieces) into a high-temperature autoclave, add the prepared acidic 3% wt NaCl solution (pH=3, fully deoxygenated), then seal the high-temperature autoclave and introduce nitrogen to deoxygenate, heat to 50°C and introduce 3MPa CO2 / 2MPaH2S, and test for 168h;

[0117] (4) After the test, the sample was taken out and cleaned with a film remover, deionized water and ethanol in turn. After being dried with cold air, it was weighed and the corrosion rate was calculated. The surface of the sample was then observed using a stereo microscope to see if there were any holes or cracks.

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

[0119] Table 1 Corrosion rate, surface state, holes and cracks of composite pipe samples in Example 1

[0120] Sample No. Corrosion rate mm / y Surface state Are there holes and cracks? 1# 0.0004 Test piece brightness no 2# 0.0005 Test piece brightness no 3# 0.0005 Test piece brightness no

[0121] Table 2 Corrosion rate, surface state, holes and cracks of composite pipe samples in Example 2

[0122] Sample No. Corrosion rate mm / y Surface state Are there holes and cracks? 1# 0.0003 Test piece brightness no 2# 0.0005 Test piece brightness no 3# 0.0006 Test piece brightness no

[0123] It can be seen from Tables 1 and 2 that the average corrosion rates of the composite pipe samples of Examples 1 and 2 are much lower than the mild corrosion standard (0.005 mm / y), and no holes or cracks are observed on the sample surfaces.

[0124] The above experiments 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 one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may 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 rather to 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; (2) Preparation of cladding powder Mix carbon powder, chromium powder, niobium powder, silicon powder, molybdenum powder, manganese powder, iron powder and nickel powder uniformly to obtain cladding layer powder and insulating layer powder respectively; (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. (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 insulation 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; (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 (1), 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).

3. The bimetallic composite pipe welding method for acidic environment according to claim 1, characterized in that: In step (2), the cladding layer powder and the insulating layer powder include, by mass percentage, 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, with the remainder being 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.

4. The bimetallic composite pipe welding method for 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.

5. 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.

6. The bimetallic composite pipe welding method for acidic environment according to claim 1, characterized in that: In step (5), 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°.

7. The bimetallic composite pipe welding method for acidic environment according to claim 1, characterized in that: In step (7), the height of the insulating layer is uniform and the single-side groove angle β is maintained at 30°±3°, and the thickness e is 2~5 mm.

8. 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.

9. The method for welding a bimetallic composite pipe for an acidic environment according to claim 1, characterized in that: In step (9), the welding material for the base layer welding is a welding wire with a composition similar to that of the inner liner pipe, wherein the mass ratio of Cr to Ni is not less than 1:3, the welding current is 90-110A, and the welding speed is 3-4cm / min; The welding material for the filling welding is a welding wire with a composition similar to that of the inner lining pipe, wherein the mass ratio of Cr to Ni is not less than 1:3, the welding current is 90~110A, and the welding speed is 4~6cm / min.

10. The bimetallic composite pipe welding method for acidic environment according to claim 1, characterized in that: In step (10), the welding material for the cap welding is a welding wire with a composition similar to that of the liner pipe, wherein the mass ratio of Cr to Ni is not less than 1:3, the welding current is 50-70A, and the welding speed is 7-9cm / min.

Images