Method for full position girth welding of metallurgically clad pipe

Abstract

The full-position girth welding method of the metallurgical composite pipe specifically comprises the following steps: step 1, selecting two metallurgical composite pipes and processing X-type grooves at pipe ends of the two pipes; step 2, moving the grooves of the two pipes to be opposite to each other to complete the alignment of the two pipes; step 3, using MIG welding process to perform single-layer single-pass girth welding on the inner base layer carbon steel at the joint; step 4, using MAG welding process to perform multi-layer multi-pass girth welding on the outer base layer carbon steel at the joint; and step 5, after the inner and outer base layer welding is completed, using DHTIG welding process to perform single-layer single-pass girth welding on the transition layer at the interface between the cladding layer and the base layer at the joint, and performing multi-layer multi-pass girth welding on the cladding layer. The present application solves the problems of dilution of the cladding layer weld and easy occurrence of reheat stress cracks in the base layer weld in the prior art, and also avoids the influence of the decrease in corrosion resistance of the cladding layer caused by heat accumulation during base layer welding.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas pipeline welding technology, specifically relating to a method for all-position circumferential welding of metallurgical composite pipes. Background Technology

[0002] Metallurgical composite pipes, with their outer carbon steel base material and inner stainless steel or nickel-based alloy cladding, possess both good strength and toughness, as well as resistance to H2S, CO2, and Cl-. - Corrosion resistance (uniform corrosion, pitting corrosion, sulfide stress corrosion cracking, hydrogen-induced cracking, etc.). Furthermore, due to the metallurgical bonding between the base layer and the coating, the interlayer shear stress reaches over 400 MPa. During pipeline service, it will not experience bulging or delamination issues due to localized temperature or stress changes, effectively improving the pipeline's bending resistance and service life. Therefore, it is defined in the industry as one of the most promising and economical product types for the future.

[0003] Currently, with the rapid development of industrial technology in my country, domestic companies have independently developed 316L austenitic stainless steel metallurgical composite pipes, 2205 duplex stainless steel metallurgical composite pipes, and ultra-high alloy N08825 and N06625 nickel-based alloy metallurgical composite pipes, and possess mass production capabilities. However, compared with developed countries in the United States, Japan, Italy, and Europe, the development of these products started later, and the technological level is uneven. For many years, domestic research institutions have focused their main technical efforts on the development of composite pipes and steel pipes, investing relatively little in the research of circumferential welding processes for composite pipe engineering applications. As a result, circumferential welding of composite pipes has become one of the major bottlenecks restricting product application.

[0004] Due to the metallurgical bonding characteristics of the stainless steel cladding (1.2-3mm) and carbon steel base (>7mm) in the thickness direction, the circumferential welding of metallurgical composite pipes is more difficult than butt welding of ordinary dissimilar metals. This is mainly manifested in three aspects: First, during the cladding welding process, Fe and C in the base carbon steel easily melt into the cladding stainless steel weld, increasing the dilution rate of the weld and reducing the corrosion resistance of the cladding weld. Second, during the base fusion welding process, high alloying elements such as Cr, Ni, and Mo in the cladding and transition layer welds excessively transfer into the base layer weld and form low-melting-point non-metallic compounds with S and P, increasing the tendency of the weld to hot cracking. Under welding stress and other conditions, reheat stress cracking is more likely to occur. Third, during the welding of the transition layer and the base layer, due to the secondary or multiple heating effects of the high-temperature arc, Cr in the cladding stainless steel weld easily precipitates and forms Cr23C6 eutectic with C, resulting in a chromium-depleted layer at the grain boundaries, further deteriorating the corrosion resistance of the cladding weld, especially significantly reducing the intergranular corrosion resistance.

[0005] In pipeline construction, a combination of hot-wire argon arc welding (GTAW) and metal arc welding (MAW) is generally used. This involves a single-sided, multi-layer, multi-pass welding process using either GTAW (Gas Tungsten Arc Welding) + GMAW (Gas Metal Arc Welding) or GTAW + SMAW (Shielded Metal Arc Welding). All welding materials used are high-alloy stainless steel wires with similar compositions to the cladding layers. The process involves first introducing argon gas into the steel pipe, then performing the GTAW root pass welding for the inner cladding layer from the outside, achieving single-sided welding and double-sided forming of the cladding layer. Finally, the GMAW or SMAW filler and cover coat are applied from the outside. The above welding process has low overall efficiency. In particular, argon gas must be introduced into the pipe as a protective gas for cladding welding. In order to achieve a good weld with double-sided forming on one side, it is necessary to minimize the dilution rate of the cladding and control key indicators such as welding parameters, temperature and thickness. This leads to the use of U-shaped bevels, which are difficult to process, inconvenient to clean and prone to mechanical damage. Summary of the Invention

[0006] The purpose of this invention is to provide a method for all-position circumferential welding of metallurgical composite pipes, which solves the problems of dilution of the cladding weld and easy occurrence of reheat stress cracks in the base weld in the prior art. At the same time, it also avoids the impact of the cladding's reduced corrosion resistance due to heat accumulation during base welding.

[0007] The technical solution adopted in this invention is a method for all-position circumferential welding of metallurgical composite pipes, specifically including the following steps: Step 1: Select two metallurgical composite pipes and machine X-shaped bevels at their ends. The bevels include an inner bevel and an outer bevel. Step 2: Move the bevel positions of the two metallurgical composite pipes to face each other to complete the alignment of the metallurgical composite pipes. Step 3: Use MIG welding process to perform single-layer, single-pass circumferential welding on the inner base carbon steel of the joint; Step 4: Use MAG welding process to perform multi-layer, multi-pass circumferential welding on the outer base carbon steel of the joint. Step 5: After the inner and outer base layer welding is completed, the DHTIG welding process is used to perform single-layer single-pass circumferential welding on the transition layer between the cladding and the base layer at the joint, and multi-layer multi-pass circumferential welding is performed on the cladding.

[0008] The invention is further characterized in that, The X-shaped bevel in step 1 is fabricated either prefabricated or processed on-site using a hydraulic beveling machine. The outer bevel angle of the X-shaped bevel is... Inner slope The blunt edge is 2mm~3mm.

[0009] In step 3, the inner base carbon steel of the joint is subjected to single-layer single-pass circumferential welding. Specifically, the inner base circumferential welding is carried out by MIG welding process starting at the 6-point position of the inner bevel. The welding wire is Φ1.0mm low silicon microalloy high strength welding wire, and the welding speed is 180m / min~220m / min.

[0010] When performing single-layer, single-pass circumferential welding on the inner base carbon steel of the joint, 99.999% pure argon gas is used as the protective gas, with a gas flow rate of 18L / min~25L / min, a welding current of 140A~230A, and a welding voltage of 24V~26V.

[0011] In step 4, the outer base carbon steel of the joint is subjected to multi-layer and multi-pass circumferential welding. Specifically, the MAG welding process is used to start single-layer and single-pass circumferential welding of the outer base from the 12 o'clock position of the outer bevel. The welding wire is Φ1.0mm micro-alloy high-strength welding wire, the welding current is 160A~240A, the welding voltage is 24V~26V, the welding speed is 200m / min~280m / min, and the overlap of the inner and outer base welds is not less than 1.5mm. Depending on the thickness of the base layer, repeat the operation after completing one weld until the circumferential seam fills the outer bevel, completing multiple layers and multiple passes of welding.

[0012] When performing multi-layer, multi-pass circumferential welding on the outer base carbon steel of the joint, a protective gas containing 20% ​​CO2 + 80% Ar is used, with an argon purity of 99.995% and a gas flow rate of 18 L / min to 25 L / min.

[0013] In step 5, the transition layer between the cladding and the base layer at the joint is welded in a single layer and a single pass using the DHTIG welding process. The transition layer circumferential weld is started at a position 100mm to 150mm away from the welding start point in step 3. The distance between the welding start point of the transition layer circumferential weld and the welding start point of the inner base layer circumferential weld in step 3 is calculated along the circumference of the pipe body. Argon gas with 99.999% purity is used as the shielding gas during the circumferential welding of the transition layer. The gas flow rate is 18L / min to 25L / min. The welding current is 100A to 160A, the hot wire current is 80A to 100A, the arc voltage is 11V to 15V, and the welding speed is 80m / min to 100m / min.

[0014] In step 5, the circumferential welding of the cladding layer is carried out by using the DHTIG welding process to rotate circumferentially at 6 points on the transition layer weld to complete the single-pass welding of the cladding layer. The welding current is 100A~180A, the hot wire current is 80A~100A, the arc voltage is 11V~15V, the welding speed is 90m / min~120m / min, and 99.999% pure argon gas is used as the shielding gas during welding with a gas flow rate of 18L / min~25L / min. Depending on the thickness of the cladding, repeat the operation after completing one weld until the inner bevel is filled with circumferential weld, thus completing multiple layers and multiple passes of welding.

[0015] Metallurgical composite pipe is a metallurgical composite pipe composed of straight seam austenitic stainless steel, double-sided stainless steel and nickel-based alloy. The outer layer of the metallurgical composite pipe is low carbon structural steel or micro-alloy high-strength pipeline steel. The pipe diameter is Φ355mm~Φ3448mm, the pipe length is 8m~12m, the coating thickness is 1.2mm~3.0mm, and the base layer thickness is 7mm~17mm.

[0016] The beneficial effects of this invention are: The all-position circumferential weld method for metallurgical composite pipes of this invention has the following three advantages: First, performing MIG welding on the inner base layer first prevents heat accumulation during subsequent multi-layer, multi-pass MAG welding of the outer base layer, which could cause the inner bevel to open and deform, resulting in micro-cracks along the blunt edge. Second, performing MAG welding on the outer base layer after completing the inner base layer welding effectively prevents high alloying elements from melting into the base layer weld, ensuring the quality of the base layer weld. Third, the DHTIG process with low dilution rate and high welding efficiency used for the transition layer and cladding layer significantly reduces the dilution rate of the weld, ensuring the corrosion resistance of the weld. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of the all-position circumferential weld method for metallurgical composite pipes of the present invention; Figure 2 This is a schematic diagram of the circumferential joint bevel of the present invention; Figure 3 This is a schematic diagram of the weld bead of the weld layer of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] The metallurgical composite pipe all-position circumferential welding method of this invention adopts a reasonable internal and external welding process and layered solid welding design, thereby minimizing the dilution rate of the cladding weld and avoiding the influence of high temperature arc on the cladding in the transition layer and the base layer, as well as the transition of high alloying elements in the base layer weld, effectively improving the corrosion resistance of the cladding weld and the mechanical properties of the base layer weld.

[0020] The specific principle is as follows: First, based on the double-layer structure of the metallurgical composite pipe and the welding requirements of dissimilar metal materials, a reasonable welding sequence was designed. Specifically, all-position welding of the inner base layer was performed first, followed by all-position welding of the outer base layer, and finally, high-alloy material welding of the transition layer and cladding was completed. This method solves the problems of reheat stress cracking that easily occurs when using low-alloy welding materials for the base layer welding process on the high-alloy welds of the cladding and transition layers welded earlier in single-sided welding, as well as the dilution problem of the cladding weld by the base layer weld. Furthermore, it avoids the adverse effect of reduced corrosion resistance of the cladding due to heat accumulation during base layer welding.

[0021] Secondly, considering the advantages and disadvantages of different welding methods and the stress-strain characteristics of welding, an X-shaped small blunt edge bevel and a combined welding process of MIG+MAG+DHTIG in all positions were designed. Specifically, the MIG method, which involves less spatter, is used for all-position welding of the inner base layer; then, the MAG method, which offers good weld spreadability and is technically mature, is used for all-position welding of the outer base layer; finally, DHTIG, with its low dilution rate and high efficiency, is used to complete the welding of the high-alloy materials for the transition layer and cladding.

[0022] The specific solution of the present invention is illustrated by the following examples.

[0023] Example 1 This invention relates to a method for all-position circumferential welding of metallurgical composite pipes, such as... Figure 1 As shown, the specific steps include: Step 1: Select two metallurgical composite pipes and machine X-shaped bevels at their ends. The bevels include an inner bevel and an outer bevel. Step 2: Move the bevel positions of the two metallurgical composite pipes to face each other, and use a pipe-specific MIG internal welding and butt jointing device to complete the butt jointing of the metallurgical composite pipes. Step 3: Use MIG welding process to perform single-layer, single-pass circumferential welding on the inner base carbon steel of the joint; MIG stands for Metal Inert-gas Welding, which is a gas shielded welding process using 100% argon or helium gas to protect the arc.

[0024] Step 4: Perform multi-layer, multi-pass circumferential welding on the outer base carbon steel of the joint using the MAG welding process; MAG stands for Metal Active Gas Arc Welding, which is a mixed gas shielded welding process in which a small amount of oxidizing gas (oxygen, carbon dioxide or a mixture thereof) is added to argon.

[0025] Step 5: After completing the welding of the inner and outer base layers, use the DHTIG welding process to perform single-layer, single-pass circumferential welding on the transition layer between the cladding and the base layer at the joint, and then perform multi-layer, multi-pass circumferential welding on the cladding. DHTIG stands for Double Hot Tungsten Inert Gas.

[0026] Furthermore, the metallurgical composite pipe is a metallurgical composite pipe composed of straight seam austenitic stainless steel, double-sided stainless steel and nickel-based alloy. The outer layer of the metallurgical composite pipe is low carbon structural steel or micro-alloy high-strength pipeline steel. The pipe diameter is Φ355mm~Φ3448mm, the pipe length is 8m~12m, the coating thickness is 1.2mm~3.0mm, and the base layer thickness is 7mm~17mm.

[0027] Example 2 This invention relates to a method for all-position circumferential welding of metallurgical composite pipes, such as... Figure 1 As shown, the specific steps include: Step 1: Select two metallurgical composite pipes and machine X-shaped bevels at their ends. The bevels include an inner bevel and an outer bevel. Furthermore, the X-type bevel can be prefabricated in the factory or processed on-site using a special hydraulic beveling machine for pipelines. When processing on-site, a lifting device is needed to lift the beveling machine and place it inside the end of the steel pipe to be processed. The position of the milling cutter and the end face of the steel pipe is adjusted, and the steel pipe is fixed to the beveling machine support using hydraulic fixing blocks. The beveling machine is then started, and the milling cutter will rotate at a certain speed to process the pipe end beveling.

[0028] Specifically, the outer bevel angle of the processed X-shaped bevel is: Inner slope The blunt edge is 2mm~3mm.

[0029] Step 2: Move the bevel positions of the two metallurgical composite pipes to face each other, and use a pipe-specific MIG internal welding and butt jointing device to complete the butt jointing of the metallurgical composite pipes. Step 3: Use MIG welding process to perform single-layer, single-pass circumferential welding on the inner base carbon steel of the joint; Step 4: Use MAG welding process to perform multi-layer, multi-pass circumferential welding on the outer base carbon steel of the joint. Step 5: After the inner and outer base layer welding is completed, the DHTIG welding process is used to perform single-layer single-pass circumferential welding on the transition layer between the cladding and the base layer at the joint, and multi-layer multi-pass circumferential welding is performed on the cladding.

[0030] Furthermore, the metallurgical composite pipe is a metallurgical composite pipe composed of straight seam austenitic stainless steel, double-sided stainless steel and nickel-based alloy. The outer layer of the metallurgical composite pipe is low carbon structural steel or micro-alloy high-strength pipeline steel. The pipe diameter is Φ355mm~Φ3448mm, the pipe length is 8m~12m, the coating thickness is 1.2mm~3.0mm, and the base layer thickness is 7mm~17mm.

[0031] Example 3 This invention relates to a method for all-position circumferential welding of metallurgical composite pipes, such as... Figure 1 As shown, the specific steps include: Step 1: Select two metallurgical composite pipes and machine X-shaped bevels at their ends. The bevels include an inner bevel and an outer bevel. Step 2: Move the bevel positions of the two metallurgical composite pipes to face each other, and use a pipe-specific MIG internal welding and butt jointing device to complete the butt jointing of the metallurgical composite pipes. Step 3: Use MIG welding process to perform single-layer, single-pass circumferential welding on the inner base carbon steel of the joint; Specifically, the inner base circumferential weld was performed using the MIG welding process, starting at 6 points on the inner bevel. A Φ1.0mm low-silicon microalloy high-strength welding wire was used. The Φ1.0mm wire allows for a higher arc current density and minimal or no spatter welding under the same current conditions. Furthermore, the low-silicon welding material avoids the formation of point-like "silicon islands" during the MIG welding process, preventing damage to the cladding layer. The welding speed was 180m / min to 220m / min.

[0032] Furthermore, in order to reduce or avoid spatter, 99.999% pure argon is used as the shielding gas when performing single-layer, single-pass circumferential welding on the inner base carbon steel of the joint. The gas flow rate is 18L / min~25L / min, the welding current is 140A~230A, and the welding voltage is 24V~26V.

[0033] Step 4: Use MAG welding process to perform multi-layer, multi-pass circumferential welding on the outer base carbon steel of the joint. Step 5: After the inner and outer base layer welding is completed, the DHTIG welding process is used to perform single-layer single-pass circumferential welding on the transition layer between the cladding and the base layer at the joint, and multi-layer multi-pass circumferential welding is performed on the cladding.

[0034] Furthermore, the metallurgical composite pipe is a metallurgical composite pipe composed of straight seam austenitic stainless steel, double-sided stainless steel and nickel-based alloy. The outer layer of the metallurgical composite pipe is low carbon structural steel or micro-alloy high-strength pipeline steel. The pipe diameter is Φ355mm~Φ3448mm, the pipe length is 8m~12m, the coating thickness is 1.2mm~3.0mm, and the base layer thickness is 7mm~17mm.

[0035] Example 4 Based on Example 3, step 4 of the all-position circumferential weld method for metallurgical composite pipe of the present invention, which involves multi-layer, multi-pass circumferential weld on the outer base carbon steel at the joint, specifically involves: using MAG welding process to perform single-layer, single-pass circumferential weld on the outer base starting at 6 points on the outer bevel; using Φ1.0mm micro-alloy high-strength welding wire (welding wire with equal or greater strength matching the base layer); welding current of 160A~240A; welding voltage of 24V~26V; welding speed of 200m / min~280m / min; and the overlap of the inner and outer base welds is not less than 1.5mm.

[0036] Depending on the thickness of the base layer, repeat the operation after completing one weld until the circumferential seam fills the outer bevel, completing multiple layers and multiple passes of welding.

[0037] Furthermore, when performing multi-layer, multi-pass circumferential welding on the outer base carbon steel of the joint, a protective gas containing 20% ​​CO2 + 80% Ar is used, with an argon purity of 99.995% and a gas flow rate of 18 L / min to 25 L / min.

[0038] Example 5 This invention relates to a method for all-position circumferential welding of metallurgical composite pipes, such as... Figure 1 As shown, the specific steps include: Step 1: Select two metallurgical composite pipes and machine X-shaped bevels at their ends. The bevels include an inner bevel and an outer bevel. Step 2: Move the bevel positions of the two metallurgical composite pipes to face each other, and use a pipe-specific MIG internal welding and butt jointing device to complete the butt jointing of the metallurgical composite pipes. Step 3: Use MIG welding process to perform single-layer, single-pass circumferential welding on the inner base carbon steel of the joint; Step 4: Use MAG welding process to perform multi-layer, multi-pass circumferential welding on the outer base carbon steel of the joint. Step 5: After the inner and outer base layer welding is completed, the DHTIG welding process is used to perform single-layer single-pass circumferential welding on the transition layer between the cladding and the base layer at the joint, and multi-layer multi-pass circumferential welding is performed on the cladding.

[0039] Furthermore, the single-layer, single-pass circumferential weld of the transition layer between the cladding and the base layer at the joint is specifically carried out by using the DHTIG welding process to start the single-layer, single-pass circumferential weld of the transition layer at a position 100mm~150mm away from the welding start point in step 3, and the distance between the welding start point of the transition layer circumferential weld and the welding start point of the inner base layer circumferential weld in step 3 is calculated along the circumference of the pipe body. Argon gas with 99.999% purity is used as the shielding gas during the circumferential welding of the transition layer. The gas flow rate is 18L / min to 25L / min. The welding current is 100A to 160A, the hot wire current is 80A to 100A, the arc voltage is 11V to 15V, and the welding speed is 80m / min to 100m / min.

[0040] Furthermore, the circumferential welding of the cladding layer is carried out by using the DHTIG welding process to rotate circumferentially at 6 points on the transition layer weld to complete the single-pass welding of the cladding layer. The welding current is 100A~180A, the hot wire current is 80A~100A, the arc voltage is 11V~15V, the welding speed is 90m / min~120m / min, and 99.999% pure argon is used as the shielding gas during welding with a gas flow rate of 18L / min~25L / min. Depending on the thickness of the cladding, repeat the operation after completing one weld until the inner bevel is filled with circumferential weld, thus completing multiple layers and multiple passes of welding.

[0041] Example 6 The present invention provides a method for all-position circumferential welding of metallurgical composite pipes, which is implemented according to the following steps: Step 1: Select two metallurgical composite pipes and machine an X-shaped bevel at each end, such as... Figure 2 As shown, the bevel includes an inner bevel and an outer bevel. The outer bevel angle of the X-type bevel is 60°, the inner bevel angle is 80°, and the blunt edge is 2.5mm.

[0042] Step 2: Move the bevel positions of the two metallurgical composite pipes to face each other, and use a pipe-specific MIG internal welding and butt jointing device to complete the butt jointing of the metallurgical composite pipes. Step 3: Use MIG welding process to perform single-layer, single-pass circumferential welding on the inner base carbon steel of the joint; Step 4: Use MAG welding process to perform multi-layer, multi-pass circumferential welding on the outer base carbon steel of the joint. Step 5: After the inner and outer base layer welding is completed, the DHTIG welding process is used to perform single-layer single-pass circumferential welding on the transition layer between the cladding and the base layer at the joint, and multi-layer multi-pass circumferential welding is performed on the cladding.

[0043] The welding parameters are shown in the table below:

[0044] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0045] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for all-position circumferential welding of metallurgical composite pipes, characterized in that, Specifically, the following steps are included: Step 1: Select two metallurgical composite pipes and process X-shaped bevels at their ends. The bevels include an inner bevel and an outer bevel. Step 2: Move the bevel positions of the two metallurgical composite pipes to face each other to complete the alignment of the metallurgical composite pipes. Step 3: Use MIG welding process to perform single-layer, single-pass circumferential welding on the inner base carbon steel of the joint; Step 4: Use MAG welding process to perform multi-layer, multi-pass circumferential welding on the outer base carbon steel of the joint. Step 5: After the inner and outer base layer welding is completed, the DHTIG welding process is used to perform single-layer single-pass circumferential welding on the transition layer between the cladding and the base layer at the joint, and multi-layer multi-pass circumferential welding is performed on the cladding.

2. The all-position circumferential weld method for metallurgical composite pipes according to claim 1, characterized in that, The X-shaped bevel in step 1 is fabricated either through prefabrication or on-site hydraulic beveling. The outer bevel angle of the X-shaped bevel is... Inner slope The blunt edge is 2mm~3mm.

3. The all-position circumferential weld method for metallurgical composite pipes according to claim 1, characterized in that, In step 3, the single-layer, single-pass circumferential welding of the inner base carbon steel at the joint is specifically carried out by using the MIG welding process to start the inner base circumferential welding at the 6-point position of the inner bevel. The welding wire is Φ1.0mm low silicon microalloy high strength welding wire, and the welding speed is 180m / min~220m / min.

4. The all-position circumferential weld method for metallurgical composite pipes according to claim 3, characterized in that, When performing single-layer, single-pass circumferential welding on the inner base carbon steel of the joint, 99.999% pure argon gas is used as the protective gas, with a gas flow rate of 18L / min~25L / min, a welding current of 140A~230A, and a welding voltage of 24V~26V.

5. The all-position circumferential welding method for metallurgical composite pipes according to claim 1, characterized in that, In step 4, the multi-layer, multi-pass circumferential welding of the outer base carbon steel at the joint is specifically carried out by using MAG welding process to start single-layer, single-pass circumferential welding of the outer base at the 12 o'clock position of the outer bevel. The welding wire is Φ1.0mm micro-alloy high-strength welding wire, the welding current is 160A~240A, the welding voltage is 24V~26V, the welding speed is 200m / min~280m / min, and the overlap of the inner and outer base welds is not less than 1.5mm. Depending on the thickness of the base layer, repeat the operation after completing one weld until the circumferential seam fills the outer bevel, completing multiple layers and multiple passes of welding.

6. The all-position circumferential weld method for metallurgical composite pipes according to claim 5, characterized in that, When performing multi-layer, multi-pass circumferential welding on the outer base carbon steel of the joint, a protective gas containing 20% ​​CO2 + 80% Ar is used, with an argon purity of 99.995% and a gas flow rate of 18 L / min to 25 L / min.

7. The all-position circumferential weld method for metallurgical composite pipes according to claim 1, characterized in that, In step 5, the single-layer, single-pass circumferential weld of the transition layer between the cladding and the base layer at the joint is specifically performed by using the DHTIG welding process to start the single-layer, single-pass circumferential weld of the transition layer at a position 100mm to 150mm away from the welding starting point in step 3. The distance between the welding starting point of the transition layer circumferential weld and the welding starting point of the inner base layer circumferential weld in step 3 is calculated along the circumference of the pipe body. Argon gas with 99.999% purity is used as the shielding gas during the circumferential welding of the transition layer. The gas flow rate is 18L / min to 25L / min. The welding current is 100A to 160A, the hot wire current is 80A to 100A, the arc voltage is 11V to 15V, and the welding speed is 80m / min to 100m / min.

8. The all-position circumferential weld method for metallurgical composite pipes according to claim 1, characterized in that, In step 5, the multi-layer, multi-pass circumferential welding of the cladding layer is specifically performed by using the DHTIG welding process to rotate circumferentially at 6 points on the transition layer weld to complete a single pass of welding of the cladding layer. The welding current is 100A~180A, the hot wire current is 80A~100A, the arc voltage is 11V~15V, the welding speed is 90m / min~120m / min, and 99.999% pure argon gas is used as the shielding gas during welding with a gas flow rate of 18L / min~25L / min. Depending on the thickness of the cladding, repeat the operation after completing one weld until the inner bevel is filled with circumferential weld, thus completing multiple layers and multiple passes of welding.

9. The method for all-position circumferential welding of metallurgical composite pipes according to claim 1, characterized in that, The metallurgical composite pipe is a metallurgical composite pipe composed of straight seam austenitic stainless steel, double-sided stainless steel and nickel-based alloy. The outer layer of the metallurgical composite pipe is low carbon structural steel or micro-alloy high-strength pipeline steel. The pipe diameter is Φ355mm~Φ3448mm, the pipe length is 8m~12m, the coating thickness is 1.2mm~3.0mm, and the base layer thickness is 7mm~17mm.

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