A welding forming process for a bimetallic composite pipe

Abstract

The present application relates to the field of composite pipe welding forming process, and particularly relates to a bimetallic composite pipe welding forming process. The scheme forms a transition layer in the form of laser cladding and flame spray welding before root welding of the base layer and welding of the composite layer, forms a continuous interface functional layer before welding, covers the bottom, sidewall and step corner of the groove. Compared with the partial transition layer prepared at the bottom of the groove in the prior art, the scheme can form a continuous protection along the groove interface, the isolation range is more complete, the channels for Fe / C migration from the bottom, the sidewall of the groove and the interface step to the composite layer are covered; the transition layer takes into account isolation, strengthening and subsequent welding fusion quality, and serves as an isolation and metallurgical control layer in the subsequent welding thermal cycle. The transition layer can be well metallurgically combined with the base layer and the composite layer, the subsequent base layer and composite layer welds can be formed by adhering to the stable bonding surface, layer peeling and debonding in operation is avoided, and the overall structural stability of the composite pipe is improved.

Description

Technical Field

[0001] This invention relates to the field of composite pipe welding and forming processes, and specifically to a bimetallic composite pipe welding and forming process. Background Technology

[0002] Rolled composite pipes typically utilize carbon steel or low-alloy steel as the base layer to bear pressure loads, while nickel-based or stainless steel cladding such as Inconel 825 or Inconel 625 provides corrosion resistance. During butt welding, elements such as Fe and C in the base layer diffuse towards the cladding layer under high-temperature thermal cycling, and the alloying elements in the cladding layer may be diluted by the base weld, leading to problems such as increased intergranular corrosion susceptibility, interface embrittlement, lack of fusion, or slag inclusions.

[0003] To address the aforementioned issues, existing technologies typically incorporate a transition layer between the base layer and the cladding layer. For example, patent CN110773891B discloses a welding method for stainless steel composite plates. The process involves: a double V-groove; first, plasma welding or laser welding to form the inner weld seam of the base layer; then, laser cladding technology to form a transition layer weld seam at the bottom of the V-groove on one side of the corrosion-resistant alloy layer; subsequently, MAG, TIG, or laser cladding to form the cladding layer weld seam; and finally, submerged arc welding to form the outer weld seam of the base layer. The advantage of this approach is that it reduces the bottom width of the cladding layer by using a narrow weld seam and reduces the amount of cladding in the cladding layer by using a bottom laser cladding transition layer.

[0004] However, the laser cladding transition layer in the above-mentioned technical solution is mainly located at the bottom of the V-groove on one side of the corrosion-resistant alloy layer, belonging to the bottom transition layer weld, which focuses on solving the problems of the bottom width of the cladding layer and local Fe diffusion. For bimetallic composite pipe welds, the base layer / cladding interface does not only have one diffusion channel at the bottom. Fe / C migration and dilution channels are also formed between the groove sidewall, the corner of the cladding layer, the root metal after root cleaning, and the subsequent cladding layer sealing weld. A simple bottom transition layer is difficult to continuously control the entire interface path, especially when the weld assembly gap and the amount of root cleaning on the inner wall fluctuate, the corner positions are still prone to becoming areas of incomplete fusion, local dilution, or weak corrosion. Summary of the Invention

[0005] The technical solution adopted by this invention to solve its technical problem is: to provide a bimetallic composite pipe welding and forming process, including the following steps: S1. Preparation of bevel: A composite bevel is processed at the end of the composite plate. The composite plate includes a base layer and a cladding layer. The base layer is a carbon steel layer, and the cladding layer is a corrosion-resistant layer. The composite bevel is an X-shaped bevel, which includes a base layer side bevel and a cladding layer side bevel. S2. Grind, degrease, remove oxide scale, and roughen the interfaces on both sides of the composite bevel, the root corner, and the area to be covered. S3. Preparation of bevel transition layer: A transition layer is prepared on the bevel side of the base layer by flame spraying process, and a transition layer is prepared on the bevel side of the cladding layer by laser cladding process. The spraying area and the cladding area continuously cover the junction of the base layer and the cladding layer. S4. Bend the composite board into a composite tube and protect the bevel transition layer; S5. Perform hot wire root welding of the FCAW-G base layer from the outside of the pipe. After the root welding is completed, check and record the residual height H and interface temperature T on the inside of the root welding. S6. After confirming the continuity of the root weld, use SAW submerged arc welding to fill and cover the base layer. S7. Cleaning the inner side of the pipe and sealing with hot wire for the GTAW-P cladding layer.

[0006] Furthermore, the bevel angle of the base layer is 28°-36°, the blunt edge height is 1.2-2.2 mm, and the assembly gap is 1.8-2.8 mm; the bevel angle of the inner side of the multilayer is 18°-24°.

[0007] Furthermore, the flame spraying is performed using oxyacetylene flame spraying equipment.

[0008] Furthermore, laser cladding employs coaxial or off-axis powder feeding.

[0009] Furthermore, the thickness of the transition layer at the base bevel and the thickness of the transition layer at the overlay bevel are both 0.5-1mm.

[0010] Furthermore, the composition of the transition layer is: Cr 18%-24%, Mo 8%-12%, Cu 1.5%-5.0%, Nb 0.8%-2.0%, Ti 0.2%-1.0%, Zr 0.01%-0.08%, Si 0.5%-1.0%, Mn 1.0%-1.4%, with the balance being Ni.

[0011] Furthermore, the minimum bending radius of the composite material is 5 times the outer diameter of the composite pipe.

[0012] Furthermore, the bending of the composite board is either cold bending at room temperature or warm bending at a forming temperature of 200℃-400℃.

[0013] Furthermore, the composite board is bent using an inner-lined mandrel-type single-curvature forming mold or a continuous multi-pass roll bending forming mold.

[0014] Furthermore, the protection of the bevel transition layer includes adding a flexible non-metallic protective pad to the composite bevel end face and the surface of the bevel transition layer.

[0015] The beneficial effects of this invention are as follows: This solution prepares a transition layer through laser cladding and flame spraying before the base layer root weld and cladding weld, forming a continuous pre-welding interface functional layer that covers the bottom, sidewalls, and step corners of the bevel. Compared to the localized transition layer prepared at the bottom of the bevel in the prior art, this solution can form continuous protection along the bevel interface, providing a more complete isolation range. The channels through which Fe / C migrates from the bottom, bevel sidewalls, and interface steps to the cladding layer are all covered. It balances isolation, strengthening, and subsequent welding fusion quality, and serves as an isolation and metallurgical control layer in the subsequent welding thermal cycle. The transition layer can achieve good metallurgical bonding with both the base layer and the cladding layer. Forming the transition layer first allows the subsequent base layer and cladding welds to adhere to a stable bonding surface, preventing interlayer peeling and debonding during operation, and improving the overall structural stability of the composite pipe. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0017] In the picture: Figure 1 A schematic diagram of the composite bevel provided by the present invention; Figure 2 This is a schematic diagram of the inner wall cladding weld of the pipe after welding in this invention; Figure 3 This is a schematic diagram of the filler weld on the outer wall base layer of the pipe after welding in this invention; Figure 4 This is a sample diagram of a pipe at a 90° position on the cross-section of the welded pipe in this invention (sampled counterclockwise from the weld). Figure 5 A sample image of the pipe at a 270° position on the cross-section of the welded pipe (sampled counterclockwise from the weld seam); Figure 6 The image shows the metallographic structure of the pipe weld after welding (after corrosion). Figure 7 The image shows the metallographic structure of the weld seam of the pipe after welding (before corrosion). Figure 8 Metallographic diagram of the pipe section at a 90° position (sampled counterclockwise from the weld) (after corrosion); Figure 9 The metallographic structure diagram of the pipe section at a 90° position (sampled counterclockwise from the weld) (when not corroded); Figure 10 Metallographic diagram of the pipe section at 270° (sampled counterclockwise from the weld seam) (after corrosion); Figure 11 The metallographic structure diagram (without corrosion) is taken at a 270° position on the pipe cross-section (sampled counterclockwise from the weld).

[0018] Explanation of reference numerals in the attached drawings: 101, base layer; 102, multi-layer; 103, multi-layer side bevel transition layer; 104, base layer side bevel transition layer. Detailed Implementation

[0019] To make the technical problem to be solved, the technical solution, and the beneficial effects of this invention clearer, the invention will now be described in detail with reference to the accompanying drawings. This drawing is a simplified schematic diagram, illustrating only the basic aspects of the invention, and therefore only shows the components relevant to the invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0020] This invention provides a welding and forming process for bimetallic composite pipes, comprising the following steps: S1. Prepare a bevel: Process a composite bevel at the end of the composite material. The composite material includes a base layer and a cladding layer. The composite bevel is an X-shaped bevel, comprising a base layer side bevel and a cladding layer side bevel. The base layer is a carbon steel layer, and the cladding layer is a corrosion-resistant layer. In this embodiment, the base layer material is X65 or X70 carbon steel, and the cladding layer material is Inconel 825 or Inconel 625.

[0021] like Figure 1 As shown, the bevel angle (a) of the base layer is 28°-36°, the blunt edge height (h) is 1.2-2.2 mm, and the assembly gap (d) is 1.8-2.8 mm; the bevel angle (b) of the inner side of the composite layer is 18°-24°.

[0022] S2. Pre-treatment of the composite bevel: Grinding, degreasing, removing oxide scale and roughening the interfaces on both sides, root corners and areas to be covered of the composite bevel to expose a metallic luster. S3. Prepare the bevel transition layer: The transition layer is prepared by flame spraying at the bevel of the base layer and by laser cladding (powder melting) at the bevel of the cladding layer. The spraying and cladding areas continuously cover the junction of the base layer and the cladding layer.

[0023] The thickness of the transition layer on both the base layer and the cladding layer is 0.5-1mm. Flame spraying is performed using oxy-acetylene flame spraying equipment. Laser cladding uses coaxial or off-axis powder feeding to clad the powder onto the cladding interface and root corner, forming a continuous metallurgical bonding transition layer. Flame spraying has lower heat input, simpler equipment, and is suitable for on-site construction. It can quickly form a transition layer before welding, reducing the diffusion of Fe and C elements from the base layer to the cladding layer and improving the surface condition of the bevel. Laser cladding results in a low dilution rate, high bonding strength, and dense structure, effectively sealing the diffusion channels at the base / cladding interface and refining grains and fixing carbon elements through microalloying elements such as Nb and Ti. Furthermore, laser cladding technology features shallow penetration and rapid solidification, reducing base layer dilution and minimizing the need to compensate for alloy content by increasing the thickness of the cladding weld. The cladding process can simultaneously repair micro-defects in the bevel, making it easier to achieve continuous fusion in subsequent FCAW-G root welding and GTAW-P cladding sealing welding.

[0024] The transition layer consists of: Cr 18%-24%, Mo 8%-12%, Cu 1.5%-5.0%, Nb 0.8%-2.0%, Ti 0.2%-1.0%, Zr 0.01%-0.08%, Si 0.5%-1.0%, Mn 1.0%-1.4%, with the balance being Ni. Zr can be removed as needed. This transition layer is compatible with Inconel 825 or Inconel 625 as cladding materials and with ERNiCrMo-3 welding material used in cladding welding, while also providing carbon fixation, grain refinement, and corrosion resistance control.

[0025] S4. Bend the composite board into a composite tube and protect the bevel transition layer; Specifically, the minimum bending radius of the composite sheet is 5 times the outer diameter of the composite pipe to avoid cracking of the transition layer at the straight bevel. The composite sheet is bent at room temperature (cold bending) or at a temperature of 200℃-400℃ (warm bending). The bending of the composite sheet uses an internally lined mandrel-type single-curvature forming die or a continuous multi-pass roll bending forming die. Protection of the bevel transition layer includes adding a flexible non-metallic protective pad to the composite bevel end face and the surface of the bevel transition layer to avoid mechanical scratches and delamination damage caused by die extrusion.

[0026] S5. Perform hot wire root welding of the base layer FCAW-G from the outside of the pipe. After the root welding is completed, check and record the residual height H and interface temperature T on the inside of the root weld.

[0027] The welding parameters used in the hot wire root welding of the FCAW-G base layer are as follows: the main welding wire is a NiCrMo-3 series flux-cored welding wire with a diameter of 1.2-1.6 mm; the auxiliary hot wire is a homologous nickel-based welding wire with a hot wire current of 30-70 A and a hot wire voltage of 5-12 V; the main welding current is 220-260 A, the arc voltage is 26-31 V, the welding speed is 480-580 mm / min, and the shielding gas is high-purity Ar (Ar content of 99.99%) or a mixture of Ar and He (He content of 25%-50%) with a flow rate of 15-22 L / min.

[0028] The control target for hot wire root welding of the base layer FCAW-G is single-pass continuous penetration, with an inner weld reinforcement height of 0.4-0.8 mm.

[0029] S6, Base SAW Fill: After confirming the continuity of the root weld, SAW submerged arc welding is used for base filling and capping. The welding wire diameter is 2.4-3.2 mm, the welding current is 250-260 A, the voltage is 28-32 V, the welding speed is 520-580 mm / min, and the minimum preheating temperature is 10℃ (if the preheating temperature is less than 10℃, flame heating is used to bring the preheating temperature to the standard). The interpass temperature is less than or equal to 175℃. (The interpass temperature is measured using a contact temperature measuring instrument, such as a thermocouple temperature measuring instrument in the prior art).

[0030] S7. Cleaning the inner side of the pipe and sealing with hot wire for the GTAW-P cladding layer.

[0031] The specific process is as follows: Remove 0.3-0.5 mm of the root surface layer from the inside of the tube, which may contain slag, oxides, or excessive Fe dilution, to expose a continuous and dense root weld metal surface. Then, use ERNiCrMo-3 hot wire for GTAW-P cladding, with a hot wire current of 70-110 A, a pulse frequency of 10-35 Hz, a peak current of 170-210 A, a base current of 80-140 A, a duty cycle of 35%-55%, and a welding speed of 120-200 mm / min.

[0032] It should be noted that when cleaning the inside of the pipe, care should be taken not to grind away the transition layer on the composite bevel.

[0033] Furthermore, the internal cleaning of the pipe and the hot wire sealing welding of the cladding GTAW-P also include: Based on the residual height (H) and penetration, the hot wire current, welding speed, interpass cooling time, and duty cycle of the cladding weld are adjusted.

[0034] Specifically, the inner reinforcement height H of the root weld is in the range of 0.4-0.8 mm. When H is too small (i.e. less than 0.4 mm), the auxiliary hot wire feeding speed of the cladding weld is increased and the hot wire current is increased to increase the amount of molten wire to fill the molten pool. The welding speed is maintained or slightly increased to strictly limit the equivalent line energy and prevent high dilution of Fe element caused by excessive deep penetration. When H is too large (i.e., greater than 0.8 mm), the auxiliary hot wire feed speed of the cladding weld is reduced and the hot wire current is lowered accordingly to reduce excessive accumulation of weld reinforcement. The welding speed is increased or the interpass cooling time is extended to accelerate heat dissipation and reduce heat input. By collecting the weld reinforcement H and interface temperature T on the inner side of the root weld and using these parameters as feedback control parameters, a control process based on parameter linkage between FCAW-G hot wire root weld and GTAW-P hot wire cladding weld is established. This allows the welding processes of the base layer and the cladding layer to coordinate with each other, and the cladding layer status can be adjusted according to the condition of the base layer root weld, thereby improving the quality of the cladding weld.

[0035] S8. Testing and Verification: The testing methods used in this invention include hardness, tensile, impact, metallographic and corrosion resistance tests, as well as macroscopic observation.

[0036] The test data of the welded pipes of the present invention are shown in Tables 1, 2 and 3.

[0037] The testing standard in Table 1 is ASTM A370-2024, with an ambient temperature / humidity of 24.5℃ / 57%RH and test conditions of room temperature.

[0038] Table 1. Data from room temperature tensile tests

[0039] The testing standard in Table 2 is ASTM A370-2024, with an ambient temperature / humidity of 25.3℃ / 54%RH, test conditions of low temperature (-46℃), and notch type of V-notch.

[0040] Table 2 Impact Test Data

[0041] The testing standard in Table 3 is ASTM A370-23, Standard Test Methods and Definitions for Mechanical Properties of Steel Products.

[0042] Table 3 Hardness Test (HV10) Data Table

[0043] The final pipeline test data after welding according to this scheme are shown in Tables 1, 2, and 3. The tensile test, impact test, and hardness test indicators all meet the requirements. Macroscopic observation results are as follows: Figure 2 , Figure 3, Figure 4 and Figure 5 As shown, the final weld has an excellent morphology, with no continuous brittle phase and obvious delamination near the interface.

[0044] The results of metallographic and corrosion resistance tests are as follows Figure 6 , Figure 7 , Figure 8 , Figure 9 , Figure 10 and Figure 11 As shown, the base material and cladding material at the butt weld joints and at 90° and 270° positions on the pipe cross-section exhibit good fusion. The average grain size of the cladding and base materials, determined using the ASTM E112 (2023) comparative method, is grade 8.5. The flux core and interface coating show good adhesion, with no obvious delamination, brittle phases, or defects. Metallographic and corrosion resistance tests are satisfactory. These indicators can be verified based on the specific pipe diameter, wall thickness, and cladding material grade.

[0045] This solution prepares a transition layer using laser cladding and flame spraying before the base layer root weld and cladding weld, forming a continuous pre-welding interface functional layer that covers the bottom, sidewalls, and step corners of the bevel. Compared to the localized transition layer prepared at the bottom of the bevel in existing technologies, this invention forms continuous physical and chemical protection along the three-dimensional geometric contour of the bevel interface, constructing a continuous barrier across the entire interface. This effectively blocks and covers the microscopic diffusion channels through which Fe and C elements migrate from the carbon steel base layer to the corrosion-resistant cladding. The transition layer prepared by this invention combines interface isolation, microstructure strengthening, and subsequent welding fusion quality, and also serves as a metallurgical control layer during the subsequent welding thermal cycle. This transition layer forms a good metallurgical bond with both the base layer and the cladding. The pre-formed transition layer provides a stable adsorption bonding surface for the subsequent deposition and crystallization of the base layer weld and the cladding weld, effectively preventing interlayer delamination and debonding defects in the composite pipe during subsequent welding and long-term operation, and significantly improving the structural integrity and microstructure stability of the overall welded joint of the bimetallic composite pipe.

Claims

1. A welding and forming process for bimetallic composite pipes, characterized in that, Includes the following steps: S1. Preparation of bevel: A composite bevel is processed at the end of the composite plate. The composite plate includes a base layer and a cladding layer. The base layer is a carbon steel layer, and the cladding layer is a corrosion-resistant layer. The composite bevel is an X-shaped bevel, which includes a base layer side bevel and a cladding layer side bevel. S2. Grind, degrease, remove oxide scale, and roughen the interfaces on both sides of the composite bevel, the root corner, and the area to be covered. S3. Preparation of bevel transition layer: A transition layer is prepared on the bevel side of the base layer by flame spraying and on the bevel side of the cladding layer by laser cladding. The spraying and cladding areas continuously cover the junction of the base layer and the cladding layer, forming a continuous pre-welding interface functional layer covering the bottom, sidewall and step corner of the bevel. S4. Bend the composite board into a composite tube and protect the bevel transition layer; Protecting the bevel transition layer includes adding a flexible non-metallic protective pad to the composite bevel end face and the surface of the bevel transition layer; S5. Perform hot wire root welding of the FCAW-G base layer from the outside of the pipe. After the root welding is completed, check and record the residual height H and interface temperature T on the inside of the root welding. S6. After confirming the continuity of the root weld, use SAW submerged arc welding to fill and cover the base layer. S7. Cleaning the inner side of the pipe and sealing with hot wire for the GTAW-P cladding layer.

2. The bimetallic composite pipe welding and forming process according to claim 1, characterized in that: The bevel angle of the base layer is 28°-36°, the blunt edge height is 1.2-2.2 mm, and the assembly gap is 1.8-2.8 mm; the bevel angle of the inner side of the multilayer is 18°-24°.

3. The bimetallic composite pipe welding and forming process according to claim 1, characterized in that: The flame spraying is performed using oxyacetylene flame spraying equipment.

4. The bimetallic composite pipe welding and forming process according to claim 1, characterized in that: Laser cladding uses coaxial or off-axis powder feeding.

5. The bimetallic composite pipe welding and forming process according to claim 1, characterized in that: The thickness of the transition layer at the base slope and the thickness of the transition layer at the overlay slope are both 0.5-1mm.

6. The bimetallic composite pipe welding and forming process according to claim 1, characterized in that: The transition layer is composed of: Cr 18%-24%, Mo 8%-12%, Cu 1.5%-5.0%, Nb 0.8%-2.0%, Ti 0.2%-1.0%, Zr 0.01%-0.08%, Si 0.5%-1.0%, Mn 1.0%-1.4%, with the balance being Ni.

7. The bimetallic composite pipe welding and forming process according to claim 1, characterized in that: The minimum bending radius of the composite material is 5 times the outer diameter of the composite pipe.

8. The bimetallic composite pipe welding and forming process according to claim 1, characterized in that: The bending of the composite board is described as either cold bending at room temperature or warm bending at a forming temperature of 200℃-400℃.

9. The bimetallic composite pipe welding and forming process according to claim 1, characterized in that: The composite board is bent using an inner-lined mandrel-type single-curvature forming mold or a continuous multi-pass roll bending forming mold.

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