Preparation method of double-layer metal sealing connecting pipe

Abstract

The invention belongs to the technical field of high-temperature sealing connection, and provides a preparation method of a double-layer metal sealing connecting pipe, which comprises the following steps: selecting two metal materials with complementary high-temperature-resistant high-strength performance and corrosion-resistant performance, respectively preparing an outer-layer pipe and an inner-layer pipe, coaxially sleeving the inner-layer pipe with the outer-layer pipe, and sealing the inner-layer pipe with the outer-layer pipe; the gap of the double-layer metal pipe is controllable, and the coaxiality of the double-layer metal pipe meets the assembly requirement; the middle of the double-layer metal pipe serves as a welding section, a plurality of resistance welding spots are arranged on the welding section in the circumferential direction, and the outer-layer pipe and the inner-layer pipe are fixedly connected into a whole through a discrete resistance spot welding technology; and the two ends of the double-layer metal pipe subjected to spot welding are subjected to spinning forming, an expansion opening structure with fillet transition is obtained, the sealing performance of the ends is enhanced, and the double-layer metal sealing connecting pipe is obtained. By means of the method, the problems that a traditional single-layer sealing pipe is low in reliability and single in material performance can be solved.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature sealing connection technology and relates to a method for preparing a double-layer metal sealing connection pipe. This method is applicable to pipeline connection scenarios with extremely high requirements for sealing performance and high-temperature resistance, such as aero-engines, gas turbines, and nuclear energy equipment. Background Technology

[0002] In high-end equipment such as aero engines, gas turbines, and nuclear energy systems, pipeline connections often need to operate stably under high temperature and high pressure environments for extended periods. Currently used single-layer metal-sealed pipe structures face the following limitations under such demanding conditions: 1. Insufficient sealing reliability: The single-layer pipe wall thickness is limited by the overall structural requirements for lightweighting and flexibility, resulting in limited elastic deformation capacity. During assembly pre-tightening or fluctuations in working pressure, it is difficult to form a uniform and continuous specific pressure on the sealing surface. Local areas are prone to micro-plastic deformation or fatigue cracking due to stress concentration, thereby causing leakage failure.

[0003] 2. Difficulty in achieving both material properties: Existing single-layer pipes are usually made of a single high-temperature alloy, but high strength and high corrosion resistance are often mutually restrictive. For example, although GH4169 alloy has excellent yield strength (≥1100 MPa) at 650℃, its chromium and molybdenum content is low, making it prone to intergranular corrosion in sulfur-, chlorine-, or oxidizing media; while GH625 alloy has excellent corrosion resistance (intergranular corrosion rate ≤0.01 mm / year), its high-temperature resistance and high strength are relatively insufficient, making it difficult to undertake high-load sealing tasks alone.

[0004] 3. Geometric instability caused by welding process: To achieve pipe end connection, circumferential welding is often required for thin-walled pipes. However, the high heat input generated by continuous welding will lead to significant thermal deformation, especially for thin-walled structures with a wall thickness of less than 0.5 mm. This can easily cause the pipe body to bend or become elliptical, and the measured coaxiality deviation often exceeds 0.1 mm, resulting in uneven contact of the flange sealing surface and seriously weakening the seal integrity.

[0005] Although existing technologies have attempted to use double-layer tube structures to separate functional requirements, they mostly rely on full welding or brazing to achieve interlayer connections. This not only results in a large heat-affected zone and high residual stress, but also fails to resolve the process conflicts between the middle connection area and the end forming area, making it difficult to meet the requirements for high reliability and long-life sealing.

[0006] Therefore, there is an urgent need for a new preparation method that can achieve reliable interlayer fixation and efficient end sealing while ensuring synergistic material properties and controlling thermal deformation, so as to break through the existing technical bottlenecks. Summary of the Invention

[0007] To address the technical problems of traditional sealing pipes, such as low reliability, easy leakage, and short lifespan under high temperature and pressure, this invention discloses a method for preparing a double-layer metal sealing connection pipe. This method is achieved through three core technologies: heterogeneous material composite, discrete spot welding connection, and axial functional partitioning forming. Specifically, the method includes the following steps: S1. Select two metal materials that complement each other in terms of high temperature and high strength performance and corrosion resistance, and make them into an outer tube and an inner tube respectively. The outer tube is coaxially mounted on the inner tube to form a double-layer metal tube with controllable gap and coaxiality that meets assembly requirements. S2. The middle part of the double-layer metal tube is used as the welding section. Multiple resistance welding points are set on the welding section along the circumference. The outer tube and the inner tube are fixedly connected into one piece by discrete resistance spot welding process. S3. Spin-form both ends of the spot-welded double-layer metal pipe to obtain an expanded structure with rounded corner transition, so as to enhance the end sealing performance and obtain a double-layer metal sealing connection pipe.

[0008] Furthermore, the inner tube is made of a corrosion-resistant alloy material, and the outer tube is made of a high-temperature resistant alloy material. The corrosion-resistant alloy material has better chemical stability than the outer tube, and the high-temperature resistant alloy material has better high-temperature resistance and high-strength performance than the inner tube.

[0009] Furthermore, the corrosion-resistant alloy material is GH625 alloy, and the high-temperature resistant alloy material is GH4169 alloy.

[0010] Furthermore, a step-by-step welding method is adopted, in which the welding of some resistance welding points is completed first, and the welding of the remaining resistance welding points is completed after a predetermined interval, in order to control heat input and reduce thermal deformation.

[0011] Furthermore, the welding section is axially separated from the spinning areas at both ends of the double-layer metal tube, so that spinning forming only acts on the non-welding areas at both ends of the double-layer metal tube.

[0012] Furthermore, the length of the non-welded area is not less than 10 mm.

[0013] In an improved embodiment of the above-described method for preparing a double-layer metal-sealed connecting pipe, the method further includes: S4. Perform gradient heat treatment on the double-layer metal sealing connection tube after spinning to obtain the final double-layer metal sealing connection tube. The gradient heat treatment includes: overall vacuum stress-relief annealing at 700°C, and local aging strengthening of the sealed connection section at both ends at 720°C.

[0014] The method for preparing a double-layer metal-sealed connecting pipe provided by this invention has the following advantages compared with the prior art: 1. By using a high corrosion-resistant alloy (such as GH625) as the inner layer that directly contacts the medium and a high-temperature and high-strength alloy (such as GH4169) as the outer layer to bear the mechanical load, a functional zoning design of internal corrosion protection and external load bearing is achieved, which effectively overcomes the shortcomings of single materials in high-temperature and high-pressure corrosive environments.

[0015] 2. By using multiple discrete resistance welding points distributed circumferentially to replace the traditional continuous weld seam, and combining them with a step-by-step welding strategy, the total heat input and heat accumulation effect are significantly reduced, and the coaxiality of the double-layer tube is controlled within ≤0.03 mm, which is far superior to the traditional process (>0.1 mm), ensuring the geometric accuracy of subsequent assembly and sealing surfaces.

[0016] 3. The middle section is set as an interlayer fixed welding section, and the two ends are reserved as non-welding areas for spinning to form an expansion joint structure. This ensures that the two are completely separated in the axial direction, avoiding damage to the integrity of the weld point caused by the plastic deformation of spinning. At the same time, it ensures that the expansion joint structure has a smooth transition and no stress concentration, which significantly improves the reliability of the end seal.

[0017] 4. By first performing overall vacuum stress-relief annealing to eliminate residual welding stress, and then performing localized aging strengthening on the end sealing area where only high strength is required, the high temperature resistance and high strength of the outer layer material are maximized without sacrificing the toughness of the weld joint, achieving a mechanical match of overall flexibility and localized toughness.

[0018] Verification showed that the double-layer metal-sealed connecting pipe prepared by the method of this invention has a leakage rate of ≤1×10⁻ under operating conditions of 650℃ and 12 MPa. 7 Pa·m³ / s, interlaminar shear strength ≥150 MPa, fatigue life ≥1×10 5 This fully meets the stringent requirements of high-end equipment such as aero engines and gas turbines for long-life, zero-leakage sealing connections. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of the preparation method of the double-layer metal sealing connecting pipe disclosed in the embodiments of the present invention; Figure 2 This is a schematic diagram of a double-layer metal-sealed connecting pipe. Detailed Implementation

[0021] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0022] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features of the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] This invention discloses a method for preparing a double-layer metal sealing connection pipe. The method uses a double-layer dissimilar alloy composite design, resistance welding lattice strengthening, and gradient heat treatment process to achieve reliable sealing, high-temperature strength provided by the outer layer, corrosion resistance guaranteed by the inner layer, and avoidance of thermal deformation during the preparation process.

[0024] Specifically, see Figure 1 As shown, the method includes the following steps: S1. Select two metal materials that complement each other in terms of high temperature and high strength performance and corrosion resistance, and make them into an outer tube and an inner tube respectively. The outer tube is coaxially mounted on the inner tube to form a double-layer metal tube with controllable gap and coaxiality that meets assembly requirements. S2. The middle part of the double-layer metal tube is used as the welding section. Multiple resistance welding points are set on the welding section along the circumference. The outer tube and the inner tube are fixedly connected into one piece by discrete resistance spot welding process. S3. Spin-form both ends of the spot-welded double-layer metal pipe to obtain an expanded structure with rounded corner transition, so as to enhance the end sealing performance and obtain a double-layer metal sealing connection pipe.

[0025] In one embodiment, the inner tube is made of a corrosion-resistant alloy material, and the outer tube is made of a high-temperature resistant alloy material, wherein the corrosion-resistant alloy material has superior chemical stability compared to the outer tube, and the high-temperature resistant alloy material has superior high-temperature resistance and high-strength properties compared to the inner tube.

[0026] More specifically, corrosion-resistant alloy materials, such as GH625 alloy, are used to prepare the inner tube. The dimensions and performance parameters of the inner tube can be designed as follows: thickness 0.4mm, length 80mm, inner diameter Φ29mm, and corrosion resistance (intergranular corrosion rate ≤0.01mm / year).

[0027] The outer tube is made of high-temperature resistant alloy material, such as GH4169 alloy. The dimensions and performance parameters of the outer tube can be designed as follows: thickness 0.15mm, length 80mm, outer diameter Φ37.5mm, yield strength ≥1100MPa (650℃).

[0028] In one embodiment, a 42.5mm section in the middle of the double-layer metal tube can be used as a welding section. Six resistance welding points are set along the circumference of this welding section and are evenly distributed in the circumference, that is, the angle interval between adjacent resistance welding points is 60°, the diameter of the resistance welding point is 2mm, the penetration depth is 0.3mm, and the metallurgical bonding of the double-layer tube is achieved by spot welding.

[0029] When performing welding operations, a step-by-step welding method can be adopted, first completing the welding of some resistance welds, and then completing the welding of the remaining resistance welds after a predetermined interval, in order to control heat input and reduce thermal deformation.

[0030] In one embodiment, the welded section is axially separated from the spinning regions at both ends of the double-layer metal tube, so that spinning is applied only to the non-welded regions at both ends of the double-layer metal tube.

[0031] Furthermore, the length of the non-welded area is not less than 10 mm.

[0032] In an improved embodiment of the above-described method for preparing a double-layer metal-sealed connecting pipe, the method further includes: S4. The double-layer metal sealing connecting pipe after spinning is subjected to gradient heat treatment to obtain the final double-layer metal sealing connecting pipe; wherein, the gradient heat treatment includes: overall vacuum stress-relief annealing at 700℃, and local aging strengthening of the sealing connecting sections at both ends at 720℃. This invention, through gradient heat treatment, performs high-frequency induction aging only on the sealing connecting sections, avoiding excessive strengthening of the welded area leading to embrittlement, and achieving an overall fatigue life ≥1×10⁻⁶. 5 (650℃, 10MPa) times.

[0033] The double-layer metal sealing connecting pipe prepared by this invention is as follows: Figure 2 As shown, its structure includes an inner metal tube, an outer metal sleeve, and a sealing layer between the two. The preparation process is illustrated below with a specific example.

[0034] (a) Material selection and preparation: The outer layer is made of GH4169 alloy tube with a thickness of 0.15mm and an outer diameter of Φ37.5mm.

[0035] The inner layer uses GH625 alloy tubing with a thickness of 0.4mm and an inner diameter of Φ29mm.

[0036] (II) Assembly of inner and outer tubes: The inner tube is inserted into the outer tube using a high-precision mandrel (Φ29.5mm diameter) with a diameter tolerance of ±0.01mm, ensuring coaxiality ≤0.03mm and the gap between intermediate welding sections is controlled to ≤0.02mm.

[0037] (iii) Resistance welding slot welding is used to connect the inner and outer tubes into a whole: High-frequency resistance welding equipment was used for welding, with the current set at 3.8kA, the voltage at 4.5V, and the time at 0.25s, forming 6 evenly distributed circumferential weld points, each with a diameter of 2mm and a penetration depth of 0.3mm. Points 1, 3, and 5 were welded first, followed by points 2, 4, and 6 after a 5-minute interval, and the weld area was cooled using localized water cooling technology.

[0038] (iv) Spin forming to create an bulging structure: The two ends are processed using a spinning machine to form the bulging structure required for a sealed connection.

[0039] (v) Perform gradient heat treatment: First, the entire section is heat-treated in a vacuum furnace (700℃×2h). Then, the sealed connection section is individually induction heated to 720℃, held for 4 hours, and then air-cooled to improve sealing performance and fatigue life.

[0040] The method of the present invention has the following advantages over traditional processes: 1. While maintaining the original structure, GH4169 and GH625 alloy materials are selected to improve corrosion resistance and mechanical strength. The double-layer tube made of heterogeneous materials can overcome the limitations of single material performance and adapt to more demanding working conditions.

[0041] 2. This invention significantly improves the contact area and fit between the sealing surfaces by designing a welding section in the middle and an expansion structure at both ends, and separating the two.

[0042] Verification showed that multiple spot welds, such as six, evenly distributed within the weld segment reduced heat input by 70% compared to traditional full welding, and reduced deformation to 0.02 mm (compared to 0.1 mm for traditional full welding). Furthermore, the use of step-by-step welding technology, which divides the spot welds into two batches, reduced the grain size of the heat-affected zone to 5-10 μm (compared to 20-30 μm for traditional single-step welding).

[0043] 3. The present invention adjusts the specific parameters of overall heat treatment and local aging according to the actual working temperature, such as appropriately increasing the aging temperature or extending the holding time, in order to obtain the best mechanical properties and microstructure.

[0044] Obviously, those skilled in the art should understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations of the embodiments of the present invention are possible for those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of making a double-layer metal-sealed connection pipe, characterized by, The application relates to a double-layer metal sealing connection pipe. The application comprises the following steps: Two metal materials with complementary high-temperature-resistant high-strength performance and corrosion resistance are selected to form an outer layer pipe and an inner layer pipe, the outer layer pipe is coaxially sleeved on the inner layer pipe to form a double-layer metal pipe with controllable gap and coaxiality meeting assembly requirements; A middle part of the double-layer metal pipe is taken as a welding section, a plurality of electric resistance welding points are arranged on the welding section in the circumferential direction, and the outer layer pipe and the inner layer pipe are fixedly connected into an integrated body through a discrete electric resistance spot welding point process; 2. The method of claim 1, wherein Both ends of the double-layer metal pipe after spot welding are respectively subjected to spinning forming to obtain an expanded opening structure with a round corner transition, so that the end sealing performance is enhanced to obtain a double-layer metal sealing connection pipe.

3. The method of claim 2, wherein The inner layer pipe is made of a corrosion-resistant alloy material, and the outer layer pipe is made of a high-temperature-resistant alloy material, wherein the corrosion-resistant alloy material has better chemical stability than the outer layer pipe, and the high-temperature-resistant alloy material has better high-temperature-resistant high-strength performance than the inner layer pipe.

4. The method of claim 1, wherein The corrosion-resistant alloy material is GH625 alloy, and the high-temperature-resistant alloy material is GH4169 alloy.

5. The method of claim 1, wherein A step-by-step welding mode is adopted to complete welding of part of the electric resistance welding points, and welding of the remaining electric resistance welding points is completed after a predetermined interval, so as to control heat input and reduce thermal deformation.

6. The method of claim 5, wherein The welding section and the spinning area at both ends of the double-layer metal pipe are separated in the axial direction, so that the spinning forming only acts on the non-welding area at both ends of the double-layer metal pipe.

7. The method of claim 1 to 6, wherein The length of the non-welding area is not less than 10 mm. The application further comprises the following steps: The double-layer metal sealing connection pipe after spinning forming is subjected to gradient heat treatment to obtain a final double-layer metal sealing connection pipe. The gradient heat treatment comprises the following steps: whole vacuum stress relief annealing at 700 DEG C, and local aging strengthening of the sealing connection section at both ends at 720 DEG C.

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