Manufacturing method of double wall pipe with bending part of concentric axis and the pipe thereby

Abstract

In conventional methods for manufacturing double-walled pipes, the inner pipe is bent without a connection, and the outer pipe is produced by fitting multiple pieces, including elbows, bent pipes, or straight pipes, onto the outside of the inner pipe and connecting them by welding. This method consumes a large amount of material, requires a significant amount of labor, and suffers from the problem of gas leakage due to welding defects. The present invention proposes an efficient method for manufacturing double-walled pipes in which both the inner and outer pipes are bent without welding connections while maintaining a concentric axis, thereby reducing production costs and labor, and eliminating the risk of gas leakage.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing a double pipe for gas supply, and more specifically, to a method for manufacturing a double pipe having a structure including an inner pipe and an outer pipe sharing a concentric axis, and capable of preventing gas leakage by reducing the welding area for bending for extension or change of direction, and to a double pipe manufactured by said method. Background Technology

[0002] Generally, among the fuel supply pipes for supplying fuel to engines in ships, vehicles, etc., the fuel supply pipe and exhaust pipe for supplying gas as fuel have a manifold-type double-pipe structure to prevent gas leakage and insulation, or to utilize the heat of the exhaust gas.

[0003] In the above double pipe, a space is formed between the inner pipe and the outer pipe, and the inner pipe and the outer pipe have a structure in which they are connected to an engine or a separate double pipe by welding or flanging. This double pipe is bent in two or three dimensions to change direction in order to be positioned according to the structure of the device to be installed. The problem to be solved

[0004] In conventional double-walled pipe manufacturing methods, the inner pipe is bent without a connection, and the outer pipe is produced by fitting multiple pieces, including elbows, bent pipes, or straight pipes, to the outside of the inner pipe and connecting them by welding. This method consumes a large amount of material, requires a significant amount of labor, and suffers from gas leakage problems due to welding defects. means of solving the problem

[0005] The present invention relates to a method for manufacturing a double tube having an inner tube (1) and an outer tube (2) for gas supply, and a bending portion having a concentric axis, comprising: an assembly pre-step (Fig. 1) of preparing the inner tube which is straight, the outer tube which is straight and shorter in length than the inner tube, two sealing caps (3) which seal both ends of the inner tube, and two sealing rings (4 to 6) which completely separate the space between the inner tube and the outer tube and maintain the connection at both ends of the inner tube and the outer tube;

[0006] An inner tube filling step (Fig. 2) comprising: an inner tube one-end sealing step in which one end of the inner tube is sealed with the sealing cap (3); an inner tube compaction step in which a filler material (21) is filled without gaps along the longitudinal direction inside the inner tube and the filled filler material is directly compacted in alignment with the longitudinal direction to increase the density of the filler material; and an inner tube other-end sealing step in which the opposite end of the inner tube is sealed with the sealing cap (3); a double tube assembly step (Fig. 3) in which a sealing ring (6) is installed to seal one end of the outer tube into which the inner tube filled with the filler material is inserted, while simultaneously penetrating the inner tube, and the sealing ring restrains one end of the outer tube and the inner tube protruding from the outer tube by the sealing ring; and a sealing ring filling step in which the filler material is compacted through a passage formed along the longitudinal direction of the space between the inner tube and the outer tube of the double tube by the sealing ring (6) to increase the density of the filler material. A double tube filling step (182) comprising a sealing ring sealing step for sealing the passage; a bending step (183) for creating one or more bending sections according to the bending angle and direction of the double tube determined by considering the springback angle of the inner tube (b in FIG. 5) occurring after bending the double tube; a separation step (184) for opening both ends of the double tube by removing the sealing rings (4 to 6) and the sealing cap (3) at both ends of the double tube having the bending sections; and a filler removal step for removing the filler filled in the internal space of the inner tube and the space between the inner tube and the outer tube. The present invention relates to a method for manufacturing a double tube comprising an outer bending angle correction step (185) that corrects the outer bending angle to be the same as the inner bending angle, wherein the central axis of the inner tube determined by the bending step considering the springback angle and the central axis of the outer bending angle determined by the outer bending angle correction step coincide, and the outer and inner tubes have concentric axes in a bending portion.

[0007] The method for manufacturing a double tube including a bending part having a concentric axis according to the present invention is characterized by bending at a bending step at a greater angle than the target bending angle (Fig. 5).

[0008] In addition, the method for manufacturing a double tube including a bending portion having a concentric axis according to the present invention is characterized by cutting both ends of the double tube, including the sealing ring and the sealing cap, in the separation step (184) to open both ends of the double tube.

[0009] In addition, the method for manufacturing a double tube including a bending section having a concentric axis according to the present invention is characterized by using a bending angle inspection jig (170) including one curved section and two straight sections in the correction step to correct the bending angle of the outer tube to be the same as the bending angle of the inner tube.

[0010] The present invention relates to a double tube produced by a method for manufacturing a double tube comprising: a pre-assembly step; an inner tube filling step; a double tube assembly step; a double tube filling step; a bending step; a separation step; a filler removal step; and an outer tube bending angle correction step; wherein the central axis of the inner tube determined by the bending step considering the springback angle and the central axis of the outer tube determined by the outer tube bending angle correction step coincide, and the outer tube and the inner tube have a concentric axis in a bending portion. Effects of the invention

[0011] The present invention provides an efficient method for manufacturing a double pipe that reduces production costs and labor while eliminating the risk of gas leakage, wherein both the inner and outer pipes are bent without welding connections and maintain a concentric axis. Brief explanation of the drawing

[0012] FIG. 1 is an example of a component included in the present invention. Figure 2 is an example of the inner tube filling step. Figure 3 shows an example of the double pipe assembly and filling steps. Figure 4 is an example of a general-purpose double-tube bending machine. FIG. 5 is an example of bending according to the present invention. Figure 6 shows a comparison of the concentricity of the double tube after bending. Figure 7 is an example showing the bending angle and springback. FIG. 8 is an example of machining a hole in the exterior. FIG. 9 is an example of a double tube according to the present invention. Figure 10 is an example of a double-pipe flange. Fig. 11 is an example of a double tube combined with a support. FIG. 12 is an example of the A-A' cross-section shown in FIG. 11. FIG. 13 is an example of the B-B' section of FIG. 11. Figure 14 is an example of an assembly drawing of internal components of a bracket. Fig. 15 is an example of a bracket. FIG. 16 is an example of a hole formed in the exterior and an exterior cut section. FIG. 17 is an example of a jig for checking the bending angle. FIG. 18 is an example showing the sequence of manufacturing a double pipe according to the present invention. FIG. 19 shows a conventional technology for connecting the bending portion of a double pipe by welding. Specific details for implementing the invention

[0013] Embodiments of the present invention are described in detail below with reference to the attached drawings. However, this description is merely an illustrative or functional description of the present invention, and since the embodiments are subject to various modifications and may take various forms, the scope of the present invention should not be interpreted as being limited by this description and the embodiments. Furthermore, the purposes or effects presented in the present invention do not imply that a specific embodiment must include all of them or only such effects; therefore, the scope of the present invention should be understood not to be limited by such interpretation. That is, the scope of the present invention extends to equivalents capable of realizing the technical concept described in the claims.

[0014] In the manufacturing method of the present invention applicable when supplying gas as fuel, the structure of the double pipe comprises an inner pipe through which gas is supplied as a first conduit, and a second conduit formed between the outer surface of the inner pipe and the inner surface of the outer pipe installed outside the inner pipe to detect gas leakage flowing through the first conduit. Additionally, flanges are attached to both ends of the double pipe for connecting to other double pipes or devices such as engines.

[0015] FIG. 1 shows the components required for the first step of manufacturing the double tube of the present invention. In the first step shown in FIG. 2, one end of the inner tube (2) is sealed with a sealing cap (3), welded, and then filled with a filler material (sand or steel balls, etc.). Afterward, the filler material filled inside the inner tube is sufficiently compacted by applying vibration or tapping the outside of the inner tube, a sealing cap (3) is inserted at the other end of the inner tube (2) and welded to seal it so that the filler material does not leak out. The steel ball material is selected based on the corrosion resistance and other factors according to the double tube material, and steel balls of the same material as the double tube material are preferred. Currently, the double tube materials mainly used in marine engines are stainless steel such as SUS 316L, Duplex 2205, and Super Duplex 2750.

[0016] In the second step shown in FIG. 3, an outer tube (2) is fitted onto the outside of an inner tube filled with filler, a sealed ring (6) is fitted onto one end of the outer tube, and a ring (4) with a filler groove is fitted onto the other end so that the outer tube and the inner tube form a concentric axis, and the inner tube (1), rings (6, 4), and outer tube (2) are welded together as one (fixed welding).

[0017] In the third step, the space between the inner tube and the outer tube is filled with filler material through the ring (4) with the filler material groove of the assembled double tube, and the filler material is compacted sufficiently densely by applying vibration or tapping the outer tube and the inner tube, and then the filler material groove is sealed by welding so that the filler material does not leak out.

[0018] The purpose of filling the space between the inner tube and the outer tube with filler material is that if a bending operation is performed using a general-purpose pipe bending machine in a double-tube state where the inner tube and the outer tube are assembled as a single unit, not only will the cross-section of the inner tube be distorted, but a problem will also occur where the center axes of the inner tube and the outer tube are not formed identically.

[0019] Therefore, by filling the inner tube with a high density so that the inner space, the space between the inner tube and the outer tube, and the outer tube become one, a bending environment is created such that it is like bending a single solid bar shape, thereby preventing the inner tube cross-section from being crushed or the central axis of the inner tube and the outer tube from becoming misaligned during the bending process.

[0020] In the fourth step, the double pipe, which has been filled with a sufficiently dense filler material between the inner pipe and the outer pipe, is bent to the outer dimensions of the outer pipe using a general-purpose pipe bending machine as shown in Fig. 4. If the double pipe bending angle in the drawing is 75 degrees, the double pipe bending angle is set to 81 degrees, and the double pipe bending operation is performed.

[0021] When a pipe is bent using a general-purpose pipe bending machine, different bending residual stresses are generated in the bending area depending on the material and specifications of the pipe. As shown in Fig. 5a, the pipe is fixed to the bending machine and the bending roller is rotated 81 degrees to bend the pipe. Then, as shown in Fig. 5b, when the clamp securing the pipe to the bending roller is released, the pipe, which was bent 81 degrees, deforms 6 degrees in the opposite direction due to the residual stress generated in the bending area during the bending process, resulting in a final bending angle of 75 degrees. The phenomenon in which the pipe returns by a certain angle in the opposite direction from the initial bending angle due to the influence of the bending residual stress is called the springback phenomenon. When the sealing caps and rings attached to both ends of the double-walled pipe that constrain the inner and outer pipes are removed after bending, a problem arises in which the concentricity between the inner and outer pipes is broken due to springback deformation in the inner pipe caused by differences in residual bending stress resulting from differences in material and specifications between the inner and outer pipes. To solve this problem, a standard operating procedure capable of correcting the misalignment of the center axes of the inner and outer pipes, as well as bending data by pipe material and specification for the bending curvature correction process, are required.

[0022] The present invention solves this problem through a process step capable of correcting the misalignment of the center axes of the inner and outer tubes and through a correction operation of the bending curvature. At this time, bending data according to the pipe material (physical properties) and specifications can be used to ensure concentricity. Figure 7 shows that pipes of the same specifications (material (physical properties) and specifications) exhibit the same amount of springback for the same bending angle, regardless of the manufacturer or heat number. The physical properties (amount of springback) related to the bending of the inner and outer tubes vary depending on the material and cross-sectional shape (outer diameter, thickness). In marine gas engines using double tubes, the pipe material is determined according to the type of fuel gas, and the pipe diameter and pipe thickness are determined according to the engine exhaust gas capacity and fuel gas supply pressure. The materials of the inner and outer tubes are determined according to the characteristics and pressure of the substance flowing in the inner tube. Typically, high pressure is applied to efficiently transport natural gas, oil gas, methane gas, and ethane gas through the inner pipe, and nitrogen gas is flowed at low pressure in the space between the inner and outer pipes to monitor for gas leakage through the inner pipe. When natural gas is used as fuel gas, a Super Duplex Pipe (SCH40S) with a thick thickness, high strength, and excellent corrosion resistance is used for the inner pipe, and a relatively thin 316L Stainless Steel Pipe (SCH10S) is used for the outer pipe. When oil gas and methane gas are used as fuel gas, a 316L Stainless Steel Pipe (SCH40S) is also used as the material for the inner pipe.

[0023] As a fifth step, the ends of the double tube, including the inner tube sealing caps at both ends of the bent double tube and the sealing ring between the inner tube and the outer tube, are cut, and all the filler material filled inside the double tube is discharged and removed. When the filler material is removed, the inner tube and the outer tube of the double tube with one end cut off are not mutually constrained, so springback occurs in the inner tube and the outer tube according to their respective bending characteristics, so the inner tube is in a state of a bending angle of 75 degrees and the outer tube is in a state of 76.8 degrees, and as shown in Fig. 5, the inner tube is pushed in the opposite direction of the bending direction inside the outer tube.

[0024] As a sixth step, as shown in FIG. 6, the center axes of the inner and outer tubes are misaligned, so that the outer tube bending angle is corrected from 76.8 degrees to 75 degrees to make them concentric axes, thereby ensuring that the inner and outer tubes have concentric axes. To accurately correct the outer tube bending angle, the actual bending angle of the inner tube formed after the double tube bending is measured, and a bending angle inspection jig (171, Template) to be used for the outer tube bending correction work at the same bending angle is fabricated and utilized. FIG. 17 shows an example of a jig having one curved section and two straight sections. When the outer tube is corrected to be the same as the inner tube bending angle, the center axes of the inner and outer tubes become concentric (63 in FIG. 6).

[0025] As a seventh step, as shown in FIG. 8, mounting holes for a bracket for installing a support and a socket for installing a gas leak detection means (sensor, sensor, etc.) can be machined on the outer surface of the bent double pipe. When machining holes on the outer surface, care must be taken to avoid damaging the inner surface of the pipe, and it is preferable to use equipment equipped with a function to set the machining depth on the drilling machine (Figs. 11–16).

[0026] As the eighth step, the outer bending angle correction work is completed so that the inner tube and the outer tube form a concentric axis, and a bracket and a socket are welded to the outer tube of the double tube, which has a hole machined for installing a bracket and a socket on the outer tube, and a support is installed on the bracket to fix the inner tube to the center of the outer tube, and then the position of the inner tube relative to the outer tube can be adjusted so that the inner tube and the outer tube form a concentric axis at both ends of the double tube (Figs. 11 to 16).

[0027] As the ninth step, with the inner and outer tubes forming a concentric axis at both ends of the double tube, the cutting positions at both ends of the inner and outer tubes are marked and cut according to the drawing dimensions to match the lengths.

[0028] As the tenth step, the inner and outer pipes of the double pipe, with both ends of the length cutting completed, and the double pipe flange are assembled. First, the inner pipe and the double pipe flange are joined by an expansion operation, and then the outer pipe and the double pipe flange are joined by welding.

[0029] FIG. 18 illustrates the double-pipe manufacturing steps of the present invention sequentially as follows, with the seventh and eighth steps omitted and simplified. An inner pipe, an outer pipe, a sealing cap, and a sealing ring are prepared for manufacturing the double pipe (181). The inner pipe is filled with a filler, and the inner pipe and the outer pipe are assembled to produce the double pipe, after which the outer pipe is filled with a filler (182). The double pipe is bent, and at this time, it is bent at an angle smaller than the bending angle indicated in the drawing (183). When the sealing rings at both ends of the double pipe are removed to discharge the filler, springback deformation occurs in the inner pipe (184). The bending angle of the outer pipe is corrected to match the bending angle of the inner pipe to match the angle in the drawing, and the centerlines of the inner pipe and the outer pipe are aligned (185). The double pipe and the double pipe flange are assembled and expanded to join the inner pipe and the double pipe flange (186). The outer pipe and the double pipe flange are welded (187). In this invention, since the bending angle of the outer tube is controlled while the inner and outer tubes are separated, a heat treatment process to relieve stress caused by bending is unnecessary. When bending is performed with the relative positions of the inner and outer tubes completely fixed by welding, a heat treatment process for stress relief is required. Furthermore, since an oxide film forms on the inner and outer tubes of the finished product after heat treatment, additional process steps and costs are required in addition to the technical difficulties involved in removing such films. This invention prevents the formation of such heat treatment films, thereby reducing the overall process time and improving process efficiency.

[0030] The manufacturing process of a GI-type marine gas engine and a gas double pipe is complex, as described in the following sequence of manufacturing processes, and has problems such as requiring a large amount of manufacturing materials and labor, difficulty in quality control due to the large number of external welded joints, and high manufacturing costs. FIG. 19 is an example of a conventional manufacturing method for making a double pipe by assembling and welding several pieces of a bent pipe and a straight pipe to form the outer pipe. The method consists of a first bending step of the inner pipe (191), a step of preparing four pieces of the outer pipe (192), a step of inserting the inner pipe into the straight part of the outer pipe (193), a second bending step of the inner pipe (194), a step of joining the remaining three pieces of the outer pipe to the inner pipe (195), a step of welding the four pieces of the outer pipe (196), a step of joining flanges to both ends (197), and welding of the outer pipe and flange joints (5 points) (198). In the step (192) of preparing the outer casing into four pieces, two bending sections are individually bent and both ends are cut to match the dimensions. In addition to significant material loss during the process of manufacturing each of the four pieces, a long production time is also required. The step (193) of inserting the inner tube into the straight outer section must be performed before the secondary bending of the inner tube. Since the area where the inner tube can be clamped for the secondary bending is reduced, there are difficulties such as the need to manufacture and utilize a special jig. In the step (197) of joining the flanges to both ends, a dedicated jig (JIG only for fit-up) must be manufactured and utilized to ensure that the inner tube and the outer casing remain concentric. Since the material of the outer casing is stainless steel, significant deformation occurs due to welding heat during welding, and welding countermeasures are required to account for thermal shrinkage and angular deformation of the weld area. Since there are many such welded joints (196, 198), the overall cost increases, including the resulting decrease in process efficiency and the cost of destructive testing (NDE, RT & PT).

[0031] Compared to such conventional technology, the advantages of the present invention, which assembles the inner and outer tubes into a double tube and bends them into a double tube state, are as follows. Since there is no need to prepare the outer tube by cutting and bending it into multiple pieces, raw materials lost due to excess length when cutting and bending into multiple pieces can be reduced, and the labor required for cutting and bending into multiple pieces can be reduced. Furthermore, the process of fitting up the flange, inner tube, and outer tube is simplified, and the fitting-up process between the outer tubes is omitted, thereby reducing the labor required for fitting up. Additionally, the welding joint between the outer tubes is omitted. Consequently, welding labor can be reduced, and delays caused by welding defects and correction welding processes are eliminated. Since there is no welding shrinkage or angular deformation, the labor required for deformation correction can be reduced, and inspection costs are lowered as the area requiring non-destructive inspection is reduced due to the omission of welding joints.

[0032] The present invention is not limited to the embodiments exemplified above and may be applied to all cases where double-walled bending is performed. The meaning of the terms used to describe the present invention should be understood as follows. Where one component is referred to as being "connected" to another component, it should be understood that it may be directly connected to the other component, or that there may be other components in between. A singular expression should be understood to include a plural expression unless the context clearly indicates otherwise, and terms such as "include" or "have" are intended to specify the existence of the described features, numbers, steps, actions, components, parts, or combinations thereof, and should be understood not to preclude the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof. Unless otherwise defined, all terms used herein have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms defined in commonly used dictionaries should be interpreted as having meanings consistent with the context of the relevant technology, and should not be interpreted as having an ideal or overly formal meaning unless explicitly defined in the present invention. Explanation of the symbols

[0033] 1 Internal organ 2 exterior 3. Sealing caps at both ends of the inner tube 4~6 Closing rings at both ends between the inner and outer tubes 21 Filler 22 fixed welding 31 Closed welding 51 Bending Roller 52. Inner or outer 53. Pressure Die 54. Clamper 61 Cutting section cross-section 62 Double tube with the inner tube offset to the left 63 Inner tube and outer tube having a concentric axis Step of machining 81 holes 82 machined holes 91 Double pipe flange 101 Double pipe flange cutting section 102 Inner tube, flange expansion joint 103 Joint for welding flange and exterior 104 Joint for welding the flange and the inner tube 111 Support 112 sensor 113 double pipe 121 Swivel Flange 131 bracket 141 plug screw 142 Square Section Room 143 bushing 144 springs 145 Vibration Damper 146 bushing 161 External cut section with exposed inner tube 162 Double pipe bending section 170 Example of a bending inspection jig 171 Example of Bending Angle Inspection Points

Claims

Claim 1 A method for manufacturing a double tube having an inner tube and an outer tube for gas supply, and including a bending portion having a concentric axis, comprising: a pre-assembly step of preparing the inner tube which is straight and the outer tube which is straight and shorter in length, two sealing caps that seal both ends of the inner tube, and two sealing rings that completely separate the space between the inner tube and the outer tube and maintain a connection at both ends of the inner tube and the outer tube; and an inner tube end sealing step of sealing one end of the inner tube with the sealing cap. An inner tube filling step comprising: an inner tube compaction step of filling the inner tube without gaps along the longitudinal direction and directly compacting the filled filling material in alignment with the longitudinal direction to increase the density of the filling material; and an inner tube end sealing step of sealing the opposite end of the inner tube with the sealing cap; a double tube assembly step comprising: a sealing ring installed to seal one end of the outer tube into which the inner tube filled with the filling material is inserted while penetrating the inner tube, and restraining one end of the outer tube and the inner tube protruding from the outer tube by the sealing ring; a sealing ring filling step of increasing the density of the filling material by compacting the filling material through a passage formed along the longitudinal direction of the space between the inner tube and the outer tube of the double tube by the sealing ring; and a sealing ring sealing step of sealing the passage; A bending step of creating one or more bending sections according to the bending angle and direction of the double tube determined by considering the springback angle of the inner tube occurring after bending the double tube; a separation step of opening both ends of the double tube by removing the sealing ring and the sealing cap at both ends of the double tube having the bending section; a filler removal step of removing the filler filled in the internal space of the inner tube and the space between the inner tube and the outer tube; and an outer tube bending angle correction step of correcting the bending angle of the outer tube to be the same as the bending angle of the inner tube.A method for manufacturing a double tube comprising a bending portion in which the center axis of the inner tube determined by a bending step considering the springback angle and the center axis of the outer tube determined by the outer tube bending angle correction step coincide, and the outer tube and the inner tube have a concentric axis. Claim 2 A method for manufacturing a double tube including a bending part having a concentric axis, characterized in that, in the first bending step, the bending is performed at a greater angle than the target bending angle. Claim 3 A method for manufacturing a double tube including a bending portion having a concentric axis, characterized in that, in the separation step, both ends including the sealing ring and the sealing cap of the double tube are cut to open both ends of the double tube. Claim 4 A method for manufacturing a double tube including a bending section having a concentric axis, characterized in that, in the correction step of claim 1, a bending angle inspection jig comprising one curved section and two straight sections is used to correct the bending angle of the outer section to be the same as the bending angle of the inner section. Claim 5 A double tube comprising a bending section having a concentric axis made by the method of claim 1.

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