Method for manufacturing half-split pipe joint

Abstract

To provide a method for manufacturing a half-split pipe joint which enables the highly productive manufacture of the half-split pipe joint excellent in dimensional accuracy with little strain even when a pipe diameter increases.SOLUTION: A method for manufacturing a half-split joint of this invention includes: a process of cutting a metal material plate to mold a first intermediate molded article 10 by press molding; a process of molding a bevel of a longitudinal pipe end part 11 of the first intermediate molded article 10; a process of partially welding the longitudinal pipe end parts 11 of the first intermediate molded article to form a second intermediate molded article 20 of a pipe joint shape; a process of partially welding a pipe end part 13 thereof; a process of executing heat treatment, dimensional correction work, and another heat treatment on the second intermediate molded article 20; and a process of cutting the second intermediate molded article 20 having finished the other heat treatment from a longitudinal center line to split into two pieces.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a half pipe joint having a shape obtained by splitting a metal pipe joint in two in the longitudinal direction. [Background technology]

[0002] Metal pipe fittings such as elbows, tees, and reducers have been widely used for connecting parts of piping. These metal pipe fittings have been manufactured by pressing metal pipes as materials, or by pressing materials cut out from metal plates and bending them in the longitudinal direction and welding them. For example, Patent Document 1 describes a method of manufacturing elbows by bending and cutting metal pipes.

[0003] In recent years, projects that use hydrogen as an energy source have been attracting attention, and as part of this project, plans are underway to build a large liquefied hydrogen carrier. Because liquefied hydrogen needs to be kept at an extremely low temperature of -253°C or lower, the piping of liquefied hydrogen carriers and liquefied hydrogen storage facilities will have a double structure consisting of an inner pipe that carries the liquefied hydrogen and an outer pipe that covers the inner pipe, with vacuum insulation between the two. Moreover, in order to carry large amounts of liquefied hydrogen, the piping will be large, with a diameter of 500 mm or more.

[0004] As shown in Figure 1(A), at the bent section 3 of the piping, the pipe is bent by pressing, or an elbow is used. When making a double-structure piping, as shown in Figure 1(B), the outer pipe can be arranged by inserting a large-diameter straight pipe 4 and a large-diameter straight pipe 5 into the outside of the inner straight pipe section 1 and straight pipe section 2. However, since the outer pipe cannot be inserted into the bent section 3 from the longitudinal direction, as shown in Figure 1(C), half-split elbows 6, which are split in half longitudinally, must be attached so as to sandwich the bent section 3 of the inner pipe from both the left and right sides, and welded along the longitudinal center line to form the state shown in Figure 2.

[0005] For this reason, a half elbow 6, which is an elbow split in two in the longitudinal direction, is required. In addition to elbows, half products split in two in the longitudinal direction are also required for branching section 7 called a tee and reduced diameter section called a reducer, as shown in Figure 3. In this specification, these half elbows, half tees, half reducers, etc. are collectively referred to as half pipe fittings.

[0006] Such a half pipe joint itself is not new, and Patent Document 2 describes a method for manufacturing a half elbow by cutting a metal plate and bending it by press forming. However, as the pipe diameter increases, the effect of springback after press forming also increases. As a result, there are problems such as large gaps and misalignments in the welded parts between the half elbows, and deformation due to distortion that is unavoidable because the half elbows are not perfectly round.

[0007] Another possible manufacturing method is to cut an elbow manufactured by the conventional method symmetrically from the center to create a half elbow. However, cutting releases internal stress, which causes deformation due to distortion, and there is a problem that the longitudinal welds of the divided half elbows are misaligned and cannot be accurately aligned. Moreover, a large cutting machine is required to cut a large diameter elbow from the center, and cutting and longitudinal bevel processing take a long time. For this reason, the cutting process becomes a bottleneck, which hinders productivity and makes mass production impossible. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 59-163025 [Patent Document 2] Japanese Patent Application Publication No. 6-26340 Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, an object of the present invention is to solve the above-mentioned conventional problems and to provide a method for manufacturing a half pipe joint that can productively produce a half pipe joint that has little distortion and excellent dimensional accuracy even when the piping diameter is large. [Means for solving the problem]

[0010] The method for manufacturing a half-split pipe joint of the present invention, which has been made to solve the above problems, includes the steps of cutting a metal material plate and rolling it into a half-cylinder or cylinder shape by press forming to form a first intermediate product with an open longitudinal pipe end, forming grooves on the longitudinal pipe end of the first intermediate product, and partially welding the longitudinal pipe ends of the first intermediate product together to form a second intermediate product in the shape of a pipe joint. At both ends of the second intermediate product in the longitudinal direction, both ends of the first intermediate product are partially welded to each other to form a circular pipe end of the second intermediate product. a step of subjecting the second intermediate molded product to a heat treatment, a step of dimensional correction processing, and a second heat treatment; and a step of cutting the second intermediate molded product that has been subjected to the second heat treatment along its longitudinal center line to divide it into two pieces.

[0011] In a first preferred embodiment, the first intermediate product is a pair of press-molded products each having a shape of two cut metal sheets rolled into a semi-cylinder shape, while in a second preferred embodiment, the first intermediate product is a press-molded product each having a shape of one cut metal sheet rolled into a cylinder with an opening between the opposing longitudinal tube ends. Effect of the Invention

[0012] According to the method for manufacturing a half-split pipe joint of the present invention, the first intermediate formed product is partially welded along the longitudinal center line to form a second intermediate formed product, which is then heat-treated and dimensionally corrected, and then split into two pieces, so that a half-split pipe joint with excellent dimensional accuracy can be manufactured, not only when the pipe diameter is small, but also when the pipe diameter is large. In addition, because the split is performed along the longitudinal center line where the pipe is partially welded, the split cutting can be performed in a short time without using a large cutting machine, and productivity can be improved. [Brief description of the drawings]

[0013] [Figure 1] FIG. 4 is an explanatory diagram of an assembly process for a double-structure pipe. [Diagram 2] FIG. 1 is a cross-sectional view of a double-structure pipe using an elbow. [Diagram 3] This is a cross-sectional view of a double-structure pipe using an elbow and a tee. [Figure 4] FIG. 2 is a perspective view showing a first intermediate molded product of the first embodiment. [Diagram 5] FIG. 13 is a perspective view showing a state in which the excess portion of the longitudinal tube end portion has been cut off. [Figure 6] FIG. 13 is a perspective view showing a state in which a longitudinal groove has been machined on a longitudinal tube end portion. [Figure 7] FIG. 2 is a perspective view showing a state in which two first intermediate products are partially welded together to form a second intermediate product. [Figure 8] 11 is a perspective view showing a state in which both longitudinal ends of the second intermediate product have been partially welded to form circular pipe ends. FIG. [Figure 9] FIG. 2 is a perspective view showing the state in which a groove has been made on the end of a circular pipe. [Figure 10] FIG. 4 is a perspective view showing a state in which the second intermediate product is divided into two pieces. [Figure 11] 4 is a flowchart showing a manufacturing method of the half elbow of the first embodiment. [Figure 12] FIG. [Figure 13] FIG. [Figure 14] FIG. 11 is a perspective view showing a first intermediate molded product of the second embodiment. [Figure 15] FIG. 13 is a perspective view showing a state in which a longitudinal groove has been machined on a longitudinal tube end portion. [Figure 16] FIG. 2 is a perspective view showing a state in which a longitudinal tube end portion of a first intermediate product is partially welded to form a second intermediate product. [Figure 17] 13 is a perspective view showing the state in which a groove has been prepared on the circular tube end of the second intermediate molded product. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Preferred embodiments of the present invention will be described below. In each of the embodiments described below, the half pipe joint is a large-diameter half elbow having a diameter of about 500 mm.

[0015] (First embodiment) First, a metal plate is cut into a required shape with an allowance for extra length, and a first intermediate product 10 as shown in FIG. 4 is formed by press molding. In the first embodiment, the first intermediate product 10 is a pair of press molded products in which two cut metal plates are rolled into a semi-cylinder shape. These first intermediate products 10 are formed symmetrically to form a pair. The metal plate is preferably a steel plate or steel strip specified in the JIS for pipe joints, but may be a steel plate or steel strip of other materials as long as it is weldable. In this embodiment, a stainless steel plate (austenitic stainless steel plate) suitable for use as an outer pipe of a double-structure pipe for liquefied hydrogen is used.

[0016] As shown in FIG. 4, the press-molded first intermediate product 10 has an open longitudinal tube end 11, and the longitudinal tube end 11 has an excess portion 12. Tube ends 13a at both ends in the longitudinal direction There is also an excess portion 14. First, the excess portion 12 of the longitudinal pipe end 11 is cut off as shown in Fig. 5, and the cut portion is further processed with a grinder to process a longitudinal groove in the longitudinal pipe end 11 as shown in Fig. 6. The longitudinal groove is a portion that is ultimately used for groove welding to integrate the two first intermediate formed products 10 together.

[0017] Next, as shown in Fig. 7, two pairs of first intermediate products 10 are joined together and partially welded along the longitudinal center line to form a second intermediate product 20 in the shape of a pipe joint. The partial welds 15 are preferably about 10 to 30 mm long, since tack welding may not be strong enough to cause breakage during subsequent heat treatment. The interval between the partial welds 15, 15 may be appropriately determined according to the longitudinal weld length.

[0018] Next, as shown in FIG. 8, a second intermediate product 20 having a pipe joint shape is At both ends in the longitudinal direction, both ends of the first intermediate formed product are partially welded to each other to form a circular tube end 13. The partial welded portion 16 must be finished to a perfect circle in the end. Circular tube end 13 In order to perform groove preparation, it is preferable to perform strong welding. The length of the partial welded portion 16 is preferably about 30 to 80 mm.

[0019] Next, the second intermediate molded product 20 is subjected to heat treatment and dimensional correction. The heat treatment is performed twice, a stress relief heat treatment and a solution heat treatment, and it is preferable to perform the first heat treatment after partial welding. The stress relief heat treatment is intended to remove internal stress generated by press working and welding, and can significantly reduce the internal stress of the second intermediate molded product 20. The second intermediate molded product 20, whose internal stress has been reduced by the first heat treatment in this manner, is then subjected to dimensional correction.

[0020] Since the quenching process of this stress relief heat treatment and the subsequent dimensional correction process also generate a small amount of internal stress, a second heat treatment is then performed. For austenitic stainless steels, solution heat treatment is required, and it is preferable to perform solution heat treatment as the second heat treatment. The purpose of solution heat treatment is to dissolve the chromium carbide precipitated in the weld heat affected zone to eliminate sensitization and to restore corrosion resistance and mechanical performance to the base material level. Specifically, the steel is charged into a heat treatment furnace, heated to 1010 to 1150°C, held for a predetermined time to dissolve the chromium carbide in the crystal, and then quenched. This solution heat treatment can almost completely eliminate the internal stress of the second intermediate formed product 20. In this embodiment, the heat treatment is performed twice, but a third heat treatment may be performed as necessary. In the case of other materials, it is preferable to perform stress relief heat treatment and final heat treatment under appropriate heat treatment conditions.

[0021] Next, as shown in FIG. 9, the second intermediate product 20 Circular tube end 13 Then, groove preparation is performed. Circular tube end 13 The process includes a step of cutting the excess portion 14 to a predetermined dimension and a step of forming a predetermined groove shape. Circular tube end 13 The joint is a strong partial weld 16, and is a perfect circle due to dimensional correction processing. Circular tube end 13 The groove preparation can be carried out easily and accurately.

[0022] Thereafter, as shown in FIG. 10, the heat-treated second intermediate product 20 is cut along the longitudinal center line of the partially welded portion to separate it into two half-shaped products 30, 30. This cutting is performed along the partially welded portion 15 and Circular tube end 13 It is only necessary to cut the partial welded portion 16. Moreover, since a large cutting machine as in the past is not necessary and cutting can be done manually using a small cutting tool, cutting can be done in a short time and productivity can be improved. Since the internal stress of the second intermediate molded product 20 is released in the stage prior to cutting, there is almost no deformation due to distortion even when it is cut. After that, the cut longitudinal groove portion is finished with a grinder to remove the traces of partial welding, and a half-split elbow is obtained. After that, surface treatment, etc. is performed as necessary.

[0023] The resulting half elbow has almost no distortion and excellent dimensional accuracy, so that the longitudinal welds of the half elbows can be accurately aligned when assembled as shown in Figure 1 (C). Specifically, even for stainless steel elbows with a pipe diameter of 500 mm or more, the half elbows manufactured by the manufacturing method of the present invention can have a maximum gap at the longitudinal center of 1 mm or less and a misalignment of 1 mm or less. In contrast, half elbows obtained by cutting the finished product from the center as in the past have a maximum gap at the longitudinal center of 5 mm or more and a misalignment of 3 mm, making welding very difficult. Furthermore, the half elbows manufactured by the manufacturing method of the present invention have a connection between the half elbow and the straight pipe sections on both sides formed in a perfect circle, Circular tube end 13 Since the reduction in circumference is small, the assembly work of the double structure pipe can be easily performed.

[0024] A flowchart of the manufacturing method of the above embodiment is shown in Fig. 11. However, the manufacturing method of the half pipe fitting of the present invention is not limited to the manufacturing method of the half elbow, and half pipe fittings such as a half tee 18 shown in Fig. 12 and a half reducer 19 shown in Fig. 13 can also be manufactured in a similar manner.

[0025] Second Embodiment In the first embodiment described above, a pair of first intermediate molded products 10 are formed from two cut metal material plates, but in the second embodiment, a single cut metal material plate is rolled into a cylindrical shape to form a first intermediate molded product 40 having an opening between the opposing longitudinal tube ends 41, 41 as shown in Figure 14.

[0026] Next, as shown in FIG. 15, shape correction and bevel processing of the longitudinal pipe end 41 are performed, and then, as shown in FIG. Circular tube ends 42 at both ends in the longitudinal direction These are partially welded to form the second intermediate product 50. Thereafter, similarly to the first embodiment, the second intermediate product 50 is subjected to heat treatment, dimensional correction processing, and heat treatment again, so that the second intermediate product 50 is formed as shown in FIG. Circular tube end 42 This is then cut along the partially welded longitudinal centerline and divided into two halves.

[0027] The second embodiment differs from the first embodiment in that the first intermediate product 40 is a single cut metal plate, but other steps are similar to those of the first embodiment, and therefore detailed explanations are omitted. Furthermore, the final step of dividing the second intermediate product 50 into two parts is also easier than the conventional method, since it is sufficient to cut the longitudinal pipe end 41, which is partially welded on one side of the longitudinal center line.

[0028] As described above, according to the present invention, a half pipe joint with little distortion and excellent dimensional accuracy can be manufactured with good productivity even when the pipe diameter is large. The present invention is suitable for a method of manufacturing a half pipe joint with a large diameter, but is not limited thereto, and it goes without saying that it can also be applied to the manufacture of half pipe joints with medium and small diameters. The half pipe joint manufactured by the present invention can be used for double-structure pipes for various applications, such as double-structure pipes for high-temperature fluids as well as double-structure pipes for cryogenic fluids such as liquefied hydrogen. In addition, the insulation method and heat retention method between the inner pipe and the outer pipe are not limited. [Explanation of symbols]

[0029] 1 Straight pipe section 2 Straight pipe section 3 Bend 4 Large diameter straight pipe 5 Large diameter straight pipe 6 Half elbow 7. Tea 10 First intermediate molded product (first embodiment) 11 Longitudinal tube end 12 Extra length 13 Circular Tube End 13a Tube end 14 Extra length 15 Partial Welding 16 Partial Weld 17 Half Tea 18 Half Reducer 20 Second intermediate molded product 30 Half-shaped product 40 First intermediate molded product (second embodiment) 41 Longitudinal tube end 42 Circular Tube End 50 Second intermediate molded product

Claims

1. A step of cutting a metal material plate and rolling it into a semi-cylinder or cylinder by press molding to form a first intermediate formed product having an open longitudinal tube end; forming a groove at a longitudinal tube end of the first intermediate formed product; a step of partially welding longitudinal pipe ends of the first intermediate product to each other to form a second intermediate product having a pipe joint shape; a step of partially welding the pipe end portion of the second intermediate formed product; a step of subjecting the second intermediate product to a heat treatment, a dimensional correction process, and a second heat treatment; cutting the second intermediate molded product after the second heat treatment along a longitudinal center line to divide it into two pieces; A method for manufacturing a half pipe joint comprising the steps of:

2. 2. The method for manufacturing a half split pipe joint according to claim 1, wherein the first intermediate formed product is a pair of press-molded products each having a shape formed by rolling two cut metal sheets into a semi-cylindrical shape.

3. The manufacturing method of a half-split pipe joint as described in claim 1, characterized in that the first intermediate formed product is a press-molded product in which a cut metal plate is rolled into a cylindrical shape with an opening between the opposing longitudinal pipe ends.

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