JPS6329636B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method for fabricating clad pipes by diffusion welding. Most common steel pipes are solid pipes such as carbon steel pipes, low-alloy steel pipes, and stainless steel pipes, which are used depending on the purpose. So-called clad pipes are often used. This clad pipe can be manufactured using methods such as overlay welding of stainless steel or the like onto the inner surface of the outer pipe, or an explosive bonding method in which the outer pipe and inner pipe are joined using explosives. However, the clad pipes manufactured by these methods have drawbacks such as large variations in quality and high cost. That is, clad pipes made by overlay welding involve welding of dissimilar materials, so welding defects are likely to occur, and it is extremely difficult to manufacture long clad pipes with small diameters, and high-precision welding equipment is necessarily required. On the other hand, clad pipes produced by the explosion bonding method have large deformation and residual stress, and also generate explosive noise during manufacture, which poses a major problem in terms of pollution and is high in cost. In addition, a method of manufacturing clad pipes by diffusion welding is also known (see Japanese Patent Application Laid-open No. 139048-1983).
This is limited to cases where the coefficient of thermal expansion of the outer tube and inner tube is special. The present inventors found that diffusion welding has the advantages of stable joint quality, small deformation, no pollution, and the ability to join dissimilar metals that are difficult to melt weld when manufacturing clad pipes. Focusing on the large number of cladding pipes, we first proposed a method that significantly improves the conventional method of manufacturing clad pipes using diffusion welding. [Refer to Special Publication No. 60-7591 (Special Publication No. 60-7591)
54-96660)] In other words, the method is ``fabricating a clad pipe in which the inner tube is pushed out by the thermal expansion of the metal material to generate a pressurizing force between the inner tube and the outer tube, and the inner tube and the outer tube are joined by diffusion welding. In the method, a half-split or multi-segmented tapered metal round rod having a coefficient of thermal expansion larger than the coefficient of thermal expansion (α ₁ ) of the inner tube material and the coefficient of thermal expansion (α ₂ ) of the outer tube material is inserted into the inner tube. A clad pipe manufacturing method characterized by providing an air vent hole in the outer pipe and performing diffusion welding. However, the above method has the disadvantage that a vacuum furnace must be used, which still limits the dimensions of the clad pipe that can be manufactured. The present invention eliminates the drawbacks of the above-mentioned methods, and provides a method in which a good-quality clad pipe can be made in a heating furnace in the atmosphere, and furthermore, when heat treatment is required after diffusion welding, rapid cooling can be performed in the same heating furnace. The present invention provides a method for manufacturing a clad pipe in which a pressurizing force is generated between an inner tube and an outer tube by thermal expansion of a metal material, and the inner tube and the outer tube are diffusion welded. This article describes a method for manufacturing clad pipes using diffusion welding, which is characterized by providing an exhaust pipe on one lid, creating a vacuum or inert gas atmosphere only at the joint between the outer and inner tubes, and heating in a normal atmospheric furnace. It is something to do. The present invention can be applied to the production of clad pipes made of various materials and shapes, clad nozzles for pressure vessels, corrosion-resistant piping, transportation pipes, and the like. Hereinafter, the present invention will be described in further detail with reference to the accompanying drawings. In order to clarify the improvement points of the present invention, the method proposed earlier in Japanese Patent Application No. 1983-1966 will first be explained with reference to FIG. FIG. 1a shows the assembly of an outer tube 1, an inner tube 2, and a tapered metal round bar 3 split in half or into multiple parts,
FIG. 1b shows a diagram of the completed assembly. In the figure, a two-part tapered metal round bar is shown, and the coefficient of thermal expansion α ₂ of this material is larger than the coefficients of thermal expansion α ₁ and α ₂ of the outer tube 1 and the inner tube 2. First, the inner tube 2 is inserted into the outer tube 1, and then the metal round rod 3 is inserted into the inner tube 2. At this time, by dividing the inserted metal round rod 3 into tapered wedge shapes 3 ₁ and 3 ₂ , it can be easily slid into the inner tube 2 by applying force to both ends. It can be firmly attached to the Further, grooves 4 are provided at both ends of the metal round rod, and the metal round rod 3 can be fixed by welding the grooves 4 while being tightly inserted into the inner tube 2. Furthermore, when inserting the metal round rod 3 into the inner tube 2, a bonding preventive agent 5 is applied to the outer surface and split surface of the metal round rod 3, and after the outer tube 1 and the inner tube 2 are diffusion welded. , it is preferable that the metal round bar 3 be easily removed. Note that it is preferable to provide an air vent hole (not shown) in the outer tube 1 to prevent air from remaining in the joint. A method of producing a clad pipe by heating the entire object to be welded shown in FIG. 1b, assembled as described above, in a vacuum furnace or an inert gas atmosphere furnace was disclosed in the aforementioned Japanese Patent Application No. 54-96669. This is the method proposed in the issue. However, in the production of clad pipes by conventional diffusion welding, including the above-mentioned method, the use of a vacuum furnace or an inert gas atmosphere furnace is unavoidable, resulting in the following drawbacks. (1) There are restrictions on the size, length, weight, etc. of the object to be welded, and the production of particularly long clad pipes requires enormous equipment costs. (2) Since it is in a vacuum, it takes a long time to heat and cool. (3) If heat treatment is required after diffusion welding, it is necessary to heat it again and perform appropriate heat treatment. The present invention has been made to eliminate these drawbacks, and will be described in detail below with reference to FIG. 2. FIG. 2a is for explaining how to assemble the outer tube 1, inner tube 2 and metal round bar 3 according to the present invention, and how to attach the lids 6, 6' which are the most characteristic feature of the present invention. FIG. b is a diagram illustrating a state in which the present invention is implemented. Mainly outer tube 1 and inner tube 2 in Fig. 2b
The assembled object to be welded consisting of the round metal bar 3 is exactly the same as that shown in FIG. 1b. The present invention provides an outer tube 1 of the assembled object to be welded.
Lids 6, 6' are attached to both ends so that the inside of the outer tube 1 can be sealed. One of the lids 6, 6' is provided with an exhaust pipe 7 through which vacuum or inert gas can be introduced.
is provided so that the joint surface between the outer tube 1 and the inner tube 2 is in a vacuum or inert atmosphere. The exhaust pipe 7 is provided with a main valve 8 and an inert gas inlet 9, and the exhaust pipe 7 and a vacuum device (not shown) are connected to each other by a flange joint 10 that is easy to attach and detach. The outer tube 1 and the lids 6, 6' and the lid 6' and the exhaust pipe 7 are joined together by welding or the like to maintain airtightness. Second
In Figure b, 11 indicates those welded parts, and 12 indicates an atmospheric furnace. Based on the configuration described above, the inside of the outer tube 1 is evacuated, inert gas is filled as necessary, and the workpiece to be welded is heated to the appropriate temperature for diffusion welding in the heating furnace 12 in the atmosphere. The inner tube 2 is pressed against the outer tube 1 by the expansion of the metal round rod 3, which has a higher coefficient of thermal expansion than the outer tube 1 and the inner tube 2, and a clad pipe can be manufactured. Moreover, according to such a configuration, after diffusion welding,
If appropriate heat treatment is required, the main valve 8 may be closed after diffusion welding, the vacuum device may be removed, and appropriate cooling treatment such as water cooling or forced air cooling may be performed. Generally, in the case of vacuum diffusion welding, the workpiece is placed in a vacuum container and heated by a heater inside the container or a heater outside the container, so even if you want to rapidly cool the workpiece after diffusion welding, it is not possible and it is unavoidable. After slow cooling, only the workpiece to be welded is heated again in an atmospheric furnace.
Appropriate cooling (quenching) is performed to heat treat the workpiece. However, according to the method of the present invention, diffusion welding can be carried out in an atmospheric furnace, and the vacuum device can be removed from the workpiece, so the workpiece can be freely cooled by air cooling, water cooling, etc., which is a significant advantage. be. That is, if carbon steel is heated to the diffusion welding temperature, the crystals of carbon steel may become coarse and the strength may decrease, so heat treatments such as normalizing, quenching, and tempering may be performed after diffusion welding. In the case of such a combination of materials, the method of the present invention allows appropriate heat treatment to be performed immediately after completion of diffusion welding, so the heat treatment can be performed at a low cost and has the effect of producing a good diffusion welded clad pipe. Example This is a specific example of diffusion welding of a low-alloy steel outer tube and a titanium inner tube, which has a smaller coefficient of thermal expansion. In other words, the low alloy steel for the outer tube has an outer diameter of 152 mm and a plate thickness of
26 mm, length 500 mm, and the inner titanium tube has an outer diameter of
99.9 mm, plate thickness 3 mm, length 500 mm, and the gap between the outer tube and inner tube was 0.1 mm/diameter. In addition, the metal round bar made of heat-resistant stainless steel, which has a higher coefficient of thermal expansion than low-alloy steel or titanium, has an outer diameter of 73.9 mm and a length of 490 mm. The inner surface of the outer tube and the outer surface of the inner tube were thoroughly degreased after being mechanically finished, and the inner tube surface was chrome plated before the inner tube was inserted into the outer tube. Next, the surface and tapered part (split part) of the heat-resistant stainless steel metal round bar that was divided into two parts were uniformly coated with a bonding prevention agent (Rubie N 5026: trade name), and after being inserted into the inner tube, the two ends were separated. The parts were welded. Next, sealing lids were attached to both ends of the low-alloy steel outer tube by welding, an exhaust pipe was attached to one of the lids, and this was connected to a vacuum device. In this example, since diffusion welding was carried out in a vacuum, no inert gas was introduced after the inside of the outer tube was evacuated using an exhaust pipe. The workpiece to be welded was placed in an atmospheric heating furnace and heated to a vacuum degree of 5×10 ^-5 torr. The heating temperature was maintained at 950°C for 2 hours to complete diffusion welding of the outer and inner tubes. After completion of diffusion welding, slow cooling causes the grains of low-alloy steel to become coarse, so in this case, after maintaining the normalization temperature at 925°C, the main valve of the exhaust pipe was closed, the exhaust pipe and vacuum device were removed, and the exhaust pipe and vacuum device were removed. The welded product was taken out of the furnace and forced air cooled to prevent grain coarsening. Although forced air cooling is used here, it will be understood that a feature of the present invention is that cooling can be performed freely depending on the combination of materials. After diffusion welding and heat treatment, after removing the sealing lid and heat-resistant stainless steel round bar, we performed ultrasonic flaw detection from the outer surface of the outer tube, inspected it, investigated the cross section, and investigated the crystal grains of the low alloy steel of the outer tube. It was confirmed that the low alloy steel and titanium were well bonded and that coarsening of the crystal grains of the low alloy steel was prevented. Other Examples Clad pipes with the material combinations shown in Table 1 were also manufactured, and it was confirmed that all good clad pipes were manufactured. Note that heat treatment immediately after diffusion welding was performed depending on the material.

【table】

[Table] Although the inner pipe material in Table 1 has a lower coefficient of thermal expansion than the outer pipe material, in the opposite combination, a good clad pipe can be manufactured by the method of the present invention without using a heat-resistant stainless steel round bar. I've confirmed it.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating an embodiment of the conventional method (Japanese Patent Application No. 54-96660), and FIG. 2 is a diagram illustrating an embodiment of a specific example of the method of the present invention.

Claims (1)

[Claims] 1. In a clad pipe production method in which pressure is generated between the inner and outer tubes by thermal expansion of a metal material and the inner and outer tubes are diffusion welded, lids are hermetically attached to both ends of the outer tube, and one lid is A method of manufacturing a clad pipe by diffusion welding, which is characterized by providing an exhaust pipe, placing only the joint between the outer pipe and the inner pipe in a vacuum or inert gas atmosphere, and heating in a normal atmospheric furnace.