JPH0469026B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a pipe with internal and external fins for high-temperature heat exchange that has excellent heat exchange efficiency and high-temperature strength. [Prior Art] Conventionally, for example, an air preheater for a high-temperature combustion device or an external heat type high-temperature heat exchanger, as shown in a partial perspective view in FIG. A pipe with inner and outer fins for high-temperature heat exchange is used, which has a structure in which fin materials 2 and 3 are joined, and these pipe materials and the inner and outer fin materials are made of austenitic stainless steel or Ni-based heat-resistant alloy. . In this conventional pipe with inner and outer fins, the inner fin material 2 is usually inserted into the pipe material 1, which is mechanically caulked to join the inner fin 2 to the inner surface of the pipe material 1, followed by the outer fin material 3. It is manufactured by welding spirally to the outer surface of the pipe material 1. [Problems to be Solved by the Invention] However, when manufacturing the above-mentioned conventional pipe with inner and outer fins, the caulking between the inner fin material and the inner surface of the pipe material becomes weak due to thermal strain generated during welding of the outer fin material. Not only that, but this deterioration in caulking is accelerated by long-term use at high temperatures, so a deterioration in heat exchange efficiency is unavoidable. For this reason, attempts have been made to join the inner fin material to the inner surface of the pipe material by brazing, but as a brazing material, P component or
Because a Ni-based alloy containing a large amount of Si is used, the ductility of the brazed joint becomes extremely low, causing cracks to occur even when a slight strain is applied. Since there is little expectation that the components in the material will diffuse into the pipe material and the inner fin material and raise the melting point of the brazed joint, it is difficult to apply the outer fin material to the outer surface of the pipe material as a subsequent process. We are aware that during welding, there are problems such as the brazed joint melting and coming off, and cracking occurring in the brazed part of the inner fin material, resulting in poor heat exchange effect and short service life. At present, it is impossible to use a pipe with inner and outer fins in which the inner fin material is caulked to the inner surface of the pipe material and the outer fin material is welded to the outer surface of the pipe material. [Means for Solving the Problems] Therefore, from the above-mentioned viewpoint, the present inventors, in order to manufacture a pipe with inner and outer fins with excellent heat exchange efficiency, particularly improve the inner fin material on the inner surface of the pipe material. As a result of research focusing on brazing filler metals suitable for brazing, we found that the filler filler metals are expressed in weight% (hereinafter % is weight%).
), Cr: less than 6 to 15%, B: 3 to 4.5%, and further contains Si: 0.1 to 3% as necessary, with the remainder consisting of Ni and unavoidable impurities. When a brazing filler metal is used, the brazing filler metal has a low melting point and excellent oxidation resistance, and during brazing, the component constituting the brazing filler metal is a pipe made of austenitic stainless steel or Ni-based heat-resistant alloy. It not only increases the melting point of the brazed joints of these parts, but also forms brazed joints with excellent high-temperature strength and ductility. Even when the outer fin material is welded, there is no cracking or peeling at the brazed part of the inner fin material, so that a pipe with inner and outer fin materials that has excellent heat exchange efficiency and high temperature strength can be obtained. We have obtained the knowledge that this will be the case. Therefore, the present invention was made based on the above knowledge, and first, a pipe material, an inner fin material, and an outer fin material, all of which are made of austenitic stainless steel or Ni-based heat-resistant alloy, are prepared. The inner surface of the pipe material contains Cr: less than 6 to 15%, B: 3 to 4.5%, and if necessary, Si: 0.1 to 3%, with the remainder being Ni and unavoidable impurities. A method of manufacturing a pipe with inner and outer fins for high-temperature heat exchange by brazing and joining the inner fin material using a brazing material having the following composition, and then welding and joining the outer fin material to the outer surface of the pipe material. It has the following characteristics. Next, the reason why the component composition of the brazing filler metal is limited as described above in the method of the present invention will be explained. (a) Cr and B When these components coexist, they lower the melting point of the brazing filler metal, improve its oxidation resistance, and are easily diffused into the pipe material and inner fin material during brazing. In addition to raising the melting point, B has the effect of imparting strength and ductility to the brazed joint, but if the content is less than 6% Cr and 3% B, the desired effects may not be achieved. On the other hand, if the content exceeds 15% for Cr and 4.5% for B, the ductility of the brazed joint will decrease and cracking will occur more easily. Content: Cr: 6 to less than 15%, B: 3
It was set at ~4.5%. (b) Si The Si component has the effect of further lowering the melting point of the brazing filler metal and improving its oxidation resistance.
It is included as necessary when these properties are particularly required, but if the content is less than 0.1%, the desired effect of improving the above effects cannot be obtained, while if the content exceeds 3%, wax Since the ductility of the bonded joint decreases, its content is set at 0.1 to 3%. In addition, in brazing the inner fin material to the inner surface of the pipe material in the method of this invention, first the above-mentioned brazing material is powdered and applied to the brazing joint of the inner fin material to the inner surface of the pipe material or the vicinity thereof. Alternatively, the above-mentioned brazing material can be made into a foil, and when inserting the inner fin material into the pipe material, this foil-shaped brazing material can be inserted into the brazed joint, and in this way the inner fin material can be inserted into the pipe material. After insertion, the pipe material can be drawn to bring the brazed joints of both parts into close contact, and then heated for brazing in a vacuum or non-oxidizing atmosphere. can. [Example] Next, the method of the present invention will be specifically explained with reference to Examples. As shown in Figure 1, JIS/SUS316, 304, and 316L have a cross-sectional shape and dimensions of maximum outer diameter: 8 mmφ x wall thickness: 0.3 mm.
(austenitic stainless steel) inner fin material, each having the dimensions shown in Table 1, and
SUS316, Hastelloy X, and Inconel 600
Pipe materials composed of pipe materials, each having the component composition shown in Table 1, and width: 25 mm x thickness:
Prepare a foil-like brazing material tape with a size of 0.025 mm, combine these parts as shown in Table 1, and attach the inner fin material to the pipe with its outer circumferential surface wrapped with the foil-like brazing material tape. The pipe material, foil brazing material, and inner fin material are brought into close contact by inserting the material into the pipe material, and then drawing it to reduce its outer diameter by 1 mm.The resulting pipe material is then :Cut to 550mm and place in brazing furnace, in vacuum, temperature: 1100

〔Effect of the invention〕

As is clear from the results shown in Table 1, in the pipes with inner and outer fins manufactured by methods 1 to 8 of the present invention, the outer fin materials are welded, and even when subjected to repeated heat cycles, Since there is no peeling or cracking at the brazed joint between the pipe material and the inner fin material, excellent heat exchange efficiency and high-temperature strength are maintained for an extremely long period of time, whereas conventional methods 1 to 3 In pipes with inner and outer fins manufactured in this way, the bond between the pipe material and the inner fin material deteriorates due to thermal strain generated during welding or added heat cycles, so it is necessary to avoid a decrease in heat exchange efficiency. It is something that cannot be done. As described above, according to the method of the present invention, even when welding the outer fin material or when using it at high temperatures,
It is possible to manufacture a pipe with inner and outer fins that does not cause peeling or cracking at the brazed joint between the pipe material and the inner fin material, and therefore the resulting pipe with inner and outer fins has excellent long-term durability. It maintains high heat exchange efficiency and high temperature strength.

[Brief explanation of the drawing]

FIG. 1 is a partial perspective view of a pipe with inner and outer fins. In the drawings, 1...pipe material, 2...inner fin material, 3...outer fin material.

Claims (1)

[Claims] 1. Prepare a pipe material, an inner fin material, and an outer fin material, all of which are made of austenitic stainless steel or Ni-based heat-resistant alloy. First, the inner surface of the pipe material is coated with Cr: 6 to 15%. The inner fin material is brazed and joined using a brazing material having a composition (the above weight %) containing B: 3 to 4.5% and the remainder consisting of Ni and unavoidable impurities, and then the pipe material A method for manufacturing a pipe with inner and outer fins for high-temperature heat exchange, characterized by welding the outer fin material to the outer surface of the pipe. 2 Prepare a pipe material, an inner fin material, and an outer fin material, all of which are made of austenitic stainless steel or Ni-based heat-resistant alloy, and first, coat the inner surface of the pipe material with Cr: 6 to less than 15%, B: 3 to The above inner fin material is joined by brazing using a brazing material having a composition (by weight) containing 4.5%, Si: 0.1 to 3%, and the remainder consisting of Ni and unavoidable impurities. A method for producing a pipe with inner and outer fins for high-temperature heat exchange, characterized in that the outer fin material is welded to the outer surface of the pipe material.