JPS60170564A - Production of bent pipe for thermal cracking and reforming reaction of hydrocarbon - Google Patents

Abstract

PURPOSE:To obtain a titled bent pipe having a double-layered structure by casting a molten metal for forming an outside layer into a master mold formed by using a single-layered bent pipe consisting of an inside layer material as a core and uniting the bent pipe and outside layer by fusion bonding. CONSTITUTION:A single-layer bent pipe (a) obtd. by hot bending of a centrifugally cast straight pipe consisting of, for example, an Fe-Cr-Mn-Nb heat resisting steel is used as a core and a master mold 2 is formed around the same by sand mold etc. While the pipe (a) is kept heated to a prescribed temp., a molten Fe- Cr-Ni heat resisting cast steel is cast as an outside layer material (b), by which a bent pipe having a two-layered structure is obtd. The respective materials of the inside and outside layers can be selected and combined as desired. Coking, carburizing, etc. on the inside wall surface of the pipe are thus suppressed by connecting the bent pipe to a straight pipe having a double-layered structure to constitute a pipe for thermal cracking and reforming reaction of hydrocarbon.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a bent tube having a two-layer structure made of a combination of different metals and used as a tube for thermal decomposition and reforming reactions of hydrocarbons.

Thermal decomposition and reforming reactions of hydrocarbons are carried out at high temperatures and pressures, so Fe-0r-Ni austenitic heat-resistant steel pipes containing large amounts of Or and Ni are generally used as reaction tubes. ing. However, this reaction tube has the disadvantage that solid carbon, which is precipitated during thermal decomposition and reforming reactions of hydrocarbons, tends to adhere to the inner wall surface of the tube. The solid carbon deposit (caulking) obstructs the flow of reactants within the tube and reduces the overall heat transfer coefficient of the tube wall, thus hindering the smooth performance of the reaction. It also promotes carburization of the tube wall and the accompanying deterioration of the tube material.

As a countermeasure to this problem, the pipe cross section was made into a two-layer structure instead of the conventional single-layer pipe, and the inner layer material was made of steel with excellent coking resistance, and the outer layer material was made of the aforementioned Fe--2, which has excellent high temperature strength.
(If 3r-Ni heat-resistant steel is used, it is possible to suppress the adhesion and deposition of solid carbon on the inner wall surface of the pipe while maintaining the required heat resistance properties with the outer layer material. Also, it is possible to suppress the adhesion and deposition of solid carbon on the inner wall surface of the pipe. Furthermore, by selecting and combining the materials for each layer in the two-layer structure, it is possible to further improve the performance and durability of the reaction tube.

Such double-layer pipes can be produced relatively easily by centrifugal casting.
Although it can be manufactured at low cost, the centrifugal casting method can only manufacture straight pipes and cannot manufacture bent pipes. If only the straight part of the reaction tube is a double layer tube,
If the bent pipes that connect the straight pipes are conventional single-layer pipes, caulking will occur intensively in the bent pipes, or the bent pipes will become weak points due to the material, causing problems in the straight pipes. The significance of using a double-layer pipe will be largely lost.

In order to solve the above problems, the present invention provides a method for manufacturing a bent pipe having a two-layer structure.

The method for manufacturing a bent tube for reaction according to the present invention involves preparing a single-layer bent tube pre-formed into a desired shape as an inner layer material, using this as a core to form an outer mold using a sand mold or a metal mold, and then A bent pipe with a two-layer structure is manufactured by casting molten metal to form the outer layer and fusing and integrating the bent pipe, which is the inner layer material installed in the mold, with the cast outer layer metal. It is something.

A concrete example of a casting method for carrying out the method of the present invention is shown in FIGS. 1 and 2. (a) is a single-layer bent pipe serving as the inner layer, which is installed as a core in the flask (1). (2)
is an outer mold, which is molded with a sand mold around the single-layer bent pipe (a) serving as the core. Single layer bent pipe (a) and outer mold (
The space defined between 2) and 2) is where the outer layer is formed by casting. The molten metal as the outer layer material is poured into this mold, and the interface between the single layer bent pipe (a) and the cast metal (b) as the inner layer material is fused and solidified, and then the feeder part (b) is solidified. - By cutting and removing 1), a bent tube consisting of two layers, an inner layer and an outer layer, can be obtained.

The single-layer bent tube (a) used as the core is, for example, a tube manufactured as a straight tube by centrifugal casting, which is machined on its inner and outer surfaces as appropriate, and then cold or heated. It may be formed into a desired shape by adding a bending process in between. Alternatively, a forged pipe, for example, a straight pipe produced by hot plastic working and subjected to bending to obtain a bent pipe, may be used.

The outer mold (2) of the single-layer bent pipe, which is the inner layer material, may be formed using a sand mold or the like using an ordinary shaping method.

Instead of a sand mold, a metal mold can also be used.

Casting of the outer layer metal molten metal may be carried out by a conventional method, but the cast outer layer metal (b) and the single layer bent pipe (a) which will be the inner layer are mixed.
In order to form a strong bonding relationship by fusion at the interface, it is desirable to preheat the single-layer bent tube prior to casting. The heating temperature is 50 to 30% higher than the melting point of the bent pipe material.
A temperature range below 00°C is suitable. The lower limit of the heating temperature is set to the melting point of -300°C because if it is lower than that, it is difficult to obtain the amount of heat necessary to promote fusion.On the other hand, the upper limit of the heating temperature is set to the melting point of -50°C. Not only does it not require any further heating in terms of calorific value, but it also causes deformation due to softening of the single-layer bent pipe, or the generation of oxide scale on the surface, which may even reduce the adhesion between the inner and outer layers. This is because there is a risk of inviting The single-layer bent tube may be heated by a suitable method such as high-frequency induction heating, resistance heating using a heating element such as a nichrome wire, or gas burner heating.

The selection and combination of materials for the inner layer and outer layer is arbitrary, but to solve the problem of solid carbon adhesion and deposition on the inner wall surface of the reaction tube, the inner layer material should not contain Ni or have a Ni content of 10%.
It is recommended to use single-layer bent pipes made of heat-resistant steel regulated as follows. The reason for limiting the amount of Ni is that Ni on the inner surface of the tube acts as a catalyst for the precipitation of solid carbon in the reaction inside the tube, and by limiting the amount of Ni to 10% or less, it is possible to prevent the deposition of solid carbon. Can be suppressed. Such heat-resistant steels include, for example, C003 to 1.5% (weight %, same hereinafter), Ni 3.0% or less, Mn6. O~15.0%,
crH), o ~ ao, o%, Nb 3.0% or less, NO
, 15% or less, the remainder substantially consisting of Fe-OrF
Preferably, e-0r-based heat-resistant steel or Fe-Cr-Ni7Mn-Nb heat-resistant steel to which 10% or less of Ni is added is preferably used. This material also has good carburization resistance as a result of the combined inclusion of Mn and Nb.

On the other hand, the outer layer material contains a large amount of Ni and Cr in order to compensate for the high temperature strength required for the reaction tube.
Heat steel, for example, C0.01~0.6%, 8i2.5% or less, Mn2.0% or less, Or20.0~80.0%, N
Fe-0r-Ni austenitic heat-resistant steel consisting of i18.0 to 40.0%, N00 15% or less, the remainder substantially Fe, or a part of Fe 5.0% or less for the purpose of improving heat resistance properties. Within this range, heat-resistant steel substituted with one or more elements selected from Mo, W, and Nb is preferably used.

To explain an example of the method of the present invention, Fe-Or
A single-layer bent pipe obtained by hot bending a centrifugally cast straight pipe made of -M n -N'b heat-resistant cast steel is used as a core, and a single-layer bent pipe is made as shown in Figs. 1 and 2. An outer mold (2) is formed around (a) using a sand mold, and the single-layer bent pipe is heated to 1100'O with a gas burner, and Fe-0r-Ni heat-resistant molten metal is added as the outer layer material. By casting (casting temperature 1600'C), a bent tube with a two-layer structure was obtained. Inner layer (single layer bent pipe) components are CO, 55%, Si
1.8%, Mn8.5%, 0r25.5%, NbQ, 4
%, N0001%, remainder substantially F61 outer layer (cast metal) component c, C0.45%, Si1.5%, Mn0.4
%, 0r26.0%, Nis 5.0%, N0001%
, the remainder is substantially Fe. Casting sizes are: outer layer thickness in order of 10, inner layer thickness 2tut, tube axis length 470ffff,
The radius of curvature of the tube axis is 1501.

The resulting bent tube was cut and cross-sectional observation revealed that the interface between the inner and outer layers was completely fused and bonded along the entire circumference and length.

As described above, according to the present invention, a reaction bent tube having a two-layer structure can be easily manufactured by casting a previously produced single-layer bent tube as a core. The materials for the inner and outer layers can be arbitrarily selected and combined depending on the purpose. Therefore, by connecting a straight pipe with a two-layer structure to form a pipe for thermal decomposition and decomposition reaction of hydrocarbons, for example, coking and carburization of the inner wall of the pipe can be alleviated, stabilizing the operation, and extending the service life. It has effects such as improvement.

In addition, the method of the present invention can be used to manufacture bent tubes for configuring piping for various uses requiring wear resistance, corrosion resistance, etc., in addition to the reaction tubes described above, by selecting and combining materials for the inner and outer layers. It is also useful as a law.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a specific example of the casting method in the present invention;
FIG. 2 is a sectional view taken along line A-A. a: Inner layer material (single layer bent pipe), b: Outer layer material (cast metal, l
: Casting flask, 2: Outer mold. Agent Patent Attorney Miyazaki New Department Figure 1A Figure 2

Claims (1)

[Claims] (1) The outer wall is formed using a sand mold or metal mold using a single-layer bent tube as the inner layer material as a core, and the inner layer material is heated to a temperature 50 to 300°C lower than its melting point. A method for manufacturing a bent pipe for thermal decomposition and reforming reactions of hydrocarbons, which has a two-layer structure and is characterized by casting molten metal.