JP3284330B2 - Pyrolysis reaction tube for ethylene production with inner protrusion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a high heat exchange performance due to projections formed on the inner surface of a tube wall, and is useful as a thermal decomposition reaction tube (ethylene cracking tube) for an ethylene production plant. It relates to a replacement tube.

[0002]

2. Description of the Related Art In a reaction tube of a pyrolysis furnace for producing ethylene,
Hydrocarbons (naphtha, natural gas, ethane, etc.) are supplied as a mixed fluid with water vapor, and are heated to the reaction temperature range by heat supply from the outside of the pipe while flowing through the pipe at high speed.
An olefin such as ethylene or propylene is obtained as a thermal decomposition reaction product. In the thermal decomposition operation, it is required to efficiently transfer heat to a fluid flowing at a high speed in a pipe, and to quickly heat and raise the temperature to a predetermined reaction temperature range.

As a countermeasure, it has been proposed to use a tube having a small diameter, and to use a tube obtained by processing the inner surface of a tube (1) into an uneven shape (6) as shown in FIG. (JP-A-58-173022, JP-A-1-127896)
No.). The former attempts to increase the heating rate of the fluid in the pipe as an effect of increasing the specific surface area of the pipe wall as the pipe diameter is reduced.However, since the reduced pipe diameter reduces the ethylene production capacity, In order to compensate for this, it is necessary to greatly increase the number of reactor tubes installed in the furnace, which inevitably complicates operation management. In the latter case, the surface area of the pipe wall can be increased while maintaining a relatively large pipe internal volume, but plastic processing (extrusion processing, etc.) for forming the pipe internal wall surface into a corrugated (6) shape is also restricted. It is difficult to expect a remarkable improvement effect of the heat transfer performance by only the wave shape effect.
As a device for improving the heat transfer performance of the tube while avoiding such difficulties, JP-A-6-109392 discloses forming a projection on the inner wall surface of the tube. This is because a helical projection is formed on the inner wall of the pipe as a stirring element for the pipe fluid, and the pipe fluid is quickly heated to the required temperature to the center of the pipe cross-section as a turbulent flow forming effect of the pipe fluid by the projection. It is to let. The effect of improving the heat transfer performance due to the formation of the projections is remarkable, and the length of the pipeline is significantly reduced,
It is possible to reduce the size of the device, simplify operation management, increase the feed speed of the fluid in the pipe, increase the production capacity, and the like.

[0004]

In the above-mentioned pyrolysis reaction in the reaction tube for ethylene production, a coking phenomenon in which solid carbon is deposited from the reaction system in the tube and adheres and deposits on the inner surface of the deposited solid carbon tube is known. Have been. Caulking is
This may cause a decrease in heat transfer performance to the fluid in the pipe.
The reaction tube [typical tube material is ASTM HP material, HK40
Material, JIS G 5122 SCH22, SCH24 and other high Ni-high Cr heat resistant alloy steels are used.] When solid carbon adheres to the inner wall surface, carbon diffuses (“carburized”) inside the pipe, Deterioration of the material (brittleness, reduction in strength, etc.) occurs. For this reason, in the actual operation, the furnace operation is periodically stopped, and the decoking operation for removing the attached solid carbon is repeatedly performed. The formation of the above-mentioned projections on the inner wall surface of the reaction tube makes it possible to dramatically increase the heat transfer performance, but on the other hand, promotes coking and carburization. The present invention suppresses and prevents such inconveniences and, while fully exhibiting the effect of improving the heat transfer efficiency by the protrusions on the inner wall surface of the pipe, heat exchange with inner protrusions to ensure efficient operation of the pyrolysis furnace. It is intended to provide service pipes.

[0005]

According to the heat exchange tube of the present invention, a protrusion made of any one of the following heat-resistant alloys A to D is formed on the inner wall surface of the tube as a stirring member for the fluid in the tube. It is characterized by having. Alloy AC: 0.02 to 0.6%, Si: 4.0% or less, Mn: 5.0% or less, Cr: 40.0 to 52.0
%, With the balance substantially consisting of Ni (Ni may be replaced by 20% or less of Co). Alloy B Alloy A: 4.0% or less, W: 1
0.0% or less, Ca: 0.5% or less, Hf: 1.0% or less, Y: 1.0% or less. Alloy, Alloy C Nb: 4.0% or less, Mo:
5.0% or less, Ti: 1.0% or less, Zr: 1.0% or less, rare earth element: 0.5% or less, B: 0.5% or less Heat-resistant alloy having a composition to which an element is added, Alloy D In the above alloy A, Al: 4.0% or less, W: 1
One or more elements selected from the group consisting of 0.0% or less, Ca: 0.5% or less, Hf: 1.0% or less, Y: 1.0% or less, and Nb: 4.0% Hereinafter, Mo: 5.0
% Or less, Ti: 1.0% or less, Zr: 1.0% or less, rare earth element: 0.5% or less, B: one or more elements selected from the group of 0.5% or less are added. Alloy having the specified composition.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The projections extend continuously or intermittently in various shapes and distribution patterns, for example, in a direction perpendicular to, parallel to, or inclined with the tube axis, or in a regular or random manner. It is formed in the form of a dotted pattern. The protrusions are formed on the underlay layer having a wider shape than the protrusions, if desired. The underlay layer is preferably formed by applying the above heat-resistant alloys A to D. The underlay layer and the projection may be a combination of the same material type (combination of alloys A, a combination of alloys B, etc.) or a combination of different material types (for example, a combination of alloy A and alloy B). The protrusions formed by applying the above heat-resistant alloy are excellent in coking resistance and carburization resistance, and also in a reaction tube for ethylene production,
Deterioration and damage due to caulking and carburizing hardly occur, and the function of the projection is stably maintained. Further, in the case where an underlay layer wider than the protrusion is provided and the protrusion is laminated thereon, the effect of preventing carburization of the protrusion and the vicinity thereof in the caulking and the base material pipe is enhanced as a laminated shape effect. The protrusions and the underlay layer can be efficiently formed as a bead overlay layer by, for example, plasma powder welding.

The reasons for limiting the components of the heat-resistant alloy used for forming the protrusions and the underlying layer are as follows (% indicating the content is% by weight). C: 0.02 to 0.6% C has an effect of increasing the high-temperature strength. The lower limit is set to 0.02% because it is necessary to obtain strength enough to withstand use in high temperature applications (about 1000 ° C. or higher) such as a reaction tube for ethylene production. The effect increases with the increase, but 0.6%
If it exceeds, the ductility of the alloy deteriorates, so this is made the upper limit.

Si: 4.0% or less Si is an element effective for improving carburization resistance and coking resistance. However, if added in a large amount, the crack susceptibility of the alloy increases, and if it exceeds 4%, the effect cannot be ignored. For this reason, it is set to 4.0% or less. Preferably,
1.5-2.5%.

Mn: 5.0% or less Mn is a desulfurizing element. By fixing S, which is an impurity, to MnS and rendering it harmless, it is effective in preventing high-temperature cracking in welding of pipe materials. The content for obtaining this effect is sufficient up to 5.0%. Preferably, it is 2.0% or less.

Cr: 40.0 to 52.0% Cr is an element necessary for enhancing high-temperature strength (high-temperature creep characteristics), oxidation resistance, carburization resistance, and coking resistance in a high-temperature region. is there. In order to obtain these effects, the content needs to be 40.0% or more. The effect increases as the amount increases, but if it exceeds 52.0%, the effect is almost saturated, so this is set as the upper limit.

N: not more than 0.3% N is inevitably mixed in the alloy as an impurity, but if the amount exceeds 0.3%, the alloy becomes hard and brittle, so that N is exceeded. must not. More preferably, 0.
03% or less.

The protrusions and the underlaying layer may be formed, if desired, together with the above-mentioned elements, in Al: 4.0% or less, W: 10% or less, C:
a: 0.5% or less, Hf: 1.0% or less, Y: 1.0%
One or more elements selected from the following group (M ₁
Element), Nb: 4.0% or less, M
o: 5.0% or less, Ti: 1.0% or less, Zr: 1.0
% Or less, rare earth element: 0.5% or less, B: heat-resistant alloy containing _one or more elements (M ₂ elements) selected from the group of 0.5% or less, or M ₁ element and M ₂ It is formed by applying a heat-resistant alloy containing elements in a complex manner.

Al: 4.0% or less Al is an element that has a remarkable effect on enhancing carburization resistance, coking resistance, oxidation resistance and the like. However, if added in a large amount, the cracking sensitivity of the alloy is increased, and welding cracks are likely to occur. Preferably, 0.5-2.
5%.

W: 10.0% or less W has an effect of improving carburization resistance. It also contributes to improvement in high-temperature strength. However, if the amount exceeds 10.0%, the ductility of the alloy is reduced, so the upper limit is 10%. Preferably, it is 0.5 to 6.0%.

Ca: 0.5% or less Ca is effective in improving carburization resistance. The reason why the upper limit is set to 0.5% is that if it exceeds this, the toughness of the alloy is reduced.

Hf: 1.0% or less Hf is an element that enhances carburization resistance. The reason why the upper limit is set to 1.0% is that if it exceeds this, the ductility of the alloy will be reduced.

Y: 1.0% or less Hf is an element that enhances carburization resistance. However, if added in a large amount, the toughness of the alloy is reduced.
The following is assumed.

Nb: 4.0% or less Nb combines with C to form NbC to enhance high-temperature strength. However, if it exceeds 4.0%, the high-temperature strength is reduced due to the coarsening of the NbC carbide to be formed and the decrease in the amount of C in the alloy. Preferably, it is 0.5 to 2.0%.

Mo: 5.0% or less Mo is a high-temperature strength improving element. However, a large amount impairs the toughness of the alloy, so that it is added within a range of 5.0% or less. Preferably, it is 0.3 to 1.5%.

Ti: 1.0% or less Ti has an effect of improving high-temperature strength. If it exceeds 1.0%, the ductility and strength of the alloy will be reduced. Preferably, it is 0.05 to 0.2%.

Zr: 1.0% or less Zr is effective in improving high-temperature strength. However, the addition of a large amount impairs the ductility and strength of the alloy. Preferably, it is 0.05 to 0.2%.

Rare earth elements: 0.5% or less Rare earth elements (La, Ce, Pr, Nd, etc.) are elements that increase the high-temperature strength. If added in a large amount, the toughness of the alloy is reduced, so the content is limited to 0.5%.

B: 0.5% or less B is a high-temperature strength improving element. When added in a large amount exceeding 0.5%, the toughness of the alloy is deteriorated.
It is added within the following range.

Ni: balance component Ni is a basic component element of the present alloy, and maintains a stable structure in a high-temperature use environment such as a reaction tube for ethylene production, and provides oxidation resistance and carburization resistance. Note that Ni
Can be partially replaced by Co (the total amount of Ni and Co is equal to the content of Ni alone). However,
If the Co content exceeds 20%, the strength of the alloy is reduced, so the content is set to 20% or less.

As the material of the metal tube on which the projections are formed, various alloys having required heat resistance properties, including various known alloys depending on the use and use conditions of the tube body, are applied. In a reaction tube for ethylene production, for example, SCH22 of JIS G5122 is used.
(0.4C-20Ni-25Cr), SCH23 (0.4C-20Ni-30Cr),
ASTM standard material HK40 material (0.4C-20Ni-25Cr), HP
(0.5C-35Ni-25Cr) or 0.5C-45Ni-30Cr-based material,
High-Ni-high-Cr alloy steels such as 0.5C-35Ni-25Cr-based materials are exemplified. Further, the heat-resistant alloy, which is a projection and its underlying layer forming alloy, is used as a tube material, and the entire thickness of the tube is formed of the alloy, or the tube has a two-layer structure of an outer layer and an inner layer,
A tube formed by applying the conventional heat-resistant alloy to the outer layer and the heat-resistant alloy to the inner layer is also preferably used.

[Evaluation of carburization resistance and coking resistance]
The carburization resistance and the coking resistance of the projection / underlay layer forming alloy of the present invention are shown below in comparison with conventional typical heat-resistant alloys.

[Table 1] (1) Test material (element content is% by weight) S1 (Invention example): C: 0.3, Si: 2.0, Mn: 0.9, Cr: 44.0, Ni: 4
8.0 S2 (Invention example): C: 0.3, Si: 2.1, Mn: 0.8, Cr: 44.0, Al: 1.
0, Ni: 48.0 S3 (Invention example): C: 0.3, Si: 2.2, Mn: 0.9, Cr: 44.3, Al: 1.
0, Nb: 1.5, Ni: 48.0 S4 (comparative example): C: 0.45, Si: 1.7, Mn: 0.9, Ni: 35.0, Cr: 2
5.0, Nb: 1.3, W: 1.0, Mo: 0.6, Fe: Bal S5 (comparative example): C: 0.45, Si: 1.7, Mn: 1.0, Ni: 35.0, Cr: 2
5.0, Nb: 1.0, Ti: 0.3 Fe: Bal

(2) Carburizing test conditions A solid carburizing agent was brought into contact with the surface of the test piece, heated to 850 ° C., heated to 1150 ° C. from the same temperature for 30 hours, and kept at that temperature for 18 hours. Cool to room temperature. This temperature increase / decrease is defined as one cycle, and is repeated 17 times. After the test, 0.
Chips were collected at intervals of 5 mm, the carbon content was measured by wet analysis, and the total amount of carbon increased by carburization (ΔC
%). Specimen size: rectangular plate (width 30, length 70, thickness 10,
mm) Carburizing agent: Dufrit KG 30

(3) Caulking test conditions As shown in FIG. 9, a test piece (TP) is placed in a space inside the pipe (P) via a test piece holder (H), and a butane-propane mixed gas is supplied. Ar gas is supplied as a carrier from one end (P ₁ ) of the tube, and a fluid in the tube is heated by a heater (K) provided on the outer wall of the tube to cause a thermal decomposition reaction. From the other end side (P ₂ ). After the test, the amount of solid carbon deposited on the surface of the test piece (mg / cm ² ) is measured.

[0029]

[Table 2] Carburizing C increase (ΔC%) Caulking amount (mg / cm ² ) S1 (Invention example) 3.9 0.31 S2 (Invention example) 2.0 0.15 S3 (Invention example) 2.20 .16 S4 (Comparative Example) 20.0 1.54 S5 (Comparative Example) 19.4

Comparative Examples S4 and S5 subjected to the above carburizing and coking tests are typical heat-resistant alloys conventionally used as reaction tube materials for ethylene production, and the heat-resistant alloys S1, S2, and S3 of the present invention are Compared with the conventional material, the carburization resistance and the coking resistance are remarkably excellent. By using the heat-resistant alloy of the present invention as a material for forming a projection (and an underlay layer) for a reaction tube for ethylene production, the reaction in the tube is improved. It is possible to reduce and alleviate the deposition (caulking) and carburization of solid carbon precipitated from the system, and to effectively prevent and prevent damage and material deterioration of the projections and the base material pipe.

Next, the shape and distribution of the protrusions and the lower layer formed on the inner wall surface of the metal tube will be described. FIG. 1 schematically shows the cross-sectional shape of the projection (2). In the drawing, an example is shown in which an underlay layer (3) is provided, and a protrusion (2) is formed thereon. As shown, the protrusion (2)
When the lamination is formed on the wider underlayer (3), the projections (2) may be formed by using the reaction tube for ethylene production.
The caulking of the surface of the tube near the front, especially the front and rear sides of the protrusion (upstream and downstream of the fluid in the pipe) (the front and rear parts of the projection are likely to cause stagnation of the fluid in the pipe and cause caulking easily) ) And accompanying carburization can be effectively suppressed and prevented by the underlaying layer.

FIGS. 2 to 9 show examples of the distribution pattern of the protrusion (2). FIG. 2 shows a projection (2) that loops around the inner wall surface (1 ₁ ) of the pipe in a direction perpendicular to the pipe axis (x).
Are repeated at appropriate intervals (Da) in the tube axis direction. FIG. 3 shows an example in which the projection (2) is formed as a spiral projection extending along the inner wall surface (1 ₁ ) of the tube at an inclination angle (θ) with respect to the tube axis. In the figure, one spiral projection (2) is formed, but the number of spiral threads is arbitrary, and the interval (Db) between adjacent screw projections is increased or decreased by increasing or decreasing the number of spiral threads.
Can be arbitrarily increased or decreased. Further, a discontinuous helical shape (for example, helical protrusions having a length that makes one round on the inner wall surface of the pipe may be repeated at appropriate intervals in the pipe axis direction) may be used. FIG. 4 shows an example in which the projection (2) is a linear projection in a direction parallel to the tube axis and formed at appropriate intervals (Dc) in the circumferential direction. FIG. 5 shows an example in which the projection (2) extending in the tube axis (x) direction of FIG. 4 is formed in a wavy meandering shape. The projection (2) orthogonal to the tube axis in FIG. 2 and the spiral projection (2) in FIG. 3 also have a corrugated shape as desired.

Each of the projections (2) shown in FIGS. 2 to 5 has a streak shape extending continuously along the inner wall surface (1 ₁ ) of the tube. However, the shape may be intermittent. FIG. 6 is a cross-section (2
₂₎ an example in which the intermittent projections (2 ₁₎ provided, Figure 7 for spiral projection of FIG. 3, FIG. 8 for parallel projections to the tube axis of FIG. 4, and FIG. 9 5 shows an example in which break points (2 ₂ ) are provided for the wavy protrusions in the tube axis direction in FIG. 5 to form intermittent protrusions (2 ₁ ). The projections are given various shapes and distribution forms other than the above, for example, a distribution pattern forming a regular or random dot pattern.

The shapes and sizes of the protrusions and the underlay layer formed on the inner wall surface of the pipe (projection height 2h, protrusion width 2w, lower underlayer layer thickness 3t and its width 3w in FIG. 1), and FIGS. The shape of the projection shown in FIG. 8 is appropriately set according to the purpose of the pipe, the use conditions, the size of the pipe, and the like. For example, for the production of ethylene the reaction tube: The shape and size of the projection-avaiable layer in the tube wall when subjected to the application of the (inner diameter of about 30 to 150 mm), the projection height 2 _h: about 2 to 15 mm, the projections width 2 _w: about 3~10m
m, the thickness of the lower layer 3 _t : about 1 to 3 mm, and the lower layer width 3 _w : about 2 _w +15 to 2 _w +25 mm. The protrusion, the protrusion interval when formed as a ring-shaped projection extending in the circumferential direction as the Figure 2 (D _a) is about 20-4
3, the inclination angle (θ) of the spiral projection of FIG. 3 is about 15 ° or more, the spiral pitch (D _b ) is about 20 to 400 mm, and the interval (D _c) of the projection parallel to the tube axis as shown in FIG. ) Is about 50mm
The following may be used. Further, in the case of intermittent form as 6-8, the intermittent projections (2 ₁₎ distance between (2 ₂₎ is about 1 to 50 mm, the length of the intermittent projections (2 ₁₎ from about 5 to A shaping mode of 100 mm can be adopted.

The projecting area in the pipe is used for the purpose and use of the pipe.
It is set appropriately according to conditions and the like. The above reaction for ethylene production
In a pipe, for example, as shown in FIG.
(A ₁), Central area (A_Two) Or exit area
(A_Three), Or their multiple areas, or from the entrance
It is formed over the entire area up to the exit side.

The projection (2) and the lower build-up layer (3) can be formed on the inner wall surface of the pipe by, for example, applying a welding method, and can be formed as a build-up layer of a weld bead. In particular, when the plasma powder welding (PTA welding) method is applied, the penetration into the base metal tube can be suppressed to a shallow level, the shape and size of the projections can be easily controlled, and the small-diameter tube ( For example, inner diameter 30 ~
In the case of (50 mm), it is excellent in torch operability, feedability of welding material, arc stability, etc., and can easily and efficiently perform projection formation on the inner wall surface of the pipe.

FIG. 11 shows an example of forming protrusions by plasma powder welding. The tube (1) is horizontally supported by a rotation drive device (not shown) so as to perform a rotational movement at a required rotational speed about the tube axis (x). (4
0) is a welding torch, (42) is a welding torch support rod, and the welding torch (40) is fixed to the support rod (42) via an arm (41). (43) is a powder supply pipe for supplying a welding material (powder) to the welding torch (40). The welding torch support rod (42) is oriented parallel to the tube axis, and is driven in the tube axis direction (arrow) by a driving device (not shown).
Are arranged in a pipe so as to be movable. In the welding apparatus thus configured, the welding torch (41) forms a build-up bead on the inner wall surface (1 ₁ ) of the pipe ( ₁ ) while rotating around the pipe axis of the pipe (1). The helical projection shown in FIG. 3 is formed by moving the support rod (42) along the tube axis direction. In the figure, since two welding torches (40) are installed on the welding torch support rod (42), two spiral projections are formed at the same time.
The number of installation bases of the welding torch (40) can be arbitrarily increased or decreased.

Further, when the welding torch support rod (42) is stopped and the build-up bead is formed while rotating the pipe (1), a ring-shaped projection as shown in FIG. 2 is formed. In the case where the build-up bead is formed while moving the welding torch (40) in the pipe axis direction in a state where the rotation of the pipe (1) is stopped, a projection extending on the pipe axis as shown in FIG. can get. Further, by causing the welding torch (40) to perform a swinging (swinging) motion in the welding operation,
As shown in FIG. 5, projections having a wavy shape are formed, and the build-up bead formation is performed intermittently.
A projection having an intermittent pattern as shown in FIG. 9 can be formed. Protrusion (2) with lower layer (3) on inner wall of pipe
When the lamination is formed, a welding torch for forming the underlay layer (3) and a welding torch for forming the protrusion may be provided side by side, and the welding work of the underlay layer and the welding work of the protrusion may be performed in parallel. it can.

[0039]

According to the present invention, projections having excellent carburization resistance and coking resistance can be formed on the inner wall surface of the pipe, and the projections and the base metal pipe can be prevented from being caulked and carburized and the accompanying problems. It is possible to stably exhibit and maintain the function as a stirring member for the fluid in the pipe due to the formation of projections, and it has great industrial utility especially as a reaction tube for an ethylene production plant. It greatly enhances practical value.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view of a projection shape.

FIG. 2 is a sectional view in the axial direction of the tube showing an example of a shape of a projection on the inner wall surface of the tube.

FIG. 3 is a sectional view in the axial direction of the tube showing an example of a shape of a projection on the inner wall surface of the tube.

FIG. 4 is a sectional view in the axial direction of the tube showing an example of a shape of a projection on the inner wall surface of the tube.

FIG. 5 is a sectional view in the axial direction of the tube showing an example of a shape of a projection on the inner wall surface of the tube.

FIG. 6 is a sectional view in the axial direction of the tube showing an example of a shape of a projection on the inner wall surface of the tube.

FIG. 7 is a sectional view in the axial direction of the tube showing an example of the shape of the projection on the inner wall surface of the tube.

FIG. 8 is a sectional view in the axial direction of the tube showing an example of a shape of a projection on the inner wall surface of the tube.

FIG. 9 is a sectional view in the axial direction of the tube showing an example of a shape of a projection on the inner wall surface of the tube.

FIG. 10 is an explanatory sectional view showing a projection forming area on an inner wall surface of a pipe.

FIG. 11 is an explanatory view showing an example of forming and forming a projection (and an underlay layer) by welding.

FIG. 12 is an explanatory diagram of a caulking test procedure.

FIG. 13 is a radial cross-sectional view showing an example of the shape of a conventional pipe inner wall surface.

[Explanation of symbols]

1: tube 1 _1: Pipe wall 2: projections 2 _1: Intermittent projections 3: avaiable layer 40: welding torch 42: welding torch supporting rod 43: Welding (powder) supply pipe

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kaoru Hamada 1-1-1, Nakamiya Oike, Hirakata City, Osaka Prefecture Kubota Corporation Hirakata Factory (56) References JP-A-5-93240 (JP, A) JP Hei 6-109392 (JP, A) JP-A-63-31535 (JP, A) JP-A-63-11644 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 19 / 05 F28F 1/40 F28F 21/08 B21D 53/06

Claims (6)

(57) [Claims] 1. A stirrer for a fluid in a pipe, on the inner wall surface of the pipe, C: 0.02 to 0.6%, Si: 4.0% or less, Mn:
5.0% or less, Cr: 40.0 to 52.0%, N: 0.
3%, the remaining part substantially Ni (Ni 20% or less of Co
Welding bi consisting heat resistant alloy consisting of the may be) replaced with
A pyrolysis reaction tube for producing ethylene having an inner surface projection having excellent carburization resistance and coking resistance, characterized in that a projection serving as a hardfacing layer is formed. 2. On the inner wall surface of the pipe, as a stirring member for the fluid in the pipe, C: 0.02 to 0.6%, Si: 4.0% or less, Mn:
5.0% or less, Cr: 40.0 to 52.0%, N: 0.
3% or less, Al: 4.0% or less, W:
10.0% or less, Ca: 0.5% or less, Hf: 1.0%
Y: 1 to 2 selected from the group of 1.0% or less
Or more elements, the balance being substantially Ni (Ni is 20
% Of a heat-resistant alloy made of a heat-resistant alloy made of a heat-resistant alloy made of a heat-resistant alloy comprising: an inner protrusion having excellent carburization resistance and coking resistance. For thermal decomposition reaction tube. 3. An agitating member for the fluid in the pipe, on the inner wall surface of the pipe, C: 0.02 to 0.6%, Si: 4.0% or less, Mn:
5.0% or less, Cr: 40.0 to 52.0%, N: 0.
Nb: 4.0% or less, M
o: 5.0% or less, Ti: 1.0% or less, Zr: 1.0
% Or less, rare earth element: 0.5% or less, B: one or more elements selected from the group of 0.5% or less,
The remaining portion is formed with a protrusion serving as a weld bead overlay layer made of a heat-resistant alloy substantially composed of Ni (Ni may be substituted with 20% or less of Co), and is resistant to carburization and coking. Pyrolysis reaction tube for ethylene production with excellent inner surface protrusion. 4. An agitating member for the fluid in the pipe, C: 0.02 to 0.6%, Si: 4.0% or less, Mn:
5.0% or less, Cr: 40.0 to 52.0%, N: 0.
3% or less, Al: 4.0% or less, W:
10.0% or less, Ca: 0.5% or less, Hf: 1.0%
Y: 1 to 2 selected from the group of 1.0% or less
Or more elements, Nb: 4.0% or less, Mo: 5.
0% or less, Ti: 1.0% or less, Zr: 1.0% or less,
Rare earth element: 0.5% or less, B: One or more elements selected from the group of 0.5% or less, and the balance is substantially Ni (Ni is replaced by 20% or less of Co). A pyrolysis reaction tube for producing ethylene having inner projections having excellent carburization resistance and coking resistance, wherein projections are formed as weld bead overlayers made of a heat-resistant alloy made of a heat-resistant alloy comprising: 5. A method according to claim 5, wherein said projection has an underlayer on the inner wall surface.
Weld bead overlay layer made of a heat-resistant alloy of the same material as the protrusion
Is formed so as to be wider than the width of the protrusion, and the protrusion is laminated on each lower embossing layer. The method according to any one of claims 1 to 4, wherein Pyrolysis reaction tube for ethylene production with inner projections with excellent carburization resistance and coking resistance. 6. The projections extend continuously or intermittently on the inner wall surface of the pipe in a direction perpendicular to, parallel to, or inclined with the pipe axis, or have a distribution form dispersed in a scattered manner. The pyrolysis reaction tube for producing ethylene having an inner surface projection having excellent carburization resistance and coking resistance according to any one of claims 1 to 5, wherein the reaction tube is formed.