JPH09243284A - Heat exchanging pipe with internal surface projection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase heat transfer performance with respect to fluid in a pipe and prevent caulking accompanied by the forming of projections and carburizing of the projection as well as the tubular body of matrix by a method wherein a reaction pipe for manufacturing ethylene is provided with projections formed on the internal surface of the same. SOLUTION: Projections are formed of an alloy, containing one to two kinds or more of elements of C: 0.1-0.6%, Si: 4.0% or less, Mn: 5.0% or less, Ni: 30.0-50.0%, Cr: 20.0-50.0%, Al: 4.0% or less, one to two kinds or more of elements selected from the group of W, Ca, Hf, Y if desired and/or one to two kinds or more of elements selected from the group B of Nb, Mo, Ti, Zr, rare earth elements, and the balance is consisting of Fe substantially. The projections can be formed by padding of welding and a lower padding layer is provided, then, the projection is formed by laminating thereon if desired. The shape of the projections is provided with various continuous or discontinuous configurations.

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 the protrusions formed on the inner surface of the pipe wall, and is useful as a thermal decomposition reaction pipe (ethylene cracking tube) in an ethylene production plant, for example. Regarding replacement tubes.

[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 while flowing through the pipe at high speed, heat is supplied to the reaction temperature range from outside the pipe,
Olefin such as ethylene and propylene is obtained as a thermal decomposition reaction product. In the pyrolysis operation, it is required to efficiently perform heat transfer to the fluid flowing at a high speed in the tube and to quickly heat and raise the temperature to a predetermined reaction temperature range.

As a measure for this, it has been proposed to use a tubular body having a small diameter, and as shown in FIG. 13, a tubular body in which the inner surface of the tubular body (1) is processed into an uneven shape (6). (JP-A-58-173022, JP-A-1-127896
Issue). The former is intended to increase the heating rate of heating the fluid in the pipe as an effect of increasing the specific surface area of the pipe wall due to the reduction of the pipe diameter, but the ethylene production capacity decreases as the pipe diameter is reduced. However, in order to compensate for this, it is necessary to significantly increase the number of reaction 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 inner volume, but there is also a restriction of plastic working (extrusion processing, etc.) for forming the pipe inner wall surface in the corrugated shape (6). In many cases, it is difficult to expect a significant improvement effect of the heat transfer performance only by the wave shape effect.
JP-A-6-109392 discloses forming projections on the inner wall surface of the tube as a device for improving the heat transfer performance of the tube while avoiding such difficulties. As a stirring element for the fluid in the pipe, a protrusion such as a spiral is formed on the inner wall surface of the pipe, and the turbulence of the fluid in the pipe is formed by the protrusion, and the fluid in the pipe is quickly heated to the required temperature up to the center of the pipe cross section. It is what makes me. The effect of improving the heat transfer performance due to the formation of this protrusion is remarkable, and the length of the pipe line is significantly shortened.
It enables downsizing of equipment, simplification of operation management, increase of feed rate of fluid in pipe, increase of production capacity, etc.

[0004]

In the thermal decomposition reaction in the ethylene production reaction tube, there is known 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. Has been. Caulking
This causes a decrease in heat transfer performance for the fluid in the pipe.
Reaction tube [ASTM HP material, HK40
Material, JIS G 5122 SCH22, SCH24 and other high Ni-high Cr heat-resistant alloy steel is used], solid carbon adheres to the inner wall surface of the pipe, carbon diffuses ("carburizing") inside the pipe, and the pipe Material deterioration (brittleness, strength reduction, etc.) occurs. Therefore, in actual operation, the furnace operation is periodically stopped, and the decoking work for removing the adhered solid carbon is repeatedly performed. Forming the aforementioned protrusions on the inner wall surface of the reaction tube makes it possible to dramatically improve the heat transfer performance, but on the other hand, it is a factor that promotes coking and carburization. The present invention suppresses such problems and fully exerts the effect of improving the heat transfer efficiency by the projections on the inner wall surface of the pipe, and at the same time, heat exchange with internal projections for ensuring efficient operation of the pyrolysis furnace. It is intended to provide a pipe.

[0005]

In the heat exchange pipe with the inner surface protrusion 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 pipe as a stirring member for the fluid in the pipe. It is characterized by Alloy AC: 0.1 to 0.6%, Si: 4.0% or less,
Mn: 5.0% or less, Ni: 30.0 to 50.0% (N
i may replace 20% or less with Co), Cr: 2
0.0-50.0%, Al: 4.0% or less, N: 0.3
% Or less, the balance is a heat-resistant alloy consisting essentially of Fe, Alloy B In the above alloy A, W: 10% or less, Ca: 0.5
% Or less, Hf: 1.0% or less, Y: 1.0% or less, a heat-resistant alloy having a composition to which one or more elements selected from the group are added. Alloy C The above alloy A, 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, one or more kinds selected from the group A heat-resistant alloy having a composition to which elements are added, Alloy D In the above alloy A, W: 10% or less, Ca: 0.5
% Or less, Hf: 1.0% or less, Y: 1.0% or less, and one or more elements selected from the group, and 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: A heat-resistant alloy having a composition to which one or more elements selected from the group of 0.5% or less are added.

[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 orthogonal to the tube axis, in a direction parallel to the tube axis, or in a direction inclined, or in a regular or random manner. It is formed in the form of a dotted pattern. The projections are, if desired, laminated and formed on the underlaying layer having a shape wider than the projections. The underlayer is preferably formed by applying the above heat-resistant alloys A to D. The underlaying layer and the protrusion can be a combination of the same material type (a 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 projection formed by applying the above heat-resistant alloy has excellent caulking resistance and carburization resistance, and even in a reaction tube for ethylene production,
Maintains stable function of protrusions, which is unlikely to deteriorate or damage due to caulking and carburizing. Further, when the underlaying layer having a width wider than that of the projection is provided and the projection is laminated on the undercoat layer, the effect of stacking can enhance the effect of preventing caulking in the projection and the vicinity thereof and carburization of the base metal tube. The protrusion 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: 0.1 to 0.6% C has the effect of increasing high temperature strength. The lower limit of 0.1% is for high temperature applications such as reaction tubes for ethylene production (about 1
This is because it is necessary to obtain strength that can withstand use at temperatures above 000 ° C. The effect increases as the amount increases, but on the other hand, the ductility of the alloy deteriorates, so the upper limit is made 0.6%. Preferably, it is 0.4 to 0.5%.

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 alloy becomes more susceptible to cracking, and if it exceeds 4.0%, its effect cannot be ignored, so the content is made 4.0% or less. Preferably,
It is 1.5 to 2.5%.

Mn: 5.0% or less Mn is a desulfurizing element, and by making S, which is an impure component, fixed and harmless as MnS, it is effective in preventing hot cracking during welding of pipe materials. A content up to 5.0% is sufficient to obtain this effect.

Ni: 30.0-50.0% Ni is a basic constituent element of the heat resistant alloy. At least 30.0% is required to stably maintain the structure in a high-temperature use environment such as a reaction tube for ethylene production and to obtain oxidation resistance and carburization resistance. The effect is increased by increasing the amount, but if the amount exceeds 50.0%, the economy is impaired.
This is the upper limit. Note that Ni can be partially replaced with Co (the total amount of Ni and Co is equal to the content of Ni alone). However, in this case, Co
If the amount exceeds 20%, the strength will be reduced.
%.

Cr: 20.0 to 50.0% Cr is an element necessary for strengthening high temperature strength (high temperature creep property) and oxidation resistance, carburization resistance and coking resistance in a high temperature range. is there. To obtain these effects, it is necessary to be 20% or more. The effect increases with increasing amount, but if it exceeds 50.0%, the effect is almost saturated, so this is the upper limit. Preferably 20.0-4
0.0%.

Al: 4.0% or less Al is an element which is extremely effective in strengthening carburization resistance, coking resistance, oxidation resistance and the like. However, if a large amount is added, the crack susceptibility of the alloy is increased and weld cracking is likely to occur, so the content is made 4.0% or less. Preferably 0.5-2.
5%.

N: 0.3% or less N is inevitably mixed in the alloy as an impure component. However, if the amount exceeds 0.3%, the alloy becomes hard and brittle. must not. More preferably, 0.
It is at most 03%.

If desired, the protrusions and the undercoat layer may contain W: 10% or less, Ca: 0.5% or less, and H together with the above elements.
f: heat-resistant alloy containing _one or more elements (M ₁ element) selected from the group of 1.0% or less and Y: 1.0% or less, Nb: 4.0% or less, Mo: 5 0.0% or less, T
i: 1.0% or less, Zr: 1.0% or less, rare earth element:
Heat-resistant alloy containing _one or more elements (M ₂ element) selected from the group of 0.5% or less and B: 0.5% or less, or containing M ₁ element and M ₂ element in combination It is formed by applying a heat resistant alloy.

W: 10.0% or less W has an effect of enhancing carburization resistance. It also contributes to the improvement of high temperature strength. However, if the amount exceeds 10.0%, the ductility and toughness of the alloy is deteriorated, so 10.0% is made the upper limit. Preferably, it is 0.5 to 6.0%.

Ca: 0.5% or less Ca is effective in improving carburization resistance. The upper limit of 0.5% is that if it exceeds this range, the ductility of the alloy is reduced.

Hf: 1.0% or less Hf is an element that enhances carburization resistance. The upper limit of 1.0% is that if it exceeds this range, the ductility and toughness of the alloy decreases.

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

Nb: 4.0% or less Nb is combined with C to form NbC to enhance high temperature strength. However, when it exceeds 4.0%, the high temperature strength is lowered due to the coarsening of the NbC carbide to be formed and the decrease in the amount of C in the alloy, so this is made the upper limit. It is preferably 0.5 to 2.0%.

Mo: 5.0% or less Mo is a high temperature strength improving element. However, since a large amount of addition impairs the ductility of the alloy, it is added within the 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 decrease, so this is the upper limit. Preferably, it is 0.05 to 0.2%.

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

Rare earth element: 0.5% or less Rare earth elements (La, Ce, Pr, Nd, etc.) are elements that enhance high temperature strength. If added in a large amount, the ductility and toughness of the alloy will be deteriorated, so the content is limited to 0.5%.

B: 0.5% or less B is a high temperature strength improving element. If added in excess of 0.5%, the toughness of the alloy will deteriorate, so 0.5%
It is added within the following range.

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

[Evaluation of carburization resistance and coking resistance]
The carburization resistance and 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 wt%) S1 (invention example): C: 0.5, Si: 1.7, Mn: 1.0, Ni: 43.0, Cr: 3
1.0, Nb: 1.0, Ti: 0.3, Al: 2.0, Fe: Bal S2 (Invention Example): C: 0.45, Si: 1.7, Mn: 1.0, Ni: 35.0, Cr:
25.0, Nb: 1.3, W: 1.0, Al: 2.0, Fe: Bal S3 (Comparative example): C: 0.45, Si: 1.7, Mn: 1.0, Ni: 35.0, Cr:
25.0, Nb: 1.3, W: 1.0, Mo: 0.6, Fe: Bal S4 (Comparative example): C: 0.45, Si: 1.7, Mn: 1.0, Ni: 35.0, Cr:
25.0, 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 and heated to 850 ° C., heated to 1150 ° C., which required 30 hours from the same temperature, and kept at that temperature for 18 hours. , Cool to room temperature. This cycle of raising and lowering the temperature is repeated 17 times. After the test, from the surface of the test piece to a depth position of 5 mm, 0.
Chips were collected at intervals of 5 mm, the carbon content was measured by wet analysis, and the total amount of carbon (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. 12, the test piece (TP) is placed in the space inside the tube body (P) through the test piece holder (H), and the butane-
Propane mixed gas is fed from one end (P ₁ ) of the pipe body using Ar gas as a carrier, and the pipe fluid is heated by a heater (K) provided on the outer wall of the pipe to cause a thermal decomposition reaction.
The reaction product is led out from the other end side (P ₂ ) of the conduit. After the test, the amount of solid carbon deposited (mg / cm ² ) on the surface of the test piece is measured.

[0029]

[Table 2] Increase in carburizing C (ΔC%) Amount of coking (mg / cm ² ) S1 (Invention example) 5.0 0.40 S2 (Invention example) 14.3 1.14 S3 (Comparative example) 20.0 1 .54 S4 (Comparative example) 19.4 1.60

The alloys S3 and S4 of the comparative examples used in the above carburizing and coking tests are typical heat-resistant alloys conventionally used as reaction tube materials for ethylene production,
The heat-resistant alloys S1 and S2 of the present invention are superior in carburization resistance and coking resistance to conventional materials, and the heat-resistant alloy of the present invention is used as a material for forming protrusions (and underlayer) on a reaction tube for ethylene production. By doing so, it becomes possible to reduce and alleviate the deposition (coking) and carburization of the solid carbon that precipitates from the reaction system in the tube, and effectively prevent and prevent the damage and material deterioration of the projection and the base material tube.

Next, the shape and distribution of the protrusions and the underlay layer formed on the inner wall surface of the metal tube will be described. FIG. 1 schematically shows the cross-sectional shape of the protrusion (2). The figure shows an example in which the lower layer (3) is provided and the protrusions (2) are laminated on the lower layer. As shown, the protrusion (2)
When it is laminated on the underlaying layer (3) having a wider width than that, the protrusion (2) is used in the use of the reaction tube for ethylene production.
Near the edge of the protrusion, especially on the front and rear sides of the protrusion (upstream and downstream of the fluid in the pipe), the caulking of the surface of the pipe (the front and rear parts of the protrusion is likely to cause stagnation of the fluid in the pipe. It is possible to effectively suppress and prevent carburization) and the accompanying carburization by the lower layer.

2 to 9 show examples of distribution patterns of the protrusions (2). FIG. 2 shows a protrusion (2) that circulates in a ring shape on the inner wall surface (1 ₁ ) of the pipe in a direction orthogonal to the pipe axis (x).
Is an example in which is repeatedly formed at appropriate intervals (Da) in the tube axis direction. FIG. 3 shows an example in which the protrusion (2) is formed as a spiral protrusion extending along the pipe inner wall surface (1 ₁ ) at an inclination angle (θ) with respect to the pipe axis. In the figure, one spiral protrusion (2) is formed, but the number of spiral protrusions is arbitrary, and the spacing (Db) between adjacent screw protrusions increases or decreases as the number of spiral protrusions increases or decreases.
Can be increased or decreased as desired. It is also possible to have a discontinuous spiral shape (for example, a spiral projection having a length that goes around the inner wall surface of the pipe is repeated at appropriate intervals in the axial direction of the pipe). FIG. 4 shows an example in which the protrusions (2) are linear protrusions parallel to the tube axis and are formed at appropriate intervals (Dc) in the circumferential direction. FIG. 5 shows an example in which the protrusion (2) extending in the tube axis (x) direction of FIG. 4 is formed in a wavy meandering shape. The projection (2) in the direction orthogonal to the tube axis in FIG. 2 and the spiral projection (2) in FIG. 3 are also given a corrugated shape if desired.

The projections (2) shown in FIGS. 2 to 5 each have a striped shape continuously extending along the inner wall surface (1 ₁ ) of the tube, but instead of the continuous shape. The shape can be intermittent. FIG. 6 shows the break point (2
₂ ) is provided as an intermittent projection (2 ₁ ). FIG. 7 shows the spiral projection of FIG. 3, FIG. 8 shows the projection parallel to the tube axis of FIG. 4, and FIG. 5 shows an example in which break points (2 ₂ ) are provided for the wavy projections in the tube axis direction of FIG. 5 to form the intermittent projections (2 ₁ ). In addition to this, the projections are provided with various shapes and distribution forms, for example, a distribution pattern forming a regular or random dotted pattern.

Shapes and sizes of protrusions / underlay layer formed on the inner wall surface of the pipe (protrusion height 2h, protrusion width 2w, underlay layer thickness 3t and its width 3w in FIG. 1), and FIGS. The shape of the protrusion shown in FIG. 8 is appropriately set depending on the use of the pipe, the use conditions, the size of the pipe body, and the like. For example, regarding the shape and size of the projection and underlay layer on the inner wall surface of the tube when it is used for an ethylene production reaction tube (inner diameter: about 30 to 150 mm), the projection height 2 _h : about 2 to 15 mm, the projection Width 2 _w : approx. 3-10 m
m, the layer thickness _{3t of} the lower layer: about 1 to 3 mm, and the lower layer width 3 _w : about 2 _w +15 to 2 _w +25 mm. When the protrusions are formed as ring-shaped protrusions extending in the circumferential direction as shown in FIG. 2, the protrusion interval (D _a ) is about 20 to 4.
00 mm, 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 spacing (D _c) of the projections parallel to the tube axis as shown in FIG. ) Is about 50 mm
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 It is possible to adopt a form of setting to 100 mm.

The area where the projection is formed in the pipe is used and used for the pipe.
It is set as appropriate according to the conditions. Reaction for ethylene production
In the case of a pipe, for example, as shown in FIG.
(A ₁), Central area (A_Two), Or output area
(A_Three), Or multiple areas of them, or from the incoming side
It is formed over the entire area from the exit side.

The projections (2) and the lower layer (3) may be formed on the inner wall surface of the pipe by applying a welding method, for example, to form a weld bead build-up layer. In particular, when the plasma powder welding (PTA welding) method is applied, it is possible to suppress the penetration into the base metal pipe body shallowly, and it is easy to control the shape and size of the protrusions, and a pipe body with a small diameter ( For example, inner diameter 30 ~
Even in the case of 50 mm), the torch operability, the welding material feeding property, the arc stability, etc. are excellent, and the projection forming work on the inner wall surface of the pipe can be easily and efficiently performed.

FIG. 11 shows an example of construction for forming protrusions by plasma powder welding. The tubular body (1) is horizontally supported by a rotary drive device (not shown) so as to perform a rotational movement at a required rotational speed about the tubular 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 the welding material (powder) to the welding torch (40). The welding torch support rod (42) is oriented parallel to the tube axis, and is driven by a drive device (not shown) in the tube axis direction (arrow).
It is arranged in the tube so that it can move. In the welding apparatus configured as described above, the welding torch (41) is used to form a build-up bead on the inner wall surface (1 ₁ ) of the pipe under the rotational movement of the pipe body (1) about the pipe axis, and the welding torch is formed. By moving the support rod (42) along the tube axis direction, the spiral projection shown in FIG. 3 is formed. In the figure, since two welding torches (40) are installed on the welding torch support rod (42), two spiral projections are simultaneously formed.
The number of installed bases of the welding torch (40) can be arbitrarily increased or decreased.

Further, when the weld bead support rod (42) is stopped from running and the build-up bead is formed while rotating the tubular body (1), a ring-shaped projection as shown in FIG. 2 is formed. When forming a weld bead while moving the welding torch (40) in the tube axis direction with the rotary motion of the tube body (1) stopped, a projection extending on the tube axis as shown in FIG. can get. Furthermore, in the welding process, by causing the welding torch (40) to perform a swing (swing) motion,
6A to 6C are formed by forming protrusions having a corrugated shape as shown in FIG. 5 and intermittently forming a build-up bead.
A protrusion having an intermittent pattern as shown in FIG. 9 can be formed. Protrusion (2) by providing a lower layer (3) on the inner wall surface of the pipe
In the case of stacking, the welding torch for forming the lower layer (3) and the welding torch for forming the protrusion are provided side by side, and the welding work of the lower layer and the welding work of the protrusion may be performed in parallel. it can.

[0039]

According to the present invention, it is possible to form a protrusion having excellent carburization resistance and coking resistance on the inner wall surface of the pipe, and prevent the caulking and carburization of the protrusion and the base material pipe body and the problems associated therewith. It becomes possible to stably maintain and maintain the function as a stirring member for the fluid in the pipe by forming the protrusions, and it has great industrial utility as a reaction pipe for an ethylene production plant. It greatly enhances the practical value.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view of a protrusion shape.

FIG. 2 is a cross-sectional view in the tube axis direction showing an example of a shape of protrusions on the inner wall surface of the tube.

FIG. 3 is a cross-sectional view in the axial direction of the tube showing an example of the form of protrusions on the inner wall surface of the tube.

FIG. 4 is a cross-sectional view in the tube axis direction showing an example of a shape of protrusions on the inner wall surface of the tube.

FIG. 5 is a cross-sectional view in the tube axis direction showing an example of the shape of the protrusions on the inner wall surface of the tube.

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

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

FIG. 8 is a cross-sectional view in the axial direction of the tube showing an example of how the projections on the inner wall surface of the tube are formed.

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

FIG. 10 is a cross-sectional explanatory view showing a projection-formed region on the inner wall surface of the pipe.

FIG. 11 is an explanatory view showing an example of forming the protrusions (and the lower 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 (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location F28F 21/08 F28F 21/08 F (72) Inventor Kaoru Hamada 1 chome, Oike Nakamiya, Hirakata, Osaka No. 1 Stock company Kubota Hirakata Factory

Claims (4)

[Claims] 1. C: 0.1 to 0.6%, Si: 4.0% or less, M
n: 5.0% or less, Ni: 30.0 to 50.0% (Ni
May replace 20% or less with Co), Cr: 2
0.0-50.0%, Al: 4.0% or less, N: 0.3
% Or less, W: 0 to 10% or less, Ca: 0 to 0.
5% or less, Hf: 0 to 1.0% or less, Y: 0 to 1.0%
One or more elements selected from the following groups, or / and Nb: 0 to 4.0% or less, Mo: 0 to 5.0
% Or less, Ti: 0 to 1.0% or less, Zr: 0 to 1.0%
Below, rare earth elements: 0 to 0.5% or less, B: 0 to 0.5
% Or less, one or more elements selected from the group below, and the balance being protrusions made of a heat-resistant alloy that is substantially Fe. Inner protrusions having excellent carburization resistance and caulking resistance. With heat exchange tube. 2. The underlayer of the heat-resistant alloy according to claim 1 is formed on the inner wall surface of the pipe so as to be wider than the width of the projection, and the projection is laminated on the underlayer. A heat exchange tube with an inner surface protrusion having excellent carburization resistance and coking resistance according to claim 1. 3. The projections are formed on the inner wall surface of the pipe, extending continuously or intermittently in the direction orthogonal to the pipe axis, in the direction parallel to the pipe axis, or in the direction inclined, or in the form of a distribution dispersed in a scattered manner. The heat exchange tube with an inner surface protrusion having excellent carburization resistance and coking resistance according to claim 1 or 2. 4. The heat exchange tube with an inner surface protrusion having excellent carburization resistance and coking resistance according to claim 1, wherein the heat exchange tube is an ethylene production reaction tube.