JP6335247B2 - Reaction tube with internal protrusion - Google Patents

Description

  The present invention relates to a reaction tube having protrusions as stirring members on the inner surface, and more specifically, to a reaction tube with inner protrusions in which the protrusions are formed by overlay welding.

  Olefins such as ethylene and propylene are obtained by circulating a raw material fluid of hydrocarbon gas (naphtha, natural gas, ethane, etc.) through a reaction tube heated from the outside, and heating the raw material fluid to a reaction temperature range to thermally decompose it. Generated.

  Since the reaction tube is exposed to a high-temperature atmosphere and is easily affected by oxidation, carburization, nitridation, etc. caused by the flowing gas, it is required to apply a material having excellent resistance to these. Therefore, the applicant has proposed a reaction tube in which an alumina barrier layer containing an Al oxide is formed on the inner surface of the tube body in Patent Document 1.

  By forming the alumina barrier layer on the inner surface of the tube body, excellent oxidation resistance, carburization resistance, nitridation resistance, etc. can be realized when used in a high temperature atmosphere.

  On the other hand, the reaction tube is required to improve heat transfer efficiency and reduce pressure loss. Therefore, the applicant has proposed a reaction tube in Patent Document 2 in which a spiral protrusion is formed as an agitating member on the inner surface of the tube body. 25Cr-Ni (SCH22), 25Cr-35Ni (SCH24), and Incoloy (trade name) are disclosed as materials for the spiral protrusions, and the protrusions are formed on the inner surface of the tube body by overlay welding.

WO2010 / 113830 publication JP 2008-249249 A

  By forming protrusions on the inner surface of the tube body, an improvement in heat transfer efficiency and a reduction in pressure loss are achieved. However, since the protrusion protrudes as compared with the inner surface of the tube main body, the gas hits stronger than the inner surface of the tube main body, and is easily affected by oxidation, carburization, nitriding, and the like. In addition, coke generated by alteration or decomposition of the hydrocarbon gas may adhere to the surface of the protrusion, leading to a decrease in heat transfer efficiency and pressure loss. Furthermore, the frequency of decoking work for removing the attached coke is increased, and there is a possibility that the operation efficiency is lowered.

  An object of the present invention is to provide a reaction tube with an inner surface protrusion capable of forming an alumina barrier layer containing Al oxide on a protrusion as a stirring member.

The reaction tube with an internal protrusion according to the present invention is
A reaction tube with an inner surface protrusion having a protrusion welded on the inner surface of the tube body,
The tube body contains 2.0% or more of Al by mass%,
The protrusions are, in mass%, C: 0.2% to 0.6%, Si: more than 0% and 1.0%, Mn: more than 0% and not more than 0.6%, Cr: 25% -35%, Ni: 35% -50%, Nb: 0.5% -2.0%, Al: 3.0% -6.0%, Y: 0.005% -0.05%, balance Fe And inevitable impurities.

  The protrusion may further include a rare earth element: 0.01% to 0.20% by mass%.

  The tube body may include Nb: more than 0% and 0.5% or less by mass%.

  It is desirable that the protrusion includes a higher concentration of Nb than the tube body.

  The protrusions preferably contain a higher concentration of Al than the tube body.

  The protrusions are, in mass%, W: more than 0% to 2.0% or less, Mo: more than 0% to 1.0% or less, and the total amount of Ti and / or Zr: more than 0% to 0 It may further include one or more elements selected from the group consisting of 0.5% or less and Hf: more than 0% and 0.5% or less.

  The protrusion has an alumina barrier layer containing Al oxide on the surface.

  The reaction tube main body needs to contain a large amount of C in order to improve the creep strength. However, when C is contained in a large amount, weldability is lowered and elongation is lowered. In particular, a material containing Al tends to cause a decrease in weldability and elongation. Therefore, in the present invention, since Nb is combined with C to form NbC by including Nb in the protrusion, the carbon concentration in the welding material can be reduced, and the weldability is improved and welding is performed. The crack is prevented. Further, Nb contained in the protrusions forms NbC (niobium carbide) at the time of welding, and can increase the creep strength by strengthening the grain boundaries. Further, when the oxide of the protrusion is removed by blasting or the like, it is easier to remove the oxide when the linearity is better, and the ability to form Al oxide can be improved. By suitably forming the alumina barrier layer on the protrusions, coking can be prevented and the thermal decomposition efficiency can be increased, so that the yield of olefin can be increased.

  Moreover, formation of Cr carbide can be suppressed by preferentially forming NbC by C in the formed protrusion. As a result, the formation of Al oxide on the protrusions can be promoted by heat treatment. Since the alumina barrier layer is formed on the protrusion, adhesion of coke can be suppressed, so that the heat transfer efficiency and pressure loss can be prevented, and the operation efficiency due to the decoking operation can also be prevented.

FIG. 1 is a cross-sectional view along the tube axis direction of a reaction tube with an internal protrusion according to an embodiment of the present invention. FIG. 2 is a photograph of Invention Example 3. FIG. 3 is a photograph of Comparative Example 1. FIG. 4 is a photograph of Comparative Example 2. FIG. 5 is a photograph of Comparative Example 3.

  Hereinafter, embodiments of the present invention will be described in detail. Unless otherwise specified, “%” means mass%.

  The reaction tube of the present invention is used as a pyrolysis tube for ethylene production, a cracking tube for hydrocarbon gas pyrolysis, and the like, and is installed in a heating furnace for producing hydrocarbons such as ethylene.

  As shown in FIG. 1, the reaction tube 10 with an inner surface protrusion of the present invention is formed by forming a protrusion 14 that is a stirring member on the inner surface of a tube body 12. The protrusion 14 can be formed by overlay welding a build-up welding powder, which will be described later, to the inner surface of the tube body 12. The protrusion 14 can be formed as a continuous spiral protrusion row as shown in FIG. The number of protrusion rows can be one or more. 1B and 1C show a shape in which a slit 16 is provided between the protrusions 14. The slits 16 can be provided parallel to the tube axis direction between adjacent protrusion rows, or can be formed by shifting the slits 16 between adjacent protrusion rows in the circumferential surface direction of the tube body 12. The protrusion 14 is not limited to the spiral protrusion row, and may be formed in a direction perpendicular to the tube axis.

  By forming the protrusions 14 on the inner surface of the tube body 12, the hydrocarbon gas flowing inside the tube body 12 generates a swirl flow that swirls around the periphery of the protrusions 14 when getting over the protrusions 14, and is agitated. Heat exchange with the tube body 12 can be performed, and the thermal decomposition efficiency can be increased as much as possible.

  The tube main body 12 uses a material containing 2.0% or more of Al. By containing 2.0% or more of Al, an alumina barrier layer containing Al oxide can be formed on the inner surface of the tube body 12 by heat treatment, and excellent oxidation resistance and resistance to use in a high temperature atmosphere. It can exhibit carburization and nitriding resistance. The tube body 12 can be manufactured, for example, by centrifugal casting.

  The tube body 12 can contain Nb. Nb can combine with C to form NbC and increase the creep strength due to grain boundary strengthening. However, even if 0.5% or more is added to the tube body 12, the effect is saturated. Therefore, even if it is contained, it is desirable that Nb exceeds 0% and is 0.5% or less.

  As this type of material, C: 0.40% to 0.60%, Si: more than 0% to 1.0% or less, Mn: more than 0% to 1.0% or less, Cr: 22% to 28% %, Ni: 29% to 37%, W: 0.5% to 2.0%, Nb: more than 0% to 0.50% or less, Al: 2.0% to 4.0%, rare earth elements: Examples include materials composed of 0.05% to 0.40%, Ti: 0.05 to 0.20%, the balance Fe and inevitable impurities. Rare earth elements mean 15 types of lanthanoids from La to Lu in the periodic table. The rare earth element is preferably composed mainly of La, and La accounts for 80% or more, preferably 90% or more of the rare earth element. In addition, P and S can be illustrated as an unavoidable impurity, and these make a total amount 0.06% as an upper limit.

  The protrusion 14 is formed by depositing a powder for overlay welding having the following composition on the inner surface of the pipe body 12 by an overlay welding method such as PPW (Plasma Powder Welding) or powder plasma welding (PTA (Plasma Transferred Arc) welding). It can be formed as a bead.

  The protrusions 14 are C: 0.2% to 0.6%, Si: more than 0% to 1.0%, Mn: more than 0% to 0.6% or less, Cr: 25% to 35%, Ni : 35% to 50%, Nb: 0.5% to 2.0%, Al: 3.0% to 6.0%, Y: 0.005% to 0.05%, balance Fe and unavoidable impurities It is formed into the same component by using the overlay welding powder. In addition, P and S can be illustrated as an unavoidable impurity, and these make a total amount 0.01% an upper limit.

  The reasons for limiting the components of the protrusions are as follows.

C: 0.2% to 0.6%
C has the effect of increasing the high temperature creep rupture strength. For this reason, at least 0.2% is contained. However, if the content is too large, the primary carbide of Cr ₇ C ₃ is likely to be widely formed, and the movement of Al that forms the alumina barrier layer in the base material is suppressed. Al shortage of supply occurs, and local breakage of the alumina barrier layer occurs, and the continuity of the alumina barrier layer is impaired. For this reason, the upper limit is set to 0.6%. The C content is more preferably 0.3% to 0.5%.

Si: more than 0% and 1.0% or less Si is contained as a deoxidizer and to improve the fluidity of the material during welding. However, if the content is too large, the high-temperature creep rupture strength is reduced and oxidation causes formation of an oxide layer with low density, and the weldability is lowered, so the upper limit is made 1.0%. The Si content is more preferably 0.6% or less.

Mn: more than 0% and not more than 0.6% Mn is contained as a deoxidizer for molten alloy and for fixing S in the molten metal. If the content is too high, MnCr ₂ O ₄ oxide Since the film is formed and the high temperature creep rupture strength is lowered, the upper limit is made 0.6%. The Mn content is more preferably 0.3% or less.

Cr: 25% to 35%
Cr is contained in an amount of 25% or more for the purpose of improving the high temperature strength and oxidation resistance. However, if the content is too large, chromium oxide (Cr ₂ O ₃ or the like) is formed and the formation of the alumina barrier layer is inhibited, so the upper limit is made 35%. The Cr content is more preferably 27% to 33%.

Ni: 35% to 50%
Ni is an element necessary for ensuring carburization resistance, oxidation resistance, and metal structure stability. Ni also has a function of improving the regeneration ability of the alumina barrier layer. In addition, when the Ni content is small, the Fe content is relatively increased, and as a result, Cr-Fe-Mn oxide is easily generated on the surface of the cast body, so that the formation of the alumina barrier layer is hindered. . For this reason, it shall contain at least 35% or more. On the other hand, even if the content exceeds 50%, the effect of the increase is saturated, so the upper limit is made 50%. The Ni content is more preferably 38% to 47%.

Nb: 0.5% to 2.0%
Nb suppresses generation of weld cracks, and further, NbC can be formed to increase the creep strength, so 0.5% or more is contained. On the other hand, Nb lowers the peel resistance of the alumina barrier layer, so the upper limit is made 2.0%. The Nb content is more preferably 1.0% to 1.5%.

Al: 3.0% to 6.0%
Al is an essential material for the Al oxide that forms the alumina barrier layer. In order to exhibit the ability to stably form and regenerate the alumina barrier layer of the protrusions 14, Al is contained in an amount of 3.0% or more. On the other hand, if the Al content exceeds 6.0%, these capacities are saturated, so the upper limit is made 6.0%. The Al content is more preferably more than 3.0% and less than 5.0%.

Y: 0.005% to 0.05%
Y is added in an amount of 0.005% or more in order to suppress meandering of the weld bead and enhance weldability during overlay welding. On the other hand, if the Y content exceeds 0.05%, the toughness of the protrusions 14 is lowered, so the upper limit is made 0.05%. The Y content is more preferably 0.01% to 0.03%.

  In addition, it is desirable to contain Y 0.002 times or more with respect to the Al content. That is, Y / Al ≧ 0.002. Thereby, the deterioration of the weldability inhibited by the addition of Al can be compensated by Y. When the following rare earth element is further added, it is desirable that (Y + rare earth element) /Al≧0.002.

  In addition, the following elements can be added to the protrusion 14.

Rare earth elements: 0.01% to 0.20%
Rare earth elements mean 15 types of lanthanoids from La to Lu in the periodic table. The rare earth element is preferably composed mainly of La, and La accounts for 80% or more, preferably 90% or more of the rare earth element. The rare earth element is contained in an amount of 0.01% or more in order to contribute to the stable forming ability of the alumina barrier layer. On the other hand, if the rare earth element content exceeds 0.20%, this ability is saturated, so the upper limit is made 0.20%. The rare earth element content is more preferably more than 0.01% and not more than 0.10%.

W: more than 0% to 2.0% or less, Mo: more than 0% to 1.0% or less, total amount of Ti and / or Zr: more than 0% to 0.5% or less, and Hf: One or more elements selected from the group consisting of more than 0% and 0.5% or less These elements have the effect of improving carburization resistance and are added to improve high-temperature strength. However, excessive addition causes a decrease in ductility, etc., so the content is as defined above.

  In the present invention, the occurrence of weld cracks is suppressed by containing Nb in the protrusion 14. Nb contained in the overlay welding powder forms NbC at the time of welding for forming the protrusion, and can increase the creep strength by strengthening the grain boundary. Moreover, Nb couple | bonds with C and forms NbC, The carbon concentration in a welding material can be reduced and weldability is improved.

  Moreover, formation of Cr carbide can be suppressed by preferentially forming NbC by C in the formed protrusion. As a result, the formation of Al oxide on the protrusions can be promoted by heat treatment. Since the alumina barrier layer is formed on the protrusion, adhesion of coke can be suppressed, so that the heat transfer efficiency and pressure loss can be prevented, and the operation efficiency due to the decoking operation can also be prevented.

  It is desirable that the Nb of the protrusion 14 is higher than the Nb concentration of the tube body 12. This is because increasing the Al concentration of the protrusions 14 increases the film forming property and at the same time the protrusions are required to have weldability, so increasing the Nb concentration makes both the film forming property and the weldability compatible. The Nb concentration of the protrusion 14 is preferably 2 times or more, and more preferably 5 times or more than the Nb concentration of the tube body 12.

  Further, by containing Al in the protrusion, an alumina barrier layer containing an Al oxide can be suitably formed by heat treatment. In this case, it is desirable that the Al content is larger than that of the tube body 12. This is because the protrusions 14 have a stronger impact on the hydrocarbon gas than the inner surface of the tube main body 12, are easily affected by oxidation, carburization, nitriding, and the like, and need to form a stable alumina barrier layer. Desirably, the Al content of the protrusion 14 is 0.5% or more as compared with the Al content of the tube body 12.

  In addition, it is possible to improve the stable formation ability of an alumina barrier layer by increasing the Al content of the tube body 12 as the protrusions 14. However, when the Al content of the tube body 12 is increased, the castability of the tube body, particularly the castability in centrifugal casting, is reduced. In addition, mechanical properties such as creep rupture strength and tensile ductility of the tube body 12 may be reduced. Furthermore, the reaction tube 10 is welded and joined together, and is installed in the heating furnace. However, when the Al content of the tube body 12 increases, the weldability thereof decreases. Therefore, in the present invention, the Al content of the tube body 12 is suppressed to be smaller than the Al content of the protrusions 14.

  As described above, the protrusion 14 contains Nb, Al, and Y, so that it has excellent weldability, high creep strength, and can enhance the ability to stably form the alumina barrier layer. Therefore, the protrusion 14 exhibits excellent oxidation resistance, carburization resistance, nitridation resistance, and the like when used in a high temperature atmosphere. Further, since coke can be prevented from adhering to the protrusions 14, it is possible to prevent a decrease in heat transfer efficiency and pressure loss. Furthermore, since the adhesion of coke is suppressed, the frequency of decoking work can be lowered and the operation efficiency can be improved.

  The reaction tube 10 with an inner surface protrusion of the present invention can be manufactured, for example, in the following manner.

<Casting of tube body 12>
The pipe body 12 is made of a molten metal having the above composition and cast into a tube by centrifugal casting, stationary casting, or the like. The present invention is particularly suitable for a pipe body manufactured by centrifugal casting. This is because, by applying centrifugal casting, a fine metal structure grows in the radial direction with the progress of cooling by the mold, and an alloy structure in which Al easily moves can be obtained. As a result, in the heat treatment described later, it is possible to obtain the tube body 12 having a coating film having an excellent strength even in an environment of repeated heating while being an alumina barrier layer thinner than the conventional one.

<Machining>
The obtained tube main body 12 is cut into a predetermined dimension, and after bending is corrected, the inner surface is subjected to roughing, and the end is subjected to groove processing for welding.

<Overlay welding of protrusion 14>
Next, build-up welding powder having the above composition is build-up welded to the inner surface of the tube body 12 by PPW, PTA welding or the like. Since the overlay welding powder contains Y in the above range, the meandering of the weld bead is suppressed, and the weldability is good. As a result, the reaction tube 10 in which the protrusions 14 are build-up welded to the inner surface of the tube body 12 is obtained.

<Inner surface fine processing>
On the inner surface of the tube main body 12 and the surface of the protrusion 14, the surface oxide remains on the molten metal portion generated by overlay welding of the protrusion 14 and the periphery thereof. These oxides are removed by grinding. In the present invention, since the protrusion has excellent weldability, the oxide can be easily removed, and the ability to form Al oxide can be improved. Examples of the grinding method include surface grinding, grinder polishing, and blasting. In particular, the blast treatment has excellent workability when there are protrusions on the inner surface.

<Heat treatment>
After subjecting the inner surface of the reaction tube 10 to fine inner surface processing, the reaction tube 10 is heat-treated in an oxidizing atmosphere, whereby an alumina barrier layer is formed on the inner surface of the tube body 12 and the surface of the protrusions 14. In addition, this heat processing can also be implemented as an independent process, and can also be implemented in the high temperature atmosphere at the time of installing and using the reaction tube 10 in a heating furnace.

The heat treatment is performed in an oxidizing atmosphere. The oxidizing atmosphere is an oxidizing environment in which an oxidizing gas containing 20% by volume or more of oxygen, steam or CO ₂ is mixed.

By performing the heat treatment, the inner surface of the tube body 12 and the surface of the protrusion 14 come into contact with oxygen, and the Al, Cr, Ni, Si, and Fe diffused on the base surface are oxidized to form an oxide layer. By performing heat treatment for 1 hour or more in a suitable temperature range of 800 ° C. or higher, Al is an oxide (Al ₂ ) in preference to Cr, Ni, Si, Fe on the inner surface of the tube body 12 and the surface of the protrusion 14. O ₃ ) is formed, and an alumina barrier layer mainly composed of Al oxide is formed. In particular, since the protrusion 14 contains Nb, C is consumed by forming NbC preferentially, and generation of Cr carbides that inhibit formation of the alumina barrier layer can be suppressed, and formation of the alumina barrier layer can be suppressed. Can be promoted.

  The reaction tube 10 of the present invention has excellent oxidation resistance, carburization resistance, nitridation resistance, and corrosion resistance when used in a high temperature atmosphere due to the alumina barrier layer formed on the inner surface of the tube body 12 and the surface of the protrusions 14. It can be maintained for a long time. In addition, since the tube body 12 has a lower Al content than the protrusions 14, the tube body 12 is excellent in mechanical characteristics, and is also excellent in weldability when installed in a heating furnace. Therefore, the lifetime of the reaction tube 10 can be greatly improved, and the operation efficiency can be increased as much as possible.

  Furthermore, since the protrusion 14 has excellent weldability and does not meander or weld cracks, it is easy to remove the oxide when removing the oxide of the protrusion 14 by blasting or the like, and improve the ability to form Al oxide. Can do. By suitably forming the Al oxide on the protrusions 14, the occurrence of coking can be reduced and the thermal decomposition efficiency can be increased, so that the yield of olefin can be increased.

  The alloy melt of the tube body 12 (Table 1: Ladle analysis) is melted by melting in the air in a high-frequency induction melting furnace, the tube body 12 (test tubes 1 to 3) is produced by centrifugal casting, and the inner surface is roughened. Along with this, machining was performed. The obtained test tube has an inner diameter of 80 mm, an outer diameter of 100 mm, and a length of 3 m.

  The obtained test tube was divided into four in the radial direction, and the protrusions 14 were build-up welded by PPW using the powder for build-up welding shown in Table 2 (Invention Examples 1 to 4, Inventive Examples 1 to 3). ). In addition, (Y + rare earth element) / Al is shown together in Table 2.

  A test tube (Invention Example 1 to Invention Example 4, Comparative Example 1 to Comparative Example 3) having protrusions is shown in FIGS. Referring to the figures, it can be seen that protrusions are formed on the inner surface of the test tube by overlay welding.

  At this stage, the weldability during overlay welding was evaluated visually. Weldability was judged as Evaluation A to Evaluation C based on superiority or inferiority of linearity, that is, the degree of meandering of the protrusions. The results are shown in Table 3.

  Referring to FIG. 2 to FIG. 5 and Table 3, it can be seen that the weldability of the protrusions of the invention example is linear without being meandered and is excellent (Evaluation A). On the other hand, as for the comparative example, the comparative example 1 has excellent weldability (evaluation A), but the comparative example 2 has a large meandering protrusion and is very inferior in weldability (evaluation C). In Comparative Example 3, there was no large meandering in the protrusions, but many minute distortions were observed, and the linearity was moderate (Evaluation B).

  The reason why the inventive example is excellent in weldability is that although it contains a large amount of Al that inhibits weldability, an amount of Y that supplements the inhibitory effect is added. Note that (Y + rare earth element) / Al was 0.002 or more (Table 2). On the other hand, Comparative Example 1 was evaluated as A because Y was not added but the content of Al hindering weldability was low. Further, Comparative Example 2 does not contain Y to compensate for the inhibitory effect despite the fact that much Al that inhibits weldability is added, and (Y + rare earth element) / Al is also 0. The protrusion meandered and the evaluation was C. Moreover, although Comparative Example 3 did not contain Y, since the content of Al was small, the weldability was better than Comparative Example 2, and the evaluation was B.

  Next, the formation ability of the alumina barrier layer was evaluated for the inventive examples and the comparative examples. Specifically, the protrusions are subjected to surface grinding, grinder polishing or blasting, heated in an oxidizing atmosphere (approximately 21% oxygen), and furnace-cooled to form an alumina barrier layer on the protrusion surface. The formation ability was evaluated by measuring area%. Table 3 shows the ability to form an alumina barrier layer for each sample material.

  Referring to Table 3, it can be seen that all the inventive examples, Comparative Example 2 and Comparative Example 3 have an alumina barrier layer forming ability as high as 90% by area or more, and are excellent in forming ability. This is presumably because a large amount of Al was included, and Nb formed NbC, thereby suppressing the formation of Cr carbides that hindered the formation of Al oxides. On the other hand, in Comparative Example 1, since the Al itself that forms the Al oxide is small, the alumina barrier layer is not formed. Further, Comparative Example 3 has a large amount of Al and a large amount of Nb. However, since the weldability is poor, the surface of the protrusion is sufficiently rough even by surface grinding, and it is considered that the formation of Al oxide is inhibited.

<Comprehensive evaluation>
Invention examples and comparative examples were comprehensively evaluated and are shown in Table 3 as “Comprehensive evaluation”. Referring to Table 3, the inventive example is excellent in the weldability of the protrusions, and further, the forming ability of the alumina barrier layer is 90% or more, and the comprehensive evaluation is A. That is, since the reaction tube 10 of the present invention is excellent in the weldability of the protrusion 14, it is easy to remove the oxide when removing the oxide of the protrusion by blasting or the like, and improve the ability to form Al oxide. Can do. Thereby, generation | occurrence | production of coking can be reduced and the thermal decomposition efficiency can be raised, As a result, the yield of an olefin can be raised. In addition, since an excellent alumina barrier layer is formed not only on the tube body 12 but also on the protrusions 14, the alumina barrier layer is difficult to peel off even when subjected to repeated heating and cooling cycles. Therefore, it can have excellent oxidation resistance, carburization resistance, nitriding resistance, corrosion resistance, caulking resistance, etc. for a long period of time when used in a high temperature atmosphere, and it also has a machine such as creep rupture strength and tensile ductility. It also has excellent characteristics and weldability between the reaction tubes 10. Furthermore, since it is difficult for coking to occur in the tube main body 12 and the protrusions 14, maintenance time and frequency of decoking work and the like can be reduced, and operational efficiency can be increased as much as possible.

  On the other hand, since the comparative example is inferior in either weldability or the ability to form an alumina barrier layer, when used as a pyrolysis tube, caulking occurs, resulting in inferior oxidation resistance, carburization resistance, and nitridation resistance. For this reason, the comprehensive evaluation was B or C.

  The above description is for explaining the present invention, and should not be construed as limiting the invention described in the claims or limiting the scope thereof. Further, the configuration of each part of the present invention is not limited to the above-described embodiment, and various modifications can be made within the technical scope described in the claims.

10 reaction tube 12 tube body 14 protrusion

Claims (7)

A reaction tube with an inner surface protrusion having a protrusion welded on the inner surface of the tube body,
The tube body contains 2.0% or more of Al by mass%,
The protrusions are, in mass%, C: 0.2% to 0.6%, Si: more than 0% and 1.0%, Mn: more than 0% and not more than 0.6%, Cr: 25% -35%, Ni: 35% -50%, Nb: 0.5% -2.0%, Al: 3.0% -6.0%, Y: 0.005% -0.05%, balance Fe And inevitable impurities,
A reaction tube with an internal protrusion characterized by that. The protrusion further includes, in mass%, a rare earth element: 0.01% to 0.20%.
The reaction tube with an internal protrusion according to claim 1. The tube main body contains Nb: more than 0% and 0.5% or less in mass%.
The reaction tube with an internal protrusion according to claim 1 or 2. The protrusion includes a higher concentration of Nb than the tube body.
The reaction tube with an internal protrusion according to claim 3. The protrusion includes a higher concentration of Al than the tube body;
The reaction tube with an internal protrusion according to any one of claims 1 to 4. The protrusions are, in mass%, W: more than 0% to 2.0% or less, Mo: more than 0% to 1.0% or less, and the total amount of Ti and / or Zr: more than 0% to 0 0.5% or less, and Hf: further including one or more elements selected from the group consisting of more than 0% and 0.5% or less,
The reaction tube with an internal protrusion according to any one of claims 1 to 5. The protrusion has an alumina barrier layer containing Al oxide on the surface,
The reaction tube with an inner surface protrusion according to claim 1.