SA517381759B1 - Heat-Resistant Tube Having Alumina Barrier Layer - Google Patents

Abstract

The present invention provides a heat-resistant tube having an alumina barrier layer in which an alumina barrier layer is favorably provided on the tube inner surface and with which the deterioration of mechanical characteristics such as creep rupture strength and tensile ductility can be prevented. A heat-resistant tube according to the present invention is a heat-resistant tube having an alumina barrier layer to be used for thermal decomposition of hydrocarbons, the alumina barrier layer including an Al oxide and being provided on an inner surface of a tube body. In the tube body, the Al content on an inner diameter side is larger than that on an outer diameter side. It is desirable that, in the tube body, the Al content on the inner diameter side is larger than that on the outer diameter side by a factor of 2 or more. It is desirable that, in the tube body, the Al content on the inner diameter side is larger by 1.3 mass% or more than that on the outer diameter side. Fig 3.

Description

Heat-Resistant Tube Having Alumina Barrier Layer FULL DESCRIPTION BACKGROUND The invention relates to a heat-resistant tube having a Bala layer of alumina and more specifically to a heat-resistant tube having an alumina barrier layer having a structure fixed on the inner surface of the tube. An austenite-based refractory alloy with excellent high temperature resistance is used in refractory tubes exposed to high temperature atmosphere; Such as reaction tubes for the production of ethylene or propylene and decomposition tubes used for the pyrolysis of hydrocriones. Despite the use of this type of austenite-based refractory alloy in a high-temperature atmosphere, ea of components (eg metal 06 Fe, ¢ Alc Sic) contained in the base material are oxidized; thus a metal oxide layer is formed on the surface. This oxide layer acts as a barrier and 0 suppresses further oxidation of the base material.However, when forming a metal oxide layer made of +© oxides (mainly composed of 3 (chromia)), the function of preventing the entry of oxygen and carbon is not LS due to "The oxides have low densities", which leads to internal oxidation of the base material in a high temperature atmosphere and thickening of the oxide layer. Moreover, it is possible to remove the thickened oxide layer during repeated cycles 5 of heating and cooling. Even in the case where no layer is removed oxide, and since the function of preventing the entry of oxygen and carbon from the outer atmosphere is not sufficient, there are bad Als in which oxygen and carbon pass through the oxide layer and cause internal oxidation or carbonization of the base material.For this cull attempts were made to increase the Al content compared to the existing content dass is general in an austenite-based refractory alloy to form a useful oxide layer made of (AI203) 0 alumina to prevent carbonization or internal oxidation. Al oxides are known to have modifiers

high density; Which makes it difficult for oxygen and kreon to pass through them; And therefore; It is proposed to form an oxide layer that includes alumina (AI203) as a primary component (ie an “alumina barrier layer”) on the inner surface of the tube (see patent documents 1 and 2; for example). Bibliography Patent Document [Patent Document A:[1 055278612l] [Patent Document A:[2 055739159l] General Description of the Invention Technical Problem 0 As a result of the increase in Al gine an improvement of the barrier function is expected by the barrier layer made of alumina. With cell, Al is the ferrite forming element; Thus, the increase in the Al content causes a problem of deterioration of the mechanical properties of the heat resistance tube; Jie Creep tear resistance, ductility and tensile strength; and the problem of degradation of weldability. The objective of the present invention is to provide a heat resistant tube where it is preferable to provide a barrier layer of 5 alumina on the inner surface of the tube which is excellent in terms of mechanical properties such as resistance to creep tearing, ductility and tensile malleability. Solution The heat-resistant tube of the present invention is a heat-resistant tube with an alumina barrier layer used for the thermal decomposition of hydrocrions; 0 The barrier layer of alumina includes Al oxide and is provided on the outer surface of the tube body;

ola on the side of the inner diameter is greater than the Al content in the body of the tube; The content (Cua

outside diameter.

It is seen that the outer diameter side refers to the outer circumference side of the cross-section thickness of the pipe

the heat resistor shown in Figure 1; And Bashir side of the inner diameter to the side of the inner circumference of it.

The cull gall from the center of the thickness of the cross section is the center in the direction of the thickness (side

medium diameter).

be required to; In the body of the tube, the Al content on the inner diameter side is greater than

Content on the outside diameter side by a factor of 2 or more.

be required to; in the body of the tube; The Al content on the inner diameter side is 1.3 7 0 by mass or more than that on the outer diameter side.

The beneficial effects of the invention

Using the heat-resistant tube incorporating an alumina barrier layer of the present invention; The content of ie on the inner diameter side of the tube body is greater than the content on the outer diameter side Al

And therefore; A barrier layer of alumina can preferably be formed on the inner surface of the tube body 5 by heating. Subsequently; The inner surface of the tube to be contacted can be supplied with a hydrocarbon gas

High temperature during pyrolysis of hydrocriones with excellent oxidation resistance; Processing resistant

Polycarbonate, resistant to nitride treatment, corrosion resistant, and the like.

On the other hand; Al rine on the outer diameter side of the tube body is small; And therefore;

Deterioration of mechanical properties such as creep tear resistance, ductility and malleability can be prevented by the tensile strength of the included Al. Furthermore it; It is easy to reduce the Al content on the outer diameter side

The body of the tube prevents the deterioration of the wettability on the outer diameter side of the tube.

Hence” as the heat-resistant tube comprising an alumina septum dish of the present invention

It comprises the body of the tube into which an oxide layer is supplied that includes alumina (81203) as a primary component

on the inner surface of the tube»; and is provided with improved oxidation resistance; and improved resistance to processing

With carbon 3 and the like and excellent mechanical properties ie resistance to rupture caused by canal, it is

It is recommended to place the heat resistant tube on a heating stove for use in a high temperature medium.

furthermore” in the heat-resistant tube incorporating an alumina Bala layer of the present invention; The Al content increases along the inner diameter of the tube body and thus JS can be regenerated

The barrier layer made of alumina by the action of the included Al even if eda is removed from the barrier layer

made of alumina inside the tube during operation or the like.

Brief description of the drawings

Figure 1 shows a heat-resistant tube incorporating an alumina barrier layer according to the embodiment of the present invention

Wad Muscat has a cross section. Fig. 2 is a schematic diagram of a centrifugal casting apparatus for the manufacture of a heat-resistant tube incorporating an alumina barrier layer according to the embodiment of the present invention. Figure 3 shows SEM images illustrating the cases of regeneration of alumina barrier layers for the example of the invention and the comparative example. Figures 3(a) and 03) are SEM images of invention example 7 and the comparative example

5 1. respectively” after process A) the barrier layer of alumina and Figures 3(b) and 3(b’) are SEM images of invention example 7 and comparative example 1; respectively; After dallas regeneration of the barrier layer made of alumina. Detailed description: Later in this (didi oll) f z ala “ag will be done for the present invention in detail.

0 A heat-resistant tube of the present invention is used as a reaction tube for the manufacture of ethylene »decomposition tube for the pyrolysis of hydrocarbons; and the like; It is provided in a hot stove for the manufacture of hydrocriones “Jie ethylene”, for example.

As shown in Figure Bo] the shall resistive tube 10 of the present invention; A barrier layer of alumina 14 comprising Al oxide which includes alumina as a primary component is formed on the inner surface of the tube body 12. The heat-resistant tube 10 may have an inner diameter of 30 to 300 cae, a length of 1000 to 6000 cae, and a thickness of is 5 to 30 mm; For example. It turns out that there are no restrictions on those dimensions. Centrifugal casting (Ka) Manufacture of refractory tube 10 using a centrifugal casting device 20 as shown in Fig. 2. For example, a centrifugal casting device 20 may include bodies in which a tubular SH frame 22 is rotated at high speed by The casting machine cylinders 21 and a molten 0 1 ingot 23 is cast into f of the sell frame 22 from a ladle 24 through a casting bucket 25. The heat-resistant tube 10 of the present invention is characterized by the content of Al on the inner diameter side (refer to fig. 1) For tube body 12 is greater than the content on the OD side (see Fig. 1).The Al content of the molten ingot poured into a metal frame from the casting bucket changes over time so as to increase the Al content on the OD side of the tube body compared to the existing content 5 on the outer diameter side thus providing the possibility of fabricating the refractory tube of the present invention.For example, the casting time is divided into early stage, middle stage, and last stage, and the Al content in the molten alloy increases at the middle and/or last stage of casting compared to the content of the early stage of casting”; and who Then facilitate the manufacture of the hall resistant tube of the invention All the early stage can be set; The middle stage” and the last stage of pouring by dividing the pouring time into three equal 0 solutions to the extent of aS for example. It turns out that the pouring time can be divided into the first half and the last half of pouring; The Al content in the molten alloy increases at the latter half. The Al content of the molten ingot in the casting bucket can be adjusted by preparing a bucket containing a molten ingot containing a small amount of Al or not containing Al and a bucket containing a molten ingot containing a large amount of Al/. alternatively” at the middle or last stage; Molten Al may be added

directly into the ladle or pouring bucket with plunger; Or a Manah block or AA ingot can be filled in the bucket. Increasing the Al content of the molten alloy cast into a metal frame at the middle and/or last stage of casting as previously described leads to the possibility of an increased Al content on the OD side of the tube body of the cast refractory tube compared to the content on the OD side Outer 0 It is shown that the Al content on the OD side of the tube body cast through centrifugal casting is increased by casting a molten Al alloy that includes a large amount of de Al “middle phase only” and not the middle and last stages or phase only recent. The reason for this is that 0 molten alloy poured at the middle stage is mixed with the molten alloy poured at the last stage by convection of the molten alloy. For example lal it is preferable that the body of the tube be made of a refractory alloy which includes at least Cr in an amount of 15 to 750 Ni in an amount of 18 to 770 and Al in an amount of 1 to J6 5 being The body of the tube is required to be made of a heat-resistant alloy which includes © in an amount of 5 to 20.7 5 in an amount of more than 70 to 72.5 or Med in an amount of more than 70 to 75 or less” Cr in an amount of 15 to 750 Ni in an amount 18 to 770 Al in a quantity of 1 to 76 Rare Earths in an amount of 0.005 to 70.4 and/or in an amount of 0.5 to 710 and/or a Mo of 0.1 to 5 and ©] and inevitable impurities as a balance. It shall be required that the former refractory aluminum alloy include at least one of those selected from the group consisting of 0 by an amount of 0.1 to 73; Ti in the amount of 0.01 to 70.6; and Zr is of an amount of 0.01 to 71.

At least one rare earth element selected from 718 « Ce may be used which is required to include the former refractory aluminum alloy 8 in an amount of 0.001 to 2.0.5 furthermore; The above refractory aluminum alloy is required to include N in an amount of 0.005 to 70.2. in addition to; The above heat-resistant aluminum alloy is required to include Ca in an amount of 0.001 to 70.5. Explanation of reasons for component limitations: Cr 15 to 750 0 The Cr content is set to 715 or more to contribute to improved high temperature resistance and cyclooxidation resistance. however; if the content is too high; Consequently, the creep tear strength of high temperature 13 decreases; Limit 1 is set up to 50 / . The N content, which ranges from 20 to 745, turns out to be more desirable. :Ni 18 to 770 5 Ala is a necessary element to ensure resistance to cyclic oxidation and stability of the metallic structure. If the Ni content is low, the © content becomes relatively large. As a result of lll possible formation of Cr-Fe—0-oxide on the surface of the casting body; Thus inhibiting the formation of the alumina barrier layer. Subsequently; Ni is set at least to 718. If the content does not exceed 770; It is imaginable to obtain the corresponding efficacy of the increased quantity; And therefore; The upper limit is set to 770. 0 turns out to be more foamy for content ranging from 20 to 750. 1A to 76

The Al content indicates an average content in the whole tube body. In dal terms of the present invention; The Al content on the OD side of the tube body of the heat-resistant tube is increased compared to the content on the OD side as previously described; Therefore, when the content of Al reaches 73, for example; The Al content on cals of inner diameter is greater than 73; While the Al content on the outer diameter side is smaller than 3, the reason for adding Al is to form an alumina barrier layer that has excellent oxidation resistance; Chrosion resistance » coking resistance; and the like on the inner surface of the tube body. On the one hand, the increase in Al content leads to deterioration of mechanical properties such as creep tear resistance, tensile strength, and deterioration of wettability. Subsequently; In the present invention; The Al content on the OD 0 side of the tube body is greater than the content on the OD side as described. Mole content is set at least to 71 preferably to form the alumina barrier layer on the OD side of the tube body. however; (sina) exceeds A/76; the effect of forming a barrier layer made of alumina on the inner diameter side of the tube body is highly saturated; thus the upper limit is set to 76 in the present invention. It turns out that the Al content is from 2.0 5 to 74.0 be more desired. In the body of the tube, it is preferable to set the Al content on the inner diameter side to be greater than the content on the outer diameter side by a factor of 2 or more” typically 2.5; more preferably 4.0. The method is suitable to form the alumina barrier layer on the inner surface of the tube body and to prevent the deterioration of the mechanical properties of the tube body. and, in a more uniform form, greater than 2.0 7 by mass or greater than the content on the outside diameter side. It is indicated that, in this specification, “7” denotes “7 by mass” unless otherwise indicated. Adjusting the Al content in this way to form the barrier layer made

— 1 0 —

of alumina on the inner surface of the tube body favorably and to prevent the deterioration of the mechanical properties of the tube body.

Furthermore it; It is preferable to set the Al content on the OD side of the tube body to

or more and the Al content on the OD side of it is adjusted to 75 or less. When the

5 The Al content on the inner diameter side is smaller than the minimum; Preferably no layer is formed

alumina diaphragm and when the Al content on the outer diameter side exceeds the upper limit; be of

Difficult to maintain mechanical properties.

©: 0.05 to 70.7

© improves pourability and enhances resistance to high temperature creep rupture. 0 therefore; © is set at least to 70.05. however; if the content is too high; probably

Initial carbide formation from 03763 in an aggravated form; Thus the movement of the uh that forms the barrier dial is suppressed

Made of alumina in the base material. as a result"; Al is supplied insufficiently to a part

The surface of the casting body and the topically alumina barrier layer are divided; Thus it is obstructed

Continuity of the alumina barrier layer. In addition to (dll) a secondary carbide is deposited in an over 5 form to reduce tensile ductility and malleability and hardness. Subsequently; The upper limit is set to 70.7.

It turns out that the C content ranging from 2 0 to 6.70 is Lge ye more than .

Si: it is more than 70 to 72.5 or less

A5 is included for the purpose of using A5 as a deoxidizing agent for the molten alloy and to enhance the liquefaction of the alloy

molten J J The content was too high; The high temperature creep decreases the tear strength 3 or the Si is oxidized to form an oxide layer that has low scattering rates and thus 3 the limit is adjusted

the highest to 72.5. A content of 5 of 72 or less turns out to be more foamy.

0: more than 70 to 75 or less

— 1 1 — MN is included for the purpose of using MN as the deoxidizing agent of the molten alloy and stabilizing 5 in the molten alloy. If the content is too high, the high-temperature creep will have a lower tear strength; And therefore; The upper limit is set to 75. An Mn content of 71.6 or less turns out to be more desirable. Rare earth element: 0.005 to 70.4

The expression 'rare earths' means 17 elements including 15 of the lanthanide series ranging from Lu Ji La in Periodic Table 3 to Nor Sc. It is preferred to include at least one rare earth pale selected from the group that makes up of Ce Yila in a refractory alloy of the present invention.The rare earth element contributes to the formation and stability of the alumina barrier layer.

0 when the alumina barrier layer is formed by heating in a high temperature oxidation atmosphere; The rare earth element in other words contained in an amount of 70.005 or more actively contributes to the composition of the alumina barrier layer. of (gal dal if the content is too high) the ductility and tensile forging and hardness decrease; thus; the upper limit is set to 70.4.

5/No: 0.5 to 710 and/or 00 : 0.1 to 75 forms only a ,Mo solution of Gla in a matrix and strengthens the austenite phase in the matrix; Thus improving resistance to creep rupture. At least one Mog // is included for this functionality. /No content is set to 70.5 or more; And the Mo content is set to 70.1 or more. However if the content of Ala and Mo content is too large ¢ UAT tensile ductility

0 and the resistance to cryonyl treatment decreases. Furthermore it; As in the case with a large © content of 3 it is possible that a primary creed of Jeu 7C3 ( Mo.

Wi.

cr) sufficed; Thus the movement of the Al that forms the alumina barrier layer in the base material is suppressed. as a result; Al is insufficiently supplied to the surface gia of the casting body and the barrier layer made of Al is split

— 1 2-

Alumina rage is thus cut off the continuity of the alumina barrier layer. Furthermore it;

And since Mog W has a large atomic radius » when JE is dissolved as Gla in the matrix; Complete

Suppression of Al movement in the basal sald inhibits the formation of the alumina barrier layer. Subsequently;

NW content is set to 710 or “Ji” and MO content is set to 75 or less. It turns out that when

Include both items Total content is preferably set to 710 or less.

in addition to; The following components may be included.

at least one chosen from the group consisting of Nb with a quantity of 0.1 to 73; Ti is an amount of

1 to 70.6 and 23 with an amount of 0.01 to 71

Zr 5 (Ti (Nb) are elements likely to form carbide materials” JS few solid 0 solutions in the matrix instead of W and 0/a. Thus” TieND ;23 does not show any specific action to shape

The barrier layer is made of alumina, but has better resistance to creep rupture. can be included

at least one Zr (Ti and 0L) as required. The Nb content is set to 70.1 or more; and

The Ti content and the Zr content are set to 01 70 or greater.

however; In the case of adding these elements in excess ¢ the ability to ductility and forging by tensile strength decreases. furthermore 5»; Nbgag reduces the removal resistance of the alumina barrier layer. Subsequently; Complete

set the upper limit of Nb content to 71.8; The upper limits of Ti content and 23 content are set to

2.0.6

8 to 70.5

Where 8 Jad shows the particle boundary strengthening of the casting body; It can be included as required. It turns out that if the content of 8 is large; Creep tear resistance decreases ‘alls’ are adjusted

Content of 8 to 70.5 or less even in the case where 8 is added.

N: 70.2 to 0.005

— 1 3 —

It does not form an Ula solution in the matrix of the alloy and has improved high temperature tensile strength. however; The N content is large and the N binds to form AIN and the ductility and tensile malleability are reduced. Therefore the content is not set to 70.2 or less. Preferably an N content from 0.06 to 70.15 2 is preferred.

Ca 5: 70.5 to 0.001

08) acts as a desulfurizing agent or an oxide desulfurizing agent 0 therefore; Ca contributes to the enhancement of LAL1 metabolites. This effect can be obtained when Ca is added in an amount of 70.001 or more. however; In dlls add an amount of 08; wettingability stops; And therefore; Ca is added in an amount of 70.5 or less.

0 In the heat-resistant tube of the invention (Jad) ¢ the heat-resistant aluminum alloy forming the body of the tube includes the aforementioned components and Fe as a balance. SP can exist; And other impurities that are mixed as in the alloy at the melting of the alloy as long as the contents of those impurities are in the range ie allowed Bale for this type of alloy material. in the body of the obtained tube; The Al content on the inner diameter side is greater than

Content on the outside diameter side. Lud Process The defective layer with bumps and depressions or irregular inclusions is found on the inner surface of the tube body obtained by centrifugal casting; Thus, the machining process is performed on the said defective layer. It turns out that the process of mechanization includes

0 Preferably a polishing process ie performed so that the surface hardness (48) of the inner surface of the tube body is 0.05 to 2.5 µm. Adjust the surface hardness (Ra) as previously mentioned and potentially suppress the formation of oxides of OF (eg.62203) on the inner surface of the tube body.

— 1 4 —

Heat treatment

The alumina barrier layer on the inner surface of the tube body is formed by heating the tube body in an oxidation atmosphere after a machining process on the inner surface. It turns out that the heat treatment can be done as a standalone step or it can be done in a high temperature atmosphere where an object is used

The tube that is installed in the heating stove.

Heat treatment is carried out in an oxidation atmosphere. The term “oxidation atmosphere” refers to an oxidation medium in which an oxidation gas containing oxygen is mixed in an amount of 20 7 by volume or more; steam; and 002. Heat treatment is done at a temperature of 900°C or higher; preferably 1000°C or above; Jag is more preferred 1 050 degrees Lge or higher6 and has a time of 90 hours or more.

when performing heat treatment; The inner surface of the tube body comes into contact with oxygen to oxidize Al SiNicCr; Fey spread on the die surface; Jolly The oxide layer is formed. Upon shal heat treatment in the foregoing temperature range Al oxides are formed prior to Fe 5 ¢ Sic NicCr of the present invention; Al gine on the side of the inner diameter of the tube body is large and therefore; Al is placed near the inner surface of the tube body preferentially bound to oxygen through heating

5 As previously described for the formation of an “alumina barrier layer” as an oxide layer incorporating Al-Oxide (A1203) as a primary component. When the tube body is heated as previously described; It is preferable to form an alumina barrier layer on the inner surface where the Al content on the inner diameter side is large; While the tube body forms a heat-resistant tube, i.e. it has excellent mechanical properties. Jie. Resistance to creep rupture.

0 and tensile ductility and malleability where Al (gine) is on the outside diameter side Dra le Al is about a component due to defective welding ALE lig the hydration. However, in the refractory tube of the present invention the Al content is On the side of the outer diameter is small, which leads to the possibility of suppressing the deterioration of wettability when the heat-resistant tube is installed in the heating stove.

— 5 1 — when the shall-resistant tube of the present invention is used in an elevated temperature atmosphere; excellent oxidation resistance can be maintained; Resistant to Crionization, Resistant to Nitriding, and Corrosion Resistant for a long period of time as an alumina barrier layer is formed on the inner surface; The mechanical properties are excellent. Moreover» “When the heat-resistant tube is installed in a heating stove; Wetting is also excellent. Thus, the life span of the heat resistance tube can be greatly improved; The efficiency of the process can be enhanced to a level as high as possible. Examples The molten alloy was produced through a melting atmosphere in a high frequency induction melting furnace”; The centrifugal casting apparatus shown in Fig. 2 was used to form tube bodies which include the 0 alloy compositions shown in the following Table 1 (Module 7: It is shown that the average AL content is used under the following conditions; followed by a machining process. Each of the bodies has The tube has an inner diameter of 80 mm, an outer diameter of 1 00 mm and a length of 250 mm before the machining process. It is shown that '" shown in Table 1 means that the component is not present in the body of the tube or is definitely embedded in the body of the tube. Table 1 N a Nm I

TTT PEE SERRE BREE Continued table 1 TTT p CCE EGE i 1 a 6 TA EEE C A L S JOD DA D I a HSS [pe] Both the tube body of the invention and comparative examples are produced by setting the total weight of the molten alloy to be poured into the casting bucket to 40 kg; Preparation of three types of molten ingot including early stage molten ingot; The molten alloy is in an intermediate stage; The molten alloy is in a final stage where the Al contents (Al inputs) are different or similar as shown in the following Table 2; pouring molten ingot in the early stage; followed by pouring of the molten alloy in the intermediate stage and the molten alloy in the last stage, in this order. Clear reasons

— 7 1 — The inconsistency of the fabricated tube body composition with the total weight of the ingot and the input of Al represented by the adhesion of ern of Al to the plunger or the amount f of melting and a shadow on it. Table 2 Input Al (kg) Ingot Molten Ingot Molten Ingot In Molten .in | In the stage: 1 ba the last stage early dla yall | average with respect to casting time; The total early stage time is set; middle stage; And the last stage to 14 to 16 seconds. The early stage is from 0 to 5 seconds; And the second 5 to 7 is the time of the middle stage, and the second 7 until after that is the time of the last stage.

— 1 8 —

after centrifugal decanting; An internal surface treatment of 2.5 mm is made on a dysfunctional layer on one side

The inner surface of each tube body obtained is such that the thickness is 7.5 mm; The paper is polished

The surface hardness (Ra) of the inner surface is 2.0 µm.

Then; For Invention Examples 1 to 7 and Comparative Examples 1 and 2; Contents are measured at three

lly pickups are located in series on the outer diameter side; At the center in the direction of the thickness (side

medium diameter); And on the inner diameter side. The measurement is performed using an X-ray analyzer

fluorochrome after cutting the tube body»; The surfaces are polished on the outer diameter side and the inner diameter side

This is to reduce the thickness by 1 to 2 cae and the middle diameter side is polished after cutting. is made

measurements at 6 positions in total; Any two positions at each of the three points Ally are 0 parts close to the ends and the center in the longitudinal direction. Table 3 shows the average Al contents (unit:

7) In invention examples 1 to 3 and comparative example 1 outside the measured tube bodies.

Table 3

Example Example Example Example Invention 1 | Invention 2 | Invention 3 | Comparative 1

The Als content obtained through previous measurements is used to calculate a content percentage

Al on the inner diameter side relative to the content on the outer diameter side (inner-5 outer content ratio); and the ratio of the Al content on the middle diameter side to the content on the outer diameter side

(Medium-external content ratio). Table 4 shows the results.

Table 4

Example Example Example Example Example Example 1 JG Example Invention | invention | invention | invention | invention | invention | invention | comparative | Comparative 1 2 3 4 5 6 7 1 2 Content Percentage |4.56 |2.55 |3.20 2.93 |2.65 4.87 |1.00 |1.00 Internal-External Content Percentage 2.88 3.75 |2.21 |2.53 2.30 |2.09 3.63 |1.00 Medium-External Renewal mm mm m 0 malleable layer ool eal dal 7Z4.0|710.4| 3.6 /6.4| 11.2 [711.2 78.4 79.2 72.8 and pulling by pull = mm mm mm mm mm inclusive

As shown in Tables 3 and 4; The Al contents are on the inner diameter side and the diameter side

The mean is greater than the content on the OD side in all examples of the invention 1 to 7. Represents

The reason for this is that a molten alloy that includes a large amount of Al is used in the phase

The middle and/or final stage of casting in the examples of the invention. In terms of gal in comparative examples 1

and 2; The Al contents on the inner diameter side and the medium diameter side are similar to the Al content

outer diameter side; Or the Al content on the side of the mean diameter is smaller than the content on

outside diameter side. The reason for this is that Al is always poured at the early stage of pouring in

comparative examples; The Al is uniformly distributed in the molten ingot in the casting bucket.

For example; The Al contents in invention example 1 and comparative example 1 are 71; However 0 Tables 3 and 4 show that the Al content on the outer diameter side of Invention Example 1 is smaller than

content in comparative example 1; (Sarg) Increase of Al contents on the medium diameter side and the diameter side

procedure. This applies to Invention Example 2 and Comparative Example 1.

The process of forming a barrier layer of alumina

The tube bodies of Invention Examples 1 to 7 and Comparative Examples 1 and 2 are heated in atmosphere (comprising oxygen 5 in an amount of about 721) at 950 °C for 24 hours and then cooled in a burner.

The cross-sections of the inner surfaces of the marked tube bodies are observed using a scanning microscope

Electronic (SEM) results oof are shown in all invention examples 1 through 7 and comparative example 2; Complete

Formation of a barrier layer made of alumina of 80 area # or more. On the other hand;

In comparative example 1; The alumina barrier layer which is smaller than 80 7 0 -_ of area is formed. The reason for this is that; In all invention examples 1 to 7 and comparative example 2;

The Al content can be increased on the inner diameter side of the tube body; In comparative example 1; He is

The Al content on the inner diameter side of the tube body is as small as 71.

It is evident that when Invention Examples 1 to 7 and Comparative Example 2 are compared; The made barrier layer is formed

of alumina on the overall surface to a large extent in the examples of invention 2 3; 5; and 7.

— 2 1 —

The process of removing the alumina barrier layer for the examples of the invention and the comparative examples; The alumina diaphragm formed on the inner surface of the tube body under the following conditions is removed to determine whether or not it is desirable to form the alumina diaphragm again at the location where the diaphragm is removed

Made of alumina.

The conditions for removal are as follows: All tube bodies are heated in atmosphere (which includes oxygen in a quantity of about 721) at 1200°C (lly above the operating temperature of a heating burner for ethylene manufacture) for 60 hours and then cooled in the burner. as a result; While the tube body is cooling, the alumina barrier layer is removed from the inner surface of the tube body due to

0 The difference in the heat shrinkage rate between the tube body and the alumina barrier layer. Figures 3(1) and 3(a) are SEM images of the tube bodies 12 of Invention Example 7 and Comparative Example 1, respectively, after the alumina barrier layer removal process. These images show that “Al(81203) oxide On the inner surface of tube body 12 it is not in the form of a layer; only gia dag of a/- oxide is on the inner surface of tube body 12.

5 Alumina barrier layer renewal process in succession; The tube bodies on which the shal is removed from the alumina barrier layer are heated in atmosphere (containing oxygen in an amount of about 721) at 950°C for 24 hours and then cooled in a hearth. The inner surface of the tube body is observed to check whether an alumina barrier layer has been formed on it again.

0 Table 4 (renewal of the layer) above shows the results. in Table 4; TAT indicates that the alumina barrier layer on the entire inner surface has been regenerated to a large extent (790 area or more) of the tube body; 8” means that an Al-oxide of 780 area or greater ily than 0 area is formed; and no A/- oxide or ©+ oxides were replenished on the remaining space; Cag it

A/-oxide is regenerated to less than 780 by area; No L/-oxide was regenerated or no Cr oxides were formed on the residual space. As shown in table od Examples of invention 2 3 are evaluated; 5; and 7 where TA stands for refresh layer; Highly regenerate alumina total barrier layer. This is because the contents of Al 5 on the inside diameter side of the tube bodies of the said invention examples are 74.0 or greater. Al is included in a large amount on the side of the inner diameter associated with the oxygen drawn through heat treatment; The preferred alumina barrier layer is thus regenerated. Invention examples are evaluated 1 4; 6 and the following comparative example 2 of the invention examples (cdi) and 87" of layer regeneration, which means that a barrier layer made of alumina of 780 area or more can be regenerated. From another Lal 0 the comparative example "CST" is evaluated for layer regeneration where the Al content on the inner diameter side of the tube body is small; This means that the alumina barrier layer is not sufficiently regenerated. Figures 3(b) and 3(b") are SEM images of the inner surfaces of the tube bodies 12 of Invention Example 7 and Comparative Example 1, respectively, after the alumina barrier layer renewal process. In the example of invention 7 the formation of the barrier layer is observed made of alumina 14 by A/- (81203) oxide on a large aggregate surface of tube body 12; formation of Cr oxides was not observed on the other hand, as shown in Figure 3(b"); In comparative example 1; The Al oxide is partially regenerated; Lad aug Formation of (Cr) oxides Al oxide is formed Explanation of the process of regeneration of the previous barrier layer made of alumina is specified. It is shown that when the barrier layer made of alumina is removed for one reason or another while both examples of the invention are used in an ethylene manufacturing apparatus” (Sa) regeneration of the barrier layer Made of alumina Bile and shal can process oxidation resistance; Crionization resistance” nitridation resistance” JST resistance “5 kopecks resistance” and the like.

— 2 3 —

Tensile test

Tension pieces were produced from the tube bodies of invention examples 1 to 7 and comparative examples 1 and 2; And done

Tensile test to measure ductility and tensile forging.

the tube body is cut in the direction of the thickness; The test piece is produced on the basis of JIS 2201 2 (flat test piece). The distance between the marks in the thickness direction of the test piece is 5.65 (S:)VS

transverse sectional area). Tensile test is performed in accordance with 2241Z 5L (Tensile Test Method

with metallic materials). It is shown that the test is performed at room temperature where the difference can be seen

The obvious comparison with the current led of the invention is conducted at an elevated temperature. Table 4 ( Midwife

forging and pulling by stretching) The previous one shows the results.

0 Table 4 showing that the examples of the invention 1 2 4; 6; 7 and Comparative Example 1 have tensile ductility, le greater than 76, and are therefore preferred. Examples of the invention 3 and 5 having tensile ductility and forging in excess of 73 Malls are also preferred. On the other hand, Comparative Example 2 has a tensile ductility and malleability of less than 73. The reason for this is that the Al contents on the outer diameter side can be reduced in the examples of the invention

5 and comparative example 1. from another dal; In comparative example 2; The Al content on the outer diameter side is large. Therefore; Al acts as a ferrite forming element; In addition; Ni-Al compound is deposited which leads to reduced ductility and tensile forging. It is clear from these results that reducing the Al contents on the OD side of the tube bodies of the examples of the invention can prevent the decrease in mechanical properties such as creep tear resistance and susceptibility to

0 Towing and forcing. Comprehensive evaluation The invention examples and comparative examples are evaluated comprehensively. The overall rating is determined as follows: In the case where the alumina barrier layer is formed at 780 by area or greater than

During the process of forming the alumina barrier layer, a layer of 780 area or more is regenerated (the rating of layer renewal is “/” or “BY”) by the alumina barrier layer renewal process. The tensile strength and malleability measured in the tensile test 73 or more, the overall assessment is “CA” and in the case where at least one of the previous criteria is not met, the overall assessment is “8”. As shown in Table 4 (Comprehensive Assessment), the overall assessment is “8” for all examples The invention" and these results show that the examples of the invention have a high ability to form and renew the barrier layer made of alumina and the ability to draw and forge with high tensile strength. The reason for the ability to form and renew the (Halal) layer made of alumina can be enhanced in that the Al content can be increased on the inner diameter side

0 for the tube body. in addition to; The reason for the excellent mechanical properties could be that the Al content on the outer diameter side of the tube body could be reduced. It is clear from the above that the Al content on the inner diameter side of the tube body is preferably greater than the content on the outer diameter side by a factor of 2 or “SST” and the Al content on the inner diameter side is preferably greater by 1.3 7 by mass or more on the outer diameter side.

5. From ga] dali for comparative example 1 where the Al content is reduced in the body of the pipe dad the “mechanical properties” can be secured, but the ability to form and regenerate the barrier layer made of alumina decreases and therefore; The overall rating is “8”. For Comparative Example 2 where the GA content is increased in the body of the tube (So chi isolates have the ability to form and regenerate the alumina barrier layer but the mechanical properties decrease; therefore, the rating is “BY Jalal) . in addition to; with regards

For comparative example 2; The content of Al is on the outer diameter side Gal and therefore; Wetting is not preferred. JUL ¢ When Comprehensively Evaluation of Refractory Tubes for Use in a High Temperature Medium” these comparative examples are excluding those of the invention. as previously described” using the heat-resistant tube incorporating the alumina barrier layer of the present invention; The alumina septum dial is less likely to dislodge even upon exposure

5 for repeated cycles of heating and cooling. If the alumina barrier layer is removed; is renewed

— 5 2 — Direct alumina barrier layer. Thus, even when used in a high-temperature atmosphere, the heat-resistant tube incorporating the alumina barrier layer of the present invention can show excellent oxidation resistance; carbon treatment resistant; resistant to nitride treatment; Corrosion Resistant; Coking Resistant; and the like for a long period of time; It is excellent in terms of mechanical properties such as resistance to creep rupture, ductility and tensile malleability. Furthermore it; The Al content on the OD side is small; Thus, the Lad heat-resistant tube shows excellent wettability when installed in a heating stove. Thus, the life span of the refractory tube can be greatly improved; The BUS can enhance the process to a level as high as possible so that the decoking time and iterations can be reduced. 0 The foregoing description is intended to illustrate the present invention; The restriction of the invention specified in the claims is not deemed to be a restriction of the scope of the invention. like that; The form of each element of the invention is not limited to the foregoing examples; (Sag) Making many adjustments in the range ml of protection elements. Reference number list 0 Heat resistant tube 5 12 Tube body 4 Alumina barrier layer

Claims (1)

Protection Elements 1- A heat-resistant tube with a barrier layer made of alumina 38 for use in the thermal decomposition of hydrocarbons. The barrier layer made of alumina is included. on aluminum oxide and is supplied on the inner surface of the tube body; The tube body includes: 5 to 750 by mass of Cr 8 to 770 by mass of Ni (1 to 76 by mass of Al Optional option (1): 0.05 to 70.7 by mass of ©; 0 7 by mass to 72.5 by mass of A5; 0 by mass to 75 by mass from (Mn 0.005 to 70.4 by mass of REE; 5 to 710 by mass of //a and/or 0.1 to 75 by mass of 0/a; and when option (1); from one choice Selected from the group consisting of 0.1 to 73 by mass (Nb), 0.01 to 70.6 by mass (Ti), 0.01 to 71 by mass (Zr), optionally 0.001 to 70.5 by mass (B) Gaal 5 0.005 to 70.2 by mass of Na Optionally 0.001 to 70.5 by mass of Ca The balance is Fe and necessary impurities; where; in the body of the tube; The Al content on the inner diameter side is greater than the content on the outer diameter side. 0 2- heat-resistant tube including barrier layer made of alumina according to claim 1; Where it is in the body of the tube; The Al content on the inner diameter side is greater than the content on the outer diameter side by a factor of 2 to 4. 3- The heat-resistant tube that includes the alumina barrier layer according to the element of protection 1 or 2; Where it is in the body of the tube; He is The aluminum content on the inner diameter side is 71.3 by mass to 72.0 mass greater than the content on the outer diameter side. 4- The heat-resistant tube which includes the barrier layer made of alumina according to claim 1; Where one of La or Ce is used in the form of a rare earth element. 5- A heating furnace that includes a heat-resistant tube that includes a barrier layer made of alumina according to protection element 1. 0 0 na 3 # a EAN ER Nl iN 3 >8 for EY ! 0 RRR Lah LN Lh SE OD side : EJ 4 from Bg 8: A E Y ) > bY 2 EY A : Sl NE: EY 3 + * 2h 1 a 0 Ning Lm i ER 1 & Me La L 1 A ibm | . 2 : 0 : 2 . a N 3 Ce 03 Re } Ri y§ 8 Hurray! SS L 5 0 3 RES 0 L SS: RSS: ْ 8 &BG; 0 ca = : en RR A L : 2 F Ty ES] : $F PNAS What RE HE eae Ld yA ' bog ? ! Ud id [ER Vl 0 : x 1 a HE a RE a ; > 3 43 b a 9 l a gen ak 1 0 ve LR p 1 l a 0 yen y 8 REY 3 > d Fone: tat JENSEN > > a 1 h an tmSY: bY a Le LE kk e N 3 count 85 ¥ LEAT bi 5 + 7 NE "> TTR 1> TRS: HEY : ge $M, } 3 a : Fi EM i pS NY en { H > 1 ¥ + ed ia Agdeh d A a RE N 1 m no lk i ¥ hE ns 3 N SN 0 : 8 a i 2 right any 8 2 vee no hayy ed: ANAT Ahsm 0 3 SRE ا ا ا ا ا ا ا : 9 i UCIT I J TEN EY {ey Gi k $F + 3d ray Re SE a d A LA 5 A NY + RS en 5 M 1 JH 68 LAH Le - . E Haha Bassi Al-Ae EE 5 «5 TIES LE Mow HEAVY 5 3 L RN Ae [ L Sayed L 3 by Nu, SAE EEE Mow Sa SE ana 8 : hy RE ER Ea Th Nady RE Ei > Ea Th Nady RE Ei > Ea YX 3 A ERR ee 8 ا Ea Th Nady RE Ei 8 Ea Th Nady RE Ei 3 3 segs 5 5 Ea Th Nady RE Ei Ei Th Nady RE Ei oF ney AER ant a oF 4 Kram M Aden Les 2 Alat YA L As aes es Fa RY FER 4 Ndji me A WY ERY Yad SUR EART Kada A HEE RE PASTRY Hig ou Pd SERRE NC ¥ 1718 0: 0: Bright A: 11 0 Fi cae SEN SR Pe, ¥ 3 WRG i REN Si AN ad § Wes RK SF No Sap 3 Na enna A CY dar EEE at To Hay TAA WN 3 enna 8 : EE “8 1 9 0 A Ji oa LE SI. aR SEE Mei NEE eet Alat Haha #34 ا ا ا fA a 0 3 0 0 ¥ fig. 8 £53 0 0 l l l a a a EN ......,, >» 49. a a Thoma Lo . _Lo a. Caan La SE. ; BB Ns A Ys _ _. Als a Ral . a - Daa for d “to say” (7) Example of the invention 1 Comparative example CF 5 {) {wl La le. Eas 2” 4.5b Si SRE IR Raa 0 L: RR RR Eas Ea LN Sa Eas Ea LN Sa Eas Ea LN Sa aaa 0 Ra SN oR A444 No M | Why Wee 0 a Lo: A oo 0 A A A A Aa Aa Aaa (7) Invention Example 1 A Comparative Example Sued Authority for Intellectual Property RE .¥ + \ A 0 § 8 Ss o + < M SNE A J > E K J TE I UN BE Ca a a a ww > Ld Ed H Ed - 2 Ld, provided that the annual financial consideration is paid for the patent and that it is not null and void for violating any of the provisions of the patent system, layout designs of integrated circuits, plant varieties and industrial designs, or its implementing regulations. Ad Issued by + bb 0.b The Saudi Authority for Intellectual Property > > > This is PO Box 1011 .| for ria 1*1 v= ; Kingdom | Arabic | For Saudi Arabia, SAIP@SAIP.GOV.SA