JPH0867952A - Corrosive gas resistant pipe and its production - Google Patents

Abstract

PURPOSE: To produce a corrosive gas resistant pipe capable of coping with the problem of corrosion caused by high temp. corrosive gases including sulfur such as hydrogen sulfide, sulfur dioxide or the like and excellent in resistance in an atmosphere at a very high temp. (such as high temp. strength). CONSTITUTION: For constituting this corrosive gas resistant pipe, on the inside of an external layer part constituted of a heat resistant steel casting, an internal layer part 2 constituted of a corrosive gas resistant alloy contg., by weight, >=50% Cr, and the balance Fe is integrally formed. Or, the internal layer part is moreover incorporated with <=6% Co, <=5% W, 0.5 to 3.5% Si, 0.5 to 1.5% Mn and 0.03 to 0.2% C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pipe (hereinafter referred to as a corrosive gas resistant pipe) which is used in a state where the inner surface or the outer surface is exposed to a high temperature atmosphere in which a corrosive gas flows, and its corrosive resistant gas. It relates to a method of manufacturing a tube.

[0002]

2. Description of the Related Art As the corrosion resistant gas pipe, for example,
A furnace tube provided in the firing furnace to fire the target substance in the tube, and a radiant tube provided in the heating furnace or the heat treatment furnace to introduce the combustion gas for indirect heating into the tube,
Boiler tubes and the like used to construct a waste heat boiler that heats water to generate steam to high temperatures are included. These tubes are usually used in a state where the inner surface or the outer surface is exposed in a high temperature atmosphere in which the corrosive gas flows. Therefore, as these tubes, a tube made of heat-resistant steel having good heat resistance and corrosion resistance, for example, a heat-resistant steel cast steel product cast into a tubular shape (specifically, JIS standard:
SCH2, SCH11, SCH13, SCH18, SC
H22) and 26.5Cr-35Ni-14Co-5.
A tube made of W heat-resistant steel (trade name: Supertherm) was used.

[0003]

By the way, in the above-mentioned corrosion-resistant gas pipe, a gas having a very strong corrosive property (for example, hydrogen sulfide, sulfurous acid gas, or a corrosive gas containing sulfur) is used. Although it may be used in a state of flowing through and exposed to an extremely high temperature atmosphere, under such severe conditions, the corrosion resistance and high temperature strength of the above conventional corrosion resistant gas pipe become insufficient. However, there is a problem that the above conventional corrosion-resistant gas pipe cannot be put to practical use. For example, in a firing furnace for producing trimanganese tetraoxide (Mn ₃ O ₄ ) used for magnets, magnetic cores, etc., the inside of the furnace tube provided in the furnace is 1000
Set to a high temperature atmosphere above ℃ and a reducing atmosphere,
In the furnace tube, manganese sulphate (MnSO ₄ · H ₂ O) as a raw material is reacted to produce trimanganese tetraoxide, but it has strong corrosiveness in the production process. Hydrogen sulfide (H ₂ S) is generated, and the hydrogen sulfide causes the inner surface of the furnace tube to be very easily corroded. Therefore, when the furnace tube is made of heat-resistant steel such as the heat-resistant steel cast product or the supertherm, the furnace tube is deteriorated in a short time due to the corrosive action of the hydrogen sulfide. In addition, there is a problem that the high temperature strength may be insufficient depending on the material. Further, in the radiant tube provided in the heating furnace or the heat treatment furnace, the inner surface is
Since it comes to be exposed to combustion gas containing a substance that has extremely high temperature and strong corrosiveness, when the radiant tube is made of heat-resistant steel such as the heat-resistant steel cast steel product or the supertherm However, there is a problem that the radiant tube is deteriorated in a short time due to the corrosion caused by the combustion gas, and the high temperature strength may be insufficient depending on the material. Further, since the outer surface of the boiler tube provided in the waste heat utilization part of the incinerator is usually exposed to sulfurous acid gas (SO ₂ ) having a strong corrosive property, the heat-resistant steel cast steel product and the supermarket When the boiler tube is made of heat-resistant steel such as Samme, the boiler tube deteriorates in a short time due to the corrosion caused by the sulfurous acid gas, etc., and high temperature strength is insufficient depending on the material. There was a problem that there was something to do. The present invention has been made by paying attention to such an actual situation, and it is possible to deal with the above-mentioned problem of corrosion caused by high-temperature corrosive gas containing sulfur, such as hydrogen sulfide and sulfurous acid gas, and at a very high temperature. It is an object of the present invention to provide a pipe for a corrosion resistant gas which is also excellent in resistance under an atmosphere (for example, high temperature strength).

[0004]

The corrosion-resistant gas pipe according to the present invention is provided with Cr:
50% (wt%, same below), balance: substantially Fe
The first feature is that the inner layer portion made of the alloy for corrosion resistant gas is formed integrally.

The corrosion-resistant gas pipe according to the present invention has Cr: 50% or more and C inside the outer layer portion made of a heat-resistant cast steel product.
o: 6% or less, W: 5% or less, Si: 0.5 to 3.5
%, Mn: 0.5 to 1.5%, C: 0.03 to 0.2
%, Balance: The second feature is that the inner layer portion made of a corrosion-resistant gas alloy consisting essentially of Fe is integrally formed.

The corrosion-resistant gas pipe according to the present invention has Cr: 50% or more and C inside the outer layer portion made of a heat-resistant cast steel product.
o: 6% or less, W: 5% or less, Si: 0.5 to 3.5
%, Mn: 0.5 to 1.5%, Mo: 5% or less, C:
0.03 to 0.2%, balance: The third feature is that an inner layer portion made of a corrosion-resistant gas alloy substantially consisting of Fe is integrally formed.

The corrosion resistant gas pipe according to the present invention has Cr: 50% or more, N, and N inside the outer layer portion made of a heat-resistant cast steel product.
i: 5% or less, Co: 6% or less, W: 5% or less, Al:
2% or less, Si: 0.5 to 3.5%, Mn: 0.5 to
1.5%, Mo: 5% or less, B: 0.8% or less, Zr:
The fourth feature is that 0.1% or less, C: 0.03 to 0.2%, and the balance: an inner layer portion made of an alloy for corrosion-resistant gas consisting essentially of Fe is integrally formed. .

[0008]

A pipe for corrosion-resistant gas having the first characteristic, a pipe for corrosion-resistant gas having the second characteristic, a pipe for corrosion-resistant gas having the third characteristic, and the fourth characteristic. Each of the corrosion-resistant pipes provided with is provided with an outer layer portion made of the above heat-resistant cast steel product and an inner layer portion made of a corrosion-resistant alloy as described in detail later. Therefore, any of the above-described corrosion-resistant gas pipes is based on excellent resistance to the high-temperature corrosion gas that constitutes the inner layer portion, the inner surface of the pipe is hydrogen sulfide, sulfurous acid gas, or the like,
In addition to being able to withstand contact with high-temperature corrosive gases containing sulfur, it has excellent strength in an extremely high-temperature atmosphere based on the high-temperature strength of the heat-resistant cast steel product that constitutes the outer layer. Like Therefore, any of the above-described corrosion-resistant gas pipes is a furnace tube provided in the firing furnace for firing the target substance in the pipe, or a heating furnace or heat treatment furnace for introducing combustion gas for indirect heating into the pipe. It can be sufficiently dealt with when the inner surface of the tube such as the radiant tube provided inside is exposed to extremely severe conditions.

Next, the reasons for limiting the components of the alloy for high-temperature corrosion-resistant gas which constitutes the inner layer portion of the above-mentioned pipe for corrosion-resistant gas will be described.

In the alloy for high temperature corrosion resistant gas which constitutes the inner layer portion of the pipe for corrosion resistant gas having the first characteristic, the reason why Cr is contained as a main component is that Cr is contained in a high temperature atmosphere of 1000 ° C. or higher. This is because it is excellent in resistance to high temperature corrosive gas containing sulfur such as hydrogen sulfide and sulfurous acid gas. However, when Cr is less than 50%, a very brittle σ phase precipitates at high temperature.
Cr: limited to 50% or more.

The reason why Cr is contained as a main component in the alloy for high-temperature corrosion resistant gas which constitutes the inner layer portion of the pipe for corrosion-resistant gas having the second characteristic is as follows. This is the same as in the case of the alloy for high-temperature corrosion resistant gas that constitutes the inner layer portion of the gas pipe. The reason for including Co is that the addition of Co improves the oxidation resistance and
This is because it contributes to facilitation of manufacturing due to the lowering of the melting point of the high Cr material. However, if the added amount of Co exceeds 6%, the hydrogen sulfide resistance and the like deteriorate, so Co: 6% or less. Also,
The reason for including W is that the addition of W contributes to the improvement of creep strength. However, if the amount of W added exceeds 5%, the oxidation resistance and toughness are adversely affected, so W: 5%
Below. In addition, the reason why Si is contained in an amount of 0.5 to 3.5% is that when Si is added in an amount of 0.5% or more, the production is facilitated by the melting point decrease of the high Cr material, the flowability of molten metal during casting is improved, Also, while contributing to the improvement of oxidation resistance, if the amount of Si added exceeds 3.5%, the toughness deteriorates. In addition, the reason for containing 0.5 to 1.5% of Mn is 0.5
%, Mn contributes to facilitating the production by lowering the melting point of the high Cr material. On the other hand, if the amount of Mn added exceeds 1.5%, it reacts with S to become MnS, and the strength cannot be maintained. is there. Further, the content of C of 0.03 to 0.2% is that when 0.03% or more of C is added, it contributes to the lowering of the melting point of the high Cr material and the solid solution strengthening, while the amount of C addition is This is because if it exceeds 1.5%, carbides will be precipitated.

In the alloy for high-temperature corrosion-resistant gas which constitutes the inner layer portion of the pipe for corrosion-resistant gas having the third characteristic, the reason why Cr is contained as a main component and Co, W, Si,
The reason for adding an appropriate amount of Mn and C is the same as in the case of the alloy for high-temperature corrosion-resistant gas that constitutes the inner layer portion of the corrosion-resistant gas pipe having the second characteristic. Further, the reason for including Mo is that the addition of Mo contributes to the improvement of creep strength. However, if the amount of addition of Mo exceeds 5%,
Mo: 5% or less because it adversely affects oxidation resistance and toughness.

In the alloy for high-temperature corrosion-resistant gas which constitutes the inner layer portion of the corrosion-resistant gas pipe having the fourth characteristic, the reason why Cr is contained as a main component, and Co, W, Si,
The reason for adding an appropriate amount of Mn, C, and Mo is the same as in the case of the high-temperature corrosion-resistant alloy forming the inner layer portion of the corrosion-resistant gas pipe having the third characteristic. Further, the reason for including Al is that the addition of Al contributes to the improvement of oxidation resistance and hydrogen sulfide resistance. However, if the added amount of Al exceeds 2%, it becomes difficult to melt and cast in the air, and the toughness is impaired. Therefore, Al: 2% or less. Further, the reason why B is contained is that the creep strength is improved by the combined addition of B and Mo, and the addition of B lowers the melting point of the high Cr material. However, if the added amount of B exceeds 0.8%, the oxidation resistance and toughness are adversely affected, so B: 0.8
% Or less. Further, the reason why Zr is contained in an amount of 0.1% or less is that the addition of 0.1% or less of Zr is useful for improving creep strength and preventing nitriding during melt casting.

[0014]

Therefore, the corrosion resistant gas pipe having the first feature, the corrosion resistant gas pipe having the second feature, the corrosion resistant gas pipe having the third feature, or the fourth feature. According to the anticorrosion gas pipe with the characteristics of, the furnace tube installed in the firing furnace for firing the target substance in the pipe, and the heating furnace and heat treatment for introducing the combustion gas for indirect heating into the pipe The entire tube is exposed to extremely severe corrosion conditions (for example, hydrogen sulfide, sulfurous acid gas, and other hot corrosive gases containing sulfur) inside the furnace, and the entire tube is extremely hot. A material very suitable for a corrosion-resistant gas pipe exposed to the atmosphere can be provided.

Further, a corrosion-resistant gas pipe having the first characteristic, a corrosion-resistant gas pipe having the second characteristic, a corrosion-resistant gas pipe having the third characteristic, or a fourth characteristic. In a pipe for corrosion-resistant gas equipped with, in the case where both ends of the outer layer portion are formed with welding groove portions, and both end portions of the inner layer portion corresponding to the formation location of the welding groove portion are removed. Is a material of the inner layer portion having poor weldability when the corrosion-resistant pipes are continuously provided in the pipe axial direction and the joints thereof are welded (that is, a brittle σ phase is likely to be generated at a high temperature, Cr is Alloy material as main component)
Of the inner layer portion is avoided by removing both ends of the inner layer portion, and the welding of the joint portion is substantially performed by welding the material of the outer layer portion having good weldability. Welding can be performed soundly.

Further, a corrosion-resistant gas pipe having the first characteristic, a corrosion-resistant gas pipe having the second characteristic, a corrosion-resistant gas pipe having the third characteristic, or a fourth characteristic. When manufacturing a pipe for corrosion resistant gas equipped with, if the inner layer portion is formed by overlaying (including thermal spraying) on the inner side of the outer layer portion made of the heat-resistant steel cast steel, the inner layer portion is thin. If so, the inner layer portion can be formed very efficiently.

Further, a corrosion-resistant gas pipe having the first characteristic, a corrosion-resistant gas pipe having the second characteristic, a corrosion-resistant gas pipe having the third characteristic, or a fourth characteristic. In producing a corrosion-resistant gas pipe provided with, the outer layer portion and the inner layer portion are formed by centrifugal casting (more specifically, molten metal for forming the outer layer portion into a centrifugal casting mold during rotation). Immediately after casting the centrifugal force to cast the outer layer portion (that is, immediately after solidifying the outer layer portion), cast the molten metal for forming the inner layer portion into the inner layer portion to centrifugally cast the inner layer portion) According to this, even when a thick-walled inner layer portion is required, the thick-walled inner layer portion can be easily formed.

Further, a pipe for a corrosion resistant gas whose outer surface is exposed to a very severe corrosive condition, for example, a boiler tube used for constructing a waste heat boiler arranged in a waste heat utilization part of an incinerator. As described above, the corrosion-resistant gas pipe having the first characteristic, the corrosion-resistant gas pipe having the second characteristic,
The anticorrosion gas pipe having the third characteristic and the anticorrosion gas pipe having the fourth characteristic are the anticorrosion gas pipe in which the relationship between the outer layer portion and the inner layer portion is reversed, that is, heat resistance. Cr: 50% or more, balance: substantially Fe on the outside of the inner layer made of cast steel
Corrosion resistant gas pipe (corresponding to the corrosion resistant gas pipe having the first feature) integrally formed with the outer layer part made of the alloy for corrosion resistant gas consisting of In addition, Cr: 50% or more, Co: 6% or less, W: 5% or less, Si: 0.5 to 3.5%, Mn: 0.5 to 1.5.
%, C: 0.03 to 0.2%, balance: Corrosion resistant gas pipe integrally formed with an outer layer part made of an alloy for corrosion resistant gas consisting essentially of Fe (resistant to the second characteristic. C) on the outside of the inner layer made of cast heat-resistant steel products)
r: 50% or more, Co: 6% or less, W: 5% or less, S
i: 0.5 to 3.5%, Mn: 0.5 to 1.5%, M
o: 5% or less, C: 0.03 to 0.2%, balance: Corrosion resistant gas pipe integrally formed with an outer layer portion made of a corrosion resistant alloy substantially consisting of Fe (third feature (Corresponding to a corrosion-resistant gas pipe equipped with), or Cr: 50% or more, Ni: 5% or less, Co: 6
% Or less, W: 5% or less, Al: 2% or less, Si: 0.5
.About.3.5%, Mn: 0.5 to 1.5%, Mo: 5% or less, B: 0.8% or less, Zr: 0.1% or less, C: 0.
03-0.2%, balance: Corrosion-resistant gas pipe integrally formed with an outer layer made of a corrosion-resistant gas alloy consisting essentially of Fe (corresponding to the corrosion-resistant gas pipe having the fourth characteristic ) Is considered.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a corrosion-resistant gas pipe according to the present invention, that is, a furnace for producing trimanganese tetraoxide (Mn ₃ O ₄ ) used for magnets, magnetic cores, etc. A longitudinal sectional view of a furnace tube is shown. A plurality of the in-furnace tubes are continuously provided in the axial direction of the tube and their joints are welded for use.

The above-mentioned corrosion-resistant gas pipe is JIS standard: SC
H2, SCH11, SCH13, SCH18, SCH2
2 etc. and ASTM standard: HK40 etc., inside the outer layer part 1 made of heat-resistant steel cast steel, Cr: 50% or more, the balance: an inner layer part made of a corrosion-resistant alloy consisting essentially of Fe (for example, formed integrally. , And is integrally formed by the above-mentioned casting or overlaying. Then, after the manufacturing, appropriate machining is performed to form welding groove portions 3 at both end edge portions of the outer layer portion 1, and the inner layer portion 2 corresponding to the formation location of the welding groove portion 3 is formed. Both ends 4 are removed. The corrosion-resistant gas pipe formed in this manner has an inner surface that is excellent in resistance to the high-temperature corrosion gas forming the inner layer portion 2.
The heat-resistant steel cast steel product, which can withstand contact with high-temperature corrosive gas containing sulfur (especially hydrogen sulfide in the furnace tube of this embodiment) such as hydrogen sulfide and sulfurous acid gas, and which constitutes the outer layer portion 1. Based on the strength of the high temperature strength of the steel, the strength in a very high temperature atmosphere is also excellent. Moreover, when the corrosion-resistant gas pipes are continuously provided in the pipe axial direction and the seam portion is welded, the inner layer portion 2 having poor weldability (because the material is made of Cr, which easily causes brittle σ phase at high temperature, By avoiding the welding of the main component alloy) by removing both ends thereof, and by substantially performing the welding of the seam portion by the welding of the outer layer portion 1 having good weldability, Welding of the seam portion can be performed soundly.

As the corrosion-resistant gas alloy constituting the inner layer portion 2, instead of the above alloy, Cr: 50% or more, C
o: 6% or less, W: 5% or less, Si: 0.5 to 3.5
%, Mn: 0.5 to 1.5%, C: 0.03 to 0.2
%, Balance: Corrosion resistant alloy consisting essentially of Fe, C
r: 50% or more, Co: 6% or less, W: 5% or less, S
i: 0.5 to 3.5%, Mn: 0.5 to 1.5%, M
o: 5% or less, C: 0.03 to 0.2%, balance: Corrosion resistant alloy consisting essentially of Fe, Cr: 50% or more,
Ni: 5% or less, Co: 6% or less, W: 5% or less, A
1: 2% or less, Si: 0.5 to 3.5%, Mn: 0.5
~ 1.5%, Mo: 5% or less, B: 0.8% or less, Z
You may employ | adopt the alloy for corrosion resistant gases which consists of r: 0.1% or less, C: 0.03-0.2%, and the balance: Fe substantially.

Next, data showing the basis for adopting the above-mentioned alloy for corrosion resistant gas as the constituent material of the inner layer portion 2 will be described. Table 1 shows the results of the investigation of the durability of the corrosion-resistant gas alloy of the corrosion-resistant gas pipe of the present invention, which is defined by the conventional corrosion-resistant gas pipe material, that is, the supertherm and JIS. Heat resistant cast steel products (specifically,
SCH2, SCH11, SCH13, SCH18, SC
It is listed in comparison with the results of the durability study of H22).

[0023]

[Table 1]

The durability was specifically investigated by carrying out the following experiment. That is, test pieces (Sample No. 1 to Sample No. 4, and Sample No. 11 to Sample No. 1) sampled from various materials in a square plate shape.
6) are embedded in the powder of manganese sulfate, and while they are set to be exposed to a high-temperature atmosphere exceeding 1000 ° C., they are loaded in a container, time is allowed to pass, and a plurality of times are set. An experiment in which the change in thickness (or change in weight) of the test piece is measured after each lapse of time, and the elapsed time until the time when the change in weight reduction reaches a certain amount (specifically, 5%) is regarded as the service life Was carried out.

From the results shown in Table 1, the conventional example (Sample No. 11)
Of the conventional example (Sample No. 12 to Sample No. 16) is 624 hours at the maximum, whereas the present invention example (Sample No. 1 and Claim 2 according to Claim 1) The service life of the sample No. 2 concerned, the sample No. 3 according to claim 3 and the sample No. 4 according to claim 4) is 1208.
It was ~ 2402 hours, and it was found that the time was sufficiently long as compared with the conventional example.

Next, another embodiment will be described. Although the above-mentioned examples were related to the furnace tube provided in the firing furnace for the production of trimanganese tetraoxide, other tube for corrosion resistant gas whose inner surface is exposed to very severe corrosion conditions is used. For example, the anticorrosion gas pipe of the present invention can be applied to a radiant tube provided in a heating furnace or a heat treatment furnace to introduce a combustion gas for indirect heating into the tube.

Further, a corrosion resistant gas pipe whose outer surface is exposed to a very severe corrosive condition, for example, a boiler tube used to construct a waste heat boiler arranged in a waste heat utilization part of an incinerator. Also in this case, the corrosion-resistant gas pipe of the above-described embodiment can be dealt with by adopting a pipe in which the relationship between the outer layer portion and the inner layer portion is reversed.

It should be noted that although reference numerals are given in the claims for convenience of comparison with the drawings, the present invention is not limited to the structures of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of a corrosion-resistant gas pipe according to the present invention.

[Explanation of symbols]

 1 Outer layer 2 Inner layer 3 Weld groove 4 Both ends

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C22C 38/00 302 Z 38/54 F16L 9/02

Claims (11)

[Claims] 1. An inner layer portion (2) made of an alloy for corrosion-resistant gas, which comprises, in weight%, Cr: 50% or more and the balance: substantially Fe inside the outer layer portion (1) made of a heat-resistant cast steel product. ) Is integrally formed for corrosion resistant gas pipe. 2. Inside the outer layer part (1) made of a heat-resistant cast steel product, in weight%, Cr: 50% or more, Co: 6% or less, W: 5% or less, Si: 0.5-3. 0.5%, Mn:
0.5 to 1.5%, C: 0.03 to 0.2%, balance: Corrosion resistant gas integrally formed with an inner layer portion (2) made of an alloy for corrosion resistant gas consisting essentially of Fe tube. 3. Cr: 50% or more, Co: 6% or less, W: 5% or less, Si: 0.5 to 3 in weight% inside the outer layer portion (1) made of a heat-resistant cast steel product. 0.5%, Mn:
0.5-1.5%, Mo: 5% or less, C: 0.03-
0.2%, balance: Corrosion resistant gas pipe integrally formed with an inner layer portion (2) made of an alloy for corrosion resistant gas consisting essentially of Fe. 4. Inside the outer layer portion (1) made of a heat-resistant cast steel product, in weight%, Cr: 50% or more, Ni: 5% or less, Co: 6% or less, W: 5% or less, Al : 2% or less,
Si: 0.5-3.5%, Mn: 0.5-1.5%, M
o: 5% or less, B: 0.8% or less, Zr: 0.1% or less, C: 0.03 to 0.2%, the balance: an inner layer portion made of a corrosion-resistant gas alloy consisting essentially of Fe. A pipe for corrosion resistant gas in which (2) is integrally formed. 5. A weld groove (3) is formed at both edge portions of the outer layer portion (1), and both end portions of the inner layer portion (2) corresponding to locations where the weld groove portion (3) is formed. The pipe for corrosion resistant gas according to any one of claims 1 to 4, wherein (4) is removed. 6. The method for manufacturing a corrosion-resistant gas pipe according to claim 1, wherein the outer layer portion (1) is provided.
Method for producing a pipe for corrosion resistant gas, wherein the inner layer portion (2) is formed by overlaying inside 7. The method for manufacturing a corrosion-resistant gas pipe according to claim 1, wherein the outer layer portion (1) is provided.
And a method for producing a corrosion-resistant gas pipe, wherein the inner layer portion (2) is formed by centrifugal casting 8. An outer layer of an inner layer made of a heat-resistant cast steel product,
% By weight, Cr: 50% or more, balance: Corrosion resistant gas pipe integrally formed with an outer layer portion made of an alloy for corrosion resistant gas consisting essentially of Fe. 9. An outer layer of an inner layer made of a heat-resistant cast steel product,
In weight%, Cr: 50% or more, Co: 6% or less, W:
5% or less, Si: 0.5 to 3.5%, Mn: 0.5 to
1.5%, C: 0.03 to 0.2%, balance: substantially F
A corrosion-resistant gas pipe integrally formed with an outer layer made of a corrosion-resistant gas alloy of e. 10. A Cr: 50% or more, Co: 6% or less, in weight%, outside the inner layer portion made of a heat-resistant cast steel product,
W: 5% or less, Si: 0.5 to 3.5%, Mn: 0.5
~ 1.5%, Mo: 5% or less, C: 0.03 to 0.2
%, Balance: Corrosion resistant gas pipe integrally formed with an outer layer portion made of an alloy for corrosion resistant gas consisting essentially of Fe. 11. A Cr: 50% or more, Ni: 5% or less, in weight%, outside the inner layer portion made of a heat-resistant cast steel product,
Co: 6% or less, W: 5% or less, Al: 2% or less, S
i: 0.5 to 3.5%, Mn: 0.5 to 1.5%, M
o: 5% or less, B: 0.8% or less, Zr: 0.1% or less, C: 0.03 to 0.2%, the balance: an outer layer portion made of an alloy for corrosion resistant gas consisting essentially of Fe. Corrosion resistant gas pipe that is integrally formed with.