JPH10204563A - Composite heat exchanger tube for waste heat boiler using exhaust gas of refuse incinerator excellent in high temperature corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a composite heat exchanger tube for an waste heat boiler using the exhaust gas of a refuse incinerator excellent in high temp. corrosion resistance by composing the tube of an external layer consisting of an Ni base alloy in which contents of Cr, Mo, Nb, Fe, C, Mg, B and Ni are specified and contents of Si, P and S being impurities are specified and an internal layer consisting of an ordinary boiler steel. SOLUTION: By using a composite tube composed of an external layer consisting of an Ni base alloy excellent in high temp. corrosion-resistance, particularly, in high temp. intergranular corrosion resistance and an internal layer consisting of an ordinary boiler steel excellent in strength and water vapor oxidation resistance, a thin heat transfer tube for a waste heat boiler having a long service life is obtd. The compsn. of the Ni base alloy is regulated to the one contg., by weight, 18.5 to 25% Cr, 16.6 to 25% Mo, 0.5 to 5% Nb, 0.01 to 7% Fe, 0.001 to 0.05% C, 0.001 to 0.1% Mg and 0.001 to 0.1% B, furthermore contg., at need, prescribed amounts of W, rare earth elements, Y, Zr, Hf, Mn and Ca, and the balance Ni with inevitable impurities, and in which the content of Si is limited to <=0.1%, the content of P is limited to <=0.03% and the content of S is limited to <=0.03% in the inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite pipe for heat transfer of a waste heat boiler utilizing refuse incineration exhaust gas, which is excellent in high-temperature corrosion resistance, particularly high-temperature intergranular corrosion resistance.

[0002]

2. Description of the Related Art Generally, a waste heat boiler is installed in a refuse incineration plant for the purpose of utilizing high-temperature latent heat of exhaust gas. Further, the composite tube for heat transfer, which is a structural member of the waste heat boiler, is made of highly corrosive HCl or SO ₂ gas, Na ₂ SO ₄
Exposed to high-temperature exhaust gas containing corrosive products such as molten sulfates such as molten chlorides such as NaCl and KCl, and placed in an environment where the sulfates and chlorides are deposited on the surface. Therefore, various materials having excellent high-temperature corrosion resistance are used for the production.

In a waste incineration plant, as a material for a heat transfer tube of a waste heat boiler utilizing the high temperature latent heat of exhaust gas, in terms of% by weight (hereinafter,% indicates% by weight), Cr: 20 to 25%, C:
r: 18 to 25%, Nb: 0.5 to 5%, Fe: 0.0
1 to 7%, C: 0.05% or less, Si: 0.1% or less,
P: 0.03% or less, S: 0.03% or less, and if necessary, (a) W: 0.1 to 2%, (b)
Rare earth element: 0.001 to 0.1%, Y: 0.001
-0.1%, Zr: 0.001-0.1%, Hf: 0.
001 to 0.1%, B: one or more of 0.001 to 0.01%, containing at least (a) and / or (b), with the balance being Ni and unavoidable impurities A heat transfer tube made of a Ni-based alloy having the following has been proposed (see JP-A-7-258781). This Ni
A heat transfer tube composed of a base alloy is incorporated in a waste heat boiler, and the waste heat boiler is installed in a waste incineration facility having a processing capacity of 200 tons / day. The surface temperature of the heat transfer tube is 500 ° C and the exhaust gas temperature is 650 ° C. 1000 hours of operation under the conditions,
After the operation was completed, the heat transfer tube was taken out, and the wall thickness and the cross-sectional microstructure in the circumferential direction were measured in a state where the ash attached to the surface and the generated scale were removed.
~ 0.25mm, maximum intergranular corrosion length is 0.01 ~ 0.0
It was 4 mm, indicating excellent high-temperature corrosion resistance. Since heat transfer tubes made of these Ni-base alloys are generally expensive, they are coated on the outside of ordinary boiler steel, and an inner layer made of ordinary boiler steel and an outer layer made of a newly developed Ni-based alloy are used. It is also known to use a composite tube made of a composite tube for heat transfer.

[0004]

On the other hand, due to the urgent energy situation in recent years, the steam condition of a waste heat boiler tends to be high temperature and high pressure in order to make maximum use of waste heat generated by incineration of refuse. The tube wall temperature of the heat transfer composite pipes rises further, and the corrosiveness of the exhaust gas tends to increase further due to the increase in the calories of waste and the increase in plastics. The composite tube has
Further high-temperature corrosion resistance is required, and further, high-temperature strength capable of reducing the wall thickness of the pipe is strongly required from the viewpoint of improving heat transfer efficiency. The Ni-based alloy described in the above-mentioned conventional Japanese Patent Application Laid-Open No. Hei 7-258781, which has been provided in response to this request, has considerably improved high-temperature corrosion resistance against exhaust gas, but is still insufficient. The service life of the heat transfer composite tube with the constructed outer layer was not satisfactory.

[0005]

Means for Solving the Problems Accordingly, the present inventors have
From the above-mentioned viewpoints, as a result of researching to develop a composite tube for heat transfer of a waste heat boiler utilizing waste incineration exhaust gas, which is more excellent in high-temperature corrosion resistance and more excellent, the results are as follows. The composite pipe for heat transfer of a waste heat boiler utilizing an incineration exhaust gas having an outer layer composed of a Ni-based alloy described in JP-A-2587871 does not have sufficient high-temperature intergranular corrosion resistance, so that highly corrosive HCl or SO _{2 is used.} Gas, Na ₂ SO ₄ , K ₂ SO
Molten sulfates such as ₄ and also NaCl, KCl, PbC
When exposed to high-temperature exhaust gas of 300 to 1000 ° C. in a state where molten chlorides such as l ₂ and ZnCl ₂ adhere and deposit on the surface, intergranular corrosion progresses, and as a result, sufficient high-temperature corrosion resistance cannot be obtained. Therefore, a sufficient life cannot be obtained. (B) When 0.001 to 0.1% of Mg is contained in the above-mentioned conventional Ni-base alloy described in JP-A-7-258781, hot workability is excellent. In addition, a Ni-base alloy with improved high-temperature intergranular corrosion resistance is obtained, and a composite tube for heat transfer of a waste heat boiler utilizing an incineration exhaust gas having an outer layer made of this Ni-base alloy is manufactured by plastic working. Is 0.00
Since the outer layer made of a Ni-based alloy containing 1 to 0.1% is excellent in hot workability, a heat transfer composite pipe excellent in adhesion to an inner layer made of ordinary boiler steel is obtained. In addition, since the high-temperature intergranular corrosion resistance is further excellent, the high-temperature corrosion resistance is further improved, and the life of the heat transfer composite tube is further extended. (C) Conventional Ni described in JP-A-7-258781. The base alloy contains 0.001 to 0.1% of Mg, and further contains 0.01 to 1.0% of Mn and C
a: Research results were obtained such that when one or two of 0.001 to 0.1% were added, more stable high-temperature corrosion resistance could be obtained.

The present invention has been made on the basis of the above-mentioned research results. (I) Cr: 18.5 to 25%, Cr: 16.6 to 25
%, Nb: 0.5 to 5%, Fe: 0.01 to 7%, C:
0.001-0.05%, Mg: 0.001-0.1
%, B: 0.001 to 0.1, and if necessary, (a) W: 0.1 to 2%, (b) rare earth element:
0.001-0.1%, Y: 0.001-0.1%, Z
r: 0.001 to 0.1%, Hf: 0.001 to 0.1
%, One or more of the above (a) and / or (b), and the remainder consists of Ni and unavoidable impurities. 1% or less, P: 0.03% or less, S:
Waste heat from waste incineration flue gas with excellent high-temperature corrosion resistance, especially high-temperature intergranular corrosion resistance, composed of an outer layer composed of a Ni-based alloy having a composition limited to 0.03% or less and an inner layer composed of ordinary boiler steel (II) In addition to the Ni-based alloy described in (I) above, Mn:
0.01-1.0% and Ca: 0.001-0.1%
Waste incineration exhaust gas excellent in high-temperature corrosion resistance, particularly high-temperature intergranular corrosion resistance, composed of an outer layer composed of a Ni-based alloy having a composition containing one or two of the above and an inner layer composed of ordinary boiler steel The composite pipe for heat transfer of a waste heat boiler is characterized.

In the composite pipe for heat transfer of a waste heat boiler utilizing refuse incineration exhaust gas excellent in high-temperature corrosion resistance according to the present invention, the outer layer made of a Ni-based alloy has an effect of ensuring high-temperature corrosion resistance, particularly high-temperature intergranular corrosion resistance. However, the inner layer made of ordinary steel for boilers serves to impart strength and steam oxidation resistance. The "ordinary boiler steel" used in the heat transfer composite pipe of the waste heat boiler utilizing waste incineration exhaust gas excellent in high-temperature corrosion resistance according to the present invention is specifically the boiler specified in JIS 3461 to 3464 and 3467 Examples thereof include carbon steel for heat exchanger, low alloy steel, ferritic stainless steel, austenitic stainless steel, and the like, and the steel type can be appropriately selected depending on the use conditions, and is not particularly limited. Further, the composite tube for heat transfer of the waste heat boiler utilizing waste incineration exhaust gas excellent in high-temperature corrosion resistance of the present invention is obtained by inserting a normal steel tube for a boiler into a tube made of a Ni-based alloy, and performing a normal plastic working process. The outer layer made of a Ni-based alloy can also be manufactured by spraying or overlay welding the new Ni-based alloy of the present invention.

The reason why the composition of the Ni-base alloy constituting the outer layer of the composite tube for heat transfer according to the present invention is limited as described above will be described. (A) Cr and Mo These components have an effect of improving high-temperature corrosion resistance and high-temperature oxidation resistance against high-temperature incineration exhaust gas in a coexisting state, and improving high-temperature strength. If any of Mo is less than 18.5% of Cr and less than 16.6% of Mo, a desired effect cannot be obtained in the above-mentioned action, while the content of Cr is also 25% even if any of Cr and Mo is used. And Mo: over 25%, the hot workability deteriorates. Therefore, the content of Cr is set to 18.5 to 25% (preferably 20%).
-23%), Cr: 16.6-25% (preferably 1
6.6-21%).

(B) Nb The Nb component has an effect of improving corrosion resistance to sulfates and chlorides, which are corrosive products in high-temperature exhaust gas. The desired effect of improving the high-temperature corrosion resistance cannot be obtained. On the other hand, if the content exceeds 5%, the hot workability decreases, so that the content is 0.5 to 5%, preferably 0.1 to 0.5%. It was determined to be 5 to 2%.

(C) Fe The Fe component has an effect of improving hot workability, but if its content is less than 0.01%, desired hot workability cannot be ensured. If the amount exceeds 7%, the toughness will decrease.
The content is determined to be 1 to 7%, preferably 0.5 to 5%.

(D) C The C component has the effect of improving the high-temperature strength. However, if its content is less than 0.001%, the desired high-temperature strength cannot be ensured. If it exceeds 0.05%, the amount of carbide present at the grain boundaries increases, and in particular, the progress of intergranular corrosion due to the molten chloride contained in the high-temperature exhaust gas is promoted. The content was determined to be 0.001 to 0.05%.

(E) Mg The Mg component has the effect of improving hot workability and improving high-temperature intergranular corrosion resistance.
If the content is less than 1%, the desired effect cannot be obtained. On the other hand, if the content exceeds 0.1%, a metal compound is formed at the grain boundary, and hot workability and high-temperature intergranular corrosion resistance are reduced. Therefore, the content was determined to be 0.001 to 0.1%, preferably 0.001 to 0.05%.

(F) B The B component has an effect of improving hot workability, but if its content is less than 0.001%, the desired effect cannot be obtained.
On the other hand, a boron compound is formed at the grain boundary where the content exceeds 0.1%, and the hot workability and the high-temperature intergranular corrosion resistance are reduced. 1
%, Desirably 0.001 to 0.01%.

(G) W Since the W component has an action of further improving the high-temperature corrosion resistance, it is contained as necessary.
If the content is less than 1%, a desired improvement effect cannot be obtained, and if the content exceeds 2%, the hot workability is reduced, so that the content is 0.1 to 2%. Desirably, it is set to 0.5 to 1.5%.

(H) Rare earth elements, Y, Zr, Hf These components have an effect of improving hot workability, so that they are contained as necessary. If the content is less than 0.001%, the desired effect of improving hot workability cannot be obtained. On the other hand, if the content exceeds 0.1%, no further improvement effect can be obtained by hot workability. Is a rare earth element: 0.001 to 0.1
%, Y: 0.001 to 0.1%, Zr: 0.001 to
0.1%, Hf: 0.001 to 0.1%.

(I) Mn, Ca Mn and Ca have a deoxidizing effect and an effect of improving corrosion resistance. Therefore, Mn and Ca are added as necessary. , Ca component 0.00
If it is less than 1%, the desired effect cannot be obtained in the above-mentioned action, while
If the content exceeds 1.0% in the Mn component and exceeds 0.1% in the Ca component, these precipitated phases are formed, and the hot workability and the corrosion resistance are reduced.
1.0%, Ca: 0.001 to 0.1%.

(J) Inevitable impurities In some cases, Si, P, S, Ti and Al are contained as inevitable impurities. If the content of the Si component exceeds 0.1%, the toughness decreases, and If S and S exceed 0.03% and 0.03%, respectively, P segregates at the grain boundaries, lowering hot workability and lowering high-temperature intergranular corrosion resistance. If the Al content exceeds 0.4%, the hot workability is impaired. Therefore, Si, P, S, Ti and Al
Are Si: 0.1% or less, P: 0.03% or less, respectively.
S: 0.03% or less, Ti: 0.4% or less, Al: 0.
Should be kept below 4%.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the composite tube for heat transfer of the present invention will be specifically described with reference to examples. Using an ordinary high-frequency melting furnace, a Ni-base alloy melt is prepared and cast into an ingot, and the ingot is subjected to hot forging at a predetermined temperature in the range of 1000 to 1250 ° C. to obtain a round bar having a diameter of 58 mm. Then, from this round bar material, outer diameter: 50.8 mm x wall thickness:
An outer tube having the component composition shown in Tables 1 to 5 was produced by cutting to a size of 4.0 mm. Further, SUS3 having an outer diameter of 42 mm and a thickness of 6.0 mm as an inner tube.
A 04 stainless steel tube was prepared. After descaling the outer tube and the inner tube, insert the inner tube inside the outer tube, perform drawing at a predetermined area reduction rate, plastically deform the outer tube, and bring the outer tube into close contact with the inner tube. To prepare a composite shell.
After placing these composite tubes in a heating furnace and maintaining them at 1180 ° C. for 1 hour, they were further rolled by a helical roll mill to obtain a composite tube 1 for heat transfer according to the present invention having dimensions of an outer layer thickness: 3 mm and a diameter: 38.1 mm. ~ 45, composite tube 1 for comparative heat transfer
To 2 and the conventional heat transfer composite tube 1 were manufactured. The composite tubes 1 and 2 for comparative heat transfer were those in which the content of Mg affecting the high-temperature intergranular corrosion resistance was out of the range of the present invention among the components of the Ni-based alloy constituting the outer layer. is there.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

[0022]

[Table 4]

[0023]

[Table 5]

Then, the various heat transfer composite tubes obtained as a result are assembled into a waste heat boiler, and the waste heat boiler is installed in a waste incineration facility having a processing capacity of 200 tons / day. Surface temperature: 500 ° C, exhaust gas temperature: 670 ° C
After 1500 hours of operation, the composite tube for heat transfer was taken out after the completion of the operation, and the thickness of the outer layer composed of the Ni-based alloy in the circumferential direction was measured in a state where ash attached to the surface and formed scale were removed. In addition to obtaining the maximum wall loss, the cross-sectional microstructure of the surface was observed to measure the maximum intergranular corrosion length. The results are shown in Tables 6 and 7.

[0025]

[Table 6]

[0026]

[Table 7]

[0027]

According to the results shown in Tables 1 to 7, the heat transfer composite tubes 1 to 45 of the present invention have a maximum performance when exposed to a waste incineration exhaust gas atmosphere at a higher temperature than the conventional heat transfer composite tube 1. From the fact that the amount of thinning is small and the maximum intergranular corrosion length is short, it can be seen that excellent high-temperature corrosion resistance is exhibited. However, as can be seen in the composite tubes for comparative heat transfer 1-2, the Ni constituting the outer layer
It is clear that if the Mg content of the base alloy is out of the range of the present invention, the high-temperature corrosion resistance, particularly the high-temperature intergranular corrosion resistance, is inferior, and as a result, the high-temperature corrosion resistance is inferior.

As described above, the composite tube for heat transfer of the present invention has much higher high-temperature corrosion resistance. To reduce the thickness of the outer layer made of an expensive Ni-based alloy, to further extend the life of the heat transfer composite pipe, and to effectively use waste heat generated by incineration of waste. Can greatly contribute to the improvement of waste heat boiler technology.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] March 27, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

[Title of the Invention] Composite tube for heat transfer of waste heat boiler utilizing waste incineration exhaust gas with excellent high temperature corrosion resistance

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite pipe for heat transfer of a waste heat boiler utilizing refuse incineration exhaust gas, which is excellent in high-temperature corrosion resistance, particularly high-temperature intergranular corrosion resistance.

[0002]

2. Description of the Related Art Generally, a waste heat boiler is installed in a refuse incineration plant for the purpose of utilizing high-temperature latent heat of exhaust gas. Further, the composite tube for heat transfer, which is a structural member of the waste heat boiler, is made of highly corrosive HCl or SO ₂ gas, Na ₂ SO ₄
Exposed to high-temperature exhaust gas containing corrosive products such as molten sulfates such as molten chlorides such as NaCl and KCl, and placed in an environment where the sulfates and chlorides are deposited on the surface. Therefore, various materials having excellent high-temperature corrosion resistance are used for the production.

In a waste incineration plant, as a material for a heat transfer tube of a waste heat boiler utilizing the high temperature latent heat of exhaust gas, in terms of weight% (hereinafter,% indicates weight%), Cr: 20 to 25%, M
o: 18 to 25%, Nb: 0.5 to 5%, Fe: 0.0
1 to 7%, C: 0.05% or less, Si: 0.1% or less,
P: 0.03% or less, S: 0.03% or less, and if necessary, (a) W: 0.1 to 2%, (b)
Rare earth element: 0.001 to 0.1%, Y: 0.001
-0.1%, Zr: 0.001-0.1%, Hf: 0.
001 to 0.1%, B: one or more of 0.001 to 0.01%, containing at least (a) and / or (b), with the balance being Ni and unavoidable impurities A heat transfer tube made of a Ni-based alloy having the following has been proposed (see JP-A-7-258781). This Ni
A heat transfer tube composed of a base alloy is incorporated in a waste heat boiler, and the waste heat boiler is installed in a waste incineration facility having a processing capacity of 200 tons / day. The surface temperature of the heat transfer tube is 500 ° C and the exhaust gas temperature is 650 ° C. 1000 hours of operation under the conditions,
After the operation was completed, the heat transfer tube was taken out, and the wall thickness and the cross-sectional microstructure in the circumferential direction were measured in a state where the ash attached to the surface and the generated scale were removed.
~ 0.25mm, maximum intergranular corrosion length is 0.01 ~ 0.0
It was 4 mm, indicating excellent high-temperature corrosion resistance. Since heat transfer tubes made of these Ni-based alloys are generally expensive, they are coated on the outside of ordinary boiler steel, and an inner layer made of ordinary boiler steel and an outer layer made of a newly developed Ni-based alloy are used. It is also known to use a composite tube made of a composite tube for heat transfer.

[0004]

On the other hand, due to the urgent energy situation in recent years, the steam condition of a waste heat boiler tends to be high temperature and high pressure in order to make maximum use of waste heat generated by incineration of refuse. The tube wall temperature of the heat transfer composite pipes rises further, and the corrosiveness of the exhaust gas tends to increase further due to the increase in the calories of waste and the increase in plastics. The composite tube has
Further high-temperature corrosion resistance is required, and further, high-temperature strength capable of reducing the wall thickness of the pipe is strongly required from the viewpoint of improving heat transfer efficiency. The Ni-based alloy described in the above-mentioned conventional Japanese Patent Application Laid-Open No. Hei 7-258781, which has been provided in response to this request, has considerably improved high-temperature corrosion resistance against exhaust gas, but is still insufficient. The service life of the heat transfer composite tube with the constructed outer layer was not satisfactory.

[0005]

Means for Solving the Problems Accordingly, the present inventors have
From the above-mentioned viewpoints, as a result of researching to develop a composite tube for heat transfer of a waste heat boiler utilizing waste incineration exhaust gas, which is more excellent in high-temperature corrosion resistance and more excellent, the results are as follows. The composite pipe for heat transfer of a waste heat boiler utilizing an incineration exhaust gas having an outer layer composed of a Ni-based alloy described in JP-A-2587871 does not have sufficient high-temperature intergranular corrosion resistance, so that highly corrosive HCl or SO _{2 is used.} Gas, Na ₂ SO ₄ , K ₂ SO
Molten sulfates such as ₄ and also NaCl, KCl, PbC
When exposed to high-temperature exhaust gas of 300 to 1000 ° C. in a state where molten chlorides such as l ₂ and ZnCl ₂ adhere and deposit on the surface, intergranular corrosion progresses, and as a result, sufficient high-temperature corrosion resistance cannot be obtained. Therefore, a sufficient life cannot be obtained. (B) When 0.001 to 0.1% of Mg is contained in the above-mentioned conventional Ni-base alloy described in JP-A-7-258781, hot workability is excellent. In addition, a Ni-base alloy with improved high-temperature intergranular corrosion resistance is obtained, and a composite tube for heat transfer of a waste heat boiler utilizing an incineration exhaust gas having an outer layer made of this Ni-base alloy is manufactured by plastic working. Is 0.00
Since the outer layer made of a Ni-based alloy containing 1 to 0.1% is excellent in hot workability, a heat transfer composite pipe excellent in adhesion to an inner layer made of ordinary boiler steel is obtained. In addition, since the high-temperature intergranular corrosion resistance is further excellent, the high-temperature corrosion resistance is further improved, and the life of the heat transfer composite tube is further extended. (C) Conventional Ni described in JP-A-7-258781. The base alloy contains 0.001 to 0.1% of Mg, and further contains 0.01 to 1.0% of Mn and C
a: Research results were obtained such that when one or two of 0.001 to 0.1% were added, more stable high-temperature corrosion resistance could be obtained.

The present invention has been made on the basis of the above research results. (I) Cr: 18.5 to 25%, Mo: 16.6 to 25
%, Nb: 0.5 to 5%, Fe: 0.01 to 7%, C:
0.001-0.05%, Mg: 0.001-0.1
%, B: 0.001 to 0.1, and if necessary, (a) W: 0.1 to 2%, (b) rare earth element:
0.001-0.1%, Y: 0.001-0.1%, Z
r: 0.001 to 0.1%, Hf: 0.001 to 0.1
%, One or more of the above (a) and / or (b), and the remainder consists of Ni and unavoidable impurities. 1% or less, P: 0.03% or less, S:
Waste heat from waste incineration flue gas with excellent high-temperature corrosion resistance, especially high-temperature intergranular corrosion resistance, composed of an outer layer composed of a Ni-based alloy having a composition limited to 0.03% or less and an inner layer composed of ordinary boiler steel (II) In addition to the Ni-based alloy described in (I) above, Mn:
0.01-1.0% and Ca: 0.001-0.1%
Waste incineration exhaust gas excellent in high-temperature corrosion resistance, particularly high-temperature intergranular corrosion resistance, composed of an outer layer composed of a Ni-based alloy having a composition containing one or two of the above and an inner layer composed of ordinary boiler steel The composite pipe for heat transfer of a waste heat boiler is characterized.

In the composite pipe for heat transfer of a waste heat boiler utilizing refuse incineration exhaust gas excellent in high-temperature corrosion resistance according to the present invention, the outer layer made of a Ni-based alloy has an effect of ensuring high-temperature corrosion resistance, particularly high-temperature intergranular corrosion resistance. However, the inner layer made of ordinary steel for boilers serves to impart strength and steam oxidation resistance. The "ordinary boiler steel" used in the heat transfer composite pipe of the waste heat boiler utilizing waste incineration exhaust gas excellent in high-temperature corrosion resistance according to the present invention is specifically the boiler specified in JIS 3461 to 3464 and 3467 Examples thereof include carbon steel for heat exchanger, low alloy steel, ferritic stainless steel, austenitic stainless steel, and the like, and the steel type can be appropriately selected depending on the use conditions, and is not particularly limited. Further, the composite tube for heat transfer of the waste heat boiler utilizing waste incineration exhaust gas excellent in high-temperature corrosion resistance of the present invention is obtained by inserting a normal steel tube for a boiler into a tube made of a Ni-based alloy, and performing a normal plastic working process. The outer layer made of a Ni-based alloy can also be manufactured by spraying or overlay welding the new Ni-based alloy of the present invention.

The reason why the composition of the Ni-base alloy constituting the outer layer of the composite tube for heat transfer according to the present invention is limited as described above will be described. (A) Cr and Mo These components have an effect of improving high-temperature corrosion resistance and high-temperature oxidation resistance against high-temperature incineration exhaust gas in a coexisting state, and improving high-temperature strength. If any of Mo is less than 18.5% of Cr and less than 16.6% of Mo, a desired effect cannot be obtained in the above-mentioned action, while the content of Cr is also 25% even if any of Cr and Mo is used. And Mo: over 25%, the hot workability deteriorates. Therefore, the content of Cr is set to 18.5 to 25% (preferably 20%).
-23%), Mo: 16.6-25% (desirably 1
6.6-21%).

(B) Nb The Nb component has an effect of improving corrosion resistance to sulfates and chlorides, which are corrosive products in high-temperature exhaust gas. The desired effect of improving the high-temperature corrosion resistance cannot be obtained. On the other hand, if the content exceeds 5%, the hot workability decreases, so that the content is 0.5 to 5%, preferably 0.1 to 0.5%. It was determined to be 5 to 2%.

(C) Fe The Fe component has an effect of improving hot workability, but if its content is less than 0.01%, desired hot workability cannot be ensured. If the amount exceeds 7%, the toughness will decrease.
The content is determined to be 1 to 7%, preferably 0.5 to 5%.

(D) C The C component has the effect of improving the high-temperature strength. However, if its content is less than 0.001%, the desired high-temperature strength cannot be ensured. If it exceeds 0.05%, the amount of carbide present at the grain boundaries increases, and in particular, the progress of intergranular corrosion due to the molten chloride contained in the high-temperature exhaust gas is promoted. The content was determined to be 0.001 to 0.05%.

(E) Mg The Mg component has the effect of improving hot workability and improving high-temperature intergranular corrosion resistance.
If the content is less than 1%, the desired effect cannot be obtained. On the other hand, if the content exceeds 0.1%, a metal compound is formed at the grain boundary, and hot workability and high-temperature intergranular corrosion resistance are reduced. Therefore, the content was determined to be 0.001 to 0.1%, preferably 0.001 to 0.05%.

(F) B The B component has an effect of improving hot workability, but if its content is less than 0.001%, the desired effect cannot be obtained.
On the other hand, a boron compound is formed at the grain boundary where the content exceeds 0.1%, and the hot workability and the high-temperature intergranular corrosion resistance are reduced. 1
%, Desirably 0.001 to 0.01%.

(G) W Since the W component has an action of further improving the high-temperature corrosion resistance, it is contained as necessary.
If the content is less than 1%, a desired improvement effect cannot be obtained, and if the content exceeds 2%, the hot workability is reduced, so that the content is 0.1 to 2%. Desirably, it is set to 0.5 to 1.5%.

(H) Rare earth elements, Y, Zr, Hf These components have an effect of improving hot workability, so that they are contained as necessary. If the content is less than 0.001%, the desired effect of improving hot workability cannot be obtained. On the other hand, if the content exceeds 0.1%, no further improvement effect can be obtained by hot workability. Is a rare earth element: 0.001 to 0.1
%, Y: 0.001 to 0.1%, Zr: 0.001 to
0.1%, Hf: 0.001 to 0.1%.

(I) Mn, Ca Mn and Ca have a deoxidizing effect and an effect of improving corrosion resistance. Therefore, Mn and Ca are added as necessary. , Ca component 0.00
If it is less than 1%, the desired effect cannot be obtained in the above-mentioned action, while
If the content exceeds 1.0% in the Mn component and exceeds 0.1% in the Ca component, these precipitated phases are formed, and the hot workability and the corrosion resistance are reduced.
1.0%, Ca: 0.001 to 0.1%.

(J) Inevitable impurities In some cases, Si, P, S, Ti and Al are contained as inevitable impurities. If the content of the Si component exceeds 0.1%, the toughness decreases, and If S and S exceed 0.03% and 0.03%, respectively, P segregates at the grain boundaries, lowering hot workability and lowering high-temperature intergranular corrosion resistance. If the Al content exceeds 0.4%, the hot workability is impaired. Therefore, Si, P, S, Ti and Al
Are Si: 0.1% or less, P: 0.03% or less, respectively.
S: 0.03% or less, Ti: 0.4% or less, Al: 0.
Should be kept below 4%.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the composite tube for heat transfer of the present invention will be specifically described with reference to examples. Using an ordinary high-frequency melting furnace, a Ni-base alloy melt is prepared and cast into an ingot, and the ingot is subjected to hot forging at a predetermined temperature in the range of 1000 to 1250 ° C. to obtain a round bar having a diameter of 58 mm. Then, from this round bar material, outer diameter: 50.8 mm x wall thickness:
An outer tube having the component composition shown in Tables 1 to 5 was produced by cutting to a size of 4.0 mm. Further, SUS3 having an outer diameter of 42 mm and a thickness of 6.0 mm as an inner tube.
A 04 stainless steel tube was prepared. After descaling the outer tube and the inner tube, insert the inner tube inside the outer tube, perform drawing at a predetermined area reduction rate, plastically deform the outer tube, and bring the outer tube into close contact with the inner tube. To prepare a composite shell.
After placing these composite tubes in a heating furnace and maintaining them at 1180 ° C. for 1 hour, they were further rolled by a helical roll mill to obtain a composite tube 1 for heat transfer according to the present invention having dimensions of an outer layer thickness: 3 mm and a diameter: 38.1 mm. ~ 45, composite tube 1 for comparative heat transfer
To 2 and the conventional heat transfer composite tube 1 were manufactured. The composite tubes 1 and 2 for comparative heat transfer were those in which the content of Mg affecting the high-temperature intergranular corrosion resistance was out of the range of the present invention among the components of the Ni-based alloy constituting the outer layer. is there.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

[0022]

[Table 4]

[0023]

[Table 5]

Then, the various heat transfer composite tubes obtained as a result are assembled into a waste heat boiler, and the waste heat boiler is installed in a waste incineration facility having a processing capacity of 200 tons / day. Surface temperature: 500 ° C, exhaust gas temperature: 670 ° C
After 1500 hours of operation, the composite tube for heat transfer was taken out after the completion of the operation, and the thickness of the outer layer composed of the Ni-based alloy in the circumferential direction was measured in a state where ash attached to the surface and formed scale were removed. In addition to obtaining the maximum wall loss, the cross-sectional microstructure of the surface was observed to measure the maximum intergranular corrosion length. The results are shown in Tables 6 and 7.

[0025]

[Table 6]

[0026]

[Table 7]

[0027]

According to the results shown in Tables 1 to 7, the heat transfer composite tubes 1 to 45 of the present invention have a maximum performance when exposed to a waste incineration exhaust gas atmosphere at a higher temperature than the conventional heat transfer composite tube 1. From the fact that the amount of thinning is small and the maximum intergranular corrosion length is short, it can be seen that excellent high-temperature corrosion resistance is exhibited. However, as can be seen in the composite tubes for comparative heat transfer 1-2, the Ni constituting the outer layer
It is clear that if the Mg content of the base alloy is out of the range of the present invention, the high-temperature corrosion resistance, particularly the high-temperature intergranular corrosion resistance, is inferior, and as a result, the high-temperature corrosion resistance is inferior.

As described above, the composite tube for heat transfer of the present invention has much higher high-temperature corrosion resistance. Therefore, the steam condition of the waste heat boiler for increasing the temperature and pressure of the waste heat boiler for effectively utilizing the waste heat generated by the incineration of refuse. To reduce the thickness of the outer layer made of an expensive Ni-based alloy, to further extend the life of the heat transfer composite pipe, and to effectively use waste heat generated by incineration of waste. Can greatly contribute to the improvement of waste heat boiler technology.

Claims (5)

[Claims] Claims: 1. A weight percentage of Cr: 18.5-25%, C
r: 16.6 to 25%, Nb: 0.5 to 5%, Fe:
0.01-7%, C: 0.001-0.05%, Mg:
0.001 to 0.1%, B: 0.001 to 0.1, and the remainder is composed of Ni and unavoidable impurities.
1% or less, P: 0.03% or less, S: 0.03% or less, characterized by comprising an outer layer composed of a Ni-based alloy having a composition limited to less than 0.03% and an inner layer composed of ordinary boiler steel. Composite tube for heat transfer of waste heat boiler using waste incineration exhaust gas with excellent high temperature corrosion resistance. 2. Cr content: 18.5 to 25% by weight, C
r: 16.6 to 25%, Nb: 0.5 to 5%, Fe:
0.01-7%, C: 0.001-0.05%, Mg:
0.001 to 0.1%, B: 0.001 to 0.1, W: 0.1 to 2%, and the remainder is composed of Ni and inevitable impurities and is included as inevitable impurities. S
i, P and S are each 0.1% or less of Si;
A garbage excellent in high-temperature corrosion resistance, comprising an outer layer made of a Ni-based alloy having a composition limited to 0.03% or less and S: 0.03% or less and an inner layer made of ordinary boiler steel. Composite tube for heat transfer of waste heat boiler utilizing incineration exhaust gas. 3. A weight percentage of Cr: 18.5 to 25%, C
r: 16.6 to 25%, Nb: 0.5 to 5%, Fe:
0.01-7%, C: 0.001-0.05%, Mg:
0.001 to 0.1%, B: 0.001 to 0.1, Rare earth element: 0.001 to 0.1%, Y: 0.
001-0.1%, Zr: 0.001-0.1%, H
f: One or two or more of 0.001 to 0.1% are contained, and the remainder consists of Ni and unavoidable impurities, and Si, P and S contained as unavoidable impurities are each Si:
0.1% or less, P: 0.03% or less, S: 0.03% or less characterized by comprising an outer layer composed of a Ni-based alloy having a composition restricted to less than 0.03% and an inner layer composed of ordinary boiler steel. Composite tube for heat transfer of waste heat boiler utilizing waste incineration exhaust gas with excellent high temperature corrosion resistance. 4. The composition according to claim 1, wherein Cr is 18.5 to 25% by weight and C is
r: 16.6 to 25%, Nb: 0.5 to 5%, Fe:
0.01-7%, C: 0.001-0.05%, Mg:
0.001 to 0.1%, B: 0.001 to 0.1, W: 0.1 to 2%, Rare earth element: 0.001 to 0.1%, Y: 0.
001-0.1%, Zr: 0.001-0.1%, H
f: One or two or more of 0.001 to 0.1% are contained, and the remainder consists of Ni and unavoidable impurities, and Si, P and S contained as unavoidable impurities are each Si:
0.1% or less, P: 0.03% or less, S: 0.03% or less characterized by comprising an outer layer composed of a Ni-based alloy having a composition restricted to less than 0.03% and an inner layer composed of ordinary boiler steel. Composite tube for heat transfer of waste heat boiler utilizing waste incineration exhaust gas with excellent high temperature corrosion resistance. 5. The Ni-base alloy according to claim 1, further comprising Mn: 0.01 to 1.0% and Ca:
A garbage excellent in high-temperature corrosion resistance, comprising an outer layer composed of a Ni-based alloy containing one or two of 0.001 to 0.1% and an inner layer composed of ordinary boiler steel. Composite tube for heat transfer of waste heat boiler utilizing incineration exhaust gas.