JPH10168554A - Method for treating surface of steel tube for sulfodation corrosion resistant and erosion-resistant boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating the surface of a steel tube making available a boiler steel tube excellent in sulfication corrosion resistance and erosion resistance. SOLUTION: The outer surface of a steel tube tube is thermally sprayed with the one obtd. by incorporating 0.3 to 8wt.% Al into a self-fluxing alloy composed of No-Cr-B-Si-C-Fe-Co, a self-fluxing alloy of Ni-Cr-B-Si-C-Fe-Co-Cu, a self-fluxing alloy of No-Cr-B-Si-C-Fe-Co-Mo-Cu or a self-fluxing alloy composed of Ni-Cr-B-Si-C-Fe-Co-Mo-W, and, fusing treatment is executed or, after the thermal spraying, it is thermally sprayed with a self-fluxing alloy contg. no Al, and fusing treatment is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for a steel pipe for a boiler having resistance to sulfidation corrosion and erosion, and relates to a coal fluidized bed boiler, an exhaust gas recovery boiler of a coke dry cooling system, and a waste heat of a cement kiln. The present invention relates to a surface treatment method for a steel pipe for a boiler which can be advantageously applied to a heat transfer pipe such as a recovery boiler, a coal combustion boiler, and a sintering apparatus for heat recovery of an iron making.

[0002]

2. Description of the Related Art Since the oil crisis in 1973, coal has been reviewed as an energy source, while effective use of energy has been further promoted. Fluid bed boilers can effectively utilize low-grade coal (for example, sub-bituminous coal) that has been buried in large quantities worldwide, and have the advantage of being highly efficient and desulfurizing in furnaces. Is high value, and many vehicles are being driven.

[0003] A fluidized bed boiler usually has a structure as shown in FIG.
Fluid medium particles (for example, limestone) 1 are charged into a furnace in an appropriate amount, air is sent upward from the lower air dispersion plate 2, and the superficial velocity is made faster than the flow start speed so that the medium particles 1 are discharged from the dispersion plate 2. Floating in the tower to create a fluidized state, into which pulverized coal or the like is fed from a coal supply nozzle 3 to make the fluidized medium particles 1
In the fluidized bed, an in-layer pipe 4 such as a boiler steel pipe for generating steam and a superheated steam pipe is installed in the fluidized bed. In the figure, 5 is an ash discharge port, 6 is a convection section heat transfer tube, 7 is a starter burner, and 8 is an air duct.

[0004] Boiler steel pipes (in-layer pipes) in these fluidized beds
4 is installed substantially horizontally with respect to the flow of the kinetic action of the fluidized media particles of the pulverized coal, so that solids such as pulverized coal and medium particles collide violently with the in-layer tube 4 and significantly wear the surface thereof. For this reason, stainless steel protectors are attached to the lower surface of the inner tube 4, but these have the drawback that the heat transfer coefficient is lowered and the cost is large.

In view of such circumstances, Japanese Patent Application Laid-Open No. 61-41 / 1986
No. 756 proposes spraying a Ni—Cr alloy or a Co—Ni—Cr—W—B—Si self-fluxing alloy on the inner tube. However, the former alloy is excellent in corrosion resistance but poor in wear resistance. Although the latter self-fluxing alloy is hard, it has a drawback that many fine cracks are generated when the sprayed coating is subjected to the fusing treatment. For this reason, even though the latter self-fluxing alloy has excellent wear resistance, a corrosive gas (a decomposition gas of an S compound contained in coal, for example, H ₂ S, COS, S
O _x, etc.) there is a drawback to corrosion damage to the steel pipe itself penetrate into the interior.

On the other hand, in a steel mill, in order to produce coke for iron making, the coal is glowed under a practically oxygen-free environment.
The process of quenching this is adopted. Conventionally, water was directly injected into red hot coke to cool it,
Recently, a method has been adopted in which a large amount of N ₂ gas is fed to digest red-hot coke, while high-temperature N ₂ gas whose sensible heat has been taken is led to a boiler to recover the heat. This waste heat recovery boiler is Coke Dry Quenching Bo
It is called iler (CDQ boiler), and is being widely used as an energy recovery boiler. As can be seen from this process, since the high-temperature N ₂ gas led to the boiler does not contain O _{2, the} S compound contained in the coal is H ₂ S, C
It exists as a compound having a high corrosion reactivity such as OS and causes severe high-temperature sulfurization corrosion.

[0007] Sulfidation corrosion generally occurs at a lower temperature than accelerated oxidation corrosion, so the temperature range of corrosion occurrence is wide, and the corrosion products (sulfides) are porous and easily peel off from the metal surface. And does not have a function as a barrier for a corrosion reaction like an oxide film. For this reason, the rate of wear of the boiler steel pipe due to sulfidation corrosion is very large. Furthermore, since high-temperature N ₂ gas contains a large amount of hard fine coke powder, wear due to abrasion is added. As a result, in CDQ boilers, measures against sulfidation corrosion and abrasion damage are as important as fluidized bed boilers. It has become.

At present, as a countermeasure against this, the aforementioned Japanese Patent Laid-Open No.
Although the Ni-Cr alloy spraying method and the self-fluxing alloy spraying method proposed in Japanese Patent No. 41756 are applied, as described above, even in this environment, the Ni-Cr alloy film has poor wear resistance, and The self-fluxing alloy film has a disadvantage that it is vulnerable to local sulfidation corrosion damage due to crack generation.

In Japanese Patent Application Laid-Open No. Sho 60-142103, MSFNi1 specified in JIS H8303 is used.
5, a method of manufacturing a heat transfer tube for a boiler coated with a self-fluxing alloy such as MSFCo1,2 and MSFWC1,2 is proposed. However, this method is simply spraying a known self-fluxing alloy established in order to obtain a spray coating with good adhesion by hard and melting on the surface of the boiler steel pipe,
Even if such a self-fluxing alloy is coated, a crack is generated in the alloy film, and it is impossible to prevent the invasion of corrosive gas through the crack and the corrosion of the base steel pipe due to the crack.

[0010]

As is apparent from the above-described mechanism of the occurrence of sulfide corrosion, even when a hard self-fluxing alloy film is formed, corrosive sulfide gas such as H ₂ S or COS is generated in the crack. Penetrates into the interior through the water and corrodes the steel pipe. Although this corrosion reaction occurs even in the self-fluxing alloy film itself, in many cases, the film contains Cr as a corrosion-resistant element in a larger amount than that of the steel pipe, so that the corrosion reaction is relatively slow. For this reason, a phenomenon has often been experienced in which the steel pipe immediately below the self-fluxing alloy spray coating is corroded and worn with the elapse of the operation time and the thermal spray coating is peeled off from the contact surface with the steel pipe as the corrosion area increases. The present invention relates to a surface treatment method which solves the above-mentioned conventional drawbacks and makes it possible to provide a steel pipe for a boiler having excellent resistance to sulfidation corrosion and erosion.

[0011]

SUMMARY OF THE INVENTION The present invention is a surface treatment method for a steel pipe for a boiler having the following constitution and having excellent resistance to sulfidation corrosion and erosion. (1) Ni-Cr-B-Si-C-Fe-
Self-fluxing alloy made of Co or Ni-Cr-B-Si-
Self-fluxing alloy consisting of C-Fe-Co-Cu or Ni-
Self-fluxing alloy consisting of Cr-B-Si-C-Fe-Co-Mo-Cu or Ni-Cr-B-Si-C-Fe-C
A sulphidation-resistant and erosion-resistant boiler characterized in that a self-fluxing alloy of o-Mo-W containing 0.3 to 8% of Al by weight is sprayed and subjected to fusing treatment. Surface treatment method for steel pipe.

(2) Ni-Cr-B-Si on the outer surface of the steel pipe
-C-Fe-Co self-fluxing alloy or Ni-Cr
A self-fluxing alloy comprising -B-Si-C-Fe-Co-Cu;
Or Ni-Cr-B-Si-C-Fe-Co-Mo-
Self-fluxing alloy made of Cu or Ni-Cr-B-Si-
After spraying an alloy containing 0.3 to 8% by weight of Al with respect to a self-fluxing alloy made of C-Fe-Co-Mo-W, Ni-Cr-B-Si-C is further sprayed thereon. -Fe-Co
Or a Ni-Cr-B-Si-C-
Self-fluxing alloy consisting of Fe-Co-Cu or Ni-Cr
-B-Si-C-Fe-Co-Mo-Cu self-fluxing alloy or Ni-Cr-B-Si-C-Fe-Co-
A surface treatment method for a boiler steel pipe having resistance to sulfidation corrosion and erosion, wherein a self-fluxing alloy made of Mo-W is sprayed and subjected to fusing treatment.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION H generated in the reduction combustion process of coal
Cr is best known as a metal element that resists corrosion of gaseous S compounds such as ₂ S and COS. This Cr is also famous as a heat-resistant and oxidation-resistant element, is a useful element that is always contained in heat-resistant alloys, and is also contained in steel tubes for boilers and many self-fluxing alloys.

On the other hand, Al, which is a characteristic component of the present invention, is completely added to the self-fluxing alloys described in JIS H8303, despite having sulfuration resistance and oxidation resistance higher than Cr. Not. This is because the purpose of the self-fluxing alloy was originally focused only on its physical properties such as its excellent hardness, adhesion, and denseness, and therefore, its chemical properties such as oxidation resistance and sulfidation resistance. The reason is that the self-fluxing alloy containing no Cr is extremely scarce, and even if the content of the self-fluxing alloy containing Cr is such that it is originally contained, the sulfide corrosion caused by H ₂ S, COS, etc. which is the object of the present invention is intended. The action has its own limits and its life is short.

According to the present invention, in order to compensate for the above-mentioned drawbacks, Al is contained in the self-fluxing alloy, thereby exhibiting a synergistic effect with Cr in the self-fluxing alloy to further improve oxidation resistance and sulfidation resistance. In addition, it became possible to form a self-fluxing alloy film having excellent oxidation resistance and sulfidation resistance in addition to conventional wear resistance.

An outline of the spraying method of the self-fluxing alloy used in the present invention is, for example, a very general method of injecting a wire of the self-fluxing alloy with compressed air while melting the wire by an electric arc, a combustible gas flame or a plasma arc. is there. Further, the fusing treatment conditions adopted in the present invention are generally an electric furnace, high-frequency induction heating,
Alternatively, the thermal spraying is performed by heating the sprayed coating to 1000 to 1300 ° C. in the atmosphere by a combustion flame of natural gas, propane, acetylene or the like. As the self-fluxing alloy used in the present invention, MSFi1, MSFi2, MSFi4 and MSFCol specified in JIS H8303 (1976) can be used. The chemical composition is shown in Table 1.

[0017]

[Table 1]

[0018]

【Example】

[Example 1] STB42 and ST were used as test boiler steel tubes.
BA24 having an outer diameter of 54 mm and a thickness of 3.2 mm was used, and Cr: 10.1, B: 1.3, belonging to MSFNi2,
Si: 2.5, C: 0.35, Fe: 2.5, Co:
0.2, Ni: a self-fluxing alloy having the remaining composition (all by weight) and Cr belonging to an alloy belonging to MSFNi4: 1
4.8, B: 3.2, Si: 3.9, C: 0.7, F
e: 3.6, Co: 0.6, Mo: 3.4, Cu: 3.
0, Ni: a self-fluxing alloy having a remaining composition (all by weight),
And Ni: 17.5, Cr: 1 belonging to MSFCol.
7.2, B: 2.5, Si: 3.3, C: 1.1, F
e: 4.0, Mo: 5.2, W: 6.1, Co: 0.05 to 8% (by weight) of each of the three types of self-fluxing alloys having the remaining composition (all by weight). %) To prepare a self-fluxing alloy, which is sprayed 300 μm onto each of the test boiler steel pipes described above, and then from 1100 to 1200 ° C.
Was subjected to a heat fusing treatment. The example of the self-fluxing alloy containing 0.05% and 0.1% of aluminum powder is a comparative example. Also, for comparison, the self-fluxing alloy was sprayed on the test boiler steel pipe in the same manner as in Example 1 except that the addition of aluminum powder to the self-fluxing alloy for thermal spraying of Example 1 was omitted.
Heat fusing treatment was performed.

(Evaluation) Cracks were observed in all of the self-fluxing alloy films of the test boiler steel tube of Example 1. However, a film containing no crack was selected and a test piece was cut out (50 m).
m length), and this was subjected to 600 ° C. H ₂ S: 1%, COS: 0.
After exposure to a gas atmosphere of 3%, H ₂ : 2%, N ₂ : residual (all by volume%) for 300 hours, the cross section of the self-fluxing alloy film is examined with an optical microscope, and the formation of a corrosion layer on the film cross section The situation was observed. Table 2 shows the results. The thickness of the corrosion product layer of the 0.05% Al content self-fluxing alloy film of the present invention was set to 1, and the corrosion amount ratio was shown by the ratio.

[0020]

[Table 2]

As is clear from Table 2, the Al content is 0.1.
Based on the 05% self-fluxing alloy film, the surface portion of the 0% self-fluxing alloy film with Al content was considerably corroded. Also, A
The corrosion amount ratio of a self-fluxing alloy film containing 0.1%
The value of 0.9 was higher than that of 5% Al content, but the content of 0.3% or more, which is an example of the present invention, has a corrosion amount ratio of 0.5 or less and the corrosion layer has a corrosion rate of 0.5 or less. It can be seen that the formation is very thin. Thus, regardless of the type (composition) of the self-fluxing alloy, it was recognized that the addition of Al improves the corrosion resistance, particularly the high-temperature sulfidation corrosion resistance.

Example 2 STB was used as a test boiler steel pipe.
42 and STBA24 outer diameter 54 mm, thickness 3.2 mm
Using Cr belonging to MSFNi1, 8.2;
B: 1.2, Si: 2.2, C: 0.18, Fe: 2.
8, Co: 0.3, Cu: 2.9, Ni: A self-fluxing alloy having the remaining composition (all in weight%) added with 3% of Al was sprayed to a thickness of 100 μm and then sprayed thereon. MSFC
Ni belonging to o1: 17.5, Cr: 17.2, B:
2.5, Si: 3.3, C: 1.1, Fe: 4.0, M
o: 5.2, W: 6.1, Co: A self-fluxing alloy having a remaining composition (all by weight) was sprayed at 200 μm, the thickness of the entire sprayed layer was set at 300 μm, and then heated to 1100 to 1200 ° C. . When the surface was inspected by color check, many cracks were generated on the surface.

For comparison, the above MSFNi1
100 μm of self-fluxing alloy (without Al), 200 μm of the above-mentioned MSFCo1 self-fluxing alloy (without Al) in the upper layer
m, and subjected to a heat fusing treatment in the same manner as in Example 2. 100m length from the above steel pipes
m test tube was cut out and subjected to a corrosion test in the same manner and under the same conditions as in Example 1. Table 4 shows the results of observing the cross section of the self-fluxing alloy film after the test using an optical microscope.

[0024]

[Table 3]

In the above Examples and Comparative Examples, cracks were not observed in the lower layer coating (MSFNi1), but a number of cracks were generated in the upper layer coating (MSFCo1). For this reason, it was observed that corrosive gas penetrated into the inside through the cracks and corroded the lower layer coating. However, the lower layer coating to which Al was added in Example was not corroded at all, and the corrosion generation area was It was limited to the upper coating only. On the other hand, since the film of the comparative example did not contain Al, both the upper and lower films were corroded, and it was confirmed that the corrosion resistance was poor.

(Embodiment 3) STB42, STBA24 and SUS321HTB steel pipes (diameter 54 x thickness 3.2 mm)
, A self-fluxing alloy spraying and fusing treatment were performed in the same manner as in Examples 1 and 2, and blast erosion resistance (hereinafter, erosion) under a high temperature environment and a high temperature corrosion environment was investigated.

FIG. 2 shows an outline of the erosion test apparatus. The test steel pipe 9 is placed in a high-temperature furnace 10, and silica sand (average particle size: 100 μm) is directed to the steel pipe from an injection nozzle 11 provided on the front face thereof, and heated by compressed air (3 kgf / cm ² ). Sprayed. The air introduced into the high-temperature furnace 10 is raised to almost the test temperature by the preheating furnace 12 and the air cyclone 13
After the silica sand is separated through, it is recycled. The corrosive gas is supplied to a cylinder 14 which has been adjusted to a predetermined composition in advance.
The flow rate can be adjusted by the flow meter 15 from above, and can be injected into the high-temperature furnace.

The erosion test in a high-temperature air environment was evaluated by spraying silica sand at a temperature of 600 ° C. for 10 hours.
The test was performed by observing the degree of reduction of the self-fluxing alloy film after the test with a microscope. Table 4 shows the results. The film of the present invention has almost the same erosion resistance as the comparative example, and no adverse effect due to the addition of Al in the self-fluxing alloy is observed.

[0029]

[Table 4]

Next, H ₂ S: 1%, COS:
0.5%, H ₂ : 2%, balance: N ₂ corrosive gas of 2.5
After passing the time, the test of spraying silica sand for 2.5 hours was repeated twice. Table 5 shows the results. In an environment where the corrosion action and the erosion action are repeated, the coating of the present invention exhibited excellent performance. The reason for this is that the film of the comparative example is eroded by corrosive gas, and a porous, poorly adherent corrosion product (sulfide) is formed on the surface thereof, and then this corrosion product is sprayed with silica sand. On the other hand, it is considered that the film of the present invention is excellent in corrosion resistance, so that the formation of a corrosion product layer is extremely thin, and good erosion was exhibited.

[0031]

[Table 5]

[0032]

According to the present invention, a thermal spray coating of a self-fluxing alloy containing 0.3 to 8% of Al is formed on the surface of a steel pipe for a boiler by adopting the above-mentioned structure, and a fusing treatment is performed. It has become possible to obtain a boiler steel pipe having excellent sulphidation and erosion resistance. In addition, after spraying an Al-containing alloy on the surface of a steel pipe for a boiler, a self-fluxing alloy containing no Al is further sprayed thereon, and this is subjected to a fusing treatment to thereby provide a boiler having excellent sulfidation resistance and erosion resistance. Steel pipes can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an example of a general coal fluidized bed boiler.

FIG. 2 is a schematic view of a corrosion erosion test apparatus for testing blast erosion resistance of a steel pipe for a boiler as an embodiment of the present invention.

[Explanation of symbols]

1 Fluid medium particles, 2 Air distribution plate, 3 Coal supply nozzle, 4 Inner layer pipe (boiler steel pipe, etc.), 5 Ash discharge port, 6 Heat transfer tube in convection section, 7 Starter burner,
8 air duct, 9 test steel pipe, 10 high temperature furnace,
12 Preheating furnace, 13 Air cyclone, 14 Corrosive gas cylinder, 15 Flow meter.

Claims (2)

[Claims] 1. The steel pipe outer surface has Ni-Cr-B-Si-
Self-fluxing alloy consisting of C-Fe-Co or Ni-Cr-
B-Si-C-Fe-Co-Cu self-fluxing alloy or Ni-Cr-B-Si-C-Fe-Co-Mo-C
Self-fluxing alloy consisting of u or Ni-Cr-B-Si-C
-Fe-Co-Mo-W self-fluxing alloy containing 0.3 to 8% by weight of Al is sprayed and subjected to fusing treatment, which is characterized by resistance to sulfidation and corrosion. Surface treatment method for erosion boiler steel pipe. 2. The steel pipe outer surface has Ni-Cr-B-Si-
Self-fluxing alloy consisting of C-Fe-Co or Ni-Cr-
B-Si-C-Fe-Co-Cu self-fluxing alloy or Ni-Cr-B-Si-C-Fe-Co-Mo-C
Self-fluxing alloy consisting of u or Ni-Cr-B-Si-C
After spraying the alloy containing 0.3 to 8% by weight of Al with respect to the self-fluxing alloy composed of -Fe-Co-Mo-W,
A self-fluxing alloy composed of Ni-Cr-B-Si-C-Fe-Co or Ni-Cr-B-Si-C-Fe
-Co-Cu self-fluxing alloy or Ni-Cr-B
-Si-C-Fe-Co-Mo-Cu self-fluxing alloy or Ni-Cr-B-Si-C-Fe-Co-M
A surface treatment method for a boiler steel tube having resistance to sulfidation corrosion and erosion, which comprises spraying a self-fluxing alloy made of oW and performing a fusing treatment.