JP2001295019A - Method for repairing thermal spray coating on inside face of nozzle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for repairing a thermal spray coating on the inside face of a nozzle by which the repair of the existing thermal spray coating formed on the inside face of the burner nozzle of a pulverized coal boiler can be performed in a short time, a newly formed thermal spray coating hardly peels off in the process of operation and driving, and desired wear resistance can be maintained. SOLUTION: At the time of repairing a wear resistant thermal spray coating formed on the inside face of a nozzle 1 used in the burner of a pulverized coal boiler, the existing thermal spray coating at the part to be repaired is subjected to blast treatment into a thermal spray coating 2 having a film thickness of 0 to 50 μm and surface roughness of >=20 Rz, and thereafter the surface of the thickness-reduced thermal spray coating 2 is subjected to spraying operation to form a new thermal spray coating 3 having wear resistance equivalent to that of the thermal spray coating 2. In the case the same substrate treatment has been performed, the adhesion between the new and old thermal spray coating 2 and 3 is improved, so that the newly formed thermal spray coating 3 is made to hardly peel off in the process of working and driving. Further, by the blast treatment, the operating time can be reduced compared to the case of the thickness reduction by a grinder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for repairing a sprayed coating for preventing abrasion applied to the inner surface of a burner nozzle of a pulverized coal-fired boiler, and in particular, to reduce the existing sprayed coating. The present invention relates to a method for repairing a sprayed coating on the inner surface of a nozzle, which employs a technique of forming a new sprayed coating after meat processing.

[0002]

2. Description of the Related Art As is well known, the inner surface of a nozzle, which is a burner component of a pulverized coal-fired boiler, is liable to wear due to collision with circulated or deflected pulverized coal. Therefore, it is indispensable to take measures against wear of the inner surface of the nozzle. Therefore, a sprayed coating of a Ni-based self-fluxing alloy excellent in high-temperature wear resistance, or a sprayed coating using a metal material as a binder for carbides, shelvings and oxides is usually provided on the inner surface of this type of nozzle. By applying a spray coating excellent in wear resistance in advance in this way,
Prevents wear on the inner surface of the nozzle.

[0003] However, the sprayed wear-resistant coating provided on the inner surface of the nozzle is inevitably subject to local wear when the plant is operated for a long time. In addition, the sprayed coating on the inner surface of the nozzle may be locally peeled off due to the effect of a heat cycle caused by stopping and starting the plant. If local wear or peeling occurs on the sprayed coating on the inner surface of the nozzle in this way, it is conceivable to replace the nozzle with a new one, but when preparing a new nozzle and performing thermal spraying on the inner surface, The disadvantage was that considerable expense had to be anticipated, and the nozzle itself was uneconomical as it was not damaged enough to require replacement.

Therefore, in consideration of cost, a method of repairing only a sprayed coating having a local abrasion or peeling inside the nozzle without replacing the nozzle is generally adopted. As a repair method of such a thermal spray coating,
Conventionally, the existing thermal spray coating is washed and dried, and then a new thermal spray coating with the same properties is applied to the surface of this thermal spray coating. A technique of applying a thermal spray coating is known.

[0005]

When repairing an existing thermal spray coating provided on the inner surface of a burner nozzle of a pulverized coal-fired boiler, a new thermal spray coating is obtained only by the surface treatment as in the above-mentioned prior art. When performing thermal spraying, there is a problem that this new thermal sprayed coating is liable to peel off during construction or operation. This is because even if cleaning and drying are performed before thermal spraying is performed to prevent the generation of oxides and the like that induce exfoliation, it is not sufficient as a base treatment for the existing thermal spray coating having high hardness at room temperature. This is due to poor adhesion between the coating and the new thermal spray coating. On the other hand, if a new thermal spray coating is applied after performing the wall thinning treatment with a grinder as in the latter conventional technique described above, there is little merit in cost because a large amount of time is required for the wall thinning treatment,
In addition, when the existing thermal spray coating is subjected to a thickness reduction treatment with a grinder, large irregularities are generated. Therefore, there is a problem that a new thermal spray coating applied to the existing thermal spray coating is easily peeled off during the construction or operation.

The present invention has been made in view of such problems of the prior art, and an object of the present invention is to repair an existing thermal spray coating provided on an inner surface of a burner nozzle of a pulverized coal-fired boiler in a short time. Another object of the present invention is to provide a method for repairing a sprayed coating on the inner surface of a nozzle, in which a newly formed sprayed coating is less likely to peel off during construction or operation and can maintain desired wear resistance.

[0007]

Means for Solving the Problems To achieve the above object, the present invention provides a method for repairing a wear-resistant sprayed coating provided on the inner surface of a nozzle used in a burner of a pulverized coal-fired boiler. After blasting the existing thermal spray coating at the repair site to reduce its thickness to 0 to 50 μm and to make the surface roughness Rz20 or more, thermal spraying is performed on the surface of the reduced thermal spray coating. A new thermal spray coating having the same abrasion resistance as the thermal spray coating was formed. As described above, if the thickness of the existing sprayed coating on the inner surface of the nozzle is reduced to 0 to 50 μm by blasting, and the surface treatment is further performed to make the surface roughness Rz20 or more, spraying is performed thereon. Since the adhesion with the new thermal spray coating to be applied is good, the newly formed thermal spray coating is less likely to peel off during application or operation. Further, in the case of the blasting process, the working time can be shortened as compared with the case where the thickness is reduced by a grinder. In addition, if such an undercoating treatment is performed, good adhesion can be obtained even if the existing sprayed coating and the newly formed sprayed coating have different compositions from each other. There is an advantage that it is not done. Further, in such a repair method, when reducing the thickness of an existing thermal spray coating, an oxide ceramic is used as a material for reducing the thickness, and the hardness is reduced by heating the thermal spray coating to 400 ° C. or higher and the melting point or lower. In addition, the working efficiency of the blasting process is improved. In addition, it is preferable that the oxide-based ceramic is made to hit the existing thermal sprayed coating at an angle of 75 to 115 °. Further, the surface roughness is set to Rz20 or more, but more preferably Rz40 or more.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.
This will be described with reference to FIGS. On the inner surface of the nozzle used in the burner of the pulverized coal-fired boiler, a Ni-based self-fluxing alloy coating or a carbide coating C
Since r3C2 / NiCr or WC-NiCr is widely used, first, the Vickers hardness of these thermal sprayed coatings at room temperature and the Vickers hardness at the time of application to an actual machine at about 400 ° C.
Investigate the Vickers hardness after being used for 0 hours or more. FIG. 1 is an explanatory diagram showing the results of measuring the Vickers hardness of each sprayed coating at room temperature, and FIG.
It is explanatory drawing which shows the result of having measured Vickers hardness of each thermal spraying coating as 1000 hours at 00 degreeC. As shown in FIGS. 1 and 2, the material used for the thermal spray coating on the inner surface of the nozzle has a high Vickers hardness of at least 700 Hv even at room temperature, and further increases in hardness when applied to an actual machine.
All Vickers hardness is 800 Hv or more.

Therefore, a plurality of test pieces are prepared by applying two types of undercoating to the sprayed coating affected by the aging effect and then applying a new sprayed coating. The presence or absence of peeling and the peeling resistance due to thermal cycling were investigated. 3 and 4 are explanatory diagrams showing the results of the investigation. However, the test pieces No. 1 and No. 2 shown in FIG. 3 were subjected to a simple surface treatment of reducing the surface roughness of the existing thermal spray coating from about 30 μm to a surface roughness of about Rz10, and then applying a new thermal spray coating. The test piece No. 3 shown in FIG.
And No. 4 are cases in which the method of the present invention is applied, and the surface roughness is reduced to Rz after reducing the thickness of the existing sprayed coating to 0 to 50 μm.
A new thermal spray coating is applied after performing a base treatment of 20 or more. In the test of the heat cycle, the state of 600 ° C. was water-cooled in consideration of the start and stop of the plant. Further, in order to obtain a surface roughness Rz20 or more of the test pieces No. 3 and No. 4, blast treatment was performed using A12O3.

As shown in FIGS. 3 and 4, simply applying a simple surface treatment to the sprayed coating affected by the aging effect is not sufficient in the peeling resistance of the new sprayed coating. Although the desired quality is not guaranteed even if repaired by the method described above, when the method of the present invention is applied, the new thermal sprayed coating has sufficient peeling resistance, so that the quality of the repaired portion can be guaranteed. In the test pieces No. 3 and No. 4 shown in FIG.
Although the old and new thermal spray coatings are made of the same material, according to an experiment conducted by the present inventors, the existing thermal spray coating is subjected to blast treatment to reduce its thickness so as to approach 0 μm, and then to reduce the surface roughness to Rz20. As described above, it has been confirmed that even if the new and old thermal spray coatings are materials having different compositions from each other (however, the wear resistance is the same), there is no problem in the peeling resistance of the new thermal spray coating.

In the repairing method, when reducing the thickness of the existing thermal sprayed coating, an oxide ceramic is used as a material for reducing the thickness, and the hardness is reduced by heating the thermal sprayed coating to 400 ° C. or higher and the melting point or lower. By doing so, the working efficiency of the blasting process is improved.

Next, an example in which the method of the present invention is actually applied to a burner nozzle will be described with reference to FIGS. FIG. 5 is a view for explaining a first application example of the present invention, in which reference numeral 1 denotes a nozzle, 2 denotes an existing thermal spray coating subjected to a thickness reduction process, 3 denotes a newly formed thermal spray coating, and 4 denotes an electromagnetic spray coating. 1 shows an expression film thickness meter. The nozzle 1 has an outer diameter of 450 mm, a thickness of 12 mm, and a material of SS400. An existing thermal spray coating 2 having a thickness of 0 to 50 μm is provided on the inner surface of the nozzle 1 by subjecting WC / Ni—Cr to thermal spraying to a thickness of 300 μm to reduce the thickness. Processing is A
This was performed using a blasting machine with 12O3 as the material for reducing the thickness. In addition, Cr3C2 / NiC
A new thermal spray coating 3 is provided by applying r to a thickness of 300 μm using a high-speed gas thermal spraying apparatus. Since the material of the nozzle 1 is SS400 (magnetic material), the electromagnetic film thickness meter 4 was used for measuring the film thickness of the thermal spray coatings 2 and 3.

FIG. 6 is a view for explaining a second application example of the present invention. Reference numeral 5 denotes an existing thermal spray coating made of a Ni-based self-fluxing alloy and subjected to a thinning treatment. A burner used therein is shown, and portions that can be regarded as equivalent to FIG. 5 are denoted by the same reference numerals. In FIG. 6, the inner surface of the nozzle 1 was spray-coated with a Ni-based self-fluxing alloy to a thickness of 1.5 mm, and the thickness was reduced to 0 to 50 μm using a blast device while heating with a burner 6. The existing thermal spray coating 5 is provided, and the heating by the burner 6 is 4
The temperature was not lower than 00 ° C. and not higher than the melting point. As described above, if the existing thermal spray coating 5 is heated to 400 ° C. or higher to reduce the hardness, the blast processing can be performed efficiently. In addition,
As in the first application example, Cr3
300 µm of C2 / NiCr using high-speed gas spraying equipment
A new thermal spray coating 3 having a thickness of 3 nm is provided. Since the material of the nozzle 1 is SS400, the electromagnetic thickness gauge 4 was used to measure the thickness of the thermal spray coatings 5 and 3.

FIG. 7 is for explaining a third application example of the present invention. Reference numeral 7 denotes a nozzle, and 8 denotes a high-frequency eddy current type film thickness meter, which can be regarded as equivalent to FIGS. The parts are denoted by the same reference numerals. 7, the shape of the nozzle 7 is the same as that of the nozzle 1 and has an outer diameter of 450 mm and a thickness of 1.
2 mm, but the nozzle 7 is made of non-magnetic SUS3
04, which is different from the nozzle 1. An existing thermal spray coating 3 having a thickness of 0 to 50 μm is provided on the inner surface of the nozzle 7 by reducing the thickness of a sprayed Cr3C2 / NiCr film having a thickness of 300 μm. Further, on the surface of the thermal spray coating 3, a new thermal spray coating 5 formed by applying a Ni-based self-fluxing alloy to a thickness of 1.5 mm is provided.
Since the material of the nozzle 7 was SUS304 (non-magnetic material), the high-frequency eddy current film thickness meter 8 was used for measuring the film thickness of these thermal spray coatings 3 and 5.

[0015]

The method for repairing a sprayed coating on the inner surface of a nozzle according to the present invention is implemented in the form described above, and has the following effects. Repair method of reducing the thickness of the existing sprayed coating on the inner surface of the nozzle to 0 to 50 μm by blasting, and further performing a base treatment to increase the surface roughness to Rz 20 or more, and then applying a new sprayed coating Therefore, the adhesion of the old and new thermal spray coatings is improved.
Therefore, the newly formed thermal spray coating is less likely to peel during construction or operation, and can maintain the desired abrasion resistance without replacing the nozzle. Required costs can be reduced and reliability can be improved. Further, in the case of the blasting process, the working time can be shortened as compared with the case where the thickness is reduced by a grinder. Moreover,
By performing such a base treatment, even if the new and old thermal spray coatings are made of materials having different compositions, good adhesion can be obtained, and there is an advantage that the repair material is not limited. Also,
In such a repair method, when an existing thermal spray coating is reduced in thickness, an oxide-based ceramic is used as a material for reducing the thickness, and the thermal spray coating is heated to 400 ° C. or higher and the melting point or lower to reduce the hardness. Processing efficiency is improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the results of measuring the hardness of a thermal spray coating at room temperature.

FIG. 2 is an explanatory view showing the results of measuring the hardness of a thermal spray coating affected by the aging effect.

FIG. 3 is an explanatory view showing the results of investigating a peeling resistance by applying a new thermal spray coating to a thermal spray coating subjected to a simple surface treatment.

FIG. 4 is an explanatory view showing a result of investigating a peeling resistance by applying a new thermal spray coating to a thermal spray coating subjected to a base treatment according to the method of the present invention.

FIG. 5 is an explanatory diagram showing a first application example of the present invention.

FIG. 6 is an explanatory diagram showing a second application example of the present invention.

FIG. 7 is an explanatory diagram showing a third application example of the present invention.

[Explanation of symbols]

 1, 7 Nozzle 2 WC / Ni-Cr sprayed coating 3 Cr3C2 / NiCr sprayed coating 4 Electromagnetic thickness gauge 5 Ni-based self-fluxing alloy spray coating 6 Burner 8 High frequency eddy current thickness gauge

Claims (4)

[Claims] When repairing a wear-resistant sprayed coating provided on an inner surface of a nozzle used in a burner of a pulverized coal-fired boiler, an existing sprayed coating at a repaired portion is subjected to blast treatment. After reducing the film thickness to 0 to 50 μm and making the surface roughness Rz20 or more, the surface of the reduced thermal spray coating is subjected to thermal spraying, and a new thermal spray having the same abrasion resistance as the thermal spray coating. A method for repairing a sprayed coating on the inner surface of a nozzle, comprising forming a coating. 2. The method for repairing a sprayed coating on the inner surface of a nozzle according to claim 1, wherein the existing sprayed coating and the newly formed sprayed coating are made of materials having different compositions from each other. 3. The method according to claim 1, wherein when reducing the thickness of the existing thermal spray coating, an oxide-based ceramic is used as a material for reducing the thickness, and the thermal spray coating is heated to 400 ° C. or higher and the melting point or lower. A method for repairing a sprayed coating on the inner surface of a nozzle, characterized in that: 4. The method according to claim 1, wherein the existing thermal spray coating and the newly formed thermal spray coating are:
A method for repairing a sprayed coating on the inner surface of a nozzle, wherein a Vickers hardness of 300 Hv or more is maintained at 400 ° C.