KR101342266B1 - Structure and method for coating of boiler tube - Google Patents

Abstract

The present invention relates to a structure and a method for coating a fluidized boiler tube. A coating structure of a fluidized boiler tube according to the present invention includes: a base coating layer, formed on a predicted part of the tube, with a first hardness which is; and a top coating layer, formed on at least a part of the top of the base coating layer, with a second hardness which is greater than the first hardness, and at least one edge part of the base coating layer is exposed by making the top coating layer on the interface of the tube and the coating layer. According to the structure and method of coating the tube of a fluidized boiler, the wear of the tube to the coating costs can be minimized by forming a dual coating layer to let the base coating layer be worn instead of the tube in a part of the boiler tube which is fragile against wear.

Description

STRUCTURE AND METHOD FOR COATING OF BOILER TUBE}

The present invention relates to a coating structure and method of the boiler tube, and more particularly to a coating structure and method of the boiler tube for minimizing the wear phenomenon at the coating layer interface of the boiler tube.

In general, a fluidized bed boiler is a fluidized bed application technology that performs relatively large-scale chemical and physical operations to produce steam by inducing a combustion reaction through intimate contact between a high-speed gas and solid particles such as coal and ash having a relatively small particle size, and limestone. Is one area.

The application of a boiler using a fluidized bed combustion furnace has the following advantages. First, there is an advantage that can be applied to the combustion of a variety of fuels, including low- and low-calorie combustion of relatively high ash and moisture content. In particular, it is recognized as a combustible technology for domestic anthracite coal that can be burned with the aid of auxiliary fuel in the general pulverized coal combustion method. Second, the high solids mixing rate and the residence time in the furnace ensure a relatively high combustion efficiency. Third, there is no need for a separate desulfurization apparatus, and there is an advantage in that the desulfurization reaction during combustion is performed by directly injecting limestone into the combustion furnace. In addition, the gas-solid contact efficiency is very high compared to the conventional bubble fluidized bed boiler, and has a feature of having a higher desulfurization efficiency from the same Ca / S molar ratio. Fourth, since combustion occurs at a relatively high temperature (900 ° C.), there is an advantage of suppressing generation of NOx. In addition, the generation of NOx can be controlled by the stepwise combustion method.In addition, the fluidized bed boiler has many advantages both domestically and internationally due to the advantages of using a relatively large particle size coal, reducing the size of the heat transfer area, and high operating rate. Combustion technology is expected to trend.

However, in the case of a fluidized bed boiler, the tube wear phenomenon due to long time operation is emerging as a big problem. As a countermeasure to solve this problem, the owners of the fluidized bed boiler are seeking solutions through improvement measures such as tube material, coating agent, and coating method.

As one of the solutions, the company's most applied method has confirmed some improved effects by applying corrosion and wear resistant coating methods, but it does not solve the serious wear phenomenon at the boundary between the coating layer and the uncoated layer.

1 to 4 show a panel structure and a welding method for preventing wear of the circulating fluidized bed boiler tube according to the prior art.

Referring to Figures 1 to 4, the conventional panel is the front and rear only bending at the site where the inclined surface and the upper straight surface of the lower cross and the left and right sides are straight panels without bending. In addition, castables have been constructed up to a portion of the bending top tube.

However, as shown in FIG. 4, the wear caused by the bed material is concentrated at the upper end of the castable, which is caused by the obstacle when the falling sand hits the tube surface. This is because the wear and tear continues to hit the end and bounce.

Therefore, as shown in FIG. 4, a certain amount of growth welding is performed on the surface of the castable upper tube to prevent tube wear, and the growth welding should be performed at least once a year.

5 is a view showing the wear phenomenon of the conventional welding welding site, the tube is hardly abrasion due to the sand and only the portion to be welded welding continues to be worn downward.

In order to improve the above-mentioned problems of the prior art, a technique of coating a metal or cermet-metal ceramic material on a part of the boiler tube such as a castable upper portion and a welded welding portion where wear occurs severely has been proposed.

6 is a view showing the coating structure and problems of the boiler tube according to the prior art.

As shown in FIG. 6A, in the prior art, a coating layer 62 having a high hardness is applied to the weld portion W to improve wear resistance and corrosion resistance at the weld portion W of the boiler tube 61. It was formed in a one-stage coating structure.

In this case, however, the wear resistance and the corrosion resistance characteristics of the welding portion W have been greatly improved, but as shown in FIG. 6 (b), the tube at the boundary portion E in contact with the tube 61 and the coating layer 62 is shown. Intensive wear has occurred, which leads to a serious problem that the replacement cycle of the tube is extremely short.

Table 1 below shows the thickness thinning state in the conventional one-stage coating application. As a result of examining the thickness thinning of A and B companies, the boiler thickness was remarkably thinner as the period (7 months, 1 year, 2 years) in all boilers.

Table 1.

Republic of Korea Patent Publication 1999-0047025

Therefore, the present invention has been made to solve the problems of the prior art as described above, the general object of the present invention is a tube of a fluidized bed boiler that can substantially compensate for the various problems caused by the limitations and disadvantages in the prior art It is to provide a coating method.

Another specific object of the present invention is to provide a tube coating method of a fluidized bed boiler that can alleviate the wear phenomenon caused by the violent movement of particles in the circulating fluidized bed.

Another specific object of the present invention is to provide a tube coating method of a fluidized bed boiler capable of minimizing wear at the corresponding location by analyzing the causes and hydraulic characteristics of the phenomena occurring predominantly at a specific location in the circulating fluidized bed. .

Another specific object of the present invention is to provide a tube coating method of a fluidized bed boiler capable of minimizing abrasion at a portion where the fire resistant material and the upper water pipe in contact with the bottom of the boiler, which are most severely worn in the circulating fluidized bed.

To this end, the tube coating structure of a fluidized bed boiler according to an embodiment of the present invention, the base coating layer of the first hardness formed on a predetermined portion of the tube; The top coating layer is formed on at least a portion of the base coating layer, and includes a top coating layer having a second hardness higher than the first hardness, wherein the top coating layer is disposed so that only the base coating layer exists at a boundary portion between the tube and the coating layer. At least one end of the base coating layer is characterized in that it is formed to be exposed.

In the tube coating structure of the fluidized bed boiler according to an embodiment of the present invention, the thickness of the base coating layer is 100 ~ 500㎛, the thickness of the top coating layer is 100 ~ 500㎛, the thickness of the top and bottom of the base coating layer exposed May be 100 to 1000 μm.

In the tube coating structure of a fluidized bed boiler according to an embodiment of the present invention, the first hardness may be 300 to 700 HV, and the second hardness may be 750 to 1000 HV.

In the tube coating structure of the fluidized bed boiler according to an embodiment of the present invention, the base coating layer is made of a metal material, the top coating layer may be made of a cermet material.

In addition, the tube coating method of a fluidized bed boiler according to an embodiment of the present invention, (A) forming a base coating layer of a first hardness on a predetermined portion of the tube; (B) a method of forming a coating layer comprising forming a top coating layer having a second hardness higher than the first hardness on at least a portion of the base coating layer, wherein only the base coating layer is formed at a boundary portion between the tube and the coating layer. The top coating layer may be formed such that at least one end of the base coating layer is exposed.

In the tube coating method of a fluidized bed boiler according to an embodiment of the present invention, the process (B) is performed by using any one of high velocity flame (HVOF) spray, arc wire, frame wire, plasma technique It can be made by coating the cermet powder on the predetermined top coating layer formation site on the base coating layer.

According to the tube coating structure and method of the fluidized bed boiler according to the present invention, it is possible to minimize the wear of the tube compared to the coating cost by forming a double coating layer to wear the base coating layer instead of the tube in the wear-vulnerable portion of the boiler tube.

In addition, according to the present invention, by forming a double coating layer using a high-speed flame spraying technique, it is possible to form a coating layer having a high hardness and dense tissue and high adhesion, and fretting, in a high temperature region of 540 ~ 900 ℃ Its excellent particle wear characteristics make it very effective in extending the life of erosion and corrosion of boiler tubes.

1 is a detailed view of the panel according to the prior art.
Figure 2 is a detailed view of the castable construction according to the prior art.
3 is a view showing the panel wear phenomenon of FIG.
Figure 4 is a detailed view of the panel growth welding according to the prior art.
5 is a view showing the panel growth welding abrasion phenomenon of FIG.
6 is a view showing the coating structure and problems of the boiler tube according to the prior art.
7 is a diagram showing the effect of the strength of the particles and the tube on the wear.
8 is a detailed view of the castable constructed kick-out panel according to an embodiment of the present invention.
9 is a flow chart showing a boiler tube coating process according to an embodiment of the present invention.
10 is a view for explaining the coating thickness for each part of the boiler tube according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. In addition, the terms described below are defined in consideration of the functions of the present invention, and these may vary depending on the intention of the user, the operator, or the precedent. Therefore, the definition should be based on the contents throughout this specification.

The present inventors first considered the behavior of the particles in the fluid in order to understand the wear phenomenon caused by the particles in the circulating fluidized bed, when the behavior of the microparticles in the fluid is expressed by the following equation.

F _E -F _D = M _P (dv _r / dt)

Here, F _E is the net external force, F _D is the drag, and M _P is the mass of the particle. The equation of motion of the particle is determined by the difference between the external force and the drag.

dv _r / dt + v _r * 18μ / ρ _P d _P ² = F _E / M _P

To sum up the above formula,

dv _r / dt + v _r / τ ' = F _E / M _P

dv _r / dt + v _r / τ ' = [(ρ _P -ρ _F ) / ρ _P ] g

Therefore, the velocity change of the particle over time is summarized as below.

v _r = v _t [1-exp (-t / τ ')]

v _t = τ'g = Cρ _P d _P ² / 18μ * g

In order to express the collision of the stationary object of the fine particles by using the above equation, the stop distance and the collision factor of the particle can be expressed as the following equation.

That is, as the diameter of the stationary object increases, the probability of collision with the fine particles decreases. This is a mathematical expression that microparticles pass through the boundary layer of particles before colliding due to the increase of the boundary area of a large stationary object while the stopping distance is very short due to the very slow end speed. In addition, the movement of large particles can be confirmed that the collision with the stationary object is easy to increase the stopping distance.

In addition, as a result of examining the tube wear and repair status of domestic circulation fluidized bed boilers with rich experience in operating and repairing the circulation fluidized bed boilers, the main damage parts and causes of boilers were as follows.

1) bottom of boiler

-Brittle by desulfurization of materials in reducing atmosphere

-Clean surface exposure by friction effect

2) Distributor plate

-Bubble cap wear-Replace with pigtail type

-Change the shape of the distributor hole (from circular to oval)

-Recycle inlet wear

3) Water wall

-Water wall refractory interface

-Combustor wall corner

-Strait wall

Irregularities

In particular, as a result of a field survey of domestic circulating fluidized bed boiler users, tube damage in circulating fluidized bed boilers appears to be the main cause of wear due to external environment rather than internal corrosion. In the wall tube, abrasion was severe, and there was a slight difference in all parts of the fluidized bed boiler such as hot cyclone inlet, ceiling, and backpass.

Accordingly, the present inventors have synthesized the above-described equations and theories and data obtained through field surveys. In order to minimize the damage of equipment due to abrasion and to minimize the wear and tear, not only the regular and systematic tube thickness management but also the intensive management of major abrasion parts is most important. It was recognized that the use of the same wear resistant material was required.

In addition, research on the effect of particle and tube strength on wear has led to the recognition of the following principles: In other words, if the strength of the particles is stronger than the strength of the tube material, the particles collided toward the front of the tube will be bounced back due to the ductility of the tube to prevent damage to the surface of the tube. (FIG. 7A). However, when a particle that is weaker than the strength of the tube collides with the surface of the tube, the impacted particles on the side exert a force due to abrasion rather than an impact and the damage of the tube surface is stronger because the strength of the tube material is stronger. It will not appear. However, the particles collided to the front of the tube will transfer all of the momentum of motion of the particles to the tube, causing a crack in the tube surface. Therefore, small cracks are generated on the tube surface, which causes severe wear on the tube front. Schematic of this, it can be represented by the correlation between the damage according to the particle strength as shown in (c) of FIG. That is, when the strength of the particles is smaller than the hardness (strength) of the tube material, it is induced by the mechanism as shown in FIG.

Based on this, it was recognized that the cause of the intensive wear of the tube at the boundary portion E in contact with the tube and the coating layer was the difference in hardness between the tube and the coating layer (see FIG. 6B).

Therefore, in the present invention, when the wear-resistant coating of the circulating fluidized bed boiler tube is formed around the boundary portion in contact with the tube, the base layer is formed by first coating with a material having a relatively small hardness difference from the tube, for example, a metal material, Corrosion and wear resistance characteristics by forming a dual coating layer (base layer, top layer) by secondary coating with a material having a relatively high hardness, for example, cermet material, on the upper portion of the base layer except for the surrounding area. While maintaining a similar degree to the conventional to prevent the tube from intensive wear at the tube and the coating layer boundary.

FIG. 8 is a detailed view of the castable kick-out panel according to an embodiment of the present invention. Referring to FIG. 8, the coating structure and method of the boiler tube according to the embodiment of the present invention will be described in detail. As follows.

As illustrated in FIG. 8, the boiler tube applied to the present embodiment employs a kick-out type panel 10, and a castable 11 of a refractory material is installed at a lower portion of the panel 10. The coating layer (C) is formed on the top of the block 11.

In the case of the kick-out type, the sand flow velocity is the fastest in the kick-out part, so that the part with low hardness selectively wears out. Accordingly, as shown in the present embodiment, the base coating layer C1 having a relatively low hardness is formed to a thickness of about 100 to 1000 μm in thickness at the kick-out boundary at the kick-out boundary, so that the base coating layer C1 is selected instead of the tube. It can be worn to prevent the wear of the tube at the site.

In FIG. 8A, the coating layer C is partially formed of only the base coating layer C1, and the remaining part is formed of a double coating layer of the base coating layer C1 and the top coating layer C2. That is, a part of the coating start part or the end part is a single coating structure in which only the base coating layer C1 is coated, and the rest is a double coating structure in which the top coating layer C2 is coated on the base coating layer C1. Such a coating structure may be formed by forming a base coating layer (C1) on the predetermined coating portion as a whole, and then forming a top coating layer (C2) on the base layer of the remaining portions other than the edge, that is, the boundary portion (E) of the tube and the coating portion. . In the present exemplary embodiment, the base coating part C1 is formed to expose about 20 cm to the top of the top coating layer C2, but the range and thickness of the base coating part C1 exposed to the top of the top coating layer C2 may be appropriately selected. At this time, the boundary portion (E) of the tube and the coating portion and the boundary portion (C3) of the base coating portion (C1) and the top coating portion (C2) are coated with a gentle curve so that the boundary portion is not prominent. Can prevent concentration

In (b) of FIG. 8, the coating layer (C) is partially composed of a double coating layer of the base coating layer (C1) and the top coating layer (C2), and the remaining part is composed of only the base coating layer (C1) or the top coating layer (C2). . That is, the boundary between the base coating layer (C1) and the top coating layer (C2) is made of a double coating layer, a portion of the start or end of the coating is coated only the base coating layer (C1), the top coating layer between the coating start and end Only (C2) is coated. The coating structure may be formed by coating the base coating layer (C1) at the beginning and the end of the predetermined coating portion and then coating the top coating layer (C2) on the remaining portions except for the boundary (E) of the edge, that is, the tube and the coating portion. Can be. Similarly, the boundary portion (E) of the tube and the coating portion and the boundary portion (C3) of the base coating portion (C1) and the top coating portion (C2) should be coated with a gentle curve so that the boundary portion is not prominent and worn on the corresponding portion. Can prevent concentration

The base coating layer C1 may be made of a metal or an alloy material as a material having a relatively low hardness (about 300 to 700 HV) than the top coating layer C2. As the material of the base coating layer (C1), for example, a powder material containing carbon (C), boron (B), silicon (Si) in the nickel-chromium (Ni-Cr) alloy base may be applied. The proportion of the powder can be appropriately adjusted. In this embodiment, Ni17Cr4Fe4Si3.5B1C powder was used, and a coating layer was formed by a high-velocity oxygen fuel (HVOF) spraying technique.

The top coating layer C2 is a material having a relatively high hardness (about 750 to 1000 HV) than the base coating layer C1, and may be composed of a cermet in which a metal material and a ceramic material are mixed. As the material of the top coating layer (C2), for example, a cermet powder material mixed with chromium carbide (Cr ₃ C ₂ ) and nickel chromium nickel (NiCr) may be applied, and the ratio of each powder may be appropriately adjusted. have. In this embodiment, Cr ₃ C ₂ 20 (Ni20Cr) powder was applied, and the coating layer was coated with a high velocity (High Velocity Oxygen Fuel (HVOF)) spraying technique to form a coating layer having a high hardness (800-1000 HV) of dense structure and high adhesion. It was. The top coating layer (C2) has excellent fretting and wear resistance in the high temperature range of 540 ~ 900 ° C, which is very effective for extending the life of corrosion and corrosion of boiler tubes. .

On the other hand, coating with a hard top coating layer (C2) material not only to the kick-out but also to the upper portion of the slow sand flow rate is most advantageous in terms of the tube's abrasion protection, but this increases the coating area. Due to the high cost, it is not applied.

In addition, since the sand is hardly touched by the pipe part upward from the castable, since the wear hardly occurs even if the coating is not performed, the coating of the smoothness at the kick-out part may be applied.

In addition, in the present embodiment has been described a structure employing a kick-out panel, it is a matter of course that can be variously applied to the site where the wear occurs without being restricted by the panel structure. For example, in the case of a welded joint where the tube and the tube are interconnected, the grinding process is smooth but there are fine protrusions, and intensive wear may occur due to collision and wear on the protrusions. Therefore, it is preferable to apply the double coating structure of the present invention to coat smoothly.

Referring to the coating method of the circulating fluidized bed boiler tube having the above configuration as follows.

FIG. 9 is a flowchart illustrating a process for coating a boiler tube according to an embodiment of the present invention. The present embodiment is a base coating layer (C1) and a tower in a circulating fluidized bed boiler using a high velocity flame spraying technique (HVOF). It is for explaining the process of coating the coating layer (C2) as an example.

Referring to FIG. 9, first, a spray equipment for high speed flame spraying is prepared (S810). Thermal spraying is a surface hardening technique that causes particles of a powder or wire type coating material (ceramic, alloy, and plastic) to be melted by a high temperature heat source (gas, plasma, arc) to the material at high speed. Technology to form. Among them, high-speed flame spraying technique uses high-pressure fuel (hydrogen, propylene or propane) and oxygen to sinter the product by impinging the coating powder on the material at supersonic speed (about 1000m / sec) in a semi-melted state at about 3000 ℃. It is a technology to form a dense coating film similar to that of ARC SPRAY and PLASMA SPRAY, which can spray and spray powder particles at a higher speed than the ARC SPRAY or PLASMA SPRAY to obtain a high-hardness thermal spray coating with excellent adhesion. have.

Next, inspect the tube appearance, such as wear, corrosion, defect state inside and outside the tube (S820).

Next, as a first grit blasting of the tube surface (S830), the tube surface is blasted using, for example, 24 mesh alumina grit, and then blasted.

Next, as a step (S840) of degreasing the coating surface, when the surface to be coated is contaminated by oil or the like, cleaning is performed using a solvent or trichloro ethanol having strong cleaning power. )do. After cleaning, inspect the residue removal.

Next, as a skin step (S850), if there is a part to be protected from blasting or coating masking using heat-resistant special glass tape or steel strip (steel strip).

Next, as a step G860 blasting the tube surface (S860), the portion to be coated is uniformly blasted using a 24 mesh alumina grit and then the blasting state is examined. At this time, the metallic luster does not remain.

After the pretreatment by the above-described step S830 to S860, to form a base coating layer (S870). As the base coating layer material, for example, a powder material containing carbon (C), boron (B), and silicon (Si) in a nickel-chromium (Ni-Cr) alloy base may be applied. I can regulate it. In the present embodiment, Ni17Cr4Fe4Si3.5B1C powder was used, and a coating layer was formed to a thickness of about 100 to 500 μm by a high-velocity oxygen spray (HVOF) spraying technique.

At this time, as shown in FIG. 10, the middle portion (b) is coated thicker than the edge portions (a, c) of the tube, which means that the middle portion (b) has a relatively higher wear rate than the edge portions (a, c). Because it is a lot.

In addition, since the top coating layer is not formed, only the base coating layer is formed, the base coating layer may be formed so as to be similar to the overall thickness of the portion where the top coating layer is formed, for example, to have a thickness of about 100 ~ 1000㎛ . Likewise, it is important to coat the step so that a step is formed smoothly in order to minimize the wear at the interface with the boiler when forming the base coating layer.

Referring to FIG. 9 again, a top coating layer is formed on the base coating layer. The top coating layer is a material having a relatively high hardness (about 800 to 900 HV) than the base coating layer, and may be composed of a cermet in which a metal material and a ceramic material are mixed. As the material of the top coating layer (C2), for example, a cermet powder material mixed with chromium carbide (Cr ₃ C ₂ ) and nickel chromium nickel (NiCr) may be applied, and the ratio of each powder may be appropriately adjusted. have. In this embodiment, Cr ₃ C ₂ 20 (Ni20Cr) powder is applied to form a top coating layer having a thickness of about 150 to 500 μm by a high speed flame spraying technique. The top coating layer formed in this way forms a dense structure with a high hardness of 800-1000 HV and a coating layer having high adhesion, and has excellent fretting and particle wear resistance in a high temperature range of 540-900 ° C. Very effective in extending the life of erosion or corrosion. In this case, the base coating layer and the top coating layer may be formed by applying any one of an arc wire, a frame wire, and a plasma in addition to a high velocity flame spray (HVOF) spraying technique.

Next, as the inspection step (S890), a visual inspection, a thickness inspection, a specimen inspection, and the like are performed.

Visual inspection is to observe the entire coated area visually and there should be no dropout, crack, or overheating of the coating layer. If defects are found, the defects should be removed by grit blasting and recoated.

The thickness test is measured by an electronic thickness meter for each one per 0.25 m 2 of the coating area, and the thickness of the top coating layer is preferably 150 μm or more at the edge and 200 μm or more at the middle.

Specimen test is to check coating thickness, micro structure, hardness test, etc. The coating thickness is 150㎛ or more at the edge part and 200㎛ or more at the middle part. Inspect the microstructure through, and examines whether the hardness of the coating layer is more than HRC 55.

Thereafter, although not shown in the drawings, the complementary thermal spray coating may be applied to a weak part of the thickness or wear.

As described above, according to the present embodiment, when the coating layer is formed on the wear-vulnerable portion of the boiler tube, the base coating layer having a relatively low hardness is formed at the bottom, and the top coating layer having a relatively hardness is formed thereon, but the coating boundary portion is the base coating layer. By forming the coating layer in a double structure so as to form only, the base coating layer having a lower hardness than the top coating layer is worn instead of the tube at the tube and coating interface. As such, by forming a double coating layer to expose a portion of the base coating layer, damage to the boiler tube may be minimized compared to the coating cost.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and similarities. For example, in the above-described embodiment, the coating method using the high speed flame spraying technique is described, but the coating layer may be formed by applying the arc spraying or the plasma spraying technique. In other words, if the internal flow rate is not fast, the arc spraying technique can be applied. In this case, the coating layer should be thickly coated to have a thickness of about 2 mm. In addition, the thickness of the base coating layer and the top coating layer or the range of the single coating layer formed only the base coating layer is not limited to the disclosed embodiment can be appropriately adjusted according to the wear portion or degree of the boiler tube.

Accordingly, the scope of the present invention should be construed as being limited to the embodiments described, and it is intended that the scope of the present invention encompasses not only the following claims, but also equivalents thereto.

10: boiler tube
11: castable
C, C1, C2: coating layer

Claims (6)

In the tube coating structure of a fluidized bed boiler,
A base coating layer of a first hardness formed on a predetermined portion of the tube; And
A top coating layer having a second hardness higher than the first hardness and overlapping at least a portion of the base coating layer; As a dual-layer coating layer comprising,
In order to prevent the tube from being concentrated at the interface between the tube and the coating layer due to the difference in hardness between the tube and the coating layer, the boundary between the tube and the coating layer is in contact with the tube as compared with the hardness difference between the top coating layer and the tube. The top coating layer is superimposed on the top of the base coating layer so that at least one end of the base coating layer extends outwardly from the edge of the top coating layer so that the base coating layer is located where the hardness difference is relatively low. Tube coating structure.
delete The tube coating structure of a fluidized bed boiler according to claim 1, wherein the first hardness is 300 to 700 HV and the second hardness is 750 to 1000 HV.
The method of claim 1,
The base coating layer is made of a metal material
The top coating layer is a tube coating structure of a fluidized bed boiler, characterized in that consisting of a cermet material.
In the tube coating method of a fluidized bed boiler,
(A) forming a base coating layer of a first hardness on a predetermined portion of the tube;
(B) a method of forming a coating layer having a dual structure, including forming a top coating layer having a second hardness higher than the first hardness on at least a portion of the base coating layer;
The top coating layer has at least one end of the base coating layer such that a base coating layer is positioned at a boundary portion between the tube and the coating layer such that a hardness difference with the tube is relatively lower than a hardness difference between the top coating layer and the tube. Method of coating a tube of a fluidized bed boiler, characterized in that overlapping is formed on top of the base coating layer to extend outwardly exposed from the edge of the coating layer.
The method of claim 5, wherein (B)
Fluidized bed boiler, characterized in that by coating the cermet powder on the predetermined top coating layer forming site on the base coating layer by using any one of high velocity flame (HVOF) spray, arc wire, frame wire, plasma. Tube coating method.

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