JP2014141699A - Anticorrosive coating film, heat transfer pipe and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anticorrosive coating film capable of not only preventing corrosion or exfoliation caused by corrosive gas or dust generated inside a waste power generation facility but also suppressing arrival thereof to a heat transfer pipe, and to provide a heat transfer pipe having the anticorrosive coating film formed thereon.SOLUTION: The anticorrosive coating film has a ground layer comprising an M-Cr-Al-Y-based alloy (M is at least one kind between Ni, Co and Fe) and a surface layer comprising stabilized ZrO, and the porosity of the surface layer is 5% or less.

Description

  The present invention relates to a corrosion-resistant coating used for a heat transfer tube of a waste power generation facility that recovers thermal energy from a high-temperature combustion exhaust gas of municipal waste, coal, or other industrial waste through a fluid such as steam or air, and the same. Relates to the heat transfer tube formed.

  In the treatment of municipal waste and industrial waste, technologies such as waste power generation that makes effective use of combustion energy have become important from the viewpoint of stable energy supply, as well as volume reduction technology by incineration. In recent years, waste power generation is expected as a countermeasure for carbon dioxide reduction and waste disposal problems, and high-efficiency power generation with a power generation efficiency of 30% or more, which is equivalent to that of a normal power plant, is desired.

  In the waste used as fuel in the waste power generation facility, in addition to combustible materials such as paper, wood and plastic, various substances are mixed unevenly. For this reason, the combustion gas of waste incinerators contains more corrosive gases such as HCl and basic salts (dust) such as sodium and potassium than the combustion gases of ordinary fossil fuels (heavy oil, coal, etc.). Contains. When these corrosive gases and dust come into contact with the heat transfer tube at a high temperature, the heat transfer tube is corroded. Since corrosion becomes severe as the temperature rises, the current waste power generation has a steam temperature set to 300 ° C. or lower, and the power generation efficiency is as low as about 5 to 15%.

  In order to improve the power generation efficiency, it is essential to increase the temperature and pressure of the steam inside the heat transfer tube. In recent years, waste power generation facilities have been increasing the temperature and pressure of steam for the purpose of improving power generation efficiency. However, corrosion of the heat transfer tubes by chlorinated gases or alkali molten salts has become severe, and deterioration of the heat transfer tubes is a problem. It has become.

  For this reason, research and development of materials that can withstand severe corrosion caused by chlorine-based gas or alkali molten salt in high-temperature waste combustion gas has been conducted, and excellent high-temperature corrosion-resistant alloy tubes such as Ni-based alloys (Alloy 625) have been developed. . However, since these alloys use a large amount of rare resources and are very expensive, a cheaper corrosion resistant material is required from the viewpoint of power generation cost.

Patent Document 1 discloses a heat transfer tube in which 50 to 85 wt% Ni-15 to 50 wt% Cr is formed as a base layer on the heat transfer tube and Al is sprayed as a surface layer. In Patent Document 2, an M-Cr-Al-Y layer (wherein M is at least one of Ni, Co, and Fe) is used as a base layer in a heat transfer tube, and 85 to 95 wt% ZrO ₂ -5 is used as a surface layer. A zirconia-coated member in which columnar crystals of ˜15 wt% Y ₂ O ₃ are formed is disclosed.

Japanese Patent Application Laid-Open No. 7-146091 Japanese Patent No. 3769065 Proceedings of the 13th National Urban Cleansing Research Conference February 1992

According to Patent Document 1, Al becomes a dense oxide film to prevent corrosion of the heat transfer tube, but it has been reported that the life of the Al coat is not long in the results of the waste incinerator (non-patent document). 1). When a single Al is exposed to an atmosphere of a molten salt adhesion site where Cl ₂ and O ₂ coexist, Al chloride volatilization and Al oxidation proceed simultaneously. Therefore, a dense oxide film that can block the entry of corrosive gas is not formed, and a porous oxide film that is easy to peel off is obtained. The oxide film repeats generation and peeling, and at the same time, consumption of Al due to volatile chloride proceeds, and the Al sprayed film disappears within a short period of time. Thus, since the Al layer formed by thermal spraying is easily peeled and corroded in the refuse incinerator, the anticorrosion effect is small.

According to Patent Document 2, since the ZrO ₂ —Y ₂ O ₃ layer is formed as columnar crystals by physical vapor deposition, cracking and peeling of the coating due to the thermal cycle inside the refuse incinerator is suppressed. The ZrO ₂ —Y ₂ O ₃ layer itself has high corrosion resistance and hardly corrodes itself. It is also possible to suppress cracking due to thermal cycling by the gaps between the columnar crystals, but this gap allows the permeation of corrosive gas and dust. Eventually, the corrosive gas and dust reach the heat transfer tube, and the heat transfer tube is corroded. Thus, the ZrO ₂ —Y ₂ O ₃ layer formed by physical vapor deposition has a small anticorrosion effect in that it allows permeation of corrosive gas and dust.

  The present invention has been made in consideration of the above circumstances, and not only does not corrode and peel off by corrosive gas or dust generated inside the waste power generation facility, but also suppresses the arrival of these heat transfer tubes. It is an object of the present invention to provide a possible corrosion-resistant coating and a heat transfer tube on which the coating is formed.

As a result of intensive studies, the present inventor has used an M—Cr—Al—Y alloy (M = Ni, Co, Fe) formed by gas spraying or plasma spraying on the surface of the heat transfer tube using a powder having a controlled particle size. It is found that the above-mentioned problems can be solved by using an undercoat layer made of) and a stabilized ZrO ₂ formed by plasma spraying using a powder having a controlled particle size.

That is, the corrosion-resistant film of the present invention has an underlayer made of an M—Cr—Al—Y alloy (M is at least one of Ni, Co, and Fe) and a surface layer made of stabilized ZrO _2. The porosity is 5% or less. Here, “porosity is 5% or less” means that when the cross section of the surface layer is observed with a scanning electron microscope at a magnification of 1000 times, the ratio of the total area of cracks and voids to the surface area of the observation screen is 5% or less. It means that.

  In this invention, it is preferable that the film thickness of the said surface layer is 10-500 micrometers. Here, the “film thickness” means a thickness measured using an electromagnetic or eddy current film thickness meter.

  According to the said structure, permeation | transmission of corrosive gas and dust can be suppressed effectively and peeling of the film resulting from the heat cycle inside an incinerator can be made hard to produce.

  In the present invention, the base layer preferably has a porosity of 1% or less.

  According to the said structure, permeation | transmission of corrosive gas and dust can be suppressed effectively.

  In this invention, it is preferable that the film thickness of the said base layer is 10-500 micrometers.

  According to the above configuration, the permeation of corrosive gas and dust can be effectively suppressed, and the thermal stress due to the expansion characteristics of the base material and the surface layer can be effectively reduced. Further, it is possible to make it difficult for the coating film to peel off due to the thermal cycle inside the incinerator.

  The coating of the present invention is suitably used for a heat transfer tube of a waste power generation facility that recovers thermal energy from a high-temperature combustion exhaust gas of municipal waste, coal, or other industrial waste through a fluid such as steam or air, and generates power. .

  The heat transfer tube of the present invention is characterized in that the above-mentioned corrosion-resistant film is formed on the surface.

The method of manufacturing corrosion-resistant film of the present invention, M-Cr-Al-Y alloy on the substrate (M is Ni, Co, at least one of Fe) to form an underlayer made of, then stabilized ZrO ₂ A method for producing a corrosion-resistant film comprising a surface layer comprising: forming a surface layer by plasma spraying a stabilized ZrO ₂ powder having an average particle size of 10 to 75 μm. Here, the “average particle size” is defined by D ₅₀ calculated on the basis of the number of particles when the particle size of an arbitrary powder is measured by a laser diffraction scattering method.

  In the present invention, an underlayer is formed by gas spraying or plasma spraying an M—Cr—Al—Y alloy powder (M is at least one of Ni, Co, and Fe) having an average particle diameter of 10 to 75 μm. Is preferred.

  According to the above configuration, it becomes easy to form a dense underlayer.

  Moreover, the manufacturing method of the heat exchanger tube of this invention forms an underlayer and a surface layer using the said method, It is characterized by the above-mentioned.

In the corrosion-resistant film of the present invention, a dense stabilized ZrO ₂ film is formed on the surface layer. Therefore, if this coating is formed on the surface of the heat transfer tube, the coating does not corrode or peel off due to the corrosive gas or dust generated inside the waste power generation equipment, but also suppresses the arrival of these gases to the heat transfer tube. It is possible to prevent deterioration of the heat transfer tube body.

Moreover, according to the method of the present invention, a dense stabilized ZrO ₂ film having a low porosity can be formed on an underlayer made of an M—Cr—Al—Y alloy. Therefore, if this method is used, a heat transfer tube having excellent corrosion resistance can be manufactured.

Hereinafter, embodiments of the present invention will be described.

The corrosion-resistant film of the present invention has a surface layer made of stabilized ZrO ₂ and an underlayer made of an M—Cr—Al—Y alloy.

Stabilized ZrO ₂ constituting the surface layer is composed mainly of ZrO ₂ and selected from Y ₂ O ₃ , MgO, CaO, SiO ₂ , CeO ₂ , Yb ₂ O ₃ , Dy ₂ O ₃ , HfO _{2 and the} like. More than one kind of stabilizer is added. Specifically, the ZrO ₂ content is 85% by mass or more, preferably 85 to 95% by mass, and the stabilizer content is 15% by mass or less, preferably 5 to 15% by mass. If the ZrO ₂ content is 85% by mass or more, the corrosion resistance of the surface layer can be ensured, and the phase from the tetragonal or cubic to monoclinic phase of ZrO ₂ generated at around 1000 ° C. in the cooling process after plasma spraying. Metastasis can also be suppressed. When the content of ZrO ₂ is less than 85% by mass, the corrosion resistance of the surface layer is lowered.

  The porosity of the surface layer is 5% or less, preferably 4% or less. By densifying the surface layer, it becomes possible to prevent corrosion of the base material caused by corrosive gas or dust permeating the coating. If the porosity of the surface layer is higher than 5%, it becomes difficult to suppress the permeation of corrosive gas and dust.

The surface layer has a thickness of 10 to 500 μm, particularly 50 to 400 μm, and more preferably 100 to 300 μm. When the film thickness of the surface layer is small, it is difficult to suppress permeation of corrosive gas and dust. On the other hand, when the film thickness of the surface layer is large, the thermal stress generated by the thermal cycle inside the refuse incinerator increases, and the surface layer is easily peeled off. The porosity of the surface layer can be adjusted by changing the particle size of the stabilized ZrO ₂ powder to be sprayed.

  The M—Cr—Al—Y alloy (M = Ni, Co, Fe) constituting the underlayer is mainly composed of Ni or Co having excellent high temperature oxidation resistance and high temperature corrosion resistance, Cr, It is an alloy to which Al and Y are added. This type of alloy is characterized in that it easily adheres to both the heat transfer tube and the surface layer.

  The porosity of the underlayer is preferably 1% or less. When the porosity of the underlayer is high, it is difficult to suppress permeation of corrosive gas and dust.

  The film thickness of the underlayer is preferably 10 to 500 μm, particularly 50 to 400 μm, and more preferably 100 to 300 μm. When the film thickness of the underlayer is thin, it is difficult to suppress permeation of corrosive gas and dust. The underlayer generally has an effect of relieving thermal stress due to the difference in thermal expansion characteristics generated at the interface between the heat transfer tube and the surface layer. However, if the underlayer thickness is small, it is difficult to obtain the effect of relieving thermal stress. On the other hand, if the film thickness of the underlayer is large, the thermal stress generated by the thermal cycle inside the refuse incinerator increases, and the underlayer easily peels off. The porosity of the underlayer can be adjusted by changing the particle size of the M-Cr-Al-Y alloy powder to be sprayed.

  The corrosion resistant coating of the present invention has a surface layer and an underlayer as described above, but one or more intermediate layers may be provided between the surface layer and the underlayer.

  The corrosion-resistant coating of the present invention is used as a protective film for heat transfer tubes of waste power generation equipment that recovers heat energy from high-temperature combustion exhaust gas of municipal waste, coal, and other industrial wastes through fluids such as steam and air. It is preferable to be used. However, it is not limited to these. For example, it can be suitably used for gas turbines, various engines, and the like.

  The heat transfer tube of the present invention preferably has the above-described corrosion-resistant coating formed thereon. In addition, as a material of a heat exchanger tube main body, the metal material which has at least one of Fe, Ni, Co, and Cr as a main component is preferable. The underlayer is preferably formed directly on the heat transfer tube body, but another layer may be provided between the heat transfer tube body and the underlayer for the purpose of improving adhesion and the like.

  Next, the manufacturing method of the corrosion-resistant film of the present invention will be described. In addition, in the following description, if the metal tube which comprises a heat exchanger tube main body is used as a base material, a heat exchanger tube can be produced.

The method of the present invention includes a step of forming an underlayer made of an M—Cr—Al—Y alloy on a substrate and a step of forming a surface layer made of stabilized ZrO ₂ on the underlayer.

  The formation of the underlayer is not particularly limited, but is preferably formed by gas spraying such as high-speed flame spraying (HVOF). By using high-speed flame spraying, it becomes easy to obtain an underlayer having good adhesion to the heat transfer tube and low porosity. Moreover, it is preferable to use the powder which consists of a M-Cr-Al-Y type alloy for the thermal spraying powder used in this case. The M-Cr-Al-Y alloy is as described above, and the description thereof is omitted here. The average particle size of the thermal spray powder is preferably 10 to 75 μm, particularly 10 to 53 μm, and more preferably 10 to 45 μm. When the particle size of the sprayed powder is large, the porosity of the lower layer formed by gas spraying is increased, and it is difficult to suppress permeation of corrosive gas and dust. In addition, if the particle size of the sprayed powder is small, clogging of the jet port called the port, which supplies the sprayed powder to gas or plasma, is likely to occur, and it takes time to form a sprayed coating with an arbitrary film thickness. Cost is likely to increase.

The surface layer is formed by a plasma spraying method. As the plasma spraying method, various methods such as an atmospheric pressure plasma spraying method and a vacuum plasma spraying method can be used. A stabilized ZrO ₂ powder is used as the thermal spraying powder used at this time. The stabilized ZrO ₂ is as described above, and the description thereof is omitted here. The average particle diameter of the thermal spray powder is 10 to 75 μm, preferably 10 to 53 μm, more preferably 10 to 45 μm. When the particle size of the sprayed powder is larger than 75 μm, the porosity of the surface layer formed by plasma spraying becomes high, and it becomes difficult to suppress permeation of corrosive gas and dust. In addition, if the particle size of the thermal spray powder is small, clogging of the spray port (port) that supplies the thermal spray powder to the plasma is likely to occur, and it takes time to form the thermal spray coating of any film thickness, resulting in high thermal spray costs. Easy to be.

  In this way, the corrosion-resistant film of the present invention can be formed on the substrate. For the purpose of improving adhesion and the like, another layer may be formed between the base material and the base layer and / or between the base layer and the surface layer.

  Hereinafter, based on an Example, this invention is demonstrated in detail.

  Table 1 shows Examples (Sample Nos. 1 to 3) and Comparative Examples (Sample No. 4) of the present invention.

  First, the SUS310S base material was degreased, washed, and then blasted. Next, high-speed flame spraying was performed using the thermal spraying powder shown in the table, and a base layer made of a CoNiCrAlY alloy was formed on the substrate with a uniform thickness. The film thickness is adjusted by first moving the spraying device parallel to the substrate and spraying, and measuring how much film thickness can be obtained at one time using a film thickness meter described later. This was done by adjusting the number of spraying.

Next, the CoNiCrAlY layer was blasted. Subsequently, atmospheric pressure plasma spraying was performed using the thermal spraying powder shown in the table, and a surface layer made of 8% Y ₂ O ₃ —ZrO ₂ was formed on the underlayer with a uniform thickness. The film thickness was adjusted by the same method as when the CoNiCrAlY alloy was sprayed.

  The porosity of the coating film thus obtained was measured. The results are shown in Table 1.

As is apparent from Table 1, in the examples of the present invention using 8% Y ₂ O ₃ —ZrO ₂ powder having an average particle diameter of 10 to 45 μm, a surface layer having a low porosity is formed, and the coating film of the comparative example It can be seen that this is superior in suppressing permeation of corrosive gas and dust.

The average particle size of the thermal spray powder when measured by a laser diffraction particle size distribution analyzer (manufactured by Shimadzu SALD-2000J), was confirmed by the value of D ₅₀ calculated by the number-based particle.

  The film thickness of the surface layer and the underlayer was confirmed by measuring with an eddy current film thickness meter (SWT-8000II, manufactured by Sanko Denshi).

  The porosity is measured with a scanning electron microscope (Hitachi S-3400 type II) for the cross-sections of Examples and Comparative Examples of the present invention, and cross-sectional photographs are taken. It was calculated as a ratio of the total area of cracks and voids in each layer. In taking a cross-sectional photograph, the observation mode was a secondary electron image, the magnification was 1000 times, and images at arbitrary three points of the base layer and the surface layer were obtained. The porosity shown in Table 1 is an average value of the porosity at these three points.

The corrosion-resistant coating film and heat transfer tube of the present invention are used for heat transfer tubes of waste power generation equipment that recovers heat energy from high-temperature combustion exhaust gas of municipal waste, coal, and other industrial wastes through fluids such as steam and air to generate power. Useful as a material and heat transfer tube.

Claims (9)

It has an underlayer made of an M-Cr-Al-Y alloy (M is at least one of Ni, Co, and Fe) and a surface layer made of stabilized ZrO ₂ , and the surface layer has a porosity of 5% or less. A corrosion-resistant coating characterized by the above.   The corrosion-resistant film according to claim 1, wherein the surface layer has a thickness of 10 to 500 μm.   The corrosion-resistant film according to claim 1, wherein the porosity of the underlayer is 1% or less.   The corrosion-resistant film according to any one of claims 1 to 3, wherein the underlayer has a thickness of 10 to 500 µm.   2. The heat transfer tube of a waste power generation facility for generating power by recovering thermal energy from a high-temperature combustion exhaust gas of municipal waste, coal, or other industrial waste through a fluid such as steam or air. Corrosion-resistant film in any one of -4.   6. A heat transfer tube, wherein the corrosion-resistant coating film according to claim 1 is formed on a surface. A method for producing a corrosion-resistant coating, comprising forming a base layer made of an M-Cr-Al-Y alloy (M is at least one of Ni, Co, and Fe) on a substrate and then forming a surface layer made of stabilized ZrO ₂ A method for producing a corrosion-resistant coating, comprising forming a surface layer by plasma spraying stabilized ZrO ₂ powder having an average particle size of 10 to 75 μm.   The underlayer is formed by gas spraying or plasma spraying M-Cr-Al-Y alloy powder (M is at least one of Ni, Co and Fe) having an average particle size of 10 to 75 µm. Item 8. A corrosion-resistant film according to Item 7. A method for producing a heat transfer tube, comprising forming an underlayer and a surface layer using the method according to claim 7 or 8.