JP2015183194A - Production method of anticorrosive coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anticorrosive coating film capable of not only preventing corrosion or exfoliation caused by sour gas generated inside a coal-fired power generation boiler but also suppressing arrival of the sour gas to a heat transfer pipe; and to provide a heat transfer pipe having the same formed thereon.SOLUTION: An anticorrosive coating film is produced by forming a ground layer comprising the M-Cr-Al-Y-based alloy (M is at least one kind of Ni, Co and Fe) on a substrate, followed by forming a surface layer by plasma-spraying mixed powder of stabilized ZrOpowder and fumed silica.

Description

  The present invention relates to a corrosion-resistant coating used for a heat transfer tube such as a coal-fired power generation that recovers thermal energy from a high-temperature gas generated by burning coal through a fluid such as steam or air, and a heat transfer tube formed with the same About.

  In thermal power generation, coal, oil, and LNG are burned with a boiler, and steam is generated using the heat of the high-temperature gas to generate power by rotating the turbine. These fuel coals and petroleum, especially coal, contain a large amount of sulfur, and the combustion gas contains acid gases such as hydrogen sulfide and sulfur oxides. When the heat transfer tube is exposed to a high-temperature gas containing acid gas for a long period of time, the heat transfer tube is corroded by the acid gas.

  Since the heat transfer tube is deteriorated due to the corrosion caused by the acid gas, it is necessary to frequently replace the heat transfer tube. Since replacement of heat transfer tubes increases power generation costs, a heat transfer tube that does not deteriorate for a longer period of time is required.

  Patent Document 1 discloses a composite material characterized by comprising 30 to 60 wt% boride and 40 to 70 wt% intermetallic compound and having a Cr content of 20 wt% or less. There is disclosed a composite coating in which cermet or ceramics is formed by thermal spraying as a base layer, a sealing treatment is performed on the surface of the base layer with an oxide ceramic, and further a glassy coating is formed.

JP 2005-213605 A JP 2001-152307 A

  According to Patent Document 1, attention is focused on borides as a main component of a surface protecting film on a member used in a high temperature environment. Boride is difficult to sinter and has poor wettability with the binder phase metal, but it is a fatal defect as a component of composite materials that borides easily form embrittlement during metallurgical bonding. Have In order to solve such a problem, attention is paid to an intermetallic compound, and this is added to a boride to form a composite material. However, the intermetallic compound described in Patent Document 1 cannot be said to have sufficient corrosion resistance in a high temperature environment.

  According to Patent Document 2, the base material is protected with a thermal spray coating of cermet or ceramic, the thermal spray coating is sealed with an oxide-based ceramic, and further, a glassy coating is formed on the surface layer. In addition to exhibiting excellent corrosion resistance against corrosive gases, the service life of the substrate is remarkably improved. However, because the oxide-based ceramics used for the glassy coating and sealing are dense, thermal stresses caused by thermal expansion and contraction due to thermal cycling when used in boilers for thermal power generation that are frequently operated and stopped. Is difficult to relieve, and the coating is easily peeled off. As a result, only the thermal spray coating protects the substrate. Since the thermal spray coating generally has pores, the acidic gas reaches the substrate through the pores, and the substrate is corroded. As described above, since the sealing treatment and the formation of the glassy film are easily peeled off by a thermal cycle, the life of the substrate cannot be extended, and the anticorrosion effect is small in this respect.

  The present invention has been made in consideration of the above circumstances, and not only does it not corrode and peel off due to high-temperature acidic gas generated in thermal power generation, particularly coal-fired power generation, but also suppresses the arrival of acidic gas to the heat transfer tube. It is an object of the present invention to provide a corrosion-resistant coating that can be used and a heat transfer tube in which the coating is formed.

As a result of intensive studies, the inventor has obtained a mixed powder of stabilized ZrO ₂ and fumed silica on an underlayer made of an M—Cr—Al—Y alloy (M is at least one of Ni, Co, and Fe). The present inventors have found that the above problem can be solved by providing a surface layer produced by thermal spraying, and propose the present invention.

That is, in the method for producing a corrosion-resistant coating according to the present invention, a base layer made of an M-Cr-Al-Y alloy (M is at least one of Ni, Co, and Fe) is formed on a substrate, and then stabilized ZrO. _A surface layer is formed by plasma spraying a mixed powder of _two powders and fumed silica. By "stabilization" in the present invention, in the cooling process after the ZrO ₂ plasma sprayed, the phase transition from tetragonal or cubic ZrO ₂ generated near 1000 ° C. to monoclinic is suppressed Means.

  According to the said structure, a precise | minute surface layer with a low porosity can be formed on the base layer which consists of a M-Cr-Al-Y type alloy.

In the present invention, it is preferable to use a mixed powder in which the mixing ratio of fumed silica to the stabilized ZrO ₂ powder is 5 to 20% by volume.

  According to the said structure, a precise | minute and highly corrosion-resistant surface layer can be obtained easily.

  In the present invention, it is preferable to use fumed silica having an average particle size of less than 1 μm.

  According to the said structure, a precise | minute surface layer can be obtained easily.

  The method for producing a heat transfer tube of the present invention is characterized in that a corrosion-resistant film is formed using the above method.

  According to the said structure, the heat exchanger tube excellent in corrosion resistance can be manufactured.

  The corrosion-resistant film of the present invention is formed by the above method.

According to the above configuration, a dense surface layer is formed because the coating is likely to have a silica component (derived from fumed silica) in the voids between the stabilized ZrO ₂ particles. Therefore, if this film is formed on the surface of the heat transfer tube, the acid gas generated in the boiler of coal-fired power generation will not only corrode and peel off the film, but it will also be possible to suppress the acid gas from reaching the heat transfer tube. The deterioration of the heat transfer tube body can be prevented. In addition, since the base layer made of an M-Cr-Al-Y alloy (M is at least one of Ni, Co, and Fe) is interposed between the base material and the surface layer, the surface layer has high adhesion, and peeling It is hard to do.

  The coating of the present invention is suitably used for a heat transfer tube for coal-fired power generation.

  The heat transfer tube of the present invention is formed as described above.

  According to the said structure, a coating film does not corrode and peel with the acidic gas which generate | occur | produces in the boiler of coal thermal power generation, and deterioration of a heat exchanger tube main body can be prevented. Moreover, since the base layer made of an M-Cr-Al-Y alloy (M is at least one of Ni, Co, and Fe) is interposed between the base material and the surface layer, the adhesion of the surface layer is high, and peeling It is hard to do.

  Hereinafter, embodiments 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 a base layer made of an M-Cr-Al-Y alloy on a base material, and a step of forming a surface layer containing stabilized ZrO ₂ and inorganic glass on the base layer. .

  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. M-Cr-Al-Y alloy (M = Ni, Co, Fe) is mainly composed of Ni or Co having excellent high-temperature oxidation resistance and high-temperature corrosion resistance, and Cr, Al, and Y are added. Alloy. This type of alloy is characterized in that it easily adheres to both the heat transfer tube and the surface layer. The average particle size of the sprayed powder is preferably 10 to 75 μm, 10 to 53 μm, and particularly 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 acidic gas. 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. As the thermal spraying powder used in this case, a mixed powder of stabilized ZrO ₂ powder and fumed silica is used.

The stabilized ZrO ₂ powder is mainly composed of ZrO ₂ , and one or more kinds 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. It is a ZrO ₂ powder to which a 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 average particle size of the stabilized ZrO ₂ powder is preferably 10 to 75 μm, 10 to 53 μm, particularly preferably 10 to 45 μm. When the average particle diameter of the stabilized ZrO ₂ powder is large, the porosity of the surface layer formed by plasma spraying becomes high, and it becomes difficult to suppress permeation of acid gas. In addition, if the average particle size of the stabilized ZrO ₂ powder is small, clogging of the spray port (port) for supplying the sprayed powder to the plasma is likely to occur, and it takes time to form a sprayed coating having an arbitrary film thickness. Thermal spraying cost tends to be high.

Fumed silica is silica fine particles synthesized by vapor phase reaction in a high-temperature hydrogen flame by vaporizing silicon chloride. The average particle size of fumed silica is preferably less than 1 μm, particularly 50 to 500 nm. If fumed silica having the above particle size is selected, fumed silica is likely to adhere to the surface of the stabilized ZrO ₂ powder due to static electricity. When the stabilized ZrO ₂ powder to which fumed silica is adhered is plasma sprayed, fumed silica is likely to gather at the ZrO ₂ particle interface during spraying, and the voids between the particles are filled with the silica component. If the average particle size of the fumed silica is too large, it becomes difficult to adhere to the surface of the stabilized ZrO ₂ powder due to static electricity. As a result, during the plasma spraying, the silica component will separate from the ZrO ₂ particles, to meet the gap between the ZrO ₂ particles in the silica component is difficult.

The mixing ratio of fumed silica to the stabilized ZrO ₂ powder is 5 to 20% by volume, preferably 5 to 15%. When the mixing ratio of fumed silica is too low, it is difficult to obtain a porosity reduction effect due to a shortage of silica components. When the mixing ratio of fumed silica is too high, the ratio of the silica component in the surface layer tends to increase, and as a result, the corrosion resistance of the surface layer decreases.

  A corrosion-resistant film can be formed on the substrate as described above. 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.

  The porosity of the surface layer of the obtained corrosion-resistant film is preferably 5% or less, particularly 4% or less. By densifying the surface layer, it becomes possible to prevent corrosion of the base material caused by the acidic gas permeating the coating. When the porosity of the surface layer is higher than 5%, it becomes difficult to suppress permeation of acid gas. 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.

  Further, the film thickness of the surface layer is preferably 10 to 500 μm, particularly 50 to 400 μm, and more preferably 100 to 300 μm. If the film thickness of the surface layer is too small, it is difficult to suppress permeation of acidic gas. On the other hand, when the film thickness of the surface layer is too large, the thermal stress generated by the heat cycle inside the boiler becomes large, and the surface layer is easily peeled off. The porosity of the surface layer can be adjusted by changing the particle size of the sprayed powder.

  The porosity of the underlayer is preferably 1% or less. When the porosity of the underlayer is high, it is difficult to suppress transmission of acid gas.

  The 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 transmission of acid gas. The underlayer generally has an effect of alleviating 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 is too thin, it is difficult to obtain the effect of mitigating thermal stress. . On the other hand, if the film thickness of the underlayer is too large, the thermal stress generated by the thermal cycle inside the boiler becomes large, 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.

  Moreover, it is preferable that the corrosion-resistant film of the present invention is used as a protective film for a heat transfer tube of coal-fired power generation that recovers thermal energy from a high-temperature combustion gas of coal via a fluid such as steam or air and generates power. However, it is not limited to these. For example, it can be suitably used for heat transfer tubes such as coal gasification combined power generation, petroleum thermal power generation, waste power generation, and geothermal power generation, gas turbines, various engines, and the like.

  Moreover, when producing a heat transfer tube using the method of the present invention, a metal material mainly comprising at least one of Fe, Ni, Co, and Cr can be selected as the material of the base material (heat transfer tube body). 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.

Hereinafter, based on an Example, this invention is demonstrated in detail.
Tables 1 and 2 show Examples (Sample Nos. 1 to 3) and Comparative Examples (Sample No. 4) of the present invention.

  First, the SUS310S base material is degreased, washed, and blasted, and an alloy powder having an average particle diameter of 10 to 45 μm made of a Co—Ni—Cr—Al—Y alloy is sprayed at high speed to provide high temperature oxidation resistance and resistance. An underlayer (Co—Ni—Cr—Al—Y alloy layer) excellent in high temperature corrosivity was obtained. The film thickness of the underlayer was uniform and was 150 to 300 μm. 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, 8% Y ₂ O ₃ —ZrO ₂ powder having an average particle size of 10 to 45 μm and Aerosil RY-50 (particle size of 0.05 to 0.5 μm) of Nippon Aerosil Co., Ltd. were each 80% by volume. The mixed powder was obtained by mixing at a ratio of -95% and 5-20%. Subsequently, the obtained mixed powder was subjected to atmospheric pressure plasma spraying on the base layer to form a surface layer. The film thickness of the surface layer was uniform and was 100 to 250 μm. Note that the thickness of the surface layer was adjusted by the same method as in the case of thermal spraying the Co—Ni—Cr—Al—Y alloy.

As a comparative example, a base layer made of a Co—Ni—Cr—Al—Y alloy was formed on a SUS310S base material in the same procedure as in the above example. Subsequently, 8% Y ₂ O ₃ —ZrO ₂ powder having an average particle size of 100 μm was subjected to atmospheric pressure plasma spraying.

  The evaluation results of each sample are shown in Tables 1 and 2.

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 determined by observing the cross sections of the examples and comparative examples of the present invention with a scanning electron microscope (Hitachi S-3400N type II), taking cross-sectional photographs, analyzing each cross-sectional photograph, and analyzing each layer with respect to the total area of the photographing location. It was calculated as a ratio of the total area of cracks and voids. 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 described in Tables 1 and 2 is an average value of the porosity at these three points.

  As is apparent from Tables 1 and 2, sample No. which is an example of the present invention. Nos. 1 to 3 had a surface layer porosity of 4%, whereas the sample No. 1 was a comparative example. The porosity of 4 was as high as 15%. That is, it was confirmed that the example of the present invention formed a film having a higher ability to suppress permeation of acidic gas than the comparative example.

  The corrosion-resistant coating and heat transfer tube of the present invention are a corrosion-resistant coating used for heat transfer tubes such as coal-fired power generation that recovers thermal energy from a high-temperature gas generated by burning coal through a fluid such as steam or air, and It is useful as a heat transfer tube that forms this.

Claims (7)

An underlayer made of an M-Cr-Al-Y alloy (M is at least one of Ni, Co, and Fe) is formed on a substrate, and then a mixed powder of stabilized ZrO ₂ powder and silica fumed silica is plasma treated A method for producing a corrosion-resistant coating, characterized by spraying to form a surface layer. _{2. The} method for producing a corrosion-resistant coating according to claim 1, wherein a mixed powder in which the mixing ratio of fumed silica to the stabilized ZrO ₂ powder is 5 to 20% by volume is used.   The method for producing a corrosion-resistant coating film according to claim 1 or 2, wherein fumed silica having an average particle diameter of less than 1 µm is used.   A method for producing a heat transfer tube, wherein a corrosion-resistant film is formed using the method according to claim 1.   A corrosion-resistant film formed by the method according to claim 1.   The corrosion-resistant coating film according to claim 5, which is used for a heat transfer tube of a coal-fired power generation heat transfer tube.   A heat transfer tube formed by the method according to claim 4.