Method for improving durability of superheater tube row and superheater tube row

Abstract

The invention provides a method for improving durability of a superheater tube row and the superheater tube row, and belongs to the technical field of superheaters. The method for improving the durability of the superheater tube row comprises the following steps: carrying out surface treatment on a superheater tube body; a FeCrMo transition layer is formed on the surface of the superheater tube body subjected to surface treatment in a laser cladding mode; a Ti3SiC2 / CoCrAlY gradient coating is formed on the surface of the superheater body subjected to laser cladding treatment in a double-nozzle plasma spraying mode; and the superheater body subjected to plasma spraying is subjected to heat treatment, stress is eliminated, and the superheater tube row with the durability improved is obtained. According to the method, the durability of the superheater tube bundle is comprehensively improved through a series of steps of surface treatment, formation of the FeCrMo transition layer through laser cladding, formation of the Ti3SiC2 / CoCrAlY gradient coating through plasma spraying, heat treatment and the like.

Description

Technical Field

[0001] This invention relates to the field of superheaters, and more particularly to a method for improving the durability of superheater tube banks and superheater tube banks. Background Technology

[0002] The superheater is a component in a boiler that further heats steam from its saturation temperature to its superheat temperature, and the superheater tube bank is a crucial part of the superheater. Because the combustion materials (coal, biomass fuel, etc.) contain corrosive elements such as sulfur (S) and chloride (Cl), these elements are transferred to the superheater tube bank area with the flow of high-temperature flue gas. Under physical and chemical action, they deposit on the superheater tube bank, causing a sharp decrease in its service life. Summary of the Invention

[0003] To address the problem of a sharp decline in the service life of superheater tube banks due to the corrosive elements in high-temperature flue gas, this invention provides a method and a superheater tube bank for improving the durability of superheater tube banks. Through a series of steps, including surface treatment, laser cladding to form a FeCrMo transition layer, plasma spraying to form a Ti3SiC2 / CoCrAlY gradient coating, and heat treatment, the durability of the superheater tube banks is comprehensively improved.

[0004] The technical solution adopted in this invention is:

[0005] A method for improving the durability of superheater tube banks includes the following steps:

[0006] Step S1: Perform surface treatment on the superheater tube body;

[0007] Step S2: A FeCrMo transition layer is formed on the surface of the superheater tube body after the surface treatment in step S1 by laser cladding.

[0008] Step S3: A Ti3SiC2 / CoCrAlY gradient coating is formed on the surface of the superheater body after the laser cladding treatment in step S2 using a dual-nozzle plasma spraying method.

[0009] Step S4: The superheater body that has undergone plasma spraying in step S3 is subjected to heat treatment to eliminate stress and obtain a superheater tube bank with improved durability.

[0010] Furthermore, in step S1, the surface treatment involves first brushing with hot water at 50-70°C or acetone, then drying, followed by sandblasting with 80-120 mesh abrasive particles at a pressure of 0.4-0.6 MPa. After sandblasting, the surface roughness Ra of the superheater tube body is 3.2-4.0 μm.

[0011] Furthermore, in step S2, the power of laser cladding is 900~1100 W, the scanning speed is 8~12 mm / s, the spot diameter is 2~3 mm, the powder feeding rate is 10~15 g / min, and the thickness of the FeCrMo transition layer is 0.2~0.3 mm.

[0012] Furthermore, in step S2, FeCrMo transition layer is formed using FeCrMo alloy powder, the elemental composition of which is: 15-20% chromium, 2-4% molybdenum, 1-2% aluminum, ≤0.05% boron, ≤0.5% silicon, 0.01-0.05% yttrium oxide, ≤0.1% carbon, with the balance being iron, and the powder particle size is 45-105 μm.

[0013] Furthermore, in step S3, the plasma spraying power is 20~30 kW, the spraying distance is 70~90 mm, the argon flow rate is 40~42 L / min, the hydrogen flow rate is 3~3.5 L / min, and the thickness of the formed Ti3SiC2 / CoCrAlY gradient coating is 1.0~1.2 mm.

[0014] Further, in step S3, during plasma spraying, one nozzle sprays Ti3SiC2 ceramic powder at a feed rate of 20-25 g / min and a spraying current of 600-650 A, while the other nozzle sprays CoCrAlY alloy powder at a feed rate of 25-30 g / min and a spraying current of 550-600 A. The Ti3SiC2 ceramic powder has the following elemental composition: titanium 55-58%, silicon 12-14%, carbon 28-30%, yttrium oxide 0.1-0.3%, iron ≤0.5%, oxygen ≤0.8%, nitrogen ≤0.1%, and a particle size of 15-45 μm. The CoCrAlY alloy powder has the following elemental composition: chromium 20-22%, aluminum 8-10%, yttrium oxide 0.3-0.5%, carbon ≤0.05%, silicon ≤0.2%, iron ≤0.5%, with the balance being cobalt, and a particle size of 20-53 μm. μm.

[0015] Furthermore, in step S3, the plasma spraying is performed multiple times, and as the number of times it is performed increases, the amount of Ti3SiC2 ceramic powder sprayed from one nozzle gradually decreases, while the amount of CoCrAlY alloy powder sprayed from the other nozzle gradually increases.

[0016] Furthermore, in step S3, the plasma spraying is performed in four stages, with a spraying thickness of 0.25~0.3 mm in each stage;

[0017] Based on the total weight of powder sprayed during each spraying operation as 100%, for the first operation: the Ti3SiC2 ceramic powder accounts for 100%, and the CoCrAlY alloy powder accounts for 0%.

[0018] Second execution: The Ti3SiC2 ceramic powder accounts for 70%, and the CoCrAlY alloy powder accounts for 30%.

[0019] Third execution: The Ti3SiC2 ceramic powder accounts for 30%, and the CoCrAlY alloy powder accounts for 70%.

[0020] Fourth execution: The proportion of Ti3SiC2 ceramic powder is 0%, and the proportion of CoCrAlY alloy powder is 100%.

[0021] Furthermore, in step S4, the heat treatment is performed in a vacuum furnace, with the temperature increased to 1000-1150 ℃ at a heating rate of 5-10 ℃ / min, held at that temperature for 2-5 h, and then cooled with the furnace.

[0022] Based on the same inventive concept, the present invention also provides a superheater tube bank, which is manufactured using the aforementioned method for improving the durability of the superheater tube bank.

[0023] The beneficial effects of this invention are:

[0024] This invention provides a method and a superheater tube bank for improving the durability of superheater tube banks. Through a series of steps including surface treatment, laser cladding to form a FeCrMo transition layer, plasma spraying to form a Ti3SiC2 / CoCrAlY gradient coating, and heat treatment, the durability of the superheater tube banks is comprehensively improved. This multi-step treatment method effectively enhances the corrosion resistance and thermal fatigue resistance of the superheater tube banks in high-temperature flue gas environments, extending their service life and reducing maintenance and replacement costs. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart illustrating a method for improving the durability of superheater tube banks in this embodiment. Detailed Implementation

[0027] The embodiments of the invention will now be described in detail with reference to the accompanying drawings.

[0028] This embodiment provides a method for improving the durability of superheater tube banks, the process of which is shown in the attached figure. Figure 1 As shown, the steps include:

[0029] Step S1: Perform surface treatment on the superheater tube body;

[0030] Step S2: A FeCrMo transition layer is formed on the surface of the superheater tube body after the surface treatment in step S1 by laser cladding.

[0031] Step S3: A Ti3SiC2 / CoCrAlY gradient coating is formed on the surface of the superheater body after the laser cladding treatment in step S2 using a dual-nozzle plasma spraying method.

[0032] Step S4: The superheater body that has undergone plasma spraying in step S3 is subjected to heat treatment to eliminate stress and obtain a superheater tube bank with improved durability.

[0033] In this embodiment, the durability of the superheater tube bank is comprehensively improved through a series of steps, including surface treatment, laser cladding to form a FeCrMo transition layer, plasma spraying to form a Ti3SiC2 / CoCrAlY gradient coating, and heat treatment. This multi-step treatment method can effectively enhance the corrosion resistance and thermal fatigue resistance of the superheater tube bank in high-temperature flue gas environments, extend its service life, and reduce maintenance and replacement costs.

[0034] In a preferred embodiment of this application, the surface treatment in step S1 involves first brushing with hot water at 50-70°C or acetone, then drying, followed by sandblasting with 80-120 mesh abrasive particles at a pressure of 0.4-0.6 MPa. After sandblasting, the surface roughness Ra of the superheater tube body is 3.2-4.0 μm.

[0035] In this embodiment, by using hot water or acetone washing and sandblasting with specific parameters, impurities, oil, and scale on the surface of the superheater tubes can be effectively removed, while achieving a suitable surface roughness (Ra 3.2~4.0 μm). This surface pretreatment enhances the adhesion between the subsequent coating and the tube body, improves the coating's adhesion and uniformity, provides a good foundation for the stability and durability of the subsequent coating, and further improves the durability of the superheater tube bank.

[0036] In a preferred embodiment of this application, the power of laser cladding in step S2 is 900~1100 W, the scanning speed is 8~12 mm / s, the spot diameter is 2~3 mm, the powder feeding rate is 10~15 g / min, and the thickness of the FeCrMo transition layer is 0.2~0.3 mm.

[0037] In this embodiment, specific power, scanning speed, spot diameter, and powder feeding rate are used during laser cladding to precisely control the formation quality of the FeCrMo transition layer. The resulting transition layer thickness is 0.2~0.3 mm, which effectively blocks the direct erosion of the tube body by corrosive elements in the high-temperature flue gas without affecting the heat conduction performance of the tube body due to excessive transition layer thickness. This optimized laser cladding parameter and transition layer thickness can significantly improve the corrosion resistance and overall performance stability of the superheater tube bank.

[0038] Furthermore, in step S2, FeCrMo transition layer is formed using FeCrMo alloy powder, the elemental composition of which is: 15-20% chromium, 2-4% molybdenum, 1-2% aluminum, ≤0.05% boron, ≤0.5% silicon, 0.01-0.05% yttrium oxide, ≤0.1% carbon, with the balance being iron, and the powder particle size is 45-105 μm.

[0039] In this embodiment, the specific elemental composition and particle size range of the FeCrMo alloy powder ensure that the transition layer possesses excellent corrosion resistance, high-temperature strength, and oxidation resistance. The appropriate proportions of elements such as chromium and molybdenum effectively improve the corrosion resistance and high-temperature oxidation resistance of the transition layer; the addition of elements such as aluminum and boron helps improve the high-temperature performance and toughness of the transition layer. A particle size range of 45–105 μm ensures both good cladding effect and the uniformity and density of the transition layer, thereby further enhancing the durability of the superheater tube bank.

[0040] In a preferred embodiment of this application, during plasma spraying in step S3, the spraying power is 20-30 kW, the spraying distance is 70-90 mm, the argon flow rate is 40-42 L / min, the hydrogen flow rate is 3-3.5 L / min, and the thickness of the formed Ti3SiC2 / CoCrAlY gradient coating is 1.0-1.2 mm.

[0041] In this embodiment, specific spraying power, spraying distance, argon flow rate, and hydrogen flow rate are used during plasma spraying to ensure the formation quality of the Ti3SiC2 / CoCrAlY gradient coating. The resulting gradient coating thickness is 1.0~1.2 mm. This thickness provides good corrosion protection in high-temperature environments, while the gradient structure effectively alleviates thermal stress concentration, improves the coating's resistance to thermal fatigue, and further enhances the durability of the superheater tube bank in high-temperature flue gas environments.

[0042] Further, in step S3, during plasma spraying, one nozzle sprays Ti3SiC2 ceramic powder at a feed rate of 20-25 g / min and a spraying current of 600-650 A, while the other nozzle sprays CoCrAlY alloy powder at a feed rate of 25-30 g / min and a spraying current of 550-600 A. The Ti3SiC2 ceramic powder has the following elemental composition: titanium 55-58%, silicon 12-14%, carbon 28-30%, yttrium oxide 0.1-0.3%, iron ≤0.5%, oxygen ≤0.8%, nitrogen ≤0.1%, and a particle size of 15-45 μm. The CoCrAlY alloy powder has the following elemental composition: chromium 20-22%, aluminum 8-10%, yttrium oxide 0.3-0.5%, carbon ≤0.05%, silicon ≤0.2%, iron ≤0.5%, with the balance being cobalt, and a particle size of 20-53 μm. μm.

[0043] In this embodiment, Ti3SiC2 ceramic powder and CoCrAlY alloy powder are sprayed separately using dual nozzles. Different powder feed rates and spraying currents allow for precise control of the spraying amount and coating composition distribution of the two powders. Ti3SiC2 ceramic powder exhibits excellent corrosion resistance and high-temperature stability, while CoCrAlY alloy powder possesses superior oxidation resistance and high-temperature strength. This dual-nozzle spraying method creates a gradient-structured coating on the superheater tube bank surface, allowing the coating to exhibit different performance advantages at different depths. This better adapts to the high-temperature flue gas environment and improves the durability of the superheater tube bank.

[0044] Furthermore, in step S3, the plasma spraying is performed multiple times, and as the number of times it is performed increases, the amount of Ti3SiC2 ceramic powder sprayed from one nozzle gradually decreases, while the amount of CoCrAlY alloy powder sprayed from the other nozzle gradually increases.

[0045] In this embodiment, plasma spraying is performed multiple times with gradually changing powder composition, resulting in a more uniform and stable gradient coating. As the number of spraying cycles increases, the amount of Ti3SiC2 ceramic powder gradually decreases while the amount of CoCrAlY alloy powder gradually increases. This gradient change allows the coating to have different compositions and properties at different depths, thus better adapting to temperature variations and corrosive elements in high-temperature flue gas environments. The gradient coating effectively alleviates thermal stress concentration problems and improves the coating's resistance to thermal fatigue and overall durability.

[0046] Furthermore, in step S3, the plasma spraying is performed in four stages, with a spraying thickness of 0.25~0.3 mm in each stage;

[0047] Based on the total weight of powder sprayed during each spraying operation as 100%, for the first operation: the Ti3SiC2 ceramic powder accounts for 100%, and the CoCrAlY alloy powder accounts for 0%.

[0048] Second execution: The Ti3SiC2 ceramic powder accounts for 70%, and the CoCrAlY alloy powder accounts for 30%.

[0049] Third execution: The Ti3SiC2 ceramic powder accounts for 30%, and the CoCrAlY alloy powder accounts for 70%.

[0050] Fourth execution: The proportion of Ti3SiC2 ceramic powder is 0%, and the proportion of CoCrAlY alloy powder is 100%.

[0051] In this embodiment, plasma spraying is performed in four stages, with clearly defined powder composition ratios and thicknesses for each spray, allowing for more precise control of the gradient coating formation process. This step-by-step spraying method ensures coating uniformity and accurate gradient changes, avoiding abrupt changes in coating composition and localized defects. The gradient coating formed in this way exhibits better corrosion resistance, thermal fatigue resistance, and overall stability, thereby significantly improving the durability of the superheater tube bank.

[0052] In a preferred embodiment of this application, the heat treatment in step S4 is performed in a vacuum furnace, with the temperature increased to 1000-1150°C at a heating rate of 5-10°C / min, held for 2-5 hours, and then cooled with the furnace.

[0053] In this embodiment, a vacuum furnace is used for heat treatment, with specific heating rates, holding temperatures, and holding times. This effectively eliminates stress generated in the coating and tube body during processing, improving the bonding strength between the coating and the tube body. Simultaneously, vacuum heat treatment prevents oxidation of the coating at high temperatures, ensuring the chemical composition and performance stability of the coating. Through this optimized heat treatment process, the overall performance of the superheater tube bank is further improved, and its durability is significantly enhanced.

[0054] The superheater tube bank manufactured using the aforementioned method for improving superheater tube bank durability in this embodiment exhibits significantly enhanced durability. This type of superheater tube bank can operate stably for extended periods in high-temperature flue gas environments, effectively resisting corrosive elements, reducing damage and maintenance costs caused by corrosion, extending service life, and improving the operating efficiency and reliability of the boiler system. This is of great significance for improving energy efficiency and reducing environmental pollution.

[0055] The following is a more specific example.

[0056] A method for improving the durability of superheater tube banks includes the following steps:

[0057] (1) The superheater tube body was brushed with acetone and dried. After drying, it was sandblasted with 80~120 mesh sand at a pressure of 0.5 MPa. After sandblasting, the surface roughness Ra of the superheater tube body was 3.6 μm.

[0058] (2) FeCrMo alloy powder, with the following elemental composition: 17.6% chromium, 2.5% molybdenum, 1.1% aluminum, ≤0.05% boron, ≤0.5% silicon, 0.01% yttrium oxide, ≤0.1% carbon, and the balance being iron, with a powder particle size of 60 μm. The laser cladding power was 1000W, the scanning speed was 10 mm / s, the spot diameter was 2.5 mm, the powder feeding rate was 10 g / min, and the thickness of the FeCrMo transition layer formed was 0.22 mm.

[0059] (3) The elemental composition of Ti3SiC2 ceramic powder is: titanium 55.6%, silicon 12.1%, carbon 28.2%, yttrium oxide 0.16%, iron ≤0.5%, oxygen ≤0.8%, nitrogen ≤0.1%, powder particle size 30 μm, powder feeding rate 20 g / min, spraying current 650 A; the elemental composition of CoCrAlY alloy powder is: chromium 21.6%, aluminum 8.4%, yttrium oxide 0.33%, carbon ≤0.05%, silicon ≤0.2%, iron ≤0.5%, balance cobalt, powder particle size 45 μm, powder feeding rate 25 g / min, spraying current 600 A. Plasma spraying is performed in 4 stages, with a spraying thickness of 0.3 mm in each stage. During plasma spraying, the spraying power was 30 kW, the spraying distance was 90 mm, the argon flow rate was 42 L / min, the hydrogen flow rate was 3.5 L / min, and the thickness of the resulting Ti3SiC2 / CoCrAlY gradient coating was 1.2 mm.

[0060] (4) Heat treatment was performed in a vacuum furnace, with a heating rate of 10 °C / min to 1150 °C, held for 2 h, and then cooled with the furnace.

[0061] The superheater tube bank prepared by the aforementioned method was compared with the superheater tube bank without any treatment. The test results are shown in Table 1 below.

[0062] Table 1 Test Results

[0063] Performance indicators Untreated superheater tube bank Treated superheater tube bank Increase percentage (%) Corrosion resistance Slight corrosion, short lifespan Excellent, corrosion rate reduced - Corrosion rate (mm / year) 0.5 0.1 80 thermal fatigue resistance Cracks are prone to occur Cracks significantly reduced - Thermal fatigue life (number of cycles) 1000 5000 400 Antioxidant properties Severe surface oxidation The oxidation rate was significantly reduced. - Oxide layer thickness (mm) 0.2 0.05 75 Coating adhesion (MPa) No coating, low adhesion ≥50 - Thermal conductivity (W / m·K) 50 45 -10 High temperature creep resistance Easily deformed The amount of deformation is significantly reduced. - Creep strain (%) 5 1 80

[0064] The data in the table shows that the treated superheater tube bank is significantly better than the untreated tube bank in terms of corrosion resistance, thermal fatigue resistance, oxidation resistance, and high-temperature creep resistance, which can effectively extend its service life and improve operational reliability.

Claims

1. A method for improving the durability of superheater tube banks, characterized in that, Includes the following steps: Step S1: Perform surface treatment on the superheater tube body; Step S2: A FeCrMo transition layer is formed on the surface of the superheater tube body after the surface treatment in step S1 by laser cladding. Step S3: A Ti3SiC2 / CoCrAlY gradient coating is formed on the surface of the superheater body after the laser cladding treatment in step S2 using a dual-nozzle plasma spraying method. Step S4: The superheater body that has undergone plasma spraying in step S3 is subjected to heat treatment to eliminate stress and obtain a superheater tube bank with improved durability.

2. The method for improving the durability of superheater tube banks according to claim 1, characterized in that, In step S1, the surface treatment involves first brushing with hot water at 50-70°C or acetone, followed by drying, and then sandblasting with 80-120 mesh abrasive particles at a pressure of 0.4-0.6 MPa. After sandblasting, the surface roughness Ra of the superheater tube body is 3.2-4.0 μm.

3. The method for improving the durability of superheater tube banks according to claim 1, characterized in that, In step S2, the power of laser cladding is 900~1100 W, the scanning speed is 8~12 mm / s, the spot diameter is 2~3 mm, the powder feeding rate is 10~15 g / min, and the thickness of the FeCrMo transition layer is 0.2~0.3 mm.

4. The method for improving the durability of superheater tube banks according to claim 1 or 3, characterized in that, In step S2, the FeCrMo transition layer is formed using FeCrMo alloy powder, which has the following elemental composition: 15-20% chromium, 2-4% molybdenum, 1-2% aluminum, ≤0.05% boron, ≤0.5% silicon, 0.01-0.05% yttrium oxide, ≤0.1% carbon, with the balance being iron, and the powder particle size is 45-105 μm.

5. The method for improving the durability of superheater tube banks according to claim 1, characterized in that, In step S3, the plasma spraying power is 20-30 kW, the spraying distance is 70-90 mm, the argon flow rate is 40-42 L / min, the hydrogen flow rate is 3-3.5 L / min, and the thickness of the Ti3SiC2 / CoCrAlY gradient coating is 1.0-1.2 mm.

6. The method for improving the durability of superheater tube banks according to claim 1 or 5, characterized in that, In step S3, during plasma spraying, one nozzle sprays Ti3SiC2 ceramic powder at a feed rate of 20-25 g / min and a spraying current of 600-650 A, while the other nozzle sprays CoCrAlY alloy powder at a feed rate of 25-30 g / min and a spraying current of 550-600 A. The Ti3SiC2 ceramic powder has the following elemental composition: titanium 55-58%, silicon 12-14%, carbon 28-30%, yttrium oxide 0.1-0.3%, iron ≤0.5%, oxygen ≤0.8%, nitrogen ≤0.1%, and a particle size of 15-45 μm. The CoCrAlY alloy powder has the following elemental composition: chromium 20-22%, aluminum 8-10%, yttrium oxide 0.3-0.5%, carbon ≤0.05%, silicon ≤0.2%, iron ≤0.5%, with the balance being cobalt, and a particle size of 20-53 μm.

7. The method for improving the durability of superheater tube banks according to claim 6, characterized in that, In step S3, plasma spraying is performed multiple times, and as the number of times it is performed increases, the amount of Ti3SiC2 ceramic powder sprayed from one nozzle gradually decreases, while the amount of CoCrAlY alloy powder sprayed from the other nozzle gradually increases.

8. The method for improving the durability of superheater tube banks according to claim 7, characterized in that, In step S3, the plasma spraying is performed in four stages, with a spraying thickness of 0.25~0.3 mm for each stage. Based on the total weight of powder sprayed during each spraying operation as 100%, for the first operation: the Ti3SiC2 ceramic powder accounts for 100%, and the CoCrAlY alloy powder accounts for 0%. Second execution: The Ti3SiC2 ceramic powder accounts for 70%, and the CoCrAlY alloy powder accounts for 30%. Third execution: The Ti3SiC2 ceramic powder accounts for 30%, and the CoCrAlY alloy powder accounts for 70%. Fourth execution: The proportion of Ti3SiC2 ceramic powder is 0%, and the proportion of CoCrAlY alloy powder is 100%.

9. The method for improving the durability of superheater tube banks according to claim 1, characterized in that, In step S4, the heat treatment is performed in a vacuum furnace, with the temperature increased to 1000-1150°C at a heating rate of 5-10°C / min, held for 2-5 hours, and then cooled in the furnace.

10. A superheater tube bank, characterized in that, It is prepared by the method for improving the durability of superheater tube bank as described in any one of claims 1 to 9.

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