Preparation method of composite pipe for water-cooled wall resistant to high-temperature molten salt corrosion and composite pipe thereof

Abstract

The preparation method comprises the following steps that S1, a base pipe is polished, oxide skin on the surface of the base pipe is removed, the surface of the base pipe is cleaned with absolute ethyl alcohol to remove stains, and the base pipe is dried with cold air; and S2, circulating cooling water is conveyed into the base tube, and meanwhile, under the action of a heat source laser beam, Ni-based alloy powder is cladded to the surface of the base tube. According to the composite pipe prepared through the method, the high-temperature molten salt corrosion resistance is effectively improved and is about 5 times that of a base pipe, the service life of a furnace pipe is prolonged, the operation rate of a generator set is increased, and the power generation cost of a waste incineration power plant is greatly reduced.

Description

Technical Field

[0001] The invention relates to the technical field of composite pipe preparation, in particular to a method for preparing a composite pipe for a water-cooled wall resistant to high-temperature molten salt corrosion and the composite pipe. Background Art

[0002] Waste incineration power generation is of great significance to improving the environment, saving resources and achieving sustainable urban development. It will become the main method of waste treatment in the future. At present, my country's waste incineration power generation is mainly based on mechanical grate incineration and circulating fluidized bed incineration. There is still a big difference between the combustion of garbage and coal. Due to the relatively high content of ash and alkaline elements in garbage, its ash accumulation is relatively serious, and the corrosion problem must be taken seriously.

[0003] The water-cooled walls of boiler tubes in waste incineration power plants are corroded by high-temperature molten salt for a long time. The surface of 20G tubes in waste incineration power plants is in a state of high-temperature corrosion for a long time. The poor corrosion resistance leads to frequent shutdowns, and the consumption of water-cooled wall tubes is large, which increases the cost of power generation. Summary of the invention

[0004] The purpose of the present invention is to overcome the problem that the existing boiler tube water-cooled wall is corroded by high-temperature molten salt for a long time, resulting in large consumption of water-cooled wall pipes and increased power generation costs, and to provide a method for preparing a composite pipe for a water-cooled wall resistant to high-temperature molten salt corrosion and the composite pipe.

[0005] A method for preparing a composite pipe for a water-cooled wall resistant to high temperature molten salt corrosion comprises the following steps:

[0006] S1: Grind the substrate to remove the oxide scale on the surface, clean the substrate surface with anhydrous ethanol to remove stains, and dry it with cold air;

[0007] S2: circulating cooling water is transported into the interior of the substrate tube, and at the same time, Ni-based alloy powder is clad onto the surface of the substrate tube under the action of the heat source laser beam.

[0008] Furthermore, the Ni-based alloy composition is Ni: 65-72wt.%, Cr: 20-25wt.%, Mo: 8-10wt.%, Nb: 3-4wt.%, Fe: 0.5-0.6wt.%, Si: 0.2-0.4wt.%, Co: 0.5wt.%, and Mn: 0.3wt.%.

[0009] Furthermore, the Ni-based alloy powder in step S2 has a size of 50 to 150 μm.

[0010] Furthermore, before laser cladding in step S2, the powder is dried in a vacuum drying oven at 110° C. for 3 to 4 hours.

[0011] Furthermore, the base pipe is a carbon steel pipe with a carbon content of 0.1wt.% to 0.2wt.% and a pipe wall thickness of more than 0.4mm.

[0012] Furthermore, the powder feeding method of laser cladding is pneumatic coaxial powder feeding, using Ar2 as the shielding gas and carrier gas. The powder is gathered under the action of the Ar2 flow and coupled with the light spot.

[0013] Furthermore, the laser cladding process parameters are: laser output power 4-5 kW, laser spot size 5.0 mm, laser scanning speed 4-8 mm / s, powder feeding rate 15-20 g / min, protective gas flow rate 15-20 L / min; the laser defocus is set to 2-3 mm.

[0014] Furthermore, the content of Fe element on the surface of the cladding layer does not exceed 5wt.%.

[0015] A composite pipe for water-cooled wall resistant to high-temperature molten salt corrosion is obtained by any one of the above preparation methods.

[0016] The beneficial effects of the present invention are as follows: on the basis of the advanced preparation technology and process of laser cladding, the composition of the Ni-based alloy of the cladding material is not changed as much as possible through the optimization of the laser process and the cooling process, so as to maximize the performance of the Ni-based alloy. The laser process reduces the heat input to the base tube by positive and negative defocusing, thereby reducing the dilution rate; the cold process increases the supercooling of the laser molten pool by circulating cooling water through the tube wall, thereby reducing the melting of the base tube to reduce the dilution effect of the Fe element of the substrate on the cladding material, and improving the corrosion resistance of the base tube. The composite tube prepared by this method effectively improves the corrosion resistance of high-temperature molten salts, which is about 5 times that of the base tube, increases the service life of the furnace tube and the operating rate of the generator set, and greatly reduces the power generation cost of the waste incineration power plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of coaxial powder feeding for laser cladding;

[0018] Figure 2 (a) is a composite tube prepared by laser cladding Ni-based alloy;

[0019] (b) is the morphology of the substrate tube in a molten salt corrosion environment at 540°C for 18 months;

[0020] (c) is the morphology of the composite pipe in a molten salt corrosion environment at 540°C for 18 months;

[0021] Figure 3 It is the thinning amount of the base pipe and composite pipe after serving for 18 months in a 540℃ molten salt corrosion environment. DETAILED DESCRIPTION

[0022] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0023] Example 1

[0024] A method for preparing a composite pipe for a water-cooled wall resistant to high temperature molten salt corrosion comprises the following steps:

[0025] S1: Grind the base tube to remove the oxide scale on the surface, clean the surface of the base tube with anhydrous ethanol to remove stains, and dry it with cold air; specifically, the base tube is a carbon steel tube with a carbon content of 0.1wt.% to 0.2wt.%, and a tube wall thickness of more than 0.4mm.

[0026] S2: circulating cooling water is transported into the substrate tube to increase the supercooling degree of the laser molten pool, refine the grains, reduce the dilution rate, and at the same time, under the action of the heat source laser beam, the Ni-based alloy powder is clad on the surface of the substrate tube. Specifically, under the action of the heat source laser beam, the Ni-based alloy powder is completely melted, the substrate is slightly melted, and the powder and the substrate are combined into one after being melted.

[0027] The Ni-based alloy comprises 65 wt.% Ni, 20.5 wt.% Cr, 10 wt.% Mo, 3 wt.% Nb, 0.5 wt.% Fe, 0.2 wt.% Si, 0.5 wt.% Co and 0.3 wt.% Mn.

[0028] The Ni-based alloy powder in step S2 is sieved through a 130-260 mesh sieve, and the powder is spherical in shape with a controlled size of 50-150 μm.

[0029] In order to prevent water vapor from being vaporized by heat and generating pores in the cladding layer, the powder is dried in a vacuum drying oven at 110° C. for 3 h before laser cladding in step S2.

[0030] like Figure 1 As shown in the figure, in the actual laser cladding process, the powder feeding method of laser cladding is pneumatic coaxial powder feeding, Ar2 is used as the protective gas and carrier gas, and the powder is gathered under the action of the Ar2 flow and coupled with the light spot. The laser scanning path is a linear reciprocating type, and its scanning motion mode is realized by a CNC programming machine tool. The overlap rate of laser scanning is 55%.

[0031] The laser cladding process parameters are: laser output power 4 kW, laser spot size 5.0 mm, laser scanning speed 4 mm / s, powder feeding rate 15 g / min, and protective gas flow rate 15 L / min; at the same time, in order to reduce the effect of the dilution rate, the laser defocus is controlled to be set to 2 mm.

[0032] Control the Fe content on the surface of the cladding layer to not exceed 5wt.%,

[0033] Example 2

[0034] A method for preparing a composite pipe for a water-cooled wall resistant to high temperature molten salt corrosion, comprising the following steps:

[0035] S1: Grind the base tube to remove the oxide scale on the surface, clean the surface of the base tube with anhydrous ethanol to remove stains, and dry it with cold air; specifically, the base tube is a carbon steel tube with a carbon content of 0.1wt.% to 0.2wt.%, and a tube wall thickness of more than 0.4mm.

[0036] S2: circulating cooling water is transported into the substrate tube to increase the supercooling degree of the laser molten pool, refine the grains, reduce the dilution rate, and at the same time, under the action of the heat source laser beam, the Ni-based alloy powder is clad on the surface of the substrate tube. Specifically, under the action of the heat source laser beam, the Ni-based alloy powder is completely melted, the substrate is slightly melted, and the powder and the substrate are combined into one after being melted.

[0037] The Ni-based alloy comprises 66 wt.% Ni, 20 wt.% Cr, 9 wt.% Mo, 3.2 wt.% Nb, 0.6 wt.% Fe, 0.4 wt.% Si, 0.5 wt.% Co and 0.3 wt.% Mn.

[0038] The Ni-based alloy powder in step S2 is sieved through a 130-260 mesh sieve, and the powder is spherical in shape with a controlled size of 50-150 μm.

[0039] In order to prevent water vapor from being vaporized by heat and generating pores in the cladding layer, the powder is dried in a vacuum drying oven at 110° C. for 3 to 4 hours before laser cladding in step S2.

[0040] like Figure 1 As shown in the figure, in the actual laser cladding process, the powder feeding method of laser cladding is pneumatic coaxial powder feeding, Ar2 is used as the protective gas and carrier gas, and the powder is gathered under the action of the Ar2 flow and coupled with the light spot. The laser scanning path is a linear reciprocating type, and its scanning motion mode is realized by a CNC programming machine tool. The overlap rate of laser scanning is 55%.

[0041] The laser cladding process parameters are: laser output power of 5 kW, laser spot size of 5.0 mm, laser scanning speed of 6 mm / s, powder feeding rate of 20 g / min, and protective gas flow rate of 16 L / min; at the same time, in order to reduce the effect of the dilution rate, the laser defocus is controlled to be set to 2 mm.

[0042] Control the Fe content on the surface of the cladding layer to not exceed 5wt.%,

[0043] Example 3

[0044] A method for preparing a composite pipe for a water-cooled wall resistant to high temperature molten salt corrosion, comprising the following steps:

[0045] S1: Grind the base tube to remove the oxide scale on the surface, clean the surface of the base tube with anhydrous ethanol to remove stains, and dry it with cold air; specifically, the base tube is a carbon steel tube with a carbon content of 0.1wt.% to 0.2wt.%, and a tube wall thickness of more than 0.4mm.

[0046] S2: circulating cooling water is transported into the substrate tube to increase the supercooling degree of the laser molten pool, refine the grains, reduce the dilution rate, and at the same time, under the action of the heat source laser beam, the Ni-based alloy powder is clad on the surface of the substrate tube. Specifically, under the action of the heat source laser beam, the Ni-based alloy powder is completely melted, the substrate is slightly melted, and the powder and the substrate are combined into one after being melted.

[0047] The Ni-based alloy comprises 64 wt.% Ni, 22.5 wt.% Cr, 9 wt.% Mo, 3 wt.% Nb, 0.5 wt.% Fe, 0.2 wt.% Si, 0.5 wt.% Co and 0.3 wt.% Mn.

[0048] The Ni-based alloy powder in step S2 is sieved through a 130-260 mesh sieve, and the powder is spherical in shape with a controlled size of 50-150 μm.

[0049] In order to prevent water vapor from being vaporized by heat and generating pores in the cladding layer, the powder is dried in a vacuum drying oven at 110° C. for 4 h before laser cladding in step S2.

[0050] like Figure 1 As shown in the figure, in the actual laser cladding process, the powder feeding method of laser cladding is pneumatic coaxial powder feeding, Ar2 is used as the protective gas and carrier gas, and the powder is gathered under the action of the Ar2 flow and coupled with the light spot. The laser scanning path is a linear reciprocating type, and its scanning motion mode is realized by a CNC programming machine tool. The overlap rate of laser scanning is 55%.

[0051] The laser cladding process parameters are: laser output power 5 kW, laser spot size 5.0 mm, laser scanning speed 8 mm / s, powder feeding rate 20 g / min, and protective gas flow rate 20 L / min; at the same time, in order to reduce the effect of the dilution rate, the laser defocus is controlled to be set to 3 mm.

[0052] Control the Fe content on the surface of the cladding layer to not exceed 5wt.%,

[0053] The following experiment was conducted using the composite tube obtained in Example 1 and a conventional 20G tube.

[0054] Experiment 1

[0055] The base tube water-cooled wall and the composite tube water-cooled wall layer were subjected to service tests at 540°C. Figure 2 (a) is a composite tube prepared by laser cladding Ni-based alloy. Figure 2 (b) is the morphology of the substrate tube in a molten salt corrosion environment at 540℃ for 18 months. Figure 2 (c) is the morphology of the composite pipe in a molten salt corrosion environment at 540°C for 18 months.

[0056] Conclusion: By comparison Figure 2 (b) Figure 2 (c) The laser cladding overlap marks of the composite tube prepared by laser cladding technology are cleaned and can be seen, and it is almost not corroded, while the base tube without laser cladding of Ni alloy is seriously corroded. The morphology images in Examples 2 and 3 are the same as those in Example 1.

[0057] Experiment 2

[0058] The base tube water-cooled wall and composite tube water-cooled wall layer were subjected to service tests at 540°C. Figure 3 The thickness reduction of the base tube and the composite tube after 18 months of service in a molten salt corrosion environment at 540°C is 0.033 mm for the composite tube and 0.155 mm for the base tube. The high temperature molten salt corrosion resistance of the composite tube is about 5 times that of the base tube. The service tests in Examples 2 and 3 are the same as those in Example 1.

[0059] Therefore, the technical solution of the present invention can effectively improve the high-temperature molten salt corrosion resistance of the boiler tube and greatly extend the service life of the composite layer.

[0060] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for preparing a composite pipe for a water-cooled wall resistant to high temperature molten salt corrosion, characterized in that: The steps include: S1: Grind the substrate to remove the oxide scale on the surface, clean the substrate surface with anhydrous ethanol to remove stains, and dry it with cold air; S2: circulating cooling water is transported into the interior of the substrate tube, and at the same time, Ni-based alloy powder is clad onto the surface of the substrate tube under the action of the heat source laser beam.

2. The method for preparing a composite pipe for a water-cooled wall resistant to high temperature molten salt corrosion according to claim 1, characterized in that: The Ni-based alloy comprises 65-72 wt. % Ni, 20-25 wt. % Cr, 8-10 wt. % Mo, 3-4 wt. % Nb, 0.5-0.6 wt. % Fe, 0.2-0.4 wt. % Si, 0.5 wt. % Co and 0.3 wt. % Mn.

3. The method for preparing a composite pipe for a water-cooled wall resistant to high temperature molten salt corrosion according to claim 1 or 2, characterized in that: The size of the Ni-based alloy powder in step S2 is 50-150 μm.

4. The method for preparing a composite pipe for a water-cooled wall resistant to high temperature molten salt corrosion according to claim 3, characterized in that: In step S2, the powder is dried in a vacuum drying oven at 110° C. for 3 to 4 hours before laser cladding.

5. The method for preparing a composite pipe for a water-cooled wall resistant to high temperature molten salt corrosion according to claim 1, characterized in that: The base pipe is a carbon steel pipe with a carbon content of 0.1wt.% to 0.2wt.% and a pipe wall thickness of more than 0.4mm.

6. The method for preparing a composite pipe for a water-cooled wall resistant to high temperature molten salt corrosion according to claim 1, characterized in that: The powder feeding method of laser cladding is pneumatic coaxial powder feeding, using Ar2 as the shielding gas and carrier gas. The powder is gathered under the action of the Ar2 flow and coupled with the light spot.

7. The method for preparing a composite pipe for a water-cooled wall resistant to high temperature molten salt corrosion according to claim 6, characterized in that: The laser cladding process parameters are: laser output power of 4-5 kW, laser spot size of 5.0 mm, laser scanning speed of 4-8 mm / s, powder feeding rate of 15-20 g / min, protective gas flow rate of 15-20 L / min; the laser defocus is set to 2-3 mm.

8. The method for preparing a composite pipe for a water-cooled wall resistant to high temperature molten salt corrosion according to claim 1, characterized in that: The content of Fe element on the surface of the cladding layer does not exceed 5wt.%.

9. A composite pipe for water-cooled wall resistant to high temperature molten salt corrosion, characterized in that: The method is obtained by any one of claims 1 to 8.

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