Method and device for improving steam oxidation resistance of 650 DEG C boiler header

Abstract

The invention discloses a method and device for improving the steam oxidation resistance of a 650 DEG C boiler header, and the method comprises the following steps: taking the sealed boiler header and a pipe connecting seat arranged on the header as a part of a gas path, and providing a medium-temperature zone environment under the condition of pure water vapor, a continuous and compact Cr2O3 film is generated in situ on the inner surface of the header and the inner surface of the pipe connecting seat by adopting a pre-oxidation method. And the header is made of a gamma '-phase reinforced Fe-Ni-Cr-based high-temperature alloy. The device comprises a water vapor generating device and a degassing device which are respectively in sealed connection with a first pipe connecting seat on a collecting box through pipelines, and a condensate water recycling device which is in sealed connection with a second pipe connecting seat on the collecting box through a pipeline, control valves are arranged on the pipelines, and other pipe connecting seats except the first pipe connecting seat and the second pipe connecting seat on the header are sealed; and heating devices are arranged on the peripheries of the collecting box and the pipe connecting seat. The steam oxidation resistance of the boiler header can be improved by combining actual production or service conditions.

Description

Technical Field

[0001] The invention relates to the technical field of boiler header metal corrosion protection, and in particular to a method and a device for improving the steam oxidation resistance of a 650°C-class boiler header. Background Art

[0002] The new generation of 650℃-class boiler headers currently under design and development will use Fe-Ni-Cr-based high-temperature alloys with excellent high-temperature strength, fatigue performance and significant cost-effectiveness. Due to the high Fe content in this type of γ′ phase precipitation-strengthened high-temperature alloy, the Cr content is usually limited to a low level (not higher than 20wt.%) to avoid the precipitation of Cr-rich harmful phases and weakening the mechanical properties of the alloy. However, when the Cr content is low, the Fe-Ni-Cr-based alloy is very likely to form Fe-rich oxides during service in a mixed atmosphere containing water vapor, and its growth rate is relatively fast, shortening the service life of the alloy at high temperatures.

[0003] As we all know, when Fe-Ni-Cr based alloys are used in high temperature environments, they often rely on a slow-growing, dense, and well-integrity Cr2O3 film to provide protection. In order to form a continuous and complete Cr2O3 film on the surface of Fe-Ni-Cr based alloys, surface treatment methods are usually used, including coating, grain refinement (shot peening, mechanical grinding), pre-oxidation, etc.

[0004] However, the coating preparation process is complicated and usually pollutes the environment. During high-temperature service, the coating also diffuses elements with the substrate, thereby damaging the mechanical properties of the alloy substrate. The refined grains can only be maintained for a limited time. Under long-term or high-temperature conditions, the grains grow and lose their effectiveness. In contrast, the pre-oxidation technology is low-cost and simple to operate. It only needs to be carried out in a vacuum heat treatment furnace or an inert gas protection furnace. By reducing the oxygen partial pressure, the critical content of selective oxidation of alloy elements is reduced, promoting the formation of Cr2O3 film. Unfortunately, due to the limitations of vacuum heat treatment equipment technology, it is not realistic to pre-oxidize the boiler header to form a Cr2O3 film in actual production. If pre-oxidation can be carried out in a non-vacuum atmosphere or non-inert gas protection, but combined with actual production or service conditions, it will greatly broaden the scope of application of the pre-oxidation theory and is very meaningful for improving the oxidation resistance of the boiler header. Summary of the invention

[0005] The purpose of the present invention is to address the problems in the above-mentioned prior art and provide a method and device for improving the steam oxidation resistance of a 650°C class boiler header. The method and device can be used to pre-oxidize a 650°C class boiler header under a non-vacuum atmosphere or non-inert gas protection in combination with actual production or service conditions, thereby effectively improving the steam oxidation resistance of the boiler header.

[0006] In order to achieve the above object, the present invention has the following technical solutions:

[0007] A method for improving the steam oxidation resistance of a 650°C class boiler header comprises the following steps:

[0008] The sealed boiler header and the pipe socket arranged on the header are used as part of the gas path. Under the condition of pure water vapor, a medium temperature zone environment is provided, and a continuous and dense Cr2O3 film is generated in situ on the inner surface of the header and the pipe socket by a pre-oxidation method.

[0009] Furthermore, the content of dissolved oxygen in the pure water vapor is not higher than 6 ppm.

[0010] Furthermore, the temperature range of the medium temperature zone is higher than 650°C but lower than 750°C.

[0011] Furthermore, the pre-oxidation treatment time is 24h to 48h.

[0012] Preferably, before pre-oxidation, the inner surfaces of the header and the connecting pipe seat are derusted, degreased, cleaned and dried.

[0013] In a preferred embodiment, the step of providing a medium temperature environment under pure water vapor conditions and using a pre-oxidation method to in-situ generate a continuous and dense Cr2O3 film on the inner surface of the header and the pipe socket specifically includes:

[0014] S1. At room temperature, introduce inert gas into the header and the connecting pipe seat to exhaust the air in the header;

[0015] S2. Heat the header and the pipe socket, and stop introducing the inert gas when the temperature reaches the set temperature of the medium temperature zone;

[0016] S3. Pump water vapor of the same temperature into the header and the connecting socket, and keep them warm to complete the pre-oxidation reaction.

[0017] Furthermore, in a preferred embodiment, after the pre-oxidation reaction is completed, the heating is stopped, the collecting tank and the connecting pipe seat are allowed to cool naturally, and the condensed water in the collecting tank and the connecting pipe seat is recovered.

[0018] Furthermore, the material of the header is a γ′ phase strengthened Fe-Ni-Cr based high temperature alloy.

[0019] Furthermore, the Cr content in the γ′ phase strengthened Fe—Ni—Cr based high temperature alloy is not less than 12% but not more than 19%, and the Fe content is not less than 30% but not more than 42%.

[0020] A device for realizing the method of improving the steam oxidation resistance of a 650°C class boiler header, comprising a steam generating device and a degassing device respectively sealed to a first connecting pipe seat on the header through pipelines, and a condensate recovery device sealed to a second connecting pipe seat on the header through pipelines; a steam valve is provided on the pipeline between the steam generating device and the header, a degassing valve is provided on the pipeline between the degassing device and the header, and a condensate recovery valve is provided on the pipeline between the condensate recovery device and the header; the connecting pipe seats on the header except the first connecting pipe seat and the second connecting pipe seat are all sealed; and a heating device is provided on the periphery of the header and the connecting pipe seats.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects:

[0022] The present invention provides a method for improving the steam oxidation resistance of a 650°C boiler header. By using a sealed boiler header and a pipe connection seat arranged on the header as part of the gas path, pre-oxidation is performed under pure water vapor conditions and a medium temperature zone environment, so that a continuous and dense Cr2O3 film can be generated in situ on the inner surface of the header and the pipe connection seat. The pre-generated Cr2O3 film is stable for a long time in the subsequent higher pure water vapor, and can effectively prevent the header from further oxidation, thereby reducing the oxidation rate of the header and improving the steam oxidation resistance of the header. The present invention solves the problem in the prior art that the pre-oxidation treatment is not suitable for improving the steam oxidation resistance of the header under non-vacuum or non-inert gas protection. At the same time, it also overcomes the disadvantage that a continuous Cr2O3 film cannot be formed by pre-oxidation of the 650°C boiler header alloy material under the same atmosphere conditions in the low temperature zone.

[0023] Furthermore, the method of improving the steam oxidation resistance of the 650°C boiler header of the present invention is carried out under pure water vapor conditions and medium temperature zone environment. The temperature range of the medium temperature zone is higher than 650°C but lower than 750°C. The mechanism of pre-oxidation is usually to utilize the activity of elements so that the alloy preferentially oxidizes the elements with higher activity under low oxygen partial pressure environment. However, the usual pre-oxidation forms a Cr2O3 film or Al2O3 film under vacuum or inert environment. The applicant has found through research that for the γ′ phase strengthened Fe-Ni-Cr based high temperature alloy used in the 650°C boiler header, the oxidation rate in water vapor and the temperature have an "inverted bell-shaped" relationship characteristic. The 650°C boiler header is placed under pure water vapor conditions and medium temperature zone environment for pre-oxidation. The requirements for the heating device are extremely low, and it is particularly suitable for the pre-oxidation of large-sized components such as boiler headers. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 A schematic diagram of a device for realizing the method for improving the steam oxidation resistance of a 650°C class boiler header according to an embodiment of the present invention;

[0026] Figure 2 This is a cross-sectional morphology diagram of Example 1 of the present invention after pre-oxidation treatment in 680° C. steam for 48 hours;

[0027] Figure 3 This is a cross-sectional morphology diagram of Example 2 of the present invention after pre-oxidation treatment in 700° C. steam for 45 hours;

[0028] Figure 4 This is a cross-sectional morphology diagram of Example 3 of the present invention after pre-oxidation treatment in 750° C. steam for 30 hours;

[0029] Figure 5 This is a cross-sectional morphology diagram of Example 4 of the present invention after pre-oxidation treatment in 690° C. steam for 48 hours;

[0030] In the attached drawings: 1-header; 2-heating device; 3-first connecting pipe socket; 4-second connecting pipe socket; 5-steam generating device; 6-degassing device; 7-condensate recovery device; 8-degassing valve; 9-condensate recovery valve; 10-steam valve. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, ordinary technicians in this field can also obtain other embodiments without making creative work.

[0032] The following examples are provided to better explain the present invention, are not limited to the best mode, and are not intended to limit the content and scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the enlightenment of the present invention or by combining the features of the present invention with other prior arts, all falls within the protection scope of the present invention. If no specific experimental steps or conditions are indicated in the examples, the operation or conditions of the conventional experimental steps described in the literature in this field can be carried out. If the manufacturer is not indicated for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0033] The applicant has found through research that the oxidation rate of Fe-Ni-Cr-based alloys in water vapor has an "inverted bell-shaped" relationship with temperature. Based on this, the present application proposes a method for improving the steam oxidation resistance of a 650°C class boiler header, comprising the following steps:

[0034] The sealed boiler header and the pipe socket arranged on the header are used as part of the gas path. Under the condition of pure water vapor, a medium temperature zone environment is provided, and a continuous and dense Cr2O3 film is generated in situ on the inner surface of the header and the pipe socket by a pre-oxidation method.

[0035] The content of dissolved oxygen in the pure water vapor is not higher than 6 ppm.

[0036] The temperature range of the medium temperature zone is higher than 650°C but lower than 750°C.

[0037] The pre-oxidation treatment time is 24h to 48h.

[0038] In a possible implementation manner, before pre-oxidation, the inner surfaces of the header and the connecting pipe socket are derusted, degreased, cleaned and dried.

[0039] In a possible implementation, the step of providing a medium temperature environment under pure water vapor conditions and using a pre-oxidation method to in-situ generate a continuous and dense Cr2O3 film on the inner surface of the header and the pipe socket specifically includes:

[0040] S1. At room temperature, introduce inert gas into the header and the connecting pipe seat to exhaust the air in the header;

[0041] S2. Heat the header and the pipe socket, and stop introducing the inert gas when the temperature reaches the set temperature of the medium temperature zone;

[0042] S3. Pump water vapor of the same temperature into the header and the connecting socket, and keep them warm to complete the pre-oxidation reaction.

[0043] In a possible implementation manner, after the pre-oxidation reaction is completed in step S3, heating is stopped to allow the header and the pipe socket to cool naturally, and condensed water in the header and the pipe socket is recovered.

[0044] Furthermore, the material of the header is a γ′ phase strengthened Fe-Ni-Cr based high temperature alloy, in which the Cr content is not less than 12% but not more than 19%, and the Fe content is not less than 30% but not more than 42%.

[0045] See also Figure 1The embodiment of the present invention also proposes a device for realizing the method of improving the steam oxidation resistance of a 650°C class boiler header, comprising a steam generating device 5 and a degassing device 6 respectively connected to a first connecting pipe socket 3 on the header 1 through pipelines, and a condensate recovery device 7 connected to a second connecting pipe socket 4 on the header 1 through pipelines.

[0046] A steam valve 10 is provided on the pipeline between the steam generating device 5 and the header 1;

[0047] A degassing valve 8 is provided on the pipeline between the degassing device 6 and the header 1;

[0048] A condensate recovery valve 9 is provided on the pipeline between the condensate recovery device 7 and the header 1 .

[0049] The remaining connecting pipe seats on the header 1 except the first connecting pipe seat 3 and the second connecting pipe seat 4 are all sealed.

[0050] A heating device 2 is provided on the outer periphery of the header 1 and the pipe socket.

[0051] The following is a detailed introduction of the method and device proposed in the present invention by taking four compositions of γ′ phase strengthened Fe-Ni-Cr based high temperature alloy as an example, as the material of 650°C class boiler header. The alloy compositions of the four compositions are shown in Table 1:

[0052] Table 1

[0053] Elements (wt%) Cr Co Mo W Al Ti Fe Si C B Ni Composition 1 19 / / 0.5 1.8 2 30 0.15 0.06 / margin Composition 2 17 2 / 0.3 1.5 2.1 40 0.1 0.04 0.003 margin Composition 3 14 / 0.8 0.2 1.4 2.1 36 0.15 0.04 0.003 margin Composition 4 12 / 0.8 0.2 1.4 2 42 0.3 0.04 0.003 margin

[0054] Example 1

[0055] The method of improving the steam oxidation resistance of a 650°C class boiler header in this embodiment comprises the following steps:

[0056] S1: The first connecting socket 3 on the manifold 1 made of composition 1 is connected to the degassing device 6 and the steam generating device 5 through a pipeline, and the second connecting socket 4 and the condensate recovery device 7 are connected through a pipeline. The other connecting sockets on the manifold 1 are sealed and serve as part of the gas circuit.

[0057] S2: At room temperature, open the degassing valve 8 provided on the connecting pipeline between the degassing device 6 and the first connecting socket 3 and the condensate recovery valve 9 provided on the connecting pipeline between the condensate recovery device 7 and the second connecting socket 4, and introduce high-purity Ar into the manifold 1 to exhaust the air in the manifold 1.

[0058] S3: The header 1 and the connecting pipe seat thereon are heated as a whole by means of the heating device 2 arranged on the periphery of the header 1. When the temperature reaches the set temperature, the degassing valve 8 is closed, and the steam valve 10 arranged on the pipeline connecting the steam generating device 5 and the first connecting pipe seat 3 is opened. Pure steam is introduced into the header 1, and the concentration of dissolved oxygen in the water is 6ppm. The steam is kept at 680°C for 48 hours, so that a continuous and dense Cr2O3 film is generated in situ on the inner surface of the header 1 and the connecting pipe seat.

[0059] S4: Stop heating, close the steam valve 10, open the degassing valve 8, introduce high-purity inert gas, and allow the header 1 to naturally cool to room temperature. The residual water vapor in the header 1 condenses and flows into the condensate recovery device 7.

[0060] Example 2

[0061] The method of improving the steam oxidation resistance of a 650°C class boiler header in this embodiment comprises the following steps:

[0062] S1: The first connecting socket 3 on the manifold 1 made of composition 2 is connected to the degassing device 6 and the water vapor generating device 5 through a pipeline, and the second connecting socket 4 and the condensate recovery device 7 are connected through a pipeline. The other connecting sockets on the manifold 1 are sealed and serve as part of the gas circuit.

[0063] S2: At room temperature, open the degassing valve 8 provided on the connecting pipeline between the degassing device 6 and the first connecting socket 3 and the condensate recovery valve 9 provided on the connecting pipeline between the condensate recovery device 7 and the second connecting socket 4, and introduce high-purity N2 into the manifold 1 to exhaust the air in the manifold 1.

[0064] S3: The header 1 and the connecting pipe seat thereon are heated as a whole by means of the heating device 2 arranged on the periphery of the header 1. When the temperature reaches the set temperature, the degassing valve 8 is closed, and the steam valve 10 arranged on the pipeline connecting the steam generating device 5 and the first connecting pipe seat 3 is opened. Pure steam is introduced into the header 1, and the concentration of dissolved oxygen in the water is 3 ppm. The steam is kept at 700°C for 45 hours, so that a continuous and dense Cr2O3 film is generated in situ on the inner surface of the header 1 and the connecting pipe seat.

[0065] S4: Stop heating, close the steam valve 10, open the degassing valve 8, introduce high-purity inert gas, and allow the header 1 to cool naturally to room temperature. The residual water vapor in the header 1 condenses and flows into the condensed water recovery device 7.

[0066] Example 3

[0067] The method of improving the steam oxidation resistance of a 650°C class boiler header in this embodiment comprises the following steps:

[0068] S1: The first connecting socket 3 on the manifold 1 made of composition 3 is connected to the degassing device 6 and the water vapor generating device 5 through a pipeline, and the second connecting socket 4 and the condensate recovery device 7 are connected through a pipeline. The other connecting sockets on the manifold 1 are sealed and serve as part of the gas circuit.

[0069] S2: At room temperature, open the degassing valve 8 provided on the connecting pipeline between the degassing device 6 and the first connecting socket 3 and the condensate recovery valve 9 provided on the connecting pipeline between the condensate recovery device 7 and the second connecting socket 4, and introduce high-purity Ar into the manifold 1 to exhaust the air in the manifold 1.

[0070] S3: The header 1 and the connecting pipe seat thereon are heated as a whole by means of the heating device 2 arranged on the periphery of the header 1. When the temperature reaches the set temperature, the degassing valve 8 is closed, and the steam valve 10 arranged on the pipeline connecting the steam generating device 5 and the first connecting pipe seat 3 is opened. Pure steam is introduced into the header 1, and the concentration of dissolved oxygen in the water is 300 ppb. The steam is kept at 750°C for 30 hours, so that a continuous and dense Cr2O3 film is generated in situ on the inner surface of the header 1 and the connecting pipe seat.

[0071] S4: Stop heating, close the steam valve 10, open the degassing valve 8, introduce high-purity inert gas, and allow the header 1 to cool naturally to room temperature. The residual water vapor in the header 1 condenses and flows into the condensed water recovery device 7.

[0072] Example 4

[0073] The method of improving the steam oxidation resistance of a 650°C class boiler header in this embodiment comprises the following steps:

[0074] S1: The first connecting socket 3 on the manifold 1 made of the material composition 4 is connected to the degassing device 6 and the water vapor generating device 5 through a pipeline, and the second connecting socket 4 and the condensate recovery device 7 are connected through a pipeline. The other connecting sockets on the manifold 1 are sealed and serve as part of the gas circuit.

[0075] S2: At room temperature, open the degassing valve 8 provided on the connecting pipeline between the degassing device 6 and the first connecting socket 3 and the condensate recovery valve 9 provided on the connecting pipeline between the condensate recovery device 7 and the second connecting socket 4, and introduce high-purity N2 into the manifold 1 to exhaust the air in the manifold 1.

[0076] S3: The header 1 and the connecting pipe seat thereon are heated as a whole by means of the heating device 2 arranged on the periphery of the header 1. When the temperature reaches the set temperature, the degassing valve 8 is closed, and the steam valve 10 arranged on the pipeline connecting the steam generating device 5 and the first connecting pipe seat 3 is opened. Pure steam is introduced into the header 1, and the concentration of dissolved oxygen in the water is 150 ppb. The steam is kept at 690°C for 48 hours, so that a continuous and dense Cr2O3 film is generated in situ on the inner surface of the header 1 and the connecting pipe seat.

[0077] S4: Stop heating, close the steam valve 10, open the degassing valve 8, introduce high-purity inert gas, and allow the header 1 to cool naturally to room temperature. The residual water vapor in the header 1 condenses and flows into the condensed water recovery device 7.

[0078] The usual pre-oxidation is to form a Cr2O3 film or Al2O3 film in a vacuum or inert environment. The applicant has found through research that for the γ′ phase-strengthened Fe-Ni-Cr-based high-temperature alloy used in the 650℃-class boiler header, there is an "inverted bell-shaped" relationship between the oxidation rate and temperature in water vapor. The 650℃-class boiler header is placed in pure water vapor conditions and a medium-temperature environment for pre-oxidation, which has extremely low requirements for the heating device and is particularly suitable for the pre-oxidation of large-sized components such as boiler headers. A continuous and dense Cr2O3 film is formed on the inner surface of the header in advance. The Cr2O3 film is stable for a long time in subsequent higher pure water vapor, which can effectively prevent the header from further oxidation, thereby reducing the oxidation rate of the header and improving the anti-steam oxidation performance of the header.

[0079] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for improving the steam oxidation resistance of a 650°C boiler header, characterized in that: The following steps are involved: The sealed boiler header and the pipe socket arranged on the header are used as part of the gas path. Under the condition of pure water vapor, a medium temperature zone environment is provided, and a continuous and dense Cr2O3 film is generated in situ on the inner surface of the header and the pipe socket by a pre-oxidation method.

2. The method for improving the steam oxidation resistance of a 650°C boiler header according to claim 1, characterized in that: The content of dissolved oxygen in the pure water vapor is not higher than 6 ppm.

3. The method for improving the steam oxidation resistance of a 650°C boiler header according to claim 1, characterized in that: The temperature range of the medium temperature zone is higher than 650°C but lower than 750°C.

4. The method for improving the steam oxidation resistance of a 650°C boiler header according to claim 1, characterized in that: The pre-oxidation treatment time is 24h to 48h.

5. The method for improving the steam oxidation resistance of a 650°C boiler header according to claim 1, characterized in that: Before pre-oxidation, the inner surfaces of the header and the connecting socket are derusted, degreased, cleaned and dried.

6. The method for improving the steam oxidation resistance of a 650°C boiler header according to claim 1, characterized in that: The steps of providing a medium temperature environment under pure water vapor conditions and using a pre-oxidation method to in-situ generate a continuous and dense Cr2O3 film on the inner surface of the header and the pipe socket specifically include: S1. At room temperature, introduce inert gas into the header and the connecting pipe seat to exhaust the air in the header; S2. Heat the header and the pipe socket, and stop introducing the inert gas when the temperature reaches the set temperature of the medium temperature zone; S3. Pump water vapor of the same temperature into the header and the connecting socket, and keep them warm to complete the pre-oxidation reaction.

7. The method for improving the steam oxidation resistance of a 650°C boiler header according to claim 6, characterized in that: After the pre-oxidation reaction is completed, the heating is stopped, the header and the pipe socket are allowed to cool naturally, and the condensed water in the header and the pipe socket is recovered.

8. The method for improving the steam oxidation resistance of a 650°C boiler header according to claim 1, characterized in that: The material of the header is a γ′ phase strengthened Fe-Ni-Cr based high temperature alloy.

9. The method for improving the steam oxidation resistance of a 650°C boiler header according to claim 8, characterized in that: The Cr content in the γ′ phase strengthened Fe—Ni—Cr based high temperature alloy is not less than 12% but not more than 19%, and the Fe content is not less than 30% but not more than 42%.

10. A device for implementing the method for improving the steam oxidation resistance of a 650°C class boiler header as claimed in any one of claims 1 to 9, characterized in that: The invention comprises a water vapor generating device (5) and a degassing device (6) which are respectively sealedly connected to a first connecting pipe seat (3) on a header (1) through pipelines, and a condensate recovery device (7) which is sealedly connected to a second connecting pipe seat (4) on the header (1) through pipelines; a water vapor valve (10) is provided on the pipeline between the water vapor generating device (5) and the header (1), a degassing valve (8) is provided on the pipeline between the degassing device (6) and the header (1), and a condensate recovery valve (9) is provided on the pipeline between the condensate recovery device (7) and the header (1); the connecting pipe seats on the header (1) other than the first connecting pipe seat (3) and the second connecting pipe seat (4) are all sealed; and a heating device (2) is provided on the periphery of the header (1) and the connecting pipe seats.

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