Method for judging creep stage of aluminum-containing heat-resistant alloy furnace tube at 1100 ℃ service temperature

Abstract

The present application belongs to the technical field of ethylene cracking furnace tube detection, and particularly relates to a method for judging the creep stage of an aluminum-containing heat-resistant alloy furnace tube at a service temperature of 1100 DEG C. 23 The present application determines the edge block precipitate M7C3 of the austenite grain boundary precipitate through microscopic structure observation and analysis of the cross section of the aluminum-containing heat-resistant alloy furnace tube, and determines the area fraction influence factor A of C6, the area fraction influence factor B of the internal fine strip-shaped precipitate M7C3 of the austenite grain boundary precipitate, and the aspect ratio influence factor C of the internal fine strip-shaped precipitate M7C3 of the austenite grain boundary precipitate; the influence function of the creep stage of the aluminum-containing heat-resistant alloy furnace tube at 1100 DEG C is designed, and the creep stage of the aluminum-containing heat-resistant alloy furnace tube can be quickly judged. The judgment method can provide a basis for evaluating the service state of the aluminum-containing heat-resistant alloy furnace tube and judging the furnace tube replacement time, and can provide a reference for petrochemical ethylene device managers to formulate maintenance strategies and ensure the safe and stable operation of the device.

Description

Technical Field

[0001] This invention belongs to the field of ethylene cracking furnace technology, and in particular, it is a method for judging the creep stage of aluminum-containing heat-resistant alloy furnace tubes at a service temperature of 1100℃. Background Technology

[0002] The ethylene cracking furnace is a core piece of equipment in a petrochemical ethylene plant, and the furnace tubes are its key components. They are typically made of heat-resistant alloy materials through centrifugal casting and include inlet and outlet tubes, with the inlet tubes operating at a temperature of 1100℃. During long-term operation, high-temperature creep is one of the main creep damage mechanisms of the furnace tubes.

[0003] Creep damage in heat-resistant alloys is generally divided into three stages: creep stage 1, creep stage 2, and creep stage 3. Creep stage 1, also known as decelerating creep stage, is characterized by a gradual decrease in the alloy strain rate with increasing creep time. This stage typically accounts for 5% to 10% of the total creep time. Creep stage 2, or steady-state creep stage, is characterized by a relatively long duration of creep, with the alloy strain rate not changing significantly with increasing creep time. This stage typically accounts for 80% to 90% of the total creep time. Creep stage 3, or accelerated creep stage, is characterized by a rapid increase in the alloy strain rate with increasing creep time until creep fracture occurs. This stage typically has a shorter duration, generally accounting for 5% to 10% of the total creep time.

[0004] For ethylene cracking furnace tubes, once creep damage enters the third stage, it is often accompanied by the formation of creep voids and creep cracks, indicating that the furnace tube material has entered the end of its creep life. To ensure the long-term safe operation of ethylene plants, timely identification of the creep damage status of furnace tubes in service, determining whether the furnace tubes are in the first or second stage of creep, and providing technical reference for determining the timing of furnace tube maintenance and replacement, thus ensuring the safe and stable operation of furnace tubes during the maintenance cycle, has become an urgent problem to be solved in the ethylene industry.

[0005] The traditional method to determine the state of creep damage in furnace tube materials is to conduct high-temperature creep tests under certain temperature and stress conditions and judge based on the creep time-strain rate curve. However, this method has two drawbacks: 1) High-temperature creep tests are conducted below the high-temperature yield strength of the furnace tube material, so the test cycle is generally long, which is difficult to meet the requirement of short maintenance cycle of ethylene plant; 2) Creep tests are destructive sampling tests, and the amount of material required for sample processing is large, which is highly destructive to the furnace tube body. Summary of the Invention

[0006] One of the objectives of the present invention is to provide a method for judging the creep stage of an aluminous heat-resistant alloy furnace tube at a service temperature of 1100°C. By conducting quantitative analysis of the microstructure characteristic parameters of the aluminous heat-resistant alloy furnace tube under service at 1100°C, the designed influence function can quickly judge the creep stage of the aluminous heat-resistant alloy furnace tube material, overcoming the disadvantages of long time consumption and high destructiveness of traditional high-temperature creep tests.

[0007] To achieve the above objective, the present invention adopts the following technical solutions. A method for judging the creep stage of an aluminous heat-resistant alloy furnace tube at a service temperature of 1100°C includes the following steps:

[0008] S1. Conduct microstructure observation and analysis at the 1 / 4 - 3 / 4 wall thickness part of the cross-section of the aluminous heat-resistant alloy furnace tube:

[0009] Measure the area S1 of the edge massive precipitate M 23 C6 of the austenite grain boundary precipitates in the furnace tube material within the field of view area S0, and calculate the area fraction A of the edge massive precipitate M 23 C6 of the austenite grain boundary precipitates in the furnace tube material within the field of view area S0, where A = S1 / S0×100%, unit 1;

[0010] Measure the area S2 of the internal fine strip precipitate M7C3 of the austenite grain boundary precipitates in the furnace tube material within the field of view area S0, and calculate the area fraction B of the internal fine strip precipitate M7C3 of the austenite grain boundary precipitates in the furnace tube material within the field of view area S0, where B = S2 / S1×100%, unit 1;

[0011] Measure the aspect ratio C of the internal fine strip precipitate M7C3 of the austenite grain boundary precipitates in the furnace tube material within the field of view area S0, unit 1;

[0012] S2. Calculate the influence function of the aluminous heat-resistant alloy furnace tube at the creep stage under the condition of 1100°C from the area fractions A, B and the aspect ratio C:

[0013] f(A,B,C) = [(aA + bB + cC) / 100]×100%

[0014] where a is 1200, b is -10, and c is -0.3;

[0015] S3. Divide the creep stage of the aluminous heat-resistant alloy furnace tube under the condition of 1100°C:

[0016] If f(A,B,C) ≤ 10%, it is determined that the creep state of the 27Cr44Ni5W3Al + micro-alloy furnace tube is the first creep stage;

[0017] If 10% < f(A,B,C) ≤ 30%, it is determined that the creep state of the 27Cr44Ni5W3Al + micro-alloy furnace tube is the initial stage of the second creep stage;

[0018] If 30% < f(A, B, C) ≤ 70%, it is determined that the creep state of the 27Cr44Ni5W3Al + microalloy furnace tube is the middle stage of the second creep stage;

[0019] If 70% < f(A, B, C) ≤ 90%, it is determined that the creep state of the 27Cr44Ni5W3Al + microalloy furnace tube is the end stage of the second creep stage.

[0020] As a further improvement to the method for judging the creep stage of the aluminous heat-resistant alloy furnace tube at a service temperature of 1100°C:

[0021] Preferably, a GX53 type Olympus metallographic microscope is used for microstructural observation, with a magnification of 1000 times. For each specimen, no less than 20 fields of view are randomly selected for microstructural observation.

[0022] Preferably, ImageProPlus6.0 software is used to analyze the microstructural photos, and the measurement data is the arithmetic mean of the measurement data of all fields of view.

[0023] Preferably, ImageProPlus6.0 software is used to analyze the microstructural photos. When selecting the area, range is selected as 10, thresh is selected as 3, smooth is selected as 1, and speed is selected as 2.

[0024] Preferably, the total precipitates in the austenite grain boundaries and grains of the furnace tube material include M 23 C6 type carbides, M7C3 type carbides and Ni3Al phase.

[0025] Preferably, the aluminous heat-resistant alloy furnace tube is a 27Cr44Ni5W3Al + microalloy furnace tube.

[0026] The beneficial effects of the present invention compared with the prior art are as follows:

[0027] 1) Under normal operating conditions, the maximum wall temperature of the furnace tube (taking 27Cr44Ni5W3Al + microalloy as an example) at the inlet of the radiant section of the aluminous heat-resistant ethylene cracking furnace can reach 1100°C. During service, under the action of high temperature and internal pressure, the furnace tube undergoes creep damage. As the service time prolongs, the degree of creep damage intensifies.

[0028] On the one hand, at 1100°C, as the service time prolongs, the fine strip-shaped M7C3 type carbides inside the austenite grain boundaries will gradually transform into massive M 23 C6 type carbides and grow at the edges of the austenite grain boundary precipitates; on the other hand, new secondary M precipitated from austenite 23C6-type carbides also accumulate at the edges of austenite grain boundary precipitates. Therefore, with prolonged service life and increased creep damage, the total number of austenite grain boundary precipitates increases, and blocky M-shaped precipitates appear at the edges of the austenite grain boundary precipitates. 23 The area of ​​C6 type carbides also increases accordingly, while the area of ​​fine strip-shaped M7C3 type carbides inside the austenite precipitates decreases accordingly.

[0029] For the fine strip-shaped M7C3 type carbides inside the austenite grain boundary precipitates, on the one hand, with the increase of service time at high temperature, the M7C3 type carbides will gradually transform into blocky M... 23 C6 type carbide transformation; on the other hand, with the deepening of creep, under the action of high temperature stress, the fine strip-shaped carbides gradually develop into shorter and thicker morphologies. Therefore, the aspect ratio of the fine strip-shaped precipitates inside the austenite grain boundary precipitates gradually decreases with the progress of creep. Typical microstructure of grain boundaries and intragranular precipitates in aluminum-containing heat-resistant alloy furnace tubes is shown in the image. Figure 1 As shown.

[0030] 2) This invention identifies the edge blocky precipitates M of austenite grain boundary precipitates. 23 The influence factors A (area fraction of C6), B (area fraction of austenite grain boundary precipitates M7C3), and C (aspect ratio of austenite grain boundary precipitates M7C3) were analyzed. An influence function was designed to determine the creep stage of the aluminum-containing heat-resistant alloy furnace tube at 1100℃, enabling rapid identification of the first and second creep stages. Creep time and strain rate curves were obtained from testing the same aluminum-containing heat-resistant alloy furnace tube before and after high-temperature service (typical creep time-strain rate curves at 1100℃ and 35MPa, and schematic diagrams of different stages are shown in [reference needed]). Figure 2 The method of this invention calculates the creep stage of the furnace tube, confirming that it can quickly and accurately assess the creep damage state of the furnace tube in service, providing a basis for furnace tube replacement time and a reference for petrochemical ethylene plant managers to formulate maintenance strategies and ensure the safe and stable operation of the plant. Attached Figure Description

[0031] Figure 1 These are typical microstructure photographs of grain boundaries and intragranular precipitates in the aluminum-containing heat-resistant alloy furnace tube of this invention;

[0032] Figure 2 This invention presents a typical creep time-strain rate curve and schematic diagrams of different stages of the aluminum-containing heat-resistant alloy furnace tube under conditions of 1100℃ and 35MPa.

[0033] Figure 3 This is a photograph of the microstructure of the No. 1 aluminum-containing heat-resistant alloy furnace tube in service in Embodiment 1 of the present invention;

[0034] Figure 4 This is the creep time-strain rate curve of the unused No. 1 aluminum-containing heat-resistant alloy furnace tube in Embodiment 1 of the present invention under conditions of 1100℃ and 17MPa.

[0035] Figure 5 This is a photograph of the microstructure of the No. 2 aluminum-containing heat-resistant alloy furnace tube in service in Embodiment 2 of the present invention;

[0036] Figure 6 This is a photograph of the microstructure of the No. 3 aluminum-containing heat-resistant alloy furnace tube in service in Embodiment 3 of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0038] Example 1

[0039] This embodiment provides a method for determining the creep stage of an aluminum-containing heat-resistant alloy furnace tube at a service temperature of 1100℃, specifically including the following steps:

[0040] S1. A 27Cr44Ni5W3Al+ microalloyed furnace tube (referred to as the No. 1 aluminum-containing heat-resistant alloy furnace tube in service) at the inlet of an ethylene cracking furnace operating at 1100℃ was selected. Microstructure was observed at half the wall thickness of the tube's cross-section using a GX53 Olympus metallographic microscope at 1000x magnification. Typical microstructure photographs are shown below. Figure 3 ;

[0041] S2. ImageProPlus 6.0 software was used to analyze the microscopic tissue images. When selecting the region, the range was set to 10, the thresh setting to 3, the smooth setting to 1, and the speed setting to 2.

[0042] The measured field area S0 shows the edge blocky precipitates M of the austenite grain boundary precipitates in the furnace tube material. 23 The area S1 of C6 is used to calculate the edge blocky precipitates M of the austenite grain boundary precipitates. 23 The area fraction of C6's area S1 relative to the field of view S0 is A = S1 / S0 × 100%, unit 1;

[0043] The area S2 of the fine strip-shaped precipitate M7C3 inside the austenite grain boundary precipitate of the furnace tube material within the field of view S0 is measured. The area fraction B of the fine strip-shaped precipitate M7C3 inside the austenite grain boundary precipitate to the field of view S0 is calculated as B = S2 / S1 × 100%, unit 1.

[0044] The aspect ratio C of the fine strip-shaped precipitates M7C3 inside the austenitic grain boundary precipitates of the furnace tube material within the field of view S0 was measured, in units of 1;

[0045] Switch to the microstructure observation interface, then randomly select 19 fields of view, and calculate the blocky precipitates M at the austenite grain boundary edges in the No. 1 aluminum-containing heat-resistant alloy furnace tube during 20 tests. 23 The area fraction of C6 is 1.1%, the area fraction of fine strip-shaped precipitates M7C3 inside the austenite grain boundary is 3.3%, and the aspect ratio C of fine strip-shaped precipitates M7C3 inside the austenite grain boundary is 9.8.

[0046] S3. Based on the percentage of time at different stages of creep, define 0%t as the time before creep begins and 100%t as the time at the end of the third stage of creep; calculate the influence function of the creep stage on the No. 1 aluminum-containing heat-resistant alloy furnace tube under 1100℃ conditions:

[0047] f(A,B,C)=[(aA+bB+cC) / 100]×100%

[0048] = [(1200×0.011-10×0.033-0.3×9.8) / 100]×100%

[0049] =10%;

[0050] S4, then f(A,B,C)≤10%, the creep state of the No.1 aluminum-containing heat-resistant alloy furnace tube is determined to be the first stage of creep.

[0051] Verification test

[0052] Furnace tubes of the same material, specification, and batch as the serviced No. 1 aluminum-containing heat-resistant alloy furnace tube, but not yet in service, were selected for high-temperature creep tests at 1100℃ and 17MPa. The creep time-strain rate curves are shown in [reference needed]. Figure 4 The total creep test time was t0, with the first, second, and third creep stages lasting t1, t2, and t3, respectively, and t0 = t1 + t2 + t3. The total creep rupture time was 154 hours, with the first, second, and third creep stages lasting 16 hours, 119 hours, and 9 hours, respectively.

[0053] A high-temperature creep test was conducted on the No. 1 aluminum-containing heat-resistant alloy furnace tube under conditions of 1100℃ and 17MPa. The total creep fracture time of the test was 140h.

[0054] Compared to new furnace tubes not yet in service, the No. 1 aluminum-containing heat-resistant alloy furnace tube in service, after a period of service at 1100℃ and 17MPa, experienced a creep life loss of 14 hours, approximately 9% of the total creep life of the new furnace tubes not yet in service. This indicates that the No. 1 aluminum-containing heat-resistant alloy furnace tube in service is in the first stage of creep. This assessment is consistent with the calculated results of the creep degree influence function.

[0055] Example 2

[0056] This embodiment provides a method for determining the creep stage of an aluminum-containing heat-resistant alloy furnace tube at a service temperature of 1100℃, specifically including the following steps:

[0057] S1. A 27Cr44Ni5W3Al+ microalloyed furnace tube (referred to as the No. 2 aluminum-containing heat-resistant alloy furnace tube in service) was selected at the inlet of an ethylene cracking furnace operating at 1100℃. Microstructure was observed at 3 / 5 of the tube's wall thickness using a GX53 Olympus metallographic microscope at 1000x magnification. Typical microstructure photographs are shown below. Figure 5 ;

[0058] S2. ImageProPlus 6.0 software was used to analyze the microscopic tissue images. When selecting the region, the range was set to 10, the thresh setting to 3, the smooth setting to 1, and the speed setting to 2.

[0059] The measured field area S0 shows the edge blocky precipitates M of the austenite grain boundary precipitates in the furnace tube material. 23 The area S1 of C6 is used to calculate the edge blocky precipitates M of the austenite grain boundary precipitates. 23 The area fraction of C6's area S1 relative to the field of view S0 is A = S1 / S0 × 100%, unit 1;

[0060] The area S2 of the fine strip-shaped precipitate M7C3 inside the austenite grain boundary precipitate of the furnace tube material within the field of view S0 is measured. The area fraction B of the fine strip-shaped precipitate M7C3 inside the austenite grain boundary precipitate to the field of view S0 is calculated as B = S2 / S1 × 100%, unit 1.

[0061] The aspect ratio C of the fine strip-shaped precipitates M7C3 inside the austenitic grain boundary precipitates of the furnace tube material within the field of view S0 was measured, in units of 1;

[0062] Switch to the microstructure observation interface, then randomly select 32 fields of view, and calculate the blocky precipitates M at the austenite grain boundary edges of the No. 2 aluminum-containing heat-resistant alloy furnace tube material in 33 tests. 23 The area fraction of C6 is 3.7%, the area fraction of fine strip-shaped precipitates M7C3 inside the austenite grain boundary is 3.0%, and the aspect ratio C of fine strip-shaped precipitates M7C3 inside the austenite grain boundary is 7.1.

[0063] S3. Based on the percentage of time at different stages of creep, define 0%t as the time before creep begins and 100%t as the time at the end of the third stage of creep; calculate the influence function of the creep stage on the No. 2 aluminum-containing heat-resistant alloy furnace tube under 1100℃ conditions:

[0064] f(A,B,C)=[(aA+bB+cC) / 100]×100%

[0065] = [(1200×0.037-10×0.030-0.3×7.1) / 100]×100%

[0066] =42%;

[0067] S4. If f(A,B,C) is between 30% and 70%, the creep state of the No. 2 aluminum-containing heat-resistant alloy furnace tube is determined to be the middle stage of the second creep stage.

[0068] Verification test

[0069] Furnace tubes of the same material, specification, and batch as the serviced No. 2 aluminum-containing heat-resistant alloy furnace tube, but not yet in service, were selected for high-temperature creep tests at 1100℃ and 17MPa. Creep time-strain rate curves were obtained. The total creep test time was t0, with the first, second, and third creep stages taking times of t1, t2, and t3, respectively, where t0 = t1 + t2 + t3. The total creep fracture time was 87 hours, with the first, second, and third creep stages taking times of 5 hours, 56 hours, and 6 hours, respectively.

[0070] High-temperature creep tests were conducted on the No. 2 aluminum-containing heat-resistant alloy furnace tube under conditions of 1100℃ and 17MPa. The total creep fracture time of the test was 20 hours.

[0071] Compared to the new furnace tubes that were not yet in service, the No. 2 aluminum-containing heat-resistant alloy furnace tube, after a period of service at 1100℃ and 17MPa, experienced a creep life loss of 67 hours, approximately 44% of the total creep life of the new furnace tubes. This indicates that the No. 2 aluminum-containing heat-resistant alloy furnace tube is in the middle of the second stage of creep. This assessment is consistent with the calculated results of the creep degree influence function.

[0072] Example 3

[0073] This embodiment provides a method for determining the creep stage of an aluminum-containing heat-resistant alloy furnace tube at a service temperature of 1100℃, specifically including the following steps:

[0074] S1. A 27Cr44Ni5W3Al+ microalloyed furnace tube (referred to as the No. 3 aluminum-containing heat-resistant alloy furnace tube in service) at the inlet of an ethylene cracking furnace operating at 1100℃ was selected. Microstructure was observed at half the wall thickness of the tube's cross-section using a GX53 Olympus metallographic microscope at 1000x magnification. Typical microstructure photographs are shown below. Figure 6 ;

[0075] S2. ImageProPlus 6.0 software was used to analyze the microscopic tissue images. When selecting the region, the range was set to 10, the thresh setting to 3, the smooth setting to 1, and the speed setting to 2.

[0076] The measured field area S0 shows the edge blocky precipitates M of the austenite grain boundary precipitates in the furnace tube material. 23 The area S1 of C6 is used to calculate the edge blocky precipitates M of the austenite grain boundary precipitates. 23 The area fraction of C6's area S1 relative to the field of view S0 is A = S1 / S0 × 100%, unit 1;

[0077] The area S2 of the fine strip-shaped precipitate M7C3 inside the austenite grain boundary precipitate of the furnace tube material within the field of view S0 is measured. The area fraction B of the fine strip-shaped precipitate M7C3 inside the austenite grain boundary precipitate to the field of view S0 is calculated as B = S2 / S1 × 100%, unit 1.

[0078] The aspect ratio C of the fine strip-shaped precipitates M7C3 inside the austenitic grain boundary precipitates of the furnace tube material within the field of view S0 was measured, in units of 1;

[0079] Switch to the microstructure observation interface, then randomly select 25 fields of view, and calculate the blocky precipitates M at the austenite grain boundary edges of the No. 3 aluminum-containing heat-resistant alloy furnace tube material in service during 26 tests. 23 The area fraction of C6 is 6.8%, the area fraction of fine strip-shaped precipitates M7C3 inside the austenite grain boundary is 2.6%, and the aspect ratio C of fine strip-shaped precipitates M7C3 inside the austenite grain boundary is 4.1.

[0080] S3. Based on the percentage of time at different stages of creep, define 0%t as the time before creep begins and 100%t as the time at the end of the third stage of creep; calculate the influence function of the creep stage on the No. 3 aluminum-containing heat-resistant alloy furnace tube under 1100℃ conditions:

[0081] f(A,B,C)=[(aA+bB+cC) / 100]×100%

[0082] = [(1200×0.068-10×0.026-0.3×4.1) / 100]×100%

[0083] =80%;

[0084] S4. If f(A,B,C) is between 70% and 90%, then the creep state of the No. 3 aluminum-containing heat-resistant alloy furnace tube is determined to be the end of the second stage of creep.

[0085] Verification test

[0086] Furnace tubes of the same material, specification, and batch as the serviced No. 3 aluminum-containing heat-resistant alloy furnace tube, but not yet in service, were selected for high-temperature creep tests at 1100℃ and 17MPa. Creep time-strain rate curves were obtained. The total creep test time was t0, with the times for the first, second, and third creep stages being t1, t2, and t3, respectively, where t0 = t1 + t2 + t3. The total creep fracture time was 154 hours, with the times for the first, second, and third creep stages being 15, 122, and 17 hours, respectively.

[0087] High-temperature creep tests were conducted on the No. 3 aluminum-containing heat-resistant alloy furnace tube under conditions of 1100℃ and 17MPa. The total creep fracture time of the test was 30 hours.

[0088] Compared to the new furnace tubes that were not yet in service, the No. 3 aluminum-containing heat-resistant alloy furnace tube, after a period of service at 1100℃ and 17MPa, experienced a creep life loss of 124 hours, approximately 81% of the total creep life of the new furnace tubes. This indicates that the No. 3 aluminum-containing heat-resistant alloy furnace tube was in the late stage of the second creep stage. This assessment is consistent with the calculated results of the creep degree influence function.

[0089] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A method for judging the creep stage of an aluminous heat-resistant alloy furnace tube at a service temperature of 1100°C, characterized in that S1. Conduct microstructure observation and analysis at the 1 / 4 - 3 / 4 wall thickness part of the cross-section of the aluminous heat-resistant alloy furnace tube. The aluminous heat-resistant alloy furnace tube is a 27Cr44Ni5W3Al + micro-alloy furnace tube: The measured field area S0 shows the edge blocky precipitates M of the austenite grain boundary precipitates in the furnace tube material. 23 The area S1 of C6 is used to calculate the edge blocky precipitates M of the austenite grain boundary precipitates. 23 The area fraction of C6's area S1 relative to the field of view S0 is A = S1 / S0 × 100%, unit 1; Measure the area S2 of the internal fine strip precipitate M7C3 of the austenite grain boundary precipitate in the field area S0 of the furnace tube material, and calculate the area fraction B of the internal fine strip precipitate M7C3 of the austenite grain boundary precipitate in the field area S0, B = S2 / S1×100%, unit 1; Measure the aspect ratio C of the internal fine strip precipitate M7C3 of the austenite grain boundary precipitate in the field area S0 of the furnace tube material, unit 1; S2. Calculate the influence function of the aluminous heat-resistant alloy furnace tube at the creep stage under the condition of 1100°C from the area fraction A, B and aspect ratio C: f(A, B, C)=[(aA + bB + cC) / 100] ×100% where a is 1200, b is -10, and c is -0.3; S3. Divide the creep stage of the aluminous heat-resistant alloy furnace tube under the condition of 1100°C: If f(A, B, C) ≤ 10%, determine that the creep state of the 27Cr44Ni5W3Al + micro-alloy furnace tube is the first creep stage; If 10% < f(A, B, C) ≤ 30%, determine that the creep state of the 27Cr44Ni5W3Al + micro-alloy furnace tube is the initial stage of the second creep stage; If 30% < f(A, B, C) ≤ 70%, determine that the creep state of the 27Cr44Ni5W3Al + micro-alloy furnace tube is the middle stage of the second creep stage; If 70% < f(A, B, C) ≤ 90%, determine that the creep state of the 27Cr44Ni5W3Al + micro-alloy furnace tube is the final stage of the second creep stage.

2. The method for determining the creep stage of an aluminum-containing heat-resistant alloy furnace tube at a service temperature of 1100°C according to claim 1, characterized in that, Use a GX53 type Olympus metallographic microscope for microstructure observation, with a magnification of 1000 times. Randomly select no less than 20 fields of view for each specimen for microstructure observation.

3. The method for determining the creep stage of an aluminum-containing heat-resistant alloy furnace tube at a service temperature of 1100°C according to claim 1 or 2, characterized in that, Use Image Pro Plus 6.0 software to conduct microstructure analysis on the metallographic microstructure photos, and the measured data is the arithmetic mean of the measured data of all fields of view.

4. The method for determining the creep stage of an aluminum-containing heat-resistant alloy furnace tube at a service temperature of 1100°C according to claim 3, characterized in that, Use Image Pro Plus 6.0 software to analyze the metallographic microstructure photos. When selecting the area, range selects 10, thresh selects 3, smooth selects 1, and speed selects 2.

5. The method for determining the creep stage of an aluminum-containing heat-resistant alloy furnace tube at a service temperature of 1100°C according to claim 1, characterized in that, The total precipitates at austenitic grain boundaries and within grains of the furnace tube material include M 23 C6 type carbides, M7C3 type carbides and Ni3Al phase.

Images