27Cr44Ni5W3Al+microalloyed furnace tube method for rapidly judging creep stage at 1050 °c service temperature

Abstract

This invention belongs to the field of ethylene cracking furnace tube testing technology, specifically involving a rapid method for determining the creep stage of a 27Cr44Ni5W3Al+ microalloyed furnace tube at a service temperature of 1050℃. This invention, through microstructural observation and analysis of the cross-section of the 27Cr44Ni5W3Al+ microalloyed furnace tube, determines the influence factors A (area fraction of austenite grain boundary precipitates), B (aspect ratio of fine strip-shaped M7C3 type carbides within the austenite grain boundary precipitates), and M7C3 type carbides at the edge of the austenite grain boundary precipitates. 23 The C6 type carbide area fraction influence factor C was used to design the influence functions of the first and second stages of creep in 27Cr44Ni5W3Al+ microalloyed furnace tubes at 1050℃, enabling rapid determination of the creep stage of the 27Cr44Ni5W3Al+ microalloyed furnace tube at 1050℃. This invention provides a basis for assessing the service status of 27Cr44Ni5W3Al+ microalloyed furnace tubes and determining replacement time, offering a reference for petrochemical ethylene plant managers to formulate maintenance strategies and ensure the safe and stable operation of the plant.

Description

Technical Field

[0001] This invention belongs to the field of ethylene cracking furnace tube testing technology, specifically relating to a rapid method for determining the creep stage of a 27Cr44Ni5W3Al+ microalloyed furnace tube at a service temperature of 1050℃. 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. The service temperature of the outlet tube wall is approximately 1050℃. 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 15% 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 70% 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 15% 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 objective of this invention is to provide a rapid method for determining the creep stage of 27Cr44Ni5W3Al+ microalloyed furnace tubes at a service temperature of 1050℃. This invention utilizes quantitative microstructural characteristic parameter analysis of 27Cr44Ni5W3Al+ microalloyed furnace tubes at 1050℃. The designed influence function can rapidly determine the creep stage of the 27Cr44Ni5W3Al+ microalloyed furnace tube material, overcoming the drawbacks of traditional high-temperature creep tests being time-consuming and highly destructive.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for rapid determination of the creep stage of a 27Cr44Ni5W3Al+ microalloyed furnace tube at a service temperature of 1050℃, comprising the following steps:

[0008] S1. Microstructure observation and analysis were performed on the cross-section of the 27Cr44Ni5W3Al+ microalloyed furnace tube at a thickness of 1 / 4 to 3 / 4 of the wall thickness:

[0009] The area of ​​austenite grain boundaries and total intragranulation precipitates S1 within the field of view S0 of the furnace tube material is measured. The area fraction A of the austenite grain boundary and total intragranulation precipitate area S1 in the field of view S0 is calculated as A = S1 / S0 × 100%, unit 1.

[0010] The aspect ratio B of the fine strip-shaped M7C3 type carbides inside the austenite grain boundary precipitates of the furnace tube material in the field of view S0 was measured, in units of 1.

[0011] The measured field area S0 shows blocky M-shaped precipitates at the edges of austenite grain boundaries in the furnace tube material. 23 C6 type carbide area S2, calculate edge blocky M 23 The area fraction of C6 type carbide area S2 relative to the total precipitate area S1 at austenite grain boundaries and within grains is C = S2 / S1 × 100%, unit 1;

[0012] S2. Calculate the influence function of the creep stage of 27Cr44Ni5W3Al+ microalloyed furnace tube at 1050℃ based on area fractions A and C and aspect ratio B:

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

[0014] Where a is 8, b is -0.5, and c is 1000;

[0015] S3. Defining the creep stage of 27Cr44Ni5W3Al+ microalloyed furnace tube at 1050℃:

[0016] If f(A,B,C)≤10%, the creep state of the 27Cr44Ni5W3Al+ microalloy furnace tube is determined to be the first stage of creep.

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

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

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

[0020] As a further improvement of the rapid judgment method for the creep stage of 27Cr44Ni5W3Al+microalloyed furnace tubes at a service temperature of 1050°C:

[0021] Preferably, a GX53 Olympus metallurgical microscope is used for microstructure observation, the magnification is 1000 times, and no less than 20 visual fields are randomly selected for each sample for microstructure observation.

[0022] Preferably, ImageProPlus 6.0 software is used to perform microstructure analysis on microstructure photos, and the measured data is the arithmetic mean of the measured data of all visual fields.

[0023] Preferably, ImageProPlus 6.0 software is used to analyze microstructure photos, when selecting a region, 10 is selected for range, 3 is selected for thresh, 1 is selected for smooth, and 2 is selected for speed.

[0024] Preferably, the austenite grain boundary precipitates include M 23 C6 type carbides, M7C3 type carbides and Ni3Al phase precipitates.

[0025] The beneficial effects of the present invention compared with the prior art are:

[0026] 1) Under normal operating conditions, except for partial inlet tubes, the tube wall temperature of the radiant section furnace tube of 27Cr44Ni5W3Al+microalloyed ethylene cracking furnace is generally 1050°C. During service, under the action of high temperature and internal pressure, creep damage occurs to 27Cr44Ni5W3Al+microalloyed furnace tubes. As the service time prolongs, the degree of creep damage intensifies.

[0027] On the one hand, under high temperature conditions, with the extension of service time, the fine strip-shaped M7C3 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 proportion of C6-type carbides also increased accordingly.

[0028] 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 morphology of the fine strip-shaped carbides also gradually develops towards shorter and coarser shapes. 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 images of grain boundaries and intragranular precipitates in 27Cr44Ni5W3Al+ microalloyed furnace tubes are shown below. Figure 1 .

[0029] 2) This invention determines the influence factors A (area fraction of austenite grain boundary precipitates), B (aspect ratio of fine strip-shaped M7C3 type carbides inside austenite grain boundary precipitates), and M7C3 type carbides at the edge of austenite grain boundary precipitates. 23 The influence factor C of the C6 type carbide area fraction was obtained; finally, the influence function for determining the first and second stages of creep in 27Cr44Ni5W3Al+ microalloyed furnace tubes at 1050℃ was obtained. An influence function for the creep stage of 27Cr44Ni5W3Al+ microalloyed furnace tubes at 1050℃ was designed, which can quickly determine the first and second stages of creep in the 27Cr44Ni5W3Al+ microalloyed furnace tube. Creep time and strain rate curves were tested on the same 27Cr44Ni5W3Al+ microalloyed furnace tubes before and after high-temperature service at 1050℃ and 18-25MPa (typical creep time-strain rate curves and schematic diagrams of different stages at 1050℃ and 25MPa are shown in...). 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

[0030] Figure 1 These are typical microstructure photographs of grain boundaries and intragranular precipitates in the 27Cr44Ni5W3Al+ microalloyed furnace tube of this invention.

[0031] Figure 2 This invention presents a typical creep time-strain rate curve and schematic diagrams of different stages of the 27Cr44Ni5W3Al+ microalloyed furnace tube under conditions of 1050℃ and 25MPa.

[0032] Figure 3 This is a photograph of the microstructure of the No. 1 27Cr44Ni5W3Al+ microalloyed furnace tube in service in Embodiment 1 of the present invention;

[0033] Figure 4 This is the creep time-strain rate curve of the unused No. 1 27Cr44Ni5W3Al+ microalloy furnace tube under 1050℃ and 18MPa conditions in Example 1 of the present invention.

[0034] Figure 5 This is a photograph of the microstructure of the No. 2 27Cr44Ni5W3Al+ microalloyed furnace tube in service in Embodiment 2 of the present invention;

[0035] Figure 6 This is the creep time-strain rate curve of the unused 2# 27Cr44Ni5W3Al+ microalloyed furnace tube under 1050℃ and 20MPa conditions in Example 2 of the present invention.

[0036] Figure 7 This is a photograph of the microstructure of the No. 3 27Cr44Ni5W3Al+ microalloyed furnace tube in service in Embodiment 3 of the present invention;

[0037] Figure 8 This is the creep time-strain rate curve of the unused No. 3 27Cr44Ni5W3Al+ microalloy furnace tube under the conditions of 1050℃ and 25MPa in Example 3 of the present invention. Detailed Implementation

[0038] 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.

[0039] Example 1

[0040] This embodiment provides a method for determining the creep stage of a 27Cr44Ni5W3Al+ microalloyed furnace tube at a service temperature of 1050℃, specifically including the following steps:

[0041] S1. A 27Cr44Ni5W3Al+ microalloyed furnace tube (designated as Service Tube No. 1) was selected at the inlet of an ethylene cracking furnace operating at 1050℃. 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 ;

[0042] 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.

[0043] The area of ​​austenite grain boundaries and total intragranulation precipitates S1 within the field of view S0 of the furnace tube material is measured. The area fraction A of the austenite grain boundary and total intragranulation precipitate area S1 in the field of view S0 is calculated as A = S1 / S0 × 100%, unit 1.

[0044] The aspect ratio B of the fine strip-shaped M7C3 type carbides inside the austenite grain boundary precipitates of the furnace tube material in the field of view S0 was measured, in units of 1.

[0045] The measured field area S0 shows blocky M-shaped precipitates at the edges of austenite grain boundaries in the furnace tube material. 23 C6 type carbide area S2, calculate edge blocky M 23 The area fraction of C6 type carbide area S2 relative to the total precipitate area S1 at austenite grain boundaries and within grains is C = S2 / S1 × 100%, unit 1;

[0046] Switch to the microstructure observation interface, and then randomly select 19 fields of view. Calculate the average area fraction (A) of the total precipitates at austenite grain boundaries and within grains of the No. 1 27Cr44Ni5W3Al+ microalloy furnace tube material in 20 tests. The average value is 35%; the average aspect ratio (B) of the strip-shaped M7C3 type carbides inside the austenite grain boundary precipitates is 10.2; and the average value of the blocky M7C3 type carbides at the edge of the austenite grain boundary precipitates is... 23 The average area fraction C of C6 type carbides is 1.1%;

[0047] 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 creep stage on the No. 1 27Cr44Ni5W3Al+ microalloyed furnace tube at 1050℃:

[0048] f(A,B,C)=[(aA+bB+cC) / 100]×100%

[0049] = [(8×0.35-0.5×10.2+1000×0.011) / 100]×100%

[0050] =8.7%;

[0051] S4, then f(A,B,C)≤10%, the creep state of the 1#27Cr44Ni5W3Al+ microalloy furnace tube is determined to be the first stage of creep.

[0052] Verification test

[0053] Furnace tubes of the same material, specification, and batch as the serviced No. 1 27Cr44Ni5W3Al+ microalloyed furnace tube, but not yet in service, were selected for high-temperature creep tests at 1050℃ and 18MPa. 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 296 hours, with the first, second, and third creep stages lasting 30 hours, 240 hours, and 26 hours, respectively.

[0054] A high-temperature creep test was conducted on the No. 1 27Cr44Ni5W3Al+ microalloyed furnace tube under conditions of 1050℃ and 18MPa. The total creep fracture time of the test was 271h.

[0055] Compared to new furnace tubes not yet in service, the No. 1 27Cr44Ni5W3Al+ microalloyed furnace tube, after a period of service at 1050℃ and 18MPa, showed a creep life loss of 25 hours, approximately 8.4% of the total creep life of the new furnace tubes not yet in service. This indicates that the No. 1 27Cr44Ni5W3Al+ microalloyed furnace tube is in the first stage of creep. This assessment is consistent with the calculated results of the creep degree influence function.

[0056] Example 2

[0057] This embodiment provides a method for determining the creep stage of a 27Cr44Ni5W3Al+ microalloyed furnace tube at a service temperature of 1050℃, specifically including the following steps:

[0058] S1. A 27Cr44Ni5W3Al+ microalloyed furnace tube (designated as service tube #2) at the inlet of an ethylene cracking furnace operating at 1050℃ was selected. Microstructure was observed at 3 / 4 of the tube's wall thickness using a GX53 Olympus metallographic microscope at 1000x magnification. Typical microstructure photographs are shown below. Figure 5 ;

[0059] 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.

[0060] The area of ​​austenite grain boundaries and total intragranulation precipitates S1 within the field of view S0 of the furnace tube material is measured. The area fraction A of the austenite grain boundary and total intragranulation precipitate area S1 in the field of view S0 is calculated as A = S1 / S0 × 100%, unit 1.

[0061] The aspect ratio B of the fine strip-shaped M7C3 type carbides inside the austenite grain boundary precipitates of the furnace tube material in the field of view S0 was measured, in units of 1.

[0062] The measured field area S0 shows blocky M-shaped precipitates at the edges of austenite grain boundaries in the furnace tube material. 23 C6 type carbide area S2, calculate edge blocky M 23 The area fraction of C6 type carbide area S2 relative to the total precipitate area S1 at austenite grain boundaries and within grains is C = S2 / S1 × 100%, unit 1;

[0063] Switch to the microstructure observation interface, and then randomly select 25 fields of view. Calculate the average area fraction (A) of the total precipitates at austenite grain boundaries and within grains of the No. 2 27Cr44Ni5W3Al+ microalloy furnace tube material in 26 tests. The average value is 47%. The average aspect ratio (B) of the strip-shaped M7C3 type carbides inside the austenite grain boundary precipitates is 7.8. The average value of the blocky M7C3 type carbides at the edge of the austenite grain boundary precipitates is... 23 The average area fraction C of C6 type carbides is 5.6%;

[0064] 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 creep stage on the No. 2 27Cr44Ni5W3Al+ microalloyed furnace tube at 1050℃:

[0065] f(A,B,C)=[(aA+bB+cC) / 100]×100%

[0066] = [(8×0.47-0.5×7.8+1000×0.056) / 100]×100%

[0067] =56%;

[0068] S4. If f(A,B,C) is between 30% and 70%, the creep state of the 2#27Cr44Ni5W3Al+ microalloy furnace tube is determined to be the middle stage of the second creep stage.

[0069] Verification test

[0070] Furnace tubes of the same material, specification, and batch as the in-service No. 2 27Cr44Ni5W3Al+ microalloyed furnace tube, but not yet in service, were selected for high-temperature creep tests at 1050℃ and 20MPa. The creep time-strain rate curves are shown in [reference needed]. Figure 6 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 280 hours, with the first, second, and third creep stages lasting 27 hours, 233 hours, and 20 hours, respectively.

[0071] High-temperature creep tests were conducted on the No. 2 27Cr44Ni5W3Al+ microalloyed furnace tube under conditions of 1050℃ and 20MPa. The total creep fracture time was 131h.

[0072] Compared to the new furnace tubes that were not yet in service, the No. 2 27Cr44Ni5W3Al+ microalloyed furnace tube, after serving for a period of time at 1050℃ and 20MPa, experienced a creep life loss of 149 hours, approximately 53% of the total creep life of the new furnace tubes. This indicates that the No. 2 27Cr44Ni5W3Al+ microalloyed 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.

[0073] Example 3

[0074] This embodiment provides a method for determining the creep stage of a 27Cr44Ni5W3Al+ microalloyed furnace tube at a service temperature of 1050℃, specifically including the following steps:

[0075] S1. A 27Cr44Ni5W3Al+ microalloyed furnace tube (designated as service tube #3) at the inlet of an ethylene cracking furnace operating at 1050℃ was selected. Microstructure was observed at 1 / 4 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 ;

[0076] 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.

[0077] The area of ​​austenite grain boundaries and total intragranulation precipitates S1 within the field of view S0 of the furnace tube material is measured. The area fraction A of the austenite grain boundary and total intragranulation precipitate area S1 in the field of view S0 is calculated as A = S1 / S0 × 100%, unit 1.

[0078] The aspect ratio B of the fine strip-shaped M7C3 type carbides inside the austenite grain boundary precipitates of the furnace tube material in the field of view S0 was measured, in units of 1.

[0079] The measured field area S0 shows blocky M-shaped precipitates at the edges of austenite grain boundaries in the furnace tube material. 23 C6 type carbide area S2, calculate edge blocky M 23 The area fraction of C6 type carbide area S2 relative to the total precipitate area S1 at austenite grain boundaries and within grains is C = S2 / S1 × 100%, unit 1;

[0080] Switch to the microstructure observation interface, and then randomly select 30 fields of view. Calculate the average area fraction (A) of the total precipitates at austenite grain boundaries and within grains of the No. 3 27Cr44Ni5W3Al+ microalloy furnace tube material in 31 tests. The average value is 49%. The average aspect ratio (B) of the strip-shaped M7C3 type carbides inside the austenite grain boundary precipitates is 5.5. The average value of the blocky M7C3 type carbides at the edge of the austenite grain boundary precipitates is... 23 The average area fraction C of C6 type carbides is 8.2%;

[0081] 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 27Cr44Ni5W3Al+ microalloyed furnace tube at 1050℃:

[0082] f(A,B,C)=[(aA+bB+cC) / 100]×100%

[0083] = [(8×0.49-0.5×5.5+1000×0.082) / 100]×100%

[0084] =83%;

[0085] S4. If f(A,B,C) is between 70% and 90%, then the creep state of the 3# 27Cr44Ni5W3Al+ microalloy furnace tube is determined to be the end of the second stage of creep.

[0086] Verification test

[0087] Furnace tubes of the same material, specification, and batch as the serviced No. 3 27Cr44Ni5W3Al+ microalloyed furnace tube, but not yet in service, were selected for high-temperature creep tests at 1050℃ and 25MPa. 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 fracture time was 101 hours, with the first, second, and third creep stages lasting 11 hours, 81 hours, and 9 hours, respectively.

[0088] High-temperature creep tests were conducted on the No. 3 27Cr44Ni5W3Al+ microalloyed furnace tube under conditions of 1050℃ and 25MPa. The total creep fracture time of the test was 15h.

[0089] Compared to the new furnace tubes not yet in service, the No. 3 27Cr44Ni5W3Al+ microalloyed furnace tube, after a period of service at 1050℃ and 25MPa, showed a creep life loss of 86 hours, approximately 85% of the total creep life of the new furnace tubes not yet in service. This indicates that the creep state of the No. 3 27Cr44Ni5W3Al+ microalloyed furnace tube is at the end of the second stage of creep. This assessment is consistent with the calculation results of the creep degree influence function.

[0090] 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 rapid determination of the creep stage of a 27Cr44Ni5W3Al+ microalloyed furnace tube at a service temperature of 1050℃, characterized in that, Comprising the following steps: S1, performing microstructure observation and analysis on the 1 / 4-3 / 4 wall thickness部位 of the cross section of a 27Cr44Ni5W3Al+microalloyed furnace tube: measuring the total area S1 of precipitates at austenite grain boundaries and within austenite grains of the furnace tube material in a field of view with area S0, calculating the area fraction A of the total area S1 of precipitates at austenite grain boundaries and within austenite grains occupying the field of view area S0, wherein A=S1 / S0×100%, with a unit of 1; measuring the aspect ratio B of fine strip-shaped M7C3-type carbides within precipitates at austenite grain boundaries of the furnace tube material in the field of view area S0, with a unit of 1; The measured field area S0 shows blocky M-shaped precipitates at the edges of austenite grain boundaries in the furnace tube material. 23 C6 type carbide area S2, calculate edge blocky M 23 The area fraction of C6 type carbide area S2 relative to the total precipitate area S1 at austenite grain boundaries and within grains is C = S2 / S1 × 100%, unit 1; S2, calculating the influence function of the 27Cr44Ni5W3Al+microalloyed furnace tube in the creep stage at 1050°C by using the area fraction A, C and the aspect ratio B: f(A,B,C)=[(aA+bB+cC) / 100]×100% wherein a is 8, b is -0.5, and c is 1000; S3, dividing the creep stages of the 27Cr44Ni5W3Al+microalloyed furnace tube at 1050°C: if f(A,B,C)≤10%, determining the creep state of the 27Cr44Ni5W3Al+microalloyed furnace tube as the first creep stage; if 10%<f(A,B,C)≤30%, determining the creep state of the 27Cr44Ni5W3Al+microalloyed furnace tube as the initial period of the second creep stage; if 30%<f(A,B,C)≤70%, determining the creep state of the 27Cr44Ni5W3Al+microalloyed furnace tube as the middle period of the second creep stage; if 70%<f(A,B,C)≤90%, determining the creep state of the 27Cr44Ni5W3Al+microalloyed furnace tube as the terminal period of the second creep stage.

2. The method for rapid determination of creep stage of 27Cr44Ni5W3Al+ microalloyed furnace tube at 1050℃ service temperature according to claim 1, characterized in that, A GX53 Olympus metallographic microscope is used for microstructure observation, with a magnification of 1000 times, and no less than 20 fields of view are randomly selected for each sample for microstructure observation.

3. The method for rapid determination of creep stage of 27Cr44Ni5W3Al+ microalloyed furnace tube at 1050℃ service temperature according to claim 1 or 2, characterized in that, Image Pro Plus 6.0 software is used to perform microstructure analysis on microstructure photos, and the measurement data is the arithmetic mean of the measurement data of all fields of view.

4. The method for rapid determination of creep stage of 27Cr44Ni5W3Al+ microalloyed furnace tube at 1050℃ service temperature according to claim 3, characterized in that, Image Pro Plus 6.0 software is used to analyze microstructure photos, when selecting regions, 10 is selected for range, 3 is selected for thresh, 1 is selected for smooth, and 2 is selected for speed.

5. The method for rapid determination of creep stage of 27Cr44Ni5W3Al+ microalloyed furnace tube at 1050℃ service temperature according to claim 3, characterized in that, Austenitic grain boundary precipitates include M 23 C6 type carbides, M7C3 type carbides and Ni3Al phase precipitates.

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