Method for predicting residual life of furnace tube of carburized ethylene cracking furnace based on small punching sampling

Abstract

The invention provides a carburized ethylene cracking furnace tube residual life prediction method based on small punched hole outer surface sampling. The method comprises the following steps: sampling the outer surface of an in-service ethylene cracking furnace tube by using a small punched hole sampling machine; performing a small-punching high-temperature creep test on the sample; carrying out equivalent stress conversion based on a creep test result; establishing an outer surface residual life prediction equation; calculating furnace tube stress and substituting the furnace tube stress into the prediction equation to obtain outer surface residual life; performing carburization-creep finite element simulation on the furnace tube of the ethylene cracking furnace; obtaining a furnace tube damage distribution condition of a finite element test result; and the overall residual life prediction is completed through the outer surface residual life and the damage distribution relationship. According to the method, furnace tube interruption or production halt is avoided, time and cost are saved, residual life prediction is carried out based on actual sampling and finite element data analysis, and the method has high reliability and accuracy and is used for early warning and maintenance decision making in advance, prolonging the service life of equipment and avoiding resource waste and accidents.

Description

Technical Field

[0001] The invention relates to a method for predicting the remaining life of a cracking furnace tube, and in particular to a method for predicting the remaining life of a carburized ethylene cracking furnace tube based on small punching sampling. Background Art

[0002] The tube of the ethylene cracking furnace is one of the important components of the petrochemical plant. The tube must be resistant to high temperatures and have good heat transfer performance. The design life of the radiation section tube is usually 100,000 hours. However, since the outer surface of the tube is in a high-temperature radiation environment close to 1000°C for a long time, the inner surface of the tube needs to transfer heat with the cracking material with high carbon potential and low oxygen pressure. Therefore, the inner surface is prone to carburization, thermal fatigue, creep and other damages, resulting in the overall actual service time of the ethylene cracking furnace tube being less than the design life. When the tube of the cracking furnace is broken or blocked, it will affect the normal operation of the cracking furnace, and have a great impact on the work of the cracking furnace, overhaul, production load arrangement, etc., resulting in unplanned shutdown, huge economic losses and safety accidents. Therefore, it is crucial for maintenance and safety management to accurately assess the remaining life of the tube, so as to provide early warning and support for maintenance decisions.

[0003] A method for predicting the remaining life of a service component based on a small punching creep technology, with publication number CN110967213A, discloses the following steps: first, using a micro-damage sampling device to dig a hemispherical test material from a service pipe, then using a wire cutting device to cut and sample from the upper surface of the test material, preparing a circular thin slice sample, grinding and polishing it, and then testing the sample according to the GB / T 29459.2-2012 test standard to obtain a small punching creep test center flexural deformation-time curve, fitting the test data to draw a Larson-Miller life prediction diagram, and reading the remaining life under different load conditions. Although compared with the traditional sampling method, the damage to the equipment caused by digging materials through small punching holes is less, if only the outer surface of the furnace tube is sampled to avoid delaying the work of the service component, due to the large difference in the remaining life of the inner and outer surfaces of the ethylene cracking furnace, this method is not applicable to the present application, and the result of the overall remaining life obtained in the end will be inaccurate.

[0004] For in-service equipment such as the radiant section tubes of ethylene cracking furnaces, conventional creep sampling will cause damage to the equipment. In addition, the radiant section tubes of ethylene cracking furnaces have high carbon potential and low oxygen pressure inside, and are subjected to high temperature heat radiation outside the tubes, resulting in differences in the degree of damage to the inner and outer surfaces. Therefore, it is urgent to develop and establish micro-damage sampling technology and remaining life prediction methods for ethylene cracking furnace tubes, which has important economic significance and engineering application value for improving the level of major equipment in the ethylene industry and ensuring its safety and reliability. Summary of the invention

[0005] In view of the above-mentioned defects of the existing remaining life prediction method, the present invention is proposed.

[0006] Therefore, the object of the present invention is to provide a method for predicting the remaining life of a carburized ethylene cracking furnace tube based on small punching sampling, by sampling the outer surface of the in-service carburized ethylene cracking furnace tube and obtaining the outer surface remaining life t r外 , and then through finite element simulation, the damage distribution relationship of the furnace tube is obtained to predict the overall remaining life of the furnace tube.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for predicting the remaining life of a carburized ethylene cracking furnace tube based on small punching sampling, the method comprising:

[0008] S1: Use a small punching sampler to sample the outer surface of the in-service carburized ethylene cracking furnace tube to obtain the remaining life t of the outer surface of the carburized ethylene cracking furnace tube r外 ;

[0009] S2: Carburizing-creep finite element simulation was performed on the carburizing ethylene cracking furnace tube in service, and the carburizing-creep damage constitutive equation was:

[0010]

[0011] Where: D1 is the creep damage variable, D2 is the carburizing damage variable, is the creep strain tensor, σ e is the Von-Mises stress, σ1 is the maximum principal stress, where σ1 is the finite element parameter, R1 is the inner radius of the furnace tube, and k c is the carburizing rate constant, t is the finite element simulation time, d cr is the critical value of carburizing damage, B, n, A, υ are material constants related to the minimum creep strain rate and creep rupture, φ is the damage constant, and α is the material constant;

[0012] According to the above constitutive equation, a subroutine suitable for Abaqus simulation software is written, and the corresponding parameter values ​​are entered. The parameter values ​​are the corresponding parameters in the above equation. After writing, it is connected to the finite element software. According to the actual working conditions of the sample to be tested, the simulated temperature and internal pressure are set, and the finite element test is carried out.

[0013] S3: Obtain damage distribution of the finite element test results of step S2;

[0014] S4: The remaining life value t of the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace obtained based on the step S1 r外 The damage distribution obtained in step S3 is used to estimate the remaining life t of the entire furnace tube of the in-service carburized ethylene cracking furnace. r整 Calculate, t r整The specific calculation formula is:

[0015] t r整 =t r内 =r*t r外

[0016] In the formula, t r整 is the overall remaining life of the in-service carburized ethylene cracking furnace tubes, t r内 is the remaining life of the inner surface of the furnace tube, t r外 is the remaining life of the outer surface of the furnace tube, r is the ratio of the outer surface of the furnace tube to the most severely damaged area in the finite element simulation in step S7, and is specifically calculated as r=1 / [(1-outer surface damage ratio) / (1-inner surface damage ratio)].

[0017] Among them, in step S1, the remaining life t of the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace is calculated. r外 The specific steps are:

[0018] S11: Use a small punching sampler to sample the outer surface of the furnace tube of the in-service carburizing ethylene cracking furnace. The small punching sampler obtains hemispherical samples of different sizes required for the test by replacing the blade. The hemispherical samples are then cut and ground to obtain samples with thickness that meets the specification requirements. Specifically, the hemispherical samples are cut with a diameter of 10mm or 8mm after wire cutting, and the thickness of the samples after grinding ranges from 0.3mm to 0.5mm.

[0019] S12: performing a small punching high temperature creep test on the sample obtained in step S11 to obtain a displacement-time curve diagram of the sample under different loads;

[0020] S13: Perform equivalent stress conversion based on the small punching creep test results of step S12 to obtain equivalent stress values ​​σ corresponding to different loads i ;

[0021] S14: Establishing the remaining life prediction equation of the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace, based on step S12, obtaining the fracture time t of the sample under different load conditions through the displacement-time curve diagram ri , t ri Substituting into the remaining life prediction equation, the Larson-Miller parameter P(σ i ) value, the Larson-Miller parameter P(σ i ) value and the equivalent stress value σ corresponding to the different loads obtained in step S13 i Perform linear fitting and obtain P(σ i ) and σ i The fitting relationship of

[0022] The remaining life prediction equation of the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace is as follows:

[0023] P(σ i )=10 -3 T(C+logt ri )

[0024] In the formula, P(σ i ) is the Larson-Miller parameter corresponding to different loads, σ i is the equivalent stress value corresponding to different loads, T is the temperature, C is the material constant, t ri is the remaining life corresponding to different loads, and i is the test number.

[0025] P(σ i ) and σ i The specific fitting steps are: the Larson-Miller parameters P(σ i ) and equivalent stress value σ i Perform scatter plot and use fitting software to perform linear fitting to obtain P(σ i ) and σ i The fitting relationship of .

[0026] S15: Calculation of stress σ in the tubes of an in-service carburized ethylene cracking furnace 炉 Substitute the remaining life prediction equation established in step S14 and P(σ i ) and σ i The remaining life t of the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace is obtained from the fitting relationship of r外 .

[0027] Specifically, the furnace tube stress σ 炉 The calculation formula is:

[0028]

[0029] Wherein, p is the working pressure of the furnace tube of the in-service carburized ethylene cracking furnace, D is the outer diameter of the furnace tube, and δ is the thickness of the furnace tube wall. In this example, p is taken as 0.43 MPa, D is taken as 68 mm, and δ is taken as 6 mm.

[0030] The present invention firstly samples the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace by a small punching sampling machine, performs a small punching high-temperature creep test on the sample, and converts the data obtained in the test into equivalent stress, establishes a residual life prediction equation for the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace, and converts the residual life t corresponding to different loads obtained in the test into equivalent stress. ri Substituting into the external surface remaining life prediction equation, the Larson-Miller parameter P(σ i ), P(σi ) and σ i Perform linear fitting and obtain the fitting relationship to calculate the furnace tube stress σ 炉 Substitute it into the outer surface remaining life prediction equation and fitting relationship to calculate the outer surface remaining life t r外 Then, the carburizing-creep finite element simulation is carried out on the carburizing ethylene cracking furnace tube, and the damage distribution is obtained. Finally, according to the damage distribution and t r外 Value, through the formula t r整 =t r内 =r*t r外 Calculation of the remaining life t of the entire furnace tube of the in-service carburized ethylene cracking furnace r整 .

[0031] Beneficial effects of the present invention:

[0032] 1. The present invention only needs to sample the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace to estimate the remaining life of the furnace tube, which is less destructive. Compared with the traditional method, the sampling step is not destructive to the furnace tube, and the step operation is simple, avoiding the interruption or shutdown of the furnace tube, saving time, and reducing the economic loss caused by the interruption of production work of the furnace tube.

[0033] 2. The present invention predicts the remaining life of the entire furnace tube of the in-service carburized ethylene cracking furnace based on actual sampling and finite element data analysis, which has high reliability and accuracy.

[0034] 3. The remaining life prediction of the furnace tubes of the in-service carburized ethylene cracking furnace based on this method can be used for early warning and provide support for maintenance decisions. It can determine when to repair or replace the furnace tubes, maximize the service life and reliability of the equipment, and avoid the waste of resources and possible accidents and losses caused by conventional fixed-cycle maintenance plans. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The present invention is a flow chart of a method for predicting the remaining life of a furnace tube of a carburized ethylene cracking furnace in service according to an embodiment of the present invention.

[0036] Figure 2 This is a creep result diagram based on sampling of the outer surface of a small punch hole according to an embodiment of the present invention.

[0037] Figure 3 This is a fitting curve diagram of the Larson-Miller method of an embodiment of the present invention.

[0038] Figure 4 This is a schematic diagram of carburizing-creep finite element damage in an embodiment of the present invention.

[0039] Figure 5 1 is a metallographic diagram of a carburizing furnace tube according to an embodiment of the present invention. DETAILED DESCRIPTION

[0040] This embodiment uses the inlet section furnace tube of the radiation section of the ethylene cracking furnace in service for about 4 years. The material is 25Cr35NiNb, the normal operating temperature is about 1000°C, and the maximum can reach 1050°C. The size is Φ68×6mm and the internal pressure is 0.43MPa.

[0041] like Figure 1 As shown, this embodiment provides a method for predicting the remaining life of a carburized ethylene cracking furnace tube based on small punching sampling. First, a small punching sampler is used to sample the outer surface of an in-service carburized ethylene cracking furnace tube, and a small punching high-temperature creep test is performed on the sample. Based on the small punching creep test results, equivalent stress conversion is performed, and then an outer surface remaining life prediction equation is established. The tube stress is calculated and substituted into the outer surface remaining life prediction equation to obtain the remaining life of the outer surface. The entire ethylene carburized cracking furnace tube is subjected to carburizing-creep finite element simulation to obtain the tube damage distribution relationship of the finite element test results. Finally, the overall remaining life prediction is completed through the remaining life of the outer surface and the tube damage distribution relationship.

[0042] The specific steps of this embodiment are as follows:

[0043] S1: Use a small punching sampler to sample the outer surface of the in-service carburized ethylene cracking furnace tube to obtain the remaining life t of the outer surface of the in-service carburized ethylene cracking furnace tube. r外 , the specific steps are as follows:

[0044] Step S11: Use a small punching sampler to sample the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace to obtain a hemispherical sample, and obtain a sample with a thickness that meets the specification requirements through cutting and grinding. The specific thickness specification requirements are: the diameter of the hemispherical sample after wire cutting is 10mm or 8mm, and the thickness of the sample after grinding is in the range of 0.3mm-0.5mm.

[0045] The outer surface of the furnace tube was sampled using a small punching sampler blade with a diameter of 26 mm and a sampling depth of 2 mm to obtain a hemispherical sample. Circular slices with a diameter of 10 mm and a thickness of 0.5 mm were obtained by wire cutting, and a small punching creep test sample with a thickness of 0.4 mm was obtained by grinding.

[0046] Step S12: Perform a small punching high temperature creep test on the sample obtained in step S11.

[0047] Set the test temperature and load, and conduct creep tests according to the test machine and relevant requirements of standard GB / T 29459.2-2012. Figure 2 Displacement-time curves of the specimen under different loads.

[0048] Step S13: Perform equivalent stress conversion based on the small punching creep test results of step S12 to obtain equivalent stress values ​​σ corresponding to different loads i .

[0049] Figure 2 In the figure, different curves are displacement curves obtained under different small punching loads, and the final fracture displacement h corresponding to different loads is i The equivalent stress value σ corresponding to different loads is required i Related, formula (1) represents F i / σ i With h i Is relevant.

[0050] F i / σ i =f(h i ) (1)

[0051] In the formula, σ i is the equivalent stress value corresponding to different loads (MPa), F i is the small punching test load (N), h i is the final fracture displacement corresponding to different loads at the center of the specimen (mm), f(h i ) is about h i function, i is the test number.

[0052] In this test, the radius of the receiving hole of the small punching die is 2 mm, and the punch diameter is 1.25 mm. According to the research conducted by CEN, under this test condition, f(h i ) The specific function is 1.72476h i -0.05638h i 2 -0.17688h i 3 , we get formula (2), and use formula (2) to calculate the equivalent stress value σ corresponding to different loads i , the equivalent stress value σ corresponding to different loads after conversion i See Table 1.

[0053] F i / σ i =1.72476h i -0.05638h i 2 -0.17688h i 3 (2)

[0054] In the formula, σ i is the equivalent stress value corresponding to different loads (MPa), F i is the small punching test load (N), hi is the final fracture displacement (mm) corresponding to different loads at the center of the specimen, and i is the test number.

[0055] The CEN mentioned above is specifically the European Committee for Standardization. The source of the research literature published by CEN is: Arunkumar, S. "Small punch creep test: an overview." Metals and Materials International 27(2021): 1897-1914.

[0056] Table 1

[0057]

[0058] Step S14: Based on step S12, the fracture time t of the sample under different load conditions is obtained through the displacement-time curve diagram. ri As shown in Table 2, the remaining life prediction equation of the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace is established, specifically, Formula 3, where t ri Substituting into equation 3, we can obtain the Larson-Miller parameter P(σ i ) values, as shown in Table 2, the Larson-Miller parameter P(σ i ) value and step S13 to obtain the equivalent stress value σ corresponding to different loads i Perform linear fitting and obtain P(σ i ) and σ i The fitting relationship of .

[0059] The life prediction equation adopts the Larson-Miller method, and the specific calculation formula is:

[0060] P(σ i )=10 -3 T(C+logt ri ) (3)

[0061] In the formula, P(σ i ) is the Larson-Miller parameter corresponding to different loads, σ i is the stress value corresponding to different loads, T is the temperature K, C is the material constant, t ri is the remaining life (h) corresponding to different loads, i is the test number;

[0062] In step S12 Figure 2 The curve diagram shown in Figure 2 shows the fracture time t under different small punching loads. ri According to the information provided by the furnace tube manufacturer, the C value is 23, and the creep test temperature T and the σ corresponding to different small punching loads arei Substituting the value into formula (3), we can get the Larson-Miller parameter P(σ) corresponding to different small punching loads in Table 2. i )value.

[0063] Table 2

[0064]

[0065] The above table 1 i and P(σ i ) are scatter plotted, with the horizontal axis being P(σ i ) value, the ordinate is σ i The value of P(σ i ) and σ i The fitting relationship (4) is: Figure 3 It is the fitting diagram.

[0066] σ i =-8.65876P(σ i )+320.71739 (4)

[0067] In the formula, σ i is the equivalent stress value corresponding to different small punching loads, P(σ i ) is the Larson-Miller parameter corresponding to different small punching loads.

[0068] Step S15: Calculate the stress σ of the furnace tube of the in-service carburized ethylene cracking furnace 炉 Substitute into the outer surface remaining life prediction equation in step S14 and P(σ i ) and σ i The remaining life t of the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace is obtained from the fitting relationship of r外 .

[0069] The remaining life t is obtained by converting and integrating formula (3) and formula (4) ri and σ i The specific relational expression is:

[0070] logt ri =1000*(σ i -320.71739) / (-8.65876*T)-C (5)

[0071] According to the furnace tube stress calculation formula (6), the furnace tube stress σ is calculated 炉 It is 2.22MPa.

[0072]

[0073] Wherein, p is the working pressure of the furnace tube of the in-service carburized ethylene cracking furnace, D is the outer diameter of the furnace tube, and δ is the thickness of the furnace tube wall. In this example, p=0.43MPa, D=68mm, and δ=6mm.

[0074] σ 炉 Substitute the value of into formula (5). In this embodiment, according to the information provided by the furnace tube manufacturer, C is taken as 23, the predicted temperature T is 1050°C, and the remaining life t of the outer surface is calculated. r外 It is 63061h.

[0075] The present invention can calculate the remaining life of the furnace tube by sampling the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace in the above manner, which is less destructive. Compared with the traditional method, the sampling step is not destructive to the furnace tube, and the step operation is simple, avoiding the interruption or shutdown of the furnace tube, saving time, and reducing the economic loss caused by the interruption of production work of the furnace tube.

[0076] Step S2: Carburizing-creep finite element simulation is performed on the furnace tubes of the in-service carburizing ethylene cracking furnace.

[0077] In this embodiment, finite element software is used to perform carburizing-creep finite element simulation on the carburizing ethylene cracking furnace tube, and the carburizing-creep damage constitutive equation is:

[0078]

[0079] Where: D1 is the creep damage variable, D2 is the carburizing damage variable, is the creep strain tensor, σ e is the Von-Mises stress (MPa), σ1 is the maximum principal stress (MPa), where σ1 is the finite element parameter and the small punching test parameter σ i Different, R i is the inner radius of the furnace tube (mm), kc is the carburizing rate constant, t is the finite element simulation time (h), d cr is the critical value of carburizing damage, B, n, A, υ are material constants related to the minimum creep strain rate and creep rupture, φ is the damage constant, and α is the material constant.

[0080] According to the above constitutive equation, a subroutine suitable for Abaqus simulation software is written, and the corresponding parameter values ​​are input. The parameter values ​​are some performance parameters of the material under the current working conditions in this embodiment. The parameters defined by the subroutine are shown in Table 3. After writing, the finite element software is connected. According to the actual working conditions of the cracking furnace tube in this embodiment, the simulation temperature is set to 1050°C and the internal pressure is set to 0.43MPa. In Table 3, B, n, A, υ are material constants related to the minimum creep strain rate and creep rupture, φ is the damage constant, and α is the material constant.

[0081] Table 3

[0082]

[0083] Step S3: Obtain damage distribution of the finite element test results of step S2.

[0084] A large number of studies have shown that the damage to the furnace tube is particularly serious on the inner and outer surfaces. According to the finite element test in step S2, Figure 4 A schematic diagram of the carburization-creep finite element inner and outer surface damage is shown in the figure. As shown in the figure, the abscissa is the percentage of the life value, and the ordinate is the percentage of the damage degree. The cracking furnace tube in this embodiment has a designed service life of 10 years and has been in service for 4 years. The corresponding abscissa value is 0.4, and the read ordinate values ​​are 0.316 and 0.096 respectively. Therefore, it can be seen that under normal operating conditions obtained by finite element simulation, the damage proportions of the inner and outer surfaces of the furnace tube that has been in service for 4 years are 0.316 and 0.096.

[0085] Step S4: The remaining life value t of the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace obtained in step S1 r外 The remaining life prediction of the entire furnace tube of the in-service carburized ethylene cracking furnace is completed based on the damage distribution of step S3. r整 .

[0086] From step S3, it can be seen that the inner surface is the most seriously damaged, so the remaining life of the inner surface is t r内 That is, the overall remaining life t r整 , t r内 It can be calculated based on the damage ratio, using formula (10) r整 =t r内 =C*t r外 The specific calculation steps are as follows:

[0087] t r整 =t r内 =C*t r外 =1 / [(1-0.096) / (1-0.316)]*63061=1 / 1.322*63061=47701h, and the overall remaining life t is obtained by calculation r整 It is 47701h.

[0088] In the formula, t r整 is the overall remaining life of the in-service carburized ethylene cracking furnace tubes, t r内 is the remaining life of the inner surface of the furnace tube, t r外 is the remaining life of the outer surface of the furnace tube, r is the ratio of the outer surface of the furnace tube to the most severely damaged area in the finite element simulation in step S7, and is specifically calculated as r=1 / [(1-outer surface damage ratio) / (1-inner surface damage ratio)].

[0089] The remaining life of the furnace tube is judged by the metallographic rating method. The degree of damage is divided into five levels. The methods for judging the degree of damage at each level are as follows:

[0090] (I) Primary carbides precipitate along the grain boundaries, secondary carbides are dispersed in the austenite matrix and tend to aggregate near the grain boundaries. The life span is within 20%.

[0091] (II) Primary carbides are connected, with few agglomerates, while secondary carbides are no longer dispersed but are clearly agglomerated inside the grains. The lifetime is about 20-40%.

[0092] (III) A series of cavities are found along the grain boundaries. Few cavities form microcracks. The primary carbides are connected in blocks, while the secondary carbides are completely dissolved. The lifespan reaches 40-60%.

[0093] (IV) Some cavities are connected to form microcracks. Some microcracks are related to cracks caused by carburization on the inner surface. The total crack portion accounts for 1 / 3–1 / 2 of the tube thickness. The consumption life is about 60-75%.

[0094] (V) Microcracks connect to form large cracks that extend toward the outer surface. The crack length is about 2 / 3 of the thickness. The furnace tube fails.

[0095] In this example, the metallographic structure of the furnace tube is as follows Figure 5 As shown; the microstructure is coarse chain carbides, and the secondary carbides in the crystal begin to aggregate from the dispersed state to form blocks, corresponding to the damage level of level III, and the service life accounts for 40%-60% of the total life, which is consistent with the remaining life obtained by the present invention, indicating the correctness and reliability of the present invention.

Claims

1. A method for predicting the remaining life of a carburized ethylene cracking furnace tube based on small punching sampling, characterized in that: The life prediction method comprises: S1: Use a small punching sampler to sample the outer surface of the in-service carburized ethylene cracking furnace tube to obtain the remaining life t of the outer surface of the in-service carburized ethylene cracking furnace tube. r外 ; S2: Carburizing-creep finite element simulation of the carburizing ethylene cracking furnace tube in service; S3: Obtain damage distribution of the finite element test results of step S2; S4: The remaining life value t of the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace obtained based on the step S1 r外 The damage distribution obtained in step S3 is used to estimate the remaining life t of the entire furnace tube of the in-service carburized ethylene cracking furnace. r整 Calculate, t r整 The specific calculation formula is: t r整 =t r内 =r*t r外 In the formula, t r整 is the overall remaining life of the in-service carburized ethylene cracking furnace tubes, t r内 is the remaining life of the inner surface of the furnace tube, t r外 is the remaining life of the outer surface of the furnace tube, r is the ratio of the outer surface of the furnace tube to the most severely damaged area in the finite element simulation in step S7, and is specifically calculated as r=1 / [(1-outer surface damage ratio) / (1-inner surface damage ratio)].

2. The method for predicting the remaining life of a carburized ethylene cracking furnace tube based on small punching sampling according to claim 1, characterized in that: In step S1, calculate the remaining life t of the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace r外 The specific steps are: S11: Use a small punching sampler to sample the outer surface of the tube of the in-service ethylene cracking furnace; S12: performing a small punching high temperature creep test on the sample obtained in step S11 to obtain a displacement-time curve diagram of the sample under different loads; S13: Perform equivalent stress conversion based on the small punching creep test results of step S12 to obtain equivalent stress values ​​σ corresponding to different loads i ; S14: Establishing the remaining life prediction equation of the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace, based on step S12, obtaining the fracture time t of the sample under different load conditions through the displacement-time curve diagram ri , t ri Substituting into the remaining life prediction equation, the Larson-Miller parameter P(σ i ) value, the Larson-Miller parameter P(σ i ) value and the equivalent stress value σ corresponding to the different loads obtained in step S13 i Perform linear fitting and obtain P(σ i ) and σ i The fitting relationship of S15: Calculation of stress σ in the tubes of an in-service carburized ethylene cracking furnace 炉 Substitute the remaining life prediction equation established in step S14 and P(σ i ) and σ i The remaining life t of the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace is obtained from the fitting relationship of r外 .

3. The method for predicting the remaining life of a carburized ethylene cracking furnace tube based on small punching sampling according to claim 2, characterized in that: In step S11, the small punching sampling machine obtains hemispherical specimens of different sizes and specifications required for the test by replacing the blades, and the hemispherical specimens are then cut and ground to obtain specimens with thicknesses that meet the specification requirements.

4. The method for predicting the remaining life of a carburized ethylene cracking furnace tube based on small punching sampling according to claim 2, characterized in that: In step S11, the diameter of the hemispherical sample after wire cutting is 10 mm or 8 mm, and the thickness of the sample after grinding is in the range of 0.3 mm-0.5 mm.

5. The method for predicting the remaining life of a carburized ethylene cracking furnace tube based on small punching sampling according to claim 2, characterized in that: In step S14, the remaining life prediction equation of the outer surface of the furnace tube of the in-service carburized ethylene cracking furnace is specifically: P(σ i )=10 -3 T(C+logt ri ) In the formula, P(σ i ) is the Larson-Miller parameter corresponding to different loads, σ i is the equivalent stress value corresponding to different loads, T is the temperature, C is the material constant, t ri is the remaining life corresponding to different loads, and i is the test number.

6. The method for predicting the remaining life of a carburized ethylene cracking furnace tube based on small punching sampling according to claim 2, characterized in that: In step S14, P(σ i ) and σ i The specific fitting steps are: the Larson-Miller parameters P(σ i ) and equivalent stress value σ i Perform scatter plot and use fitting software to perform linear fitting to obtain P(σ i ) and σ i The fitting relationship of .

7. The method for predicting the remaining life of a carburized ethylene cracking furnace tube based on small punching sampling according to claim 2, characterized in that: The furnace tube stress σ in step S15 炉 The calculation formula is: Wherein, p is the working pressure of the furnace tube of the in-service carburized ethylene cracking furnace, D is the outer diameter of the furnace tube, and δ is the thickness of the furnace tube wall. In this example, p=0.43MPa, D=68mm, and δ=6mm.

8. The method for predicting the remaining life of a carburized ethylene cracking furnace tube based on small punching sampling according to claim 1, characterized in that: In step S2, finite element software is used to perform carburizing-creep finite element simulation on the carburizing ethylene cracking furnace tube, and the carburizing-creep damage constitutive equation is: Where: D1 is the creep damage variable, D2 is the carburizing damage variable, is the creep strain tensor, σ e is the Von-Mises stress, σ1 is the maximum principal stress, where σ1 is the finite element parameter, R1 is the inner radius of the furnace tube, and k c is the carburizing rate constant, t is the finite element simulation time, d cr is the critical value of carburizing damage, B, n, A, υ are material constants related to the minimum creep strain rate and creep rupture, φ is the damage constant, and α is the material constant; According to the above constitutive equation, a subroutine suitable for Abaqus simulation software is written, and the corresponding parameter values ​​are entered. The parameter values ​​are the corresponding parameters in the above equation. After writing, it is connected to the finite element software. According to the actual working conditions of the sample to be tested, the simulated temperature and internal pressure are set, and the finite element test is carried out.

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