Method and system for predicting creep life of high-temperature component under complex working condition

Abstract

The invention discloses a method and a system for predicting creep life of a high-temperature component under a complex working condition. According to the method, the performance degradation behavior caused by corrosion, oxidation and creep of the high-temperature part under the complex working conditions of deep peak regulation, rapid load change and the like of the power station boiler is researched through a method of combining theoretical analysis, simulation calculation, experimental characterization and data processing, and a three-dimensional geometric model and a multi-physical field model of the high-temperature part are constructed. The method comprises the following steps: calculating the temperature distribution of a high-temperature heat-resistant material under thermal and cold cycling, carrying out mechanical analysis on a model according to the obtained temperature distribution, calculating a stress field generated in the thermal and cold cycling process, obtaining parameters related to a Marson-Miller creep model, deducing a Marson-Miller service life prediction model of the high-temperature heat-resistant material, and evaluating the creep service life of the high-temperature heat-resistant material in combination with the creep service life evaluation under the actual pipe wall thinning rate. The creep life of the high-temperature part under the combined action of steam-flue gas side corrosion and oxidation is predicted; and a more accurate life evaluation scheme with a wider application range can be provided.

Description

Technical Field

[0001] This invention belongs to the field of component life prediction technology, specifically relating to a method and system for predicting the creep life of high-temperature components under complex working conditions. Background Technology

[0002] Currently, my country has over 3,000 coal-fired power generating units, of which more than 800 are supercritical or higher, and 43% of these units have been in service for over ten years, a proportion that is increasing annually. Many subcritical and higher-level power plant boilers that have been in service for over ten years frequently experience unplanned shutdowns due to creep, corrosion, and oxidation in their high-temperature pressure-bearing components, leading to pipe blockages, ruptures, and cracks. These incidents severely hinder the long-term, safe, and efficient operation of thermal power generating units, thus constraining the healthy and stable development of the national economy. Although existing research has focused on single or combined failure mechanisms such as header creep, damage to heat-resistant steel welded joints, and corrosion and oxidation at high temperatures, research on the quantitative assessment of combined damage to long-serving pressure-bearing components, heat-resistant steel, and welded joints remains relatively scarce, and a systematic and rapid life assessment technology has not yet been established. In the context of deep peak shaving in boilers, high-temperature heating surfaces are subject to deterioration factors such as overheating, corrosion, oxidation, and creep, resulting in thinning, deformation, cracking, and even pipe rupture accidents.

[0003] The harsh working environment makes wear and explosion prevention of high-temperature heating surfaces in boilers particularly important, but currently there are no quantitative methods for analysis and prediction. For power plant boilers operating under complex conditions such as deep peak shaving and rapid load fluctuations, the damage mechanisms and life assessment technologies for key high-temperature components (such as main steam pipes, water-cooled walls, and superheaters) subjected to corrosion, oxidation, creep, and their superimposed effects require a comprehensive research approach integrating theoretical analysis, numerical simulation, laboratory experiments, and field testing. A deeper understanding is still needed of the performance degradation phenomena of these high-temperature components under the aforementioned complex operating conditions caused by the combined effects of multiple damage factors, especially the interaction between corrosion and oxidation in high-temperature components, the thermodynamic coupling effect of oxide films in superheaters and reheaters, and the creep composite damage mechanism of high-temperature pipes.

[0004] Patent CN116050228A discloses a creep life prediction method for welded joints of P92 main steam pipelines. This method, based on graded microstructure technology, uses data collection and graded microstructure analysis, combined with finite element analysis to obtain the maximum principal stress, and constructs a creep life prediction model. It considers the evolution of microstructure and creep pores to accurately predict the creep life of P92 steel welded joints. The method emphasizes incorporating the reduction in creep life caused by microstructure deterioration into the life assessment of P92 steel welded joints, thereby improving the accuracy of creep life prediction. Patent CN115712984A discloses a method for assessing the remaining life of boiler heating surface tubes. It adopts an assessment method based on the interaction between corrosion thinning and creep damage. By determining the equivalent calculation temperature, calculation pressure, Larson-Miller parametric equation, and corrosion thinning rate of the tube wall, the service life of the new tube is calculated and subtracted from the cumulative service time to obtain the remaining life. However, it does not comprehensively consider the coupling of multiple physical fields to obtain a more accurate temperature field and stress field, and uses a simplified calculation method, mainly based on empirical formulas and theoretical calculations. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for predicting the creep life of high-temperature components under complex operating conditions. Based on the complex damage mechanism of key high-temperature components under complex operating conditions such as deep peak shaving and rapid load change, a life assessment technology for high-temperature components considering complex damage such as corrosion, oxidation, and creep is established, providing support for the safe and flexible operation of power plant boilers.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a method for predicting the creep life of high-temperature components under complex operating conditions, which includes the following steps: Construct a three-dimensional high-temperature component model of a power plant boiler; The three-dimensional high-temperature component model is imported into the fluid calculation software. The physical parameters, boundary conditions and assumptions of the finite element simulation are configured according to the actual working conditions. The convective heat transfer fluid-structure interaction model of the steam side and the flue gas side inside and outside the pipe is set up to construct a multi-physics field model that couples flow and heat transfer. Finite element simulation calculation is performed to obtain the temperature field distribution of the entire model field. Based on the temperature field distribution of the entire model obtained, solid mechanics analysis is performed on the model to obtain the stress-strain field distribution model of the pipeline under the fluid-structure interaction of flue gas outside the pipe and steam inside the pipe. Parameters related to the Larson-Miller creep model were obtained, and the data were fitted using data processing software to obtain the Larson-Miller life prediction model for heat-resistant materials. The creep life of high-temperature components is obtained by modifying the life prediction model of the heat-resistant material based on the pipe wall thinning rate.

[0007] Furthermore, the construction of a three-dimensional high-temperature component model for a power plant boiler includes: taking a section of pipe for three-dimensional modeling, forming a metal oxide film on the outside of the pipe, with the outer layer of the oxide film being rich in Fe oxides and the inner layer being a region rich in Fe-Cr oxides.

[0008] Furthermore, the boundary conditions for the finite element simulation include: inlet steam velocity, outlet steam pressure, steam flow rate, flue gas composition, flue gas temperature, and steam state parameters. The physical parameters include: density, thermal expansion coefficient, Poisson's ratio and elastic modulus, specific heat capacity, convective heat transfer coefficient between flue gas and metal pipe wall, internal thermal conductivity of heat-resistant steel, and convective heat transfer coefficient between high-temperature steam and metal pipe wall. Furthermore, the boundary conditions for the finite element simulation include: the assumptions include: the oxide film of the heat-resistant steel is considered to be linearly elastic and isotropic; Only thermal stress and mechanical stress caused by changes in steam pressure inside the pipe are considered, while the stress effect caused by oxide film growth is ignored. The oxide film bonded well to the metal substrate and to each oxide film layer, without considering contact thermal resistance, and the oxide film did not peel off. The model does not consider the variation of steam temperature along the length of the pipe; Under thermal and mechanical loads, the oxide film did not crack or peel off.

[0009] Furthermore, based on the obtained temperature field distribution of the entire three-dimensional high-temperature component model, solid mechanics analysis is performed on the three-dimensional high-temperature component model to obtain the stress-strain field distribution model of the pipeline under the fluid-structure interaction of flue gas outside the pipe and steam inside the pipe. This includes: importing the flue gas temperature and steam velocity inside the pipe into the simulation software to obtain the temperature field distribution of the heat exchanger pipeline; setting the thermal boundary conditions of the three-dimensional high-temperature component model in the fluid calculation module; calculating the temperature field of the three-dimensional high-temperature component model under the coupling of high-temperature flue gas and steam inside the pipe; importing the obtained temperature field results into the Transient Structural module and applying solid mechanics boundary conditions to calculate the stress field model of the pipeline under the flue gas-steam temperature field.

[0010] Furthermore, several creep specimens were prepared using high-temperature materials, and high-temperature creep tests were conducted to obtain parameters related to the Larson-Miller creep model.

[0011] Furthermore, the tube wall thinning rate was obtained using the following method: Several creep specimens were prepared from commonly used boiler component materials. Several sets of temperature conditions were set to conduct high-temperature creep tests and obtain the corresponding temperature, stress and crack initiation time curves. Based on the basic form of the Larson-Miller parametric equation, the stress, temperature and cracking time obtained from the high-temperature creep cracking test are fitted to obtain the values ​​of unknown parameters in the Larson-Miller equation for different materials, and the Larson-Miller lifetime prediction model for different heat-resistant materials is derived. Several metal plate samples were prepared using commonly used boiler component materials. The metal plate samples were subjected to corrosion and oxidation tests under high-temperature flue gas and high-temperature steam conditions. The samples that had completed their service were characterized microscopically, and the thickness of the oxide film on the flue gas side and the steam side and the thinning rate of the metal material were measured.

[0012] Furthermore, by modifying the lifetime prediction model of the heat-resistant material based on the pipe wall thinning rate, the following formula is obtained for calculating the creep lifetime of high-temperature components:

[0013] in, t r Let be the working life at the pipe wall thinning rate k, and n be the stress exponent. The lifetime is the one obtained from the Larson-Miller lifetime prediction model.

[0014] Furthermore, the formula for calculating the pipe wall thinning rate is as follows:

[0015] in, t op The time the pipe fitting has been in operation. W The initial thickness of the pipe wall. W f Given the current pipe wall thickness, k The rate at which the pipe wall thins.

[0016] In a second aspect, the present invention provides a creep life prediction system for high-temperature components under complex working conditions, including a model building module, a temperature field distribution calculation module, a stress-strain field distribution model building module, a model parameter calculation module, and a prediction module. The model building module is used to build three-dimensional high-temperature component models of power plant boilers; The temperature field distribution calculation module is used to import the three-dimensional high-temperature component model into the fluid calculation software, configure the physical parameters, boundary conditions and assumptions of the finite element simulation according to the actual working conditions, set the convective heat transfer fluid-structure interaction model of the steam side and flue gas side inside and outside the pipe, construct a multi-physics model that couples flow and heat transfer, and perform finite element simulation calculations to obtain the temperature field distribution of the entire model. The stress-strain field distribution model construction module performs solid mechanics analysis on the model based on the temperature field distribution of the entire model obtained, and obtains the stress-strain field distribution model of the pipeline under the fluid-structure interaction of flue gas outside the pipe and steam inside the pipe. The model parameter calculation module obtains parameters related to the Larson-Miller creep model, and uses data processing software to fit the data to obtain the Larson-Miller life prediction model for heat-resistant materials. The prediction module combines the pipe wall thinning rate to correct the lifespan obtained from the Larson-Miller lifespan prediction model for heat-resistant materials, thus obtaining the creep lifespan of high-temperature components.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: This invention numerically simulates the temperature distribution and stress-strain results of high-temperature components under a temperature field. High-temperature creep tests are conducted under specific temperature conditions, and corresponding temperature, stress, and cracking time curves are obtained. Based on the Larson-Miller parametric equations, the stress, temperature, and fracture time obtained from the high-temperature creep fracture tests are fitted using computational software to obtain Larson-Miller life prediction models for different materials. Considering the service conditions of different heat-resistant steels on the steam and flue gas sides, and taking into account the influence of corrosion / oxidation behavior on the material's creep life, the Larson-Miller life prediction model is modified by combining the creep life of high-temperature components obtained from the Larson-Miller life prediction model with the test results of heat-resistant materials under high-temperature steam and flue gas conditions. This modification is further enhanced by considering the wall thinning of high-temperature pressure-bearing components due to creep, flue gas-steam side corrosion, and oxidation. This helps to establish a more accurate and widely applicable life assessment model and structural integrity evaluation system. By considering the coupling effect of multiple factors, a high-temperature component life assessment technology considering combined damage such as corrosion, oxidation, and creep is established, providing effective support for the safe and flexible operation of power plant boilers. Attached Figure Description

[0018] To clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A flowchart for assessing the combined damage and lifespan of typical high-temperature components under complex operating conditions; Figure 2 The numerical model and mesh generation results of the pipeline in this invention; Figure 3 This is a radial temperature distribution cloud map of the cross-section of the pipe of the present invention; Figure 4 This is a cloud diagram showing the stress distribution of the oxide film at the interface between the present invention and the metal substrate; Figure 5 This is the stress distribution of the high-temperature component of the present invention at a certain moment during the coupled heat transfer process of flue gas and steam. Figure 6 This is a graph showing the discrete points and fitting curves of the Larson-Miller parametric equations for the heat-resistant material of this invention; Figure 7 The images show the electron microscope and energy dispersive spectroscopy (EDS) results of the oxide film on the sample after the corrosion test of the heat-resistant material according to this invention.

[0020] Figure 8 The images show the electron microscope and energy dispersive spectroscopy (EDS) results of the oxide film on the sample after the oxidation test of the heat-resistant material according to this invention.

[0021] Figure 9 The present invention incorporates fitting of component life curves considering the combined effects of creep, flue gas-steam side corrosion, and oxidation, based on pipe wall thinning. Detailed Implementation

[0022] To enhance the understanding of the present invention by those skilled in the art, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments mentioned represent only a portion of the examples of the invention, and not its entire scope. Based on these embodiments, all other embodiments that can be derived by those skilled in the art without inventive modification are considered to be within the scope of protection claimed by the present invention.

[0023] A method for predicting the creep life of high-temperature components under complex operating conditions is described below: (1) A three-dimensional calculation model was constructed for the high-temperature components of a power plant boiler.

[0024] (2) Import the high-temperature component model constructed in step (1) into the fluid calculation software. In the software, the physical parameters, boundary conditions, and necessary assumptions required for finite element simulation are configured according to the actual working conditions. Based on this, a convective heat transfer fluid-structure interaction model is set, which couples the convective heat transfer between the steam side and the flue gas side inside and outside the pipe. Subsequently, a multiphysics pipe model integrating flow and heat transfer characteristics is constructed, and finite element simulation is performed in the fluid calculation software to calculate the temperature field distribution inside the high-temperature component.

[0025] (3) Based on the temperature field distribution data obtained in step (2), an in-depth solid mechanics analysis was conducted on the model. The stress-strain field distribution of the high-temperature component under the fluid-structure interaction of flue gas and steam was obtained.

[0026] (4) To study the performance of the heat-resistant material, several creep specimens were prepared using high-temperature materials, and high-temperature creep tests were conducted. Parameters related to the Larson-Miller creep model were obtained through the tests, and the Larson-Miller parametric equation for the heat-resistant material was established. Furthermore, oxidation tests were conducted on the material in a high-temperature steam environment, and corrosion tests were performed in a high-temperature flue gas environment. The evolution law of the material's creep composite performance under high-temperature steam environment was summarized. Based on this, a thinning failure analysis was performed on the pipe wall, and the oxidation characteristics of the material were studied. Finally, a life assessment method for high-temperature components under the combined action of the flue gas and steam sides was derived.

[0027] (5) Based on the Larson-Miller equation for heat-resistant materials obtained in step (4), the test results of heat-resistant materials under high-temperature steam and flue gas conditions, and the life prediction formulas for high-temperature components under creep, flue gas-steam side corrosion and oxidation, a method for predicting the creep life of high-temperature components under complex working conditions is obtained.

[0028] You can also find the parameters related to the Larson-Miller creep model by consulting industry manuals.

[0029] The following is a detailed explanation of this application in conjunction with the accompanying drawings.

[0030] based on Figure 1 The flowchart of the method for predicting the creep life of high-temperature components under complex operating conditions is shown below. The specific implementation method is as follows: First, considering the load changes during actual boiler peak shaving, this invention focuses on typical high-temperature components of the boiler. The elemental composition of the selected heat-resistant materials is shown in Table 1. Based on the cross-sectional microscopic characterization data, the initial model is set with an outer Fe3O4 oxide film and an inner Fe-Cr oxide film of ferrite T91, both with a thickness of 100 μm. Before numerical simulation, the model is meshed, and the quality of the mesh determines the accuracy and cost of the calculation results, significantly impacting subsequent calculations. As an example, this invention divides the pipeline model into five different global mesh sizes: 0.002 m, 0.001 m, 0.0005 m, 0.0004 m, and 0.0003 m, corresponding to 1.89 million, 3.77 million, 5.02 million, 6.57 million, and 8.11 million meshes, respectively. Temperature is highly sensitive to changes in mesh size during the simulation; therefore, the radial temperature distribution along the pipeline at a steam temperature of 550°C is calculated to verify the influence of mesh size on the simulation. Calculation results show that when the global mesh size is 0.0003m, 0.0004m, and 0.0005m, the radial temperature distribution of the pipeline is stable and no longer fluctuates with the decrease of the mesh size, indicating that the simulation results tend to be stable. This also confirms that the global mesh size has no impact on the accuracy of the simulation results, indicating that the calculation results have high stability and repeatability under this mesh size. In the subsequent simulation calculations of this invention, a mesh model with a global mesh size of 0.0004m was selected. Under this condition, the high-temperature component model under the initial operating conditions was specifically divided into a total of 6,575,583 elements, generating 29,197,557 nodes. Based on the above assumptions and simplification methods, the local mesh refinement of the high-temperature component model and the oxide film thin layer is as follows. Figure 2 As shown.

[0031] Furthermore, considering the changes in steam and flue gas parameters during actual peak shaving of the unit, this invention selected four calculation conditions under different load conditions, as detailed in Table 2. The operating condition under full load is considered the initial operating condition. Since the lower limit of the boiler's deep peak shaving load is approximately 30%, this invention calculated the operating parameters of the unit under four operating conditions as it decreased from full load to within 30% during deep peak shaving. The assumptions for the multiphysics coupling model of the heat exchanger piping are as follows: The oxide film on heat-resistant steel is considered to be linearly elastic and isotropic; Only thermal stress and mechanical stress caused by changes in steam pressure inside the pipeline are considered, while the stress effect caused by oxide film growth is ignored. The oxide film bonded well to the metal substrate and to each oxide film layer, without considering contact thermal resistance, and the oxide film did not peel off. The model does not consider the variation of steam temperature along the length of the pipe; Under thermal and mechanical loads, the oxide film did not crack or peel off.

[0032] The temperature field model uses a thermal resistance-temperature difference model to calculate the steady-state temperature distribution of the pipe wall and oxide film. The applied heat load conditions correspond to the third type of boundary conditions, specifying the temperatures of steam and flue gas, and the convective heat transfer coefficients are calculated based on relevant parameters. The formula for calculating the thermal resistance is as follows: (1) Where R is the thermal resistance; h s and h g The heat transfer coefficients are for the steam side and the flue gas side. k ox and k met Let be the thermal conductivity of the oxide film and the pipe wall metal. D and d are the inner and outer diameters of the pipe, respectively.

[0033] Calculate the convective heat transfer coefficients of steam and flue gas. h s and h g The equation is as follows: (2) (3) The coefficient λ is 1. k s and k g Let be a constant; in this example, we take . k s and k g It is 0.0699.

[0034] This invention employs the finite volume method and utilizes the RNG k-ε model to consider different thermal characteristics, mass conservation equations, momentum conservation equations, and energy conservation equations during the heat transfer process.

[0035] The mass conservation equation is as follows: (4) The momentum conservation equation is as follows: (5) The energy conservation equation is as follows: (6) The turbulent kinetic energy k and its transport equations were examined using the RNG model, and convection coupling was performed on the three-dimensional model of the pipe and the high-temperature fluid. The turbulent transport equations are expressed as follows: (7) The transport equation for the turbulent kinetic energy dissipation rate ε is as follows: (8) Where ρ is the fluid density, u Indicates flow rate, p Indicates pressure, μ Indicates viscosity. C The constants representing the turbulence model, C p λ represents specific heat, and λ represents thermal conductivity. Indicates dynamic viscosity, σ k and σ ε Prandtl number represents the turbulent kinetic energy and turbulent dissipation rate, and τ represents the stress tensor. The steam within the pipe is modeled using a real gas-water medium from the NIST model. During calculations, relevant parameters from the NIST database can be accessed based on the temperature and pressure on the steam side. The upper end of the pipe is fixed, while the lower end is free to extend. The radial temperature distribution along the pipe cross-section under four operating conditions is shown below. Figure 3 As shown, under high load conditions, the temperature difference between the inner wall of the steam side and the outer wall of the flue gas side is 18K, while under low load conditions, the temperature difference between the two walls reaches 25K, indicating that the temperature difference between the two walls of the pipeline increases as the load decreases during the deep peak shaving process of the unit. A temperature step occurs at the inner and outer oxide films, and there is a large temperature gradient in the oxide film layer. Due to the uneven temperature distribution between the pipeline and the oxide film during the load change process, the temperature gradient generates alternating thermal stress.

[0036] Table 1. Elemental composition of the materials (wt%)

[0037] Table 2 Calculation parameters under different working conditions

[0038] Furthermore, based on the temperature field distribution, the data was imported into the TransientTemperature module (i.e., the transient thermal module) in the ANSYS Workbench simulation software, and solid constraints and thermal boundary conditions were applied to calculate the stress field model of the pipeline under the flue gas-steam temperature field. The relevant parameters affecting thermal stress and thermal deformation are shown in Table 3. When the ambient temperature deviates from the material's growth temperature, thermal stress is generated in the metal matrix and oxide film, calculated using the following formula: (9) in: E ox , a , ΔT, δ met and δ oxThese represent Young's modulus, coefficient of thermal expansion, Poisson's ratio, temperature change, metal thickness, and oxide film thickness, respectively. The thermal stress in the oxide film is affected not only by temperature deviation and the difference in the coefficients of thermal expansion between the oxide film and the metal, but also by the relative values ​​of the oxide film thickness and the metal thickness. Compared to the oxide film, the metal tube wall has a larger relative thickness, resulting in higher thermal stress.

[0039] Von Mises equivalent stress The calculation formula is as follows: (10) in: It is the Von Mises equivalent stress at node i; , , It is the principal stress (including tensile stress and compressive stress) at node i. Figure 4 This is the stress concentration region at the interface between the oxide film and the metal substrate. Figure 5 This is a stress distribution diagram of the entire heat exchanger piping. The stress is greatest on the high-temperature flue gas side, gradually decreasing towards the steam side, with significant stress occurring at the interface between the substrate and the oxide film.

[0040] Subsequently, several standard creep specimens of the heat-resistant material were prepared and creep rupture tests were conducted on a creep testing machine. The tests were carried out according to ASTM E139 standard under different stress and temperature combinations. The obtained parameter data related to the Larson-Miller creep model were used to fit and obtain the Larson-Miller parametric equation for the T91 heat-resistant material.

[0041] The specific steps involve preparing several creep standard specimens using the same material as T91 heat-resistant steel, conducting high-temperature creep tests, and obtaining several sets of stress, temperature, and crack initiation time data. Using Matlab software, the stress, temperature, and crack initiation time data obtained from the high-temperature creep tests are fitted, and the parameters of the Larson-Miller equation are solved based on the equation to obtain the Larson-Miller equation for the T91 material.

[0042] In this stage, high-temperature creep tests were conducted according to the "Methods for Tensile Creep and Duration Testing of Metals". Subsequently, Matlab software was used to process the stress, temperature, and fracture time data obtained from the tests to fit the parameters of the Larson-Miller equation. The following are the specific derivation steps of the Larson-Miller equation parameters: The Larson-Miller parametric method is applicable to creep life assessment of carbon steel and alloy steel heat-receiving surface pipes, pipelines, and headers above 450℃. It is derived from the Arrhenius equation. (11) in, Let A be the creep variable in the steady-state phase, Q be the atomic activation energy, and k be the Boltzmann constant. Taking the natural logarithm of both sides of the equation, we get: (12) in =ε r / t r , where ε r For total creep variables, t r Substituting the total creep-induced cracking time into the above formula, we get: (13) Let: lnA - lnε r =C, then: (14) Where C is the Larson-Miller constant, and P is the Larson-Miller parameter. C The value of is related to the material itself. P It is a quantity related to the working stress σ of the material. The Larson-Miller parameter expression is: (15) P ( σ The parameter can be represented by the following polynomial: (16) in, C For material constants, C 0、 C 1. C 2 and C 3 represents the Larson-Miller polynomial fitting parameters.

[0043] To facilitate data fitting in Matlab, C Taking a value of 20, the formula is rearranged to obtain: (17) Based on the derived Larson-Miller parametric equations and the stress-creep cracking time data in Table 4, the curve fitting tool in Matlab mathematical analysis software was used to obtain the values ​​in the Larson-Miller parametric equations. C 0、 C 1. C 2 and CThe value of 3 is used to substitute into formula (16) to obtain the Larson-Miller parameter equation for the T91 material. The Larson-Miller curve obtained by fitting the data points using Matlab is shown below. Figure 6 As shown, where C 0、 C 1. C 2 and C The values ​​for 3 are 24037.37, -44.49, 0.19678, and -4.1178, respectively. The lifespan of the heat-resistant material is assessed based on the obtained curve equations and under actual operating conditions.

[0044] Furthermore, several metal liner samples were prepared from boiler component materials. These samples were taken from the T91 pipe. Corrosion and oxidation tests were conducted on the samples under high-temperature flue gas and high-temperature steam conditions. Microscopic characterization was performed on the samples after service termination. The microscopic morphology of the steam oxide film under an electron microscope is shown below. Figure 7 As shown, the flue gas side is as follows Figure 8 As shown. The integrity of the oxide film was observed, and the thinning of the pipe wall on the flue gas side and steam side was measured separately. The formula for calculating the pipe wall thinning rate is as follows: (18) in, t op This represents the time the pipe has been running, in hours. W The initial thickness of the pipe wall. W f This is the current pipe wall thickness, in millimeters. k The tube wall thinning rate is expressed in millimeters per hour.

[0045] The formula for calculating the creep life of heat-resistant components subjected to the combined effects of creep, flue gas-steam side corrosion, and oxidation is shown below: (19) in, t r The working life at the pipe wall thinning rate k is expressed in hours; n is the stress exponent, which is generally taken as 4. Table 3 Parameters of Metal and Oxide Film Materials

[0046] Corrected calculation based on pipe wall thinning t nr The lifetime prediction results at different temperatures are as follows: Figure 9As shown, under conditions of 878K temperature and 100MPa stress, the oxide film thickness on the flue gas side is 238μm, and the oxide film thickness on the steam side is 291μm, with a measured pipe wall thinning of approximately 0.24mm. For example, the predicted lifespan calculated using the Larson-Miller parametric equation is 100,000h. Combining this with the component lifespan calculation formula for heat-resistant materials under the combined effects of creep, flue gas-steam side corrosion, and oxidation, the estimated lifespan of the heat-resistant steel is fitted to 78,062h, which is significantly lower than the estimated value calculated using the Larson-Miller parametric equation and conforms to the actual service life of heat-resistant materials under real-world operating conditions. The method of this invention can more accurately predict the creep lifespan of components under the combined effects of flue gas-steam side corrosion and oxidation under complex operating conditions.

[0047] This invention studies the performance degradation behavior of high-temperature components under complex operating conditions such as deep peak shaving and rapid load changes in power plant boilers, caused by corrosion, oxidation, and creep. A three-dimensional geometric model and a multiphysics model of the high-temperature components are constructed to calculate their temperature distribution under thermal cycling. Based on the obtained temperature distribution, mechanical analysis is performed on the model to calculate the stress field generated during thermal cycling. High-temperature corrosion / oxidation tests and high-temperature creep tests are conducted to obtain parameters related to the Larson-Miller creep model, thereby deriving the Larson-Miller life prediction model for high-temperature heat-resistant materials. Combining creep, flue gas-steam side corrosion, and oxidation life assessment methods for high-temperature pressure-bearing components, data processing software is used to assess creep life at actual pipe wall thinning rates to predict the creep life of high-temperature components under the combined effects of steam-flue gas side corrosion and oxidation.

[0048] It should be noted that any parts not mentioned in this invention can be achieved by using or referencing existing technologies.

[0049] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for predicting the creep life of high-temperature components under complex operating conditions, characterized in that, It includes the following steps: Construct a three-dimensional high-temperature component model of a power plant boiler; The three-dimensional high-temperature component model is imported into the fluid calculation software. The physical parameters, boundary conditions and assumptions of the finite element simulation are configured according to the actual working conditions. The convective heat transfer fluid-structure interaction model of the steam side and the flue gas side inside and outside the pipe is set up to construct a multi-physics field model that couples flow and heat transfer. Finite element simulation calculation is performed to obtain the temperature field distribution of the entire model field. Based on the temperature field distribution of the entire model obtained, solid mechanics analysis is performed on the model to obtain the stress-strain field distribution model of the pipeline under the fluid-structure interaction of flue gas outside the pipe and steam inside the pipe. Parameters related to the Larson-Miller creep model were obtained, and data processing software was used to fit the data to obtain the Larson-Miller life prediction model for heat-resistant materials. The creep life of high-temperature components is obtained by modifying the life prediction model of the heat-resistant material based on the pipe wall thinning rate.

2. The method for predicting the creep life of high-temperature components under complex working conditions as described in claim 1, characterized in that, The construction of a three-dimensional high-temperature component model for a power plant boiler includes: taking a section of pipe for three-dimensional modeling, forming a metal oxide film on the outside of the pipe, with the outer layer of the oxide film being rich in Fe oxides and the inner layer being a region rich in Fe-Cr oxides.

3. The method for predicting the creep life of high-temperature components under complex working conditions according to claim 1, characterized in that, The boundary conditions for the finite element simulation include: inlet steam velocity, outlet steam pressure, steam flow rate, flue gas composition, flue gas temperature, and steam state parameters. The physical parameters include: density, thermal expansion coefficient, Poisson's ratio and elastic modulus, specific heat capacity, convective heat transfer coefficient between flue gas and metal pipe wall, internal thermal conductivity of heat-resistant steel, and convective heat transfer coefficient between high-temperature steam and metal pipe wall.

4. The method for predicting the creep life of high-temperature components under complex working conditions according to claim 1, characterized in that, The boundary conditions for the finite element simulation include: the assumptions include that the oxide film of the heat-resistant steel is considered to be linearly elastic and isotropic; Only thermal stress and mechanical stress caused by changes in steam pressure inside the pipe are considered, while the stress effect caused by oxide film growth is ignored. The oxide film bonded well to the metal substrate and to each oxide film layer, without considering contact thermal resistance, and the oxide film did not peel off. The model does not consider the variation of steam temperature along the length of the pipe; Under thermal and mechanical loads, the oxide film did not crack or peel off.

5. The method for predicting the creep life of high-temperature components under complex working conditions according to claim 1, characterized in that, Based on the obtained temperature field distribution of the three-dimensional high-temperature component model, solid mechanics analysis is performed on the three-dimensional high-temperature component model to obtain the stress-strain field distribution model of the pipeline under the fluid-structure interaction of flue gas outside the pipe and steam inside the pipe. This includes: importing the flue gas temperature and steam velocity inside the pipe into the simulation software to obtain the temperature field distribution of the heat exchanger pipe; setting the thermal boundary conditions of the three-dimensional high-temperature component model in the fluid calculation module; calculating the temperature field of the three-dimensional high-temperature component model under the coupling of high-temperature flue gas and steam inside the pipe; importing the obtained temperature field results into the Transient Structural module and applying solid mechanics boundary conditions to calculate the stress field model of the pipeline under the flue gas-steam temperature field.

6. The method for predicting the creep life of high-temperature components under complex working conditions according to claim 1, characterized in that, Several creep specimens were prepared using high-temperature materials, and high-temperature creep tests were conducted to obtain parameters related to the Larson-Miller creep model.

7. The method for predicting the creep life of high-temperature components under complex working conditions according to claim 1, characterized in that, The tube wall thinning rate was obtained using the following method: Several creep specimens were prepared from commonly used boiler component materials. Several sets of temperature conditions were set to conduct high-temperature creep tests and obtain the corresponding temperature, stress and crack initiation time curves. Based on the basic form of the Larson-Miller parametric equation, the stress, temperature and cracking time obtained from the high-temperature creep cracking test are fitted to obtain the values ​​of unknown parameters in the Larson-Miller equation for different materials, and the Larson-Miller lifetime prediction model for different heat-resistant materials is derived. Several metal plate samples were prepared using commonly used boiler component materials. The metal plate samples were subjected to corrosion and oxidation tests under high-temperature flue gas and high-temperature steam conditions. The samples that had completed their service were characterized microscopically, and the thickness of the oxide film on the flue gas side and the steam side and the thinning rate of the metal material were measured.

8. The method for predicting the creep life of high-temperature components under complex working conditions according to claim 1, characterized in that, The creep life calculation formula for high-temperature components is obtained by modifying the life prediction model of the Larson-Miller heat-resistant material based on the pipe wall thinning rate as follows: in, t r Let be the working life at the pipe wall thinning rate k, and n be the stress exponent. The lifetime is the one obtained from the Larson-Miller lifetime prediction model.

9. The method for predicting the creep life of high-temperature components under complex working conditions according to claim 1, characterized in that, The formula for calculating the pipe wall thinning rate is as follows: in, t op The time the pipe fitting has been in operation. W The initial thickness of the pipe wall. W f Given the current pipe wall thickness, k The rate at which the pipe wall thins.

10. A creep life prediction system for high-temperature components under complex working conditions, characterized in that, It includes a model building module, a temperature field distribution calculation module, a stress-strain field distribution model building module, a model parameter calculation module, and a prediction module; The model building module is used to build three-dimensional high-temperature component models of power plant boilers; The temperature field distribution calculation module is used to import the three-dimensional high-temperature component model into the fluid calculation finite element analysis. According to the actual working conditions, the physical parameters, boundary conditions and assumptions of the finite element simulation are configured. The convective heat transfer fluid-structure interaction model of the steam side and flue gas side inside and outside the pipe is set up to construct a multi-physics model that couples flow and heat transfer, and finite element simulation calculation is performed to obtain the temperature field distribution of the entire model. The stress-strain field distribution model construction module performs solid mechanics analysis on the model based on the temperature field distribution of the entire model obtained, and obtains the stress-strain field distribution model of the pipeline under the fluid-structure interaction of flue gas outside the pipe and steam inside the pipe. The model parameter calculation module obtains parameters related to the Larson-Miller creep model, and uses data processing software to fit the data to obtain the Larson-Miller life prediction model for heat-resistant materials. The prediction module combines the pipe wall thinning rate to correct the lifespan obtained from the Larson-Miller lifespan prediction model for heat-resistant materials, thus obtaining the creep lifespan of high-temperature components.

Images