Method for evaluating high-temperature corrosion fatigue damage of steel structure

Abstract

The application discloses a kind of steel structure high-temperature corrosion fatigue damage evaluation methods, comprising the following steps: the unified continuous damage mechanics model of coupling high-temperature creep damage, corrosion damage and mechanical fatigue damage is established, and the total damage variable of the model is the function of environmental temperature, stress parameter, current damage state, corrosion medium concentration and time;Using the high-temperature effect factor and corrosion environment factor, the actual stress amplitude of structure is equivalently corrected, and the equivalent stress amplitude under high-temperature corrosion environment is obtained, and preliminary prediction of fatigue life is carried out based on the equivalent stress amplitude and material reference S-N curve.The steel structure high-temperature corrosion fatigue damage evaluation method quantifies the dynamic influence of corrosion on microdamage as a coupling parameter, breaks through the limitations of traditional evaluation methods, and realizes the whole-chain evaluation from macroscopic performance-microdamage-corrosion effect by combining multi-scale microcharacterization and theoretical model.

Description

Technical Field

[0001] This invention relates to the field of structural safety assessment technology, specifically to structural safety assessment and durability analysis of engineering structures serving in high-temperature environments, and more specifically to a method for evaluating high-temperature corrosion fatigue damage of steel structures. Background Technology

[0002] Steel structures used in high-temperature operating environments such as coal-fired power plants and nuclear power equipment are typically subjected to cyclic loads formed by thermal and mechanical stresses. Under the coupling effect of corrosive media (such as high-temperature and high-pressure supercritical water) in high-temperature environments and cyclic loads, materials are prone to corrosion fatigue damage, leading to early failure. For example, the prior art, disclosed in CN118446060A, describes a method, system, equipment, and medium for evaluating the fatigue performance of corroded steel structures. This method includes: acquiring characteristic parameters of the corroded steel structure to be evaluated and inputting them into a pre-constructed fatigue crack propagation life prediction model considering the pitting-crack mode, outputting the fatigue crack propagation life of the corroded steel structure to be evaluated; wherein the pre-constructed fatigue crack propagation life prediction model considering the pitting-crack mode is constructed based on an empirical calculation formula for the fatigue crack tip stress intensity factor and combined with Paris fatigue fracture theory; based on reliability assessment theory and combined with the fatigue crack propagation life of the corroded steel structure to be evaluated, the fatigue performance of the corroded steel structure to be evaluated is assessed, obtaining the fatigue performance evaluation result; this invention does not require repeated calls to finite element software for calculation, and the evaluation result has higher accuracy.

[0003] For example, a method for simulating and predicting the corrosion fatigue evolution process of steel structures, as disclosed in the prior art (CN119601135B), includes: establishing a global finite element stress simulation model of the steel structure, wherein a notch is reserved on the global finite element stress simulation model for inserting a local finite element corrosion fatigue simulation model of the steel structure; establishing a local finite element corrosion fatigue simulation model of the steel structure, wherein the local finite element corrosion fatigue simulation model of the steel structure includes coupled and related finite element corrosion simulation units and finite element fatigue simulation units of the steel structure; inserting and binding the local finite element corrosion fatigue simulation model of the steel structure into the notch of the local finite element corrosion fatigue simulation model of the steel structure to form a global finite element corrosion fatigue simulation model of the steel structure; and obtaining the simulation and prediction results of the corrosion fatigue evolution process of the steel structure through the calculation of the global finite element corrosion fatigue simulation model of the steel structure. This achieves multi-scale, coupled simulation of the entire process of corrosion pit formation and crack propagation.

[0004] Traditional fatigue damage assessment methods often consider mechanical loads or corrosive environments in isolation, treating fatigue and corrosion as two independent processes linearly superimposed, or only considering corrosion fatigue at room temperature. These methods neglect the dynamic interactions between corrosion and microscopic damage such as dislocation evolution, grain boundary cracking, and oxide film rupture, failing to fully account for the nonlinear synergistic effects among "high temperature-corrosion-fatigue," leading to assessment results that are either risky or uneconomical. They also struggle to accurately characterize the actual damage state of materials. Currently, there is a lack of practical methods that can effectively couple temperature, corrosion damage, and cyclic stress, and perform full-lifecycle quantification and real-time / stage-based evaluation of high-temperature corrosion fatigue damage. Summary of the Invention

[0005] The purpose of this invention is to provide a method for evaluating high-temperature corrosion fatigue damage of steel structures, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for evaluating high-temperature corrosion fatigue damage of steel structures, comprising the following steps: S1: Establish a unified continuous damage mechanics model that couples high-temperature creep damage, corrosion damage and mechanical fatigue damage. The total damage variable of the model is a function of ambient temperature, stress parameters, current damage state, concentration of corrosive medium and time. S2: Determine the high-temperature effect factor of the ambient temperature on the fatigue performance of the material through experiments or standard data. The corrosion environment factors of the effective cross-section of the component, including the concentration of the corrosive medium and time. ,in The SN curves were obtained by fatigue tests on materials at different temperatures and compared with a reference temperature. Normalization yields the result, and The relationship between oxidation weight gain rate and corrosive medium concentration can be established through accelerated corrosion and oxidation tests. and time The power function relationship is obtained; S3: Using the high temperature effect factor and corrosion environment factor, the actual stress amplitude of the structure is equivalently corrected to obtain the equivalent stress amplitude under high temperature corrosion environment, and fatigue life is preliminarily predicted based on the equivalent stress amplitude and the material reference SN curve. S4: Based on the damage threshold, the fatigue life process of the structure is divided into the crack initiation stage and the crack propagation stage, and the damage is quantified by the modified linear cumulative damage model and the crack propagation model based on fracture mechanics, respectively. S5: Integrates real-time or phased structural monitoring data, calculates the current total damage level, and performs safety status classification and remaining life prediction based on preset damage thresholds.

[0007] Furthermore, in S1, the expression for the unified continuous damage mechanics model is: .

[0008] As a further step, in step S3, the equivalent stress amplitude The calculation formula is: ,in This represents the measured stress amplitude, and simultaneously the equivalent stress amplitude. The calculation method can also be .

[0009] Furthermore, in S4, the damage degree during the crack initiation stage... Adopting the modified Linear cumulative damage calculation: ,in Based on the current equivalent stress amplitude The number of failure cycles obtained from the baseline SN curve.

[0010] As a further step, in step S4, the damage degree during the crack propagation stage... With crack length Correspondingly, the crack propagation rate was adjusted for temperature and corrosion environment. Formula description.

[0011] As a further step, in S5, the total damage degree ,in This is the stage transition coefficient; when the crack is in the initiation stage, =0.

[0012] As a further step, the structural monitoring data in step S5 includes at least stress-strain data, ambient temperature data, and corrosion monitoring data obtained by sensors.

[0013] A computer-readable storage medium having a computer program stored thereon that, when executed by a processor, implements the above-described method steps.

[0014] An electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the method described above.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: the high-temperature corrosion fatigue damage evaluation method for steel structures quantifies the dynamic influence of corrosion on micro-damage (such as oxide film rupture and grain boundary corrosion) into coupling parameters, breaks through the limitations of traditional evaluation methods, and achieves a full-chain evaluation from macroscopic performance to micro-damage to corrosion effect through multi-scale micro-characterization and theoretical model combination, as shown in the following content.

[0016] 1. By establishing a unified damage model, a quantitative description of the nonlinear synergistic effect of high temperature, corrosion, and fatigue was achieved for the first time at the engineering application level, improving the assessment accuracy. It can also be directly applied to the life prediction of austenitic steel under high temperature and corrosion environment, providing guidance for equipment maintenance and material optimization.

[0017] 2. The method covers the entire life cycle process from uniform damage to crack initiation and crack propagation, providing a more complete evaluation. It can be seamlessly integrated with structural health monitoring systems, dynamically updating damage status and remaining life prediction using real-time data to achieve intelligent early warning. Based on the theoretical model, a simplified engineering evaluation path based on environmental factors is proposed, which is easier for engineers to understand and apply. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall process of the present invention; Figure 2 This is a schematic diagram illustrating the influence of high-temperature and corrosive environmental factors on the SN curve of the material in this invention. Figure 3 This is a schematic diagram illustrating the accumulation and early warning of high-temperature corrosion fatigue damage based on monitoring data, as presented in this invention.

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figures 1-3 The present invention provides the following technical solution: Example

[0021] S1: Establish a coupled damage constitutive model Based on continuous damage mechanics, a unified continuous damage mechanics model coupling high-temperature creep damage, corrosion damage, and fatigue damage is constructed. The model's expression is: ,in, The total damage variable is a function of ambient temperature, stress parameters, current damage state, corrosive medium concentration, and time, where 0 ≤ 0. <1, in =1 indicates that it is invalid. The number of load cycles, The absolute temperature of the environment. The stress amplitude, For average stress, This refers to the concentration of the corrosive medium (or the corrosion equivalent parameter). For time, function Comprehensively reflects temperature The effects of corrosion rate on the degradation of material elastic modulus and fatigue strength, the time-varying weakening of effective load-bearing cross-sectional area, and the damage accumulation law under cyclic stress.

[0022] S2: Determine environmental acceleration factors High temperature effect factor High-temperature fatigue tests were conducted to obtain data at different temperatures. The SN curve of the steel is normalized to obtain the value relative to the reference temperature. Fatigue strength reduction factor Corrosive environmental factors This involves establishing the rate of oxidative weight gain through accelerated corrosion or oxidation tests. and and time The power function relationship can be used to derive the effective stress concentration factor or section loss rate, where the power function relationship can be... ; Or corrosion damage : Introducing corrosion damage factors (Positively correlated with corrosion product thickness and grain boundary corrosion depth): ,in For corrosion time, , This is the environmental correlation coefficient.

[0023] Step S3: Correct the SN curve and damage evolution law The environmental acceleration factor, namely the high-temperature effect factor and the corrosion environment factor, is introduced into the system based on... In the modified model of linear cumulative damage theory, the equivalent stress amplitude under high-temperature corrosion environment The calculation method is as follows Then, the corrected equivalent stress amplitude is used. By referring to the baseline SN curve of the material under a reference environment (normal temperature, non-corrosive), fatigue life prediction is performed, and the equivalent stress amplitude is... The calculation method can be adopted in a more general form: .

[0024] S4: Implement full life-cycle damage assessment Stage A (before crack initiation): Adopt the correction in step S3. Rule, calculate cumulative damage ,in In the first The actual number of cycles under each load block Based on the current equivalent stress amplitude And the number of failure cycles predicted by the current damage state (obtained from the baseline SN curve).

[0025] Stage B (Crack Propagation Stage): When the damage level Exceeding the threshold (Corresponding to macroscopically detectable cracks) then, a fracture mechanics-based approach is adopted. The formula is used for evaluation, where the crack propagation rate parameter is... and The damage level at this stage is dynamically adjusted based on the current ambient temperature and corrosion rate. With crack length Related.

[0026] S5: Integrated Evaluation and Early Warning Real-time or interim data (stress spectrum, temperature, corrosion sensor data) acquired by the structural health monitoring (SHM) system are input into the above model to calculate the current total damage level. ,in The stage transition coefficient is based on a preset damage threshold (e.g., ...). =0.3 warning, =0.7 Danger) Issue different levels of safety warnings and output the remaining fatigue life estimate.

[0027] Taking the steel structure of the flue gas duct at the tail end of a power plant as an example: 1. Data Acquisition: Monitoring yielded stress spectra at key nodes ( =80MPa, =20MPa), average temperature =150℃, in the flue gas =0.1%, material is Q345B steel; 2. Model parameter determination: obtained from experiments, (150℃) = 0.85, obtained from fitting corrosion data. ( (in terms of days) 3. Damage calculation: 1 year of operation ( =365 days later, calculate the current equivalent stress amplitude. , The single-cycle damage increment under the current state is obtained by querying the baseline SN curve, and the stress spectrum for that period is counted cyclically to accumulate the damage. ; 4. Evaluation Output: Calculate the current total damage level. =0.25, which is less than the warning threshold of 0.3. The system outputs "Status is normal, remaining lifespan estimated". The conclusion was "years," and the next check-up time was recommended. Example

[0028] In addition to the fatigue damage evaluation method that combines high-temperature factors and corrosion factors mentioned above, this embodiment also discloses the following scheme, specifically a high-temperature corrosion fatigue damage evaluation method for austenitic steel that considers the effect of corrosion on microscopic damage: 1. Corrosion fatigue test design: Select typical austenitic steel specimens (such as 316L, 304H, etc.), process them into standard fatigue specimens, and conduct high-temperature corrosion fatigue tests (temperature 600-800℃, corrosive medium is a mixed gas or liquid salt film simulating the service environment); use a "mechanical load-corrosion environment" synchronous loading device to record the load-displacement curves, corrosion product composition, and micromorphological changes under different cycles. 2. Extraction of microscopic damage characteristic parameters: Corrosion parameters: The thickness of corrosion products, grain boundary corrosion depth, and oxide film crack density were determined by scanning electron microscopy and energy dispersive spectroscopy (SEM); the austenitic steel samples after high-temperature corrosion fatigue test were subjected to gradient thinning (from the surface corrosion layer to the substrate), and TEM thin sections were prepared by focused ion beam (FIB) to ensure that the corrosion products, oxide film / substrate interface and subsurface microstructure were included. Mechanical damage parameters: Dislocation density and dislocation wall / cell structure size were observed using transmission electron microscopy (TEM), and grain boundary orientation difference and grain deformation were analyzed by electron backscatter diffraction (EBSD). Coupled damage parameter: Define the "corrosion-mechanical damage coupling factor" to characterize the contribution of corrosion to the initiation (e.g., stress concentration caused by oxide film rupture) and propagation (e.g., accelerated intergranular crack propagation due to grain boundary corrosion).

[0029] Data standardization processing Normalize the parameters for different cycle times, for example, convert the dislocation density into a "relative damage index" (actual density / initial density) to eliminate the influence of material batch differences.

[0030] 3. Construction of Damage Assessment Model Based on damage mechanics theory, a fatigue damage evolution equation incorporating corrosion factors is established: ,in, Total damage For pure mechanical fatigue damage, For corrosion damage, For the coupling coefficient (obtained through fitting experimental data), set a damage threshold (e.g., when...). ≥0.8 Material failure is determined when the value is ≥0.8 (quantitative evaluation is achieved by combining microscopic damage parameters).

[0031] detail: (1) Definition of damage variables Pure mechanical damage :based on The formula, combined with the dislocation density evolution equation: ,in For the cycle number, For dislocation density, For material constants; corrosion damage Introducing "corrosion damage factor" (Positively correlated with corrosion product thickness and grain boundary corrosion depth): ,in For corrosion time, This is the environmental correlation coefficient; (2) Modeling of coupling mechanism Synergistic effect term: Define the "corrosion-mechanical interaction coefficient". The effect of stress concentration after oxide film rupture on promoting microcrack formation is characterized. ,in Calibrated by high-temperature in-situ tensile-corrosion test, with values ​​ranging from 0.1 to 0.5; (3) Threshold determination when When the density is ≥0.9, the material is determined to have entered the "rapid failure stage", and the microcrack density (≥5 cracks / mm²) is used as an auxiliary criterion.

[0032] Model Validation Methods • Experimental verification: Comparative experiments were conducted in supercritical water environments with different parameters (pressure and temperature), and the coupling coefficient was adjusted. The error between the model's predicted lifetime and the actual number of failure cycles should be ≤8%.

[0033] • Sensitivity analysis: Using the controlled variable method, corrosion parameters (such as corrosion product thickness) were changed individually to verify the model's response sensitivity to corrosion micro-damage.

[0034] The experimental steps are as follows: 1. Sample Preparation: 316L austenitic steel was selected and machined into smooth cylindrical samples with a diameter of 8 mm and a gauge length of 50 mm. The surface was polished to... ≤0.2μm.

[0035] 2. Corrosion fatigue test: Conducted in a high-temperature corrosion fatigue testing machine at 700℃, with air containing 5% SO2 as the corrosive medium, a loading frequency of 1Hz, and a stress ratio of... =0.1, total number of cycles 10 7 Second-rate.

[0036] 3. Microscopic characterization: 10 per cycle 5 Secondary sampling was performed, and SEM was used to observe the thickness of surface corrosion products (such as Cr2O3 and Fe3O4) and crack distribution; TEM was used to statistically analyze dislocation density (cycle 10).5 Approximately 5 × 10¹ 4 m⁻², repeating 5×10 5 The next increase was 2×10¹ 5 EBSD analysis showed that corrosion increased the grain boundary orientation difference by 15%-20%, promoting the initiation of intergranular cracks.

[0037] 4. Model Validation: The coupling coefficients are obtained by fitting experimental data. =0.35, when the total damage degree When the coefficient of performance (COP) is 0.8, the error between the predicted failure cycles and the actual test results is ≤5%. Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for evaluating high-temperature corrosion fatigue damage of a steel structure, characterized by: Includes the following steps: S1: Establish a unified continuous damage mechanics model that couples high-temperature creep damage, corrosion damage and mechanical fatigue damage. The total damage variable of the model is a function of ambient temperature, stress parameters, current damage state, concentration of corrosive medium and time. S2: determining the high temperature effect factor of the environmental temperature on the material fatigue performance by test or standard data, respectively and the corrosion environmental factor of the corrosion medium concentration and time on the effective cross section of the component wherein the S-N curve of the material at different temperatures is obtained by fatigue test and normalized relative to the reference temperature T0, and the power function relationship between the oxidation weight gain rate and the corrosion medium concentration and time can be obtained by corrosion oxidation acceleration test; S3: Using the high temperature effect factor and corrosion environment factor, the actual stress amplitude of the structure is equivalently corrected to obtain the equivalent stress amplitude under high temperature corrosion environment, and fatigue life is preliminarily predicted based on the equivalent stress amplitude and the material reference SN curve. S4: Based on the damage threshold, the fatigue life process of the structure is divided into the crack initiation stage and the crack propagation stage, and the damage is quantified by the modified linear cumulative damage model and the crack propagation model based on fracture mechanics, respectively. S5: Integrates real-time or phased structural monitoring data, calculates the current total damage level, and performs safety status classification and remaining life prediction based on preset damage thresholds.

2. The method for evaluating high-temperature corrosion fatigue damage of steel structures according to claim 1, characterized in that: In S1, the expression of the unified continuous damage mechanics model is .

3. The method for evaluating high-temperature corrosion fatigue damage of steel structures according to claim 1, characterized in that: In step S3, the equivalent stress amplitude is calculated by wherein is the measured stress amplitude, and the equivalent stress amplitude is calculated by .

4. The method for evaluating high-temperature corrosion fatigue damage of steel structures according to claim 1, characterized in that: In S4, the damage degree during the crack initiation stage The modified Miner linear cumulative damage rule is used for calculation: ,in Based on the current equivalent stress amplitude The number of failure cycles obtained from the baseline SN curve.

5. The method for evaluating high-temperature corrosion fatigue damage of steel structures according to claim 1, characterized in that: In step S4, the damage degree during the crack propagation stage With crack length Correspondingly, the crack propagation rate was adjusted for temperature and corrosion environment. Formula description.

6. The method for evaluating high-temperature corrosion fatigue damage of steel structures according to claim 1, characterized in that: In S5, the total damage degree ,in This is the stage transition coefficient; when the crack is in the initiation stage, =0.

7. The method for evaluating high-temperature corrosion fatigue damage of steel structures according to any one of claims 1-6, characterized in that: The structural monitoring data in step S5 includes at least stress-strain data, ambient temperature data, and corrosion monitoring data obtained by sensors.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps of the method described in any one of claims 1-7.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the method as described in any one of claims 1-7.

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