Evaluation method for creep-fatigue interaction of high-temperature component of thermal power generating unit and application

Abstract

The invention discloses an evaluation system and method for creep-fatigue interaction of a high-temperature component of a thermal power generating unit. The method comprises the following steps: firstly, acquiring the working temperature, accumulative operation time, start-stop times, virtual stress amplitude and material performance parameters of the high-temperature component; dividing different working conditions based on the accumulated operation time, and calculating creep damage of each working condition; in combination with the virtual stress amplitude and the material parameters, the fatigue cycle number is solved through iteration, and linear accumulated fatigue damage is calculated; dynamically selecting a current damage point and a starting point and an ending point of the latest cycle period, and substituting into a nonlinear three-point fitting function to determine a parameter a for controlling the nonlinear degree; generating a fitting curve according to the value a, and calculating an intersection point of the fitting curve and the damage criterion critical line; calculating the remaining life based on the intersection point coordinates, and making a maintenance strategy according to the a value. According to the system and the method, the creep-fatigue interaction effect is quantified through dynamic nonlinear fitting, a dominant damage mechanism is accurately identified, and the life prediction precision and the maintenance strategy pertinence are improved.

Description

Technical Field

[0001] This invention relates to the field of measurement and testing technology, specifically to an evaluation method and application for the creep-fatigue interaction of high-temperature components in thermal power units. Background Technology

[0002] Thermal power units are a crucial component of the power system, providing a significant amount of baseload electricity. However, with increasing environmental requirements and a focus on energy efficiency, thermal power plants are facing pressure to upgrade and innovate. Against this backdrop, high-temperature components, such as boiler superheaters and reheater tubes, endure extremely high temperatures and stresses during operation, leading to creep and fatigue damage. Creep is the process by which materials gradually undergo plastic deformation over time under constant stress, while fatigue refers to the phenomenon where materials develop cracks and eventually fail under cyclic stress. When these two mechanisms act simultaneously, complex interactive effects occur, accelerating the aging and damage process of materials, thus affecting the safety and economic efficiency of the unit.

[0003] Currently, existing technologies for evaluating high-temperature components in thermal power units have both significant advantages and limitations. Experimental testing can provide accurate material property data, but it is time-consuming and costly; numerical simulation, through methods such as finite element analysis, can quickly predict damage, but it relies on accurate input parameters and has limited accuracy in simulating complex situations; damage accumulation laws such as Miner's rule are easy to apply, but they ignore the interactions between different damage mechanisms; online monitoring and diagnostic systems can monitor equipment status in real time and optimize maintenance strategies, but they face challenges in terms of data accuracy and reliability. Overall, these methods provide powerful tools for understanding and managing the aging of high-temperature components, but there is still room for improvement in applicability, accuracy, and efficiency.

[0004] Chinese invention patent CN107677547A provides a method for characterizing the fatigue, creep, and fatigue-creep interaction unified life of materials. It solves the problem of life characterization and prediction of materials under low-cycle fatigue, creep, and fatigue-creep interaction conditions. However, the applicable operating conditions of this patent are harsh, and it is only applicable to laboratory TiAl high-temperature alloys (aero-engines). Moreover, the model fitting form is a static power function, which cannot be flexibly adjusted in real time to adapt to different operating conditions, resulting in poor universality. At the same time, this patent lacks the ability to determine the dominant mechanism. The model is a fixed formula and lacks real-time performance. The calculation uses the least squares method and is processed offline after the experiment, resulting in slow calculation speed. Furthermore, it does not involve subsequent maintenance strategies for laboratory TiAl high-temperature alloys (aero-engines).

[0005] Against this backdrop, in-depth research and effective management of creep-fatigue interactions in high-temperature components of thermal power units can significantly improve equipment safety and reliability, prevent accidents by identifying potential faults early, rationally plan maintenance strategies to extend equipment lifespan, reduce unnecessary downtime and lower operating costs, and optimize component design and material selection to enhance the durability and stability of new equipment. To ensure the safe and stable operation of thermal power units and extend their service life, developing and applying an evaluation method for creep-fatigue interactions in high-temperature components of thermal power units is of great significance. Summary of the Invention

[0006] The purpose of this invention is to provide an evaluation system and method for creep-fatigue interaction of high-temperature components in thermal power units, in order to solve the problems of traditional methods ignoring creep-fatigue interaction, static models being unable to adapt to dynamic working conditions, and lacking the ability to identify the dominant damage mechanism.

[0007] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0008] An evaluation method for creep-fatigue interaction of high-temperature components in thermal power units, comprising:

[0009] S1: Collect parameters of high-temperature components of thermal power units, including: operating temperature, cumulative operating time, number of start-stop cycles, and virtual stress amplitude S. eq And the creep constant, elastic modulus E, and fatigue strength coefficient σ′ of high-temperature components of thermal power units. f Fatigue strength index b, fatigue ductility coefficient ε′ f Fatigue ductility index c;

[0010] S2: Based on the cumulative operating time, the operating conditions of thermal power units are divided into startup conditions, steady-state conditions, peak-shaving and load-increasing conditions, peak-shaving and load-reducing conditions, and shutdown conditions. The creep damage D under each condition at the stated operating temperature is calculated based on the creep constant of the high-temperature component materials of the thermal power unit. c ;

[0011] S3: Virtual stress amplitude S based on high-temperature components of thermal power units eq Number of start-stop cycles, and the elastic modulus E and fatigue strength coefficient σ′ of high-temperature components in thermal power units. f Fatigue strength index b, fatigue ductility coefficient ε′ f The fatigue ductility index c is used to calculate the number of fatigue cycles N. f Fatigue damage D is calculated using a linear cumulative model. f ;

[0012] S4: Select the current damage point P0(x0, y0), the point P1(x1, y1) before the start of fatigue in the most recent cycle, and the point P2(x2, y2) after the completion of the most recent fatigue calculation, and substitute them into the nonlinear three-point fitting function to determine the parameter a that controls the degree of nonlinearity.

[0013] S5: Generate a fitted curve based on the parameter a, and calculate its intersection point (D) with the critical line of the damage criterion. f0 D c0 );

[0014] S6: Based on intersection point (D) f0 D c0 Calculate the remaining lifetime t r And a maintenance strategy is formulated based on the value of parameter a.

[0015] To optimize the above technical solution, the specific measures also include:

[0016] creep damage D in step S2 c The calculation formula is:

[0017]

[0018] Among them, t i t represents the operating time of high-temperature components of a thermal power unit under operating condition i. ri The creep fracture time of high-temperature components of thermal power units under type i operating conditions.

[0019] In step S3, fatigue damage D f The calculation method is as follows:

[0020] First, calculate the virtual stress amplitude S. eq :

[0021] S eq =σ′ f ·(N f ) b +E·ε′ f ·(N f ) c

[0022] Then, the number of fatigue cycles N is determined by the bisection method. f After obtaining the initial values, further solutions are needed:

[0023] f(N f )=σ′ f ·(N f ) b +E·ε′ f ·(N f ) c -S eq

[0024] f′(N f )=b·σ′ f ·(N f ) b-1 +E·c·ε′ f ·(N f ) c-1

[0025] In the formula, S eq Represents the virtual stress amplitude, σ′ f N represents the fatigue strength coefficient. f ε′ represents the number of fatigue cycles, b represents the fatigue strength index, E is the elastic modulus of the high-temperature component material of the thermal power unit, and ε′ represents the fatigue cycle number. f is the fatigue ductility coefficient, and c is the fatigue ductility index;

[0026] The formula is updated iteratively:

[0027]

[0028] Iterative calculation until f(N) is reached. f ) less than the set threshold |f(N) f )|<10 -4 The number of fatigue cycles required to obtain the fatigue life is obtained.

[0029] The formula for linear cumulative fatigue damage is:

[0030]

[0031] Where n is the actual number of internal cycles of the component under the i-th operating condition with a time interval of Δt, and N fi This represents the number of fatigue cycles of high-temperature components in a thermal power unit under operating condition i.

[0032] The formula for the nonlinear three-point fitting function in step S4 is:

[0033]

[0034] Where x represents cumulative fatigue damage, y represents cumulative creep damage, and a is a parameter that controls the degree of nonlinearity;

[0035] Substitute the current damage point P0(x0, y0), the point P1(x1, y1) before the start of fatigue in the most recent cycle, and the point P2(x2, y2) after the completion of the most recent fatigue calculation into the nonlinear three-point fitting function to obtain the parameter a that controls the degree of nonlinearity.

[0036] In step S5, the method for nonlinear fitting and intersection point calculation is as follows:

[0037] By intersecting the nonlinear three-point fitting function with the critical line of the damage criterion, the intersection point (D) is solved. f0 D c0 ), to obtain the interaction life of creep and fatigue, where D f0 It is the maximum cumulative fatigue damage, D c0 It is the maximum cumulative creep damage.

[0038] The remaining lifespan calculation method in step S6 is as follows:

[0039] The total cycle life of the component under this working condition is obtained by using the x-coordinate of the intersection point of the fitted curve and the critical line of the damage criterion. Then, the number of cycles already completed is subtracted from the total life to obtain the remaining number of cycles, thereby calculating the remaining life of the component.

[0040] The remaining life of a component under operating condition i is expressed as:

[0041] t r =Δt[(x0-D f0 )·N fi ]

[0042] In the formula, Δt is the time interval, x0 is the current fatigue damage value, and D f0 To fit the damage critical value, i.e. the maximum cumulative fatigue damage, N fi Let i be the number of fatigue cycles under working condition i.

[0043] The maintenance strategy in step S6 is as follows:

[0044] When parameter a < 2, the curve is nearly linear, indicating that creep-fatigue synergy dominates; Execution cycle assessment and incremental maintenance: Set the time for life assessment, local maintenance and comprehensive inspection in sequence;

[0045] When 2 ≤ parameter a ≤ 5, the curve exhibits moderate nonlinearity, indicating a significant fatigue-creep interaction; during planned maintenance, the focus should be on inspecting the welds and corner areas of high-temperature components in thermal power units.

[0046] When parameter a > 5, the curve exhibits strong nonlinearity, indicating that a single mechanism dominates; when creep damage D c Fatigue damage D f Extend the steady-state operation time before starting and stopping, when fatigue damage D f > Creep damage D c Reduce the frequency or magnitude of peak shaving.

[0047] This invention also proposes an evaluation system for the creep-fatigue interaction of high-temperature components in thermal power units, comprising:

[0048] Data Acquisition Module: Used to collect parameters of high-temperature components in thermal power units, including operating temperature, cumulative operating time, number of start-stop cycles, and virtual stress amplitude S. eq Creep constant, elastic modulus E, and fatigue strength coefficient σ′ of high-temperature components in thermal power units f Fatigue strength index b, fatigue ductility coefficient ε′ f Fatigue ductility index c;

[0049] The calculation module divides the operating conditions of thermal power units into startup, steady-state, peak-shaving and load-increasing, peak-shaving and load-reducing, and shutdown conditions based on cumulative operating time, and calculates the creep damage D for each condition. c Based on virtual stress amplitude S eq Calculate the number of fatigue cycles N f Fatigue damage D is calculated using a linear cumulative model. f ;

[0050] Analysis module: Dynamically determines damage points P0(x0, y0), P1(x1, y1), and P2(x2, y2), substitutes them into a nonlinear three-point fitting function to determine the parameter 'a' controlling the degree of nonlinearity; generates a fitting curve based on parameter 'a', and calculates the intersection point (D) between the fitting curve and the critical line of the damage criterion. f0 D c0 Based on the intersection point (D) f0 D c0 Calculate the remaining lifetime t r And a maintenance strategy is formulated based on the value of parameter a.

[0051] The system is used to perform an evaluation method for creep-fatigue interaction of high-temperature components in thermal power units, as described above.

[0052] The present invention also proposes an electronic device, characterized in that it includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, it implements the above-described evaluation method for creep-fatigue interaction of high-temperature components of thermal power units.

[0053] The present invention also proposes a computer-readable storage medium storing a computer program that causes a computer to execute an evaluation method for creep-fatigue interaction of high-temperature components in thermal power units as described above.

[0054] Compared with the prior art, the beneficial effects of the present invention are:

[0055] 1. This invention takes into account the influence of creep-fatigue interaction, and can identify the dominant role of fatigue and creep under different working conditions, thereby accurately predicting which damage mechanism dominates the failure of the component. Through this mechanism, the interaction between fatigue and creep can be accurately captured, further optimizing the assessment method of damage accumulation, making the damage prediction of high-temperature pressure-bearing components of thermal power units more accurate and closer to the failure mechanism under actual working conditions.

[0056] 2. This invention employs a nonlinear algorithm to effectively identify the potential damage risks of high-temperature components in thermal power units under the interaction of fatigue and creep. Compared with traditional linear algorithms, the nonlinear algorithm can delve deeper into the complex interaction between fatigue and creep damage, rather than simply adding fatigue and creep damage together. This avoids the errors caused by considering fatigue or creep alone, making the prediction results closer to the dynamic failure process under actual operating conditions.

[0057] 3. This evaluation method has excellent universality and can effectively address the impact of different load conditions (such as peak load) on unit performance. By accurately simulating the interaction between creep and fatigue, it can adapt to various complex load changes, especially in the environment of unit peak operation, and can accurately assess the cumulative effects of fatigue and creep.

[0058] 4. This invention provides a more scientific basis for unit maintenance planning through accurate damage accumulation and life assessment, avoiding equipment failures caused by delayed maintenance and reducing the risk of sudden shutdowns.

[0059] 5. Implementing this method helps reduce unnecessary maintenance costs and improve the overall operating efficiency of the unit. By effectively predicting remaining lifespan, the unit can avoid excessively extended maintenance cycles and reduce unplanned downtime caused by equipment failure.

[0060] 6. In this invention, the real-time linkage between the virtual stress amplitude Seq and the nonlinear fitting parameter a enables the system to dynamically capture transient stress impacts during peak-shaving conditions. Attached Figure Description

[0061] Figure 1 This is a flowchart of the present invention.

[0062] Figure 2 This is a creep-fatigue damage assessment diagram.

[0063] Figure 3 These are the nonlinear fitting curves corresponding to different values ​​of a. Detailed Implementation

[0064] The present invention will be further described in detail below through specific embodiments, but it should not be construed as limiting the scope of the subject matter of the present invention to the following embodiments. All technologies implemented based on the above content of the present invention fall within the scope of the present invention.

[0065] This invention provides a method for evaluating the creep-fatigue interaction of high-temperature components in thermal power units, comprising:

[0066] S1: Collect parameters of high-temperature components of thermal power units, including: operating temperature, cumulative operating time, number of start-stop cycles, and virtual stress amplitude S. eq And the creep constant, elastic modulus E, and fatigue strength coefficient σ′ of high-temperature components of thermal power units. f Fatigue strength index b, fatigue ductility coefficient ε′ f Fatigue ductility index c;

[0067] High-temperature components of thermal power units include the main steam section, superheated steam section, and high-temperature reheated steam section of steam pipelines; major components include main steam tees, superheated steam headers, superheated steam header heads, high-temperature reheated steam equal diameter tees, high-temperature reheated steam Y-type tees, as well as straight pipes, connecting elbows, boiler drums, and water-cooled walls.

[0068] S2: In accordance with the requirements of GB / T30580-2014 "Technical Guidelines for Life Assessment of Main Pressure-Bearing Components of Power Plant Boilers", the Larson-Miller parameter method is used to divide the operating conditions of thermal power units into startup conditions, steady-state conditions, peak-shaving and load-increasing conditions, peak-shaving and load-reducing conditions, and shutdown conditions based on the cumulative operating time. The creep damage D under each condition at the stated operating temperature is calculated based on the creep constant of the high-temperature component materials of the thermal power unit. c Creep damage formula D c for:

[0069]

[0070] Among them, t i t represents the operating time of a component under operating condition i. ri Let be the creep fracture time of the component under operating condition i. The accumulation of creep damage will provide a basis for subsequent analysis.

[0071] The operating conditions of thermal power units are divided into startup condition, steady-state condition, peak shaving and load increase condition, peak shaving and load decrease condition, and shutdown condition, and the creep damage D is calculated for each condition. c This damage model is applicable to all five working conditions mentioned above.

[0072] S3: Fatigue damage calculation is based on stress amplitude and the fatigue properties of component materials. First, the virtual stress amplitude S is calculated. eq:

[0073] S eq =σ′ f ·(N f ) b +E·ε′ f ·(N f ) c

[0074] Then, the number of fatigue cycles N is determined by the bisection method. f The initial values ​​are then determined, and the Newton-Raphson method is used to further solve for them.

[0075] f(N f )=σ′ f ·(N f ) b +E·ε′ f ·(N f ) c -S eq

[0076] f′(N f )=b·σ′ f ·(N f ) b-1 +E·c·ε′ f (N f ) c-1

[0077] In the formula, S eq Represents the virtual stress amplitude, σ′ f N represents the fatigue strength coefficient. f ε′ represents the number of fatigue cycles, b represents the fatigue strength index, E is the elastic modulus of the high-temperature component material of the thermal power unit, and ε′ represents the fatigue cycle number. f is the fatigue ductility coefficient, and c is the fatigue ductility index;

[0078] E is the elastic modulus of the material. The value of the elastic modulus of the component material will change under different temperatures. Here, the elastic modulus is taken as the value at the highest temperature in the working condition. Therefore, the value of the elastic modulus is different for different working conditions.

[0079] The formula is updated iteratively:

[0080]

[0081] Iterative calculation until f(N) is reached. f If the number of fatigue cycles is less than the set threshold, the number of fatigue cycles required to obtain the fatigue life is obtained.

[0082] In the Newton-Raphson method for iteratively solving fatigue life, the set convergence threshold is a key parameter controlling the balance between algorithm accuracy and computational efficiency. It is generally set as follows:

[0083] Relative error threshold:

[0084] Or absolute residual threshold: |F(N) f )|<10 -3 ~10 -5

[0085] The residual termination criterion used in this invention is |f(N) f )|<10 -4 It balances computational stability and efficiency.

[0086] That is, in this invention, f(N) f If |f(N) is less than the set threshold, it means that |f(N) f )|<10 -4 .

[0087] Similarly, according to the requirements of GB / T 30580-2014 "Technical Guidelines for Life Assessment of Main Pressure-Bearing Components of Power Plant Boilers", the linear cumulative fatigue damage formula is:

[0088]

[0089] Where n is the actual number of internal cycles of the component under the i-th operating condition with a time interval of Δt, and N fi This represents the number of fatigue cycles of high-temperature components in a thermal power unit under operating condition i.

[0090] 'n' represents the number of cycles, and 'Δt' represents the length of one cycle. For example, a steam pipeline has been in operation for 27 years, with a total operating time of 172,130 hours, and 178 start-ups and shutdowns, averaging one start-up and shutdown every 967 hours, or 6.6 start-ups and shutdowns per year. This 967 hours represents the time from start-up operation, through steady-state operation, through a selection process for peak shaving, and finally to shutdown operation. Start-up operation lasts approximately 8 hours, shutdown operation approximately 2 hours, and steady-state operation, without peak shaving, lasts 957 hours. If peak shaving is required, more detailed unit operating data is needed.

[0091] The damage formula described above requires calculating each working condition separately and then summing the damage. Therefore, Δt needs to be determined based on the type of working condition.

[0092] For example, based on the data above, there were a total of 178 start-stop cycles, with a start-stop interval of 967 hours. Therefore, the Δt for the start-up condition is 8 hours, the Δt for the stop-down condition is 2 hours, and the total number of start-stop cycles (n) is 178.

[0093] However, if we add the condition that during a single start-up and shutdown cycle, after the unit has been operating in steady-state condition for 317 hours, it undergoes 2 hours of peak load increase, then continues steady-state operation for another 317 hours, followed by another 2 hours of peak load decrease, and then enters steady-state operation for another 317 hours, then the Δt for peak load increase and peak load decrease is 2 hours, and n = 178 cycles. Meanwhile, the Δt for steady-state operation is 317 hours, and n = 534 cycles.

[0094] S4: In nonlinear algorithms, creep and fatigue damage interact. This is based on the following nonlinear three-point fitting function:

[0095]

[0096] Where x represents cumulative fatigue damage, y represents cumulative creep damage, and a is a constant controlling the degree of nonlinearity; to obtain the fitting curve, three key points need to be selected:

[0097] Substitute the current damage point P0(x0, y0), the point P1(x1, y1) before the start of fatigue in the most recent cycle, and the point P2(x2, y2) after the completion of the most recent fatigue calculation into a nonlinear three-point fitting function to obtain the parameter 'a' that controls the degree of nonlinearity. Using this parameter 'a', the interaction between fatigue damage and creep damage is calculated.

[0098] S5: After obtaining the constant 'a', use the nonlinear fitting curve (nonlinear three-point fitting function) and... Figure 2 The critical lines of the damage criteria in the creep-fatigue damage assessment diagram shown (the critical lines here are obtained according to GB / T 30580—2014 "Technical Guidelines for Life Assessment of Main Pressure-Bearing Components of Power Plant Boilers") intersect. The intersection point (D) is determined by solving... f 0, D c0 ), to obtain the interaction life of creep and fatigue, where D f 0 represents the maximum cumulative fatigue damage, D c0 It is the maximum cumulative creep damage.

[0099] The specific process is as follows:

[0100] Find the intersection point with the critical line of the damage criterion in the creep-fatigue damage assessment diagram based on the fitted curve.

[0101] If the fatigue damage is significant, the fitted curve will be biased towards point P2, and the intersection point D will be biased towards point P2. f 0 has a larger weight; if creep damage is significant, the fitted curve will be closer to point P0, and the intersection point D... c0 It has a relatively large weight.

[0102] S6: Use the interaction intersection (D) f 0, Dc0 By combining creep and fatigue damage accumulation, the remaining life of the component is assessed.

[0103] Specifically: by using the x-coordinate of the intersection point of the fitted curve and the critical line of the damage criterion, the total cycle life of the component under this working condition can be obtained. Then, the number of cycles already completed is subtracted from the total life to obtain the remaining number of cycles, thereby calculating the remaining life of the component.

[0104] For example, the remaining life of the component under operating condition i:

[0105] t r =Δt[(x0-D f0 )·N fi ]

[0106] In the formula, Δt is the time interval, x0 is the current fatigue damage value, and D f 0 represents the fitted damage threshold, i.e., the maximum cumulative fatigue damage, N. fi Let i be the number of fatigue cycles under working condition i.

[0107] This invention also proposes a maintenance strategy for high-temperature components of thermal power units based on the change in the parameter 'a' that controls the degree of nonlinearity.

[0108] Specifically as follows:

[0109] The parameter 'a' serves as a control parameter for the degree of nonlinearity in the creep-fatigue interaction, and its magnitude reflects the degree of bias towards the dominant damage mechanism.

[0110] In some implementations, if parameter a < 2 and the curve is close to linear, it indicates that creep-fatigue co-dominates, and periodic assessment + gradual maintenance is recommended;

[0111] The specific method of periodic assessment + incremental maintenance is as follows: set the time for conducting one operational data retrospective and life assessment, the first local maintenance, and the second comprehensive inspection, and adjust the maintenance interval and degree according to the life prediction trend to achieve the optimal balance between safe operation and cost.

[0112] Specific examples are as follows:

[0113] I. Periodic Assessment (Regular Monitoring)

[0114] A full life assessment is conducted every 24 months to promptly identify whether operational deviations will cause changes in the damage mechanism (whether the value of parameter 'a' increases).

[0115] In some implementations, the evaluation content includes:

[0116] 1. Archive operating conditions (start-stop frequency, steady-state duration);

[0117] 2. Ultrasonic thickness measurement in key areas;

[0118] 3. Update the simulation of temperature and stress fields;

[0119] 4. Recalculate the current fatigue / creep damage value and the trend of parameter a;

[0120] II. First Gradual Maintenance (to be implemented 36 months after service commencement)

[0121] The aim is to preventively repair local damage caused by early low-cycle fatigue and delay overall lifespan decline.

[0122] 1. Perform magnetic particle testing and local heat treatment on vulnerable points (such as welds and corner areas);

[0123] 2. If microcracks are found, perform local repair welding or post-weld heat treatment.

[0124] III. The strategy of incremental maintenance thereafter (the second maintenance will be performed at the 72nd month of service).

[0125] 1. Strategy Logic: Extend the next maintenance cycle after each maintenance, unless the value of parameter 'a' increases rapidly or D... f / D c A mutation occurred;

[0126] If the value of parameter a remains less than 2 and the damage growth is stable, the third maintenance can be extended to 96 months.

[0127] If fatigue damage is found D f If the value increases significantly, immediately switch to the fast recognition strategy corresponding to parameter a>5 for advance maintenance.

[0128] 2. Maintenance method:

[0129] In some implementations, secondary maintenance involves full-section ultrasonic testing combined with industrial endoscopy; if necessary, small sections of the pipeline are replaced.

[0130] If 2≤a≤5, the curve exhibits moderate nonlinearity and significant fatigue-creep interaction. It is recommended to focus on inspecting fatigue hotspots such as welds and corners during the planned maintenance cycle.

[0131] If a > 5, it indicates a significant dominant mechanism bias, and the judgment should be based on the location of the damage point in the current service life.

[0132] (1) If creep damage D c Significantly greater than fatigue damage D f It is recommended to extend steady-state operation and reduce start-stop operations to lower the creep accumulation rate;

[0133] (2) If fatigue damage D f Greater than creep damage Dc It is recommended to adjust the peak amplitude or frequency to reduce thermal shock and cyclic load.

[0134] In another embodiment of the present invention, an evaluation system for creep-fatigue interaction of high-temperature components in thermal power units is proposed, comprising:

[0135] Data Acquisition Module: Used to collect parameters of high-temperature components in thermal power units, including operating temperature, cumulative operating time, number of start-stop cycles, and virtual stress amplitude S. eq Creep constant, elastic modulus E, and fatigue strength coefficient σ′ of high-temperature components in thermal power units f Fatigue strength index b, fatigue ductility coefficient ε′ f Fatigue ductility index c.

[0136] Calculation module: Divides the operating conditions of thermal power units into startup condition, steady-state condition, peak shaving and load increase condition, peak shaving and load decrease condition, and shutdown condition, and calculates the creep damage D for each condition. c Based on virtual stress amplitude S eq Calculate the number of fatigue cycles N f Fatigue damage D is calculated using a linear cumulative model. f .

[0137] Analysis module: Dynamically determines damage points P0(x0, y0), P1(x1, y1), and P2(x2, y2), substitutes them into a nonlinear three-point fitting function to determine parameter a; identifies the dominant damage mechanism based on the value of a, and calculates its intersection point (D) with the critical line of the damage criterion. f0 D c0 Based on the intersection point (D) f0 D c0 Calculate the remaining lifetime t r And a maintenance strategy is formulated based on the value of parameter a.

[0138] The system is used to perform an evaluation method for creep-fatigue interaction of high-temperature components in thermal power units, as described above.

[0139] In another embodiment of the present invention, an electronic device is proposed, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements an evaluation method for creep-fatigue interaction of high-temperature components of thermal power units as described above.

[0140] In another embodiment of the present invention, a computer-readable storage medium is provided storing a computer program that causes a computer to execute an evaluation method for creep-fatigue interaction of high-temperature components of thermal power units as described above.

[0141] In the embodiments disclosed in this application, a computer storage medium may be a tangible medium that may contain or store programs for use by or in conjunction with an instruction execution system, apparatus, or device. The computer storage medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of computer storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0142] In some implementations, taking a superheated steam pipeline as an example, the pipeline material is 12Cr1MoV. The virtual stress amplitude is obtained through finite element thermodynamic simulation. The basic material constants are shown in Table 1, and the elastic modulus E is taken according to different service temperatures, as shown in Table 2.

[0143] Table 1 Low-cycle fatigue parameters of 12Cr1MoV steel

[0144] Material <![CDATA[σ f / E]]> b <![CDATA[ε f ]]> c 12Cr1MoV 0.00345 -0.0678 0.6114 -0.6389

[0145] Table 2 Elastic modulus values ​​of 12Cr1MoV at different temperatures

[0146]

[0147] 2. Thermo-coupling transient analysis was performed using finite element method software to obtain the virtual stress amplitude S of the superheated steam pipeline under each operating condition. eq The specific data is shown in Table 3.

[0148] Table 3 Virtual stress amplitude S of superheated steam pipeline under different operating conditions eq

[0149] Service type start up steady state Peak shaving and load reduction Peak shaving and load increase shutdown <![CDATA[S eq / MPa]]> 58 62 61 64 27

[0150] 3. Based on the component's design life of 300,000 hours and the continuous operating time under each working condition, initialize the fatigue cycle count and repeat the iterative formula:

[0151]

[0152] Until f(N) f If the number of fatigue cycles is less than the set threshold, the number of fatigue cycles required for fatigue life is obtained. The initial number of fatigue cycles and the number of fatigue cycles after iteration are shown in Table 4.

[0153] Table 4. Number of fatigue cycles after initialization and iteration of superheated steam pipelines under different operating conditions during a single start-up and shutdown of the unit.

[0154]

[0155]

[0156] Total fatigue damage: D f =0.0194

[0157] 4. Assuming steady-state creep is dominant, the Larson-Miller method is used to calculate the creep life.

[0158] With 5661 hours of steady-state operation per year, accumulating to approximately 96237 hours over 17 years, the corresponding creep life is 180000 hours. Therefore:

[0159]

[0160] like Figure 2 As shown, the three-point fitting yields: a = 6.15, the fitting center point, which belongs to the obvious creep-dominated damage mechanism, and the intersection with the critical line is (0.08823, 0.2504);

[0161] Then the remaining lifetime t r for:

[0162] N remain = (0.08823 - 0.0194) × 318 ≈ 21.88794

[0163] Therefore, it can operate in a steady state for approximately t r =21.88794 × 943.5 = 20651 hours, which is approximately 3.6 years.

[0164] This invention references superheated steam pipelines that have been in service for 17 years under different operating conditions, and verifies the results by comparing the creep curve dot method and the fatigue crack propagation method:

[0165] The creep life was measured according to GB / T 2039-2012 "Metallic Materials Uniaxial Tensile Creep Test Method" standard. A constant stress of 250MPa was applied at 550℃, and the equivalent life was measured to be 98,000 hours.

[0166] The fatigue life was measured according to GB / T 15248-2008 "Metallic Materials Axial Constant Amplitude Low Cyclic Fatigue Test Method". Under the equivalent stress amplitude of 62MPa, the measured life was approximately 3.4 to 3.8 years.

[0167] like Figure 3 As shown, the nonlinear fitting curves for different values ​​of 'a' exhibit the following trends:

[0168] The smaller the value of a (e.g., a=1), the closer the curve is to the diagonal, and the weaker the coupling between fatigue and creep.

[0169] As the value of a increases, the curve exhibits an S-shape or a step shape, demonstrating strong nonlinear behavior;

[0170] When a = 200, the curve almost degenerates into the Heaviside function, indicating that the interaction effect is dominated by the dominant mechanism, which is suitable for rapid identification of extreme fatigue-dominated or creep-dominated effects.

[0171] In this embodiment, the fitting result for the superheated steam pipeline is a = 6.15, which is a typical creep-dominated mechanism. The life assessment t... r The lifespan is approximately 3.6 years, therefore the following maintenance strategy is recommended:

[0172] It is not recommended to increase the frequency of start-stop operations or shorten the operating cycle within the next three years;

[0173] Under conditions of more than 5,000 hours of steady-state operation per year, ultrasonic and magnetic particle combined testing shall be carried out once every 12 months;

[0174] It is recommended to conduct a comprehensive metallographic and wall thickness inspection in the 2.5th year, and update the a-value based on the new operating data to verify the model.

[0175] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent substitutions, and improvements made by those skilled in the art to the above embodiments without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for evaluating the creep-fatigue interaction of high-temperature components in thermal power units, characterized in that, include: S1: Collect parameters of high-temperature components of thermal power units, including: operating temperature, cumulative operating time, number of start-stop cycles, and virtual stress amplitude S. eq And the creep constant, elastic modulus E, and fatigue strength coefficient σ′ of high-temperature components of thermal power units. f Fatigue strength index b, fatigue ductility coefficient ε′ f Fatigue ductility index c; S2: Based on the cumulative operating time, the operating conditions of thermal power units are divided into startup conditions, steady-state conditions, peak-shaving and load-increasing conditions, peak-shaving and load-reducing conditions, and shutdown conditions. The creep damage D under each condition at the stated operating temperature is calculated based on the creep constant of the high-temperature component materials of the thermal power unit. c ; S3: Virtual stress amplitude S based on high-temperature components of thermal power units eq Number of start-stop cycles, and the elastic modulus E and fatigue strength coefficient σ′ of high-temperature components in thermal power units. f Fatigue strength index b, fatigue ductility coefficient ε′ f The fatigue ductility index c is used to calculate the number of fatigue cycles N. f Fatigue damage D is calculated using a linear cumulative model. f ; S4: Select the current damage point P0(x0, y0), the point P1(x1, y1) before the start of fatigue in the most recent cycle, and the point P2(x2, y2) after the completion of the most recent fatigue calculation, and substitute them into the nonlinear three-point fitting function to determine the parameter a that controls the degree of nonlinearity. S5: Generate a fitted curve based on the parameter a, and calculate its intersection point (D) with the critical line of the damage criterion. f0 D c0 ); S6: Based on intersection point (D) f0 D c0 Calculate the remaining lifetime t r And a maintenance strategy is formulated based on the value of parameter a.

2. The evaluation method for creep-fatigue interaction of high-temperature components in thermal power units according to claim 1, characterized in that: creep damage D in step S2 c The calculation formula is: Among them, t i t represents the operating time of high-temperature components of a thermal power unit under operating condition i. ri The creep fracture time of high-temperature components of thermal power units under type i operating conditions.

3. The evaluation method for creep-fatigue interaction of high-temperature components in thermal power units according to claim 1, characterized in that: In step S3, fatigue damage D f The calculation method is as follows: First, calculate the virtual stress amplitude S. eq : S eq =σ′ f ·(N f ) b +E·e′ f ·(N f ) c Then, the number of fatigue cycles N is determined by the bisection method. f After obtaining the initial values, further solutions are needed: f(N f )=σ′ f ·(N f ) b +E·e′ f ·(N f ) c -S eq f′(N f )=b·σ′ f ·(N f ) b-1 +E·c·e′ f ·(N f ) c-1 In the formula, S eq Represents the virtual stress amplitude, σ′ f N represents the fatigue strength coefficient. f ε′ represents the number of fatigue cycles, b represents the fatigue strength index, E is the elastic modulus of the high-temperature component material of the thermal power unit, and ε′ represents the fatigue cycle number. f is the fatigue ductility coefficient, and c is the fatigue ductility index; The formula is updated iteratively: Iterative calculation until f(N) is reached. f ) less than the set threshold |f(N) f )|<10 -4 The number of fatigue cycles required to obtain the fatigue life is obtained. The formula for linear cumulative fatigue damage is: Where n is the actual number of internal cycles of the component under the i-th operating condition with a time interval of Δt, and N fi This represents the number of fatigue cycles of high-temperature components in a thermal power unit under operating condition i.

4. The evaluation method for creep-fatigue interaction of high-temperature components in thermal power units according to claim 1, characterized in that: The formula for the nonlinear three-point fitting function in step S4 is: Where x represents cumulative fatigue damage, y represents cumulative creep damage, and a is a parameter that controls the degree of nonlinearity; Substitute the current damage point P0(x0, y0), the point P1(x1, y1) before the start of fatigue in the most recent cycle, and the point P2(x2, y2) after the completion of the most recent fatigue calculation into the nonlinear three-point fitting function to obtain the parameter a that controls the degree of nonlinearity.

5. The evaluation method for creep-fatigue interaction of high-temperature components in thermal power units according to claim 1, characterized in that: In step S5, the method for nonlinear fitting and intersection point calculation is as follows: By intersecting the nonlinear three-point fitting function with the critical line of the damage criterion, the intersection point (D) is solved. f0 D c0 ), to obtain the interaction life of creep and fatigue, where D f0 It is the maximum cumulative fatigue damage, D c0 It is the maximum cumulative creep damage.

6. The evaluation method for creep-fatigue interaction of high-temperature components in thermal power units according to claim 1, characterized in that: The remaining lifespan calculation method in step S6 is as follows: The total cycle life of the component under this working condition is obtained by using the x-coordinate of the intersection point of the fitted curve and the critical line of the damage criterion. Then, the number of cycles already completed is subtracted from the total life to obtain the remaining number of cycles, thereby calculating the remaining life of the component. The remaining life of a component under operating condition i is expressed as: t r =Δt[(x0-D f0 )·N fi ] In the formula, Δt is the time interval, x0 is the current fatigue damage value, and D f0 To fit the damage critical value, i.e. the maximum cumulative fatigue damage, N fi Let i be the number of fatigue cycles under working condition i.

7. The evaluation method for creep-fatigue interaction of high-temperature components in thermal power units according to claim 1, characterized in that: The maintenance strategy in step S6 is as follows: When parameter a < 2, the curve is nearly linear, indicating that creep-fatigue synergy dominates; Execution cycle assessment and incremental maintenance: Set the time for life assessment, local maintenance and comprehensive inspection in sequence; When 2 ≤ parameter a ≤ 5, the curve exhibits moderate nonlinearity, indicating a significant fatigue-creep interaction; during planned maintenance, the focus should be on inspecting the welds and corner areas of high-temperature components in thermal power units. When parameter a > 5, the curve exhibits strong nonlinearity, indicating that a single mechanism dominates; when creep damage D c Fatigue damage D f Extend the steady-state operation time before starting and stopping, when fatigue damage D f > Creep damage D c Reduce the frequency or magnitude of peak shaving.

8. An evaluation system for creep-fatigue interaction of high-temperature components in thermal power units, characterized in that, include: The data acquisition module is used to collect parameters of high-temperature components in thermal power units, including the operating temperature, cumulative operating time, number of start-stop cycles, and virtual stress amplitude S of the high-temperature components. eq Creep constant, elastic modulus E, and fatigue strength coefficient σ′ of high-temperature components in thermal power units f Fatigue strength index b, fatigue ductility coefficient ε′ f Fatigue ductility index c; The calculation module is used to divide the operating conditions of thermal power units into startup conditions, steady-state conditions, peak-shaving and load-increasing conditions, peak-shaving and load-reducing conditions, and shutdown conditions based on the cumulative operating time, and to calculate the creep damage D for each condition. c Based on virtual stress amplitude S eq Calculate the number of fatigue cycles N f Fatigue damage D is calculated using a linear cumulative model. f ; The analysis module dynamically determines damage points P0(x0, y0), P1(x1, y1), and P2(x2, y2), substitutes them into a nonlinear three-point fitting function to determine the parameter 'a' that controls the degree of nonlinearity; generates a fitting curve based on parameter 'a', and calculates the intersection point (D) between this fitting curve and the critical line of the damage criterion. f0 D c0 Based on the intersection point (D) f0 D c0 Calculate the remaining lifetime t r And a maintenance strategy is formulated based on the value of parameter a.

9. An electronic device, characterized in that, include: The memory, the processor, and the computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, it implements the evaluation method for creep-fatigue interaction of high-temperature components of thermal power units as described in any one of claims 1-7.

10. A computer-readable storage medium storing a computer program that causes a computer to perform the evaluation method for creep-fatigue interaction of high-temperature components of thermal power units as described in any one of claims 1-7.

Images