Method for carrying out combined use evaluation on pressed element based on special FAD curve

Abstract

The invention discloses a method for carrying out combined use evaluation on a pressed element based on a special FAD curve, and relates to the technical field of pressed element evaluation. According to the method for carrying out combined use evaluation on the pressed element, when the pressed element is not safe due to the crack plane type defect, parameter reduction processing is carried out to obtain a critical parameter point, then the critical parameter point is converted into a parameter of pressure or crack size, and the value to which the pressure should be reduced can be known; or the safety can be ensured only by reducing the size of the crack. According to the method, the stress condition of the pressed element under heat-fluid-solid two-way coupling under the actual working condition is obtained through field acquisition of operation data and finite element simulation, so that a more accurate special FAD diagram is obtained, and scientific evaluation in use is made, so that an enterprise can accurately evaluate the safety degree and state of boiler equipment through the method, and the safety performance of the boiler equipment is improved. Therefore, a reasonable decision is made, and considerable safety and economic benefits are brought to enterprises.

Description

Technical Field

[0001] The present invention belongs to the technical field of evaluation of pressure-bearing components, and particularly relates to a method for evaluating the fitness for service of pressure-bearing components based on a dedicated FAD curve. Background Art

[0002] Pressure-bearing components such as boilers, pressure vessels, and pressure pipelines operate under high-temperature and high-pressure environments for a long time and are prone to cracks. Once the cracks expand, it may lead to leakage or even explosion of the pressure-bearing components of the boiler, causing serious safety accidents. Cracks will affect the overall performance and lifespan of the boiler. By studying and dealing with crack problems, the negative impact on the boiler can be reduced, ensuring the safe and stable operation of the boiler, which is conducive to the sustainable development of enterprises and the improvement of economic benefits.

[0003] Generally, in order to ensure safety at the initial design of pressure-bearing components, a large safety margin is given. If, according to traditional practices, flat-type non-standard defects are immediately eliminated, such as by stopping for repairs or replacing the pressure-bearing components, this approach is not necessarily scientific in fact, easily causing waste of resources and having a greater impact on production. Therefore, it is very necessary and meaningful to evaluate the fitness for service of pressure-bearing components containing flat-type defects.

[0004] Fitness for service refers to analyzing the safety status of a pressure-bearing component with defects to determine whether it can continue to be used or under what state parameters it can be used. As Figure 1 shown, when the evaluation point representing the pressure-bearing component with defects is located below the left of the curve, it can be considered that the pressure-bearing component is safe under the evaluation state. If the evaluation point is located above the right of the curve, the defects of the pressure-bearing component are unacceptable.

[0005] Therefore, it is crucial to obtain an accurate FAD evaluation curve. However, for some pressure-bearing components, especially boilers, due to their complex structures and complex operating conditions, non-uniform structural stress and thermal stress distributions will be generated inside the materials of these components. If calculated according to traditional stress manuals, it is very difficult to obtain an accurate stress intensity factor K I and the reference stress solution σ ref . Then, the load ratio L r and the fracture ratio K r required for evaluation will also be inaccurate; furthermore, the simple evaluation and conventional evaluation adopted in China are both for stress analysis of pressure-bearing components without cracks to obtain approximate reference stresses. However, in actual working conditions, the complex structure and the crack itself will both affect the stress distribution, resulting in a greatly reduced reference value of the simplified reference stress solution and the stress intensity factor; in addition, the analysis of various types of cracks in China is only limited to the case of pressure vessels with a small thickness-to-diameter ratio, and it cannot be applied to the case of thick-walled pipes of high-parameter boilers. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for evaluating the fitness for service of pressure-bearing components based on a dedicated FAD curve. Through the two-way coupling analysis of the actual multi-stress field conditions of typical pressure-bearing components, and by drawing an accurate FAD diagram based on the mechanical property data of in-service materials, the fracture mechanics theory is used to evaluate the fitness for service of pressure-bearing components with planar defects, and quantitative suggestions for defect elimination or adjustment of boiler operating parameters are given, which has practical guiding significance for the safe operation of pressure-bearing components.

[0007] To solve the above technical problems, the present invention is realized through the following technical solutions: The present invention is a method for evaluating the fitness for service of pressure-bearing components based on a dedicated FAD curve, including the following steps:

[0008] (1) Obtain the drawings of the pressure-bearing component and the dimensions of the on-site measurement components, and establish a finite element simulation model of the full-size or its partially symmetric structure after obtaining the corresponding dimension data (such as support and suspension, gravity, and wind load, etc.).

[0009] (2) Use non-destructive testing methods to accurately quantify and locate the size and position of planar defects (such as planar crack defects). The non-destructive testing methods include endoscopes, magnetic particle inspection, radiography, ultrasonic testing, and phased array testing, etc. When cutting sample testing is allowed, the non-destructive testing methods that can also be used include metallography and scanning electron microscopy, etc., in order to obtain the accurate length and depth of planar defects.

[0010] (3) Obtain the physical parameters of the material of the pressure-bearing component, and obtain the fracture property parameters (such as K IC ) and mechanical property parameters (such as tensile strength σ m and yield strength σ b ) of the material through mechanical property tests if necessary.

[0011] (4) Obtain the actual operating conditions of the boiler (such as pressure, temperature, fluid flow rate, and load conditions, etc.) for setting accurate boundary conditions during finite element simulation.

[0012] (5) Calculate the J integral, K I , σ ref , K r , L r , σ p; The J-integral is calculated by the following method: The position and size of the planar defect are obtained through step (2), and it is equivalent to a crack-like defect. A crack module including a semi-elliptical surface crack is inserted into the established simulation model. The spider grid and the influence sphere region of the crack are established by writing in the finite element APDL language. After setting the external environment parameters obtained in step (4) as boundary conditions and loading them for calculation, the J-integral of the crack is finally obtained.

[0013] (6) By gradually increasing the working pressure, the J-integral at each working pressure is calculated, and the elastic-plastic J-integral is converted into the linear-elastic stress intensity factor K. I , and the ratio between the two is calculated through a large number of trial-and-error methods using fracture mechanics theory to obtain K. r ; After drawing the FAD curve, the K r and L r corresponding values are fitted to draw a professional FAD evaluation curve.

[0014] The stress intensity factor K I is calculated by the following formula: The σ ref is calculated by the following formula: σ ref = F ref · σ p ; The K r is calculated by the following formula: When L r = 1,

[0015] (7) Through numerical processing of the actual situation and actual material parameters by means of finite element simulation, the stress state of the pressure-bearing component containing defects is obtained, the stress values of each point in the cross-section are acquired, the function of the stress distribution is calculated, the stress intensity factor K I is obtained, and σ ref is calculated, then K r and L r are calculated and the coordinates are plotted in the special FAD curve to obtain whether the pressure-bearing component can continue to be in service.

[0016] (8) When it is concluded that the defect makes the pressure-bearing component unsafe, parameter reduction processing is carried out to obtain the critical parameter point, and then the critical parameter point is converted into parameters of pressure or crack size, and then it can be known to what value the pressure should be reduced, or to what size the crack needs to be reduced to ensure safety (the parameters to be reduced include pressure and temperature. By reducing the parameters, the curve point moves along the line connecting to the origin, and the value of the intersection point with the FAD curve is the critical parameter point).

[0017] The present invention has the following beneficial effects: By collecting on-site operating data and through finite element simulation, the stress conditions under the thermal-fluid-solid bidirectional coupling of the pressure-bearing components under actual working conditions are simulated, so as to obtain a more accurate dedicated FAD diagram, and a scientific fitness-for-service evaluation is made. This enables enterprises to accurately evaluate the safety level and status of their boiler equipment through this method, so as to make reasonable decisions and bring considerable safety and economic benefits to the enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 It is the FAD curve graph of the defective pressure-bearing component in the prior art.

[0020] Figure 2 It is the finite element model of the high-temperature header in the present invention.

[0021] Figure 3 It is the mesh diagram of the crack and the affected area in the present invention.

[0022] Figure 4 It is the spider mesh diagram of the crack tip after magnification in the present invention.

[0023] Figure 5 It is the semi-elliptical crack model diagram of the pressure-bearing component in the present invention.

[0024] Figure 6 It is the J integral distribution diagram at the crack in the present invention.

[0025] Figure 7 It is the dedicated FAD curve graph in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0027] The key technical problems to be solved by this application are as follows: When a pressure-bearing component operates under high temperature and high pressure, once cracks occur, or planar defects such as lack of fusion, incomplete penetration, and deep undercut left during its manufacturing and installation have a great impact on its safety. Planar defects, especially cracks, have the following characteristics: (1) The tip position of the crack will cause stress concentration, resulting in the stress intensity factor at the crack changing with the size of the crack; (2) Under specific conditions, cracks have the property of expandability. When the boiler parameters change, it may lead to the accelerated extension of the crack, thus triggering its failure or even an accident.

[0028] After a pressure-bearing equipment is in service, if planar defects such as cracks, lack of fusion, incomplete penetration, and deep undercut that can be regularized as crack treatment are found, the measure that can be taken is fitness-for-service assessment. Then, studying whether the crack will expand or whether it can be retained is the key technology that needs to be solved. Since there are many influencing factors for crack expansion, such as the stress condition on the vertical plane at the crack extension tip, crack size, crack position, the crack resistance performance of the material itself, etc., among which the stress condition is the most complex. It is difficult to accurately calculate using traditional fracture mechanics under complex structures and working conditions. Therefore, it will be an operable research method to import the actual operating conditions, the actual size of the component, and the crack position distribution into the finite element simulation, and conduct a full-size and full-condition simulation. Through finite element simulation and transformation, the integral and stress intensity factor of the target structure are obtained, and then through a large number of operations, an accurate FAD curve that conforms to the actual working conditions is obtained.

[0029] For a specific pressure-bearing component, the accurate FAD curve can be used to evaluate whether it is safe to retain planar defects under the actual operating conditions of the component, and can also be used to infer whether planar defects will cause fracture failure, collapse failure, etc. of the pressure-bearing component. If an enterprise has insufficient time for maintenance during the overhaul period and it is difficult to eliminate the crack defects that have been evaluated as unacceptable, the FAD curve diagram can be used to give quantitative monitoring parameters to guide the operation of the boiler, so as to ensure the safety of equipment and personnel.

[0030] This application conducts a two-way coupling analysis of the actual multi-stress field conditions of typical pressure-bearing components, draws an accurate FAD diagram based on the mechanical property data of in-service materials, uses fracture mechanics theory to conduct fitness-for-service assessment on pressure-bearing components with planar defects, and gives quantitative suggestions for defect elimination or adjustment of boiler operating parameters, which has practical guiding significance for the safe operation of pressure-bearing components.

[0031] Please refer to Figure 1-7 , the present invention is a method for conducting fitness-for-service assessment on a pressure-bearing component based on a dedicated FAD curve, including the following steps:

[0032] (1) Obtain the drawings of the pressure-bearing components and the dimensions of the on-site measurement parts, and establish a finite element simulation model of the full-size or its partially symmetric structure after obtaining the corresponding dimension data (such as support and suspension, gravity, and wind load, etc.); Taking the high-temperature header of a power plant boiler as an example below, establish a finite element numerical model of the header Figure 2 as shown;

[0033] (2) Use non-destructive testing methods to accurately quantify and locate the size and position of planar defects (such as planar crack defects); Detection means such as endoscopes, magnetic particle, ray, ultrasonic, phased array, etc. can be used. If cutting sample testing is allowed, then metallography, scanning electron microscopy, etc. can also be used to obtain the accurate length and depth of defects such as cracks;

[0034] (3) Obtain the physical parameters of the materials of the pressure-bearing components, and obtain the fracture performance parameters (such as K IC ) and mechanical property parameters (such as tensile strength σ m and yield strength σ b ) of the materials through mechanical property tests when necessary;

[0035] (4) Obtain the actual operating conditions of the boiler (such as pressure, temperature, fluid flow rate, and load conditions, etc.), which are used to set accurate boundary conditions during finite element simulation;

[0036] (5) Calculate the J integral, K I , σ ref , K r , L r , σ p of the component with planar defects under the coupling of multiple stress fields; The J integral is calculated and obtained through the following method: Obtain the position and size of the planar defect through step (2), equivalent it to a crack-type defect, and insert a crack module in the established simulation model. The crack module includes a semi-elliptical surface crack; It is written through the finite element APDL language to establish the spider grid and influence sphere region of the crack, such as Figure 3 , Figure 4 , Figure 5 as shown. After setting the external environment parameters obtained in step (4) as boundary conditions and loading for calculation, the J integral of this crack is finally obtained, such as Figure 6 as shown;

[0037] (6) By gradually loading the working pressure, calculate the J integral at each working pressure, and convert the elastic-plastic J integral into the linear elastic stress intensity factor K I , calculate using fracture mechanics theory, and obtain the ratio between the two and get K r through a large number of trial-and-error methods; After drawing the FAD curve graph (note that the loaded pressure needs to include the actual working pressure), the continuously trial-and-error obtained K r and Lr Draw a professional FAD evaluation curve by fitting the corresponding values;

[0038] The stress intensity factor K I is calculated by the following formula: The σ ref is calculated by the following formula: σ ref = F ref ·σ p ; The K r is calculated by the following formula: As Figure 6 shown, when L r = 1,

[0039] (7) Through numerical processing of the actual situation and actual material parameters by means of finite element simulation, obtain the stress state of the pressure-bearing component with defects, obtain the stress values of each point in the cross-section, calculate the function of the stress distribution, obtain the stress intensity factor K I , and calculate σ ref , then calculate K r and L r and plot the coordinates in the special FAD curve to obtain whether the pressure-bearing component can continue to be in service;

[0040] (8) When it is found that the defect makes the pressure-bearing component unsafe, perform parameter reduction processing to obtain the critical parameter point, and then convert the critical parameter point into parameters of pressure or crack size, then it can be known to what value the pressure should be reduced, or to what size the crack needs to be reduced to ensure safety (the parameters to be reduced include pressure and temperature, and by reducing the parameters, the curve point moves along the connection line of the coordinate origin, and the value of the intersection point with the FAD curve is the critical parameter point). Therefore, this curve is actually used to guide the pressure-bearing equipment with excessive flat defects, and specific values for quantitatively adjusting the working pressure and temperature are given.

[0041] In the description of this specification, the descriptions referring to terms such as "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0042] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A method for evaluating the suitability of a pressure-bearing component based on a dedicated FAD curve, characterized in that: The steps include: (1) Obtain the drawings of the pressure-bearing components and the dimensions of the components measured on site, and after obtaining the corresponding dimensional data, establish a finite element simulation model of the full-size or partially symmetrical structure; (2) Use nondestructive testing to accurately and quantitatively locate the size and position of planar defects; (3) Obtain the physical parameters of the pressure component material and, if necessary, obtain the fracture performance parameters and mechanical performance parameters of the material through mechanical property tests; (4) Obtain the actual operating conditions of the boiler to set accurate boundary conditions during finite element simulation; (5) Calculate the J integral and K of the element with planar defects under the condition of multiple stress field coupling I , σ ref , K r , L r , σ p ; (6) By gradually loading the working pressure, the J integral at each working pressure is calculated, and the elastic-plastic J integral is converted into the linear elastic stress intensity factor K I , using fracture mechanics theory to calculate, after a lot of trial and error, the ratio between the two was calculated and K was obtained r ; After drawing the FAD curve, the K obtained by trial and error r and L r The corresponding values ​​are fitted to draw the professional FAD assessment curve; (7) The actual situation and actual material parameters are numerically processed through finite element simulation to obtain the stress state of the defective pressure component, obtain the stress value of each point in the cross section, calculate the stress distribution function, and obtain the stress intensity factor K I , and calculate σ ref , then calculate K r and L r The coordinates are plotted on a dedicated FAD curve to determine whether the pressure component can continue to serve; (8) When it is concluded that the defect has caused the pressure-bearing component to be unsafe, the parameter reduction process is performed to obtain the critical parameter point, and then the critical parameter point is converted into a parameter of pressure or crack size. It can be known to what value the pressure should be reduced, or to what size the crack needs to be reduced to ensure safety.

2. A method for evaluating the suitability of a pressure-bearing component based on a dedicated FAD curve according to claim 1, characterized in that: The corresponding dimensional data in step (1) include support, gravity and wind load.

3. A method for evaluating the suitability of a pressure-bearing component based on a dedicated FAD curve according to claim 1, characterized in that: The planar defects in step (2) include cracks, and the nondestructive testing methods include endoscope, magnetic powder, X-ray, ultrasound and phased array; When cut sample testing is allowed, other non-destructive testing methods include metallography and scanning electron microscopy to obtain the precise length and depth of planar defects.

4. A method for evaluating the suitability of a pressure-bearing component based on a dedicated FAD curve according to claim 1, characterized in that: The fracture performance parameters in step (3) include K IC , the mechanical performance parameters include tensile strength σ m and yield strength σ b .

5. A method for evaluating the suitability of a pressure-bearing component based on a dedicated FAD curve according to claim 1, characterized in that: The actual operating conditions of the boiler in step (4) include pressure, temperature, fluid flow rate and load conditions.

6. A method for evaluating the suitability of a pressure-bearing component based on a dedicated FAD curve according to claim 1, characterized in that: The J integral in step (5) is calculated by the following method: The position and size of the plane defect are obtained through step (2), and the plane defect is equivalent to a crack defect. A crack module is inserted into the established simulation model, and the crack module includes a semi-elliptical surface crack; The spider grid and influence sphere area of ​​the crack are established by writing the finite element APDL language. The external environment parameters obtained in step (4) are set as boundary conditions and then loaded for calculation, and finally the J integral of the crack is obtained.

7. A method for evaluating the suitability of a pressure-bearing component based on a dedicated FAD curve according to claim 1, characterized in that: The stress intensity factor K I Calculated by the following formula: The σ ref It is calculated by the following formula: ref =F ref ·σ p ; The K r Calculated by the following formula: When L r =1, 8. A method for evaluating the suitability of a pressure-bearing component based on a dedicated FAD curve according to claim 1, characterized in that: The parameters to be reduced in step (8) include pressure and temperature. By reducing the parameters, the curve point is connected along the coordinate origin line, and the value of the intersection with the FAD curve is the critical parameter point.

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