Damage tolerance assessment method and system for high temperature pipelines under creep fatigue loads

Abstract

The present invention relates to a method and system for assessing the damage tolerance of a high-temperature pipeline under creep fatigue load, and relates to the field of damage tolerance. The method comprises: establishing a pipeline finite element model containing cracks of different sizes and performing numerical calculations to obtain the stress intensity factor of the crack tip in the pipeline; obtaining a crack propagation model and pipeline crack size; determining the creep fatigue crack propagation rate according to the pipeline crack size; calculating the crack propagation life according to the stress intensity factor and the creep fatigue crack propagation rate; determining the fracture toughness according to the pipeline crack size; calculating the residual strength of the pipeline according to the fracture toughness and the pipeline crack size; constructing a damage tolerance assessment diagram of the high-temperature pipeline under creep fatigue load according to the crack propagation life and the residual strength. The present invention can provide ideas for the damage tolerance assessment of pipeline structures, assist in the fracture assessment and residual life prediction of pipelines, and provide guidance and suggestions for the maintenance and overhaul of their structures.

Description

Technical Field

[0001] The invention relates to the field of damage tolerance, and in particular to a method for evaluating the damage tolerance of a high-temperature pipeline structure under creep fatigue load. Background Art

[0002] With the development of fracture mechanics theory and the increasing demand for failure analysis of complex structures during processing, transportation and use, scholars have gradually realized that damage tolerance assessment is necessary. Damage tolerance theory is a structural design theory that exists to establish the relationship between structural residual strength, crack growth rate and equipment maintenance cycle. Failure is mainly caused by cracks that are not easy to find inside the structure. Cracks will increase the risk of component failure under the action of loads. With the increase in service time, long-term exposure to harsh working environments will greatly reduce the remaining life of complex structures.

[0003] As the requirements for equipment reliability and residual strength continue to increase, scholars have begun to pay attention to the damage tolerance assessment method of cracked structures. Therefore, the present invention proposes a damage tolerance assessment method and system for high-temperature pipelines under creep fatigue loads. Based on the method of the present invention, key indicators such as stress intensity factor, crack growth life, fracture toughness and residual strength related to the crack size of cracked pipelines can be obtained, so as to assess the damage tolerance of cracked pipelines. This method is of great significance for studying the damage tolerance assessment of pipeline structures. Summary of the invention

[0004] The purpose of the present invention is to provide a method and system for damage tolerance assessment of high-temperature pipelines under creep fatigue loads, to provide ideas for damage tolerance assessment of pipeline structures, to assist in fracture assessment and remaining life prediction of pipelines, and to provide guidance and suggestions for maintenance and overhaul of their structures.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A damage tolerance assessment method for a high temperature pipeline under creep fatigue load, comprising:

[0007] Establish a finite element model of a pipeline with cracks of different sizes;

[0008] Performing numerical calculation on the pipeline finite element model to obtain a stress intensity factor at a crack tip in the pipeline;

[0009] Obtain crack growth model;

[0010] Obtaining a pipeline crack size of the crack growth model;

[0011] Determining a creep fatigue crack growth rate based on the pipeline crack size;

[0012] Calculating the crack growth life according to the stress intensity factor and the creep fatigue crack growth rate, wherein the crack growth life is the life span experienced by the crack growing from a certain initial size to a certain critical size;

[0013] determining fracture toughness based on the crack size of the pipeline;

[0014] Calculating the residual strength of the pipeline based on the fracture toughness and the pipeline crack size;

[0015] According to the crack growth life and the residual strength, a damage tolerance assessment diagram of the high-temperature pipeline under the creep fatigue load is constructed, and the damage tolerance assessment diagram is used to assess the damage tolerance of the high-temperature pipeline under the creep fatigue load.

[0016] Optionally, the stress intensity factor is calculated using the following formula:

[0017]

[0018] Among them, K is the stress intensity factor; Y is the shape factor; σ is the stress; a is the crack size.

[0019] Optionally, the crack growth rate is calculated using the following formula:

[0020]

[0021] K max =ΔK / (1-R)

[0022] f=(T+t h ) -1

[0023] Where da / dN is the crack growth rate; ΔK is the stress intensity factor range variable; C and n are fitting parameters obtained from fatigue crack growth experiments; A and m are fitting parameters obtained from creep crack growth experiments; D, q, p are 1 , p 2 , p 3 All are material parameters; K max is the maximum stress intensity factor; R is the stress ratio; f is the frequency; T is the cycle of the loading and unloading process; t h Hold time for creep load.

[0024] Optionally, the crack growth life is calculated using the following formula:

[0025]

[0026] Where, N is the crack growth life; a 0 is the initial crack size; a c is the critical crack size.

[0027] Optionally, the residual strength is calculated using the following formula:

[0028]

[0029]

[0030] Among them, σ rs is the residual strength; K IC is the fracture toughness expressed by the critical crack tip stress intensity factor, recorded as the first fracture toughness; a c is the critical crack size; E is the elastic modulus of the pipeline material; ν is the Poisson's ratio of the pipeline material, J IC It is the fracture toughness expressed by the critical J integral and is recorded as the second fracture toughness.

[0031] A damage tolerance assessment system for high temperature pipelines under creep fatigue loads, comprising:

[0032] Pipeline finite element model building module, used to build pipeline finite element models containing cracks of different sizes;

[0033] A stress intensity factor calculation module, used for performing numerical calculation on the pipeline finite element model to obtain a stress intensity factor at a crack tip in the pipeline;

[0034] A crack extension model acquisition module, used to obtain a crack extension model;

[0035] A pipeline crack size acquisition module, used to acquire the pipeline crack size of the crack propagation model;

[0036] A creep fatigue crack growth rate determination module, used to determine the creep fatigue crack growth rate according to the pipeline crack size;

[0037] A crack growth life calculation module, used to calculate the crack growth life according to the stress intensity factor and the creep fatigue crack growth rate, wherein the crack growth life is the life span experienced by the crack growing from a certain initial size to a certain critical size;

[0038] A fracture toughness determination module, used to determine the fracture toughness according to the crack size of the pipeline;

[0039] A residual strength calculation module, used for calculating the residual strength of the pipeline according to the fracture toughness and the pipeline crack size;

[0040] The damage tolerance assessment module is used to construct a damage tolerance assessment diagram of the high-temperature pipeline under creep fatigue load according to the crack growth life and residual strength, and the damage tolerance assessment diagram is used to assess the damage tolerance of the high-temperature pipeline under creep fatigue load.

[0041] Optionally, the stress intensity factor calculation module uses the following formula for calculation:

[0042]

[0043] Among them, K is the stress intensity factor; Y is the shape factor; σ is the stress; a is the crack size.

[0044] Optionally, the creep fatigue crack growth rate determination module is calculated using the following formula:

[0045]

[0046] K max =ΔK / (1-R)

[0047] f=(T+t h ) -1

[0048] Where da / dN is the crack growth rate; ΔK is the stress intensity factor range variable; C and n are fitting parameters obtained from fatigue crack growth experiments; A and m are fitting parameters obtained from creep crack growth experiments; D, q, p1, p2, and p3 are all material parameters; K max is the maximum stress intensity factor; R is the stress ratio; f is the frequency; T is the cycle of the loading and unloading process; t h Hold time for creep load.

[0049] Optionally, the crack extension life calculation module uses the following formula for calculation:

[0050]

[0051] Where, N is the crack growth life; a 0 is the initial crack size; a c is the critical crack size.

[0052] Optionally, the residual strength calculation module uses the following formula for calculation:

[0053]

[0054]

[0055] Among them, σ rs is the residual strength; K IC is the first fracture toughness; a c is the critical crack size; E is the elastic modulus of the pipeline material; ν is the Poisson's ratio of the pipeline material, J IC is the second fracture toughness.

[0056] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0057] The present invention proposes a method and system for evaluating the damage tolerance of high-temperature pipelines under creep fatigue loads. Based on this method, key indicators such as stress intensity factor, crack growth life, fracture toughness and residual strength related to the crack size of cracked pipelines can be obtained, so as to evaluate the damage tolerance of cracked pipelines. This method is of great significance for studying the damage tolerance evaluation of pipeline structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0059] Figure 1 This is a flow chart of the damage tolerance assessment method of a high-temperature pipeline under creep fatigue load of the present invention;

[0060] Figure 2 The geometric dimensions and crack dimensions of the pipeline selected in the embodiment of the present invention are shown in FIG.

[0061] Figure 3A This is a finite element model diagram of a half pipeline structure in an embodiment of the present invention;

[0062] Figure 3B This is the mesh diagram of the local refinement of the crack tip of the pipeline finite element model;

[0063] Figure 4 is a crack growth life curve diagram of a pipeline in an embodiment of the present invention;

[0064] Figure 5 The fracture toughness and constraint parameter A of the DP2-A52 steel used in the embodiment of the present invention are d J between IC / J ref -A d Correlation line graph;

[0065] Figure 6 The J integral and the constraint parameter A are obtained according to the finite element model of the pipeline with cracks of different sizes established in the embodiment of the present invention. d J / J between ref -A d Correlation line graph;

[0066] Figure 7 It is an interactive diagram of a fracture curve and a force-to-break curve in an embodiment of the present invention;

[0067] Figure 8It is a residual strength curve diagram of a pipe with cracks of different sizes in an embodiment of the present invention;

[0068] Fig. 9 This is a damage tolerance assessment diagram of a high-temperature pipeline structure under creep fatigue load in an embodiment of the present invention;

[0069] Fig.10 This is a module diagram of the damage tolerance assessment system for high-temperature pipelines under creep fatigue loads of the present invention. DETAILED DESCRIPTION

[0070] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0071] The purpose of the present invention is to provide a method and system for damage tolerance assessment of high-temperature pipelines under creep fatigue loads, to provide ideas for damage tolerance assessment of pipeline structures, to assist in fracture assessment and remaining life prediction of pipelines, and to provide guidance and suggestions for maintenance and overhaul of their structures.

[0072] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0073] like Figure 1 As shown, the present invention provides a method for evaluating the damage tolerance of a high-temperature pipeline under creep fatigue load, comprising the following steps:

[0074] Step 101: Establish a finite element model of a pipeline containing cracks of different sizes.

[0075] Step 101 specifically includes: according to the real geometry and real working conditions of the pipeline structure, a finite element model of the pipeline with cracks of different sizes is established in ABAQUS, appropriate loads and boundary conditions are set, and the constitutive parameters corresponding to the material are input into the model, further including the following steps:

[0076] Step S11: Figure 2 As shown in the figure, the outer diameter of the pipe is 406 mm, the inner radius is 396.5 mm, and the wall thickness is 9.5 mm. A pipe model with cracks of different sizes is established in the finite element software ABAQUS. According to the symmetry of the pipe, one-half of the structure is selected to establish the finite element model, as shown in the figure. Figure 3AAs shown. The internal working pressure of the pipeline is 1.55MPa, and the axial force generated by the internal pressure is 15.41MPa. The pipeline sample material is DP2-A52 steel, and the constitutive parameters of DP2-A52 steel used in this model are input into the model, as shown in Table 1:

[0077] Table 1: Constitutive parameters of DP2-A52 steel used in this model

[0078]

[0079] Step S12: Add cracks of different sizes to the pipeline model through the Interaction module. The crack sizes are assumed to be 16.7 mm, 33.4 mm, and 41.7 mm. All models are analyzed using linear reduced integration three-dimensional elements (C3D8R). The front end of the crack is divided into finer grids, such as Figure 3B As shown. The model contains a total of 60080 units.

[0080] Step 102: numerically calculate the pipeline finite element model to obtain the stress intensity factor of the crack tip in the pipeline.

[0081] Step 102 specifically includes: performing numerical calculation on the finite element model of the pipeline containing cracks of different sizes to obtain the stress intensity factor of the crack tip in the pipeline containing cracks of different sizes, further including the following steps:

[0082] Step S21: During finite element calculation, in the History Output Request interface in the Step module, add the set history output variable of the crack stress intensity factor K;

[0083] Step S22: Perform finite element calculation on four pipeline models with different crack sizes. After the calculation is completed, in the Visualization module, obtain the historical output data of the stress intensity factor K. The stress intensity factor K and the crack size satisfy the following relationship:

[0084]

[0085] Where Y is the shape factor; σ is the stress; a is the crack size.

[0086] The shape coefficient Y can be obtained by fitting the above formula, and the specific data are shown in Table 2:

[0087] Table 2: Stress intensity factor K of pipes with different crack sizes

[0088]

[0089]

[0090] Step 103: Obtain a crack growth model.

[0091] Step 104: Obtain the pipeline crack size of the crack growth model.

[0092] Step 105: Determine the creep fatigue crack growth rate according to the pipeline crack size.

[0093] Step 106: Calculate the crack growth life according to the stress intensity factor and the creep fatigue crack growth rate. The crack growth life is the life span that a crack experiences when it grows from a certain initial size to a certain critical size.

[0094] Steps 103-106 are specifically: determining the creep fatigue crack growth rate related to the pipeline crack size, and further calculating the crack growth rate from a certain initial size a 0 Expand to a certain critical size a c The life span experienced; specifically including the following steps:

[0095] Step S31: According to the published literature [Yang H, Bao R, Zhang J, et al. Crack growth behavior of a nickel-based powder metallurgy superalloy under elevated temperature [J]. International Journal of Fatigue, 2011, 33 (4): 632-641.], Yang's crack growth model is selected. The model uses stress intensity factor K as the fracture parameter and can more accurately describe the crack growth behavior of the component. The crack growth rate curve satisfies the following relationship:

[0096]

[0097] K max =ΔK / (1-R)

[0098] f=(T+t h ) -1

[0099] Where da / dN is the crack growth rate; ΔK is the stress intensity factor range variable; C and n are fitting parameters obtained from fatigue crack growth experiments; A and m are fitting parameters obtained from creep crack growth experiments; D, q, p are 1 , p 2 , p 3 All are material parameters; K max is the maximum stress intensity factor; R is the stress ratio; f is the start-stop frequency; T is the time of the loading and unloading process; t his the continuous operation time of the pipeline. The specific data are shown in Table 3:

[0100] Table 3: Crack growth model parameter data

[0101]

[0102] Step S32: According to the selected crack growth model, the crack size a is integrated to obtain the crack growth life of the component, and the crack growth life curve of the pipe with different crack sizes is obtained, such as Figure 4 Its lifespan satisfies the following relationship:

[0103]

[0104] Where N is the crack growth life; a 0 is the initial crack size. In this example, it is assumed that a 0 0.5mm; a c is the critical crack size, a is the crack length, da is the difference between the cracks at two moments, and dN is the difference between the number of cycles at two moments. c For cracks of different sizes, the crack growth life obtained is also different.

[0105] Step 107: Determine the fracture toughness according to the pipeline crack size.

[0106] Step 107 is specifically: calculating the fracture toughness related to the pipeline crack size, where K IC is the fracture toughness expressed by the critical crack tip stress intensity factor, recorded as the first fracture toughness; J IC is the fracture toughness expressed by the critical J integral, recorded as the second fracture toughness; and δ c It is the fracture toughness expressed by the critical crack tip opening displacement and is recorded as the third fracture toughness.

[0107] Generally, fracture toughness is obtained through standard specimens, but specimens of the same material and specific structures have different fracture toughness. One of the key technologies of the present invention is to convert the fracture toughness of the specimen into the fracture toughness of the structure (pipeline) through finite element method.

[0108] Step 107 further includes the following steps:

[0109] Step S41: The fracture toughness and constraint parameter A of the DP2-A52 steel used in this embodiment d There is a specific unified relationship between IC / J ref -A d The correlation line is the fracture curve of the material, such as Figure 5As shown. The vertical coordinate of the correlation line is J IC / J ref , J IC is the second fracture toughness of the material, J ref is the fracture toughness of the reference sample. In the fracture curve, J IC is the data obtained from the experiment, J ref is the data of one of the reference samples, A d The data is simulated by finite element. Constraint parameter A d Satisfies the following relationship:

[0110] A d =δ / δ ref

[0111] Where, δ is the crack tip opening displacement (CTOD value) of the specimen or structural crack; δ ref is the CTOD value of the standard high-constraint reference specimen at fracture, and the specific data are shown in Table 4;

[0112] Table 4: Fracture toughness and constraint parameters of SEN(B) specimens with different in-plane constraints

[0113]

[0114]

[0115] Step S42: Based on the established finite element model of the cracked pipe, obtain the J integral and the constraint parameter A d The correlation line between IC / J ref -A d Correlation line, this correlation line is the crack opening force curve of the material. In the crack opening force curve, J IC is the data obtained by finite element calculation, J ref is the data of the finite element model of one of the reference specimens, A d It is also the data simulated by finite element.

[0116] Among them, the fracture curve and the opening force curve have the same horizontal and vertical coordinates, but the curve data points and slopes are different.

[0117] like Figure 6 As shown;

[0118] Step S43: The intersection of the fracture curve and the opening force curve is the cracking point of the sample. The ordinate of the intersection is equal to the fracture toughness J of the reference sample. ref The product of is the second fracture toughness J related to the crack size of the pipeline IC ,like Figure 7 The fracture toughness of pipes with different crack sizes is shown in Table 5:

[0119] Table 5: Fracture toughness of pipes with different crack sizes

[0120]

[0121] Step 108: Calculate the residual strength of the pipeline according to the fracture toughness and the pipeline crack size.

[0122] Step 108 specifically includes: calculating the residual strength of the pipeline based on the fracture toughness and crack size associated with the pipeline crack size, and further includes the following steps:

[0123] Step S51: Based on the fracture toughness in step S43, calculate the residual strength of the pipe containing cracks of different sizes. rs Satisfies the following relationship:

[0124]

[0125]

[0126] In the formula, K IC is the first fracture toughness; E is the elastic modulus of the material, the elastic modulus of DP2-A52 steel is 224000MPa; ν is the Poisson's ratio of the material, its value is 0.3; J IC is the second fracture toughness.

[0127] Step S52: Based on the residual strength results of the pipelines with cracks of different sizes in step S41, a residual strength curve of the pipeline is drawn, such as Figure 8 shown.

[0128] Step 109: constructing a damage tolerance assessment diagram of the high-temperature pipeline under creep fatigue load according to the crack growth life and residual strength, wherein the damage tolerance assessment diagram is used to assess the damage tolerance of the high-temperature pipeline under creep fatigue load.

[0129] Step 109 is specifically: combining the crack growth life curve in step S32 and the residual strength curve in step S52, establishing and drawing Fig. 9 The damage tolerance assessment diagram of a cracked pipe is shown.

[0130] In addition, based on the above method, the present invention also provides a damage tolerance assessment system for high temperature pipelines under creep fatigue load, comprising:

[0131] The pipeline finite element model building module 201 is used to build a pipeline finite element model containing cracks of different sizes.

[0132] The stress intensity factor calculation module 202 is used to perform numerical calculation on the pipeline finite element model to obtain the stress intensity factor of the crack tip in the pipeline.

[0133] The crack extension model acquisition module 203 is used to acquire the crack extension model.

[0134] The pipeline crack size acquisition module 204 is used to acquire the pipeline crack size of the crack growth model.

[0135] The creep fatigue crack growth rate determination module 205 is used to determine the creep fatigue crack growth rate according to the pipeline crack size.

[0136] The crack growth life calculation module 206 is used to calculate the crack growth life according to the stress intensity factor and the creep fatigue crack growth rate. The crack growth life is the life span experienced by the crack growing from a certain initial size to a certain critical size.

[0137] The fracture toughness determination module 207 is used to determine the fracture toughness according to the pipeline crack size.

[0138] The residual strength calculation module 208 is used to calculate the residual strength of the pipeline according to the fracture toughness and the pipeline crack size.

[0139] The damage tolerance assessment module 209 is used to construct a damage tolerance assessment diagram of the high-temperature pipeline under creep fatigue load according to the crack growth life and residual strength, and the damage tolerance assessment diagram is used to assess the damage tolerance of the high-temperature pipeline under creep fatigue load.

[0140] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0141] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for evaluating the damage tolerance of a high-temperature pipeline under creep fatigue load, characterized in that: include: Establish a finite element model of a pipeline with cracks of different sizes; Performing numerical calculation on the pipeline finite element model to obtain a stress intensity factor at a crack tip in the pipeline; Obtain crack growth model; Obtaining a pipeline crack size of the crack growth model; The creep fatigue crack growth rate is determined according to the pipeline crack size, and the crack growth rate is calculated using the following formula: K max =ΔK / (1-R) f=(T+t h ) -1 Where da / dN is the crack growth rate; ΔK is the stress intensity factor range variable; C and n are fitting parameters obtained from fatigue crack growth experiments; A and m are fitting parameters obtained from creep crack growth experiments; D, q, p1, p2, and p3 are all material parameters; K max is the maximum stress intensity factor; R is the stress ratio; f is the frequency; T is the cycle of the loading and unloading process; t h Holding time for creep load; The crack growth life is calculated according to the stress intensity factor and the creep fatigue crack growth rate. The crack growth life is the life span experienced by the crack growing from a certain initial size to a certain critical size. The crack growth life is calculated using the following formula: Where N is the crack growth life; a0 is the initial crack size; a c is the critical crack size; determining fracture toughness based on the crack size of the pipeline; Calculating the residual strength of the pipeline based on the fracture toughness and the pipeline crack size; According to the crack growth life and the residual strength, a damage tolerance assessment diagram of the high-temperature pipeline under the creep fatigue load is constructed, and the damage tolerance assessment diagram is used to assess the damage tolerance of the high-temperature pipeline under the creep fatigue load.

2. The damage tolerance assessment method for high temperature pipelines under creep fatigue load according to claim 1 is characterized in that: The stress intensity factor is calculated using the following formula: Among them, K is the stress intensity factor; Y is the shape factor; σ is the stress; a is the crack size.

3. The damage tolerance assessment method for high temperature pipelines under creep fatigue load according to claim 1 is characterized in that: The residual strength is calculated using the following formula: Among them, σ rs is the residual strength; K IC is the fracture toughness expressed by the critical crack tip stress intensity factor, recorded as the first fracture toughness; a c is the critical crack size; E is the elastic modulus of the pipeline material; ν is the Poisson's ratio of the pipeline material, J IC It is the fracture toughness expressed by the critical J integral and is recorded as the second fracture toughness.

4. A damage tolerance assessment system for high temperature pipelines under creep fatigue load, characterized in that: include: Pipeline finite element model building module, used to build pipeline finite element models containing cracks of different sizes; A stress intensity factor calculation module, used for performing numerical calculation on the pipeline finite element model to obtain a stress intensity factor at a crack tip in the pipeline; A crack extension model acquisition module, used to obtain a crack extension model; A pipeline crack size acquisition module, used to acquire the pipeline crack size of the crack propagation model; The creep fatigue crack growth rate determination module is used to determine the creep fatigue crack growth rate according to the pipeline crack size. The creep fatigue crack growth rate determination module adopts the following formula for calculation: K max =ΔK / (1-R) f=(T+t h ) -1 Where da / dN is the crack growth rate; ΔK is the stress intensity factor range variable; C and n are fitting parameters obtained from fatigue crack growth experiments; A and m are fitting parameters obtained from creep crack growth experiments; D, q, p1, p2, and p3 are all material parameters; K max is the maximum stress intensity factor; R is the stress ratio; f is the frequency; T is the cycle of the loading and unloading process; t h Holding time for creep load; The crack growth life calculation module is used to calculate the crack growth life according to the stress intensity factor and the creep fatigue crack growth rate. The crack growth life is the life span experienced by the crack from a certain initial size to a certain critical size. The crack growth life calculation module adopts the following formula for calculation: Where N is the crack growth life; a0 is the initial crack size; a c is the critical crack size; A fracture toughness determination module, used to determine the fracture toughness according to the crack size of the pipeline; A residual strength calculation module, used for calculating the residual strength of the pipeline according to the fracture toughness and the pipeline crack size; The damage tolerance assessment module is used to construct a damage tolerance assessment diagram of the high-temperature pipeline under creep fatigue load according to the crack growth life and residual strength, and the damage tolerance assessment diagram is used to assess the damage tolerance of the high-temperature pipeline under creep fatigue load.

5. The damage tolerance assessment system for high temperature pipelines under creep fatigue load according to claim 4 is characterized in that: The stress intensity factor calculation module uses the following formula for calculation: Among them, K is the stress intensity factor; Y is the shape factor; σ is the stress; a is the crack size.

6. The damage tolerance assessment system for high temperature pipelines under creep fatigue load according to claim 4, characterized in that: The residual strength calculation module uses the following formula for calculation: Among them, σ rs is the residual strength; K IC is the fracture toughness expressed by the critical crack tip stress intensity factor, recorded as the first fracture toughness; a c is the critical crack size; E is the elastic modulus of the pipeline material; ν is the Poisson's ratio of the pipeline material, J IC It is the fracture toughness expressed by the critical J integral and is recorded as the second fracture toughness.

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