A method for predicting the remaining life of a pipeline with multiple cracks in a weld weakness area

Abstract

The application discloses a pipeline residual life prediction method for welding weak area multi-cracks, which comprises the following steps: constructing composite excitation of the pipeline, simulating multi-crack propagation of the pipeline, and calculating residual life of the pipeline. The load spectrum of the pipeline system is simulated in the time domain to obtain a random time domain signal opposite to the load spectrum. The pipeline is subjected to modal analysis to obtain the inherent frequency of the pipeline. The resonance excitation of the pipeline is constructed through the maximum amplitude of acceleration and the inherent frequency of the pipeline. Then, the pressure on the inner wall surface of the pipeline is extracted through the CFX software, and the fluid pulsation excitation prestress field and the resonance excitation are added to the OTM framework. Through the simulation of the most dangerous collinear double-crack condition in the multi-cracks in the OTM framework, the pipeline residual life prediction method considering the welding weak area multi-cracks is established.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of an aero-engine pipeline system, and particularly relates to a pipeline residual life prediction method for multiple cracks in a welding weak area. BACKGROUND

[0002] The aero-engine pipeline system faces a complex vibration environment during the flight of an aircraft and the like. Structural failure caused by vibration is particularly serious. High-cycle fatigue failure of the aero-engine under complex vibration loads is the main cause of pipeline failure. After the pipeline design is completed, the fatigue strength of the pipeline is checked, which is a necessary link in the pipeline design. However, there are two difficulties in checking the fatigue strength of the pipeline.

[0003] 1) There is a lack of effective analysis means for the fatigue strength of the pipeline under complex excitation. The pipeline bears random vibration excitation and fluid excitation, which is a typical complex excitation, and the life solution based on single excitation is not accurate. Most existing scholars predict the fatigue life of the pipeline by simulating the maximum stress under the influence of single excitation. There is still a lack of effective evaluation means for the fatigue strength of the pipeline under complex excitation.

[0004] 2) The calculation of the pipeline life does not consider the welding life weak area. The pipeline is usually connected to the pipeline joint by welding and the like. The welding causes initial defects such as pores in the local area of the pipeline. These initial defects can cause the pipeline life to decrease sharply. In actual structures, multiple fatigue crack sources are generated by surface processing and welding inclusions, which is a typical multiple crack problem. Most of the current research on cracks focuses on a single crack. These methods only consider the expansion of the main crack and do not consider the interaction between the cracks, resulting in inaccurate life results. SUMMARY

[0005] In view of the above problems, the present application aims to provide a pipeline residual life prediction method for multiple cracks in a welding weak area, a method for adding random vibration excitation and fluid pulsation excitation in the calculation framework is proposed, which solves the problem of difficulty in adding complex excitation. And under the action of complex excitation, a numerical calculation method for accurately predicting the residual life of multiple cracks in the welding weak area of the pipeline is established.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows: a pipeline residual life prediction method for multiple cracks in a welding weak area, comprising the following steps:

[0007] 1) Constructing the complex excitation of the pipeline

[0008] Based on the time domain simulation of the load spectrum of the pipeline system, the resonance excitation and fluid pulsation excitation of the pipeline are obtained.

[0009] 2)Pipe multi-crack propagation simulation

[0010] Based on the pipe model of multiple initial cracks and pipe structure parameters, the numerical simulation of multiple cracks in the same line is carried out to obtain the crack propagation results of the pipe under the initial multiple cracks in the same line.

[0011] 3)Pipe residual life calculation

[0012] The obtained resonance excitation, fluid pulsation excitation and crack propagation results are integrated and added to the strong fluid-solid coupling framework to calculate the residual life of the pipe.

[0013] Further, the obtaining of the resonance excitation in step 1) includes the following sub-steps:

[0014] S1, time domain simulation of the load spectrum of the pipe system is carried out to obtain a random time domain signal corresponding to the load spectrum.

[0015] S2, rainflow counting analysis is performed on the random time domain signal to obtain the acceleration time domain maximum amplitude data of the random time domain signal.

[0016] S3, the material parameter data of each part of the pipe is obtained, and modal analysis is performed on the pipe to obtain the natural frequency of the pipe.

[0017] S4, the acceleration time domain maximum amplitude data and the natural frequency of the pipe are used to establish the resonance excitation of the pipe.

[0018] Further, the resonance excitation of the pipe established in step S3 is:

[0019] (1)

[0020] In the formula, a is the change rule of acceleration of the pipe two ends and the pipe support surface with time t, A is the maximum amplitude obtained after random vibration excitation time domain simulation, is the first order natural frequency after modal analysis of the pipe.

[0021] Further, the obtaining of the fluid pulsation excitation in step 1) includes the following sub-steps:

[0022] S5, the fluid pulsation excitation frequency is calculated based on the pipe structure data.

[0023] S6, the fluid pulsation excitation period is calculated according to the fluid pulsation excitation frequency.

[0024] S7, the fluid flow rate of the pipe is calculated, and the mean value and amplitude of the fluid pulsation are obtained.

[0025] S8, the fluid pressure pulsation is calculated based on the fluid pulsation excitation frequency, the fluid pulsation excitation period, and the mean value and amplitude of the fluid pulsation to obtain the fluid pulsation excitation to the inner wall of the pipe.

[0026] Further, the fluid pulsation excitation comprises the following process:

[0027] Fluid pulsation excitation is:

[0028] (2)

[0029] In the formula, N is the rotating speed, Z is the number of plungers.

[0030] Period of fluid pulsation excitation T is:

[0031] (3)

[0032] The calculation of the oil flow rate is:

[0033] (4)

[0034] In the formula, u is the oil flow rate, in m / s; Q is the rated flow of the plunger pump, in ml / s; d is the inner diameter of the conduit, in mm.

[0035] Pressure pulsation P The calculation is:

[0036] (5)

[0037] In the formula: a is the mean value of the oil pulsation; b is the amplitude value of the oil pulsation.

[0038] Further, step 2) the multi-crack propagation simulation of the pipeline is:

[0039] S9, based on the pipeline model of multiple initial cracks and the pipeline structure parameters, using the eigen-fracture algorithm, performing numerical simulation of the collinear multi-cracks in the OTM framework, and obtaining the crack propagation results of the pipeline under the initial collinear multi-cracks.

[0040] Further, the calculation process of step S8 is as follows:

[0041] For an elastic body that can restore its original shape after removing external force, its energy is as follows: (6)

[0042] In the formula, Ω is the area where the elastic body is located; is the three-dimensional entity edge; C is the crack area set; the entity edge includes the part bearing external load , and the other part is marked as , u is displacement, W is elastic strain energy density, S is external force acting area; and As follows:

[0043] (7)

[0044] (8)

[0045] In the formula, Is a preset boundary condition.

[0046] The energy of the elastic body is:

[0047] (9)

[0048] In the formula, Indicates, by To The sudden displacement of the crack tip.

[0049] The intrinsic displacement calculation based on the elastic body energy is: (10).

[0050] The beneficial effects of the present application are: the present application adds random vibration excitation and pulse excitation at the same time under the fluid-solid coupling framework, and calculates the residual life of multiple cracks in the pipeline welding weak area. Compared with the current research which mostly focuses on the fatigue life calculation under single excitation, the method proposed by the present application restores the real working condition of the engine pipeline system more accurately. At the same time, the current research on cracks mostly focuses on single crack. These methods only consider the expansion of the main crack and do not consider the interaction between cracks, resulting in an overly optimistic calculation of the residual life of the pipeline. The present application proposes a residual life calculation method for multiple cracks in the pipeline welding weak area based on the optimal transport meshless method (OTM), which solves the problem of grid limitation of finite element algorithm under the premise of considering the interaction between cracks, and further accurately predicts the residual life of multiple cracks in the pipeline welding weak area. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 The flow chart of resonance excitation extraction of the present application.

[0052] Figure 2 The load spectrum diagram of the pipeline system of the present application.

[0053] Figure 3 The time domain simulation result diagram of the random vibration signal of the present application.

[0054] Figure 4 The diagram of the pipeline of the present application applying fixed constraints.

[0055] Figure 5 The modal analysis diagram of the pipeline of the present application.

[0056] Figure 6 Flow chart for extracting distribution of pressure on inner wall of pipeline by fluid pulsation excitation of the present application.

[0057] Figure 7 Diagram for setting boundary of fluid of the present application.

[0058] Figure 8 Diagram for extracting pressure on inner wall of pipeline of the present application.

[0059] Figure 9 Diagram for calculating eigenfracture method of the present application.

[0060] Figure 10 For the present application, add parallel collinear double cracks in pipeline welding area (a) pipeline mesh model (b) local mesh encryption in pipeline welding area (c) add parallel collinear double cracks at weld position, crack length is 0.38mm.

[0061] Figure 11 Diagram for multiple crack propagation in pipeline welding area of the present application.

[0062] Figure 12 For the present application, stress concentration phenomenon occurs in first stage welding area and crack tip, initial multiple crack area crack starts to expand and merge, accompanied by multiple new defects.

[0063] Figure 13 For the present application, double cracks continue to expand at opposite tips, making initial cracks connected to each other, forming a large crack, leading to pipeline life decline.

[0064] Figure 14 For the present application, initial multiple cracks merge into growing cracks and continue to expand, merge with newly generated defects, until fracture. DETAILED DESCRIPTION

[0065] In order to enable those skilled in the art to better understand the technical solutions of the present application, the technical solutions of the present application are further described below in combination with the drawings and examples.

[0066] In the early hydraulic pipeline design process of the aircraft, due to the selection of a higher safety factor, the strength margin is sufficient, so that the working stress of the filled pipeline is lower than the allowable stress of the pipeline, and the fatigue strength problem is not prominent. The research on the filled pipeline is also concentrated on the dynamic response under the action of a single excitation. However, modern aviation hydraulic systems are developing towards high pressure, large load and light weight, and the strength reserve is getting less and less, and the fatigue problem is highlighted. And considering that the pipeline has a welding and other multi-crack sources and other weak areas, these areas have inclusions, voids and other initial crack sources, which can cause a sharp decline in the service life of the pipeline. Therefore, only under the action of composite excitation, the method for predicting the residual life of the pipeline in the welding weak area of multiple cracks can more accurately evaluate the structural safety of the pipeline system. Therefore, the application provides a pipeline residual life prediction method for welding weak area multiple cracks, comprising the following steps:

[0067] 1) Constructing a composite excitation of the pipeline

[0068] Based on the time domain simulation of the load spectrum of the pipeline system, the resonance excitation and the fluid pulsation excitation of the pipeline are obtained, and the resonance excitation specifically includes the following sub-steps:

[0069] S1, time domain simulation of the load spectrum of the pipeline system is performed to obtain a random time domain signal corresponding to the load spectrum;

[0070] S2, rainflow counting analysis is performed on the random time domain signal to obtain the acceleration time domain maximum amplitude data of the random time domain signal;

[0071] S3, the material parameter data of each part of the pipeline is obtained, and modal analysis is performed on the pipeline to obtain the natural frequency of the pipeline;

[0072] S4, the acceleration time domain maximum amplitude data and the natural frequency of the pipeline are used to establish the resonance excitation of the pipeline. The calculation formula of the resonance excitation of the pipeline is:

[0073] (1)

[0074] In the formula, a is the change rule of the acceleration of the pipeline two ends and the surface of the pipeline support with time t, A is the maximum amplitude obtained after time domain simulation of the random vibration excitation, is the first-order natural frequency obtained after modal analysis of the pipeline.

[0075] The fluid pulsation excitation includes the following sub-steps:

[0076] S5, the fluid pulsation excitation frequency is calculated through the pipeline structure data;

[0077] S6, the fluid pulsation excitation period is calculated according to the fluid pulsation excitation frequency;

[0078] S7, calculate the fluid flow rate of the pipeline, and obtain the mean value and amplitude of the fluid pulsation;

[0079] S8, calculate the fluid pressure pulsation based on the fluid pulsation excitation frequency, fluid pulsation excitation period, and the mean value and amplitude of the fluid pulsation, and obtain the fluid pulsation excitation to the inner wall of the pipeline.

[0080] The parameters in the above sub-steps are calculated as follows:

[0081] Fluid pulsation excitation is:

[0082] (2)

[0083] In the formula, N is the rotational speed, Z is the number of plungers;

[0084] The period of fluid pulsation excitation T is:

[0085] (3)

[0086] The calculation of oil flow rate is:

[0087] (4)

[0088] In the formula, u is the oil flow rate, unit: m / s; Q is the rated flow of the plunger pump, unit: ml / s; d is the inner diameter of the conduit, unit: mm;

[0089] Pressure pulsation P is calculated as:

[0090] (5)

[0091] In the formula: a is the mean value of the oil pulsation; b is the amplitude of the oil pulsation.

[0092] 2) Pipeline multi-crack propagation simulation

[0093] Based on the pipeline model of multiple initial cracks and pipeline structure parameters, the numerical simulation of multiple collinear cracks is carried out to obtain the crack propagation results of the pipeline under the initial multiple collinear cracks, for the following steps:

[0094] S9, based on the pipeline model of multiple initial cracks and pipeline structure parameters, the numerical simulation of multiple collinear cracks is carried out in the OTM framework using the eigen fracture algorithm to obtain the crack propagation results of the pipeline under the initial multiple collinear cracks. The calculation process is as follows:

[0095] For the elastic body which can restore to the original shape after removing the external force, the energy is as follows:

[0096] (6)

[0097] In the formula, Ω is the area where the elastic body is located; is the three-dimensional entity edge; C is the crack area set; the entity edge includes the part bearing external load , another part is marked as , u is displacement, W is elastic strain energy density, and S is the area of external force action; and as follows:

[0098] (7)

[0099] (8)

[0100] In the formula, is the preset boundary condition;

[0101] The energy of the elastic body is:

[0102] (9)

[0103] In the formula, , when to , the abrupt displacement of the crack tip;

[0104] The intrinsic displacement calculation based on the energy of the elastic body is:

[0105] (10).

[0106] 3) Pipeline residual life calculation

[0107] The obtained resonance excitation, fluid pulsation excitation and crack propagation results are integrated and added to the strong fluid-solid coupling framework to calculate the residual life of the pipeline.

[0108] Embodiment

[0109] As shown in the resonance excitation extraction flowchart shown in Figure 1 , first, the load spectrum of the pipeline system ( Figure 2 ) is simulated in the time domain to obtain a random time domain signal corresponding to the load spectrum, and the random time domain signal is subjected to rain flow counting analysis ( Figure 3 ) to obtain the acceleration time domain maximum amplitude information of the random signal.

[0110] To obtain the inherent frequency of the pipe and other information, modal analysis of the pipe is needed. The material models of the pipe parts are shown in Table 1. The material of the conduit is 0cr18ni9, the material of the metal felt is LY12-M, the material of the sleeve is LY12-CZ, the material of the bracket is 2B06, and the material of the bolt is 30CrMnSiA. The start and end positions of the pipe and the contact surface of the bracket are set as fixed constraints Figure 4 , and the modal and random vibration stress distribution of the pipe are calculated to obtain Figure 5 and Table 2. Thus, the inherent frequency information of the pipe is obtained.

[0111] Table 1 Material parameters for dynamic response simulation of the pipe

[0112]

[0113] Table 2 First three order inherent frequencies of the pipe

[0114]

[0115] Resonance excitation of the pipe is established:

[0116] (1)

[0117] In the formula, a is the acceleration of the pipe at both ends and the surface of the pipe bracket as a function of time t, A is the maximum amplitude obtained after time domain simulation of the random vibration excitation, is the first order inherent frequency after modal analysis of the pipe. In the simulation in this paper A= 0.0047 m / s 2 ，W 0 = 806.7 rad / s.

[0118] Through time domain simulation of the load spectrum, the most dangerous resonance excitation in the random excitation is obtained. The purpose of this section is to obtain the pressure of the fluid pulsation excitation on the inner wall surface of the pipe, so as to provide the OTM with the dynamic stress of the pipe under the combined excitation. The specific flow is as shown in Figure 6 . The calculation of the pressure of the fluid pulsation excitation on the inner wall surface of the pipe is based on the CFX software.

[0119] Figure 4 The pipe structure in uses a 9-plunger pump, the maximum rotational speed of which is 4200 r / min, and the rated flow is 270 ml / s, so the fluid pulsation excitation generated is

[0120] (2)

[0121] In the formula, N is the rotational speed, and Z is the number of plungers. The frequency of the fluid pulsation excitation generated by the plunger pump is f =630Hz .

[0122] The period T of the fluid pulsation excitation is:

[0123] (3)

[0124] The period T of the fluid pulsation excitation is: T =0.00158 s Since the stress response of the structure cannot reach a steady state in the first few periods, the simulation selects 10 periods. Therefore, the total time solved by CFX is 0.016s.

[0125] In CFX, the solution type is set to transient analysis, and the solution time and time step of the fluid are set. The calculation formula of the oil flow rate is

[0126] (4)

[0127] In formula 4, u is the oil flow rate, the unit is m / s; Q is the rated flow of the plunger pump, the unit is ml / s; d is the inner diameter of the conduit, the unit is mm. The inner diameter of the hydraulic conduit is d =13mm, the rated flow of the plunger pump is Q =270 ml / s ; the oil flow rate is u =2 m / s The mean and amplitude of the oil pulsation are 28MPa and 2.1MPa respectively, and the pressure pulsation function can be expressed as formula 5:

[0128] (5)

[0129] The left side is the fluid inlet surface, and the flow rate is set to be perpendicular to the cross section. The right side is the fluid outlet, and the outlet pressure is set to formula (5). The pressure on the inner wall surface of the pipeline is extracted, 1000 sampling points are set on the inner wall surface of the pipeline Figure 8 ), the pressure field on the inner wall of the pipeline is obtained, and the pre-load for OTM calculation is obtained.

[0130] The crack simulation of OTM mainly depends on the eigenfracture method, which only needs to give the energy release rate coefficient of the material, and can simulate the expansion process of the crack group. Therefore, the present application realizes the crack tip cracking simulation based on the eigenfracture method and the OTM method. The eigenfracture method is shown in Figure 9 , and the area where the elastomer is located is Ω. The edge of the three-dimensional entity is , and the crack region set is C. The edge of the entity mainly includes two parts, one part bears external load and is marked as , and the other part is marked as Therefore, the elastic body that can restore its original shape after the external force is removed can be obtained, and its energy is as follows:

[0131] (6)

[0132] wherein, and As follows

[0133] (7)

[0134] (8)

[0135] wherein, is a preset boundary condition. Therefore, the energy of the elastic body is not difficult to be given as:

[0136] (9)

[0137] wherein, represents, when to , the sudden displacement of the crack tip.

[0138] Schmidt, Li, et al. proposed an eigen-displacement method based on the elastic body energy.

[0139] (10).

[0140] Based on the optimal transport meshless method, the multi-crack propagation of the pipeline welding weak area is carried out. The grid file of the pipeline with an initial crack in this paper is as shown in Figure 10 The crack propagation algorithm adopts the eigen-fracture algorithm, and the simulation process is a pipeline model containing two initial cracks Figure 10 (c). In this model, the initial length of the two cracks is 0.38 mm, and the width is 0.1 mm. The collinear parallel double cracks have the greatest impact on the structure life, and are the most dangerous multi-crack situation. Therefore, the multi-cracks are arranged in parallel, and the collinear double crack situation is simulated. The optimal transport method is used to simulate the numerical simulation of the pipeline welding area with parallel double cracks. The total simulation time is 0.0016 s. The main related parameters of the numerical simulation algorithm are shown in Table 3.

[0141] Table 8 OTM simulation of pipeline dynamic stress related calculation parameters under composite excitation

[0142]

[0143] Based on the above discrete model, material parameters, initial conditions (including added excitation and OTM parameters), and boundary conditions Figure 7Using the calculated parameters (as shown), the pipeline model was numerically simulated with initial multiple crack clusters. The crack propagation results of the pipeline structure under initial collinear double cracks were obtained as follows: Figure 11 .pass Figure 11 It can be observed that for welded regions containing multiple initial cracks, the propagation of multiple cracks in the welded region mainly includes three stages.

[0144] The first stage is characterized by stress concentration in the welded area and at the crack tip due to the presence of the initial crack. Figure 12 As stress concentration occurs, cracks propagate and grow at their relative tips in the double-crack region, and the two cracks tend to merge and connect. In addition to the propagation of the existing double cracks, multiple small defects appear on the surface of the collinear region between the two cracks. These surface defects are only one unit deep and do not penetrate the pipe wall. During this stage, the double cracks gradually merge and propagate into a single crack.

[0145] The second stage is that the two cracks continue to expand from their relative tips until they connect with each other, forming a large crack. Figure 13 At this point, the initial cracks in the welded area merged from the original small cracks (length less than 0.38 mm) into a single visible long crack (length greater than 0.7 mm). As the double cracks in the pipe welded area merged, the defects on the outer surface of the pipe wall further increased, gradually merging into new small cracks.

[0146] In the third stage, the merged long cracks continue to expand. Figure 14 The cracks gradually merge with newly formed defects on the outer surface of the pipe wall until fracture. The simulation process reveals that weak areas, such as welded areas, have multiple initial defects. Although each initial defect may be small (crack length less than 0.38 mm), due to excitation and external loads, these initial cracks merge, creating a macroscopically visible crack. This results in a significant error in the pipeline lifespan estimate compared to calculating only one crack, leading to an overly optimistic lifespan prediction for weak areas such as welded areas. Therefore, for weak areas such as welded areas, after welding, non-destructive testing should be used to detect the presence of collinear or adjacent pores within the welded area.

[0147] This invention has the following innovative features:

[0148] 1) A method for extracting pipeline resonance excitation based on load spectrum is proposed. Then, the pressure on the inner wall surface of the pipeline is extracted by CFX software. Finally, the extracted resonance excitation and fluid pulsation excitation are added to the strong fluid-structure interaction (OTM) framework by clustering algorithm to complete the addition of composite excitation of engine pipeline system.

[0149] 2) Pipeline resonance excitation extraction method based on load spectrum, time domain simulation is carried out on the load spectrum of the pipeline system, random time domain signals relative to the load spectrum are obtained, modal analysis is carried out on the pipeline, the natural frequency of the pipeline is obtained, and the maximum amplitude of acceleration and the natural frequency of the pipeline are used to construct the pipeline resonance excitation.

[0150] 3) Fluid pulsation excitation prestress field adding based on clustering algorithm, since there is no correspondence between the inner wall pressure sampling point and the OTM grid file, the inner wall surface nodes are clustered according to the distance from the sampling point, and are divided into 100 sets. The load of the pressure sampling point is applied to each set to realize the addition of the fluid pulsation excitation prestress field in the OTM.

[0151] 4) Random resonance excitation and fluid pulsation excitation adding method based on strong fluid-solid coupling framework (OTM). The random vibration excitation, fluid pulsation excitation and discrete model, material parameters, initial conditions and boundary conditions extracted above are added to the strong fluid-solid coupling (OTM) of the application.

[0152] 5) Multi-crack propagation of pipeline welding weak area based on optimal transport meshless method. The multi-cracks are arranged in parallel to simulate the collinear double-crack condition. The optimal transport method is used to simulate the numerical simulation of the parallel double-crack existing in the pipeline welding area.

[0153] 6) Application of crack propagation simulation algorithm based on eigenfracture. The application of the optimal transport meshless method in crack propagation is mainly based on the eigenfracture algorithm, which solves the dependence of the existing finite element method on the grid, so that the crack propagation result has good physical correlation.

[0154] 7) Multi-crack propagation numerical prediction under the OTM framework of the application. The multi-cracks are arranged in parallel to simulate the collinear double-crack condition. Based on the above-mentioned composite excitation, the numerical simulation of the parallel double-crack existing in the pipeline welding area is carried out in the OTM framework of the application.

[0155] The principle of the application is: the load spectrum of the pipeline system is time domain simulated to obtain random time domain signals relative to the load spectrum. Modal analysis is carried out on the pipeline to obtain the natural frequency of the pipeline. The maximum amplitude of acceleration and the natural frequency of the pipeline are used to construct the pipeline resonance excitation. Then the pressure of the inner wall surface of the pipeline is extracted by CFX software, and the fluid pulsation excitation prestress field and the resonance excitation are added to the OTM framework. By simulating the most dangerous collinear double-crack condition in the multi-crack in the OTM framework, a multi-crack residual life prediction method considering the pipeline welding weak area is established.

[0156] The above shows and describes the basic principles, main features and advantages of the present application. The present application can also have various changes and improvements without departing from the spirit and scope of the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. A method for predicting the remaining life of a piping having a welded weak area with multiple cracks, characterized by, The method comprises the following steps: 1) constructing a composite excitation of the pipeline Based on the time domain simulation of the pipeline system load spectrum, the resonance excitation and the fluid pulsation excitation of the pipeline are obtained; 2) multi-crack propagation simulation of the pipeline Based on the pipeline model of multiple initial cracks and the pipeline structure parameters, the numerical simulation of the collinear multiple cracks is carried out to obtain the crack propagation results of the pipeline under the initial collinear multiple cracks; 3) calculation of the remaining life of the pipeline The obtained resonance excitation, fluid pulsation excitation and crack propagation results are integrated and added to the strong fluid-solid coupling framework to calculate the remaining life of the pipeline; The obtaining of the resonance excitation in step 1) comprises the following sub-steps: S1, time domain simulation of the load spectrum of the pipeline system to obtain a random time domain signal corresponding to the load spectrum; S2, rainflow counting analysis of the random time domain signal to obtain the acceleration time domain maximum amplitude data of the random time domain signal; S3, obtaining the material parameter data of each part of the pipeline, and carrying out modal analysis on the pipeline to obtain the natural frequency of the pipeline; S4, establishing the resonance excitation of the pipeline through the acceleration time domain maximum amplitude data and the natural frequency of the pipeline; The obtaining of the fluid pulsation excitation in step 1) comprises the following sub-steps: S5, calculating the fluid pulsation excitation frequency through the pipeline structure data; S6, calculating the fluid pulsation excitation period according to the fluid pulsation excitation frequency; S7, calculating the fluid flow rate of the pipeline and obtaining the pulsation mean value and amplitude of the fluid; S8, calculating the fluid pressure pulsation based on the fluid pulsation excitation frequency, the fluid pulsation excitation period, and the pulsation mean value and amplitude of the fluid to obtain the fluid pulsation excitation to the inner wall of the pipeline; Step 2) multi-crack propagation simulation of the pipeline is: S9, based on the pipeline model of multiple initial cracks and the pipeline structure parameters, the numerical simulation of the collinear multiple cracks is carried out in the OTM framework by using the eigen-fracture algorithm to obtain the crack propagation results of the pipeline under the initial collinear multiple cracks.

2. The method of claim 1, wherein, The resonance excitation of the pipeline established in step S4 is: ; In the formula, a is the change rule of acceleration of both ends of the pipeline and the surface of the pipeline support with time t, A is the maximum amplitude obtained after time domain simulation of random vibration excitation, is the first-order natural frequency after pipeline modal analysis.

3. The method of claim 1, wherein: The fluid pulsation excitation comprises the following processes: Fluid pulsation excitation is: ; wherein N is the rotational speed, Z is the number of plungers; Period of fluid pulsation excitation T is: ; The calculation of the oil flow rate is: ; wherein u is the oil flow rate in m / s; Q is the plunger pump rated flow in ml / s; d is the conduit inner diameter in mm; Pressure pulsations P The calculation is: ; In the formula, a is the pulsation mean value of the oil, and b is the pulsation amplitude of the oil.

4. The method of claim 1, wherein, The calculation process of step S9 is as follows: For an elastic body that can restore its original shape after removing external force, its energy is as follows: ; where Ω is the region of the elastomer; is a three-dimensional solid edge; C is a set of crack regions; solid edge includes a portion subjected to an external load , another portion is marked as , u is displacement, W is elastic strain energy density, S is the area of external force action; and as follows: ; In the formula, is a preset boundary condition; The energy of the elastic body is: ; wherein represents, by to the crack tip; and The calculation of the eigen-displacement based on the energy of the elastic body is:

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