A method and device for analyzing the life of high-temperature pipelines in power plants based on biaxial stress

Abstract

The present invention discloses a method and device for analyzing the life of a high-temperature pipeline of a power station based on biaxial stress. The analysis method includes: performing a stress analysis on the high-temperature pipeline of the power station, ignoring the radial stress and interlayer interaction of the pipeline, and considering the pipeline as a biaxial stress state; performing a stress analysis on a sample of a small punch test of the high-temperature pipeline of the power station, and establishing a connection with the stress of the high-temperature pipeline of the power station in the biaxial stress state to determine the test force of the small punch test; determining the effective wall thickness of the high-temperature pipeline of the power station to be tested, and obtaining the small punch test data of the high-temperature pipeline of the power station with the effective wall thickness under the test force condition of the small punch test, so as to obtain the life of the high-temperature pipeline of the power station to be tested. The present invention regards the pipeline as a multi-layer structure and ignores the interaction between layers; attributes the force of the pipeline to the action of the annular stress and the axial stress, and regards it as being in a biaxial stress state. Such an analysis method makes the force of the pipeline closer to the actual stress state.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline life analysis, and in particular to a method and device for analyzing the life of a high-temperature pipeline of a power station based on biaxial stress. Background Art

[0002] At present, the life analysis method of high-temperature pipelines in power plants is mainly based on the endurance strength data of pipeline materials. The analysis process is as follows: a section of pipe is cut from the pipeline, processed into an endurance strength specimen, and an endurance strength test is carried out under different stress conditions at the service temperature. The fracture stress and fracture time are recorded, and the fracture stress-time curve is drawn. Then, the remaining life is extrapolated to evaluate the life. There are two problems with this method. The first is that the stress state of the specimen is different from that of the actual service pipeline, which causes a large error in the evaluation. The specimen of the endurance strength test is in a uniaxial tensile stress state, while the actual pipeline is in a triaxial stress state; the second is that the sampling process of cutting a section of the pipeline and the pipeline recovery process are huge. In response to the second problem, a pipeline life assessment technology based on the micro-specimen method has emerged. This method can achieve micro-damage sampling, but the assessment process still uses the test results of the micro-specimen to convert into endurance strength data, and then conducts the assessment. There are two errors in this assessment process: one is that the conversion process is an empirical formula, which has a large error; the other is that the assessment process still uses the endurance strength extrapolation method, which itself has errors.

[0003] For the life analysis of high-temperature pipelines in power plants, a simplified, highly accurate method that is closer to the actual stress is needed. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a method for analyzing the life of a high-temperature pipeline in a power station based on biaxial stress, comprising:

[0005] A stress analysis is performed on the high-temperature pipeline of the power station, ignoring the radial stress and interlayer interaction of the pipeline, and the pipeline is regarded as a biaxial stress state;

[0006] Conduct stress analysis on the small punch test specimens of the power station high-temperature pipeline specimens, and establish a connection with the stress of the power station high-temperature pipeline in the biaxial stress state to determine the test force of the small punch test;

[0007] Determine the effective wall thickness of the power plant high temperature pipeline to be tested, and obtain the small punch test data of the power plant high temperature pipeline with effective wall thickness under the test force conditions of the small punch test, so as to obtain the life of the power plant high temperature pipeline to be tested.

[0008] Furthermore, the pipeline is considered to be in a biaxial stress state of being subjected to hoop stress and axial stress.

[0009] Furthermore, the hoop stress is,

[0010]

[0011] The axial stress is,

[0012]

[0013] Among them, σ α , σ L , P, Di, and Do are the hoop stress, axial stress, working pressure, inner diameter, and outer diameter of the high-temperature pipeline of the power station, respectively.

[0014] Furthermore, stress analysis is performed on the specimens of the small punch test of the high-temperature pipeline of the power station, and a connection is established with the stress of the high-temperature pipeline of the power station in the biaxial stress state to determine that the test force of the small punch test includes:

[0015] The small punch test of the high-temperature pipeline sample of the power station is regarded as a flat plate tensile test. In the steady-state creep stage, the deflection, deformation angle and thickness of the sample are regarded as constant, and the following equilibrium relationship exists:

[0016] F = 2πrtσ1cosθ;

[0017] σ2=σ1sinθ;

[0018] Where F is the test force of the small punch test, σ1 is the stress balanced with the loading load of the small punch test, and σ2 is the stress of the specimen caused by the balance with σ1 at the specimen radius r;

[0019] Let σ1=σ α , then there is,

[0020]

[0021]

[0022] Further, the determining of the effective wall thickness of the power station high temperature pipeline to be tested, and obtaining the small punch test data of the power station high temperature pipeline with the effective wall thickness under the test force condition of the small punch test, thereby obtaining the life of the power station high temperature pipeline to be tested includes,

[0023] The high-temperature pipeline of the power station to be tested is divided into inner and outer wall thickness, limit minimum wall thickness and effective wall thickness. The effective wall thickness of the high-temperature pipeline of the power station to be tested is the total wall thickness of the high-temperature pipeline of the power station to be tested minus the inner and outer wall thickness and the limit minimum wall thickness;

[0024] Under the test force conditions of the small punch test, a small punch test is carried out on the high-temperature pipeline of the power station with an effective wall thickness, and the deflection-time curve is obtained to determine the fracture time and obtain the life of the high-temperature pipeline of the power station to be tested.

[0025] Furthermore, the formula for obtaining the life of the high-temperature pipeline of the power station to be tested is:

[0026]

[0027] Among them, S is the life of the power station high-temperature pipeline to be tested, n and m are the number of layers and total number of layers of the power station high-temperature pipeline with effective wall thickness for small punch test, S 0(n) is the fracture time of a high-temperature pipeline sample in a power station, K is the safety factor, and N is the expansion factor.

[0028] Furthermore, the K is greater than 0.1 and less than 1.0;

[0029] The value of N is greater than 0.3 and less than 1.0.

[0030] Furthermore, the thickness of the inner and outer walls is 1 to 5 mm;

[0031] The limiting minimum wall thickness is determined based on the pipeline strength check.

[0032] The present invention also provides a device for analyzing the life of a high-temperature pipeline in a power station based on biaxial stress, comprising:

[0033] The pipeline state analysis module performs stress analysis on the high-temperature pipelines of the power station, ignoring the radial stress and interlayer interaction of the pipelines and treating the pipelines as a biaxial stress state;

[0034] The stress relationship establishment module performs stress analysis on the small punch test specimens of the power station high-temperature pipeline specimens, and establishes a relationship with the stress of the power station high-temperature pipeline in the biaxial stress state to determine the test force of the small punch test;

[0035] The pipeline life prediction module determines the effective wall thickness of the power plant high-temperature pipeline to be tested, and obtains the small punch test data of the power plant high-temperature pipeline with effective wall thickness under the test force conditions of the small punch test, thereby obtaining the life of the power plant high-temperature pipeline to be tested.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The present invention regards the pipeline as a multi-layer structure and ignores the interaction between layers. In addition, because radial stress is compressive stress, compressive stress will not cause damage to the pipeline. The radial stress of the pipeline is also ignored, and the force on the pipeline is attributed to the effects of annular stress and axial stress, and is regarded as being in a biaxial stress state. This analysis method makes the force on the pipeline closer to the actual stress state. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] 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 or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 A flow chart showing a method for analyzing the life of high-temperature pipelines in power plants based on biaxial stress is shown;

[0040] Figure 2 A schematic diagram of a device for conducting a small punch test on a specimen is shown;

[0041] Figure 3 A schematic diagram of the small punch test process is shown;

[0042] Figure 4 A typical deflection curve for a small punch test is shown;

[0043] Figure 5 A schematic diagram showing the small punch test as a flat plate tensile test is shown;

[0044] Figure 6 The schematic diagram of the structure of the life analysis device of the high temperature pipeline of the power station based on the biaxial stress is shown;

[0045] Description of reference numerals:

[0046] 1. Punch; 2. Press block; 3. Specimen. DETAILED DESCRIPTION

[0047] The following will be combined with the specific embodiments of the present invention and the drawings of the specification 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.

[0048] like Figure 1 As shown, in one embodiment of the present invention, a method for analyzing the life of a high-temperature pipeline in a power station based on biaxial stress is provided, comprising the following steps:

[0049] S101. Perform stress analysis on a high-temperature pipeline of a power station, ignore radial stress and interlayer interaction of the pipeline, and regard the pipeline as a biaxial stress state.

[0050] Since the radial stress of the high-temperature pipeline of the power station is compressive stress, this stress has no effect on the damage of the pipeline. Therefore, this radial stress is ignored and only the annular stress and axial stress are considered. The annular stress and axial stress caused by the internal pressure are shown in Equation 1 and Equation 2 respectively:

[0051]

[0052]

[0053] Among them, σ α , σ L , P, Di, and Do are the hoop stress, axial stress, working pressure, inner diameter, and outer diameter of the high-temperature pipeline of the power station, respectively.

[0054] It can be seen from equations 1 and 2 that the hoop stress caused by the internal pressure is greater than the axial stress. Under the thin-wall assumption, the hoop stress caused by the internal pressure is twice the axial stress. However, in actual situations, the axial stress should be added to the axial stress caused by the additional load.

[0055] S102. Perform stress analysis on the specimens of the power station high-temperature pipeline in the small punch test, and establish a connection with the stress of the power station high-temperature pipeline in the biaxial stress state to determine the test force of the small punch test.

[0056] The small punch specimen is a thin circular specimen with a thickness of 0.5mm to 1.0mm. The test process is to apply a constant load to the center of the circular specimen at a certain temperature, record the deformation of the center of the specimen, that is, the deflection of the center of the specimen, and obtain the deflection-time curve. Figure 2 and Figure 3 As shown, before the test begins, the sample 3 is placed in the middle of the pressing block 2 and pressed tightly. The temperature begins to rise. After the temperature reaches the service temperature of the pipeline, it is kept warm for a certain period of time. After the temperature is uniform, the punch 1 starts to load. The load is determined according to the pipeline stress analysis. During this process, the sample begins to deform. The deformation at the center of the sample can be recorded to obtain the deflection-time curve. The time when the sample breaks is the fracture time. The typical deflection curve is shown in Figure 4 shown.

[0057] In the specific small punch test, the small punch test of the high-temperature pipeline specimen of the power station is regarded as a flat plate tensile test, such as Figure 5 As shown, in the steady-state creep stage, the change of the sample deflection δ is very small and can be regarded as constant, then the deformation angle θ of the sample can also be regarded as constant, and the thickness t of the sample is also regarded as constant. The force of the sample at different cross sections at a distance r from the center of the sample is different, so the deflection, deformation angle and thickness of the sample are regarded as constant, and the following equilibrium relationship exists

[0058] F = 2πrtσ1 cosθ (Equation 3);

[0059] σ2=σ1sinθ (Equation 4);

[0060] Where F is the test force of the small punch test, σ1 is the stress balanced with the loading load of the small punch test, and σ2 is the stress of the specimen caused by the balance with σ1 at the specimen radius r;

[0061] Let σ1=σ α , then there is,

[0062]

[0063]

[0064] According to the actual small punch test, θ and r are distributed in a small range. Based on this, multiple different test forces F are predetermined. The small punch test is carried out under multiple test force F conditions. The test temperature of the small punch is the same as the service temperature of the high-temperature pipeline of the power station. Multiple deflection-time curves and fracture times can be obtained.

[0065] S103, determining the effective wall thickness of the power station high temperature pipeline to be tested, and obtaining small punch test data of the power station high temperature pipeline with effective wall thickness under the test force condition of the small punch test, so as to obtain the life of the power station high temperature pipeline to be tested.

[0066] The pipe wall thickness is divided into three parts: the inner and outer wall surfaces, the extreme minimum thickness part, and the load-bearing part (effective wall thickness). There are many defects on the inner and outer surfaces of the wall, generally 1 to 5 mm each, and this part does not participate in the life assessment. The extreme minimum wall thickness means that the pipeline will be quickly damaged under this wall thickness. The wall thickness is determined according to the pipeline strength check, and the safety factor is not considered during the strength check. Among them, the inner and outer wall surfaces and the extreme minimum thickness do not participate in the damage changes of the pipeline, and this part does not participate in the life assessment. Only the effective wall thickness participates in the life assessment. Through this classification, it is characterized that the failure of the high-temperature pipelines of the power station is a low-stress brittle fracture, which is more in line with the actual situation, that is, the high-temperature pipelines of the power station did not undergo obvious plastic deformation in the early stage of failure, but cracking without obvious plastic deformation occurred at the time of failure, and the fracture showed a brittle fracture phenomenon.

[0067] Subsequently, a small punch test is performed on the high-temperature pipeline of the power station with effective wall thickness under the test force conditions of the small punch test, and the deflection-time curve is obtained to determine the fracture time and obtain the life of the high-temperature pipeline of the power station to be tested. Due to the limitation of the small punch test on the thickness of the sample, the samples of the high-temperature pipeline of the power station with effective wall thickness are divided into multiple layers. Because the pipeline always has certain defects, there is also a certain synchronization phenomenon in the evolution of damage between layers. Therefore, the safety factor K (0.1, 1.0) and the expansion factor N (0.3, 1.0) need to be considered. The formula for the life of the high-temperature pipeline of the power station to be tested is,

[0068]

[0069] Among them, S is the life of the power station high-temperature pipeline to be tested, n and m are the number of layers and total number of layers of the power station high-temperature pipeline with effective wall thickness for small punch test, S 0(n) is the fracture time of a high-temperature pipeline sample in a power station, K is the safety factor, and N is the expansion factor.

[0070] like Figure 6 As shown, another embodiment of the present invention provides a device for analyzing the life of a high-temperature pipeline in a power station based on biaxial stress, comprising:

[0071] The pipeline state analysis module performs stress analysis on the high-temperature pipelines of the power station, ignoring the radial stress and interlayer interaction of the pipelines and treating the pipelines as a biaxial stress state;

[0072] The stress relationship establishment module performs stress analysis on the small punch test specimens of the power station high-temperature pipeline specimens, and establishes a relationship with the stress of the power station high-temperature pipeline in the biaxial stress state to determine the test force of the small punch test;

[0073] The pipeline life prediction module determines the effective wall thickness of the power plant high-temperature pipeline to be tested, and obtains the small punch test data of the power plant high-temperature pipeline with effective wall thickness under the test force conditions of the small punch test, thereby obtaining the life of the power plant high-temperature pipeline to be tested.

[0074] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for analyzing the life of high-temperature pipelines in power plants based on biaxial stress, characterized in that: include, A stress analysis is performed on the high-temperature pipeline of the power station, ignoring the radial stress and interlayer interaction of the pipeline, and the pipeline is regarded as a biaxial stress state; Conduct stress analysis on the small punch test specimens of the power station high-temperature pipeline specimens, and establish a connection with the stress of the power station high-temperature pipeline in the biaxial stress state to determine the test force of the small punch test; Determine the effective wall thickness of the power station high temperature pipeline to be tested, and obtain the small punch test data of the power station high temperature pipeline with effective wall thickness under the test force condition of the small punch test, so as to obtain the life of the power station high temperature pipeline to be tested; The high-temperature pipelines of the power station are regarded as being in a biaxial stress state, being subjected to hoop stress and axial stress; Among them, the hoop stress of the high-temperature pipeline of the power station is, ； The axial stress of the high-temperature pipeline of the power station is, ； in, σ α , σ L , P , Di , Do They are the hoop stress, axial stress, working pressure, inner diameter and outer diameter of the high temperature pipeline of the power station; The stress analysis of the small punch test specimens of the power station high temperature pipeline specimens is carried out, and the stress of the power station high temperature pipeline in the biaxial stress state is established to determine the test force of the small punch test, including: The small punch test of the high-temperature pipeline sample of the power station is regarded as a flat plate tensile test. In the steady-state creep stage, the deflection and deformation angle of the sample are θ ,thickness t Assuming it is constant, there is the following equilibrium relationship: ； ； in, F is the test force of the small punch test, σ 1 is the stress balanced with the loading load of the small punch test, σ 2 is the sample radius r Department and σ 1. Stress of the specimen caused by equilibrium; make , then there is, ； 。 2. The method for analyzing the life of high-temperature pipelines in power plants based on biaxial stress according to claim 1 is characterized in that: The determining of the effective wall thickness of the power station high temperature pipeline to be tested, and obtaining the small punch test data of the power station high temperature pipeline of the effective wall thickness under the test force condition of the small punch test, thereby obtaining the life of the power station high temperature pipeline to be tested includes: The high-temperature pipeline of the power station to be tested is divided into inner and outer wall thickness, limit minimum wall thickness and effective wall thickness. The effective wall thickness of the high-temperature pipeline of the power station to be tested is the total wall thickness of the high-temperature pipeline of the power station to be tested minus the inner and outer wall thickness and the limit minimum wall thickness; Under the test force conditions of the small punch test, a small punch test is carried out on the high-temperature pipeline of the power station with an effective wall thickness, and the deflection-time curve is obtained to determine the fracture time and obtain the life of the high-temperature pipeline of the power station to be tested.

3. The method for analyzing the life of high-temperature pipelines in power plants based on biaxial stress according to claim 2 is characterized in that: The formula for obtaining the life of the high-temperature pipeline of the power station to be tested is: ； in, S is the life of the high-temperature pipeline of the power station to be tested, n and m are the number of layers and the total number of layers of the small punch test for the high-temperature pipeline of the power station with effective wall thickness, S 0(n) is the fracture time of a high-temperature pipeline sample of a power station, K is the safety factor, N is the expansion factor.

4. The method for analyzing the life of high-temperature pipelines in power plants based on biaxial stress according to claim 3 is characterized in that: Said K The value of is greater than 0.1 and less than 1.0; Said N The value is greater than 0.3 and less than 1.

0.

5. The method for analyzing the life of high-temperature pipelines in power plants based on biaxial stress according to claim 2 is characterized in that: The thickness of the inner and outer walls is 1-5 mm; The limiting minimum wall thickness is determined based on the pipeline strength check.

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