Steam turbine welded rotor damage tolerance accounting method and system

Abstract

The invention discloses a steam turbine welded rotor damage tolerance accounting method and system, and relates to the field of rotor damage tolerance accounting. The problems that an existing rotor damage defect accounting method is complex in calculation process, errors are prone to occurring in calculation, and accuracy is difficult to guarantee are solved. The method comprises the following steps: firstly, calculating the crack size after crack propagation caused by low-cycle fatigue in the life period, determining the size after high-cycle fatigue crack propagation generated in the life period according to the crack size, and calculating a low-cycle fatigue crack strength factor and a high-cycle fatigue crack strength factor by utilizing the size after high-cycle fatigue crack propagation; whether the rotor can complete high-cycle and low-cycle fatigue service tasks or not is judged through two judgment formulas based on the two strength factors, and the accounting process is simple in calculation, high in accuracy and convenient to implement. The method is mainly applied to steam turbine rotor damage defect accounting.

Description

Technical Field

[0001] The present invention relates to the field of rotor damage tolerance calculation. Background Art

[0002] A steam turbine is a rotary power machine that converts thermal energy into mechanical energy and is widely used in industries such as electric power, navigation, and metallurgy. With the development of industry, steam turbines are gradually developing towards larger volume, higher power, and greater weight. At the same time, for issues such as overspeed, high load, manufacturing problems, and quality problems, the situation is becoming increasingly severe. In order to ensure the efficient and stable operation of the steam turbine rotor, defect calculation and determination of damage tolerance have become a major issue. At present, the methods for calculating rotor damage defects have basically formed a system, but the calculation means are relatively backward, using manual calculation or calculation with a calculator or computer;

[0003] For the current technology, the calculation process is complex, requiring multiple iterative calculations, and the calculation contains exponential terms. Even a small data difference will produce a large error, which makes it difficult to guarantee the accuracy of the calculation results. Secondly, the calculation process consumes a large amount of time and requires multiple verifications, which not only wastes human resources but also affects work efficiency. Finally, the existing manual calculation method is prone to calculation errors, which not only affects the accuracy of the calculation results but also increases the difficulty of subsequent work. Therefore, the above problems need to be solved. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems that the existing rotor damage defect calculation method has a complex calculation process, is prone to calculation errors, and it is difficult to guarantee accuracy. The present invention provides a method for calculating the damage tolerance of a welded rotor of a steam turbine.

[0005] The method for calculating the damage tolerance of a welded rotor of a steam turbine includes the following processes:

[0006] S1. According to the initial crack size a of the rotor, calculate the size a' after crack propagation under low-cycle fatigue during cold start;

[0007] S2. According to the size a' after crack propagation during cold start, calculate the size a'' after crack propagation under low-cycle fatigue during warm start;

[0008] S3. According to the size a'' after crack propagation during warm start, determine the low-cycle fatigue crack intensity factor K and the high-cycle fatigue crack intensity factor ΔK;

[0009] S4. Judge whether there is If the result is yes, it is determined that the rotor can complete the low-cycle fatigue service task; otherwise, it is determined that the rotor cannot complete the low-cycle fatigue service task; K IC is the material fracture toughness;

[0010] Judge whether there is If the result is yes, it is determined that the rotor can complete the high-cycle fatigue service task; otherwise, it is determined that the rotor cannot complete the high-cycle fatigue service task; ΔK TH is the material fracture threshold value.

[0011] Preferably,

[0012]

[0013] where C and m are the first and second properties of the material respectively, Δσ′ is the maximum stress during cold start of the low-cycle fatigue unit, and N′ is the number of start-stop cycles during cold start within the service life.

[0014] Preferably,

[0015] where C and m are the first and second properties of the material respectively, Δσ″ is the maximum stress during warm start of the low-cycle fatigue unit, and N″ is the number of start-stop cycles during warm start within the service life.

[0016] Preferably, σ is the stress under low-cycle fatigue.

[0017] Preferably, Δσ is the stress under high-cycle fatigue, which is 2 times the bending stress generated by the self-weight of the rotor.

[0018] The damage tolerance accounting system for a steam turbine welded rotor includes a storage device, a processor, and a computer program stored in the storage device and executable on the processor. The processor executes the computer program to implement the damage tolerance accounting method for the steam turbine welded rotor as described.

[0019] Advantages of the present invention:

[0020] Based on the operating characteristics of the rotor, once the high-cycle fatigue crack growth condition is met, the entire rotor will be completely broken in half within a few days. Therefore, defects that meet the high-cycle fatigue growth condition are not allowed. Thus, the present invention provides a new damage tolerance accounting method for a steam turbine welded rotor. First, calculate the crack size after crack growth caused by low-cycle fatigue during the service life. Determine the size after high-cycle fatigue crack growth during the service life based on this crack size. Calculate the low-cycle fatigue crack intensity factor and the high-cycle fatigue crack intensity factor using the size after high-cycle fatigue crack growth. Based on the two intensity factors, determine whether the rotor can complete the high- and low-cycle fatigue service tasks through two judgment formulas. This accounting process is implemented by a computer, is simple to calculate, and the decimal places in the program accounting process can be retained up to 16 decimal places at most, with high calculation accuracy and easy implementation. At the same time, it ensures the operation reliability and safety of the high steam turbine system and accelerates the digital transformation of the factory.

[0021] In specific applications, new accounting methods can be introduced in the field of safety evaluation of welded rotors to enhance data readability and improve the level of intelligence; promote the integration of traditional methods and intelligence, significantly improving calculation efficiency and competitiveness; at the same time, in order to ensure quick start-up learning and avoid errors, excessive redundant parts are discarded. Brief Description of the Drawings

[0022] Figure 1 It is a schematic diagram of the principle of the method for calculating the damage tolerance of the welded rotor of the steam turbine described in the present invention. Specific Embodiments

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0024] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0025] Rotor fatigue fracture is divided into two forms, namely high-cycle fatigue and low-cycle fatigue. Generally, the stress suffered by high-cycle fatigue is relatively small, and the stress of low-cycle fatigue is relatively large. Correspondingly, high-cycle fatigue only meets the crack propagation condition when the crack size is relatively large, and low-cycle fatigue meets the crack propagation condition when the crack size is relatively small. Generally, the crack fracture mode to be judged is that after the crack is formed, it meets the crack propagation condition of low-cycle fatigue, and as the crack expands, it meets the condition of high-cycle fatigue and fractures quickly. Therefore, it is necessary to calculate the size after crack propagation to determine whether the service task can be completed during the service life, and a method for calculating the damage tolerance of the welded rotor of the steam turbine is provided.

[0026] Specific Embodiment 1. In combination with Figure 1 Describe this embodiment. The method for calculating the damage tolerance of the welded rotor of the steam turbine described in this embodiment includes the following processes:

[0027] S1. According to the initial crack size a of the rotor, calculate the size a' of the crack after propagation under low-cycle fatigue during cold start.

[0028] Furthermore,

[0029] where C and m are the first and second properties of the material respectively, Δσ' is the maximum stress during cold start of the low-cycle fatigue unit, and N' is the number of start-up and shutdown times during cold start within the service life.

[0030] S2. Calculate the size a″ of the crack after warm start under low-cycle fatigue according to the size a′ of the crack after cold start crack propagation;

[0031]

[0032] Where C and m are the first and second properties of the material respectively, Δσ″ is the maximum stress during warm start of the low-cycle fatigue unit, and N″ is the number of start-stop cycles during warm start within the service life.

[0033] S3. Determine the low-cycle fatigue crack intensity factor K and the high-cycle fatigue crack intensity factor ΔK according to the size a″ of the crack after warm start;

[0034] S4. Judge whether there is If the result is yes, it is determined that the rotor can complete the low-cycle fatigue service task; otherwise, it is determined that the rotor cannot complete the low-cycle fatigue service task; K IC is the material fracture toughness;

[0035] Judge whether there is If the result is yes, it is determined that the rotor can complete the high-cycle fatigue service task; otherwise, it is determined that the rotor cannot complete the high-cycle fatigue service task; ΔK TH is the material fracture threshold.

[0036] Furthermore, σ is the stress under low-cycle fatigue.

[0037] Furthermore, Δσ is the stress under high-cycle fatigue, which is twice the bending stress generated by the self-weight of the rotor.

[0038] In this embodiment, since there are multiple processes for rotor startup, and no high-cycle fatigue occurs under the condition of passing the entire calculation, so we only consider low-cycle fatigue. The stress magnitudes in different processes are inconsistent, so iteration is required to take into account all startup conditions.

[0039] First, calculate the crack size after crack propagation caused by low-cycle fatigue within the service life. Determine the crack size after high-cycle fatigue crack propagation during the service life based on this crack size. Calculate the low-cycle fatigue crack intensity factor and the high-cycle fatigue crack intensity factor using the crack size after high-cycle fatigue crack propagation. Based on the two intensity factors, judge whether the rotor can complete the high- and low-cycle fatigue service tasks through two judgment formulas. This calculation process is simple, highly accurate, and easy to implement. At the same time, it ensures the operation reliability and safety of the high-pressure steam turbine system and accelerates the digital transformation of the factory.

[0040] The method for calculating the damage tolerance of a welded rotor of a steam turbine proposed by the present invention can greatly improve the calculation efficiency and accuracy of the rotor damage tolerance, thereby ensuring the safe and stable operation of the steam turbine.

[0041] Specific Embodiment 2. The damage tolerance accounting system for a steam turbine welded rotor described in this embodiment includes a storage device, a processor, and a computer program stored in the storage device and operable on the processor. The processor executes the computer program to implement the damage tolerance accounting method for a steam turbine welded rotor as described in Specific Embodiment 1.

[0042] Verification Test:

[0043] The effectiveness of the present invention is illustrated by the following verification tests, specifically:

[0044] Comparisons are made by manually accounting for 10 positions of a rotor. The traditional method takes one and a half hours, while the accounting method of the present invention only takes 10 minutes. Most of the time for the calculation of the present invention is consumed in manually entering data. If data is entered in Excel, the default is 8 decimal places, and from initially retaining 8 decimal places to 16 significant figures in the program, the maximum error is reduced by 7%.

[0045] At the same time, due to the semi-automated operation of the program, the error rate of manual calculation can be greatly reduced. From initially having about one position error in manually calculating a rotor to now having basically no errors, the workload of reexamination is reduced, work efficiency is improved, and important data support is provided for the design, manufacture, and maintenance of steam turbines, which is of great significance for improving reliability and safety.

[0046] Although the present invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed, as long as they do not deviate from the spirit and scope of the present invention as defined by the appended claims. It should be understood that different dependent claims and the features described herein can be combined in a manner different from that described in the original claims. It should also be understood that the features described in connection with a single embodiment can be used in other described embodiments.

Claims

1. A method for calculating damage tolerance of a steam turbine welded rotor, characterized in that: The method includes the following steps: S1. Calculate the size a′ of the cold start crack extension under low cycle fatigue according to the initial crack size a of the rotor; S2. Calculate the size a″ of the warm-state crack extension under low-cycle fatigue based on the size a′ of the cold-state crack extension; S3. Determine the low-cycle fatigue crack intensity factor K and the high-cycle fatigue crack intensity factor ΔK according to the size a″ after the warm-state starting crack propagates; S4. Determine whether it exists If the result is yes, it is determined that the rotor can complete the low-cycle fatigue service mission, otherwise, it is determined that the rotor cannot complete the low-cycle fatigue service mission; K IC is the fracture toughness of the material; Determine whether it exists If the result is yes, it is determined that the rotor can complete the high-cycle fatigue service mission, otherwise, it is determined that the rotor cannot complete the high-cycle fatigue service mission; ΔK TH is the material fracture threshold.

2. The damage tolerance calculation method for a steam turbine welded rotor according to claim 1, characterized in that: Among them, C and m are the first and second properties of the material respectively, Δσ′ is the maximum stress during cold start of the low-cycle fatigue unit, and N′ is the number of starts and stops during cold start during the service life.

3. The method for calculating damage tolerance of a steam turbine welded rotor according to claim 1, characterized in that: Among them, C and m are the first and second properties of the material respectively, Δσ″ is the maximum stress during warm start of the low-cycle fatigue unit, and N″ is the number of starts and stops during warm start during the service life.

4. The method for calculating damage tolerance of a steam turbine welded rotor according to claim 1, characterized in that: σ is the low cycle fatigue stress.

5. The method for calculating damage tolerance of a steam turbine welded rotor according to claim 1, characterized in that: Δσ is the high cycle fatigue stress, which is twice the bending stress generated by the rotor's own weight.

6. A damage tolerance calculation system for a steam turbine welded rotor, comprising a storage device, a processor, and a computer program stored in the storage device and executable on the processor, characterized in that: The processor executes a computer program to implement the damage tolerance calculation method for a steam turbine welded rotor as claimed in any one of claims 1 to 5.

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