Impact turbine runner bucket defect allowable limit value determination method

Abstract

The invention relates to the technical field of impulse water turbines, in particular to an impulse water turbine runner bucket defect allowable limit value determination method, which comprises the following steps of: dividing a runner bucket into different partitions, and respectively defining allowable safety coefficients for the partitions according to the safety level difference of the different partitions; according to the obtained dynamic stress calculation result, a defect crack stress intensity factor is calculated based on a fracture mechanics method; according to the obtained stress intensity factor calculation result, the defect crack non-expansion safety coefficient of each partition of the runner bucket is calculated; the obtained crack non-expansion safety coefficient and the defined allowable safety coefficient are used as judgment conditions, and a defect allowable limit value for guaranteeing crack non-expansion is determined. According to the method, the defect allowable limit value of the impact type runner bucket meeting the safety and stability requirements can be determined according to the actual stress state, and the problem of cost waste caused by insufficient setting basis of the defect limit value and blind repair during flaw detection of the runner bucket is solved.

Description

Technical Field

[0001] The invention relates to the technical field of impulse turbines, and in particular to a method for determining an allowable limit value of defects of an impulse turbine runner bucket. Background Art

[0002] The runner bucket is the core component of the impulse turbine, responsible for converting the gravitational potential energy of the water body into mechanical energy. During operation, it is subjected to the impact force from the DC nozzle, which has high-frequency alternating characteristics, resulting in the risk of fatigue damage and defect crack propagation of the runner bucket. In order to ensure the safe and stable operation of the unit and prevent fatigue damage and defect crack propagation of the runner bucket, it is necessary to set the defect tolerance limit for flaw detection. The existing defect tolerance limit is usually determined according to the relevant inspection standards. The limit value in the standard is irrelevant to the stress level at the location of the defect, resulting in defects that do not endanger the safe and stable operation of the runner bucket being forced to be repaired until the standard defect tolerance limit requirements are met. This imprecise method of determining the defect tolerance limit and unscientific defect handling requirements have led to a series of problems such as extended production and manufacturing cycle of the runner bucket, increased labor and material costs, and increased risk of defect repair. Summary of the invention

[0003] In order to solve the above technical problems, the present invention proposes a method for determining the allowable limit of defects of the impulsive turbine runner bucket, which can determine the allowable limit of defects of the impulsive turbine runner bucket that meets the safety and stability requirements according to the actual stress state, and solve a series of problems such as insufficient basis for setting defect limits and blind repairs during flaw detection of the runner bucket, extended production and manufacturing cycle, increased labor and material costs, and increased risk of defect repair.

[0004] The present invention is achieved by adopting the following technical solutions:

[0005] A method for determining an allowable limit value of a defect of a runner bucket of an impulse turbine comprises the following steps:

[0006] Step S1, dividing the runner bucket into different zones according to the importance of different zones of the runner bucket and the differences in material processes, namely, the water cutting blade, the welding surface, the root of the water dividing blade, the bucket body and the hub;

[0007] Step S2, defining an allowable safety factor for each partition according to the difference in safety levels of the different partitions divided in step S1;

[0008] Step S3, calculating the dynamic stress of the runner bucket based on the fluid-solid coupling method;

[0009] Step S4, defining a crack size matrix consisting of different crack depths and different crack lengths;

[0010] Step S5, calculating the defect crack stress intensity factor based on the fracture mechanics method according to the dynamic stress calculation result obtained in step S3;

[0011] Step S6, calculating the safety factor of non-extension of defect cracks in each partition of the runner bucket according to the calculation result of the stress intensity factor obtained in step S5;

[0012] Step S7, using the crack non-extension safety factor obtained in step S6 and the allowable safety factor defined in step S2 as judgment conditions, determine the defect tolerance limit that ensures that the crack does not extend.

[0013] According to the importance of different areas of the runner bucket and the differences in material technology, that is, the differences in stress levels of various parts of the runner bucket, and the differences between forgings and welding materials in various parts, the runner bucket is divided into different zones Z i .

[0014] According to the stress levels of different partitions divided in step S1, the differences in metal material properties and the actual damage, different safety levels are determined, and the allowable safety factor [n i ].

[0015] Establish a numerical simulation model of the runner bucket fluid and solid structure, define reasonable boundary conditions and loads, complete the runner bucket fluid-solid coupling stress solution, and solve the dynamic stress σ through fast Fourier transform i .

[0016] Comprehensively consider the defect shape, defect direction, defect detection, defect repair and other factors, determine the key parameters of defects that affect safety, and define the crack depth b j and different crack lengths a j The crack size matrix [b j ,a j ].

[0017] According to the dynamic stress calculation results obtained in step S3, the defect crack stress intensity factor K is calculated based on the fracture mechanics method. Iij , the simplified calculation formula is:

[0018]

[0019] Among them, K Iij is the crack stress intensity factor, σ i is the dynamic stress of the runner bucket, b j is the crack depth, a j is the crack length.

[0020] According to the calculation results of the stress intensity factor obtained in step S5, the safety factor n of the non-extension of the defect crack in each partition of the runner bucket is calculated.i , the calculation formula is:

[0021] n i =ΔK th / K Iij

[0022] Among them, n i K is the safety factor of crack non-extension, Iij is the crack stress intensity factor, ΔK th is the crack extension threshold.

[0023] The crack non-extension safety factor obtained in step S6 and the allowable safety factor defined in step S2 are used as the judgment conditions, that is, n i ≥[n i ], determine the defect tolerance limit [b i ] and [a i ].

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention divides the runner bucket into different zones according to the importance of different areas and the differences in material processes, and further defines an allowable safety factor for each zone according to the differences in safety levels of the different zones. This approach is more in line with actual engineering needs and can avoid blindly unified defect detection limits.

[0026] 2. The dynamic stress of the runner bucket is calculated based on the fluid-solid coupling method, and a crack size matrix consisting of different crack depths and different crack lengths is defined. According to the obtained dynamic stress calculation results, the stress intensity factor of the defect crack is calculated based on the fracture mechanics method. This method can effectively improve the accuracy of the stress state calculation.

[0027] 3. Based on the calculation results of the stress intensity factor, the safety factor of non-extension of defect cracks in each partition of the runner bucket is calculated. The obtained safety factor of non-extension of cracks and the defined allowable safety factor are used as judgment conditions to determine the defect tolerance limit that ensures that cracks do not extend. The correlation between the stress state and the defect tolerance limit is innovatively realized. While ensuring safety, it can significantly reduce the workload of unnecessary defect repairs, thereby significantly saving cost and time. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a flow chart of the method for determining the allowable limit of impingement turbine runner bucket defects.

[0029] Figure 2 This is a schematic diagram of the impact wheel bucket partition. DETAILED DESCRIPTION

[0030] The present application is further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present application.

[0031] The flow of the method for determining the allowable limit of impulsive turbine runner bucket defects is as follows: Figure 1 As shown, the first specific implementation mode includes the following steps:

[0032] Step S1, dividing the runner bucket into different zones according to the importance of different zones of the runner bucket and the differences in material processes, namely, the water cutting blade 1, the welding surface 2, the root of the water dividing blade 3, the bucket body 4 and the hub 5;

[0033] Step S2, defining an allowable safety factor for each partition according to the difference in safety levels of the different partitions divided in step S1;

[0034] Step S3, calculating the dynamic stress of the runner bucket based on the fluid-solid coupling method;

[0035] Step S4, defining a crack size matrix consisting of different crack depths and different crack lengths;

[0036] Step S5: Calculate the defect crack stress intensity factor based on the fracture mechanics method according to the dynamic stress calculation result obtained in step S3;

[0037] Step S6: Calculate the safety factor of non-propagation of defect cracks in each partition of the runner bucket according to the calculation result of the stress intensity factor obtained in step S5;

[0038] Step S7: Using the crack non-extension safety factor obtained in step S6 and the allowable safety factor defined in step S2 as judgment conditions, determine the defect tolerance limit that ensures that the crack does not extend.

[0039] In this implementation, a method for determining the allowable limit of defects in the impeller bucket of an impulse turbine is established according to the process. According to the actual stress state, the allowable limit of defects in the impeller bucket that meets the safety and stability requirements is determined, thereby solving a series of problems caused by insufficient basis for setting defect limits during flaw detection of the impeller bucket and blind repairs, such as extended production and manufacturing cycle, increased labor and material costs, and increased risk of defect repair.

[0040] Specific implementation method 2: Figure 1 As shown, this embodiment further defines S1 of the specific embodiment 1. In this embodiment, in S1, the runner bucket is divided into different partitions Z according to the importance of different areas of the runner bucket and the difference in material process, that is, the difference in stress levels of various parts of the runner bucket, and the difference between forgings and welding materials of various parts. i .

[0041] In this implementation, different parts of the bucket are divided into different zones according to stress and material differences, which provides basic conditions for determining the allowable defect limit values ​​by zone.

[0042] Specific implementation method three: Figure 1 As shown, this embodiment further limits S2 of the specific embodiment 1. In this embodiment, in S2, different safety levels are determined according to the stress levels of different partitions divided in step S1, the differences in metal material properties and the actual damage conditions, and the allowable safety factor [n i ].

[0043] In this embodiment, the allowable safety factor of each partition of the runner bucket is set according to the difference in safety levels of different partitions, providing a basis for evaluating defect safety.

[0044] Specific implementation method four: Figure 1 As shown, this embodiment further limits S3 of the specific embodiment 1. In this embodiment, in S3, a numerical simulation model of the runner bucket fluid and solid structure is established, reasonable boundary conditions and loads are defined, the runner bucket fluid-solid coupling stress solution is completed, and the dynamic stress σ is solved by fast Fourier transform. i .

[0045] In this embodiment, a numerical simulation method is used to solve the stress distribution that changes with time when the runner bucket is in working condition, and dynamic stress data is extracted from each partition stress curve for calculation of the defect crack stress intensity factor.

[0046] Specific implementation method five: Figure 1 As shown, this embodiment further limits S4 of the specific embodiment 1. In this embodiment, in S4, factors such as defect shape, defect direction, defect detection, and defect repair are comprehensively considered to determine the key defect parameters that characterize the safety, and define the crack depths b j and different crack lengths a j The crack size matrix [b j ,a j ].

[0047] In this implementation, based on the principle of conservative calculation, key parameters characterizing defects are simplified, and crack depth and length are used as key parameters affecting the stress intensity factor for subsequent calculations.

[0048] Specific implementation method six: Figure 1As shown, this embodiment further limits S5 of the specific embodiment 1. In this embodiment, in S5, the defect crack stress intensity factor K is calculated based on the fracture mechanics method according to the dynamic stress calculation result obtained in step S3. Iij , the simplified calculation formula is:

[0049]

[0050] Among them, K Iij is the crack stress intensity factor, σ i is the dynamic stress of the runner bucket, b j is the crack depth, a j is the crack length.

[0051] In this implementation, based on the principle of conservative calculation, the defect stress intensity factor calculation formula is simplified, and a new simplified calculation formula is established, which has strong practicality.

[0052] Specific implementation method seven: Figure 1 As shown, this embodiment further limits S6 of the specific embodiment 1. In this embodiment, in S6, according to the calculation result of the stress intensity factor obtained in step S5, the safety factor n of the non-extension of the defect crack in each partition of the runner bucket is calculated. i , the simplified calculation formula is:

[0053] n i =ΔK th / K Iij

[0054] Among them, n i K is the safety factor of crack non-extension, Iij is the crack stress intensity factor, ΔK th is the crack extension threshold.

[0055] In this implementation, the safety factor of non-extension of defect cracks in each partition of the runner bucket is obtained for subsequent defect safety evaluation.

[0056] Specific implementation method eight: Figure 1 As shown, this embodiment further limits S7 of the specific embodiment 1. In this embodiment, in S7, the crack non-extension safety factor obtained in step S6 and the allowable safety factor defined in step S2 are used as the judgment conditions, that is, n i ≥[n i ], determine the defect tolerance limit [b i ] and [a i ].

[0057] In this implementation, by comparing the defect crack non-extension safety factor with the allowable value, the defect tolerance limit for crack non-extension is obtained, which is used to guide design development and on-site testing.

[0058] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, it should be clear to those skilled in the art that the technical solutions described in the above embodiments may be modified, or some or all of the technical features therein may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the allowable limit of impulsive turbine runner bucket defects. Its characteristics include the following steps: Step S1, dividing the runner bucket into different zones according to the importance of different zones of the runner bucket and the differences in material processes, namely, the water cutting blade (1), the welding surface (2), the root of the water dividing blade (3), the bucket body (4) and the hub (5); Step S2, defining an allowable safety factor for each partition according to the difference in safety levels of the different partitions divided in step S1; Step S3, calculating the dynamic stress of the runner bucket based on the fluid-solid coupling method; Step S4, defining a crack size matrix consisting of different crack depths and different crack lengths; Step S5, calculating the defect crack stress intensity factor based on the fracture mechanics method according to the dynamic stress calculation result obtained in step S3; Step S6, calculating the safety factor of non-extension of defect cracks in each partition of the runner bucket according to the calculation result of the stress intensity factor obtained in step S5; Step S7, using the crack non-extension safety factor obtained in step S6 and the allowable safety factor defined in step S2 as judgment conditions, determine the defect tolerance limit that ensures that the crack does not extend.

2. The method for determining the allowable limit of defects of a runner bucket of an impulse turbine according to claim 1, characterized in that: According to the importance of different areas of the runner bucket and the differences in material technology, that is, the differences in stress levels of various parts of the runner bucket, and the differences between forgings and welding materials in various parts, the runner bucket is divided into different zones Z i .

3. The method for determining the allowable limit of defects of a runner bucket of an impulse turbine according to claim 2, characterized in that: According to the stress levels of different partitions divided in step S1, the differences in metal material properties and the actual damage, different safety levels are determined, and the allowable safety factor [n i ].

4. The method for determining the allowable limit of defects of a runner bucket of an impulse turbine according to claim 1, characterized in that: Establish a numerical simulation model of the runner bucket fluid and solid structure, define reasonable boundary conditions and loads, complete the runner bucket fluid-solid coupling stress solution, and solve the dynamic stress σ through fast Fourier transform i .

5. The method for determining the allowable limit of defects of a runner bucket of an impulse turbine according to claim 1, characterized in that: Comprehensively consider the defect shape, defect direction, defect detection, and defect repair factors, determine the key parameters of defects that affect safety, and define the crack depth b j and different crack lengths a j The crack size matrix [b j ,a j ].

6. A method for determining the allowable limit of defects of a runner bucket of an impulse turbine according to claim 4, characterized in that: According to the dynamic stress calculation results obtained in step S3, the defect crack stress intensity factor K is calculated based on the fracture mechanics method. Iij , the simplified calculation formula is: Among them, K Iij is the crack stress intensity factor, σ i is the dynamic stress of the runner bucket, b j is the crack depth, a j is the crack length.

7. The method for determining the allowable limit of defects of a runner bucket of an impulse turbine according to claim 1, characterized in that: According to the calculation results of the stress intensity factor obtained in step S5, the safety factor n of the non-extension of the defect crack in each partition of the runner bucket is calculated. i , the calculation formula is: of i =ΔK th / K Iij Among them, n i K is the safety factor of crack non-extension, Iij is the crack stress intensity factor, ΔK th is the crack extension threshold.

8. The method for determining the allowable limit of defects of a runner bucket of an impulse turbine according to claim 1, characterized in that: The crack non-extension safety factor obtained in step S6 and the allowable safety factor defined in step S2 are used as the judgment conditions, that is, n i ≥[n i ], determine the defect tolerance limits [b] and [a] to ensure that the crack does not extend.

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