A method for quantitatively evaluating residual wall thickness of steam turbine blade based on alternating electromagnetic field

Abstract

The application discloses a steam turbine blade residual wall thickness quantitative evaluation method based on alternating electromagnetic field, a phase characteristic detection method based on alternating electromagnetic field, and constructs a universal non-dimensional equation and a phase relationship function, and combines a known thickness test block calibration environment coefficient to realize accurate quantitative evaluation of the steam turbine blade residual wall thickness. The method effectively overcomes the limitations of the existing amplitude method which is susceptible to the lift-off effect, material characteristic fluctuation and background magnetic field interference, significantly improves the detection precision and stability, simplifies the calculation process, enhances the detection applicability and reliability, and provides strong support for predictive maintenance and life management of the steam turbine blade.

Description

Technical Field

[0001] This invention relates to the field of turbine blade inspection, and in particular to a method for quantitatively evaluating the residual wall thickness of turbine blades based on alternating electromagnetic fields. Background Technology

[0002] Steam turbines are core power equipment in energy, electricity, and ship propulsion fields, and the condition of their blades directly affects the safety and efficiency of the entire system. Operating under high temperature, high pressure, and high speed, blades are subjected to various factors such as centrifugal force, airflow vibration, and environmental corrosion, which can lead to thinning of the blade wall. Thinning weakens blade strength, disrupts balance, and can cause blade breakage, resulting in safety accidents or even shutdowns and economic losses. Therefore, regular, accurate, and efficient quantitative detection of the residual blade wall thickness is crucial and forms the basis for predictive maintenance and lifespan management.

[0003] Alternating electromagnetic field (ACFM) testing is a widely used non-destructive testing method. The current mainstream technology mainly relies on analyzing the amplitude characteristics of the magnetic field signal to establish the correlation with the wall thickness. However, this method has the following fatal weaknesses: (1) It is susceptible to interference: the amplitude is very sensitive to the small distance between the probe and the surface (lift-off effect), the small fluctuations in the electromagnetic properties of the material itself, and environmental electromagnetic noise. These interferences will mask the true wall thickness change signal; (2) It is difficult to work normally at the critical wall thickness: when the wall thickness is very thin (close to the skin depth), the relationship between the amplitude and the thickness becomes irregular and nonlinear, making it difficult to establish a reliable calculation model; (3) It is susceptible to background magnetic field interference: in areas with complex structures, strong background magnetic fields will seriously interfere with the accurate measurement of the amplitude of the target area.

[0004] Therefore, there is an urgent need to propose a new method for detecting turbine blades to break through the bottleneck of existing detection technologies and ultimately achieve accurate quantitative evaluation. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a quantitative assessment method for residual wall thickness of steam turbine blades based on electromagnetic fields, which has strong anti-interference ability, is applicable to the critical wall thickness region, and is resistant to background magnetic field interference.

[0006] The technical solution adopted by this invention to solve its technical problem is: to provide a method for quantitatively evaluating the residual wall thickness of turbine blades based on electromagnetic fields, comprising the following steps:

[0007] S1. Obtain the dimensionless equation parameter terms: Obtain the phase correlation terms of the turbine blades. π 1. Wall thickness related items π 2. Coil-related items π 3. Dimensionless related terms π 4 and dimensionless related terms π 5;

[0008] The dimensionless related terms π 4. To detect the tilt angle of the probe i ;

[0009] The dimensionless related terms π 5 represents the coil turns ratio of the detection probe. p ;

[0010] S2. Construct dimensionless equations: based on the phase correlation terms of the turbine blades. π 1. Wall thickness related items π 2. Coil-related items π 3. Dimensionless related terms π 4 and dimensionless related terms π 5. Construct dimensionless equations;

[0011] S3. Calculate the skin depth for finding the extreme values. d p Phase correlation terms for turbine blades with different wall thicknesses π 1 and excitation angular frequency oh Fit the relationship curve and determine when the phase correlation term π When the maximum or minimum value is reached, the corresponding maximum or minimum excitation angular frequency is... oh p Then calculate the skin depth of the maximum value. d p ;

[0012] S4. Constructing the phase relationship function: Obtaining the environmental coefficient H env Phase constant β Detection probe lifting l 0. The maximum excitation angular frequency of the turbine blade oh p , maximizing skin depth d p Excitation angular frequency oh Wall thickness c Establish phase with magnetic field signal f Related phase relationship functions;

[0013] S5. Calibrate phase reference parameters f 0 An AC electromagnetic field detection probe was used to scan a defect-free turbine blade test block of known thickness to obtain the phase of the magnetic field signal. f 0 As a baseline parameter;

[0014] S6. Calculate the environmental coefficient after calibration. H env0Based on the phase relationship function described in step S4 and the magnetic field signal phase reference parameter described in step S5 f 0 Calculate the environmental factor during the detection of the calibrated probe. H env0 ;

[0015] S7. Obtain the phase distortion variable Δ f' An AC electromagnetic field detection probe is used to scan a turbine blade test block to obtain the phase of the magnetic field signal at defect-free locations. f 0 ' Phase with the magnetic field signal at the defect location f x ' The phase distortion Δ of the magnetic field signal was calculated. f' ;

[0016] The phase distortion Δ of the magnetic field signal f' = f 0 ' - f x ' ;

[0017] S8. Calculate the wall thickness reduction Δ c' Based on the phase relationship function described in step S4 and the calibrated environmental coefficient described in step S6 H env0 The phase distortion Δ of the magnetic field signal mentioned in step S7 f' Calculate the wall thickness reduction Δ c' ;

[0018] S9. Calculate the residual wall thickness C r Based on the turbine blade wall thickness c and the wall thickness reduction amount △ mentioned in step S8 c' Calculate the residual wall thickness of the turbine blades C r ;

[0019] The residual wall thickness of the steam turbine blade Cr = c -△ c' .

[0020] Preferably, in step S1, the phase correlation term π 1. The calculation formula is as follows (1):

[0021]

[0022] In equation (1), f The phase of the magnetic field signal. s The electrical conductivity of the turbine blades. oh The excitation angular frequency of the turbine blades. m 0 The permeability of the turbine blades. L This refers to the length of the turbine blade core.

[0023] The formula for calculating the wall thickness-related term π2 is as follows (2):

[0024]

[0025] In equation (2), s The electrical conductivity of the turbine blades. m 0 The permeability of the turbine blades. l 0 indicates that the detection probe has been removed. c For the thickness of the turbine blade wall. f The phase of the magnetic field signal;

[0026] The formula for calculating the coil-related term π3 is as follows (3):

[0027]

[0028] In equation (3), d To detect the characteristic dimensions of the probe coil, D Detect the diameter of the probe coil.

[0029] Preferably, in step S2, the dimensionless equation constructed is shown in formula (4):

[0030]

[0031] In equation (4), for π 1, for π 2, for π 3, i for π 4, p for π 5.

[0032] Preferably, in step S3, the maximum / minimum value is the skin depth. d p The calculation formula is as follows (5):

[0033]

[0034] In equation (5), s The electrical conductivity of the turbine blades. m 0 The permeability of the turbine blades. oh p Phase correlation term π 1. The excitation angular frequency corresponding to the maximum or minimum value.

[0035] Preferably, in step S4, the constructed phase relationship function is as shown in formula (6):

[0036]

[0037] In equation (6), l 0 indicates that the detection probe has been removed. oh p Phase correlation term π The excitation angular frequency corresponding to the maximum or minimum value is 1. d p For optimal skin depth, H env For environmental factors, oh The excitation angular frequency of the turbine blades. β The phase constant, c This refers to the wall thickness of the steam turbine blades.

[0038] Preferably, in step S6, the environmental coefficient during probe detection is measured after calibration. H env0 The calculation formula is as follows (7):

[0039]

[0040] In equation (7), β The phase constant, l 0 indicates that the detection probe has been removed. oh p Phase correlation term π The excitation angular frequency corresponding to the maximum or minimum value is 1. f 0 The phase of the magnetic field signal. oh The excitation angular frequency of the turbine blades. d p The optimal skin depth is determined by the maximum value.

[0041] Preferably, in step S8, the wall thickness reduction amount Δ c' The calculation formula is as follows (8):

[0042]

[0043] In equation (8), d p For optimal skin depth, H env0 This refers to the environmental factor during probe testing after calibration. oh The excitation angular frequency of the turbine blades.β The phase constant, l 0 indicates that the detection probe has been removed. oh p Phase correlation term π 1. The extremum excitation angular frequency corresponding to the extreme value, Δ f' This represents the phase distortion of the magnetic field signal.

[0044] The beneficial effects of this invention are as follows: By employing a phase characteristic detection method based on alternating electromagnetic fields, and constructing a universal dimensionless equation and phase relationship function, combined with environmental coefficients calibrated using test blocks of known thickness, a precise quantitative assessment of the residual wall thickness of turbine blades can be achieved. This method effectively overcomes the limitations of existing amplitude methods, which are susceptible to lift-off effects, material property fluctuations, and background magnetic field interference. It significantly improves the accuracy and stability of the detection, simplifies the calculation process, and enhances the applicability and reliability of the detection, providing strong support for predictive maintenance and life management of turbine blades. Attached Figure Description

[0045] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a flowchart illustrating a quantitative assessment method for residual wall thickness of steam turbine blades based on alternating electromagnetic fields provided in this application.

[0047] Figure 2 The phase of the magnetic field signal in this application f With turbine blade wall thickness c Relationship curve diagram;

[0048] Figure 3 This is a graph showing the relationship between the phase of the induced current inside the turbine blade at different depths and the depth at which it is located.

[0049] Figure 4 This is a phase-related item in this application. π 1. Turbine blade wall thickness c Angular frequency of excitation signal oh Relationship curve diagram;

[0050] Figure 5 The phase of the magnetic field signal in the defect-free case in the embodiment. f Line graph;

[0051] Figure 6 The residual wall thickness due to unknown corrosion defects in the example Cr magnetic field signal phase f Line graph;

[0052] Figure 7 This is a comparison chart showing the detection accuracy of the phase detection method of this application and the existing amplitude detection method under different theoretical wall thicknesses. Detailed Implementation

[0053] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] like Figure 1 As shown, this invention proposes a quantitative assessment method for the residual wall thickness of turbine blades based on alternating electromagnetic fields. The method directly quantifies the residual wall thickness of turbine blades using a phase characteristic detection method based on alternating electromagnetic fields. The assessment method includes the following steps:

[0055] S1. Obtain the dimensionless equation parameter terms: Obtain the phase correlation terms of the turbine blades. π 1. Wall thickness related items π 2. Coil-related items π 3. Dimensionless related terms π 4 and dimensionless related terms π 5;

[0056] Among them, dimensionless related terms π 4. To detect the tilt angle of the probe i ;

[0057] Dimensionless related terms π 5 represents the coil turns ratio of the detection probe. p ;

[0058] Phase correlation terms π 1. The calculation formula is as follows (1):

[0059]

[0060] In equation (1), f The phase of the magnetic field signal. s The electrical conductivity of the turbine blades. oh The excitation angular frequency of the turbine blades. m 0 The permeability of the turbine blades. L This refers to the length of the turbine blade core.

[0061] The formula for calculating the wall thickness-related term π2 is as follows (2):

[0062]

[0063] In equation (2), s The electrical conductivity of the turbine blades. m 0 The permeability of the turbine blades. l 0 indicates that the detection probe has been removed. c For the thickness of the turbine blade wall. f The phase of the magnetic field signal;

[0064] The formula for calculating the coil-related term π3 is as follows (3):

[0065]

[0066] In equation (3), d To detect the characteristic dimensions of the probe coil, D Detect the diameter of the probe coil.

[0067] In step S1, the phase of the magnetic field signal is first obtained. f Turbine blade conductivity s Angular frequency of turbine blade excitation oh Magnetic permeability of steam turbine blades m 0 Turbine blade core length L Detection probe lifting l 0. Turbine blade wall thickness c Detection probe coil characteristic dimensions d Detection probe coil diameter D Detection probe tilt angle i Detection probe coil turns ratio p Then, based on the corresponding calculation formulas, the relevant parameters required to construct the dimensionless equation for phase change are collected, laying a theoretical foundation for wall thickness inversion. The parameters used to construct the dimensionless equation specifically include the phase correlation terms of the turbine blades. π 1. Wall thickness related items π 2. Coil-related items π 3. Dimensionless related terms π 4 and dimensionless related terms π 5.

[0068] Among them, in obtaining the phase of the magnetic field signal f Turbine blade conductivity s Angular frequency of turbine blade excitation oh Magnetic permeability of steam turbine blades m 0 Turbine blade core length L These are used to calculate the phase correlation term. πIn the relevant terms of 1, length [L], time [T], mass [M], and current [I] are selected as the basic dimensions for dimensional analysis of the relevant physical quantities, including the conductivity of the turbine blades. s The dimensions can be expressed as [M] -1 L -3 T 3 I 2 ], turbine blade excitation angular frequency oh The dimensions can be expressed as [T] -1 ], turbine blade permeability m 0 The dimensions can be expressed as [MLT] -2 I -2 ], length of turbine blade magnetic core L The dimension of the excitation signal angular frequency ω can be expressed as [L], and the dimension of the magnetic field signal phase can be expressed as [L]. f It is dimensionless.

[0069] Obtaining the conductivity of steam turbine blades s Magnetic permeability of steam turbine blades m 0 Detection probe lifting l 0. Turbine blade wall thickness c Magnetic field signal phase f These are used to calculate the wall thickness-related terms. π In the relevant items of 2, length [L], time [T], mass [M], and current [I] are selected as the basic dimensions to perform dimensional analysis on the relevant physical quantities. The dimension of the probe lifting l0 can be expressed as [L], and the dimension of the wall thickness c can be expressed as [L].

[0070] In obtaining the characteristic dimensions of the detection probe coil d Detection probe coil diameter D Used to calculate coil-related terms π In step 3, length [L], time [T], mass [M], and current [I] are selected as the basic dimensions to perform dimensional analysis on the relevant physical quantities, and the characteristic dimensions of the probe coil are also analyzed. d Detection probe coil diameter D The dimension of can be expressed as [L].

[0071] Detection probe tilt angle i Ratio of the number of turns to the detection probe coil p It is dimensionless and can be directly used as π Items related to the tilt angle of the detection probe π 4. Satisfy π 4= i The number of turns ratio of the detection probe coil is related to the following items. π 5. Satisfy π 5= p .

[0072] S2. Construct dimensionless equations: based on the phase correlation terms of the turbine blades. π 1. Wall thickness related items π 2. Coil-related items π 3. Dimensionless related terms π 4 and dimensionless related terms π 5. Construct dimensionless equations.

[0073] The dimensionless equation constructed is shown in formula (4):

[0074]

[0075] In equation (4), for π 1, for π 2, for π 3, i for π 4, p for π 5.

[0076] like Figure 2 As shown, the dimensionless equation constructed in step S2 is specifically based on Buckingham's equation. π Constructed by the theorem, satisfying π 1= f ( π 2, π 3, π 4, π 5) The constructed dimensionless equation is a universal model that can eliminate the influence of absolute dimensions, laying the foundation for subsequent wall thickness inversion.

[0077] S3. Calculate the skin depth for finding the extreme values. d p Phase correlation terms for turbine blades with different wall thicknesses π 1 and excitation angular frequency oh Fit the relationship curve and determine when the phase correlation term π When the maximum or minimum value is reached, the corresponding maximum or minimum excitation angular frequency is... oh p Then calculate the skin depth of the maximum value. d p ;

[0078] Among them, the most valuable skin depth d p The calculation formula is as follows (5):

[0079]

[0080] In equation (5), s The electrical conductivity of the turbine blades. m 0 The permeability of the turbine blades. oh p Phase correlation term π 1. The excitation angular frequency corresponding to the maximum or minimum value.

[0081] Among them, the phase correlation terms of turbine blades with different wall thicknesses π 1 and excitation angular frequency oh The linear relationship curve obtained by fitting is as follows: Figure 2 As shown. From Figure 3 It can be seen from this that when the phase correlation term π When the maximum value is achieved, the corresponding extreme excitation angular frequency is... oh p And calculate the skin depth of the extreme value d p With wall thickness c There exists a unique correspondence. It should be noted that research has found that variations in wall thickness affect the extreme excitation angular frequency. oh p and the most valuable skin depth d p The impact is minimal and can be ignored in calculations. This method significantly reduces the number of parameters and iterative complexity in the inversion calculation process, eliminating the need to refit the optimal excitation angular frequency for different thicknesses. oh p With maximum skin depth d p This simplifies the calculation process while improving quantification accuracy, thus enhancing the practicality and engineering applicability of the method.

[0082] S4. Constructing the phase relationship function: Obtaining the environmental coefficient H env Phase constant β Detection probe lifting l 0. The maximum excitation angular frequency of the turbine blade oh p , maximizing skin depth d p Excitation angular frequency oh Wall thickness c Establish phase with magnetic field signal f Related phase relationship functions;

[0083] The constructed phase relationship function is shown in formula (6):

[0084]

[0085] In equation (6), l0 indicates that the detection probe has been removed. oh p Phase correlation term π The excitation angular frequency corresponding to the maximum or minimum value is 1. d p For optimal skin depth, H env For environmental factors, oh The excitation angular frequency of the turbine blades. β The phase constant, c This refers to the wall thickness of the steam turbine blades.

[0086] Among them, see Figure 4 The phase relationship function constructed based on the implicit function theorem directly establishes the phase of the magnetic field signal. f With turbine blade wall thickness c The relationship between the phase distortion Δ and the phase change of the magnetic field is used for subsequent analysis. f' This lays the foundation for extrapolating the residual wall thickness of steam turbine blades.

[0087] also, H env It is only related to the probe's environmental coefficient, coil characteristic dimensions, and number of coil turns.

[0088] S5. Calibrate phase reference parameters f 0 An AC electromagnetic field detection probe was used to scan a defect-free turbine blade test block of known thickness to obtain the phase of the magnetic field signal. f 0 As a baseline parameter;

[0089] The specific implementation method involves technicians preparing a defect-free turbine blade test block of known thickness and using an AC electromagnetic field defect detection probe to scan the surface of the test piece in parallel to obtain the phase of the magnetic field signal. f 0 Its signal form is as follows Figure 5 As shown. This application selects the average magnetic field signal phase of a defect-free turbine blade test block of a certain thickness. f 0 As a benchmark parameter, this effectively overcomes the drawbacks of traditional amplitude signals being susceptible to lift-off effects, fluctuations in material electromagnetic properties, and interference from environmental noise. It provides a stable and reliable benchmark reference for subsequent calibration of relevant parameters, accurate extraction of phase distortion at defects, and wall thickness inversion, significantly improving the anti-interference capability and repeatability of quantitative assessment.

[0090] S6. Calculate the environmental coefficient after calibration. H env0 Based on the phase relationship function described in step S4 and the magnetic field signal phase reference parameter described in step S5 f 0Calculate the environmental factor during the detection of the calibrated probe. H env0 ;

[0091] Among them, the environmental factor during the detection of the calibrated probe. H env0 The calculation formula is as follows (7):

[0092]

[0093] In equation (7), β The phase constant, l 0 indicates that the detection probe has been removed. oh p Phase correlation term π The excitation angular frequency corresponding to the maximum or minimum value is 1. f 0 The phase of the magnetic field signal. oh The excitation angular frequency of the turbine blades. d p The optimal skin depth is determined by the skin depth.

[0094] The environmental factor during detection by the calibrated probe was calculated. H env0 It can eliminate factors that affect the final test results, such as individual differences between different detection probes and fluctuations in the inherent properties of materials, thus eliminating the deviation between theoretical predictions and actual test values ​​and avoiding the unreliability of the final test results caused by these external factors.

[0095] S7. Obtain the phase distortion variable Δ f' An AC electromagnetic field detection probe is used to scan a turbine blade test block to obtain the phase of the magnetic field signal at defect-free locations. f 0 ' Phase with the magnetic field signal at the defect location f x ' The phase distortion Δ of the magnetic field signal was calculated. f' ;

[0096] The phase distortion Δ of the magnetic field signal f' = f 0 ' - f x ' ;

[0097] By separately acquiring the phase of the magnetic field signal at the defect-free location f 0 ' Phase with the magnetic field signal at the defect location f x' Then, the phase distortion Δ of the final magnetic field signal is calculated. f' It can effectively eliminate background noise and minimize the various factors that affect the final detection results.

[0098] S8. Calculate the wall thickness reduction Δ c' Based on the phase relationship function described in step S4 and the calibrated environmental coefficient described in step S6 H env0 The phase distortion Δ of the magnetic field signal mentioned in step S7 f' Calculate the wall thickness reduction Δ c' ;

[0099] Among them, the wall thickness reduction △ c' The calculation formula is as follows (8):

[0100]

[0101] In equation (8), d p For optimal skin depth, H env0 This refers to the environmental factor during probe testing after calibration. oh The excitation angular frequency of the turbine blades. β The phase constant, l 0 indicates that the detection probe has been removed. oh p Phase correlation term π 1. The extremum excitation angular frequency corresponding to the extreme value, Δ f' This represents the phase distortion of the magnetic field signal.

[0102] S9. Calculate the residual wall thickness C r Based on the turbine blade wall thickness c and the wall thickness reduction amount △ mentioned in step S8 c' Calculate the residual wall thickness of the turbine blades C r ;

[0103] The residual wall thickness of the steam turbine blade Cr = c -△ c' .

[0104] Thus, this invention provides a quantitative assessment method for the residual wall thickness of turbine blades based on alternating electromagnetic fields, which constructs a dimensionless parameter system with phase as the core through dimensional analysis. π 1, π 2, π 3, π 4, π5) And establish a dimensionless equation; then determine the maximum and minimum excitation angular frequencies that are independent of thickness through the phase-frequency response. oh p and the most valuable skin depth d p This significantly simplified the model and reduced the number of computational parameters. Based on this, a phase relationship function was established using the implicit function theorem, and an explicit expression for the wall thickness reduction was derived. Finally, the environmental coefficient was obtained through non-destructive calibration. H env0 The phase distortion Δ is calculated by combining the measured phase signals from the defect-free and defect-prone areas. f' To achieve residual wall thickness C r The invention achieves accurate inversion. It effectively overcomes the problems of traditional amplitude methods being susceptible to lift-off, electromagnetic characteristic fluctuations, and background magnetic field interference, significantly improving the accuracy, stability, and operational efficiency of quantitative assessment of blade corrosion defects, and is suitable for engineering applications.

[0105] The application and effects of the present invention will be further illustrated below through specific embodiments:

[0106] S1. Obtain the dimensionless equation parameter terms: Obtain the phase correlation terms of the turbine blades. π 1. Wall thickness related items π 2. Coil-related items π 3. Dimensionless related terms π 4 and dimensionless related terms π 5;

[0107] Among them, dimensionless related terms π 4. To detect the tilt angle of the probe i ;

[0108] Dimensionless related terms π 5 represents the coil turns ratio of the detection probe. p ;

[0109] S2. Construct dimensionless equations: based on the phase correlation terms of the turbine blades. π 1. Wall thickness related items π 2. Coil-related items π 3. Dimensionless related terms π 4 and dimensionless related terms π 5. Construct dimensionless equations;

[0110] In the specific implementation of this application, the detection probe is lifted out. l 0 represents 1 mm, which is the thickness of the turbine blade wall. c The diameter is 3mm to 7mm (with an interval of 0.5mm).

[0111] S3. Calculate the skin depth for finding the extreme values. dp Phase correlation terms for turbine blades with different wall thicknesses π 1 and excitation angular frequency oh Fit the relationship curve and determine when the phase correlation term π When the maximum or minimum value is reached, the corresponding maximum or minimum excitation angular frequency is... oh p Then calculate the skin depth of the maximum value. d p ;

[0112] In the specific implementation of this application, the turbine blade wall thickness c Specifically, the blades are 2mm, 4mm, and 6mm, and the excitation angular frequency range of the turbine blades is 0 to 35000Hz.

[0113] S4. Constructing the phase relationship function: Obtaining the environmental coefficient H env Phase constant β Detection probe lifting l 0. The maximum excitation angular frequency of the turbine blade oh p , maximizing skin depth d p Excitation angular frequency oh Wall thickness c Establish phase with magnetic field signal f Related phase relationship functions;

[0114] S5. Calibrate phase reference parameters f 0 An AC electromagnetic field detection probe was used to scan a defect-free turbine blade test block of known thickness to obtain the phase of the magnetic field signal. f 0 As a baseline parameter;

[0115] In the specific implementation of this application, the thickness of the defect-free turbine blade test block is 7mm, and the average value of the magnetic field phase at multiple locations on the test block is used as the reference parameter.

[0116] S6. Calculate the environmental coefficient after calibration. H env0 Based on the phase relationship function described in step S4 and the magnetic field signal phase reference parameter described in step S5 f 0 Calculate the environmental factor during the detection of the calibrated probe. H env0 ;

[0117] S7. Obtain the phase distortion variable Δ f' An AC electromagnetic field detection probe is used to scan a turbine blade test block to obtain the phase of the magnetic field signal at defect-free locations. f0 ' Phase with the magnetic field signal at the defect location f x ' The phase distortion Δ of the magnetic field signal was calculated. f' ;

[0118] The phase distortion Δ of the magnetic field signal f' = f 0 ' - f x ' ;

[0119] In this specific implementation, an aluminum specimen with a cylindrical defect is used as the defect test block, with a wall thickness of 7 mm, a defect diameter of 60 mm, and a residual wall thickness of 4 mm. The magnetic field signal phase detection signal is as follows: Figure 6 As shown. The phase of the magnetic field signal at the defect-free location of this test block was obtained. f 0 ' =24° and the phase of the magnetic field signal at the defect location f x ' =22.8°, the phase distortion of the magnetic field signal is obtained as Δ. f' = f 0 ' - f x ' =1.2°.

[0120] S8. Calculate the wall thickness reduction Δ c' Based on the phase relationship function described in step S4 and the calibrated environmental coefficient described in step S6 H env0 The phase distortion Δ of the magnetic field signal mentioned in step S7 f' Calculate the wall thickness reduction Δ c' ;

[0121] In the specific implementation of this application, after calculation using formula (8), we obtain △ c' =2.951mm.

[0122] S9. Calculate the residual wall thickness C r Based on the turbine blade wall thickness c and the wall thickness reduction amount △ mentioned in step S8 c' Calculate the residual wall thickness of the turbine blades C r ;

[0123] The residual wall thickness of the steam turbine blade Cr= c -△ c' .

[0124] In the specific implementation of this application, Cr = c -△ c' =7-2.951=4.049mm, the relative error is about 1.2%.

[0125] A comparison of the detection accuracy of the phase detection method in this application with existing amplitude detection methods under different theoretical wall thicknesses is shown in the figure. Figure 7 .

[0126] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A method for quantitatively evaluating the residual wall thickness of steam turbine blades based on alternating electromagnetic fields, characterized in that, The method includes the following steps: S1. Obtain the dimensionless equation parameter terms: Obtain the phase correlation terms of the turbine blades. π 1. Wall thickness related items π 2. Coil-related items π 3. Dimensionless related terms π 4 and dimensionless related terms π 5; The dimensionless related terms π 4. To detect the tilt angle of the probe θ ; The dimensionless related terms π 5 represents the coil turns ratio of the detection probe. p ; S2. Construct dimensionless equations: based on the phase correlation terms of the turbine blades. π 1. Wall thickness related items π 2. Coil-related items π 3. Dimensionless related terms π 4 and dimensionless related terms π 5. Construct dimensionless equations; S3. Calculate the skin depth for finding the extreme values. δ p Phase correlation terms for turbine blades with different wall thicknesses π 1 and excitation angular frequency ω Fit the relationship curve and determine when the phase correlation term π When the maximum or minimum value is reached, the corresponding maximum or minimum excitation angular frequency is... ω p Then calculate the skin depth of the maximum value. δ p ; S4. Constructing the phase relationship function: Obtaining the environmental coefficient H env Phase constant β Detection probe lifting l 0. The maximum excitation angular frequency of the turbine blade ω p , maximizing skin depth δ p Excitation angular frequency ω Wall thickness c Establish phase with magnetic field signal φ Related phase relationship functions; S5. Calibrate phase reference parameters φ 0 An AC electromagnetic field detection probe was used to scan a defect-free turbine blade test block of known thickness to obtain the phase of the magnetic field signal. φ 0 As a baseline parameter; S6. Calculate the environmental coefficient after calibration. H env0 Based on the phase relationship function described in step S4 and the magnetic field signal phase reference parameter described in step S5 φ 0 Calculate the environmental factor during the detection of the calibrated probe. H env0 ; S7. Obtain the phase distortion variable Δ φ' An AC electromagnetic field detection probe is used to scan a turbine blade test block to obtain the phase of the magnetic field signal at defect-free locations. φ 0 ' Phase with the magnetic field signal at the defect location φ x ' The phase distortion Δ of the magnetic field signal was calculated. φ' ; The phase distortion Δ of the magnetic field signal φ' = φ 0 ' - φ x ' ; S8. Calculate the wall thickness reduction Δ c' Based on the phase relationship function described in step S4 and the calibrated environmental coefficient described in step S6 H env0 The phase distortion Δ of the magnetic field signal mentioned in step S7 φ' Calculate the wall thickness reduction Δ c' ; S9. Calculate the residual wall thickness C r Based on the turbine blade wall thickness c and the wall thickness reduction amount △ mentioned in step S8 c' Calculate the residual wall thickness of the turbine blades C r ; The residual wall thickness of the turbine blade Cr = c -△ c' .

2. The method for quantitatively evaluating the residual wall thickness of turbine blades based on alternating electromagnetic fields according to claim 1, characterized in that, In step S1, the phase correlation term π 1. The calculation formula is as follows (1): In equation (1), φ The phase of the magnetic field signal. σ The electrical conductivity of the turbine blades. ω The excitation angular frequency of the turbine blades. μ 0 The permeability of the turbine blades. L This refers to the length of the turbine blade core. The formula for calculating the wall thickness-related term π2 is as follows (2): In equation (2), σ The electrical conductivity of the turbine blades. μ 0 The permeability of the turbine blades. l 0 indicates that the detection probe has been removed. c For the thickness of the turbine blade wall. φ The phase of the magnetic field signal; The formula for calculating the coil-related term π3 is as follows (3): In equation (3), d To detect the characteristic dimensions of the probe coil, D Detect the diameter of the probe coil.

3. The method for quantitatively evaluating the residual wall thickness of turbine blades based on alternating electromagnetic fields according to claim 1, characterized in that, In step S2, the dimensionless equation constructed is shown in formula (4): In equation (4), for π 1, for π 2, for π 3, θ for π 4, p for π 5.

4. The method for quantitatively evaluating the residual wall thickness of turbine blades based on alternating electromagnetic fields according to claim 1, characterized in that, In step S3, the extreme value approaching skin depth δ p The calculation formula is as follows (5): In equation (5), σ The electrical conductivity of the turbine blades. μ 0 The permeability of the turbine blades. ω p Phase correlation term π 1. The maximum excitation angular frequency corresponding to the maximum value.

5. The method for quantitatively evaluating the residual wall thickness of turbine blades based on alternating electromagnetic fields according to claim 1, characterized in that, In step S4, the constructed phase relationship function is shown in formula (6): In equation (6), l 0 indicates that the detection probe has been removed. ω p Phase correlation term π The excitation angular frequency corresponding to the maximum or minimum value is 1. δ p For optimal skin depth, H env For environmental factors, ω The excitation angular frequency of the turbine blades. β The phase constant, c This refers to the wall thickness of the steam turbine blades.

6. The method for quantitatively evaluating the residual wall thickness of turbine blades based on alternating electromagnetic fields according to claim 1, characterized in that, In step S6, the environmental factor during the detection of the calibrated detection probe is... H env0 The calculation formula is as follows (7): In equation (7), β The phase constant, l 0 indicates that the detection probe has been removed. ω p Phase correlation term π The excitation angular frequency corresponding to the maximum or minimum value is 1. φ 0 The phase of the magnetic field signal. ω The excitation angular frequency of the turbine blades. δ p The optimal skin depth is determined by the maximum value.

7. The method for quantitatively evaluating the residual wall thickness of turbine blades based on alternating electromagnetic fields according to claim 1, characterized in that, In step S8, the wall thickness reduction amount Δ c' The calculation formula is as follows (8): In equation (8), δ p For optimal skin depth, H env0 This refers to the environmental factor during probe testing after calibration. ω The excitation angular frequency of the turbine blades. β The phase constant, l 0 indicates that the detection probe has been removed. ω p Phase correlation term π 1. The extremum excitation angular frequency corresponding to the maximum or minimum value, Δ φ' This represents the phase distortion of the magnetic field signal.

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