A frequency-wavenumber domain imaging method suitable for high temperature pipeline defect detection

Abstract

The present application relates to the technical field of pipeline defect detection, in particular to a frequency-wavenumber domain imaging method suitable for high-temperature pipeline defect detection, which mainly solves the technical problem that the existing FK domain imaging method is difficult to be applied to high-temperature pipeline defect detection imaging. The frequency-wavenumber domain imaging method suitable for high-temperature pipeline defect detection comprises the following steps: signal acquisition; data preprocessing and gated direct wave signal interception; construction of time scale scaling factor; acquisition of frequency-dependent amplitude compensation factor; phase velocity extraction; gated defect echo signal interception, frequency domain transformation, frequency-dependent amplitude compensation and wavenumber domain transformation; Stolt mapping reconstruction; two-dimensional inverse Fourier transformation; normalization and image display. The imaging method effectively improves the imaging efficiency and significantly improves the imaging position error and focusing state.

Description

Technical Field

[0001] This invention relates to the field of pipeline defect detection technology, specifically a frequency-wavenumber domain imaging method suitable for detecting defects in high-temperature pipelines. Background Technology

[0002] High-temperature pipelines are widely used in industries such as energy, chemical, nuclear power and metallurgy. During their service life, due to thermal fatigue, oxidation corrosion and mechanical stress, defects such as cracks, holes and corrosion thinning are easily generated in the pipe wall. If these defects are not detected in time, they will seriously threaten the safe operation of the equipment.

[0003] Electromagnetic ultrasonic guided wave testing technology has become the preferred approach for online inspection of high-temperature pipelines due to its advantages such as no need for coupling agents, non-contact operation, and adaptability to high temperatures. Frequency-wavenumber domain (FK domain) imaging methods are computationally efficient and adaptable to multi-mode guided waves. Combining them with electromagnetic ultrasonic guided wave technology can achieve visualized location and quantitative assessment of defects in high-temperature pipelines. However, existing FK domain imaging methods are mostly designed based on normal temperature conditions and do not fully consider the special effects of high-temperature environments. They have significant shortcomings in actual inspection and cannot meet the requirements for accurate inspection. The specific reasons are as follows: High temperatures change parameters such as the elastic modulus and density of pipeline materials, causing guided wave velocity drift, amplitude attenuation, and dispersion shift. Existing FK domain imaging methods do not introduce temperature compensation mechanisms and use normal temperature parameters for calculation, resulting in model mismatch, low high-temperature imaging accuracy, large location deviation, and increased artifacts. Summary of the Invention

[0004] In order to solve the problem that existing FK domain imaging methods are difficult to apply to high-temperature pipeline defect detection imaging, this invention provides a frequency-wavenumber domain imaging method suitable for high-temperature pipeline defect detection.

[0005] This invention is achieved using the following technical solution:

[0006] A frequency-wavenumber domain imaging method suitable for detecting defects in high-temperature pipelines includes the following steps:

[0007] Step 1: At room temperature, acquire signals using a dual-path sensor to obtain a set of raw A-scan signals at a reference temperature; at the target temperature, acquire signals using a dual-path sensor to obtain... The original A-scan signal at the target temperature;

[0008] Step 2: Analyze the raw A-scan signals obtained in Step 1 at a set of reference temperatures. The original A-scan signals at the target temperature were sequentially subjected to DC removal and Gaussian filtering to obtain a set of preprocessed A-scan signals at the reference temperature. The A-scan signal preprocessed at the target temperature is then compared with the A-scan signal preprocessed at a set of reference temperatures using a direct-path window. A gated direct wave signal at a reference temperature is obtained by extracting a portion of the preprocessed A-scan signal at the target temperature. Gated direct wave signal at a target temperature;

[0009] Step 3: Construct a time-scale scaling factor based on the gated direct wave signal at the target temperature and the gated direct wave signal at the reference temperature obtained in Step 2;

[0010] Step 4: Obtain the frequency-related amplitude compensation factor based on the gated direct wave signal at the target temperature and the gated direct wave signal at the reference temperature obtained in Step 2.

[0011] Step 5: Obtained from Step 2 Phase velocity extraction is performed by selecting any gated direct wave signal at any target temperature from the gated direct wave signals at each target temperature.

[0012] Step 6: Apply the timescale scaling factor obtained in Step 2 to the timescale scale constructed in Step 3. The A-scan signal, after preprocessing at the target temperature, is time-scaled and pre-corrected, and then obtained by defect echo window extraction. The gated defect echo signal after time-scale pre-correction at the target temperature, for The gated defect echo signals after time-scale pre-correction at each target temperature are sequentially subjected to frequency domain transformation and frequency-related amplitude compensation, and then arranged along the scanning direction to obtain the frequency-spatial domain signal of the gated defect echo. Finally, the frequency-spatial domain signal of the gated defect echo is transformed by wavenumber domain to obtain the two-dimensional frequency-wavenumber domain signal of the gated defect echo.

[0013] Step 7: Reconstruct the two-dimensional frequency-wavenumber domain signal of the gated defect echo obtained in Step 6 by Stolt mapping to obtain the two-dimensional wavenumber domain signal of the gated defect echo.

[0014] Step 8: Perform a two-dimensional inverse Fourier transform on the two-dimensional wavenumber domain signal of the gated defect echo obtained in Step 7 to obtain the imaging result;

[0015] Step 9: Normalize and display the imaging results obtained in Step 8.

[0016] Furthermore, the specific steps of step three are as follows:

[0017] 21. Obtained from step two Select any one gated direct wave signal at a target temperature from the gated direct wave signals at the target temperature, and perform a Hilbert transform on the gated direct wave signal at that target temperature to obtain the analytic signal of the gated direct wave signal at the target temperature. Its expression is:

[0018] ;

[0019] in, The gated direct wave signal at the target temperature. For time, For the target temperature, Represents the Hilbert transform operator. The imaginary unit;

[0020] Based on the analytical signal of the gated direct wave signal at the target temperature Obtain the corresponding instantaneous envelope Its expression is:

[0021] ;

[0022] 22. Perform a Hilbert transform on the gated direct-path signal at the reference temperature obtained in step two to obtain the analytic signal of the gated direct-path signal at the reference temperature. Its expression is:

[0023] ;

[0024] in, The gated direct-path signal at the reference temperature. For reference temperature;

[0025] Based on the analytical signal of the gated direct wave signal at the reference temperature Obtain the corresponding instantaneous envelope Its expression is:

[0026] ;

[0027] 23. The instantaneous envelope corresponding to the gated direct wave signal at the target temperature. Instantaneous envelope corresponding to the gated direct wave signal at the reference temperature The cross-correlation function of the two The expression is:

[0028] ;

[0029] Among them, reference temperature Take a room temperature of 25℃. This is the time offset. Target temperature The corresponding instantaneous envelope is shifted on the time axis. The following signal;

[0030] 24. Based on the cross-correlation function Obtain the time delay difference between the gated direct wave signal at the target temperature and the gated direct wave signal at the reference temperature. Its expression is:

[0031] ;

[0032] in, To make the cross-correlation function To obtain the maximum value value;

[0033] 25. Based on the time delay difference between the gated direct wave signal at the target temperature and the gated direct wave signal at the reference temperature. Obtain the group delay of the gated direct wave signal at the target temperature relative to the gated direct wave signal at the reference temperature. Its expression is:

[0034] ;

[0035] in, The group delay of the gated direct wave signal at the reference temperature is the arrival time of the envelope peak of the gated direct wave signal at the reference temperature.

[0036] 26. Let the distance between the transmitting sensor and the receiving sensor be... ,but

[0037] Group velocity of gated direct-wave signal at reference temperature for:

[0038] ;

[0039] Group velocity of gated direct-wave signal at target temperature for:

[0040] ;

[0041] 27. Based on the group velocity of the gated direct wave signal at the target temperature group velocity of gated direct-path signal at reference temperature Constructing timescale scaling factor Its expression is:

[0042] .

[0043] Furthermore, the specific steps of step four are as follows:

[0044] 31. Let the Fourier spectrum of the gated direct-path signal at the reference temperature and the Fourier spectrum of the gated direct-path signal at the target temperature be respectively... and Then the reference temperature Normalized spectrum of gated direct wave signal and target temperature Normalized spectrum of gated direct wave signal The expressions are as follows:

[0045] ;

[0046] ;

[0047] in, The effective frequency range of the gated direct-wave signal at the reference temperature. Reference temperature The maximum value of the Fourier spectrum amplitude of the gated direct-wave signal within the effective frequency range. Target temperature The maximum value of the Fourier spectrum amplitude of the gated direct wave signal within the effective frequency range;

[0048] 32. Frequency-dependent amplitude compensation factor The expression is:

[0049] ;

[0050] in, The preset regularization variable has a value range of 1. This is used to prevent numerical instability caused by an excessively small denominator.

[0051] Furthermore, the specific steps of step five are as follows:

[0052] 41. Regarding the results obtained in step two Select any one gated direct wave signal at any target temperature from the gated direct wave signals at each target temperature. Perform a Fourier transform to obtain the corresponding frequency domain signal. ;

[0053] The gated direct wave signal at the reference temperature obtained in step two Perform a Fourier transform to obtain the corresponding frequency domain signal. ;

[0054] 42. Let the center frequency of the gated direct-path signal be... The corresponding center angular frequency of the gated direct wave ,but

[0055] The gated direct wave signal at the target temperature at the center angular frequency The spectral phase at that point is:

[0056] ;

[0057] Gated direct wave signal at reference temperature at center angular frequency The spectral phase at that point is:

[0058] ;

[0059] The phase difference between the gated direct wave signal at the reference temperature and the gated direct wave signal at the target temperature Satisfying the formula:

[0060] ;

[0061] in, It is an unknown integer; due to group delay Phase difference They satisfy an approximate relationship Therefore, through group delay The estimated phase difference is obtained. Then, substitute the estimated phase difference into the phase difference formula to deduce the integer value. Finally, the integer derived from the reverse will be... Substituting into the phase difference formula, a relatively accurate phase difference is obtained. ;

[0062] 43. Based on the relatively accurate phase difference obtained in step 42 The gated direct wave signal at the target temperature at its center angular frequency was obtained. phase velocity at :

[0063] .

[0064] Furthermore, the specific steps of step six are as follows:

[0065] 51. Using the timescale scaling factor constructed in step three For the results obtained in step two The A-scan signal preprocessed at the target temperature is time-scaled and pre-corrected to obtain... A-scan signal pre-corrected with time scale at the target temperature;

[0066] 52. Yes The A-scan signal, after time-scale pre-correction at the target temperature, is used to extract gated defect echo signals using a defect echo window. Then, the intercepted gated defect echo signal Perform a Fourier transform to obtain the frequency domain signal of the gated defect echo. ;

[0067] 53. The frequency-related amplitude compensation factor obtained in step four. Frequency domain signal acting on gated defect echo The frequency domain signal of the gated defect echo after frequency correlation amplitude compensation was obtained. ;

[0068] ;

[0069] 54. Frequency domain signal of gated defect echo after frequency correlation amplitude compensation. Arranged along the scanning direction, the frequency-spatial domain signal of the gated defect echo is obtained. ;

[0070] 55. Frequency-spatial domain signal of gated defect echo The horizontal axis of the scanning direction Perform a Fourier transform to obtain the two-dimensional frequency-wavenumber domain signal of the gated defect echo. Its expression is:

[0071] ;

[0072] in, The transverse wavenumber is the wavenumber in the scanning direction, which is obtained by analyzing the abscissa of the scanning direction. Discrete wavenumber sequence obtained by performing a one-dimensional Fourier transform; The Hanning window function is applied in the scanning direction to suppress spectral leakage.

[0073] Furthermore, the specific steps of step seven are as follows:

[0074] 61. Using Stolt interpolation to... Planar resampling to The plane, the mapping satisfies:

[0075] ;

[0076] in, For the longitudinal equivalent wavenumber, Furthermore, to satisfy the interpolation angular frequency of the above mapping, Target temperature Below the interpolated angular frequency Phase velocity at that location;

[0077] 62. The approximate non-dispersion case based on the SH0 mode (the SH0 mode is the zeroth-order horizontal shear mode), since... At this point, the expression for the interpolated angular frequency simplifies to:

[0078] ;

[0079] 63. Introducing Jacobian weights through variable substitution (Jacobian weights are the same as Jacobian determinant weights). Its expression is:

[0080] ;

[0081] 64. Two-dimensional wavenumber domain signal of gated defect echo after Stolt interpolation Represented as:

[0082] .

[0083] Furthermore, the specific steps of step eight are as follows;

[0084] Two-dimensional wavenumber domain signal after Stolt interpolation Perform a two-dimensional inverse Fourier transform to obtain the imaging results at the target temperature. Its expression is:

[0085] ;

[0086] in, This represents the two-dimensional inverse Fourier transform operator.

[0087] Furthermore, the specific steps of step nine are as follows:

[0088] Imaging results The normalization and image display format are as follows:

[0089] ;

[0090] in, This represents the maximum amplitude of the imaging result across the entire two-dimensional imaging region.

[0091] The beneficial effects of this invention are as follows: The method described in this invention performs synergistic correction of propagation timescale, frequency-related phase, and spectral amplitude structure under high temperature conditions, and constructs a fast imaging framework by combining Stolt interpolation, which effectively reduces computational complexity and improves imaging efficiency, significantly improves imaging position error and focusing state, and solves the technical problem that existing FK domain imaging methods are difficult to apply to high-temperature pipeline defect detection imaging. Attached Figure Description

[0092] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0093] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0094] Figure 1 This is a flowchart of the imaging method described in this invention;

[0095] Figure 2 This is a schematic diagram of the imaging results after using the existing FK domain imaging method described in the background art to image a 2mm through hole defect and a 2mm semi-through hole defect in a P91 material pipe at 25℃.

[0096] Figure 3 This is a schematic diagram of the imaging results after using the existing FK domain imaging method described in the background art to image a 2mm through-hole defect and a 2mm semi-through-hole defect in a P91 material pipe at 300℃.

[0097] Figure 4 This is a schematic diagram of the imaging results after imaging a 2mm through-hole defect and a 2mm semi-through-hole defect in a P91 material pipe at 300℃ using the imaging method described in this invention.

[0098] Figure 5 This is a schematic diagram of the imaging results after using the existing FK domain imaging method described in the background art to image a 2mm through-hole defect and a 2mm semi-through-hole defect in a P91 material pipe at 600℃.

[0099] Figure 6 This is a schematic diagram of the imaging results after imaging a 2mm through-hole defect and a 2mm semi-through-hole defect in a P91 material pipe at 600℃ using the imaging method described in this invention.

[0100] Figure 7 This is a schematic diagram of the imaging result after imaging a 5×2mm groove defect in a P91 material pipe at 300℃ using the existing FK domain imaging method described in the background art.

[0101] Figure 8 This is a schematic diagram of the imaging result after imaging a 5×2mm groove defect in a P91 material pipe at 300℃ using the imaging method described in this invention.

[0102] Figure 9This is a schematic diagram of the imaging result after imaging a 5×2mm groove defect in a P91 material pipe at 630℃ using the existing FK domain imaging method described in the background art.

[0103] Figure 10 This is a schematic diagram of the imaging result after imaging a 5×2mm groove defect in a P91 material pipe at 630℃ using the imaging method described in this invention.

[0104] Figure 11 This is a schematic diagram of the imaging results after using the existing FK domain imaging method described in the background art to image a 2mm through hole defect and a 2mm semi-through hole defect in a 15CrMoV material pipe at 300℃.

[0105] Figure 12 This is a schematic diagram of the imaging results after imaging a 2mm through-hole defect and a 2mm semi-through-hole defect in a 15CrMoV material pipe at 300℃ using the imaging method described in this invention.

[0106] Figure 13 This is a schematic diagram of the imaging results after using the existing FK domain imaging method described in the background art to image a 2mm through hole defect and a 2mm semi-through hole defect in a 15CrMoV material pipe at 300℃.

[0107] Figure 14 This is a schematic diagram of the imaging results after imaging a 2mm through-hole defect and a 2mm semi-through-hole defect in a 15CrMoV material pipe at 630℃ using the imaging method described in this invention. Detailed Implementation

[0108] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0109] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0110] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0111] like Figure 1 As shown, a frequency-wavenumber domain imaging method suitable for detecting defects in high-temperature pipelines includes the following steps:

[0112] Step 1: At room temperature, acquire signals using a dual-path sensor to obtain a set of raw A-scan signals at a reference temperature; at the target temperature, acquire signals using a dual-path sensor to obtain... The original A-scan signal at the target temperature;

[0113] Step 2: Analyze the raw A-scan signals obtained in Step 1 at a set of reference temperatures. The original A-scan signals at the target temperature were sequentially subjected to DC removal and Gaussian filtering to obtain a set of preprocessed A-scan signals at the reference temperature. The A-scan signal preprocessed at the target temperature is then compared with the A-scan signal preprocessed at a set of reference temperatures using a direct-path window. A gated direct wave signal at a reference temperature is obtained by extracting a portion of the preprocessed A-scan signal at the target temperature. Gated direct wave signal at a target temperature;

[0114] Step 3: Construct a time-scale scaling factor based on the gated direct wave signal at the target temperature and the gated direct wave signal at the reference temperature obtained in Step 2;

[0115] The specific steps are as follows:

[0116] 21. Obtained from step two Select any one gated direct wave signal at a target temperature from the gated direct wave signals at the target temperature, and perform a Hilbert transform on the gated direct wave signal at that target temperature to obtain the analytic signal of the gated direct wave signal at the target temperature. Its expression is:

[0117] ;

[0118] in, The gated direct wave signal at the target temperature. For time, For the target temperature, Represents the Hilbert transform operator. The imaginary unit;

[0119] Based on the analytical signal of the gated direct wave signal at the target temperature Obtain the corresponding instantaneous envelope Its expression is:

[0120] ;

[0121] 22. Perform a Hilbert transform on the gated direct-path signal at the reference temperature obtained in step two to obtain the analytic signal of the gated direct-path signal at the reference temperature. Its expression is:

[0122] ;

[0123] in, The gated direct-path signal at the reference temperature. For reference temperature;

[0124] Based on the analytical signal of the gated direct wave signal at the reference temperature Obtain the corresponding instantaneous envelope Its expression is:

[0125] ;

[0126] 23. The instantaneous envelope corresponding to the gated direct wave signal at the target temperature. Instantaneous envelope corresponding to the gated direct wave signal at the reference temperature The cross-correlation function of the two The expression is:

[0127] ;

[0128] Among them, reference temperature Take a room temperature of 25℃. This is the time offset. Target temperature The corresponding instantaneous envelope is shifted on the time axis. The following signal;

[0129] 24. Based on the cross-correlation function Obtain the time delay difference between the gated direct wave signal at the target temperature and the gated direct wave signal at the reference temperature. Its expression is:

[0130] ;

[0131] in, To make the cross-correlation function To obtain the maximum value value;

[0132] 25. Based on the time delay difference between the gated direct wave signal at the target temperature and the gated direct wave signal at the reference temperature. Obtain the group delay of the gated direct wave signal at the target temperature relative to the gated direct wave signal at the reference temperature. Its expression is:

[0133] ;

[0134] in, The group delay of the gated direct wave signal at the reference temperature is the arrival time of the envelope peak of the gated direct wave signal at the reference temperature.

[0135] 26. Let the distance between the transmitting sensor and the receiving sensor be... ,but

[0136] Group velocity of gated direct-wave signal at reference temperature for:

[0137] ;

[0138] Group velocity of the gated direct wave signal at the target temperature for:

[0139] ;

[0140] 27. Based on the group velocity of the gated direct wave signal at the target temperature group velocity of gated direct-path signal at reference temperature Constructing timescale scaling factor Its expression is:

[0141] ;

[0142] Step 4: Obtain the frequency-related amplitude compensation factor based on the gated direct wave signal at the target temperature and the gated direct wave signal at the reference temperature obtained in Step 2.

[0143] The specific steps are as follows:

[0144] 31. Given the Fourier spectrum of the gated direct-wave signal at the reference temperature and the target temperature... The Fourier spectra of the gated direct wave signals are as follows: and Then the reference temperature Normalized spectrum of gated direct wave signal and target temperature Normalized spectrum of gated direct wave signal The expressions are as follows:

[0145] ;

[0146] ;

[0147] in, The effective frequency range of the gated direct-wave signal at the reference temperature. Reference temperature The maximum value of the Fourier spectrum amplitude of the gated direct-wave signal within the effective frequency range. Target temperature The maximum value of the Fourier spectrum amplitude of the gated direct wave signal within the effective frequency range;

[0148] 32. Frequency-dependent amplitude compensation factor The expression is:

[0149] ;

[0150] in, The preset regularization variable has a value range of 1. This is used to prevent numerical instability caused by an excessively small denominator;

[0151] Step 5: Obtained from Step 2 Phase velocity extraction is performed by selecting any gated direct wave signal at any target temperature from the gated direct wave signals at each target temperature.

[0152] The specific steps are as follows:

[0153] 41. Regarding the results obtained in step two Select any one gated direct wave signal at any target temperature from the gated direct wave signals at each target temperature. Perform a Fourier transform to obtain the corresponding frequency domain signal. ;

[0154] The gated direct wave signal at the reference temperature obtained in step two Perform a Fourier transform to obtain the corresponding frequency domain signal. ;

[0155] 42. Let the center frequency of the gated direct-path signal be... The corresponding center angular frequency of the gated direct wave ,but

[0156] The gated direct wave signal at the target temperature at the center angular frequency The spectral phase at that point is:

[0157] ;

[0158] Gated direct wave signal at reference temperature at center angular frequency The spectral phase at that point is:

[0159] ;

[0160] The phase difference between the gated direct wave signal at the reference temperature and the gated direct wave signal at the target temperature Satisfying the formula:

[0161] ;

[0162] in, It is an unknown integer; due to group delay Phase difference They satisfy an approximate relationship Therefore, through group delay The estimated phase difference is obtained. Then, substitute the estimated phase difference into the phase difference formula to deduce the integer value. Finally, the integer derived from the reverse will be... Substituting into the phase difference formula, a relatively accurate phase difference is obtained. ;

[0163] 43. Obtain a relatively accurate phase difference based on step 42. The target temperature is obtained. The gated direct wave signal at the center angular frequency phase velocity at :

[0164] ;

[0165] Step 6: Apply the timescale scaling factor obtained in Step 2 to the timescale scale constructed in Step 3. The A-scan signal, after preprocessing at the target temperature, is time-scaled and pre-corrected, and then obtained by using a defect echo window. The gated defect echo signal after time-scale pre-correction at the target temperature, for The gated defect echo signals after time-scale pre-correction at each target temperature are sequentially subjected to frequency domain transformation and frequency-related amplitude compensation, and then arranged along the scanning direction to obtain the frequency-spatial domain signal of the gated defect echo. Finally, the frequency-spatial domain signal of the gated defect echo is transformed by wavenumber domain to obtain the two-dimensional frequency-wavenumber domain signal of the gated defect echo.

[0166] The specific steps are as follows:

[0167] 51. Using the timescale scaling factor constructed in step three For the results obtained in step two The A-scan signal preprocessed at the target temperature is time-scaled and pre-corrected to obtain... A-scan signal pre-corrected with time scale at the target temperature;

[0168] 52. Yes The A-scan signal, after time-scale pre-correction at the target temperature, is used to extract gated defect echo signals using a defect echo window. Then, the intercepted gated defect echo signal Perform a Fourier transform to obtain the frequency domain signal of the gated defect echo. ;

[0169] 53. The frequency-related amplitude compensation factor obtained in step four. Frequency domain signal acting on gated defect echo The frequency domain signal of the gated defect echo after frequency correlation amplitude compensation was obtained. ;

[0170] ;

[0171] 54. Frequency domain signal of gated defect echo after frequency correlation amplitude compensation. Arranged along the scanning direction, the frequency-spatial domain signal of the gated defect echo is obtained. ;

[0172] 55. Frequency-spatial domain signal of gated defect echo The horizontal axis of the scanning direction Perform a Fourier transform to obtain the two-dimensional frequency-wavenumber domain signal of the gated defect echo. Its expression is:

[0173] ;

[0174] in, The transverse wavenumber is the wavenumber in the scanning direction, which is obtained by analyzing the abscissa of the scanning direction. Discrete wavenumber sequence obtained by performing a one-dimensional Fourier transform; The Hanning window function applied in the scanning direction is used to suppress spectral leakage;

[0175] Step 7: Reconstruct the two-dimensional frequency-wavenumber domain signal of the gated defect echo obtained in Step 6 by Stolt mapping to obtain the two-dimensional wavenumber domain signal of the gated defect echo.

[0176] The specific steps are as follows:

[0177] 61. Using Stolt interpolation to... Planar resampling to The plane, the mapping satisfies:

[0178] ;

[0179] in, For the longitudinal equivalent wavenumber, Furthermore, to satisfy the interpolation angular frequency of the above mapping, Target temperature Below the interpolated angular frequency Phase velocity at that location;

[0180] 62. The approximate non-dispersion case based on the SH0 mode (the SH0 mode is the zeroth-order horizontal shear mode), since... At this point, the expression for the interpolated angular frequency simplifies to:

[0181] ;

[0182] 63. Introducing Jacobian weights through variable substitution Its expression is:

[0183] ;

[0184] 64. Two-dimensional wavenumber domain signal of gated defect echo after Stolt interpolation Represented as:

[0185] ;

[0186] Step 8: Perform a two-dimensional inverse Fourier transform on the two-dimensional wavenumber domain signal of the gated defect echo obtained in Step 7 to obtain the imaging result;

[0187] The specific steps are as follows:

[0188] Two-dimensional wavenumber domain signal after Stolt interpolation Perform a two-dimensional inverse Fourier transform to obtain the imaging results at the target temperature. Its expression is:

[0189] ;

[0190] in, This represents the two-dimensional inverse Fourier transform operator;

[0191] Step 9, Normalization and Image Display: Normalize and display the imaging results obtained in Step 8.

[0192] Imaging results The normalization and image display format are as follows:

[0193] ;

[0194] in, This represents the maximum amplitude of the imaging result across the entire two-dimensional imaging region.

[0195] To verify the effectiveness of the imaging method described in this invention, the following experiment was conducted:

[0196] Experiment 1: Imaging of a 2 mm through-hole defect (TH defect) and a 2 mm semi-through-hole defect (HTH defect) in a P91 material pipe:

[0197] The existing FK domain imaging method described in the background section is used to image 2 mm through-hole defects (through-hole defects are also known as TH defects) and 2 mm semi-through-hole defects (semi-through-hole defects are also known as HTH defects) in P91 material pipes:

[0198] When the pipe temperature is 25℃, when using the existing FK domain imaging method described in the background art, the bright spots of through-hole defects and semi-through-hole defects in the imaging results are concentrated, and the imaging position basically matches the actual position, such as... Figure 2 As shown in the figure, the circles represent the actual locations of the 2 mm through-hole defect and the 2 mm half-through-hole defect.

[0199] When the pipe temperature is 300℃, the bright spots of through-hole and semi-through-hole defects in the imaging results are somewhat blurry, and the imaging position deviates slightly from the actual position. Figure 3 As shown; when imaging using the imaging method described in this invention, the bright spots of through-hole defects and semi-through-hole defects in the imaging results are concentrated, and the imaging position matches the actual position with high accuracy, such as... Figure 4 As shown;

[0200] When the pipe temperature is 600℃, the bright spots of through-hole and semi-through-hole defects in the imaging results are very blurry, and the imaging position deviates significantly from the actual position. Figure 5 As shown; when imaging using the imaging method described in this invention, the bright spots of through-hole defects and semi-through-hole defects in the imaging results are concentrated, and the imaging position matches the actual position with high accuracy, such as... Figure 6 As shown;

[0201] Experiment 2: Imaging a 5×2 mm groove defect in a P91 material pipe;

[0202] When the pipe temperature is 300℃, the bright spot of the groove defect in the imaging result is somewhat blurry, and the imaging position deviates slightly from the actual position. Figure 7 As shown; when imaging using the imaging method described in this invention, the bright spots of groove defects in the imaging results are concentrated, and the imaging position matches the actual position with high accuracy, such as... Figure 8 As shown in the figure, the rectangle represents the actual location of the 5×2 mm groove defect;

[0203] When the pipe temperature is 630℃, the bright spot of the groove defect in the imaging result is somewhat blurry, and the imaging position deviates significantly from the actual position. Figure 9 As shown; when imaging using the imaging method described in this invention, the bright spots of groove defects in the imaging results are concentrated, and the imaging position matches the actual position with high accuracy, such as... Figure 10 As shown;

[0204] Experiment 3: Imaging of 2 mm through-hole defects (through-hole defects are also known as TH defects) and 2 mm semi-through-hole defects (semi-through-hole defects are also known as HTH defects) in 15CrMoV material pipes.

[0205] When the pipe temperature is 300℃, the bright spots of through-hole and semi-through-hole defects in the imaging results are somewhat blurry, and the imaging position deviates significantly from the actual position. Figure 11 As shown; when imaging using the imaging method described in this invention, the bright spots of through-hole defects and semi-through-hole defects in the imaging results are concentrated, and the imaging position matches the actual position with high accuracy, such as... Figure 12 As shown;

[0206] When the pipe temperature is 630℃, the bright spots of through-hole and semi-through-hole defects in the imaging results are very blurry, and the imaging position deviates significantly from the actual position. Figure 13 As shown; when imaging using the imaging method described in this invention, the bright spots of through-hole defects and semi-through-hole defects in the imaging results are concentrated, and the imaging position matches the actual position with high accuracy, such as... Figure 14 As shown;

[0207] As can be seen from the above, the imaging method described in this invention has good focusing stability and positioning accuracy for high-temperature pipes with different materials and different defects, and the imaging accuracy is high.

[0208] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. A frequency-wavenumber domain imaging method suitable for detecting defects in high-temperature pipelines, characterized in that, Includes the following steps: Step 1: At room temperature, acquire signals using a dual-path sensor to obtain a set of raw A-scan signals at a reference temperature; at the target temperature, acquire signals using a dual-path sensor to obtain... The original A-scan signal at the target temperature; Step 2: Analyze the raw A-scan signals obtained in Step 1 at a set of reference temperatures. The original A-scan signals at the target temperature were sequentially subjected to DC removal and Gaussian filtering to obtain a set of preprocessed A-scan signals at the reference temperature. The A-scan signal preprocessed at the target temperature is then compared with the A-scan signal preprocessed at a set of reference temperatures using a direct-path window. A gated direct wave signal at a reference temperature is obtained by extracting a portion of the preprocessed A-scan signal at the target temperature. Gated direct wave signal at a target temperature; Step 3: Construct a time-scale scaling factor based on the gated direct wave signal at the target temperature and the gated direct wave signal at the reference temperature obtained in Step 2; Step 4: Obtain the frequency-related amplitude compensation factor based on the gated direct wave signal at the target temperature and the gated direct wave signal at the reference temperature obtained in Step 2. Step 5: Obtained from Step 2 Phase velocity extraction is performed by selecting any gated direct wave signal at any target temperature from the gated direct wave signals at each target temperature. Step 6: Apply the timescale scaling factor obtained in Step 2 to the timescale scale constructed in Step 3. The A-scan signal, after preprocessing at the target temperature, is time-scaled and pre-corrected, and then obtained by defect echo window extraction. The gated defect echo signal after time-scale pre-correction at the target temperature, for The gated defect echo signals after time-scale pre-correction at each target temperature are sequentially subjected to frequency domain transformation and frequency-related amplitude compensation, and then arranged along the scanning direction to obtain the frequency-spatial domain signal of the gated defect echo. Finally, the frequency-spatial domain signal of the gated defect echo is transformed by wavenumber domain to obtain the two-dimensional frequency-wavenumber domain signal of the gated defect echo. Step 7: Reconstruct the two-dimensional frequency-wavenumber domain signal of the gated defect echo obtained in Step 6 by Stolt mapping to obtain the two-dimensional wavenumber domain signal of the gated defect echo. Step 8: Perform a two-dimensional inverse Fourier transform on the two-dimensional wavenumber domain signal of the gated defect echo obtained in Step 7 to obtain the imaging result; Step 9: Normalize and display the imaging results obtained in Step 8.

2. The frequency-wavenumber domain imaging method for detecting defects in high-temperature pipelines according to claim 1, characterized in that, The specific steps for step three are as follows:

21. Obtained from step two Select any one gated direct wave signal at a target temperature from the gated direct wave signals at the target temperature, and perform a Hilbert transform on the gated direct wave signal at that target temperature to obtain the analytic signal of the gated direct wave signal at the target temperature. Its expression is: ； in, The gated direct wave signal at the target temperature. For time, For the target temperature, Represents the Hilbert transform operator. The imaginary unit; Based on the analytical signal of the gated direct wave signal at the target temperature Obtain the corresponding instantaneous envelope Its expression is: ； 22. Perform a Hilbert transform on the gated direct-path signal at the reference temperature obtained in step two to obtain the analytic signal of the gated direct-path signal at the reference temperature. Its expression is: ； in, For the gated direct wave signal at the reference temperature, For reference temperature; Based on the analytical signal of the gated direct wave signal at the reference temperature Obtain the corresponding instantaneous envelope Its expression is: ； 23. The instantaneous envelope corresponding to the gated direct wave signal at the target temperature. Instantaneous envelope corresponding to the gated direct wave signal at the reference temperature The cross-correlation function of the two The expression is: ； Among them, reference temperature Take room temperature 25℃, This is the time offset. Target temperature The corresponding instantaneous envelope is translated on the time axis. The following signal; 24. Based on the cross-correlation function Obtain the time delay difference between the gated direct wave signal at the target temperature and the gated direct wave signal at the reference temperature. Its expression is: ； in, To make the cross-correlation function To obtain the maximum value value; 25. Based on the time delay difference between the gated direct wave signal at the target temperature and the gated direct wave signal at the reference temperature. Obtain the group delay of the gated direct wave signal at the target temperature relative to the gated direct wave signal at the reference temperature. Its expression is: ； in, The group delay of the gated direct wave signal at the reference temperature is the arrival time of the envelope peak of the gated direct wave signal at the reference temperature.

26. Let the distance between the transmitting sensor and the receiving sensor be... ,but Group velocity of gated direct-wave signal at reference temperature for: ； Group velocity of gated direct-wave signal at target temperature for: ； 27. Based on the group velocity of the gated direct wave signal at the target temperature group velocity of gated direct-path signal at reference temperature Constructing timescale scaling factor Its expression is: 。 3. The frequency-wavenumber domain imaging method for detecting defects in high-temperature pipelines according to claim 2, characterized in that, The specific steps for step four are as follows:

31. Suppose the Fourier spectrum of the gated direct-wave signal at the reference temperature is related to that at the target temperature. The Fourier spectra of the gated direct wave signals are as follows: and Then the reference temperature Normalized spectrum of gated direct wave signal and target temperature Normalized spectrum of gated direct wave signal The expressions are as follows: ； ； in, The effective frequency range of the gated direct-wave signal at the reference temperature. Reference temperature The maximum value of the Fourier spectrum amplitude of the gated direct-wave signal within the effective frequency range. Target temperature The maximum value of the Fourier spectrum amplitude of the gated direct wave signal within the effective frequency range; 32. Frequency-dependent amplitude compensation factor The expression is: ； in, The preset regularization variable has a value range of 1. .

4. The frequency-wavenumber domain imaging method for detecting defects in high-temperature pipelines according to claim 3, characterized in that, The specific steps for step five are as follows:

41. Regarding the results obtained from step two Select any one gated direct wave signal at any target temperature from the gated direct wave signals at each target temperature. Perform a Fourier transform to obtain the corresponding frequency domain signal. ; The gated direct wave signal at the reference temperature obtained in step two Perform a Fourier transform to obtain the corresponding frequency domain signal. ; 42. Let the center frequency of the gated direct-path signal be... The corresponding center angular frequency of the gated direct wave ,but The gated direct wave signal at the target temperature at the center angular frequency The spectral phase at that point is: ； Gated direct wave signal at reference temperature at center angular frequency The spectral phase at that point is: ； The phase difference between the gated direct wave signal at the reference temperature and the gated direct wave signal at the target temperature Satisfying the formula: ； in, It is an unknown integer; due to group delay Phase difference They satisfy an approximate relationship Therefore, through group delay The estimated phase difference is obtained. Then, substitute the estimated phase difference into the phase difference formula to deduce the integer value. Finally, the integer derived from the reverse will be... Substituting into the phase difference formula, a relatively accurate phase difference is obtained. ; 43. Based on the relatively accurate phase difference obtained in step 42 The gated direct wave signal at the target temperature at its center angular frequency was obtained. phase velocity at : 。 5. A frequency-wavenumber domain imaging method for detecting defects in high-temperature pipelines according to claim 4, characterized in that, The specific steps for step six are as follows:

51. Using the timescale scaling factor constructed in step three For the results obtained in step two The A-scan signal preprocessed at the target temperature is time-scaled and pre-corrected to obtain... A-scan signal pre-corrected with time scale at the target temperature; 52. Yes The A-scan signal, after time-scale pre-correction at the target temperature, is used to extract gated defect echo signals using a defect echo window. Then, the intercepted gated defect echo signal Perform a Fourier transform to obtain the frequency domain signal of the gated defect echo. ; 53. The frequency-related amplitude compensation factor obtained in step four. Frequency domain signal acting on gated defect echo The frequency domain signal of the gated defect echo after frequency correlation amplitude compensation was obtained. ; ； 54. Frequency domain signal of gated defect echo after frequency correlation amplitude compensation. Arranged along the scanning direction, the frequency-spatial domain signal of the gated defect echo is obtained. ; 55. Frequency-spatial domain signal of gated defect echo The horizontal axis of the scanning direction Perform a Fourier transform to obtain the two-dimensional frequency-wavenumber domain signal of the gated defect echo. Its expression is: ； in, The transverse wavenumber is the wavenumber in the scanning direction, which is obtained by analyzing the abscissa of the scanning direction. Discrete wavenumber sequence obtained by performing a one-dimensional Fourier transform; The Hanning window function applied in the scanning direction.

6. The frequency-wavenumber domain imaging method for detecting defects in high-temperature pipelines according to claim 5, characterized in that, The specific steps for step seven are as follows:

61. Using Stolt interpolation to... Planar resampling to The plane, the mapping satisfies: ； in, For the longitudinal equivalent wavenumber, Furthermore, to satisfy the interpolation angular frequency of the above mapping, At the target temperature, the interpolation angular frequency Phase velocity at that location; 62. Approximate non-dispersion case based on SH0 mode, due to At this point, the expression for the interpolated angular frequency simplifies to: ； 63. Introducing Jacobian weights through variable substitution Its expression is: ； 64. Two-dimensional wavenumber domain signal of gated defect echo after Stolt interpolation Represented as: 。 7. The frequency-wavenumber domain imaging method for detecting defects in high-temperature pipelines according to claim 6, characterized in that, The specific steps for step eight are as follows: Two-dimensional wavenumber domain signal after Stolt interpolation Perform a two-dimensional inverse Fourier transform to obtain the imaging results at the target temperature. Its expression is: ； in, This represents the two-dimensional inverse Fourier transform operator.

8. A frequency-wavenumber domain imaging method for detecting defects in high-temperature pipelines according to claim 7, characterized in that, The specific steps for step nine are as follows: Imaging results The normalization and image display format are as follows: ； in, This represents the maximum amplitude of the imaging result across the entire two-dimensional imaging region.

Images