Crack quantification method and system for suppressing ACFM lift-off effect

Abstract

The present invention discloses a crack quantification method and system for suppressing ACFM lift-off effect. It includes: obtaining magnetic field scanning signals of cracked specimens at different lift-off heights; the magnetic field scanning signals include first-direction magnetic field signals and second-direction magnetic field signals; extracting the first-direction magnetic field signals at different lift-off heights, performing two regularization processes to obtain regularized detection signals, and extracting the amplitudes corresponding to each trough; extracting the corresponding positions of the crests and troughs of the irregular second-direction magnetic field signals, and calculating the position spacing; using the corresponding amplitudes of each trough to quantify the crack depth, and using the position spacing of the crests and troughs to quantify the crack length. The present application performs multiple regularization processes on the magnetic field signal to obtain a characteristic curve that is not affected by the lift-off height, and the characteristic value is substituted into the fitting formula to obtain the crack depth. The processed characteristic value signal is not affected by the lift-off height, which reduces the experimental error.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic field detection technology, and in particular to a crack quantification method and system for suppressing ACFM lift-off effect. Background Art

[0002] Marine pipelines are key facilities for transporting oil and natural gas because of their advantages such as tensile resistance, pressure resistance and fatigue resistance. However, marine pipelines work in harsh seawater environments for a long time and are subject to the combined effects of multiple loads, which makes it very easy to produce defects such as cracks. If these cracks are not discovered and quantitatively evaluated in time at the early stage, they will leave safety hazards and even cause major safety accidents. Alternating Current Field Measurement (ACFM) technology uses alternating current to generate an electromagnetic field in a conductor, and identifies and evaluates defects in the material by detecting changes in the electromagnetic field. As a new type of non-contact non-destructive testing technology, there is no need to clean the surface coating of the test piece during testing, and the magnetic field characteristic signals can be used to characterize and quantify defects such as cracks.

[0003] During the service process, marine pipelines will be subject to seawater corrosion, impact and wear from ocean currents and gravel, and seabed sediment and biological attachments will also accumulate on the surface, resulting in an uneven pipeline surface, causing the ACFM probe to lift off during the detection process. The interference signal generated by the lift-off effect will greatly affect the accuracy of the crack characteristic signal, resulting in inaccurate crack quantitative characterization. Therefore, it is necessary to propose a crack quantification method that can suppress the ACFM lift-off effect, weaken the influence of the lift-off effect on the detection signal during the detection process, and improve the accuracy of the crack length and depth quantification.

[0004] At present, the patent for the crack quantification method retrieved is "Three-dimensional size assessment method of corrosion defects of underwater structures based on AC electromagnetic field" (application number CN111189905B). This method measures the amplitude of the background magnetic field characteristic signal Bx0 at different lift-off heights, obtains the curve formula of the characteristic value and lift-off height through normalization and polynomial fitting, and scans the specimen with corrosion pits based on this formula to obtain the inversion image and size information of the defect. This method mainly uses the background magnetic field Bx0 and lift-off height fitting formula to evaluate the size of the corrosion pit defect. Therefore, the inspection results obtained by this type of technology are very dependent on the lift-off height, and the field application has limitations, which will lead to large errors in the detection results. Summary of the invention

[0005] Therefore, the purpose of the present invention is to provide a crack quantification method that suppresses the ACFM lift-off effect. By performing primary and secondary regularization processing on the magnetic field signal Bx obtained by crack scanning, a characteristic curve Bx / Bz signal that is not affected by the lift-off height is obtained, and the trough amplitude of the curve is extracted as the quantitative characteristic value of the defect depth. The characteristic value is brought into the fitting formula of cracks of different depths and the trough amplitude to obtain the crack depth. Therefore, the processed characteristic value signal is not affected by the lift-off height, reducing the experimental error caused by the lift-off height fitting formula, which is quite different from the previous invention patent.

[0006] In order to achieve the above object, an embodiment of the first aspect of the present invention provides a crack quantification method for suppressing ACFM lift-off effect, comprising the following steps:

[0007] S1, obtaining magnetic field scanning signals of cracked specimens at different lift-off heights; the magnetic field scanning signals include a first direction magnetic field signal Bx1 and a second direction magnetic field signal Bz1;

[0008] S2, extracting the first direction magnetic field signal at different lift-off heights, performing a regularization process on the first direction magnetic field signal to obtain a first regularization detection signal Bx2, and then performing a second regularization process to obtain a second regularization detection signal Bx3;

[0009] S3, extracting the amplitude corresponding to each trough of the secondary regularized detection signal Bx3;

[0010] S4, extracting the corresponding positions of the crests and troughs of the irregular second directional magnetic field signal Bz1, and calculating the position spacing;

[0011] S5. quantify the crack depth using the corresponding amplitude of each trough in S3, and quantify the length using the position spacing of the peaks and troughs described in S4.

[0012] Further preferably, the magnetic field scanning signals of the test piece at different lift-off heights include:

[0013] An ACFM probe is excited by an AC excitation signal of 10 kHz, and the ACFM probe is used to scan the tape test piece at different lift-off heights; the different lift-off heights include 1 mm, 2 mm, 3 mm and 4 mm.

[0014] Further preferably, in S2, the one-time regularization processing includes the following process:

[0015] S201, calculating the maximum and minimum values ​​of the first direction magnetic field signal Bx1 extracted at different lift-off heights;

[0016] S202: According to the maximum value and the minimum value, a regularized detection signal Bx2 is obtained according to the following formula:

[0017] ;

[0018] Among them, Bx1 is the first direction magnetic field signal, Bx1 max is the maximum value; Bx1 min is the minimum value.

[0019] Further preferably, in S2, the secondary regularization processing includes the following process:

[0020] S203, calculating the mean value Bx2 for the first regularized detection signal Bx2 at different lift-off heights mean and standard deviation Bx2 std The calculation formula of the mean is ,in is the number of data, and the formula for calculating the standard deviation is ;

[0021] S204, using the obtained first regularization detection signal Bx2 and mean value Bx2 mean and standard deviation Bx2 std After that, the secondary regularized detection signal Bx3 is calculated using the following formula:

[0022] .

[0023] Further preferably, in S5, the quantifying the crack depth by using the amplitude corresponding to each trough in S3 includes:

[0024] Establish a crack depth fitting relationship;

[0025] The amplitude corresponding to each trough of the secondary regularized detection signal Bx3 is input into the established fitting relationship to obtain the crack depth.

[0026] The present invention also provides a crack quantification system for suppressing ACFM lift-off effect, which is used to implement the crack quantification method for suppressing ACFM lift-off effect, comprising:

[0027] A detection module, used to obtain magnetic field scanning signals of cracked specimens at different lift-off heights; the magnetic field scanning signals include a first direction magnetic field signal Bx1 and a second direction magnetic field signal Bz1;

[0028] A data regularization processing module extracts the first direction magnetic field signal at different lift-off heights, performs a regularization process on the first direction magnetic field signal to obtain a first regularization detection signal Bx2, and then performs a second regularization process to obtain a second regularization detection signal Bx3;

[0029] The crack quantification module extracts the amplitude corresponding to each trough of the secondary regularized detection signal Bx3; extracts the corresponding positions of the peaks and troughs of the unregularized second direction magnetic field signal Bz1, and calculates the position spacing;

[0030] The crack depth is quantified using the corresponding amplitude of each trough, and the crack length is quantified using the position spacing of the peaks and troughs;

[0031] Further preferably, the regularization processing module includes performing a regularization processing according to the following process:

[0032] Calculate the maximum and minimum values ​​of the first direction magnetic field signals extracted at different lift-off heights;

[0033] According to the maximum value and the minimum value, a regularized detection signal Bx2 is obtained according to the following formula:

[0034] ;

[0035] Among them, Bx1 is the first direction magnetic field signal, Bx1 max is the maximum value; Bx1 min is the minimum value.

[0036] Further preferably, the regularization processing module further includes performing secondary regularization processing according to the following process:

[0037] For the regularized detection signal Bx2 at different lift-off heights, calculate the mean value Bx2 mean and standard deviation Bx2 std The calculation formula of the mean is ,in is the number of data, and the formula for calculating the standard deviation is ;

[0038] Using the obtained regularized detection signal Bx2 and mean value Bx2 mean and standard deviation Bx2 std After that, the secondary regularized detection signal Bx3 is calculated using the following formula:

[0039] .

[0040] A crack quantification method and system for suppressing ACFM lift-off effect disclosed in the present application has at least the following advantages over the prior art:

[0041] The present invention weakens the influence of the lift-off effect on the detection signal, mainly performs secondary regularization processing on the detection signal, and extracts new characteristic signals based on the secondary regularization signal to characterize the crack depth. The calculation process is simple and the field adaptability is strong. The detection result is less affected by factors such as probe jitter and lift-off effect, and the accuracy of crack depth and length quantification can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A flow chart of a crack quantification method for suppressing ACFM lift-off effect provided by the present invention;

[0043] Figure 2 The X-direction magnetic field intensity image is obtained after the ACFM probe provided in the embodiment of the present invention scans the cracked specimen at different lift-off heights;

[0044] Figure 3 The magnetic field intensity image in the Z direction is obtained after the ACFM probe scans the cracked specimen at different lift-off heights;

[0045] Figure 4 A regularized processing flow chart provided in an embodiment of the present invention;

[0046] Figure 5 A first regularized result image of the magnetic field strength in the X direction under different lift-off heights provided in an embodiment of the present invention;

[0047] Figure 6 It is a secondary regularized result image of the X-direction magnetic field strength under different lift-off heights provided in an embodiment of the present invention;

[0048] Figure 7 The amplitude image corresponding to the trough extracted according to the quadratic regularized X-direction magnetic field intensity provided in the embodiment of the present invention;

[0049] Figure 8 It is a position spacing image corresponding to the peaks and valleys extracted according to the irregular Z-direction magnetic field intensity provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The present invention is further described in detail below through the accompanying drawings and specific embodiments.

[0051] like Figure 1 As shown, an embodiment of the present invention provides a crack quantification method for suppressing ACFM lift-off effect, comprising the following steps:

[0052] S1. Obtaining magnetic field scanning signals of a cracked specimen at different lift-off heights; the magnetic field scanning signals include a first direction magnetic field signal Bx1 and a second direction magnetic field signal Bz1; wherein the magnetic field scanning signals of the cracked specimen at different lift-off heights include:

[0053] An ACFM probe is excited by an AC excitation signal of 10kHz, and the cracked specimens at different lift-off heights are scanned by the ACFM probe; the different lift-off heights include 1mm, 2mm, 3mm and 4mm. After the lift-off height of the ACFM probe reaches 4mm, the signal curves at different lift-off heights are very different. The ACFM crack quantification method for suppressing the lift-off effect processes the probe detection signal and is independent of the material properties. It is applicable to both ferromagnetic metal materials and non-ferromagnetic metal materials. The first direction magnetic field signal and the second direction magnetic field signal are the X-direction magnetic field signal and the Z-direction magnetic field signal, respectively. The cracked specimen is scanned by the probe to obtain the X-direction magnetic field signal Bx1 and the Z-direction magnetic field signal Bz1 at different lift-off heights. The Bx1 image is shown in Figure 2 As shown, the Bz1 image is Figure 3 shown.

[0054] S2, extracting the first direction magnetic field signal at different lift-off heights, performing a regularization process on the first direction magnetic field signal to obtain a first regularization detection signal Bx2, and then performing a second regularization process to obtain a second regularization detection signal Bx3; Figure 4 As shown, the first regularization process and the second regularization process are described in detail below.

[0055] The one-time regularization process includes the following steps:

[0056] S201, calculating the maximum and minimum values ​​of the first direction magnetic field signals extracted at different lift-off heights;

[0057] S202, obtaining a regularized detection signal Bx2 according to the maximum value and the minimum value according to the following formula;

[0058] ;

[0059] Among them, Bx1 is the first direction magnetic field signal, Bx1 max is the maximum value; Bx1 min is the minimum value.

[0060] The result after one regularization is as follows Figure 5 As shown, this is a regularized result image of the magnetic field strength in the X direction under different lift-off heights.

[0061] Further preferably, in S2, the secondary regularization processing includes the following process:

[0062] S203, calculating the mean value Bx2 for the first regularized detection signal Bx2 at different lift-off heights mean and standard deviation Bx2 std The calculation formula of the mean is ,in is the number of data, and the formula for calculating the standard deviation is ;

[0063] S204, using the obtained first regularization detection signal Bx2 and mean value Bx2 mean and standard deviation Bx2 std Then, the first regularized detection signal Bx2 is subtracted from the calculated mean value Bx2 mean Then, divide by the standard deviation Bx2 std , the secondary regularized detection signal Bx3 is obtained. The secondary regularized detection signal Bx3 is calculated using the following formula

[0064] .

[0065] The image after secondary regularization is as follows Figure 6 As shown, the quadratic regularization result image of the magnetic field strength in the X direction under different lift-off heights.

[0066] S3, extracting the amplitude corresponding to each trough of the secondary regularized detection signal Bx3;

[0067] S4, extracting the corresponding positions of the crests and troughs of the irregular second directional magnetic field signal Bz1, and calculating the position spacing;

[0068] S5. quantify the crack depth using the amplitude corresponding to each trough in S3, and quantify the crack length using the position spacing of the peaks and troughs described in S4.

[0069] The crack length and depth are quantified using ACFM detection signals. The characteristic signals that can be used are the change in the peak-to-trough amplitude of the magnetic field in the X direction and the distance between the peak-to-trough position of the magnetic field in the Z direction.

[0070] like Figure 7 As shown in Figure 2, the Bz1 peak-to-trough spacing can be used to quantify the crack length, such as Figure 8 As shown. It can be seen that at four lift-off heights of 1mm, 2mm, 3mm and 4mm, the troughs of the detection signal Bx3 corresponding to the same depth crack intersect at one point, and the corresponding amplitudes are the same, indicating that the selected feature point is not affected by the change in lift-off height, but only related to the crack depth. The Bz curves used to detect the defect length are almost overlapped, indicating that this method can suppress the interference of the lift-off effect on the quantification of crack depth and length, and improve accuracy.

[0071] Further preferably, in S6, the quantifying the crack depth by using the amplitude corresponding to each trough in S4 includes:

[0072] Establish a crack depth fitting relationship;

[0073] The amplitude corresponding to each trough of the secondary regularized detection signal Bx3 is input into the established fitting relationship to obtain the crack depth.

[0074] Further preferably, the establishing of the crack depth fitting relationship comprises the following steps:

[0075] The secondary regularized detection signal Bx3 corresponding to different lift-off heights is expressed in the same coordinate system;

[0076] Extract the amplitude information corresponding to different troughs from the secondary regularized detection signal Bx3 curve corresponding to different lift-off heights;

[0077] The amplitudes corresponding to different troughs are curve-fitted to obtain a crack depth fitting curve, and a crack depth fitting relationship is obtained according to the crack depth fitting curve.

[0078] The present invention also provides a crack quantification system for suppressing ACFM lift-off effect, which is used to implement the crack quantification method for suppressing ACFM lift-off effect, comprising:

[0079] The detection module is used to obtain the magnetic field scanning signal of the cracked specimen at different lift-off heights; the magnetic field scanning signal includes the first direction magnetic field signal Bx1 and the second direction magnetic field signal Bz1; the detection module uses an ACFM probe and uses a 10kHz AC signal to excite the excitation coil; the lift-off heights are set to 1mm, 2mm, 3mm and 4mm respectively, and the probe is used to scan the cracked specimen to obtain the X-direction magnetic field signal Bx1 and the Z-direction magnetic field signal Bz1 at different lift-off heights. The Bx1 image is as follows Figure 2 As shown, the Bz1 image is Figure 3 shown.

[0080] A data regularization processing module extracts the first direction magnetic field signal at different lift-off heights, performs a regularization process on the first direction magnetic field signal once, obtains a first regularization detection signal Bx2, and then performs a second regularization process on the first direction magnetic field signal to obtain a second regularization detection signal Bx3;

[0081] Further preferably, Figure 4 As shown, the regularization processing module includes performing a regularization processing according to the following process:

[0082] Calculate the maximum and minimum values ​​of the first direction magnetic field signals extracted at different lift-off heights;

[0083] According to the maximum value and the minimum value, a regularized detection signal Bx2 is obtained according to the following formula:

[0084] ;

[0085] Among them, Bx1 is the first direction magnetic field signal, Bx1 max is the maximum value; Bx1 min is the minimum value.

[0086] The result after one regularization is as follows Figure 5 shown.

[0087] Further preferably, the regularization processing module further includes performing secondary regularization processing according to the following process:

[0088] For the regularized detection signal Bx2 at different lift-off heights, calculate the mean value Bx2 mean and standard deviation Bx2 std The calculation formula of the mean is ,in is the number of data, and the formula for calculating the standard deviation is ;

[0089] Using the obtained regularized detection signal Bx2 and mean value Bx2 mean and standard deviation Bx2 std After that, the secondary regularized detection signal Bx3 is calculated using the following formula: Figure 6 shown.

[0090] .

[0091] The crack quantification module extracts the amplitude corresponding to each trough of the secondary regularized detection signal Bx3; extracts the corresponding positions of the peaks and troughs of the unregularized second direction magnetic field signal Bz1, and calculates the position spacing;

[0092] The crack depth is quantified using the corresponding amplitude of each trough, and the crack length is quantified using the position spacing of the peaks and troughs;

[0093] Establish a crack depth fitting relationship;

[0094] The amplitude corresponding to each trough of the secondary regularized detection signal Bx3 is input into the established fitting relationship to obtain the crack depth.

[0095] Among them, the establishment of crack depth fitting relationship includes:

[0096] The secondary regularized detection signal Bx3 corresponding to different lift-off heights is expressed in the same coordinate system;

[0097] Extract the amplitude information corresponding to different troughs from the secondary regularized detection signal Bx3 curve corresponding to different lift-off heights;

[0098] The amplitudes corresponding to different troughs are curve-fitted to obtain a crack depth fitting curve, and a crack depth fitting relationship is obtained according to the crack depth fitting curve.

[0099] like Figure 7 As shown in Figure 1, the Bz1 peak-to-trough distance can be used to quantify the crack length. Figure 8 As shown, it can be seen that under the four lift-off heights of 1mm, 2mm, 3mm and 4mm, the troughs of the detection signal Bx3 corresponding to the same depth crack intersect at one point, and the corresponding amplitudes are the same, indicating that the selected feature point is not affected by the change in lift-off height and is only related to the crack depth. The Bz curves used to detect the defect length are almost identical, indicating that this method can suppress the interference of the lift-off effect on the quantification of crack depth and length, and improve accuracy.

[0100] Another embodiment of the present application also includes identifying and analyzing the changing trend of pipeline cracks according to the crack quantitative relationship proposed in the present application. A pipeline finite element model simulating the crack evolution process is established using Abaqus software, and the crack characteristics are introduced into the model through the detection signal of the probe and the crack quantitative relationship to update the model; external pressure in a first direction is applied to the model with cracks to obtain a stress distribution cloud map of the crack area, and further, external pressure in multiple directions is applied to obtain stress cloud maps in multiple directions at the crack, and multiple stress cloud maps are input into the neural network model to output the features closest to the crack evolution trend, thereby realizing the life prediction of the cracked pipeline.

[0101] Obviously, the above embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. A crack quantification method for suppressing ACFM lift-off effect, characterized in that: The following steps are involved: S1, obtaining magnetic field scanning signals of cracked specimens at different lift-off heights; the magnetic field scanning signals include a first direction magnetic field signal Bx1 and a second direction magnetic field signal Bz1; S2, extracting the first direction magnetic field signal Bx1 at different lift-off heights, performing a regularization process on the first direction magnetic field signal Bx1 to obtain a first regularization detection signal Bx2, and then performing a second regularization process to obtain a second regularization detection signal Bx3; the first regularization process, The process includes: S201, calculating the maximum value Bx1 for the first direction magnetic field signal Bx1 extracted at different lift-off heights max and minimum value Bx1 min ; S202, according to the maximum value Bx1 max and minimum value Bx1 min , a regularized detection signal Bx2 is obtained according to the following formula; ； Among them, Bx1 is the first direction magnetic field signal, Bx1 max is the maximum value; Bx1 min is the minimum value; The secondary regularization process includes the following steps: S203, calculating the mean value Bx2 for the first regularized detection signal Bx2 at different lift-off heights mean and standard deviation Bx2 std The calculation formula of the mean is ,in is the number of data, and the formula for calculating the standard deviation is ; S204, using the obtained first regularization detection signal Bx2 and mean value Bx2 mean and standard deviation Bx2 std , the following formula is used to calculate the secondary regularized detection signal Bx3: ； S3, extracting the amplitude corresponding to each trough of the secondary regularized detection signal Bx3; S4, extracting the corresponding positions of the crests and troughs of the irregular second directional magnetic field signal Bz1, and calculating the position spacing; S5. quantify the crack depth using the amplitude corresponding to each trough in S3, and quantify the crack length using the position spacing of the peaks and troughs described in S4.

2. The crack quantification method for suppressing ACFM lift-off effect according to claim 1, characterized in that: In S1, the magnetic field scanning signal of the cracked specimen at different lift-off heights is obtained, wherein the different lift-off heights include 1 mm, 2 mm, 3 mm and 4 mm.

3. The crack quantification method for suppressing ACFM lift-off effect according to claim 1, characterized in that: In S5, the quantification of the crack depth using the amplitude corresponding to each trough in S3 includes: Establish a crack depth fitting relationship; The amplitude corresponding to each trough of the secondary regularized detection signal Bx3 is input into the established fitting relationship to obtain the crack depth.

4. A crack quantification system for suppressing ACFM lift-off effect, used for implementing the crack quantification method for suppressing ACFM lift-off effect as described in any one of claims 1 to 3, characterized in that: include: A detection module, used to obtain magnetic field scanning signals of a cracked specimen at different lift-off heights; the magnetic field scanning signals include a first direction magnetic field signal and a second direction magnetic field signal; The data regularization processing module extracts the first direction magnetic field signal Bx1 at different lift-off heights, performs a regularization process on the first direction magnetic field signal Bx1, obtains a regularized detection signal Bx2, and then performs a secondary regularization process to obtain a secondary regularized detection signal Bx3; the regularization processing module includes performing a regularization process according to the following process: Calculate the maximum and minimum values ​​of the first direction magnetic field signals extracted at different lift-off heights; According to the maximum value and the minimum value, a regularized detection signal Bx2 is obtained according to the following formula: ； Among them, Bx1 is the first direction magnetic field signal, Bx1 max is the maximum value; Bx1 min is the minimum value; The regularization processing module also includes performing secondary regularization processing according to the following process: For the regularized detection signal Bx2 at different lift-off heights, calculate the mean value Bx2 mean and standard deviation Bx2 std The calculation formula of the mean is ,in is the number of data, and the formula for calculating the standard deviation is ; Using the obtained regularized detection signal Bx2 and mean value Bx2 mean and standard deviation Bx2 std After that, the secondary regularized detection signal Bx3 is calculated using the following formula: ； The crack quantification module extracts the amplitude corresponding to each trough of the secondary regularized detection signal Bx3; extracts the corresponding positions of the peaks and troughs of the unregularized second direction magnetic field signal Bz1, and calculates the position spacing; The crack depth is quantified using the amplitude corresponding to each trough, and the crack length is quantified using the position spacing between the peaks and troughs.

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