CN117781974A - Non-contact pipeline thickness measurement method without pipeline material parameters - Google Patents
Non-contact pipeline thickness measurement method without pipeline material parameters Download PDFInfo
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Abstract
The invention discloses a non-contact pipeline thickness measurement method without pipeline material parameters, which comprises the steps of placing an EMAT transducer on the inner surface of a pipeline with constant arc length, measuring a group of ultrasonic time domain signals, and obtaining the time required by the propagation arc length of an inner surface mode guided wave; substituting the time of the obtained signal into the derived formula to calculate the thickness of the pipeline. The invention does not need to calibrate the speed in advance, the thickness measurement result is very little influenced by the defect, the excitation frequency (a certain frequency interval) and the material parameter, and the measurement can be completed only at one side, so that the whole thickness of the pipeline can be measured, and the connection with the depth of the corrosion defect can be established when the pipeline with the corrosion defect is measured.
Description
Technical Field
The invention relates to a metal thickness measuring method, in particular to a non-contact pipeline thickness measuring method without pipeline material parameters.
Background
Steel pipelines are very easy to be corroded by fluid in the use process, the thickness is changed, certain key physical properties of the materials are reduced, so that serious safety accidents are caused, the pipelines are required to be regularly detected and maintained in order to avoid the accidents, the internal working conditions of the in-service pipelines are complex, and the screening of the pipelines is very challenging to be quick and reliable in result.
In the conventional method for measuring the thickness of the metal, the thickness measurement is carried out by utilizing the product of the propagation time of ultrasonic waves in the thickness direction of the metal and the bulk wave speed of the measured object, and in order to better couple the excited ultrasonic energy from the sensor to the measured object, a compression wave probe is generally used, and the measurement precision is high. But the disadvantage is also apparent that the body wave velocity of the object to be measured needs to be known in advance. In the case where the composition of the measured object, the type of alloy cannot be completely determined or the ultrasonic speed is changed due to high temperature, stress and microstructure changes and the measured object has defects, the measurement results of the conventional thickness measurement method and the method for measuring the thickness of the pipe using the guided wave characteristic quantity are severely affected, resulting in the occurrence of unstable measurement results and reduced accuracy.
Disclosure of Invention
The invention aims to provide a non-contact pipeline thickness measuring method without pipeline material parameters.
In order to achieve the above purpose, the invention is implemented according to the following technical scheme:
the invention comprises the following steps:
1) The EMAT transducer is placed on the inner surface of the pipeline at a constant arc length, a group of ultrasonic time domain signals are measured, and the inner surface SH is obtained 0 Time t required for modal guided wave to propagate arc length S 1 ；
Then the EMAT transducer is moved to the arc length of the excitation transducer at the distance from the outer surface of the pipeline, and a second group of ultrasonic time domain signals are measured to obtain SH 0 Time t required for modal guided wave to propagate arc length distance on outer surface 2 ；
2) At a known pipe outer diameter R b In the case of (2), the obtainedTime t of arrival of two sets of signals 1 、t 2 Substituted into formula R a /R b ＝t 2 /t 1 The inner diameter R of the pipeline is obtained a Bringing it into the formula h=r b -R a The thickness of the pipe can be obtained.
When only one side of the pipe can be measured, time t 2 Calculated by the following formula:
wherein θ is Central angle Represents the central angle corresponding to the arc length of the outer surface S, alpha represents the angular phase speed corresponding to the inner surface of the pipeline, t 1 SH in SH guided wave indicating short propagation distance 0 Time of mode reaching point A, t 1 ' represent SH in SH guided wave with long propagation distance 0 The time when the mode reaches the point A; t is t 2 SH in SH guided wave indicating short propagation distance 0 The time the mode arrives at the inner surface in the same radial direction as the outer surface arc length S; due to S in the formula Outer part ，t 1 ，t 1 ' are all known values, so t 2 Can be expressed by the formulaAnd (5) calculating to obtain the product.
3) In the case that the pipeline under test is an in-service pipeline, the calculated t is utilized 2 The B-point positioning of the EMAT receiving transducer is performed (as shown in fig. 2B), with the positioning formula as follows:
by the formulaObtaining a corresponding central angle theta when the arc length S of the outer surface is obtained, after the transducer is placed, measuring a group of time domain signals, wherein the propagation time of SH0 mode guided waves with short propagation distance to the receiving transducer is represented, the propagation time of SH0 mode guided waves with long propagation distance to the receiving transducer is represented, after the two times are read, the angular phase speed alpha of the SH waves propagating on the inner surface of the pipeline is obtained through a formula, and the central angle theta and the angular phase speed alpha are substituted into the formula>The time t when the SH0 mode guided wave reaches the point B for the first time can be obtained 2 If the pipe is a defect-free pipe, the pipe diameter can be calculated by the formula R a /R b ＝t 2 /t 1 ，h＝R b -R a Calculating the thickness of the pipeline, if the pipeline is in-service pipeline, then t 2 Substitution formula->Is calculated S 2 Is determined to be S 2 And then, performing the calculation in the step 2) again, so that the thickness of the measured pipeline can be calculated.
The beneficial effects of the invention are as follows:
compared with the prior art, the non-contact pipeline thickness measuring method does not need to calibrate the speed in advance, the thickness measuring result is influenced by defects, excitation frequency (within a certain interval) and material parameters very little, and meanwhile, the measurement can be completed only on one side, so that the whole thickness of a pipeline can be measured, and in addition, when the pipeline with corrosion defects is measured, the connection with the depth of the corrosion defects can be established. Has popularization and application values.
Drawings
FIG. 1 is a schematic diagram of the present invention; in fig. 1, (a) is the time required for SH guided waves on the inner and outer surfaces of a pipe to propagate for the same arc length distance, and (b) is the propagation time of SH guided waves on the inner and outer surfaces of the pipe when the central angles of the inner surface of the pipe and the arc length of the outer surface of the pipe are the same;
FIG. 2 is a diagram of experimental techniques; in fig. 2, (a) shows a diagram of two sides of a pipeline to be measured by a thickness measuring method, and (b) shows an experimental operation diagram of one side of the pipeline to be measured;
FIG. 3 is a flow chart of experimental steps;
FIG. 4 is a schematic diagram of an experimental configuration apparatus;
FIG. 5 is a plot of experimental received signals; in fig. 5, (a) shows ultrasonic time domain signals on a defect-free iron pipe at an excitation frequency of 398kHz, and (b) shows the distance between excitation transducers;
FIG. 6 shows the measurement results at different excitation frequencies, in FIG. 6, (a) shows the time when SPSH0 (SH 0 mode-guided wave having a short propagation distance) reaches A, B for the first time, and (b) shows the measured pipe thickness at different excitation frequencies;
FIG. 7 shows a layout of a defective iron pipe and a transducer to be tested
FIG. 8 is a graph showing the relationship between different defect depths and the arrival time of SPSH0 (SH 0 mode-guided wave with short propagation distance) at A, B
FIG. 9 is a graph of transducer versus defect; in fig. 9, (a) indicates that the defect is between two transducers, (b) indicates that the excitation transducer is directly above the defect, and (c) indicates that the excitation transducer is above the defect;
FIG. 10 is a diagram of the placement of signals directly opposite the excitation and receiving transducers; in fig. 10, (a) represents the time when the sphh 0 arrives at point a, and (B) represents the time when the sphh 0 arrives at point B;
FIG. 11 is a graph of experimental signals at point A received with an outer radius of 136mm iron pipe, an excitation frequency of 398kHz, and a pulse period of 5.
Detailed Description
The invention will be further described with reference to the accompanying drawings and specific embodiments, wherein the exemplary embodiments and descriptions of the invention are for purposes of illustration, but are not intended to be limiting.
As shown in fig. 1: from the simulation signals of fig. 1, it is obtained that in the same pipeline, the SH wave excited from a certain fixed point has a velocity of the SH wave on the outer surface of the pipeline greater than that on the inner surface of the pipeline, and the arrival time of the SH wave is consistent at the same central angle on the inner and outer surfaces, based on the above findings, theoretical support is established as follows:
C r ＝r×α (1)
wherein C is r The linear velocity in the circumferential direction of the material particles at a distance r from the centre of the pipe, α being the angular phase velocity. At the same time, in the same pipe, all material particles lying on the same radial line should have the same phase factor, that is to say the angular velocity is the same.
θ＝α×t (2)
According to the formula (3), when the central angles are identical, the required propagation times are also identical since the angular phase velocities thereof are identical. The arc length distance calculation formula of SH wave propagating on the inner surface and the outer surface of the pipeline is as follows:
S inner part ＝C r ×t 1 ＝R a ×α×t 1 (4)
S Outer part ＝C r ×t 1 ＝R b ×α×t 2 (5)
Wherein S is the arc length of SH guided wave propagation on the inner surface and the outer surface, R a 、R b Respectively the inner and outer radius of the pipeline, t 1 、t 2 The time required for the inside and outside surfaces SH to guide the propagation of the S arc length, respectively. When the arc lengths propagated by the inner and outer surfaces are equal: s is S Inner part ＝S Outer part
Comparing equation (4) with equation (5):
so simplifying equation (6) can be obtained:
R a /R b ＝t 2 /t 1 (7)
at the outer radius R of the pipe b The inside diameter R can be calculated by the above formula (7) under known conditions a Thickness of:
h＝R b -R a (8)
according to the above experimental operation, as shown in fig. 2 (a), an EMAT transducer is placed on the inner surface of a pipeline in a manner of one-to-one and one-to-one, and a set of ultrasonic time domain signals are measured to obtain an inner surface SH 0 Time t required for mode guided wave to propagate S arc length 1 Then the receiving transducer is moved to the position of the outer surface of the pipeline at the distance from the S arc length of the exciting transducer, and a second group of ultrasonic time domain signals are measured to obtain SH 0 Time t required for modal guided wave to propagate S distance on outer surface 2 At a known pipe outer diameter R b In the case of (2), the time t of the two signals obtained 1 、t 2 Substituting into the formula (7) to obtain the inner diameter R of the pipeline a And then bringing the thickness into a formula (8) to obtain the thickness of the pipeline.
But such an operation requires a separate measurement of a set of data on both sides of the pipe. However, in many cases in engineering practice, only one side can be measured, and the time t is inspired by the formula (3) because the time required for SH guided waves to propagate to the inner and outer surfaces with the same central angle θ is the same 2 Can be calculated by the formulas (9), (10) and (11).
Wherein:
wherein θ is Central angle Represents the central angle corresponding to the arc length of the outer surface S, alpha represents the angular phase speed corresponding to the inner surface of the pipeline, t 1 Represents the time of arrival of SH0 mode at point A in SP wave (SH guided wave with short propagation distance), t 1 ' indicates the time for the SH0 mode to reach point a in the LP wave (SH guided wave with long propagation distance). t is t 2 The time for the SH0 mode in the SP wave (SH guided wave having a short propagation distance) to reach the inner surface in the same radial direction as the arc length of the outer surface S is represented. Due to S in the above formula Outer part ，t 1 ，t 1 ' are all known values, so t 2 Can be calculated by the formula (11). If the pipe is a bare pipe, at the outer diameter R b Under known conditions, the pipe thickness can then be calculated directly by equation (7). If the pipeline to be tested is an in-service pipeline, under the condition of complex internal working condition, for the accuracy of the measurement result, the calculated t is utilized 2 And (3) carrying out B-point positioning of the EMAT receiving transducer, wherein the positioning formula is as follows:
the modified experimental operation is shown in fig. 2b, and the algorithm flow is shown in fig. 3.
In FIG. 3, S represents the arc length distance between the exciting EMAT transducer and the receiving EMAT transducer placed on the inner surface, the corresponding central angle θ for the outer surface arc length S is obtained by equation (9), and after the transducers are placed, a set of time domain signals are measured, wherein t is 1 Representing the propagation time of SPSH0 (SH 0 mode guided wave with short propagation distance) to the receiving transducer for the first time, t 1 ' represent propagation time of LPSH0 (SH 0 mode guided wave with long propagation distance) reaching receiving transducer for the first time, obtain angular phase velocity alpha of SH wave propagating on inner surface of pipeline through formula (10) after reading the two times, obtain time t of SH0 mode guided wave reaching B point in FIG. 2 for the first time by substituting central angle θ and angular phase velocity alpha into formula (11) 2 If the pipe being measured is a defect-free pipe, in the case of a pipe outside diameter of a known value,the thickness of the pipeline can be calculated according to formulas (7) and (8), and if the pipeline is an in-service pipeline, the internal working condition is complex, and t is calculated for the accuracy of the measurement result 2 Substituting into formula (12) to perform positioning of point B in FIG. 2 (B), i.e. calculate S 2 After the position of the point B is determined, the measured pipe thickness can be calculated after a single stage 2.
The feasibility of the pipeline thickness measurement method and the influence of the excitation frequency, the defect depth, the position of the defect relative to the transducer and the pipeline thickness measurement precision are verified through experiments. The experimental configuration herein is shown in fig. 4, with a 4mm array period for the PPMEMAT transducer used and a 5 pulse period.
1.1 feasibility verification:
the detection system for measuring the thickness of the pipeline by using the method is shown in fig. 4, and the system consists of an oscilloscope, an excitation source, an impedance matcher, an EMAT transducer and an upper computer. The detection steps are as follows:
1) Determining the interval arc length distance S between transducers by adopting an EMAT transducer which is transmitted and received
2) Determining the appropriate excitation frequency in an appropriate manner (e.g. frequency sweep)
3) And storing ultrasonic time domain data, reading the required peak time, and calculating the thickness of the measured pipeline by using a calculation method shown in a third graph.
1.1.1 FIG. 5 shows an experiment for measuring the thickness of a pipe according to the procedure described in 1.1 using the present method
1) The outer radius of the pipeline measured by the experiment is R b Iron pipe with wall thickness of 6mm =136 mm
2) The PPM array period of the EMAT transducer used in the experiment is 4mm, and the arc length distance between the excitation transducer and the receiving transducer is 290mm.
The following table shows the results and errors of the measured pipe thickness
List one
1.2 influence of frequency on accuracy:
when the excitation frequency is not at the optimum frequency, i.e. the excitation frequency is less than the optimum excitation frequency or greater than the optimum excitation frequency, this results in an excited SH 0 The dispersion degree is more serious when the excitation frequency is far away from the optimal excitation frequency, and the severity of the dispersion phenomenon can influence the SH 0 The reading of the modal guided wave propagation time, this effect will give uncertainty to the measurement results. To verify the effect of frequency on the method, the invention was carried out in the interval [348kHz, 447 kHz]The test is performed with a step length of 10kHz, and the measured object is an iron pipe with an outer diameter of 272mm, a wall thickness of 6mm and no defects. .
By reading the time when the SPSH0 mode guided wave and the LPSH0 mode guided wave with different excitation frequencies reach the receiving transducer for the first time, t 1 ' and t under different excitation frequencies is calculated 2 The resulting data is obtained by combining the values of t at each frequency as shown in FIG. 6 (a) 1 And t 2 Substituting the values into equations (7), (8) then calculates the measured thickness values of the pipe at different excitation frequencies, as shown in FIG. 6 (b), from which it can be seen that the values are measured at the frequency interval [ 356 kHz,438kHz]The thickness error between the two is between 0.4 and 3 percent, and when the excitation frequency is outside the interval, the thickness measurement error is increased to 9 to 16 percent.
1.3 influence of defect depth on precision:
in order to verify the effect of defect depth on the method, the invention detects an iron pipe with a nominal outer diameter of 220mm and axial grooving defect and defect depths of 2mm, 3mm and 4mm respectively, positions the defect at a distance of 113mm from an excitation transducer, wherein the distance S between the two transducers is 280mm, as shown in figure 7, the excitation frequency is 398kHz, and SPSH read from an acquired ultrasonic time domain signal is selected 0 Time t of first arrival at point A (SH 0 mode-guided wave with short propagation distance) 1 And calculated SPSH 0 Time t of first arrival at point B (SH 0 mode guide wave with short propagation distance) 2 Substituting the results into formulas (7) and (8) to obtain a second thickness result table. From Table II we can see if the test object isThe depth variation with defects and defects has less impact on the accuracy of the thickness measurement methods herein. The correlation of different defect depths with the time to reach A, B for SPSH0 (SH 0 mode-guided wave with short propagation distance) is shown in FIG. 9.
Influence of two different depth defects on measurement accuracy
1.4 influence of defect location on precision
Because of the characteristics of the PPMEAT receiving signal, the situation that the receiving transducer is placed just above the defect and some unknown influences cause the error to become large is considered to be possible in practical engineering application, and in order to avoid the situation, the influence of the defect position on the precision is explored.
In order to clarify the influence of the defect position on the precision, the invention adopts a controlled variable method to fix the depth, the width and the length of the defect, only one variable of the defect position is remained, and the detected object is an iron pipe with a notch defect with the depth of 4mm and the outer diameter of 220 mm. The positions of the defects are respectively as follows: three positions between the two transducers, below the receiving transducer, and directly below the receiving transducer are shown in fig. 10, respectively.
By conducting experiments on three different positions, the data read in each case and the thickness measurement result of the pipeline are shown in table four, and from the table, we can see that the measurement result is very close to the thickness of the real pipeline regardless of the position of the defect relative to the transducer, and the thickness measurement error is between 0.71% and 1.5%. The variation of the defect depth has very little effect on the thickness measurement method proposed by the present invention. Influence of the position of the four defects relative to the transducer on the thickness measurement accuracy
1.5 influence of distance between transducers on accuracy
Since the principle of the method is to use circumferential SH 0 The mode guided waves are used for measuring the thickness of the pipeline and positioning defects, and the conventional PPMEAT transducer is used for bidirectionally exciting SH guided waves, so that the distance between the transducers can influence the identification accuracy and efficiency of observers on different modes of the excited SH guided waves. In this case, the invention sets up the experiment of putting two transducers opposite to each other, so as to discuss the influence of the distance between the exciting and receiving transducers on the precision, and the measured object is a flawless iron pipe with an outer diameter of 220mm and a thickness of 6 mm. The experimental received signals are shown in fig. 10 (a) (b).
In FIG. 10 (a), since the propagation distance of the SP wave (SH guided wave with short propagation distance) is equal to that of the LP wave (SH guided wave with short propagation distance), only two wave packets, SH respectively 0 Mode guided wave, SH 1 Since the propagation distance of the SP wave (SH guided wave having a short propagation distance) is not equal to that of the LP wave (SH guided wave having a short propagation distance) due to the movement of the transducer by a certain distance in fig. 10 (b), the SP wave and the LP wave can be distinguished and verified by calculation. The propagation time shown in a and b in the figure is substituted into a formula (7), the calculated result is substituted into a formula (8), the measured thickness is 5.22mm, and the measured thickness is substituted into a formula (17), so that the relative error is 13%, therefore, the influence of the overlapping of the SP wave time domain signal and the LP wave time domain signal on the precision of the method is large, and the situation is avoided as much as possible in engineering practice.
1.6 distance setting between transducers
When the excitation frequency is the optimal frequency, the wavelength of the PPMEAT is 8mm, and the pulse period number is 5, the minimum arc length distance S between the excitation transducer and the receiving transducer is not overlapped in a mode. Through the experimental signals shown in FIG. 11, V is calculated SH0 And V SH1 3070m/s and 2443m/s, respectively. And measure SH 0 The time width of the modal guided wave is 0.0178ms, and the method comprises the following steps:
s is more than or equal to 133.5mm, and the conclusion that the excitation transducer and the receiving transducer are prevented from being placed right opposite to each other is obtained according to experiments, so that the minimum perimeter D of the pipeline is more than 267mm, that is to say, the minimum inner radius Ra of the iron pipeline is more than 42.5mm.
1.7 resolution:
the relation of the thickness variation with the measured time is required, and t=s/(ra×α) can be known by the formula (4), so the variation of time is calculated from the following formula:
wherein V is s For SH0, the radius r in the pipeline 1 Speed at time V s ' SH0 is the radius r in the pipeline 2 Speed at time r 1 For the inner radius of the pipe before the thickness change, r 2 For the inner radius of the pipe after the thickness change, t is SH measured before the thickness change of the pipe 0 The time to reach point A, t' is the SH measured after the thickness of the pipe is changed 0 The time to reach point A is obtained by combining the above equations:
where Δr represents the varying thickness, since it is necessary to satisfy the condition S. Gtoreq.133.5 mm for the distance setting between transducers in (1.6), t=43.5 μs (in SH) when the distance between transducers is equal to 133.5mm and r2=42.5 mm 0 Calculated as shear wave velocity 3070m/s in aluminum tubing), Δt=0.102 μs=10.2×10-2 μs when Δr= ±0.1mm (where ±represents an increase or decrease in thickness), i.e., it is stated that Δt varies by 0.1 μs when the tubing thickness Δr varies by 0.1mm, 0.01 μs when Δr varies by 0.01mm, and 0.001 μs=1 ns when Δr varies by 0.001 mm.
The sampling rate of the oscilloscope is 2.5GS/s, and the sampling rate is calculated according to the maximum sampling interval formula:
Ts＝1/fs(16)
where Ts is the sampling interval and fs is the sampling rate, and the sampling interval of the oscilloscope is 0.4x10s-9s=0.4ns, so that the resolution limit of the method proposed herein can reach 0.001mm in theory, and can reach 0.01mm in the conventional case.
2, experimental results and error source analysis:
2.1 analysis of experimental results:
the feasibility of the proposed pipeline thickness measurement method, the influence of the excitation frequency, the defect depth, the defect relative transducer position and the distance between the excitation transducer and the receiving transducer on the pipeline thickness measurement precision are verified through experiments, the measurement thickness is calculated, and the error of each condition and the precision influence degree on the method can be obtained after the calculated measurement thickness is substituted into the formula (17).
Difference＝100×(EMAT/Fact-1)(17)
In the experimental result in fig. 5 (a), the relative error obtained after substituting the measured result into the formula (17) is 0.6%, and this result well proves that the feasibility of the proposed method in thickness measurement is tested against factors that may affect the precision, such as defect depth, relative position between transducer and defect, opposite placement of transducer and excitation frequency, and the experimental result obtained by testing shows that the defect depth, excitation frequency, relative position between transducer and defect, have very small influence on the precision and are all within an acceptable range. But when the two transducers are in the facing position, the method thickness measurement accuracy is greatly affected.
2.2 error Source analysis
The error sources of the method mainly comprise the following points: 1. operational error, for measuring time t 2 While moving to the position, the deviation may not be generated by moving to the calculated position completely, which is a major cause of the error. 2. Time observation errors, the time taken herein is the peak time of the wave packet observed from the oscilloscope, which inevitably produces some misalignment due to human observation, resulting in the actual arrival of the observed time and signalThere is some error in time, which is also a major cause of measurement errors.
Conclusion 3:
based on the new discovery that SH guided waves show speed differences on the inner surface and the outer surface of a pipeline, the invention provides a new pipeline thickness measurement method, and the influence of the excitation frequency, the defect depth, the pipeline coating and the relative position between transducers on a thickness measurement result is verified by using a flawless iron pipe with an outer diameter of 272mm and a thickness of 6mm and a flawless iron pipe with a notched defect with an outer diameter of 220mm and a thickness of 6 mm. According to experimental results, besides the fact that the relative positions among transducers have a large influence on thickness measurement results, the error is kept between 0.6% and 3% in a certain excitation frequency range, the method is proved to be capable of realizing thickness measurement of a pipeline, the degree of influence of external factors on the thickness measurement error is small, meanwhile, the relation between the propagation time of SH0 mode guided waves and the defect depth is established, the method has a certain potential on quantification of corrosion defects, the difficulty in detection of an in-service pipeline is that certain parameters in the material are changed due to the fact that the internal working condition of the material is complicated caused by long-term operation, the change of the parameters influences the propagation speed and the phase of guided waves in the pipeline, and the influence of the change of the factors on the thickness measurement method is reflected on the propagation time of received ultrasonic time domain signals, but when the measurement results are substituted into a thickness calculation formula, the influence is basically counteracted. The method for measuring the thickness of the pipeline solves the problem of difficult detection of the pipeline in service to a great extent, and the principle of the method can be applied to lamb waves.
The technical scheme of the invention is not limited to the specific embodiment, and all technical modifications made according to the technical scheme of the invention fall within the protection scope of the invention.
Claims (3)
1. A non-contact pipeline thickness measuring method without pipeline material parameters is characterized in that: the method comprises the following steps:
placing EMAT transducers at a constant arc length in a pipeAn inner surface, a group of ultrasonic time domain signals are measured to obtain an inner surface SH 0 Time t required for modal guided wave to propagate arc length S 1 ；
Then the EMAT transducer is moved to the arc length of the excitation transducer at the distance from the outer surface of the pipeline, and a second group of ultrasonic time domain signals are measured to obtain SH 0 Time t required for modal guided wave to propagate arc length distance on outer surface 2 ；
At a known pipe outer diameter R b In the case of (2), the time t of the two signals obtained 1 、t 2 Substituted into formula R a /R b ＝t 2 /t 1 The inner diameter R of the pipeline is obtained a Bringing it into the formula h=r b -R a The thickness of the pipe can be obtained.
2. The non-contact tubing thickness measurement method without tubing material parameters of claim 1, wherein: when only one side of the pipe can be measured, time t 2 Calculated by the following formula:
wherein θ is Central angle Represents the central angle corresponding to the arc length of the outer surface S, alpha represents the angular phase speed corresponding to the inner surface of the pipeline, t 1 SH in SH guided wave indicating short propagation distance 0 Time of mode to reach point A, t' 1 SH in SH guided wave indicating long propagation distance 0 The time when the mode reaches the point A; t is t 2 SH in SH guided wave indicating short propagation distance 0 Mode arrival and outer surface arc lengthTime at the inner surface in the same radial direction at S; due to S in the formula Outer part ，t 1 ，t' 1 Are all known values, so t 2 Can be expressed by the formulaAnd (5) calculating to obtain the product.
3. The non-contact tubing thickness measurement method without tubing material parameters of claim 2, wherein: in the case that the pipeline under test is an in-service pipeline, the calculated t is utilized 2 And (3) carrying out B-point positioning of the EMAT receiving transducer, wherein the positioning formula is as follows:
by the formulaObtaining a corresponding central angle theta when the arc length S of the outer surface is obtained, and measuring a group of time domain signals after the transducer is placed, wherein t is 1 Representing the propagation time, t 'of SH0 mode guided waves with short propagation distance reaching a receiving transducer for the first time' 1 Representing the propagation time of SH0 mode guided waves with long propagation distance reaching a receiving transducer for the first time, and reading t 1 、t' 1 After these two times by the formula>Obtaining the angular phase velocity alpha of SH wave propagating on the inner surface of the pipeline, and substituting the central angle theta and the angular phase velocity alpha into the formula +.>The time t when the SP SH0 mode guided wave reaches the point B for the first time can be obtained 2 If the pipe is a defect-free pipe, the pipe diameter can be calculated by the formula R a /R b ＝t 2 /t 1 ，h＝R b -R a Calculating the thickness of the pipeline, if the pipeline is in-service pipeline, then t 2 Substitution formula->Is calculated S 2 Is determined to be S 2 After which the above calculation is performed once, the measured pipe thickness can be calculated.
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