CN109668505B - Method for measuring wall thickness of pulse ACFM ferromagnetic metal structure - Google Patents
Method for measuring wall thickness of pulse ACFM ferromagnetic metal structure Download PDFInfo
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- CN109668505B CN109668505B CN201910018077.4A CN201910018077A CN109668505B CN 109668505 B CN109668505 B CN 109668505B CN 201910018077 A CN201910018077 A CN 201910018077A CN 109668505 B CN109668505 B CN 109668505B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
- G01B7/06—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness
Abstract
The invention discloses a method for measuring the wall thickness of a pulse ACFM ferromagnetic metal structure, which comprises the steps of loading a pulse signal into an excitation coil, inducing a uniform electric field on the ferromagnetic metal structure through a U-shaped magnetic core, enabling a uniform current on the surface to permeate into the ferromagnetic metal structure along with time, simultaneously picking up a magnetic field signal Bx which exponentially decays along with time by a tunnel magnetoresistive sensor, filtering and amplifying the magnetic field signal in the sensor, converting the magnetic field signal into a digital signal through an acquisition card, carrying out exponential fitting on the decay section of the digital signal, enabling the decay coefficient of the fitting to be in a linear relation with the wall thickness, calibrating by using a ferromagnetic metal material with known thickness to obtain a wall thickness measuring formula, calculating the wall thickness of the same material and lifting away from the ferromagnetic metal structure by using the formula, and having simple operation of the wall thickness measuring mode without polishing and smearing a coupling agent, the coating layer does not need to be removed, the measurement precision is high, and the anti-interference capability is strong.
Description
Technical Field
The invention relates to the field of nondestructive detection signal processing, in particular to a method for measuring the wall thickness of a pulse ACFM ferromagnetic metal structure
Background
In the industrial field, ferromagnetic metal materials are widely used, such as oil pipelines, jacket platforms, coiled tubing, etc., and since ferromagnetic metal structures are exposed to high temperature, high pressure, moisture and corrosive media for a long time, the wall thickness of the ferromagnetic metal structures is easily reduced, the strength of the ferromagnetic metal structures is weakened, the ferromagnetic metal structures fail, and safety accidents are caused, the wall thickness of the ferromagnetic metal structures needs to be measured regularly.
At present, the main wall thickness measuring technology is mainly an ultrasonic detection technology, but ultrasonic detection needs to remove an outer coating layer, a couplant needs to be coated and the like, the operation is complex, the efficiency is low, an alternating current magnetic field detection (ACFM) technology is a novel electromagnetic nondestructive detection technology, however, the ACFM technology is only used for detecting cracks at present, a detection object is single, the wall thickness is measured by mainly utilizing the peak value, the peak time and the zero crossing time of signals in the conventional pulse eddy current detection technology, the interference of the variation of excitation signal voltage and current signals is easy to generate, a detection sensor utilizes a detection coil, the detection sensitivity is small, and the error is large.
Disclosure of Invention
The invention aims to solve the problem of providing a ferromagnetic metal structure wall thickness measuring method based on pulse ACFM, which is simple to operate, does not need to polish the pipe wall, does not need a coupling agent, and can realize the measurement of the ferromagnetic metal wall thickness under the condition of keeping certain lift-off; the alternating current excitation signal of the conventional ACFM is changed into the pulse excitation signal, so that the thickness of the ferromagnetic metal can be measured, and the function of the ACFM is expanded; the attenuation section of the pulse response signal is utilized to carry out exponential fitting, the characteristic value of the obtained wall thickness measurement is irrelevant to the current of the excitation signal, the anti-interference capability is strong, the detection sensor adopts a high-resolution tunnel magnetoresistive sensor, the detection sensitivity is higher, and the measurement result is more accurate.
The invention provides a ferromagnetic metal structure wall thickness measuring method based on pulse ACFM, which comprises the following steps
S1: loading a pulse signal with the frequency of W0 on an excitation coil of a detection probe, wherein the excitation coil is wound on a U-shaped magnetic core, and a tunnel magnetoresistive sensor is positioned in the middle position below the U-shaped magnetic core;
s2: under the condition of same lift-off, different wall thicknesses b of the same material are detected by using the detection probe described in S1nThe ferromagnetic material is used for measurement, the tunnel magnetoresistive sensor picks up a magnetic field signal Bx of a period T0 in space, the signal in the magnetic field sensor is filtered, amplified and converted into a digital signal by an acquisition card, the digital signal is respectively a signal from the peak value to the time period of 0.5T 0, and an exponential function is used
Fitting, taking fitting coefficient cn；
S3: by fitting coefficient cnOn the abscissa, wall thickness bnAs ordinate, linear fitting b is carried outn＝p*cn+ q, obtaining coefficients p and q;
s4: on the premise of ensuring the same lift-off and the same material, placing the probe on metal with unknown wall thickness, fitting the obtained signal according to the method of S2 to obtain a coefficient cxSubstituting the values p and q obtained from S2 into formula bx＝p*cx+q，bxI.e. the measured wall thickness.
Preferably, the frequency W0 is 1Hz-200 Hz.
Preferably, the axial magnetic field signal of one period T0 can be obtained by means of external triggering, limited sampling.
Further, N is a natural number greater than 1.
Drawings
FIG. 1 is a schematic diagram of wall thickness measurement in the embodiment of the present application
FIG. 2 is a diagram of a wall thickness measuring probe in the embodiment of the present application
FIG. 3 is a signal diagram of electric field and magnetic field in the wall thickness measurement in the embodiment of the present application
FIG. 4 is a graph of fitting time periods in an embodiment of the present application
FIG. 5 is a wall thickness fitting chart in the example of the present application
FIG. 6 is a wall thickness dynamic measurement chart in the embodiment of the present application
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention is further described in detail with reference to the accompanying drawings and specific embodiments, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. Other embodiments, which can be derived by those skilled in the art from the embodiments of the present invention without inventive step, are within the scope of the present invention.
As shown in fig. 2, the measurement structure mainly includes exciting coil 1, U type magnetic core 2, detection sensor 3, by survey structure 4, exciting coil is the enameled wire, the diameter and the number of turns of coil can change, U type magnetic core is used for playing the effect of gathering magnetism, it is bigger to make the penetrating degree of induced current, detection sensor adopts tunnel magnetoresistive sensor, the magnetic field signal of X direction is Bx, for traditional coil sensor, tunnel magnetoresistive sensor's sensitivity is higher than coil sensor far away, the precision of detection is higher.
Further, as shown in fig. 3, pulse signals are loaded at two ends of the exciting coil, induced currents on the structure to be detected can permeate from the surface of the structure to the inside along with time, the permeation speeds of the induced currents with different wall thicknesses are different, further, the attenuation rules of a magnetic field above the structure are different, the magnetic field signal Bx is exponentially attenuated, the attenuation rules are irrelevant to the magnitude of exciting signal currents, the anti-interference capability is strong, the tunnel magnetoresistive sensor is used for picking up the magnetic field signal Bx in the space, and the magnetic field signal Bx is filtered and amplified, and an acquisition card is used for converting an analog signal into a digital signal.
Taking T0 as 50, optimizing T0, and obtaining different optimal T0 values in different wall thickness measurement ranges; n is 4, N is a natural number more than 2, and at least two points are needed to obtain a straight line through fitting, but the larger the value of N is, the more accurate the measurement result is.
Applying a periodic pulse excitation signal with a frequency of 50Hz to both ends of the excitation coil to measure the known wall thickness bnThe carbon steel materials of 3.5mm, 4mm, 4.5mm and 5mm were measured, and the peak value of the obtained characteristic signal to a signal of 0.01s was respectively subjected to exponential analysis as shown in FIG. 4
Fitting to obtain a fitting coefficient cnRespectively-8.411, -8.524, -8.668 and-8.773, by fitting coefficient cnOn the abscissa, wall thickness bnAs ordinate, linear fitting b is carried outn＝p*cn+ q, as shown in fig. 5, gives the coefficients p-4.051, q-30.56; measuring the carbon steel material with the wall thickness to be measured, and performing index on the signal from the peak value of the obtained characteristic signal to 0.01s
Fitting to obtain a fitting coefficient cxEquation b, substituted into fit, -8.28x＝-4.051*cx30.56, obtaining the wall thickness b to be measuredxIs 2.98 mm.
According to the steps, a fitting formula b ═ p × c + q is obtained in advance, the processes of collecting and fitting are continuously circulated by using periodic pulse signals, a retriggerable function and a limited sampling mode, the continuous measurement of the wall thickness is realized, the measuring probe is moved, the dynamic measurement of the wall thickness is realized, and the measurement result is shown in fig. 6.
The invention has the advantages of
(1) Simple operation, no need of polishing pipe wall and no need of coupling agent
(2) The alternating current excitation of the traditional alternating current electromagnetic field detection technology is changed into pulse excitation, and the functions of the alternating current electromagnetic field detection technology are expanded
(3) The detection signal is independent of the excitation signal current, and the anti-interference capability is strong
(4) The detection precision is high
The above embodiments are provided to further explain the objects, technical solutions and advantages of the present invention in detail, it should be understood that the above embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalents, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (1)
1. The invention provides a method for measuring the wall thickness of a pulse ACFM ferromagnetic metal structure, which comprises the following steps
S1: loading a pulse signal with the frequency of W0 on an excitation coil of a detection probe, wherein the frequency of W0 is 1Hz-200Hz, the excitation coil is wound on a U-shaped magnetic core, and a tunnel magnetoresistive sensor is positioned in the middle position below the U-shaped magnetic core;
s2: under the condition of same lift-off, different wall thicknesses b of the same material are detected by using the detection probe described in S1nThe ferromagnetic metal structure is used for measurement, n is a natural number larger than 1, a magnetic field signal Bx of one period T0 in space is picked up by the tunnel magnetoresistive sensor in an external triggering and limited sampling mode, the signal in the tunnel magnetoresistive sensor is filtered and amplified and converted into a digital signal by an acquisition card, the signals from the peak value of the digital signal to the time period of 0.5T 0 are respectively taken, and an exponential function is used
Fitting, taking fitting coefficient cn；
S3: by fitting coefficient cnOn the abscissa, wall thickness bnAs ordinate, linear fitting b is carried outn＝p*cn+ q, obtaining coefficients p and q;
s4: on the premise of ensuring the same lift-off and the same material, the probe is placed on a ferromagnetic metal material with unknown wall thickness, and the obtained signals are fitted according to the method of S2 to obtain the coefficient cxSubstituting the values p and q obtained from S3 into formula bx＝p*cx+q，bxI.e. the measured wall thickness.
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| CN110672001A (en) * | 2019-10-24 | 2020-01-10 | 中航通飞华南飞机工业有限公司 | Method and device for measuring thickness of non-ferromagnetic material on surface of ferromagnetic material |
| CN111288883A (en) * | 2019-12-23 | 2020-06-16 | 陕西国防工业职业技术学院 | Method for detecting wall thickness of metal pipeline by transient electromagnetic method |
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