CN103353479B - A combined detection method of electromagnetic ultrasonic longitudinal guided wave and magnetic flux leakage detection - Google Patents

Abstract

The invention discloses the lossless detection method that a kind of electromagnetic acoustic longitudinal wave guide and stray field are compound, in the ultimate principle of Magnetic Flux Leakage Inspecting, add electromagnetic acoustic (EMAT) excitation variable winding and electromagnetic acoustic (EMAT) receiving coil.Magnetic Flux Leakage Inspecting is only used when detection process is normally carried out.When Magnetic Flux Leakage Inspecting finds defect, electromagnetic acoustic (EMAT) excitation variable winding will inspire ultrasonic longitudinal wave guide at inner surface of steel plate to be measured.It is analyzed by the ultrasonic longitudinal wave guide signal that electromagnetic acoustic (EMAT) receiving coil is picked up, so that it may know the presence or absence of inner surface of steel plate defect to be measured, thus realize the resolution to steel plate inner and outer surfaces defect to be measured.This method effectively overcomes that prior art is the highest to the judgement effect accuracy rate of defect, detect slow shortcoming, also has the advantage such as simple in construction, little, the non-contact measurement of information processing capacity.

Description

A combined detection method of electromagnetic ultrasonic longitudinal guided wave and magnetic flux leakage detection

technical field

The invention relates to the field of non-destructive testing, in particular to a combined testing method of electromagnetic ultrasonic longitudinal guided wave and magnetic flux leakage testing.

Background technique

Since long-distance oil and gas pipelines have been widely used as a means of energy transportation in recent years, the scale of laying oil and gas pipelines and storage tanks has become extremely large. With the gradual aging of existing equipment and the continuous deterioration of crude oil quality, it has become very important to detect its safety and reliability. Steel plate defects used in long-distance pipelines and storage tanks can be mainly divided into two categories, namely "external corrosion" and "internal corrosion". "External corrosion" is generally caused by groundwater or rainwater erosion around the steel plate; "internal corrosion" is generally caused by corrosive impurities contained in crude oil and steel plates. The corrosion mechanisms of the two are different, so there are also obvious differences in the corresponding treatment methods. However, at present, most of the existing non-destructive testing equipment at home and abroad are based on magnetic flux leakage detection, and the magnetic flux leakage detection technology can excite similar magnetic flux leakage signals on the inner and outer surfaces of the steel plate, which makes the traditional magnetic flux leakage detection methods unable to effectively distinguish the magnetic flux leakage on the steel plate. Internal and external surface defects.

Chinese Patent No. CN101354380A discloses a non-destructive testing method combining eddy current and electromagnetic ultrasound. This method uses the skin effect of eddy current testing to detect defects on the inner surface of the steel plate to be tested. However, the electromagnetic ultrasonic part of this method uses surface waves for detection, so the detection sensitivity of the outer surface defects of the tested steel plate is low.

Application publication number CN102661995A discloses a non-destructive testing method combining electromagnetic ultrasonic and magnetic flux leakage. This method uses the principle of combining electromagnetic ultrasonic thickness measurement and magnetic flux leakage detection to realize the positioning and differentiation of defects on the inner and outer surfaces of the steel plate to be tested. At the same time, the actual shape information of the defect can be extracted. However, this method needs to be combined with the time difference information and amplitude information of the ultrasonic echo to make a comprehensive judgment when performing electromagnetic ultrasonic thickness measurement.

Contents of the invention

The main purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art, and propose a detection method combining electromagnetic ultrasonic longitudinal guided wave and magnetic flux leakage detection.

The present invention adopts following technical scheme:

A detection method combining electromagnetic ultrasonic longitudinal guided wave and magnetic flux leakage detection, characterized in that: comprising the following steps

1) Apply a permanent magnet excitation magnetic field to the steel plate to be tested, magnetize the measured area to a saturated state, and detect whether a magnetic flux leakage signal is generated, if not, go to step 2); if yes, go to step 3);

2) Move the permanent magnet excitation field, change the measured area, and repeat step 1);

3) receiving and processing the magnetic flux leakage signal, judging whether the measured area is defective according to the magnetic flux leakage signal, if not, then proceed to step 2), if so, proceed to step 4);

4) Apply the alternating magnetic field generated by the alternating excitation signal to the measured area, receive and process the ultrasonic longitudinal guided wave generated on the inner surface of the measured area, and compare the obtained ultrasonic longitudinal guided wave signal amplitude A with the set threshold A0 for comparison, if A<A0, it is determined that the defect is located on the inner surface of the tested area of the steel plate to be tested; if A≥A0, it is determined that the defect is located on the outer surface of the tested area of the steel plate to be tested;

5) Repeat step 2) until the surface of the steel plate to be tested is completely detected.

Further, in step 1), the magnetic flux leakage detection unit applies a permanent magnet excitation magnetic field to the steel plate to be tested and detects whether a magnetic flux leakage signal is generated. The magnetic flux leakage detection unit includes two permanent magnets, a U-shaped magnetic core and a Hall element. The permanent magnets are respectively located at both ends of the U-shaped magnetic core, and the Hall element measures the leakage magnetic field generated in the steel plate to be tested with the set lift-off value H1.

Further, in step 3), the magnetic flux leakage signal is processed by a signal processing unit, which is connected to the Hall element and includes a magnetic flux leakage signal channel, a magnetic flux leakage conditioning module, an A/D converter and a microcomputer system, The received magnetic flux leakage signal is sent to the magnetic flux leakage signal channel, and then sent to the microcomputer system for processing after amplification, filtering and sampling. When the microcomputer system detects a sudden increase in the magnetic flux leakage signal, it means that the measured area on the steel plate to be tested is Flawed.

Further, the microcomputer system of the signal processing unit may adopt a single-chip microcomputer, DSP, ARM system or PC.

Further, in step 4), the electromagnetic ultrasonic detection unit applies an alternating magnetic field to the measured area of the steel plate to be tested and detects the ultrasonic longitudinal guided wave signal generated. The electromagnetic ultrasonic detection unit includes two permanent magnets, a U-shaped magnetic core, an electromagnetic Ultrasonic excitation coil and electromagnetic ultrasonic receiving coil, the two permanent magnets are respectively located at the two ends of the U-shaped magnetic core, the electromagnetic ultrasonic excitation coil and the electromagnetic ultrasonic receiving coil are respectively placed inside the two permanent magnets, and the electromagnetic ultrasonic excitation coil is separated by a set distance. The value H2 is placed above the measured area of the steel plate to be tested.

Further, the electromagnetic ultrasonic excitation coil and the electromagnetic ultrasonic receiving coil are broken line coils, the broken line spacing l is equal and determined by the speed C of the surface wave propagating in the steel plate to be tested and the frequency f of the excitation signal current, and the relationship satisfies: l= C/2f.

Further, the signal processing unit is connected to the electromagnetic ultrasonic receiving coil and also includes an ultrasonic echo signal channel and an ultrasonic conditioning module. The ultrasonic longitudinal wave guide signal is sent to the ultrasonic conditioning module through the ultrasonic echo signal channel for amplification and filtering, and then Sampling and quantification is performed by the A/D converter, and the sampling value is sent to the microcomputer system, which analyzes the amplitude of the ultrasonic longitudinal guided wave signal, and compares the obtained signal amplitude A with the set threshold A0.

Further, the lift-off value H1 is 0.3-2.5 mm, and H2 is 0.5-3 mm.

Further, in step 4), the alternating excitation signal adopts a sine wave pulse with a frequency f of 50kHz-2MHz.

Further, in step 4), the A0 is the amplitude of the ultrasonic longitudinal guided wave signal obtained by detecting and processing the measured area of the steel plate to be tested without defects.

As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following beneficial effects:

1. Compared with the combined detection method of eddy current and electromagnetic ultrasonic, this method combines the electromagnetic ultrasonic longitudinal guided wave detection with the magnetic flux leakage detection method, thus realizing the differential detection of inner and outer surface defects of the steel plate to be tested;

2. Compared with the combined detection method of electromagnetic ultrasonic thickness measurement and magnetic flux leakage detection, the electromagnetic ultrasonic longitudinal guided wave detection method adopted in this method is more sensitive to the inner surface defects of the steel plate to be tested. The detection unit works after finding the magnetic flux leakage signal, so the detection speed of the whole detection process mainly depends on the magnetic flux leakage detection, and the detection speed is faster;

3. Since the electromagnetic ultrasonic (EMAT) detection unit only needs to judge the amplitude of the received ultrasonic longitudinal guided wave signal, the detection method is simpler, combined with its faster detection speed, it can meet the needs of online detection.

Description of drawings

Fig. 1 is a figure showing the structure of the probe device involved in the method of the present invention;

Fig. 2 is the schematic diagram of the principle of using leakage magnetic field to detect steel plate defects in this method;

Fig. 3 is the echo signal waveform obtained by the electromagnetic ultrasonic receiving coil when the defect of the steel plate to be tested exists on the outer surface;

Fig. 4 is the echo signal waveform obtained by the electromagnetic ultrasonic receiving coil when the defect of the steel plate to be tested exists on the inner surface;

In the figure: 1. U-shaped magnetic core; 2. Permanent magnet; 3. Hall element; 4. Electromagnetic ultrasonic (EMAT) excitation coil; 5. Electromagnetic ultrasonic (EMAT) receiving coil; 6. Steel plate to be tested.

detailed description

The present invention will be further described below through specific embodiments.

Referring to Fig. 1 and Fig. 2, they are schematic diagrams of the probe device involved in the present invention, the probe device includes a magnetic flux leakage detection unit and an electromagnetic ultrasonic (EMAT) detection unit. Among them, the magnetic flux leakage detection unit is composed of a permanent magnet 2, a U-shaped magnetic core 1, and a Hall element 3; the electromagnetic ultrasonic (EMAT) detection unit is composed of a permanent magnet 2, a U-shaped magnetic core 1, an electromagnetic ultrasonic (EMAT) excitation coil 4, Electromagnetic ultrasonic (EMAT) receiving coil 5 is composed. The magnetic flux leakage detection unit is shared with the permanent magnet 2 and the U-shaped magnetic core 1 of the electromagnetic ultrasonic detection unit. The electromagnetic ultrasonic excitation coil 4 and the electromagnetic ultrasonic receiving coil 5 are placed inside the two permanent magnets 2 respectively, and placed above the measured area of the steel plate 6 to be tested with a set lift-off value H2. The tested area is the lower area between the two permanent magnets 2 on the steel plate 6 to be tested. The Hall element 3 is placed between the electromagnetic ultrasonic excitation coil 4 and the electromagnetic ultrasonic receiving coil 5 to measure the leakage magnetic field generated in the steel plate 6 to be tested with a set lift-off value H1. In addition, it also includes a signal processing unit connected to the Hall element 3 and the electromagnetic ultrasonic receiving coil 5. The signal processing unit includes an ultrasonic echo signal channel, a magnetic flux leakage signal channel, an ultrasonic conditioning module, a magnetic flux leakage conditioning module, an ultrasonic power amplifier module, A/D converter and microcomputer system, etc. The microcomputer system can use single-chip microcomputer, DSP, ARM system or PC.

The basic principle of the present invention is to add an excitation-extraction device composed of an electromagnetic ultrasonic excitation coil 4 and an electromagnetic ultrasonic receiving coil 5 on the basis of the traditional magnetic flux leakage detection principle. When the magnetic flux leakage detection unit finds a defect, the electromagnetic ultrasonic receiving coil 5 is responsible for receiving the ultrasonic longitudinal guided wave excited by the electromagnetic ultrasonic excitation coil 4 and propagating along the inner surface of the steel plate 6 to be tested. By analyzing the ultrasonic longitudinal guided wave signal through the signal processing unit, the positioning of the inner and outer surfaces of the defects of the steel plate 6 to be tested can be realized.

The detection method of electromagnetic ultrasonic longitudinal guided wave and magnetic flux leakage detection composite of the present invention, the steps are as follows:

1) The magnetic flux leakage detection unit works, as shown in Figure 1 and Figure 2, two permanent magnets 2 apply a permanent magnet excitation magnetic field to the measured area of the steel plate 6 to be tested, so that the measured area of the steel plate 6 to be tested is magnetized to a saturated state, At this time, if there is a defect in the measured area of the steel plate 6 to be tested, a part of the magnetic field will leak into the air, so it is detected whether a magnetic flux leakage signal is generated, if not, enter step 2); if so, enter step 3).

2) Move the probe device, change the area to be measured, and repeat step 1).

3) The Hall element 3 receives the magnetic flux leakage signal and sends it to the magnetic flux leakage signal channel of the signal processing unit. After amplification, filtering and sampling, it is sent to the microcomputer system for processing. The microcomputer system judges the measured area according to the magnetic flux leakage signal Whether there is a defect, when the microcomputer system detects a sudden increase in the magnetic flux leakage signal, indicating that there is a defect on the steel plate 6 to be tested, then enter step 4); if not, enter step 2).

4) The microcomputer system controls the electromagnetic ultrasonic detection unit to start working, and applies the permanent magnet excitation magnetic field and the alternating magnetic field generated by the alternating excitation signal to the measured area at the same time. Under the combined action of the excitation signal of the electromagnetic ultrasonic excitation coil 4, the magnetostrictive force and the Lorentz force are simultaneously applied to form an ultrasonic longitudinal guided wave, which propagates along the inner surface of the steel plate 6 to be tested, as shown in Figure 1 , when an inner surface defect is encountered, the generated ultrasonic longitudinal guided wave will attenuate, and finally be picked up by the electromagnetic ultrasonic receiving coil 5 whose lift-off value is set to H2.

The picked-up ultrasonic longitudinal guided wave signal is sent to the ultrasonic conditioning module through the ultrasonic echo signal channel for amplification and filtering, then sampled and quantized by the A/D converter, and finally the sampled value is sent to the microcomputer system. The microcomputer system analyzes the amplitude of the ultrasonic longitudinal guided wave signal. Comparing the obtained signal amplitude A with the set threshold A0, if the signal waveform of the ultrasonic longitudinal guided wave is similar to that shown in Figure 3, and the signal amplitude A exceeds the set threshold A0, it means that the electromagnetic ultrasonic wave excited by the electromagnetic ultrasonic excitation coil 4 The signal does not attenuate significantly, indicating that there is no defect on the inner surface, and then verify that the defect exists on the outer surface of the steel plate 6 to be tested; if the waveform of the ultrasonic longitudinal guided wave signal is similar to that shown in Figure 4, and the signal amplitude A does not exceed the set threshold A0, it means that The electromagnetic ultrasonic signal emitted by the electromagnetic ultrasonic excitation coil 5 is obviously attenuated, indicating that defects exist on the inner surface of the steel plate 6 to be tested. Repeat step 2) until all the surfaces of the steel plate 6 to be tested are detected.

Further, the electromagnetic ultrasonic excitation coil 4 and the electromagnetic ultrasonic receiving coil 5 are both broken-line coils, and the broken-line spacing of the broken-line coils is closely related to the energy conversion efficiency of the electromagnetic ultrasonic signal excitation process and the receiving process. Since the energy conversion efficiency of the ultrasonic longitudinal guided wave signal is the highest when the excitation signal frequency f is consistent with the resonant frequency of the steel plate 6 to be tested, it can be obtained according to the sound wave velocity formula that the distance between the electromagnetic ultrasonic excitation coil 4 and the electromagnetic ultrasonic receiving coil 5 is 1 , and l and the excitation signal frequency f need to satisfy the relationship l=C/2f, where C is the transmission speed of the sound wave in the steel plate 6 to be tested.

Furthermore, a large number of experiments and theoretical studies have proved that the signal strength of magnetic flux leakage and ultrasonic longitudinal guided wave in the air will decay exponentially with the increase of the lift-off value of the sensor. Therefore, in order to obtain a sufficiently strong magnetic flux leakage signal and ultrasonic longitudinal guided wave signal to improve the sensitivity of the probe device, it is necessary to reduce the lift-off value of the Hall element 3 and the electromagnetic ultrasonic excitation coil 4 and the electromagnetic ultrasonic receiving coil 5 in the probe as much as possible. In order to meet the detection needs and actual conditions, the lift-off value H1 of the Hall element 3 and the lift-off value H2 of the electromagnetic ultrasonic excitation coil 4 and the electromagnetic ultrasonic receiving coil 5 can be set to 0.3-2.5mm and 0.5- 3mm.

Further, the frequency f of the excitation signal applied to the electromagnetic ultrasonic excitation coil 4 is related to the thickness of the steel plate 6 to be tested. Since the skin effect depth of the steel plate 6 to be tested approximately satisfies the formula Where μ is the magnetic permeability of the steel plate 6 to be tested, σ is the electrical conductivity of the steel plate 6 to be tested, and ω=2πf is the angular frequency of the excitation signal. In order to effectively use the electromagnetic ultrasonic excitation coil 4 to excite the surface guided wave propagating along the inner surface of the steel plate 6 to be tested, the parameters of the steel plate 6 to be tested are substituted, so the frequency f of the excitation signal is selected between 50kHz-2MHz, and Meet testing needs.

Further, the above-mentioned A0 can be obtained by detecting the intact steel plate position by the electromagnetic ultrasonic detection unit. The specific method can be obtained by detecting a steel plate test piece with no defects on the inner surface. It can also be obtained by the electromagnetic ultrasonic testing unit performing electromagnetic ultrasonic testing on the parts of the steel plate where no defects are found in the magnetic flux leakage testing after the normal testing starts.

The above is only a specific embodiment of the present invention, but the design concept of the present invention is not limited thereto, and any insubstantial changes made to the present invention by using this concept should be an act of violating the protection scope of the present invention.

Claims (8)

1. the detection method that an electromagnetic acoustic longitudinal wave guide is compound with Magnetic Flux Leakage Inspecting, it is characterised in that: bag Include following steps

1) steel plate to be measured is applied permanent magnet excitation magnetic field, tested region is magnetized to saturation, detection Whether produce magnetic leakage signal, if it is not, enter step 2)；The most then enter step 3)；

2) movable permanent magnet excitation field, changes tested region, repeats step 1)；

3) receive magnetic leakage signal and process, judging that this tested region is the most defective according to magnetic leakage signal, If it is not, then enter step 2), the most then enter step 4)；

4) tested region is applied the alternating magnetic field produced by alternating excitation signal again, receives table in tested region Ultrasonic longitudinal wave guide that face produces also processes, by the threshold of the ultrasonic longitudinal wave guide signal amplitude A that obtains with setting Value A0 compares, if A is ＜ A0, then judges that defect is positioned at the inner surface in this tested region of steel plate to be measured；If A >=A0, then judge that defect is positioned at the outer surface in this tested region of steel plate to be measured；

5) step 2 is repeated), until surface of steel plate to be measured all detects complete；

In step 1) in, and detected whether steel plate to be measured applying permanent magnet excitation magnetic field by Magnetic Flux Leakage Inspecting unit Producing magnetic leakage signal, this Magnetic Flux Leakage Inspecting unit includes two permanent magnets, U-shaped magnetic core and Hall element, two permanent magnets Lay respectively at the two ends of U-shaped magnetic core, Hall element with set lift-off value H1 in steel plate to be measured produce leakage Magnetic field measures；

In step 4) in, by electromagnetic acoustic detector unit, the tested region of steel plate to be measured is applied alternating magnetic field And detection produce ultrasonic longitudinal wave guide signal, electromagnetic acoustic detector unit include two permanent magnets, U-shaped magnetic core, Electromagnetic acoustic excitation variable winding and electromagnetic acoustic receiving coil, two permanent magnets lay respectively at the two ends of U-shaped magnetic core, Electromagnetic acoustic excitation variable winding and electromagnetic acoustic receiving coil are respectively placed in the inner side of two permanent magnets, and electromagnetic acoustic swashs Hair line circle is placed in the tested overlying regions of steel plate to be measured with lift-off value H2 set.

The detection method that a kind of electromagnetic acoustic longitudinal wave guide the most as claimed in claim 1 is compound with Magnetic Flux Leakage Inspecting, its It is characterised by: in step 3) in, by signal processing unit, magnetic leakage signal is processed, this signal processing Unit is connected with Hall element and includes magnetic leakage signal passage, leakage field conditioning module, A/D converter and microcomputer system System, delivers to magnetic leakage signal passage by the magnetic leakage signal received, amplified, filter and sample after give microcomputer System processes, and when microsystem detects that magnetic leakage signal increases suddenly, then this quilt on steel plate to be measured is described Survey region existing defects.

The detection side that a kind of electromagnetic acoustic longitudinal wave guide the most according to claim 2 is compound with Magnetic Flux Leakage Inspecting Method, it is characterised in that: the microsystem of described signal processing unit, use single-chip microcomputer, DSP, ARM system Or PC.

The detection side that a kind of electromagnetic acoustic longitudinal wave guide the most as claimed in claim 3 is compound with Magnetic Flux Leakage Inspecting Method, it is characterised in that: described electromagnetic acoustic excitation variable winding and electromagnetic acoustic receiving coil are broken line coil, folding Frequency f of distance between centers of tracks l speed C that is equal and that propagated in steel plate to be measured by surface wave and pumping signal electric current is certainly Fixed, its relation meets: l=C/2f.

The detection side that a kind of electromagnetic acoustic longitudinal wave guide the most as claimed in claim 3 is compound with Magnetic Flux Leakage Inspecting Method, it is characterised in that: described signal processing unit is connected with electromagnetic acoustic receiving coil and also includes ultrasonic time Ripple signalling channel and ultrasonic conditioning module, ultrasonic longitudinal wave guide signal is sent to via ultrasound echo signal passage Ultrasonic conditioning module is amplified, filters, and is then passed through A/D converter and carries out sample quantization, sample magnitude Being admitted to microsystem, ultrasonic longitudinal wave guide signal amplitude is analyzed by microsystem, the signal that will obtain Amplitude A compares with setting threshold value A 0.

The detection side that a kind of electromagnetic acoustic longitudinal wave guide the most as claimed in claim 1 is compound with Magnetic Flux Leakage Inspecting Method, it is characterised in that: described lift-off value H1 be 0.3-2.5mm, H2 be 0.5-3mm.

The detection side that a kind of electromagnetic acoustic longitudinal wave guide the most as claimed in claim 1 is compound with Magnetic Flux Leakage Inspecting Method, it is characterised in that: in step 4) in, described alternating excitation signal uses frequency f to be 50kHz-2MHz Sinusoidal wave pulse.

The detection side that a kind of electromagnetic acoustic longitudinal wave guide the most as claimed in claim 1 is compound with Magnetic Flux Leakage Inspecting Method, it is characterised in that: in step 4) in, described A0 is to the tested region not having defective steel plate to be measured Carry out detecting and process the ultrasonic longitudinal wave guide signal amplitude obtained.