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GB/T 20935.3-2018: Metal materials -- Method of electromagnetic acoustic inspection -- Part 3: Standard practice for ultrasonic surface examinations using electromagnetic acoustic transducer (EMAT) techniques
Status: Valid GB/T 20935.3: Evolution and historical versions
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| GB/T 20935.3-2018 | English | 279 |
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Metal materials -- Method of electromagnetic acoustic inspection -- Part 3: Standard practice for ultrasonic surface examinations using electromagnetic acoustic transducer (EMAT) techniques
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GB/T 20935.3-2018
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| GB/T 20935.3-2009 | English | 474 |
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Method of electromagnetic acoustic inspection for metal materials -- Part 3: Standard test method for ultrasonic surface examinations using electromagnetic acoustic transducer (EMAT) techniques
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GB/T 20935.3-2009
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PDF similar to GB/T 20935.3-2018
Basic data | Standard ID | GB/T 20935.3-2018 (GB/T20935.3-2018) | | Description (Translated English) | Metal materials -- Method of electromagnetic acoustic inspection -- Part 3: Standard practice for ultrasonic surface examinations using electromagnetic acoustic transducer (EMAT) techniques | | Sector / Industry | National Standard (Recommended) | | Classification of Chinese Standard | H26 | | Classification of International Standard | 77.040.20 | | Word Count Estimation | 14,168 | | Date of Issue | 2018-03-15 | | Date of Implementation | 2018-12-01 | | Issuing agency(ies) | State Administration for Market Regulation, China National Standardization Administration | GB/T 20935.3-2018: Metal materials -- Method of electromagnetic acoustic inspection -- Part 3: Standard practice for ultrasonic surface examinations using electromagnetic acoustic transducer (EMAT) techniques
---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
Metal materials--Method of electromagnetic acoustic inspection--Part 3. Standard practice for ultrasonic surface examinations using electromagnetic acoustic transducer(EMAT)techniques
ICS 77.040.20
H26
National Standards of People's Republic of China
Replace GB/T 20935.3-2009
Electromagnetic ultrasonic testing method for metal materials
Part 3. Using electromagnetic ultrasonic transducers
Technique for ultrasonic surface inspection
Part 3. Standardpracticeforultrasonicsurfaceexaminationsusing
Published on.2018-03-15
2018-12-01 implementation
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
China National Standardization Administration issued
Foreword
GB/T 20935 "Electromagnetic Ultrasonic Testing Method for Metal Materials" is divided into the following three parts.
--- Part 1. Guide to electromagnetic ultrasonic transducers;
--- Part 2. Methods for ultrasonic testing using electromagnetic ultrasonic transducer technology;
--- Part 3. Ultrasonic surface detection using electromagnetic ultrasonic transducer technology.
This part is the third part of GB/T 20935.
This part is drafted in accordance with the rules given in GB/T 1.1-2009.
This part replaces GB/T 20935.3-2009 "Electromagnetic Ultrasonic Testing Methods for Metallic Materials - Part 3. Using Electromagnetic Ultrasonic Transducers
The method of technology for ultrasonic surface inspection", compared with GB/T 20935.3-2009, the main technical changes are as follows.
--- The items in the scope were merged, and the original standard "1.6 part of the standard unit with international units" and "1.7 headquarters" were deleted.
Do not discuss security issues related to use. It is the responsibility of the user to establish procedures for the safety and health of the person before use.
Set its scope of application. (see Chapter 1,.2009 editions 1.6 and 1.7);
--- Amend the 8.4 "NdFeB permanent magnets can be used for all electromagnetic ultrasonic transducer surface wave technology" to "at room temperature (nominal temperature)
When used below 82 ° C), NdFeB permanent magnets can be used for all electromagnetic ultrasonic transducer surface wave technology. At high temperatures
In use, it may be necessary to use more complex magnetization techniques, such as electromagnets or special permanent magnets designed for high temperatures. " (see 8.4,.2009)
Version 8.4);
--- "As with piezoelectric ultrasound, the surface roughness of the workpiece has a great influence on the attenuation. When using an electromagnetic ultrasonic transducer, it is lifted off.
Changes in the gap may lead to false positives, and when the piezoelectric ultrasonic technique uses the attenuation method, the lift-off will not be caused by the use of the couplant
The change in signal amplitude is modified as "in piezoelectric ultrasonic technology, surface roughness has a great influence on attenuation. Using electromagnetic ultrasonic exchange
In the case of energy technology, a change in lift distance can lead to false positives. However, if all the sensors are the same when testing
The piezoelectric ultrasonic technology using the coupling attenuation compensation method can keep the signal level stable. " (see 10.3.3,.2009)
Version 10.2.7);
--- Added general requirements to the test method (see 10.1);
--- Added "and re-test all materials detected after the most recent sensitivity calibration" (see 10.1.4);
--- Added "In fact, the weld height and root signal are not detected due to the formation of diffraction, just like the specular reflector will reverse the signal
Shoot the same. This makes it possible to perform a linear scan of the weld and detect surface discontinuities in all directions, and the detection is not
The reflected signal to the weld height. "(see 10.4.2,.2009 edition 10.3.5).
This part was proposed by the China Iron and Steel Association.
This part is under the jurisdiction of the National Steel Standardization Technical Committee (SAC/TC183).
This section drafted by. Iron and Steel Research Institute, Steel Research Institute Testing Technology Co., Ltd., Metallurgical Industry Information Standards Institute.
The main drafters of this section. Fan Hong, Zhang Jianwei, Liu Guanglei, Liu Tao, Zhang Ke, Dong Li.
The previous versions of the standards replaced by this section are.
---GB/T 20935.3-2009.
Electromagnetic ultrasonic testing method for metal materials
Part 3. Using electromagnetic ultrasonic transducers
Technique for ultrasonic surface inspection
1 Scope
This part of GB/T 20935 gives the use of electromagnetic ultrasonic transducer (EMAT) technology to detect material surface discontinuities (eg.
Cracks, cracks, folds, cold partitions, delamination, leakage, unfused) and near surface discontinuities that are less than or equal to the surface wavelength range
An overview, significance, and use of the principles of sexuality, and specifies the application conditions, techniques, devices, calibrations, test methods, results determination, and test reports.
This section applies to the detection of the production process of the product, the detection of the final product and the detection of the repair.
This section applies to non-contact detection techniques that use electromagnetic methods to excite surface waves in materials and their applicable materials, including non-ferrous
Magnetic and ferromagnetic conductive materials.
Note. This section does not provide criteria for assessing discontinuities. The determination, grading and final assessment of discontinuities are not based on other technical specifications or agreements.
The continuation type, size, location, and orientation are judged to be qualified.
2 Normative references
The following documents are indispensable for the application of this document. For dated references, only dated versions apply to this article.
Pieces. For undated references, the latest edition (including all amendments) applies to this document.
GB/T 9445 Non-destructive testing personnel qualification and certification
GB/T 11343 non-destructive testing contact ultrasonic oblique probe detection method
GB/T 12604.1 Non-destructive testing terminology ultrasonic testing
GB/T 12604.6 Non-destructive testing term eddy current testing
GB/T 20935.1 Electromagnetic Ultrasonic Testing Methods for Metallic Materials - Part 1. Guide to Electromagnetic Ultrasonic Transducers
3 Terms and definitions
The terms and definitions defined in GB/T 12604.1, GB/T 12604.6 and GB/T 20935.1 apply to this document.
4 Principles Overview
4.1 This section describes the use of electromagnetic methods to excite surface wave technology, through the reflection of reflected or transmitted waves at the discontinuous interface of sound waves, detection
A discontinuity in the surface or near surface of the material.
4.2 Figure 1 shows a typical electromagnetic ultrasonic transducer device that produces surface waves. The applied magnetic field B0 is parallel to the surface of the ferromagnetic material, if the line
The circle is designed such that the magnetic field B0 can also be perpendicular to the surface, which can be provided by a permanent magnet, a pulsed electromagnet or a direct current electromagnet. RF foldback
The coil is placed flat on the surface of the material to be inspected, and the magnetic lines of force are tangential to the coil and perpendicular to the coil conductor. RF generated by a dedicated pulse generator
The pulse train excites the coil, and induces a current on the surface of the material to be inspected, and the current interacts with the external magnetic field through the Lorentz force, and the time-varying magnetic field also
Vibration is generated by the interaction of magnetostrictive and ferromagnetic materials. The vibration is transmitted to the solid lattice to form a sound source, which in turn radiates surface acoustic waves.
The folded loop shown in Fig. 1 excites a bidirectional wave, and a unidirectional wave can also be excited by a specially designed folded loop.
Description.
1 --- foldback coil;
2 --- surface acoustic wave pulse;
B0---additional magnetic field;
FL---Lorentz force.
Figure 1 Typical electromagnetic ultrasonic transducer device for generating surface waves
4.3 Figure 2 shows a typical folded-back coil that excites a surface wave. The foldback coil should satisfy equation (1) to generate surface waves.
vR=2Df (1)
In the formula.
vR --- surface wave velocity in meters per second (m/s);
D --- the spacing of adjacent conductors in the coil, in meters (m);
f --- Frequency in Hertz (Hz).
Description.
D---the spacing of adjacent conductors in meters (m).
Figure 2 Typical foldback coil for exciting surface waves
4.4 Surface discontinuity causes surface waves to be reflected or transmitted through wave attenuation, which can be detected by pulse reflection or one-shot.
The reflected or attenuated ultrasonic waves propagate to the electromagnetic ultrasonic transducer where the conductor material vibrates. The vibration in the transducer magnetic field is connected
The receiving coil senses a voltage that can be measured.
5 Meaning and use
5.1 Compared with conventional piezoelectric ultrasound, the obvious advantages of electromagnetic ultrasonic transducer technology are in the flexible excitation mode and the absence of couplant.
Electromagnetic ultrasonic transducers efficiently excite surface waves.
5.2 Since the electromagnetic ultrasonic transducer can efficiently excite surface waves, and the surface wave can sensitively detect the surface and near surface discontinuity, it can be used
In the case of traditional penetration and magnetic particle testing, although effective but not suitable for use.
5.3 Because electromagnetic ultrasonic transducer technology is non-contact detection, it can be used for high-speed automatic detection, dynamic detection, long-distance or dangerous places.
Detection, high temperature and detection of rough surfaces.
5.4 The purpose of this section is to enhance electromagnetic ultrasonics as an alternative to traditional infiltration and magnetic particle methods for material surface and near surface discontinuities.
Detection technology.
5.5 The use of electromagnetic ultrasonic transducers and the choice of operating parameters depend on the geometry of the material being tested and the approximate position of the expected discontinuity.
The placement, size, orientation, and reflectivity should also be aware of the allowable lift-off range of the electromagnetic ultrasonic transducer and the physical laws of ultrasonic propagation. This section
Specialized in the application of electromagnetic ultrasonic surface inspection.
6 Application conditions
6.1 Staff qualifications
If the contract requires, the personnel performing the tests in this part shall obtain the technical assets identified by the relevant departments according to GB/T 9445 or equivalent standards.
Grid, and authorized by the employer. The criteria for the qualification basis (including the version number) should be stated in the contract.
6.2 Methods and techniques
The methods and techniques recommended in this section should be used unless specifically specified. The specially designated technology shall be indicated in the contract between the parties.
6.3 Surface preparation
Surface preparation prior to testing shall be in accordance with 10.2.2 unless otherwise stated.
6.4 Detection timing and scope
The timing and scope of the test should be specified in the contract.
6.5 Report content and acceptance criteria
Unless otherwise stated, the test report shall be consistent with the requirements of Chapter 12. The acceptance criteria shall comply with the relevant standards or in the contract between the parties.
It is prescribed.
6.6 Re-examination clause after repair and rework
This section does not include the re-examination clause after repair and rework, and if necessary, it can be explained in the contract between the two parties.
7 technology
7.1 Overview
This section describes the following three different electromagnetic ultrasonic surface wave detection techniques.
a) detecting the reflection of surface waves by pulse reflection or one-shot technique;
b) detecting the transmission attenuation of the surface wave by using a one-shot technique;
c) Surface wave diffraction techniques using focused rewinding coils.
7.2 Pulse echo or one-shot and one-shot reflected wave technology
This technique is similar to conventional ultrasound in that it uses a (pulse echo method) or two (one-shot-and-received-wave method) electromagnetic ultrasonic transducers.
A surface wave reflected from the defect is received to detect the defect. The advantage of this technology is simplicity. The disadvantage is that it is difficult to set the scan path carefully.
Detection of discontinuities in all orientations, as well as in weld inspection, reflections from the root and residual height of the weld can interfere with or even bury the discontinuity
signal. When such interference occurs, one of the other two techniques described below should be avoided.
7.3 Transmitted wave attenuation technology
An example of the most common sensor arrangement for wave attenuation techniques is shown in Figure 3. It is detected by recording the attenuation of the ultrasonic signal.
Measure discontinuity. The sensor uses a small permanent magnet to create a narrow surface beam that is perpendicular to each other. It is best to use a two-channel electromagnetic ultrasonic instrument, or
Use a single channel instrument. When a single channel is used, the transmitting coil and the receiving coil are respectively connected in series, and a pair of transmitting and receiving sensors are connected
The distance is slightly lengthened to separate the two received signals in time. This arrangement allows two sets of transducer coils to be connected simultaneously to one
On the channel. One advantage of the attenuation technique is that it is sensitive to discontinuities in all directions. Another advantage is that it can be scanned on both sides of the weld.
And the scanning surface on each side is very large. The disadvantages of the attenuation technique are related to the beam width. to meet the minimum 6 dB attenuation, the beam should be narrow or focused.
Description.
1---power supply;
2---EMAT pulse receiving unit;
3---computer or oscilloscope;
4---no defect signal;
5---the signal when there is a defect;
R---receiving coil;
T---transmitting coil.
Figure 3 attenuation technology
7.4 Diffraction technology
The principle of the diffraction technique is shown in Figure 4. Electromagnetic ultrasonic transducer (transmitting coil and receiving coil) or one pulse with two focal lines overlapping
The reflective electromagnetic ultrasonic transducer is placed at an angle (diffraction angle) with the center line of the weld, and the root and the residual height of the weld are specularly reflected.
The reflected signal is not received by the receiving coil. Diffraction techniques can be used to detect discontinuities over a wide range of angles. Single point diffraction or
Multi-dot diffraction depends on the ratio of discontinuity to the wavelength of the ultrasonic wave. Natural defects (such as fatigue cracks) have many points of diffraction source interface, so
With this technology, natural defects of several tens of millimeters in length can be effectively detected. The surface wave can be approximated to the focus area (this area can be up to one
One of the significant advantages of this is that choosing the right depth of focus increases the coverage of each scan. For most welds, from
One half of the weld can be scanned on one side of the weld. In addition to cracks parallel to the incident beam, a single electromagnetic ultrasonic transducer sensor is flexible
The discontinuity of all orientations is sensitively detected. Two sensors with positive and negative diffraction angles can sensitively detect discontinuities in all orientations.
Description.
1 --- specular reflector (weld seam height or root);
2 --- Weld center line;
3 --- discontinuity;
4 --- weld;
5 --- specular reflector;
6 --- focal line coincident EMAT transmission and reception;
7 --- Receive signal;
8 --- transmitting signal;
9 --- The defect wavefront detected by the receiving coil;
10---The specular reflection that is not detected by the receiving coil.
Figure 4 Diffraction technology
8 devices
8.1 Composition
The device consists of an electromagnetic ultrasonic transducer sensor and an instrument. The sensor consists of a radio frequency coil and a magnet. The instrument is pulsed/connected.
Receiver, data acquisition system, display device (such as oscilloscope), impedance matching network, preamplifier (recommended) and connected pulser/receiver
The shield cable consists of the sensor to the sensor.
8.2 Coil design
8.2.1 The foldback coil is used to generate surface waves. To obtain the specified frequency, the design of the coil conductor spacing is given in 4.3. The coil can be focused or
Unfocused, depending on the technology used and the resolution and sensitivity required. Figure 5 shows a typical focus coil design
Number, similar to diffraction technique. Many electromagnetic ultrasonic transducer coils are made by photolithographically etching printed wiring on flexible polyamide film.
The surface of the coil has a thin layer of foam and is coated with high molecular weight polyethylene or titanium with a thickness of 0.0254mm~0.127mm.
Grinding layer. The purpose of the wear layer is to ensure a constant liftoff value of the electromagnetic ultrasonic transducer coil. The wear layer can be flexible to accommodate irregularities
Or a curved surface. Polyamide film typically has a thickness of 0.0254 mm or 0.0508 mm. For the weld height, for surface roughness
The impact is minimal, and the lower limit frequency should be selected for each method.
Description.
1---incentive part;
2---receiving part;
3---frequency design (see Table 1);
4---width, size is 25.4mm;
5---maximum focal length, size 38mm;
6---the angle is 19.416°;
7---load, length 152mm (not drawn to scale);
8---load, 1.27mm wide, conductor spacing 1.27mm.
Fig. 5 Design parameters of the focusing coil of a typical electromagnetic ultrasonic transducer
Table 1 transducer frequency design unit is mm
frequency
Number of finger coils
(total)
Line distance conductor width
1MHz 4 1.524 0.762
2MHz 8 0.762 0.381
3MHz 8 0.508 0.254
4MHz 10 0.381 0.1905
8.2.2 The typical operating frequency of the diffraction technique is 1 MHz, and the typical operating frequency of the attenuation technique is 2 MHz. For attenuation technology
The coil is shown in Figure 6. The extension of the polyamide film should be fixed in a mechanical fixture that holds the magnetic poles.
The unit is mm
Figure 6 Typical electromagnetic ultrasonic transducer coil for attenuation technology
8.3 Coil excitation
A dedicated high power RF transmit circuit should be used to excite the coil in bursts of several cycles.
8.4 Magnetic field
NdFeB permanent magnets can be used in all electromagnetic ultrasonic transducer surface wave technologies at ambient temperatures (nominal temperatures below 82 °C).
In high temperature applications, more complex magnetization techniques may be required, such as electromagnets designed for high temperatures or special permanent magnets. For attenuation technology
And the typical magnet size of the diffraction technique and the direction of the resulting magnetic induction B are shown in Figure 7, the direction of B and the RF coil and the inspection
The surface is vertical. Permanent magnets are compact for field use sensors; pulse electromagnets or DC magnets can be used if required
iron. For ferromagnetic materials, the direction of the magnetic field can be parallel or perpendicular to the detection surface. For non-ferromagnetic materials, the direction of the magnetic field should be perpendicular to
Detection surface.
The unit is mm
Figure 7 permanent magnet
8.5 Instruments
The receiving unit is composed of a signal processing and a data collecting circuit, and can perform gain adjustment and filtering processing on the electromagnetic ultrasonic transducer signal, and transmit
This is also the function of the ultrasound equipment. The operator can acquire and analyze the electromagnetic ultrasonic transducer signals in a variety of ways. Computer with A/D turn
The plate change and the corresponding ultrasonic flaw detection software can form an effective configuration. It is also possible to use a simple configuration similar to a conventional ultrasonic instrument, such as
Output the analog signal to the oscilloscope to display the detection result. In addition, in order to provide accurate triggering for signal acquisition, a pulse generator should be used.
The synchronization circuit of the receiver.
8.6 Comparative sample
8.6.1 General requirements
The comparative specimen used for system calibration shall have the same material, thickness, surface condition and heat treatment state as the material to be inspected. In addition to adjustment
Except for the artificial injury required for sensitivity, there should be no discontinuity on the comparison sample that affects the normal indication of artificial injury. Length and width of artificial injury
And depth should be consistent with the acceptance criteria.
8.6.2 Specific requirements
Since electromagnetic ultrasonic transducers are typically bidirectional, boundary reflections are confused with contrasting artificial injury reflections. So should be the designer
The location of the work injury and its geometry to avoid the above interference.
8.6.3 Comparative specimens for surface inspection of welded parts
8.6.3.1 The comparative specimen used for system calibration shall have the same material, weld magnetic properties, thickness, surface condition and heat as the weld to be inspected.
Process status and have a certain length. There should be no discontinuities in the sample that affect the normal indication of artificial injury. The choice of artificial injury should be
Cover the entire weld zone with the specified sensitivity level and direction. Comparative artificial injuries are generally made by electro-erosion equipment or machining equipment.
8.6.3.2 Artificial injuries shall be made in the welded joint, the weld heat affected zone of the base metal or the base metal parallel to the weld according to the acceptance criteria of the welded parts.
8.6.3.3 The orientation and length, depth and width of the groove may be specified by the user or both parties, and may also be consistent with the acceptance criteria of the welded parts.
8.6.3.4 Groove depth is the value from the surface to the deepest and shallowest of the trough. Measurement methods can be optical, complex, mechanical or other techniques.
The groove depth is usually defined as a percentage of the nominal thickness.
8.6.3.5 The location and geometry of the artificial injury should be designed to avoid interference between edge reflection and artificial injury reflection.
9 check
9.1 Since electromagnetic ultrasonic transducers are not as general-purpose as traditional piezoelectric devices, designers should be able to demonstrate electromagnetic super-use before use.
The acoustic transducer meets the sensitivity and frequency characteristics requirements. For this purpose it is necessary to calibrate the electromagnetic ultrasonic transducer system with a comparative sample.
9.2 Prior to testing, the electromagnetic ultrasonic transducer system shall be calibrated using the specimens required by the standard or specified in the protocol.
9.3 The comparative sample shall have similar ultrasonic characteristics to the material to be tested. For special applications, it shall be selected in accordance with the requirements of Chapter 8.
9.4 As with conventional ultrasound, attenuation compensation should be performed if the magnitude of the artificial injury signal on the comparison specimen is different from the material being tested.
9.5 When equipment or operator changes, the equipment should be re-calibrated using a comparative sample.
9.6 During the test, the equipment shall be calibrated every 4 hours or as specified in the agreement to ensure the accuracy of the electromagnetic ultrasonic transducer system.
Sex. Whenever the signal differs by 10% or more from the initial calibration, the device should be adjusted.
9.7 When the electromagnetic ultrasonic transducer...
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