GB/T 5248-1998 Eddy current flaw detection method for copper and copper alloy seamless pipes
Some standard content:
GB/T 5248--1998
This standard adopts ASTME243-90 "Electromagnetic (eddy current) testing of copper and copper alloy tubes" in terms of scope of application, instruments and equipment, and artificial standard defects.
This standard is a revision of GB5248-85. On the basis of the original standard, the specifications of copper tubes for flaw detection are appropriately expanded to include coils. Some provisions are made on the main functions and technical indicators of instruments, detection coils and transmission equipment for eddy current flaw detection of copper tubes. The artificial standard defect adopts a circular through hole. The flaw detection sensitivity adjustment and flaw detection steps are modified. From the date of implementation, this standard will replace GB5248-85 "Eddy current flaw detection method for seamless copper and copper alloy tubes". Appendix A of this standard is the appendix of the standard.
This standard is proposed by China Nonferrous Metals Industry Corporation. This standard is under the jurisdiction of the Standard Metrology Institute of China Nonferrous Metals Industry Corporation. This standard is drafted by the Nondestructive Testing Center of China Nonferrous Metals Industry Corporation. The main drafting units of this standard are: China Nonferrous Metals Industry Corporation Nondestructive Testing Center, Shanghai Nonferrous Metals Industry Corporation Copper Tube Company.
The main drafters of this standard are: Zhao Xujiang, Xu Xinxiong, Zhang Jianguo, Shi Heping. This standard was first issued on July 2, 1985. 209
1 Scope
National Standard of the People's Republic of China
Eddy current testing method for copper and copper alloy seamless tubesCopper and copper alloy-seamlesstubes-eddy current testing methodThis standard specifies the eddy current testing method for copper and copper alloy round seamless tubes (hereinafter referred to as tubes). GB/T5248—1998
Replaces GB5248-85
This standard is applicable to straight or coiled tubes (including internally threaded tubes), with specifications: outer diameter: $4~50mm; wall thickness: 0.3~~3.0mm. The types of defects detected are mainly cracks, inclusions, peeling, bruises and other metallurgical and mechanical defects that destroy the continuity of metal on the inner and outer surfaces of the pipe and the inside of the pipe wall.
The method described in this standard uses a through-type detection coil system and single-frequency excitation. The excitation frequency range is generally 1 to 125kHz. Note: Eddy current flaw detection of copper pipes should be automatically performed on the transmission device. If manual eddy current flaw detection is required, it can be determined by negotiation between the supply and demand parties. 2 Definitions
This standard adopts the following definitions.
2.1 Eddy current testing is a method of detecting whether there are defects in the test piece by using the principle of electromagnetic induction to generate eddy currents on the surface and near the surface of the conductive test piece. 2.2 Encircling coil
Refers to the annular coil and components surrounding the outer wall of the test piece. 2.3 Excitation frequency refers to the fundamental frequency of the alternating current supplied to the excitation coil in the detection coil. 2.4 Phase analysis method phase analysis
is an analysis method that identifies various variables in the test piece based on the difference in the phase angle of the detection signal. 2.5 Modulation analysis method modulation analysis is an analysis method that uses the difference in the modulation frequency of the modulation envelope on the carrier signal to identify various variables in the test piece. 2.6 Signal to noise ratio signal to noise ratio refers to the ratio of the defect signal amplitude to the maximum noise amplitude at the output end of the eddy current flaw detector 2.7 Saturation magnetization magnetic saturation magnetization of the inspected area of the test piece, thereby suppressing the noise generated by the uneven magnetic permeability of the test piece. 2.8 Speed-sensitive instrument speed-sensitive instrument instrument that will produce a signal response to changes in the flaw detection speed. 2.9 Speed-insensitive instrument speed-insensitive instrument instrument that will not produce a signal response to changes in the flaw detection speed. 2.10 Edge effect
when the detection coil is at the end of the pipe, the interference signal generated by the distortion of the eddy current flow path. Fill factor of the detection coil2.11
Approved by the State Administration of Quality and Technical Supervision on July 15, 1998210
Implemented on February 1, 1999
It is a size factor.
Where: n——fill factor of the detection coil; d-——outer diameter of the pipe;
D——inner diameter of the detection coil.
GB/T5248—1998
n= (d/D)2
2.12Difference of induced-potential is the difference in induced voltage between the windings when the detection coil is connected differentially. When there is a test piece in the detection coil, it is loaded zero potential. When there is no test piece in the detection coil, it is unloaded zero potential. 3 Principle and method overview
3.1 When the alternating magnetic field approaches the pipe to be tested, eddy currents and corresponding eddy current magnetic fields are generated on its surface and near the surface. The function of the eddy current magnetic field is to weaken and offset the excitation magnetic field. The degree of weakening and offset depends on the physical properties of the inspected pipe. Defects in the pipe will change these effects and cause the impedance of the detection coil to change. Through the signal processing of the instrument, it can be assessed whether the inspected pipe has defects. 3.2 Eddy current flaw detection of pipes is usually carried out by allowing the inspected pipe to pass through one or more detection coil windings using the same excitation frequency along its length. The impedance of the measuring coil winding changes due to changes in the specifications, electrical conductivity, magnetic permeability of the pipe, and metallurgical or mechanical processing defects that destroy the continuity of the metal in the pipe. When the pipe passes through the detection coil, the changes in electromagnetic induction caused by these variables of the pipe generate signals, which are processed by the instrument's phase analysis, modulation analysis and other signal processing, and recorded through sound and light alarms, marking, printing and other devices. 3.3 Eddy current flaw detection is a non-destructive testing method for products. Defects located on the inner and outer surfaces of the pipe and in the pipe wall will generate eddy current distortion signals. The sensitivity of the flaw detection should be able to detect defects that exceed the equivalent of artificial standard defects. The size of artificial standard defects should not be interpreted as the minimum size of defects that can be detected by eddy current testing. Since the detection sensitivity is related to the eddy current density, and the eddy current density decreases exponentially with the increase of the distance from the outer surface of the pipe inside the pipe wall, the detection sensitivity will also decrease accordingly. 3.4 Some signals obtained by this method may not be related to the quality of the product. For example, the signals generated by dents and fixture marks that have no effect on the use of the product. Any alarm signal exceeding the alarm level shall be treated as an alarm. 3.5 When the end of the pipe passes through the detection coil in the eddy current testing method, there will be an end effect. There is an undetectable end area (i.e., fertilization area). 3.6 For longitudinal defects of the pipe that change continuously and slowly, the signal may not always reach the alarm level. 3.7 Pipes containing magnetic materials (such as copper-nickel alloy pipes) may lead to inaccurate detection results due to their inherent non-uniform magnetic permeability. Saturation magnetization technology can usually be used to eliminate them. 4 Instruments and equipment
4.1 The eddy current flaw detection system mainly includes eddy current flaw detection instruments, detection coils and transmission devices. It may also include a detection coil base, an electrical control system, a saturation magnetization device, etc.
4.2 Eddy current flaw detection instrument: Eddy current flaw detection instrument should have units or functions such as excitation, amplification, signal processing (including phase analysis, modulation analysis, etc.), signal display, sound and light alarm, end signal elimination, sorting, marking, and printing signal output. 4.2.1 The output frequency of the excitation signal should be consistent with the frequency displayed by the instrument. The deviation should not exceed 5%. 4.2.2 The signal display can be a loss display of the impedance plane, or a unidirectional or bidirectional amplitude display. 4.2.3 The gain (or attenuator) should have sufficient margin for the corresponding artificial standard defect, not less than 10dB. And the vertical linearity with the waveform display is good.
4.3 Detection coil: The detection coil is generally composed of a differential coil consisting of a single or multiple groups of measuring coils and an excitation coil. Excited at a single frequency.
4.3.1 The inner diameter of the detection coil matches the outer diameter of the inspected pipe, and its filling coefficient is not less than 0.60. 4.3.2 The no-load and loaded zero potentials of the detection coil should be close. The difference between the no-load zero potential and the loaded zero potential and the ratio of the no-load zero potential should not be greater than 30%.
4.4 The adjustment range of the detection coil base must be adapted to the specifications of the inspected pipe. Its accuracy should be able to meet the requirements of the comprehensive performance of eddy current flaw detection equipment 21
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GB/T 5248--1998
4.5 The transmission device mainly includes the feed and discharge racks, the material diverter, the transmission roller, the guide device, the finished product sorting and other parts. The action of each mechanism should be smooth, and the inspected pipe should be concentrically passed through the detection coil under the condition of minimum vibration. 4.6 During the actual flaw detection process, the eddy current flaw detection equipment is not allowed to cause mechanical damage to the inspected pipe. 4.7 The transmission device should be able to reliably and smoothly transmit the inspected pipe and maintain a stable transmission speed. If a speed-sensitive eddy current flaw detection instrument is used, the fluctuation range of the transmission speed shall not exceed ±5%. 4.8 The saturation magnetization device should be able to produce sufficient saturation magnetization in the inspected area of the pipe to eliminate the interference signal caused by its uneven magnetic permeability.
4.9 The comprehensive performance indicators of the eddy current flaw detection system shall comply with the provisions of Table 1. The test methods for each indicator shall be carried out in accordance with Appendix A. Table 1 Comprehensive performance indicators of eddy current flaw detection system Circumferential sensitivity
≤3dB
Signal-to-noise ratio
≥10 dB
5 Artificial standard defect sample tube
End cannot be detected
(blind area)
≤100mm
All-day lack of light
Size resolution
Artificial defects
Misreporting rate
False alarm rate
Long-term stability
Sensitivity dB value fluctuation
5.1 Artificial standard defect sample tube is a pipe with artificial standard defects after processing. It is used to adjust the detection sensitivity; test the comprehensive performance of the flaw detection system, and is the acceptance standard for the product inspection by eddy current flaw detection method. 5.2 The selection of artificial standard defect sample tube must be a low-noise pipe with the same material grade, specification, surface state, and heat treatment state as the inspected pipe, and without natural defects.
5.3 The artificial standard defect is a radial circular through hole perpendicular to the pipe wall. 5.4 The length of the artificial standard defect sample tube should be greater than 2m, the curvature should not be greater than 1.5mm/m, and the corresponding relationship between its aperture size and the outer diameter and wall thickness of the inspected pipe should comply with the provisions of Table 2. The artificial standard defect sample tube should not have processing burrs and processing deformation of the pipe wall. The aperture deviation of the circular through hole should not be greater than ±0.05mm. Table 2 Artificial standard defect aperture size
Pipe outer diameter
>6～10
≥10～16
>16～20
>20～30
>30～35
>35~45
>45～50
Pipe wall thickness
No regulation
No regulation
No regulation
Artificial standard defect aperture
5.5 Artificial standard defect sample pipe is processed with 5 through holes of the same aperture along the axial direction. Among them, 2 through holes are 100mm away from the pipe end respectively, and the spacing between the middle 3 through holes is 500mm, and they are distributed 120° apart in the circumferential direction. It can be made according to Figure 1a or Figure 1b, Figure 1c. 212
GB/T5248—1998
500500
dtAperture of artificial standard defect; d—outer diameter of pipe, T—wall thickness of pipe Figure 1 Sample tube of artificial standard defect Figure
5.6 If the sample tube of artificial standard defect generates a signal other than that generated by the artificial standard defect, it shall be replaced. 5.7 If artificial standard defects of other shapes or sizes are required, it can be determined by negotiation between the supply and demand parties. 6 Flaw detection steps
6.1 The commissioning and operation personnel of the eddy current flaw detection system shall comply with the requirements of Chapter 8. 120
6.2 Eddy current flaw detection can be carried out in the processing state before the final heat treatment of the copper tube or in the state after the final heat treatment. 6.3 The appearance size and surface quality of the tube shall be inspected before eddy current flaw detection. 6.4 Tube eddy current flaw detection instruments and equipment should be preheated and stabilized before debugging and flaw detection. 6.5 Select the appropriate excitation frequency to debug the flaw detection sensitivity of eddy current flaw detection instruments and equipment. 6.5.1 Select the appropriate detection coil according to the specifications of the inspected pipe. 6.5.2 Select the artificial standard defect sample pipe that meets the requirements of Chapter 5. 6.5.3 Eddy current flaw detection instruments and equipment operate normally at a determined flaw detection speed. Debug the eddy current flaw detection instrument so that the artificial standard defect signal just alarms and the signal-to-noise ratio is not less than 10dB. 6.6 After confirming the flaw detection sensitivity value, eddy current flaw detection can be carried out on each pipe. 6.7 If necessary, a saturation magnetization device can be used to achieve saturation magnetization in the inspected area. 6.8 Before starting the flaw detection and during the flaw detection process, the flaw detection sensitivity should be calibrated every 2 hours in accordance with the requirements given in 6.5.3.
6.9 If the change in sensitivity data is greater than 2dB during calibration, the pipes tested with the last calibration sensitivity as the standard shall be retested.
6.10 If the inspector has any doubts about the defect signal, retest shall be carried out. 213
GB/T 5248—1998
6.11 The end of the pipe (except coil) is allowed to have an undetectable area (blind area) of no more than 100 mm. 7 Evaluation of inspection results
7.1 All those without alarm signals are qualified for eddy current inspection. 7.2 For straight pipes, all those with alarm signals are unqualified for eddy current inspection. If there are any doubts about the defect signal, retest shall be carried out. 7.3 For coils, all those with defect signal alarms are unqualified for eddy current inspection. The marking can be printed directly on the pipe through the marking device, or it can be determined by negotiation between the supply and demand parties.
8 Qualification of Eddy Current Flaw Detectors
Eddy current flaw detectors must undergo professional training and assessment. According to the requirements of the purchaser, the supplier shall provide an eddy current flaw detection report issued by a person with a technical qualification certificate of eddy current flaw detection level I or above recognized by the relevant department. 9 Eddy Current Flaw Detection Report
Eddy current flaw detection report shall include the following contents:a) pipe manufacturer;
b) flaw detection date;
c) brand, specification, state, batch number, etc. of the inspected pipe;d) name, model, main parameters of eddy current flaw detection instrument, including excitation frequency, phase, filtering, etc.;e) detection coil number and inner diameter;
f) transmission model and number,
g) flaw detection speed;
h) actual number of flaws detected. This includes the number of alarm roots and the number of qualified roots for eddy current flaw detection,i) flaw detection personnel and their signatures, review personnel and their signatures;j) date of filling in the flaw detection report.
A1 Content
GB/T 5248—1998
Appendix A
(Appendix to the standard)
Test method for comprehensive performance of eddy current automatic flaw detection equipment for copper and copper alloy seamless pipes This appendix specifies the test conditions, methods and test items for the comprehensive performance of eddy current automatic flaw detection equipment for copper and copper alloy seamless pipes, as well as the minimum performance indicators that should be achieved.
A2 Test conditions
A2.1 Eddy current flaw detection instruments and equipment shall comply with the provisions of Chapter 4. A2.2 During the test, the flaw detection speed shall be 50~~60m/min. The excitation frequency, gain, phase, filtering, flaw detection speed, pipe diameter, inner diameter of the detection coil and other parameters shall be recorded truthfully. If saturation magnetization is used, the magnetization current shall also be recorded. A3 Artificial standard defect sample pipe
A3.7 The production of artificial standard defect sample pipe shall comply with the provisions of Chapter 5. A3.2 The outer diameter of the artificial standard defect sample tube for testing should be made according to the types of products commonly used by the tested equipment and the upper limit specifications of the outer diameter size of the tube that the equipment can detect.
A4 Test items and methodsbzxZ.net
A4.1 Circumferential sensitivity difference
Adjust the dB value of the flaw detection sensitivity so that the three artificial defects in the middle of the artificial standard defect sample tube just alarm, and the alarm is triggered for 5 consecutive walks. Record the sensitivity dB value at this time. Adjust the dB value of the flaw detection sensitivity so that the three artificial defects in the middle of the artificial standard defect sample tube just do not alarm, and the alarm is triggered for 5 consecutive walks. Record the sensitivity dB value at this time. △dB = dB1 -- dB2
Where.AdB—-circumferential sensitivity difference;
dB1-—sensitivity dB value at which the three artificial defects in the middle of the artificial standard defect sample tube just alarm; dB2~—--sensitivity dB value at which the three artificial defects in the middle of the artificial standard defect sample tube just do not alarm. A4.2 Signal-to-noise ratio
Adjust the dB value of the flaw detection sensitivity so that the noise just alarms. Note the sensitivity dB value at this time. Test 5 times in a row. S/N = dB1 - dB3
Where: S/N-—Signal-to-noise ratio;
dB1-—--The sensitivity dB value of the 3 artificial defects in the middle of the standard artificial defect sample tube just alarms; dB3-—The sensitivity dB value of the noise just alarms. A4.3 Missing alarm rate
..(Al)
（A2）
Increase the sensitivity by 2dB based on the flaw detection sensitivity value of dB1, and run 50 times in a row. Note the number of missed reports of artificial defects K (Ni/(N2 × 50)J × 100%
Where: K,-—Missing alarm rate;
N,-——Number of missed defects;
N2—Number of artificial defects in the artificial standard defect sample tube. ·(A3)
A4.4 False alarm rate
GB/T5248—1998
Increase the sensitivity by 2dB based on the detection sensitivity value of dB1, and walk 50 times continuously. Record the number of false alarms exceeding the number of artificial defect alarms. In each walk, 1 or more false alarms are recorded as 1 false alarm. K, = (Ns/50) × 100%
Where: K2-
False alarm rate;
N. Number of false alarms.
A4.5 Undetectable end area (blind area)
(A4)
Increase the sensitivity by 2dB based on the detection sensitivity value of dB1, and walk 3 times continuously. Under the premise that the end effect of the pipe is removed, the two artificial defects at both ends of the artificial standard defect sample tube are alarmed. Test 3 times continuously. The distance between the artificial defects at both ends and the pipe end is the length of the undetectable area. A4.6 Artificial defect size resolution
Make a sample tube according to Figure A1. Under the same sensitivity dB value, the difference between the artificial defect aperture that just alarms and the artificial defect aperture that just does not alarm is the artificial defect size resolution. Test 3 times continuously. dz-d3
Where: ---artificial defect size resolution; dz artificial defect aperture that just alarms,
d3 artificial defect aperture that just does not alarm. 3-- dd,
200200
-200 1200
d,-artificial standard defect aperture, dz=d,—0. 2 mm,d—outer diameter of pipe;T--pipe wall thickness diagramA1 Defect size resolution sample tube diagram
A4.7 Long-term stability
After the flaw detection equipment has been running continuously for 2 hours, retest the circumferential sensitivity difference and signal-to-noise ratio according to A4.1 and A4.2 respectively. Test three times in a row.
The minimum index that long-term stability should achieve is that the fluctuation of the sensitivity dB value is no more than 2dB, and it can still meet the requirements of A4.1 and A4.2.
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