GB/T 34370.7-2020 PDF English
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Nondestructive testing of amusement equipment - Part 7: Eddy current testing
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GB/T 34370.7-2020: PDF in English (GBT 34370.7-2020) GB/T 34370.7-2020
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 97.200.40
Y 57
Nondestructive Testing of Amusement Equipment - Part 7:
Eddy Current Testing
ISSUED ON: NOVEMBER 19, 2020
IMPLEMENTED ON: JUNE 1, 2021
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 4
1 Scope ... 5
2 Normative References ... 5
3 Terms and Definitions ... 6
4 Method Summary ... 6
5 Safety Requirements ... 6
6 Personnel Requirements ... 7
7 General Requirements for Testing Equipment ... 7
7.1 Testing System ... 7
7.2 Testing Instruments ... 8
7.3 Testing Coil ... 8
7.4 Auxiliary Testing Equipment ... 8
8 Test Pieces ... 8
8.1 Standard Test Piece ... 8
8.2 Comparative Test Piece ... 9
9 Testing Process Procedures ... 9
9.1 General Testing Process Procedures ... 9
9.2 Testing Process Card ... 10
10 Eddy Current Testing of Component Base Metal Placement Coils ... 11
10.1 Object Under Test ... 11
10.2 Testing Requirements ... 11
10.3 Eddy Current Testing System ... 11
10.4 Testing Procedures ... 13
10.5 Identification and Analysis of Response Signals ... 15
10.6 Evaluation of Testing Results ... 15
11 Eddy Current Testing of Component Weld Placement Coils ... 16
11.1 Object under Test ... 16
11.2 Preparation before Testing ... 16
11.3 Testing Equipment ... 17
11.4 Calibration Test Block ... 19
11.5 Testing Procedures ... 20
11.6 Evaluation and Processing of Testing Results ... 21
12 Eddy Current Testing of Pipe Through Coils ... 26
13 Measurement of Covering Layer Thickness ... 27
13.1 Magnetic Method ... 27
13.2 Eddy Current Method ... 29
14 Evaluation of Testing Results ... 31
14.1 Signal Analysis ... 31
14.2 Evaluation and Processing of Testing Results ... 31
15 Testing Record and Report ... 32
15.1 Testing Record ... 32
15.2 Testing Report ... 32
Nondestructive Testing of Amusement Equipment - Part 7:
Eddy Current Testing
1 Scope
This Part of GB/T 34370 specifies the eddy current testing and covering layer thickness
measurement method for amusement equipment.
This Part is applicable to the eddy current testing of base metal and weld surface and near-
surface defects of metal components of amusement equipment.
2 Normative References
The following documents are indispensable to the application of this document. In terms of
references with a specified date, only versions with a specified date are applicable to this
document. In terms of references without a specified date, the latest version (including all the
modifications) is applicable to this document.
GB/T 5126 Eddy Current Inspection Method for Cold Drawn Thin Wall Tubes of Aluminum
and Aluminum Alloy
GB/T 5248 Electromagnetic (eddy-current) Examination of Copper and Copper Alloy Seamless
Tube
GB/T 7735 Automated Eddy Current Testing of Seamless and Welded (except submerged arc-
welded) Steel Tubes for Detection of Imperfections
GB/T 12604.6 Non-destructive Testing - Terminology - Eddy Current Testing
GB/T 12969.2 Method of Eddy Current Inspection for Titanium and Titanium Alloy Tubes
GB/T 14480.3 Non-destructive Testing Instruments - Equipment for Eddy Current Examination
- Part 3: System Characteristics and Verification
GB/T 20306 Amusement Devices Terminology
GB/T 20737 Non-destructive Testing - General Terms and Definitions
GB/T 23601 Method of Eddy Current Testing for Titanium and Titanium Alloy Bars and Wires
GB/T 30565 Non-destructive Testing - Eddy Current Testing - General Principles
GB/T 34370.1 Nondestructive Testing of Amusement Equipment - Part 1: General Requirement
GB/T 34370.3 Nondestructive Testing of Amusement Equipment - Part 3: Magnetic Particle
process include at least:
a) Testing personnel shall abide by the on-site safety requirements of the equipment
under test, and in accordance with the requirements of the testing location, wear
protective work clothes and relevant protective equipment;
b) Care shall be taken to avoid various safety hazards, such as: bruises, electric shock,
falling, squeezing, shearing, entanglement, slipping, drowning and burns, etc.;
c) Current short circuit may cause electric shock, thereby causing harm to the human
body;
d) The temperature and relative humidity of the testing site may cause harm to the human
body and testing instruments and equipment;
e) There shall be no magnetic fields, vibrations, corrosive gases and other interference
near the testing site that may affect the normal operation of the instruments and
equipment.
6 Personnel Requirements
The personnel engaged in eddy current testing of amusement equipment shall comply with the
relevant regulations of GB/T 34370.1.
7 General Requirements for Testing Equipment
7.1 Testing System
7.1.1 The eddy current testing system generally includes eddy current testing instrument, testing
coil and auxiliary device.
7.1.2 The eddy current testing system shall be able to excite the testing coil with an alternating
signal of appropriate frequency and be able to sense and process the response of the testing coil
to changes in the electromagnetic characteristics of the object under test.
7.1.3 The performance of the eddy current testing system shall satisfy the requirements of this
Part and relevant standards. The test items and test methods related to the instrument
performance shall comply with the relevant requirements of GB/T 14480.3.
7.1.4 The testing capability shall satisfy the requirements determined by product acceptance
standards or technical contracts.
7.1.5 Under the following circumstances, a comparative test block shall be used to check and
re-test the sensitivity of the eddy current testing system:
a) Before and after every testing;
b) When it is suspected that the testing system is not normally operating;
c) When the specifications of the object under test change;
d) During continuous testing, check and re-test once every 2 hours;
e) When the parties to the contract have disputes or deem it necessary.
7.1.6 The edge effect influence zone shall satisfy the relevant requirements of product
acceptance standards or technical contracts.
7.2 Testing Instruments
7.2.1 The eddy current testing instrument shall generally have the functions of excitation,
amplification, signal processing, signal display, audible and visual alarms, and signal output.
7.2.2 The testing instrument shall have the function of displaying the amplitude and phase of
the testing signal. The excitation frequency adjustment and gain range of the instrument shall
satisfy the testing requirements.
7.2.3 The testing instrument shall be able to promptly and accurately record the output signal
of the testing coil.
7.3 Testing Coil
The form of the testing coil and relevant parameters shall be compatible with the testing
instrument used, the object under test and the testing requirements.
7.4 Auxiliary Testing Equipment
7.4.1 The magnetizing device shall be able to continuously perform saturation magnetization
on the workpiece under test or part of it. If the workpiece under test is not allowed to have
residual magnetism, a demagnetization device shall also be equipped.
7.4.2 The mechanical transmission device shall be able to ensure smooth relative movement in
a prescribed mode between the workpiece under test and the testing coil and shall not cause
surface damage to the workpiece under test.
8 Test Pieces
8.1 Standard Test Piece
8.1.1 The standard workpiece is used to test the performance of the eddy current instrument.
8.1.2 The artificial grooves and materials of the standard workpiece shall respectively comply
with the corresponding provisions of this Part.
l) Auxiliary devices (magnetic saturation device, mechanical transmission device,
recording device and demagnetization device, etc.);
m) Evaluation and grading of testing results;
n) Testing record and report format;
o) Data archiving;
p) Signatures of preparation (level), auditing (level) and approving personnel, and dates.
9.2 Testing Process Card
For eddy current testing of various workpieces, in accordance with the actual situation, GB/T
34370.1, this Part and the general testing process procedures, formulate the eddy current testing
process card. The content of the testing process card shall at least include:
a) Process card No.;
b) Implemented standard and quality level requirements;
c) Information of the workpiece under test: name, model, serial No., material,
specifications and dimensions, thermal treatment state and welding type, etc.;
d) Testing equipment: name, specifications, model and serial No., etc.;
e) Probe, transmission device, comparative test block specifications and artificial defect
dimensions, performance inspection items, timing and performance indicators;
f) Testing process parameters: including probe parameter size and model;
g) Instrument settings, such as: main frequency of testing, gain, phase and filtering, etc.;
h) Timing of testing;
i) Testing area and surface requirements;
j) Schematic diagram of testing parts;
k) Testing ratio;
l) Requirements of testing environment;
m) Regulations of testing identification;
n) Testing operating procedures and scanning sequences;
o) Specific requirements for testing records, testing diagrams and data evaluation;
p) Signatures of preparation (level) and auditing (level) personnel, and dates.
10 Eddy Current Testing of Component Base Metal
Placement Coils
10.1 Object Under Test
The object under test is regular or irregular structural parts and base materials made of metal,
including flat plates with a thickness of 3 mm and above, pipes with a diameter of 30 mm a
wall thickness of 3 mm and above, and rods with a diameter of 12 mm and above.
10.2 Testing Requirements
10.2.1 The area under test shall be free of grease, oil, rust or other substances that may hinder
testing; there shall be no magnetic powder on the surface of non-magnetic workpiece under test.
If the above-mentioned requirements are not satisfied, they shall be removed without damaging
the surface of the component under test.
10.2.2 The testing surface shall be smooth, with a surface roughness not greater than 6.3 m.
The ratio of the signal obtained from the artificial defects of the comparative test piece to the
noise signal obtained from the testing surface shall not be less than 5 : 1.
10.2.3 The thickness of the non-conductive covering layer of the part under test generally does
not exceed 150 m, otherwise, a non-conductive film of similar thickness shall be used to cover
the artificial defects of the comparative test piece to compensate for and adjust the testing
sensitivity.
10.3 Eddy Current Testing System
10.3.1 System composition
The eddy current testing system at least consists of an eddy current testing instrument, a probe,
a comparative test block and auxiliary devices. Among them, auxiliary devices (such as:
magnetic saturation device, mechanical transmission device, recording device and
demagnetization device, etc.); are also an important constituent part of the testing system and
plays a vital role. The eddy current testing system can be automatic, semi-automatic or manual
testing systems.
10.3.2 Eddy current testing instrument
10.3.2.1 The eddy current testing instrument shall have impedance plane display and time base
display modes.
10.3.2.2 It shall be able to generate changes in the continuous induced eddy current signal by
adjusting the testing frequency, response signal phase and gain.
10.3.3 Probe
The appropriate testing frequency shall be determined in accordance with the results of
comprehensive debugging on the comparative test piece and workpiece under test.
10.4.1.2 In order to enhance testing reliability, multi-frequency testing method can be adopted
to comprehensively determine the characteristics of defects by comparing the amplitude or
impedance plane trajectory of defect signals at different frequencies.
10.4.2 Phase adjustment
10.4.2.1 The phase adjustment of the instrument shall be conducive to the distinction and
identification of the defect response signal and the lift-off interference signal. Usually, the phase
of the lift-off signal is adjusted to the horizontal direction, and the phase difference between the
artificial defect response signal and the lift-off signal is as large as possible.
10.4.2.2 The eddy current response signal will change as the testing frequency changes. When
changing the testing frequency, the phase of the lift-off signal shall be re-adjusted, so that it is
in the horizontal direction.
10.4.2.3 If necessary, the phase difference between the artificial defect response signal and the
lift-off signal can be increased by adjusting the vertical and horizontal ratio of the artificial
defect response signal.
10.4.3 Sensitivity setting
10.4.3.1 On the comparative test piece, use the specified acceptance level to debug the testing
sensitivity, so that when the testing coil passes the artificial defect as the acceptance level, the
response amplitude of the artificial defect signal is not lower than 40% of the full scale, and the
ratio of the artificial defect signal to the noise signal is not less than 5 : 1.
10.4.3.2 If necessary, the alarm area of the instrument can be set in accordance with the artificial
defect response signal as the acceptance sensitivity.
10.4.4 Scanning
10.4.4.1 During the scanning process, the probe shall be perpendicular to the surface of the
workpiece under test. When testing the curved surface and edge of a part, a special-purpose
testing coil can be used to ensure the stability of the electromagnetic coupling.
10.4.4.2 The scanning speed during testing shall be the same as the speed during instrument
calibration.
10.4.4.3 The influence of component edges shall not cause the signal-to-noise ratio to be less
than 3 : 1.
10.4.4.4 When an abnormal response signal is found during scanning, the area under test with
signal response shall be repeatedly scanned to observe the repeatability of the response signal
and compare it with the artificial defect response signal on the comparative test piece.
regarded as caused by defects, and the direction, length or area and type of the defects shall be
evaluated in accordance with 10.5.2.
10.6.2 For surface defects, based on the comparison of the response signal amplitude with the
response signal amplitude of the relevant depth artificial defects on the comparative test block,
the depth of the defects causing the response signal can be evaluated. The phase of the defect
response signal can be used as reference information for the depth evaluation of surface defects.
10.6.3 Based on the technical conditions of the relevant products or the acceptance criteria
agreed with the entrusting party, a conclusion on whether the component under test is qualified
or not shall be made.
10.6.4 When the product technical conditions and relevant technical agreements do not provide
acceptance criteria, only a quantitative evaluation of the defects found can be provided, without
a conclusion of qualification or failure.
11 Eddy Current Testing of Component Weld Placement
Coils
11.1 Object under Test
11.1.1 The object under test is welds of regular or irregular components made of metal materials,
including the welds and heat affected zones of plates with a thickness of 3 mm and above, and
pipes with a diameter of 30 mm a wall thickness of 3 mm and above.
11.1.2 The placement coils are applicable to the testing of surface openings and near-surface
planar defects in welds and heat affected zones.
11.1.3 The object under test may be various forms of naturally formed weld surfaces with
coatings, but extremely rough surfaces may affect the testing effect.
11.2 Preparation before Testing
11.2.1 The area under test shall be free of grease, oil, rust or other substances that may hinder
testing.
11.2.2 Before testing, the type of filler metal, location and range of the weld to be tested,
geometric shape of the weld surface, as well as surface condition, coating type and thickness
shall be grasped.
11.2.3 Eddy current testing is related to the proximity of the probe and the surface under test.
The geometric shape and surface condition of the weld surface under test shall ensure good
contact between the probe and the testing surface. When performing eddy current testing on
welds, take into account the irregular shapes of the weld surface, welding spatter, weld beadings,
corrosions and paint peeling, which may change the distance between the probe and the surface
under test and cause noise, thereby affecting the sensitivity of testing.
11.2.4 For certain types of conductive material-coated components, such as: galvanized and
thermal sprayed aluminum, etc., on the surface. When using the eddy current method for testing,
these conductive metal materials may be deposited in the cracks opened on the surface, thereby
affecting the testing effect, resulting in the impossibility of effectively testing possible crack
defects.
11.3 Testing Equipment
11.3.1 Testing instruments
The testing instruments shall have the function of signal phase and amplitude display and
analysis, and at least satisfy the following requirements:
a) The eddy current instruments shall be able to work at a certain selected frequency
point in the range from 1 kHz ~ 1 MHz.
b) After the compensation for balancing and lift-off effects, the signal amplitude of a 1
mm deep artificial defect on the calibration test block (coated thickness test piece)
shall reach the full screen; the signal amplitude of a 0.5 mm deep artificial defect is
at least 50% of that of a 1 mm artificial defect.
c) They shall be able to display the impedance plane diagram of the defect signal and
have a signal trace freezing function. The signal trace shall be clearly visible under
daylight, lighting or no lighting conditions on the testing site.
d) Phase control shall enable the signal to rotate through a full angle (360) in steps of
no greater than 10.
e) They can perform phase and amplitude analysis on any vector on the signal
impedance plane diagram and can compare the current signal with the previously
stored reference signal for analysis.
f) On the premise of ensuring the functionality, sensitivity and resolution of the entire
system, an extension cable can be used to connect the probe and the instrument.
g) When operating with a relatively long extension cable, the instrument shall have a
device that allows the operator to perform remote signal display.
11.3.2 Testing probes
11.3.2.1 Probe for weld coating thickness measurement and material evaluation
While operating in the absolute mode at a frequency of 1 kHz ~ 1 MHz and lifting off the
workpiece under test or the calibration test block, it shall be able to generate a full-screen lift-
off signal on the instrument. All probes shall be clearly marked with the frequency range, in
which, they operate (see Figure 4).
11.5 Testing Procedures
11.5.1 Surface preparation before testing
Before the testing, the surface condition of the test piece shall be confirmed, including coating
type and thickness, weld shape and morphology, so as to ensure that it satisfies the testing
requirements.
11.5.2 Estimation of weld coating thickness and evaluation of the conformity of the
material under test with the calibration test block material
The coating thickness on the weld surface is generally uneven, but due to its impact on testing
sensitivity, before weld testing, it is necessary to estimate the maximum coating thickness in
the heat affected zone.
Use the probe of 11.3.2 to respectively obtain the lift-off signals of the calibration test block
and the test piece. Through comparison, the coating thickness on the test piece can be estimated,
with reference to Figure 4 and Figure 5.
The deviation of the lift-off signal of the test piece from the lift-off signal of the calibration test
block shall be within the range of 5, otherwise, the calibration test block shall be re-processed
using materials closer to the test piece.
11.5.3 Testing of welds of ferromagnetic materials
11.5.3.1 Frequency selection
The frequency shall be adjusted for optimal sensitivity in accordance with lift-off and other
undesirable signals. Under normal circumstances, a frequency of approximately 100 kHz is
recommended.
11.5.3.2 Calibration
The calibration process is carried out in accordance with the following steps:
a) Calibrate the probe by scanning the artificial grooves on the calibration test block.
During calibration, the surface of the grooves shall be covered with a layer of non-
conductive elastic gasket, the thickness of which is equal to or greater than the coating
thickness of the workpiece under test.
b) Adjust the signal amplitude of the 1 mm deep groove to about 80% of the full-screen
height. Then, adjust the sensitivity level to compensate for the impact of the geometric
shape of the workpiece.
c) Calibration checks shall be periodically carried out, at least at the beginning and end
of testing and every time the working conditions change. Each calibration shall be
recorded.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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