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GB/T 32547-2016 (GBT 32547-2016)

Chinese Standard: 'GB/T 32547-2016'
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BASIC DATA
Standard ID GB/T 32547-2016 (GB/T32547-2016)
Description (Translated English) Method for magnetic flux leakage testing of round steel
Sector / Industry National Standard (Recommended)
Classification of Chinese Standard H26
Classification of International Standard 77.040.20
Word Count Estimation 10,130
Date of Issue 2016-02-24
Date of Implementation 2016-11-01
Quoted Standard GB/T 9445; GB/T 12604.5; YB/T 145; YB/T 4289
Drafting Organization Steel Research Institute; Metallurgical Industry Information Standards Institute; Fangda Special Steel Technology Co., Ltd.; Daye Special Steel Co Ltd; Shougang Corporation; Xingtai Iron and Steel Co., Ltd.
Administrative Organization National Steel Standardization Technical Committee (SAC/TC 183)
Regulation (derived from) National Standard Announcement No
Proposing organization China Iron and Steel Association
Issuing agency(ies) Administration of Quality Supervision, Inspection and Quarantine of People's Republic of China; Standardization Administration of China
Summary This standard specifies the terms and definitions, detection principles, testing methods, comparative samples, testing equipment, testing conditions and procedures, results determination and test report of ferromagnetic round steel magnetic flux leakage testing. This standard applies to the diameter of 10 mm ~ 350 mm round steel (including wire) surface and near surface magnetic flux leakage detection. Other specifications can refer to this standard.

GB/T 32547-2016
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.040.20
H 26
Method for magnetic flux leakage
testing of round steel
圆钢漏磁检测方法
ISSUED ON: FEBRUARY 24, 2016
IMPLEMENTED ON: NOVEMBER 01, 2016
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 3 
1 Scope ... 4 
2 Normative references ... 4 
3 Terms and definitions ... 4 
4 Testing principle ... 4 
5 Testing method ... 5 
6 Comparative sample ... 6 
7 Testing equipment ... 8 
8 Testing conditions and steps ... 10 
9 Result determination ... 11 
10 Testing report ... 12 
Foreword
This Standard was drafted in accordance with the rules given in GB/T 1.1-2009.
This Standard was proposed by China Iron and Steel Association.
This Standard shall be under the jurisdiction of National Technical Committee
on Steels of Standardization Administration of China (SAC/TC 183).
The drafting organizations of this Standard: Iron and Steel Research Institute,
Metallurgical Industry Information Standards Institute, Steel Yannak Testing
Technology Co., Ltd.
Main drafters of this Standard: Fan Hong, Zhang Jianwei, Dong Li, Xu Lei,
Zhang Ke, Shen Haihong, Jia Huiming.
Method for magnetic flux leakage
testing of round steel
1 Scope
This Standard specifies terms and definitions, testing principle, testing method,
comparative sample, testing equipment, testing conditions and steps, result
determination and testing report for magnetic flux leakage testing of round steel.
This Standard is applicable to magnetic flux leakage testing on surface and
near surface of round steel of which diameter is 10mm ~ 350mm (including
steel wire). Other specifications shall refer to this Standard for implementation.
2 Normative references
The following referenced documents are indispensable for the application of
this document. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any
amendments) applies.
GB/T 9445, Non-destructive testing - Qualification and certification of
personnel
GB/T 12604.5, Non-destructive testing - Terminology - Terms used in
magnetic particle testing
YB/T 145, Die Casting and Size Measurement Method of Artificial Defects
on the Reference Sample Pipes
YB/T 4289, Measurement Method of Comprehensive Properties for
Automatic Magnetic Flux Leakage Flaw Detection System for Steel Tubes
3 Terms and definitions
For the purposes of this document, the terms and definitions defined in GB/T
12604.5 apply.
4 Testing principle
After ferromagnetic round steel is magnetized, the existence of discontinuity on
surface or near surface of round steel makes magnetic line on surface or near
surface of round steel distorted so as to generate a leakage magnetic field. Use
a testing element (such as Hall element, magneto-sensitive diode or induction
coil) that is sensitive to magnetic field to move on surface of magnetized round
steel (or round steel is moving, testing element is fixed). When passing through
defect, testing element interacts with leakage magnetic field to generate
electrical signal, which shall be used to determine that defect exists. The deeper
defect is buried below round steel surface, the lower sensitivity it shall be tested
out.
When defect orientation is perpendicular to direction of magnetic line, leakage
magnetic field strength is the largest at the defect, and testing sensitivity is also
the highest. As defect orientation is skewed, leakage magnetic field strength
gradually decreases. When two orientations are consistent, leakage magnetic
field strength is close to zero. Therefore, when longitudinal magnetization
testing equipment is used, it is insensitive to oblique defect reaction, then it is
easy to form a blind corner area.
5 Testing method
5.1 Testing mode
In order to detect vertical defect on surface and near surface of round steel, it
needs to use circumferential magnetization testing mode, as shown in Figure 1.
According to difference between probe and movement mode of round steel,
vertical testing is divided into two categories: rotating-probe type and fixed-
probe type. Rotating-probe type refers to that probe rotates and tested round
steel moves in straight line to complete scanning of entire surface, as shown in
Figure 1a). Fixed-probe type refers to that probe is fixed and tested round steel
moves forward spirally to complete scanning of entire surface, as shown in
Figure 1b).
Figure 1 -- Vertical testing schematic
Magnetic
yoke
Rotating direction of probe
Probe
Round
steel Round steel
Magnetic
pole
Probe
Rotating direction of probe
a) Rotating-probe type b) Fixed-probe type
5.2 Magnetization mode
According to magnetization mode of round steel, testing method is divided into
DC magnetization and AC magnetization.
a) DC magnetization
DC current excites electromagnet to generate a magnetic field. Use this
magnetic field to magnetize tested round steel. DC magnetization
efficiency is low. Magnetization intensity can be adjusted by controlling
current size.
b) AC magnetization
AC current excites electromagnet to generate a magnetic field. Use this
magnetic field to magnetize tested round steel. It is easy for AC magnetic
field to generate skin effect and eddy current in tested round steel; and as
current frequency increases, depth of magnetization decreases.
Therefore, only defect on surface or near surface of tested round steel can
be tested. AC magnetization efficiency is high. Magnetization intensity can
be adjusted by controlling current size.
6 Comparative sample
6.1 Use
Comparative sample is used to test sensitivity of magnetic flux leakage testing
equipment, to measure overall performance of testing equipment as well as to
calibrate equipment during testing process. Size of artificial defect on
comparative sample shall not be interpreted as the minimum size of defect that
magnetic flux leakage testing equipment may detect.
6.2 Material
Nominal specification of comparative sample shall be same with that of tested
round steel. Surface conditions and electromagnetic properties are same or
similar. On comparative sample, there shall be no discontinuity that affects
normal indication of artificial defect.
6.3 Length and straightness
Length and straightness of comparative sample shall meet requirements of
testing method and testing equipment.
6.4 Artificial defect
6.4.1 Shape
Artificial defect shall be processed into rectangular, U-shaped, V-shaped
longitudinal grooves. Longitudinal groove is parallel to round steel axis. Groove
centerline shall pass through round steel axis.
6.4.2 Position
6.4.2.1 Straight line transmission testing of comparative sample
Five longitudinal grooves of same size are processed on surface of comparative
sample, see Figure 2. Three artificial defects are in the middle of sample.
Circumferential interval is 120° to each other. Axial distance shall be such that
the artificial defect display signal can be clearly distinguished and not more than
200 mm. The rest two artificial defects are respectively at places not more than
200 mm from the ends of sample. For straight-line transmission testing of round
steel, it may also refer to 6.4.2.2 to make comparative sample. But when
comparative sample is used to test sensitivity of magnetic flux leakage testing
equipment, to measure overall performance of testing equipment as well as to
calibrate equipment during testing process, it shall make artificial defect on
comparative sample respectively at 0°, 120°, 240° for testing. Artificial defect
cannot be added to both ends of coil round steel wire sample.
Figure 2 -- Schematic of comparative sample
6.4.2.2 Spiral transmission testing of comparative sample
Three longitudinal grooves of same size are processed on surface of
comparative sample. One artificial defect is located in the middle of sample.
The rest two are respectively at places not greater than 200 mm far from sample
end.
6.4.3 Size
Artificial defect size (groove depth, groove width, groove length) can, according
to round steel product standard, select sizes in Table 1. Or agreed by the
supplier and the purchaser in contract, use groove depth that is half of diameter
tolerance specified according to round steel product standard as testing criteria.
For size of longitudinal groove, use h to represent depth, use b to represent
mm
width and use L to represent length. Groove depth at least cannot be less than
half of product tolerance.
Table 1 -- Size and quality level of artificial defect
mm
Quality level
Size of artificial defect
Groove depth h
Allowable
deviation of
groove depth
Groove width b Groove length L
1 0.10
±0.02 ≤0.3
20~40
2 0.15
3 0.20
4 0.30
±0.05 ≤0.5
5 0.40
6 0.50
7 0.60
8 0.80
9 1.00
6.4.4 Production and measurement
Size and allowable deviation of longitudinal groove shall meet requirements of
Table 1. Processing-production method is recommended to use spark erosion
machining method, machining method or corrosion method. Measurement
method is performed according to YB/T 145. It may use complex method or
other methods.
7 Testing equipment
Testing equipment usually consists of rotary scanning device, feed drive
mechanism, magnetization device, magnetic flux leakage sensor, electronic
instrument, mechanical transmission.
7.1 Rotary scanning device
Rotary scanning device leads magnetization device and magnetic flux leakage
sensor to surround round steel that is passing through in straight line, rotating
at a constant speed to form spiral scanning on round steel surface. In order to
reliably test defect’s leakage magnetic field, polar boots of magnetization device
rotate around round steel at a constant speed. Magnetic flux leakage sensor
sticks on round steel surface or keeps a constant spacing from round steel
surface.
7.2 Feed drive mechanism
Feed drive mechanism ensures that round steel concentrically passes through
rotary scanning device, making polar boots of magnetization device and
magnetic flux leakage sensor remain a constant clearance with round steel.
7.3 Magnetization device
Magnetization device applies magnetic field to round steel testing area that acts
on magnetic flux leakage sensor, so as to make it near saturation.
Magnetization device can be permanent magnet, direct current electromagnet
or alternating current electromagnet. When permanent magnet is used, in order
to achieve a suitable level of magnetization, there shall be means to adjust
magnetic pole gap. Excitation current of direct current electromagnet or
alternating current electromagnet shall be continuously adjustable; and there
shall be current intensity display device.
7.4 Magnetic flux leakage sensor
Sensor is used to test defective magnetic field in round steel. Magnetic flux
leakage sensor consists of one or more detection elements. It is used to test
magnetic flux change. Detection element of magnetic flux leakage sensor can
be induction coil, Hall element, magnetic sensitive diode, magnetic control
switch or magnetic resistance. To ensure testing sensitivity and signal-to-noise
ratio, the maximum axial width of each detection element in sensor is 30 mm.
In magnetic flux leakage sensor, there shall be a sufficient number of detection
elements (i.e. sensor length) to ensure that when scanning round steel surface
at a required speed, it shall achieve 100% scanning.
Depth and orientation of surface defect affect amplitude of receiving signal.
During testing, as spacing between magnetic flux leakage sensor and round
steel increases, sensitivity shall be significantly reduced. Therefore, sensor
shall be remained clean and stably contact with round steel surface. If there is
gap, it shall ensure that sensor remains a constant distance from round steel
surface.
7.5 Magnetic flux leakage testing instrument
Magnetic flux leakage testing instrument is used to amplify and process signals
from sensor and implement an alarm. Each channel shall be able to respectively
control respective sensitivity and threshold, so as to independently set
threshold to determine as waste. Magnetic flux leakage testing instrument shall
have marking function to record testing signal and control detected defect.
Magnetic flux leakage testing instrument shall especially pay attention to
prevent noise interference.
7.6 Mechanical transmission
Mechanical transmission makes tested round steel concentrically pass through
testing host (rotary scanning device) at a constant speed. According to different
testing mode, mechanical transmission can drive round steel spirally forward or
straightly forward.
8 Testing conditions and steps
8.1 Testing conditions
8.1.1 Testing is usually carried out after round steel is processed.
8.1.2 The ratio of surface roughness of tested round steel to specified artificial
defect size is not greater than 1:3. There shall be no iron filings, no burrs at the
end. Straightness meets the requirements of testing equipment.
8.1.3 Overall performances of testing system such as signal-to-noise ratio,
circumferential sensitivity difference, false negative rate, false positive rate, end
dead zone and stability shall meet requirements of YB/T 4289.
8.1.4 Magnetic flux leakage testing equipment shall be calibrated regularly
(calibration period is generally less than 1 year). It shall be used within validity
period.
8.1.5 Testing equipment shall be operated by testing personnel who have
obtained technical qualification of Level 1 and above identified by relevant
departments in accordance with the requirements of GB/T 9445. When it is
tested by a third party, it must be approved by both parties. The person who
issues testing report shall obtain technical qualification certificate of Level 2 and
above identified by relevant department in accordance with the requirements of
GB/T 9445.
8.2 Testing steps
8.2.1 Power on, pre-heating of instrument
Testing instrument shall be powered on, preheated before debugging, so as to
ensure stable performance during instrument use.
8.2.2 Equipment adjustment
8.2.2.1 Perform adjustment of scanning device, adjustment of testing sensitivity
for equipment.
8.2.2.2 Adjustment of scanning device: according to round steel size and testing
requirements, adjust probe scanning speed and round steel running speed, so
as to endure probe coverage. Relative to round steel, probe is fed spirally. It
shall ensure probe performs 100% scanning to round steel surface. At the same
time, there shall be a repeated coverage that is no less than 10%.
8.2.2.3 Adjustment of testing sensitivity: in order to fully display artificial defect
on comparative sample, adjust variable parameters such as magnetization
current, gain and filtering.
8.2.3 Tested sensitivity
Before testing, based on the above adjustments, use selected testing speed to
continuously run comparative sample. Ensure it passes at least 3 times. All
artificial defects on comparative sample each time shall be able to alarm reliably.
Use as tested sensitivity.
8.2.4 Testing
Perform testing after the above debugging is completed.
8.2.5 Equipment calibration
When equipment is continuously used, it shall at least calibrate once every 4h
according to steps in 8.2.3. If requirements are met, it shall continue testing;
otherwise conduct re-debugging according to 8.2.2~8.2.3. Re-test round steel
that has been calibrated by the previous equipment.
8.2.6 End blind area testing
End blind area of round steel may use other testing methods to ensure its
quality (excluding coil round steel wire).
9 Result determination
9.1 Quality level
Artificial defect size (groove depth, groove width, groove length) can, according
to round steel product standard, select sizes in Table 1. Or agreed by the
supplier and the purchaser in contract, quality level is carried out according to
Table 1. Selection of quality level shall consider factors such as surface
roughness, straightness and machining status of tested round steel.
9.2 Accepted product
For round steel that has been tested as above, if there is no super alarm
threshold defect signal, it shall be determined that it has passed magnetic flux
leakage testing.
9.3 Suspicious product
During round steel testing (excluding coil round steel wire), if there is super
alarm threshold defect signal, it shall be determined as suspicious product of
magnetic flux leakage testing. At this moment, re-perform magnetic flux leakage
testing according to the method specified based on this Standard. During re-
testing of magnetic flux leakage, if there is no super alarm threshold defect
signal, this round steel shall be determined that it has passed magnetic flux
leakage testing. If super alarm threshold defect signal appears again, it shall be
processed as suspicious product.
9.4 Disposal of suspicious product
For suspicious product, accord......
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