GB/T 32547-2016 English PDF (GBT32547-2016)

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GB/T 32547-2016: Method for magnetic flux leakage testing of round steel
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
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 com...