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GB/T 34370.5-2017 PDF in English


GB/T 34370.5-2017 (GB/T34370.5-2017, GBT 34370.5-2017, GBT34370.5-2017)
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GB/T 34370.5-2017: PDF in English (GBT 34370.5-2017)

GB/T 34370.5-2017
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 97.200.40
Y 57
Nondestructive testing of amusement equipment -
Part 5. Ultrasonic testing
ISSUED ON. SEPTEMBER 29, 2017
IMPLEMENTED ON. APRIL 01, 2018
Issued by. General Administration of Quality Supervision, Inspection and
Quarantine;
Standardization Administration of PRC.
Table of Contents
Foreword ... 4 
1 Scope ... 5 
2 Normative references ... 5 
3 Terms and definitions ... 6 
4 Summary of method ... 9 
5 Safety requirements ... 10 
6 Personnel requirements ... 10 
7 Testing equipment ... 10 
8 Testing procedure ... 16 
9 Preparation before testing ... 18 
10 Ultrasonic testing and quality grading of raw materials and components .. 20 
11 Ultrasonic testing of welded joint of amusement equipment ... 41 
12 Ultrasonic testing of in-use amusement equipment ... 69 
13 Ultrasonic thickness measurement of pulse reflection type ... 76 
14 Ultrasonic test report ... 77 
Appendix A (Normative) Performance requirements of double-crystal straight
probe ... 78 
Appendix B (Normative) Lateral-wave testing of steel plates for amusement
equipment ... 80 
Appendix C (Normative) Lateral-wave testing of steel forgings for amusement
equipment ... 83 
Appendix D (Informative) Method for adjusting the bottom-wave of workpiece
... 85 
Appendix E (Normative) Ultrasonic angle beam probe testing of steel forgings
for amusement equipment ... 87 
Appendix F (Normative) Axial lateral-wave testing of seamless steel tubes for
amusement equipment ... 90 
Appendix G (Normative) Ultrasonic testing method and quality grading of cast
iron parts ... 92 
Appendix H (Normative) Ultrasonic testing of austenitic stainless-steel butt-
welded joint ... 100 
Appendix I (Normative) Determination of the difference in acoustic energy
transmission loss ... 105 
Appendix J (Informative) Dynamic waveform of echo ... 108 
Appendix K (Normative) Phased array ultrasonic testing method ... 112 
Appendix L (Normative) Determination of flaw height by -6 dB method ... 125 
Appendix M (Normative) Typical calibration block for measurement ... 128 
Nondestructive testing of amusement equipment -
Part 5. Ultrasonic testing
1 Scope
This part of GB/T 34370 specifies the requirements for ultrasonic testing
methods, quality grading, ultrasonic thickness measurement methods for
amusement equipment.
This part applies to ultrasonic testing of metal raw materials, parts, welded joints
for amusement equipment, as well as ultrasonic testing of metal parts and
welded joints for use in amusement equipment.
2 Normative references
The following documents are essential to the application of this document. For
the dated documents, only the versions with the dates indicated are applicable
to this document; for the undated documents, only the latest version (including
all the amendments) are applicable to this standard.
GB/T 7233.1 Steel castings - Ultrasonic examination - Part 1. Steel castings
for general purposes
GB/T 11344 Non-destructive testing - Practice for measuring thickness by
ultrasonic pulse-echo contact method
GB/T 12604.1 Non-destructive testing - Terminology - Terms used in
ultrasonic testing
GB/T 20306 Amusement devices terminology
GB/T 20737 Non-destructive testing - General terms and definitions
GB/T 27664.1 Non-destructive testing - Characterization and verification of
ultrasonic test equipment - Part 1. Instruments
GB/T 27664.2 Non-destructive testing - Characterization and verification of
ultrasonic test equipment - Part 2. Probes
GB/T 29302 Non-destructive testing instruments - Characterization and
verification of phased array ultrasonic examination systems
GB/T 34370.1 Nondestructive testing of amusement equipment - Part 1.
General requirement
JB/T 8428 Non-destructive testing - General specification for ultrasonic
blocks
JB/T 9214 Non-destructive testing - Test methods for evaluating
performance characteristics of A-scan pulse-echo ultrasonic testing systems
JB/T 10062 Testing methods for performance of probes used in ultrasonic
flaw testing
JB/T 11604 Non-destructive testing instruments - Ultrasonic thickness gauge
JB/T 11731 Non-destructive testing - General specification for ultrasonic
phased array probe
JB/T 11779 Non-destructive testing instrument - Specifications for phased
array ultrasonic detectors
3 Terms and definitions
The terms and definitions as defined in GB/T 12604.1, GB/T 20306, GB/T
20737, GB/T 34370.1 as well as the following terms and definitions apply to this
document.
3.1
Loss of back reflection caused by flaws BG/BF (dB)
The ratio of the first bottom-wave amplitude BG in a flaw-free region which
is close to the flaw to the first bottom-wave amplitude BF in the flaw region,
expressed by the value of sound pressure level (dB).
3.2
Basic and scanning sensitivities
The basic sensitivity generally refers to the recording sensitivity, which is
usually used for the quantitation of flaws and the classification of flaws. The
scanning sensitivity mainly refers to the actual testing sensitivity. In order not
to miss recording flaws or certain specific flaws, to ensure the safety of the
amusement equipment, the actual testing is usually carried out by a high
testing sensitivity for scanning. In principle, the scanning sensitivity shall not
be lower than the basic sensitivity.
probes.
7.1.2 Ultrasonic testing equipment shall have a certificate of product quality or
a certificate of conformity.
7.2 Testing equipment
7.2.1 Basic requirements for type-A pulse reflection ultrasonic tester.
a) For the type-A pulse reflection ultrasonic detector, the error of the
measured value of the transmitted pulse’s repetition frequency as
compared with the nominal value is not more than 10%; the error of the
measured value of the transmitted pulse’s voltage as compared with the
nominal value is not more than 20%; the error of the measured value of
the transmitted pulse’s width as compared with the nominal value is not
more than 10%; the rising time of the transmitted pulse is not more than
25 ns;
b) For the type-A pulse reflection ultrasonic detector, the measurement of the
working frequency based on -3 dB shall include at least the range of 0.5
MHz ~ 10 MHz. The error between the measured value and the nominal
value of the upper and lower limits of each band is not more than 20%;
c) The Type-A pulse reflection ultrasonic detector shall have a continuously
adjustable attenuation or gain of more than 80 dB. The minimum stepping
stage shall be not more than 2 dB per step. The accuracy is that the
cumulative error in any continuous 20 dB is not more than 1.7 dB, the
cumulative error in any continuous 60 dB is not more than 3 dB;
d) The performance indicators are tested according to the requirements of
GB/T 27664.1.
7.2.2 Basic requirements for ultrasonic thickness gauges.
a) When the ultrasonic thickness gauge is used for thickness measurement
of wall thickness less than 10 mm, the maximum allowable indication error
is ±0.1 mm; when it is used for thickness measurement of wall thickness
greater than 10 mm, the maximum allowable indication error is ± (0.1+H/
100) mm, where H is the nominal value of the standard-thickness block;
b) The indication stability of the ultrasonic thickness gauge is not more than
0.2 mm;
c) The performance indicators are tested according to the requirements of
JB/T 11604.
7.2.3 Basic requirements for phased array ultrasonic detectors.
be not less than 32 dB, the sensitivity margin of the instrument’s angle
beam probe combination shall be not less than 42 dB;
e) The far-field resolution of the instrument’s direct probe combination shall
be not less than 20 dB, the far-field resolution of the instrument’s angle
beam probe combination shall be not less than 12 dB;
f) When the maximum testing sound path of the workpiece is reached, the
effective sensitivity margin shall not be less than 10 dB;
g) The performance indicators are tested according to the requirements of
JB/T 10062 and JB/T 9214.
7.4.2 System performance requirements for ultrasonic thickness gauges and
probes.
a) The error of the combined frequency of the instrument and the probe as
compared with the nominal frequency shall not exceed ±10%;
b) The performance indicators are tested according to the requirements of
JB/T 10062.
7.4.3 System performance requirements for phased array ultrasonic detectors
and probes.
a) The performance of the phased array ultrasonic testing system includes.
determining the beam profile, the beam deflection range, the array
element’s validity, the software calculation function, the receiver gain
linearity;
b) The performance indicators are tested according to the requirements of
GB/T 29302.
7.4.4 It shall test the combined performance of the test instrument and the probe
in the following cases.
a) Newly purchased ultrasonic detectors and/or probes;
b) After the detector and probe are repaired or their main parts replaced;
c) When the testing personnel has doubts.
7.5 Test block
7.5.1 Test block for type-A pulse reflection ultrasonic testing
7.5.1.1 Standard test block
7.5.1.1.1 Standard test block means a block of material which has the specified
7.6.1.1 Calibration, verification and intermediate verification shall be performed
on standard test blocks.
7.6.1.2 During calibration, verification and intermediate verification shall be
such that the main sound beam of the probe is vertically aligned with the
reflecting surface of the reflector, to obtain a stable and maximum reflected
signal.
7.6.2 Calibration, verification, intermediate verification or inspection
7.6.2.1 It shall carry out at least one calibration of the ultrasonic detector. The
calibration requirements shall meet the requirements of the calibration
procedures of ultrasonic detector.
7.6.2.2 It shall carry out at least one verification of the surface corrosion and
mechanical damage of the test block annually.
7.6.2.3 It shall carry out the immediate verification and recording of the system
performance of the ultrasonic detector and probes at least once every 6 months.
The testing requirements shall meet the requirements of 7.4.
7.6.2.4 Before each testing, check whether the appearance of the equipment,
cable connection and display of power-on signal are normal.
7.6.2.5 During calibration, immediate verification and inspection, any controller
that affects the linearity of the instrument (such as suppression or filter switches)
shall be placed in the “off” position or at the lowest level.
7.7 Recheck of newly-purchased probes and testing process
7.7.1 Determination of newly-purchased probe
7.7.1.1 The newly-purchased probe shall have the specification of probe’s
performance parameters. Before the use of the newly-purchased probes, it
shall determine such main parameters as leading-edge distance, K-value, main
beam deviation, sensitivity margin, resolution, and so on.
7.7.1.2 The determination method shall be according to the relevant provisions
of JB/T 10062 and meet the requirements.
7.7.2 Pre-testing determination of instrument and probe system
7.7.2.1 For the use of the instrument-angle beam probe system, before testing,
it shall determine the leading-edge distance, K-value, main beam deviation,
adjust and re-check the scanning range and the scanning sensitivity. Before
each testing, it shall set the time baseline and sensitivity, meanwhile refer to the
impact of temperature. When the time baseline and sensitivity are set, the
difference between the temperature and the tested workpiece does not exceed
far as possible during the testing.
9.2.2 The surface quality of the tested workpiece shall pass the visual
inspection. All rust, splash or dirt that affect ultrasonic testing shall be removed,
the surface roughness shall meet the testing requirements. The irregular state
of the surface shall not affect the correctness and completeness of the testing
results, otherwise it shall be properly treated.
9.3 Requirements for scanning coverage
9.3.1 It shall be ensured that the ultrasonic beam may scan the entire testing
area of the workpiece during the testing.
9.3.2 Each scanning coverage of the probe shall be greater than 15% of the
diameter of the probe or preferentially meet the testing coverage requirements
of the corresponding clauses.
9.4 Requirements for probe’s movement speed
9.4.1 The scanning speed of the probe shall not exceed 150 mm/s.
9.4.2 When using automatic alarm device for scanning, the scanning speed
shall be determined by comparison test.
9.5 Requirements for scanning sensitivity
9.5.1 The scanning sensitivity shall normally not be lower than the basic
sensitivity and shall be according to the relevant clauses.
9.5.2 Before each testing, the set temperature of time baseline, the sensitivity
shall differ from the temperature of the tested workpiece for not more than 15 °C.
9.6 Coupling agent
9.6.1 It shall use the coupling agents that have good sound transmission and
do not damage the testing surface, such as engine oil, paste, glycerin, water.
9.6.2 The selection of the coupling agents shall take into account the
requirements of the conditions and environment of use.
9.7 Sensitivity compensation
9.7.1 Coupling compensation. In the testing and flaw quantitation, it shall
compensate the coupling loss caused by surface roughness.
9.7.2 Attenuation compensation. In the testing and flaw quantitation, it shall
compensate the testing sensitivity degradation and flaw quantitation error
caused by material attenuation.
the ratio of the height of the first reflected wave of flaw to the height of the
first reflected wave of the bottom-surface is 50%. At this time, the moving
distance of the probe’s center is the indicated length of the flaw, the
probe’s center point is the boundary point of the flaw. The results as
measured by the two methods are based on the more serious ones.
c) When using a single straight probe to determine the boundary range or
indicated length of the flaw, move the probe to reduce the height of the
reflected wave of the flaw wave to 25% of the full-scale of the fluorescent
screen under the basic sensitivity condition or otherwise allow the ratio of
the height of the first reflected wave of flaw to the height of the first
reflected wave of the bottom-surface is 50%. At this time, the moving
distance of the probe’s center is the indicated length of the flaw, the
probe’s center point is the boundary point of the flaw. The results as
measured by the two methods are based on the more serious ones.
d) When determining the boundary range or indicated length of the flaw in
10.1.7.1 c), move the probe (single straight probe or double straight probe)
to increase the height of the first reflected wave of the bottom-surface to
50% of the full-scale of the screen. At this point, the moving distance of
the probe’s center is the indicated length of the flaw, the probe’s center
point is the boundary point of the flaw.
e) When the thickness of the plate is small and it is necessary to use the
second flaw wave and the second bottom wave to evaluate the flaw, the
testing sensitivity shall be calibrated by the corresponding second
reflected wave.
10.1.8 Evaluation method of flaws
10.1.8.1 Rules for evaluating the indicated length of flaw.
a) The maximum indicated length of a single flaw is used as the indicated
length of the flaw;
b) If the indicated length of a single flaw is less than 40 mm, it may not record
it.
10.1.8.2 Rules for the evaluation of the indicated area of a single flaw.
a) The indicated area of a single flaw is used as the single indicated area of
this flaw;
b) When the adjacent spacing between several flaws is less than 100 mm or
the spacing is less than the indicated length of the adjacent small flaw
(whichever is larger), use the sum of the flaw area of all pieces as the
indicated area of a single flaw.
b) Determination of the basic sensitivity of the double-crystal straight probe.
Use a corresponding test block, to sequentially test a set of Φ2 flat-bottom
hole test blocks (at least 3) of different inspection distances. Adjust the
attenuator to make the distance-amplitude curve of the double-crystal
straight probe, use it as the basic sensitivity.
10.2.5.2 The scanning sensitivity shall generally not be lower than the
equivalent diameter of Φ2 mm flat-bottom hole at the maximum testing sound
path.
10.2.6 Testing
10.2.6.1 The coupling method is generally a direct contact method.
10.2.6.2 Sensitivity compensation. It shall carry out coupling compensation,
attenuation compensation, curved-surface compensation according to the
actual situation during testing.
10.2.6.3 Scanning method.
a) Radial testing shall be performed by selecting a probe which has a smaller
wafer size as much as possible;
b) It shall carry out scanning along a spiral line or the circumference, the
travel shall overlap sometimes, the scanning plane shall cover the entire
cylindrical surface;
c) For the axial testing, it shall carry out scanning from the both end surfaces
of the bar, to avoid the impacts of edge effects on the testing results.
10.2.7 Determination and recording of flaws
10.2.7.1 The determination of the flaw is based on the amplitude of the reflected
wave. Generally, it shall use the distance-amplitude curve method or the
calculation method to determine the flaw equivalent.
10.2.7.2 When using the calculation method, if the material’s attenuation factor
exceeds 4 dB/m, it shall consider correction. The attenuation factor is
determined as specified in 10.3.6.3.
10.2.7.3 For the flaws in one of the following cases, it shall record its amplitude
and location.
a) A single flaw which has a reflected wave equivalent greater than Φ2 mm;
b) Flaw which has a loss of back reflection greater than 8 dB.
10.2.8 Quality grading
10.3.2.1 Testing shall generally be carried out after heat treatment and before
the machining of holes, benches and other structures. The surface roughness
of the testing surface is Ra ≤ 6.3 µm.
10.3.2.2 Forgings shall be subjected to longitudinal wave testing.
10.3.2.3 Forgings are generally to be tested by straight probes. The cylindrical
and annular forgings shall also be subjected to the angle beam probe testing.
10.3.2.4 When the thickness of the forging in the testing direction exceeds 400
mm, it shall be tested from the two opposite end faces.
10.3.2.5 The transverse wave testing of cylindrical and annular forgings shall
be carried out according to Appendix C. The scanning locations and acceptance
criteria shall be agreed upon by both parties through negotiation.
10.3.3 Selection of probe
10.3.3.1 The selection of straight probes shall meet the following requirements.
a) It shall use the single-crystal straight probe, the nominal frequency of the
probe shall be in the range of 1 MHz ~ 5 MHz;
b) The effective diameter of the single-crystal straight probe’s wafer shall be
in the range of Φ10 mm ~ Φ40 mm.
10.3.3.2 The selection of the angle beam probe shall meet the following
requirements.
a) The probe shall be in good contact with the tested workpiece;
b) The nominal frequency of the probe is mainly 2 MHz ~ 5 MHz, the area of
the probe’s wafer is 80 mm2 ~ 625 mm2.
10.3.4 Test block
10.3.4.1 The production of test blocks shall be according to the provisions of
7.5.
10.3.4.2 The control test block may be made of one of the following materials.
a) The excess part of the tested material (when the size is sufficient);
b) Materials of the same steel type and heat treatment status as the tested
material;
c) Materials that have the same or similar acoustic properties as the tested
material.
not applicable to ultrasonic testing of cast steel welded joints, butt-welded joints
of steel tubes which have an outer diameter of less than 159 mm, fillet welds of
tube sockets which have an inner diameter of less than or equal to 200 mm,
nor for the ultrasonic testing of the longitudinal welded joints which have an
outer diameters smaller than 250 mm or an inner-to-outer diameter ratio less
than 70%.
11.2 Grade of testing technology
11.2.1 Grading of testing technology
11.2.1.1 The grades of ultrasonic testing technology are divided into A, B, C.
11.2.1.2 The selection of the technology grades of ultrasonic testing shall
comply with the provisions of relevant specifications, standards and design
drawings for manufacturing and installation. They shall be selected according
to the importance of the components of the amusement equipment and the
relevant product standards. Ultrasonic testing of the welded joints of
amusement equipment during the manufacture and installation shall generally
be carried out by the use of the grade B ultrasonic testing technology. For the
welded joints of particularly importance, it may use the grade C ultrasonic
testing technology for testing.
11.2.2 Testing requirements for testing technologies of different grades
11.2.2.1 It is applicable to flat sheet’s butt-welded joints. Other forms of welded
joints may refer to it.
11.2.2.2 Grade A testing.
a) Grade A testing is suitable for the testing of welded joints which have a
workpiece of thickness 8 mm ~ 40 mm.
b) It may use an angle beam probe of refraction angle (K-value) to perform
testing at both sides of the single face of the welded joint by the direct-
wave method and the primary reflected wave method. If subject to the
restrictions of conditions, it may also choose double-face single-sided or
single-face single-sided testing.
c) It generally does not require testing of lateral flaws.
11.2.2.3 Grade B testing.
a) Grade B is suitable for the testing of welded joints which have a workpiece
of thickness 8 mm ~ 200 mm.
b) When testing the longitudinal flaws, when the thickness of the base-metal
is 8 ≤ t < 40 mm, use a K-value probe to carry out the single-face double-
sided testing of the welded joint by the primary reflection method; when
the thickness of the base-metal is 40 mm ≤ t < 100 mm, it may use a K-
value probe to carry out double-face double-sided testing of the welded
joint, it may also use two K-value probes to carry out the single-face
double-sided (double-face single-sided) testing of the welded joint; when
the thickness of the base-metal is 100 mm ~ 200 mm, it shall use two K-
value probes to carry out the double-face double-sided testing of the
welded joint by the use of direct wave.
c) Grade B shall be subjected to the testing of lateral flaws. In case of testing
by the use of angle beam probe, it may perform the oblique parallel
scanning at the edges of both sides of the welded joint, allowing the probe
to be 10° ~ 20° to the center line of the welded joint. For the base-metal
which has a thickness of 8 ≤ t ≤ 100 mm, it may use one type of probe to
carry out the single-face oblique parallel scanning. For the base-metal
which has a thickness of 100 < t ≤ 200 mm, it shall use two types of probes
to carry out single-face oblique parallel scanning.
11.2.2.4 Grade C testing.
a) Grade C is suitable for the testing of welded joints which have a workpiece
of thickness 8 mm ~ 400 mm.
b) When using the grade C testing, it shall smoothen the excess weld metal
of the welded joint. For the base-metal area of the welded joint which is
subjected to scanning by an angle beam probe, it shall use the straight
probe for testing, according to the method as specified in 11.4.4.7.
c) When testing the longitudinal flaws, when the thickness of the base-metal
is 8 ≤ t < 15 mm, use a K-value probe to carry out single-face double-sided
testing of the welded joint by the use of primary reflection method, it may
also use two types of K-value probes to carry out the single-face double-
sided (double-face single-sided) testing of the welded joint. When the
thickness of the base-metal is 15 mm ≤ t < 40mm, it shall use two types
of K-value probes to carry out the double-face double-sided testing of the
welded joint. When the thickness of the base-metal is 40 mm ≤ t < 100
mm, it shall use two types of K-value probes to carry out the double-face
double-sided testing of the welded joint. When the thickness of the base-
metal is 100 mm ≤ t < 400 mm, it shall use two types of K-value probes
and the direct wave to carry out the double-face double-sided testing of
the welded joint.
d) Grade C shall be used for testing of lateral flaws. In case of testing by the
angle beam probe, it may carry out the oblique parallel scanning at the
edges of both sides of the welded joint, allowing the probe to be 10° ~ 20°
to the center line of the welded joint. For the base-metal which has a
P - Span, in millimeters (mm);
t - Thickness of workpiece, in millimeters (mm);
K - The tangent of the refraction angle of the probe;
β - The refraction angle of the probe, in degrees (°).
c) When tested by the straight beam method, the width of the probe's moving
zone shall be greater than or equal to 0.75P.
11.4.5.3 Preparation of testing surface.
a) In the probe’s moving zone, it shall remove welding spatter, iron filings, oil
dirt, or other impurities. The testing surface shall be flat, to facilitate the
scanning of the probe. The surface roughness Ra shall be not more than
6.3 μm, it generally shall be polished. When using the straight beam
method for testing, the probe’s moving zone shall be greater than or equal
to 0.75P.
b) For the weld whose excess weld metal is removed, it shall grind the excess
weld metal to be flush with the adjacent base-metal. For the weld whose
excess weld metal is reserved, if there are undercuts, large ridges and
depressions on the surface of the weld, they shall also be ground
appropriately, and a smooth transition made to avoid affecting the
evaluation of the test results.
11.4.5.4 Testing of base-metal.
a) For grade C testing, make the sound beam of the angle beam probe pass
through the base-metal’s area. It shall first use the straight probe for
testing, to check the presence of delamination or other types of flaws that
affect the testing results of the angle beam probe. This testing is only
recorded, which does not belong to the acceptance testing of the base-
metal.
b) The key points of the base-metal testing are as follows.
1) Testing method. Contacted pulse reflection method, which uses a
straight probe with a frequency of 2 MHz ~ 5 MHz, the wafer’s diameter
is 10 mm ~ 25 mm;
2) Testing sensitivity. adjust the second bottom-wave of the flaw-free
position to 100% of the full-scale of the fluorescent screen;
3) Where the flaw signal’s amplitude exceeds 20% of the full-scale of the
fluorescent screen, the surface of the workpiece shall be marked and
recorded.
shall move the probe to the position where the maximum reflected wave signal
of the flaw occurs, measure the amplitude, determine its zone in the distance-
amplitude curve.
11.4.8.3 The determination of the flaw position shall be based on the position
of the maximum reflected wave of the flaw, it shall provide the position and
depth of the flaw on the weld.
11.4.8.4 The flaw’s equivalent diameter Φ shall be determined according to the
maximum reflection amplitude of the flaw. The flaw’s equivalent diameter Φ is
expressed by the equivalent diameter of flat-bottom hole. It is mainly used for
straight probe testing. It may be calculated by formula. The flaw’s equivalent
size can be determined by comparing the distance-amplitude curve with the test
block.
11.4.8.5 It shall use the maximum reflected amplitude of the flaw to determine
the indicated length ΔL of the flaw. The flaw’s indicated length ΔL is tested by
the following method.
a) When the flaw’s reflected wave has only one high point which is located
in or above the zone II, use the -6 dB method to measure its indicated
length;
b) When the peak-value of the reflected wave of the flaw changes, there are
multiple high points which are located in or above the zone II, it shall use
the tip -6 dB method to measure its indicated length;
c) When the flaw’s reflection peak is located in the zone I, if it is considered
necessary to record it, move the probe left and right to reduce the
amplitude to the evaluation line, thereby determining the flaw’s indicated
length.
11.4.9 Ev......
 
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.