GB/T 6402-2024 English PDF (GBT6402-2024)

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GB/T 6402-2024: Method for ultrasonic testing of steel forgings
GB/T 6402-2024
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.040.20
CCS H 26
Replacing GB/T 6402-2008, GB/T 1786-2008
Method for Ultrasonic Testing of Steel Forgings
ISSUED ON: SEPTEMBER 29, 2024
IMPLEMENTED ON: APRIL 1, 2025
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative References ... 5
3 Terms and Definitions ... 5
4 Terms of Agreement ... 6
5 General Requirements ... 6
6 Testing Equipment ... 8
7 Comparison Test Block ... 8
8 Testing ... 9
9 Classification ... 14
10 Assessment of Discontinuity ... 17
11 Recording Levels and Acceptance Criteria ... 17
12 Testing Report ... 20
Appendix A (informative) Maximum Testable Depth of Circumferential Shear Wave
Scanning ... 22
Appendix B (informative) Method of Sensitivity Adjustment Using Workpiece Bottom
Wave ... 24
Appendix C (normative) Ultrasonic Testing of Forging Tortillas ... 26
Appendix D (informative) Correspondence between DAC (%) Amplitude and dB Value
... 29
Method for Ultrasonic Testing of Steel Forgings
1 Scope
This document specifies the general requirements, testing equipment, comparison test block,
testing implementation, classification, assessment, recording levels, acceptance standards and
testing report of ultrasonic testing of steel forgings.
This document is applicable to ultrasonic pulse reflection testing of ferritic, martensitic and
ferritic-martensite steel forgings, austenitic and austenitic-ferritic stainless-steel forgings. It
also applies to the ultrasonic testing of forged high-temperature alloys and alloy steel tortillas.
Steel forgings with other structures may take this as a reference.
2 Normative References
The content of the following documents constitutes indispensable clauses of this document
through normative references in the text. 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 9445 Non-destructive Testing - Qualification and Certification of NDT Personnel
GB/T 12604.1 Non-destructive Testing - Terminology - Ultrasonic Testing
GB/T 20737 Non-destructive Testing - General Terms and Definitions
GB/T 23905 Non-destructive Testing - Blocks for Ultrasonic Testing
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 39239 Non-destructive Testing - Ultrasonic Testing - Characterization and Sizing of
Discontinuities
GB/T 39242 Non-destructive Testing - Ultrasonic Testing - Sensitivity and Range Setting
3 Terms and Definitions
The terms and definitions defined in GB/T 12604.1 and GB/T 20737 are applicable to this
document.
the integrity of the finished product, then, it shall be removed.
NOTE: suitable coupling agents include water (with or without anti-corrosion agents or softeners),
grease, oil, glycerin and aqueous pastes, etc.
5.3 Timing of Testing
Unless otherwise specified in the product standard, ultrasonic testing shall be performed after
final heat treatment. Forgings that cannot be tested after the final heat treatment shall be tested
at a certain suitable stage before that. For cylindrical and rectangular forgings that require
drilling, ultrasonic testing should be performed before drilling.
5.4 Testing Procedures
5.4.1 Ultrasonic testing shall be performed in accordance with testing procedures. When it is
specified by a product standard, the testing procedures shall be submitted to the demand-side
for approval before testing.
5.4.2 The testing procedures shall be one of the following:
---product technical specifications;
---special-purpose procedures;
---designated part of this document.
5.4.3 The testing procedures shall at least include the following content:
---a description of the workpiece under test;
---reference documents;
---qualification and certification requirements for testing personnel;
---timing of testing;
---testing areas specified in the applicable quality grade;
---requirements for the condition of the testing surface;
---coupling agent;
---a description of testing equipment and accessories;
---equipment performance inspection and setup;
---scanning mode;
---a description and sequence of testing operations;
---record / rating;
---discontinuity characterization;
---acceptance criteria;
---testing report.
6 Testing Equipment
6.1 Ultrasonic Testing Instrument
The ultrasonic testing instrument shall comply with the requirements of GB/T 27664.1.
6.2 Probes
6.2.1 Conventional straight probe and angle probe shall comply with the requirements of GB/T
27664.2. If further information is required, other probes may be used for supplementary testing,
but the supplementary probes cannot be used for the initial discontinuity testing.
6.2.2 The nominal frequency of the probes is between 1 MHz ~ 10 MHz.
6.2.3 The nominal diameter of the transducer shall be between 10 mm ~ 40 mm.
6.2.4 The refraction angle of the angle probe shall be between 35 ~ 70. The effective area of
the nominal transducer shall be between 20 mm2 ~ 625 mm2.
6.2.5 The near-surface testing may use double crystal probe.
6.2.6 The shape grinding method of the probe contact surface shall comply with GB/T 39242.
6.3 Combined Equipment Performance Inspection
The performance of combined equipment (ultrasonic testing instrument and probe) shall be
regularly inspected.
7 Comparison Test Block
7.1 The production and inspection of comparison test block shall comply with the requirements
of GB/T 23905.
7.2 When adopting the Distance Amplitude Curve (DAC) technique for sensitivity setting and
the amplitude of the reflector is referenced to determine the size of the discontinuity,
comparison test block shall be provided. The surface condition of the comparison test block
shall be the same or similar to that of the workpiece under test. Unless otherwise specified, the
comparison test block shall be able to cover at least 3 artificial reflectors throughout the entire
testing depth range.
The testing sensitivity shall ensure the testing of the minimum discontinuity required by the
recording level in the specified quality grade. The methods described in 8.3.2 and 8.3.3 shall be
used. The corresponding probe shall be used to set the testing sensitivity, and the setting
procedures shall comply with the requirements of GB/T 39242.
8.3.2 Straight probe
Testing sensitivity can be determined using one of the following methods:
a) The Distance Amplitude Curve (DAC) method;
b) The Distance Gain Size (DGS) method (only applicable when the probe contact
surface has not been grounded);
c) When the testing surface is parallel to the bottom surface or is a cylindrical surface,
and the thickness or diameter is greater than 3 times the near-field area of the probe,
the bottom wave reflection method can be used (see Appendix B).
8.3.3 Angle probe
Testing sensitivity can be determined using one of the following methods:
a) The DAC method, and a 3 mm diameter transverse hole shall be used;
b) The DGS method (only applicable when th...