GB/T 6402-2024Methods for the ultrasonic testing of steel forgings (English PDF)

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.

5.4.3 The testing procedures shall at least include the following content.

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.

8.1 Surface Condition

8.1.1 The scanned surface shall be free of defects, such as. scale, dirt, paint and pits that may affect coupling. If the above situation occurs, appropriate methods shall be used to remove or machine them, so as to satisfy the testing requirements.

8.1.2 When forgings are delivered in forged surface condition, if they can satisfy the specified quality grade inspection requirements, they can be directly tested. NOTE. when it is difficult to conduct comprehensive testing of the forging surface, the method of shot blasting, sandblasting or surface grinding can be used for surface treatment, so as to ensure acoustic coupling. Usually, it merely applies to quality grade 1.

8.2 Testing Range

8.2.1 Classification of forgings This document divides forgings into 4 categories in accordance with shape and production method, see Table

1.Categories 1, 2 and 3 are simply shaped forgings, and Category 4 is complexly shaped forgings or complex parts of forgings.

8.2.2 Simply shaped forgings

8.2.2.1 Table 2 provides the testing range of Categories 1, 2 and 3 forgings when scanning with

8.2.3 Complexly shaped forgings For complexly shaped forgings or complex parts of forgings (Category 4) and small-diameter forgings, the supply-side and the demand-side shall negotiate the scanning requirements, which shall at least include. probe angle, scanning direction and scanning range (grid or 100%).

8.3 Testing Sensitivity

8.3.1 General requirements 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

8.3.3 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.

8.3.3 Angle probe Testing sensitivity can be determined using one of the following methods.

8.3.4 Sensitivity in repeated testing If repeated testing is performed, the method of setting sensitivity is the same as

8.3.2 and 8.3.3.

8.4 Transmission Corrections

8.4.1 General requirements When the comparison test block is used to assess indications, the ultrasonic material attenuation and surface loss generated in the test block shall be consistent with that of the workpiece under test. Otherwise, transmission corrections shall be adopted to compensate for material attenuation and surface loss differences. When it is known that the attenuation is negligible, no correction is required.

8.4.3 Angle probe The comparison technology specified in GB/T 39242 can also be used for transmission correction.

8.5 Pulse Repetition Frequency If the pulse repetition frequency is adjustable, it should be high enough to ensure adequate screen brightness and testing of all relevant indications. When testing materials with long sound path and low attenuation, on the premise that no phantom waves are generated, the pulse repetition frequency shall be as high as possible.

8.6 Scanning

8.6.1 General requirements The minimum scanning range required shall depend on the category of forgings, and whether grid scanning or 100% scanning is used shall be specified in the contract. 8.6.2 100% scanning The overlap between two adjacent probe scan traces is at least 10% of the transducer size.

9.1.1 Type I diagram

9.1.1.1 As the probe moves, Type A display shows a single clear indication that smoothly rises to the maximum amplitude, and then, smoothly drops to 0 (see Figure 1). In Type A display, the X-axis is the time or sound path of the A-scan display at the fixed probe position. In the dynamic waveform diagram, the X-axis is the probe scanning displacement corresponding to the amplitude envelope curve, and the Y-axis is the echo amplitude.

9.1.1.2 Figure 1 is a dynamic echogram of the sound beam profile drawn with a transverse hole,

9.1.2 Type II diagram As the probe moves, Type A display shows a single clear indication that smoothly rises to the maximum amplitude, which is sustained with or without amplitude change, and then, smoothly falls to 0 (see Figure 2). In Type A display, the X-axis is the time or sound path of the A-scan display at the fixed probe position.