This standard specifies the methods and grading of results for ultrasonic crack detection of marine steel forgings.
This standard is applicable to direct contact pulse reflection ultrasonic crack detection for marine steel forgings with nominal thickness or diameter greater than 100mm.
This standard is not applicable to such coarse-grained materials as austenitic stainless steel, nor the transverse wave crack detection for annular and cylindrical forgings with the ratio of inner radius to outer radius less than 72%.
2 Normative references
ZBY 230 General technical specification for A-mode ultrasonic crack detector
ZBY 232 Technical conditions for No. 1 standard test block for ultrasonic crack detection
3 Crack detection operator
The crack detection operator must have the Ultrasonic Crack Detection Qualification Certificate issued by the China Accreditation Committee for Ship Non-destructive Testing Qualification.
4 Crack detection device
4.1 Crack detector
A-mode ultrasonic crack detector is used, and its properties shall meet ZBY 230.
4.2 Probe
4.2.1 The nominal frequency of the probe is 2.5 MHz, and 1.25 MHz or 5 MHz may also be used.
4.2.2 The wafer diameter of the normal probe is 20 mm, and probes with diameter of 28 mm or 14 mm may also be used.
4.2.3 The hard protective film material of the probe is alumina ceramics, and the soft protective film material is polyurethane soft film.
4.3 Test blocks
4.3.1 Standard test block
The standard test block for detecting instruments and probes is No.1 standard test block, which shall meet the requirements of ZBY 232.
4.3.2 Reference test block
The reference test block is CTK-D, and the dimension of the test block is shown in Figure 1.
4.3.2.1 Technical requirements for CTK-D test block
The dimensional deviation is ±0.1 mm, and the test block is made of the same materials with the forging or materials with same or similar acoustic characteristics as the forging. The test block shall be free of defects with a diameter greater than 1 mm flat-bottomed hole equivalent in its inner part. The test block shall be normalized before processing, and the grain size shall be Grade 7.
4.3.2.2 Application of CTK-D test block
Place the probe at place a or b of the CTK-D test block (Figure 1), and adjust the time axis scale by multiple reflections of the bottom wave of the test block. The flat bottom hole of φ4×200 is used as the reference for adjusting or approving crack detection sensitivity. Three flat-bottomed holes of φ8 mm×40 mm, φ4 mm×30 mm, and φ4 mm×20 mm are used for quantitative reference of near-field defects.
4.3.3 Other test blocks
Other test blocks conforming to ZBY 232 may also be used.
4.4 Coupling medium
Engine oil, transformer oil, glycerin, or other coupling medium with good sound permeability or wettability shall be used. The same coupling medium shall be used for sensitivity calibration and crack detection. For forgings with small curvature radius, the viscosity of coupling medium shall be appropriately increased.
