T9074-AS-GIB-010/271 Rev 1
B.2.7 Planar Discontinuity. Discontinuities, such as cracks, incomplete fusion or incomplete penetration that exhibit two-dimensional characteristics and have vertical height through the material.
B.2.8 Specular Reflection. A specular reflection is a direct reflection from any discontinuity.
B.2.9 Tip Signal. Energy generated from the sound beam that is diffracted from the tip of a planar discontinuity.
B.2.10 Volumetric Discontinuity. Embedded discontinuities, such as slag or porosity that exhibit three-dimensional characteristics (usually globular) and are typically not surface connected.
B.3 EQUIPMENT.
B.3.1 Ultrasonic Instrument. The ultrasonic inspection instrument shall be of the pulse-echo, A-scan type. The ultrasonic instrument shall meet the basic instrument qualification requirements specified (see 6.5.1.1). The instrument shall have the ability to correct for depth and surface distance when evaluating discontinuities on curved components if calibrations are performed on flat standards. B.3.2 Transducers. Straight beam and angle beam transducers used for characterization and sizing shall have a frequency range of 2.25 MHz to 10 MHz and beam angles of 45, 60, 70, and 80 degrees. The tolerance for each shear wave angle is ±3 degrees. The use of frequencies or beam angles outside this range shall require NAVSEA approval. When shear wave transducers are used, the actual beam angle shall be determined and used for all dimensioning calculations. B.3.3 Calibration Blocks and Reference Standards. Calibration standards shall be machined from the same material type or from acoustically similar material as defined in 6.2.1. The calibration standard shall contain notches that cover the full range of thickness being evaluated. Flat standards may be used on all diameters provided the UT instrument has a built in function for curvature correction. If curvature correction is not available, calibration standards shall have the same radius within 5 percent of the material being examined. Calibration standards for the 30-70-70 ID creeping wave sizing technique shall have approximately the same thickness as the piece being inspected.
B.3.4 Couplant. Couplant shall be in accordance with 6.3.4.
B.4 CALIBRATIONS.
B.4.1 Calibration. The instrument shall be calibrated as required over the full range of component thickness. For longitudinal and shear wave transducers, tip signals from the calibration notches shall be calibrated to 50-60 percent full screen height. Tip signals are typically low amplitude and require additional gain. The gain may be increased from 6 to 14 dBs for exploring and evaluating discontinuities. Gain settings above +14 dB are not allowed without NDT Examiner approval. B.4.1.1 Curved Surfaces. When inspecting welds where the material is curved in the direction of the sound beam, discontinuities will be measured deeper on the instrument CRT screen and digital depth than they are actually located. When calibration is performed on flat calibration blocks, electronic curvature correction shall be used to correct for discontinuity depth and projected distance. The curvature correction shall be turned off when calibration of the instrument is performed on flat calibration blocks. Once the calibration is complete, the curvature correction shall be programmed as applicable, and verified by comparing the digital depth reading of a notch in the flat calibration block to a “check” value supplied by the cognizant NDT Examiner for the particular radius and transducer angle being used. B.4.2 Calibration Interval. Calibration shall be verified prior to scanning and at the completion of the inspection. A field standard that includes intermediary reflectors may be used in lieu of a complete calibration check when performed at least once every 4 hours during the inspection, at any change of equipment (instrument, search unit, cable, etc.), or whenever the calibration is in doubt. If the calibration check indicates that a reading is more than 10 percent of the true value or 0.050 inch, whichever is less, from the original calibration reading, the equipment shall be recalibrated and all components inspected since the last valid calibration shall be re-inspected.
B-2
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