T9074-AS-GIB-010/271 Rev 1
B.6.5 Transducer Skew. The transducer shall be skewed from 0 to approximately 30 degrees off normal and the signal shall be monitored to determine whether or not the signal is maintained. A planar discontinuity will result in a rapid drop in signal amplitude. A volumetric discontinuity will result in more consistent signal amplitude, regardless of the orientation of the transducer to the discontinuity. B.6.6 Orbit the Discontinuity. The transducer shall be orbited around the discontinuity, always oriented toward the center of the discontinuity to peak the signal. The reflected signal shall be monitored as the discontinuity is circled 360 degrees. The amplitude of the signal in the longitudinal and transverse directions (relative to the weld) shall be compared. A planar discontinuity will exhibit a significant difference in signal amplitude between the two major planes of the discontinuity. Volumetric discontinuities will exhibit more consistent signal amplitude. B.6.7 30-70-70 Creeping Wave Technique. The 30-70-70 creeping wave technique uses a search unit (e.g., WSY 70) that produces a shear wave at a nominal angle of 30 degrees and a mode-converted longitudinal wave at a nominal angle of 70 degrees. The scanning surface and back surface must be reasonably parallel to apply this technique. The 30-70-70 creeping wave technique does not measure the discontinuity depth but provides relative discontinuity height. The 30-70-70 creeping wave technique shall be applied to determine if the discontinuity is ID connected (i.e. observed presence of the CE-2 signal). The discontinuity shall be scanned with the 30-70-70 ID creeping wave technique and interrogated from all directions.
B.7 SIZING DISCONTINUITIES.
B.7.1 Sizing Volumetric Discontinuities/Rapid Drop Method. Volumetric discontinuities shall be sized using the rapid drop method. The recorded depth shall be the minimum and maximum perpendicular distance from the scanning surface. The range of depth is determined by: a. Maximizing the indication. b. Moving the search unit toward the discontinuity and recording the depth where the indication begins to drop rapidly toward the baseline. c. Moving the search unit away from the discontinuity and recording the depth where the indication begins to drop rapidly toward the baseline. B.7.2 Sizing Planar Discontinuities. Planar discontinuities shall be examined for signals originating from discontinuity tips. Use AATT with shear wave angles of 45, 60, and 70 degrees and the 80-degree HAL technique for sizing planar discontinuities. The half-skip technique shall be used where possible to evaluate all planar discontinuities. Full skip should only be used when the half skip techniques prove inconclusive or when it’s not practical to inspect using the half skip technique (see scanning considerations noted in B.5.5). Planar discontinuities that do not produce tip signals shall be sized by the rapid drop method. B.7.2.1 Straight Beam Longitudinal Wave Technique. The discontinuity shall be scanned with a dual element straight beam transducer. A dual element transducer may detect tip signals (AATT Technique) for a planar discontinuity. Some discontinuities such as an embedded crack may display both a top and bottom tip simultaneously. The minimum and maximum discontinuity dimensions shall be recorded from these tip signals. B.7.2.2 Absolute Arrival Time Technique (AATT). Shear wave transducers with refracted angles of 45, 60, and 70 degrees shall be used for the AATT. The direct arrival time from the tip signal is measured. This measurement is the ligament above the discontinuity, or the distance from the discontinuity tip signal to the examination surface. It is necessary to maximize the tip signal for calibration and measurement when using the AATT technique. B.7.2.3 High-Angle Techniques. The HAL technique and 70-degree shear wave technique shall be used to size discontinuities that are within ½ inch of the inspection surface. The HAL and 70-degree shear technique are absolute arrival time techniques that makes use of high-angle longitudinal waves and shear waves to locate the discontinuity tip. These methods measure the remaining ligament of material above the discontinuity. Tip signals shall be maximized for calibration
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