T9074-AS-GIB-010/271 Rev 1
other extremity. Irrespective of the height of the DRL, when the half amplitude signal from the end of the discontinuity as determined by this method is below 20 percent of full screen height, the end of the discontinuity shall be defined where the signal crosses 20 percent of full screen height. The length of the discontinuity shall be defined as the distance between these two marks. The length, depth, position within the inspection zone, and maximum signal amplitude shall be determined and reported for discontinuities yielding signal amplitudes equal to or exceeding the DRL. 6.6.4.3.5 Transverse Discontinuities (Special Case). This procedure shall be used only when specifically invoked. To detect transverse discontinuities, welds shall be in a flush ground or flat-topped (not less than 75 percent of the width of the weld bead) condition, sufficient to permit adequate sound penetration into the weld. An ultrasonic instrument with a calibrated gain control (see 6.5.1.1.4) shall be used. Instrument gain shall be increased over the normal calibration level by 6 dB. Scanning shall be performed as specified in 6.6.4.3.4.2, but with the following modifications: Transducer shall be 2.25 MHz, 60-degree angle (45-degree for T m greater than 3 inches), with an element size of not greater than ½ inch. For the detection of transverse discontinuities, the indication amplitude must equal or exceed 20 percent screen height while maintaining the transducer orientation within plus or minus 15 degrees of the weld axis. Any indication detected during this scan shall be further evaluated by turning the transducer and scanning as specified in 6.6.4.3.4.1. If this further evaluation does not detect the same indication at a level that equals or exceeds 20 percent screen height, then the indication shall be classified as a suspected transverse crack. Suspected transverse cracks shall be sized for vertical height as specified in 6.6.4.4.2.4 (a) through (c).
6.6.4.4 Specific Requirements for Tee Welds that Are Not Volumetrically Inspected.
6.6.4.4.1 Detection of Lack of Penetration in Full Penetration Tee Welds. This section specifies the requirements to be used for the ultrasonic inspection of tee welds for discontinuities in the root area. The depth of the inspection zone shall be limited to through member plate thickness plus ¼ inch, minus ⅛ inch. The width of the inspection zone shall be limited to the thickness of the attachment member (see figure 6-9). The inspection shall employ the pulse-echo longitudinal wave testing technique. 6.6.4.4.1.1 Search Units. The size of the transducer used for inspection shall not have an active element size greater than ¾-inch diameter or the thickness of the attachment member, whichever is less. The inspection frequency shall not be less than 2.0 MHz. 6.6.4.4.1.2 Calibration. The instrument range and delay controls shall be adjusted to discriminate and indicate signals on the viewing screen from the inspection zone. The sweep line shall be marked indicating through member plate thickness minus ⅛ inch and plate thickness plus ¼ inch. The instrument gain shall be adjusted to peak the first back reflection from the plate adjacent to the weld not less than once each foot along the length of the weld as specified hereafter. The viewing screen shall be divided into three zones with horizontal lines at 20 percent (the DRL) and 65 percent (the ARL) of full screen height. The instrument gain control shall be adjusted so that the peak of the first back reflection coincides with the 80 percent line. 6.6.4.4.1.3 Procedure. The width of the inspection zone, as determined by ultrasonic or mechanical means, shall be located and marked on the test surface. The weld shall be continuously scanned within the width of the inspection zone (see figure 6-9). If a discontinuity is located, the equipment gain shall be recalibrated on the through member plate adjacent to the discontinuity. The search unit shall then be positioned to maximize the discontinuity signal. To determine the length of a discontinuity, the search unit shall be moved along the axis of the discontinuity in one direction from the position of maximum signal amplitude. When the amplitude drops below the DRL, the scanning surface shall be marked at the position indicated by the center of the search unit. This shall be one extremity of the discontinuity. The process shall be repeated to determine the other extremity. The length of the discontinuity shall be the distance between these two marks. The maximum signal amplitude and length of discontinuities within the inspection zone shall be determined and reported for discontinuities yielding a signal amplitude equal to or exceeding the DRL. 6.6.4.4.2 Detection of Discontinuities into the Through Member. This section specifies the ultrasonic inspection requirements to be used for the detection of discontinuities extending into the through member of full and partial penetration tee welds.
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