Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing, UT

B-Scan Presentation
The B-scan presentations is a profile (cross-sectional) view of the test
specimen. In the B-scan, the time-of-flight (travel time) of the sound energy is
displayed along the vertical axis and the linear position of the transducer is
displayed along the horizontal axis. From the B-scan, the depth of the
reflector and its approximate linear dimensions in the scan direction can be
determined. The B-scan is typically produced by establishing a trigger gate on
the A-scan. Whenever the signal intensity is great enough to trigger the gate,
a point is produced on the B-scan. The gate is triggered by the sound
reflecting from the backwall of the specimen and by smaller reflectors within
the material. In the B-scan image above, line A is produced as the transducer
is scanned over the reduced thickness portion of the specimen. When the
transducer moves to the right of this section, the backwall line BW is
produced. When the transducer is over flaws B and C, lines that are similar to
the length of the flaws and at similar depths within the material are drawn on
the B-scan. It should be noted that a limitation to this display technique is that
reflectors may be masked by larger reflectors near the surface.