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

Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing

Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing

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In fact, the actual beam profile is complex, with pressure gradients in both the<br />

transverse and axial directions. In the beam profile illustration below, red<br />

represents areas of highest energy, while green and blue represent lower<br />

energy.<br />

The exact shape of the beam in a given case is determined by transducer<br />

frequency, transducer diameter, and material sound velocity. The area of<br />

maximum energy a short distance beyond the face of the transducer marks<br />

the transition between beam components known as the near field and the far<br />

field, each of which is characterized by specific types of pressure gradients.<br />

Near field length is an important factor in ultrasonic flaw detection, since it<br />

affects the amplitude of echoes from small flaws like cracks, but it is usually<br />

not a significant factor in thickness gauging applications.

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