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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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179. Low frequency sound waves are not generally used to test thin materials<br />

because of:<br />

A. The rapid attenuation of low frequency sound<br />

B. Incompatible wavelengths<br />

C. Poor near-surface resolution<br />

D. None of the above will actually limit such a test<br />

Hint:<br />

Zf = D 2 /4 λ = D 2 x f /4V , Lower the frequency shorter the Near Field.<br />

However the resolution is impaired with longer wavelength.<br />

During the above assessment, is the Near Field effect omitted due to probe<br />

set-up e.g. Delay Line etc.? Or the Near Field may not necessary<br />

undetectable except the “Dead Zone”.

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