ASNT NDT III UT flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Acoustic impedance

The product of material density and sound velocity (Z = ρc). Differences in acoustic impedance at an interface determine how much ultrasonic energy is reflected versus transmitted.

First critical angle

The incidence angle at which the refracted longitudinal wave reaches 90 degrees and disappears in the second medium, leaving only a refracted shear wave.

Near field length

For a circular piston transducer, N = D squared divided by four wavelengths. Within this distance the beam has complex pressure variations and is not used for accurate sizing.

Wavelength relationship

Wavelength equals sound velocity divided by frequency. Higher frequency gives shorter wavelength, improving the ability to resolve small reflectors but increasing attenuation.

Attenuation

Loss of ultrasonic energy as the beam travels through material, caused by absorption and scattering. It rises with frequency and is quantified in decibels per unit length.

Mode conversion

Change of wave type, such as longitudinal to shear, occurring at an interface or boundary. It depends on incidence angle and the acoustic properties of both media.

Vertical linearity

A performance check confirming that the displayed echo amplitude changes proportionally to the input signal across the usable screen height, ensuring accurate amplitude comparison.

Horizontal linearity

A check confirming that echo positions on the time base correspond accurately to known distances, so depth and sound-path readings are reliable.

Distance amplitude correction

An electronic or plotted correction that compensates for attenuation and beam spread with depth, so equal-sized reflectors at different depths display comparable amplitudes.

Dead zone

The near-surface region where echoes from a reflector merge with the transmit pulse and cannot be resolved. It depends on pulse length and damping.

A-scan display

A plot of echo amplitude versus time or distance along a single beam path, used to locate and size reflectors in the test piece.

Transducer damping

Backing material in the transducer that shortens the pulse and broadens bandwidth, improving axial resolution and reducing the dead zone.

Scan index increment

The spacing between adjacent scan passes. It is chosen relative to beam width or element size so that no region of the test volume is missed.

Reference reflector

A known artificial flaw such as a flat-bottom hole, side-drilled hole, or notch used to set sensitivity and to compare against detected indications.

Transfer correction

A gain adjustment accounting for differences in surface finish, couplant, and attenuation between the calibration block and the actual test piece.

Scanning gain

Additional gain above reference sensitivity applied during scanning to ensure detection of small or poorly oriented reflectors, with indications evaluated at reference gain.

Procedure essential variables

Parameters such as frequency, transducer size, angle, couplant, and calibration method that, if changed, require requalification of the technique.

Recording threshold

The indication amplitude or size above which a reflector must be documented in the test record, independent of whether it is rejectable.

6 dB drop method

A sizing technique in which the probe is moved until echo amplitude falls to half its peak value; the resulting travel distance estimates reflector length.

Indication versus defect

An indication is any signal on the display; a defect is an indication evaluated as a genuine discontinuity that fails acceptance criteria.

Sound path to depth

Depth below the surface equals sound path multiplied by the cosine of the refracted angle; surface distance equals sound path times the sine of the angle.

Tip diffraction sizing

A technique using diffracted signals from the upper and lower tips of a reflector to estimate its through-wall height independent of amplitude.

Evaluation

The process of comparing recorded indication characteristics against the acceptance criteria of the applicable code to determine accept or reject disposition.

Written practice

The employer's document describing how personnel are trained, examined, and certified in accordance with the governing qualification standard.

Calibration traceability

The documented chain linking measurement equipment and reference blocks to national standards, ensuring that readings are reliable and defensible.

Acceptance criteria

The limits defined by the applicable code or specification against which indications are evaluated to determine whether a component is acceptable.

Record retention

The requirement to keep examination records, calibration data, and certification documents for the period specified by the governing standard or contract.

Specification versus code

A code sets broad mandatory requirements while a specification states project-specific details; the more restrictive applicable requirement generally governs.

Level II responsibilities

A certified Level II performs and calibrates tests, interprets and evaluates results per established procedures, and reports findings; may supervise Level I personnel.

Level III responsibilities

A certified Level III develops and approves procedures, interprets codes and standards, establishes techniques, and provides technical direction for the method.

Qualification versus certification

Qualification is the demonstrated physical and technical ability to perform a task; certification is the formal written confirmation issued by the certifying authority.

Vision requirement

A periodic near-vision acuity and color perception check required by qualification standards to ensure reliable interpretation of test indications.

Certification examination

An assessment typically combining general, specific, and practical elements that verifies a candidate's knowledge and skill for a given method and level.