PCN NDT Ultrasonic Testing Level 2 Exam flashcards

32 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 = ρV); determines reflection and transmission at interfaces. Units are Rayl (kg/m²s).

Near field length

For a circular piston transducer, N = D²/(4λ); within this distance the beam is complex and amplitude does not follow inverse square law.

Beam spread angle

Half-angle to first null: sin θ = 1.22 λ/D. To −6 dB: sin θ = 0.51 λ/D. Smaller wavelength or larger diameter gives narrower beam.

Snell's law

sin θ₁ / sin θ₂ = V₁ / V₂. Used to calculate refracted angle in angle beam testing and to determine critical angles.

First critical angle

Incident angle at which refracted longitudinal wave is 90°; beyond it only shear wave propagates. θ = sin⁻¹(V₁/V₂) using longitudinal velocities.

Second critical angle

Incident angle at which refracted shear wave is 90°; beyond it total reflection occurs. θ = sin⁻¹(V₁/Vs₂).

Skip distance

For angle beam, the surface distance from index point to where the beam first hits the back wall: skip = 2T tan θ, where T is thickness.

DAC curve

Distance Amplitude Correction: a curve showing echo amplitude from a reference reflector versus distance, used to compensate for beam spread and attenuation.

TCG

Time Corrected Gain: electronic gain that increases with time to flatten the DAC curve, making indications of equal size appear equal amplitude regardless of depth.

6 dB drop method

Sizing technique where probe is moved until echo amplitude falls to half (−6 dB) of maximum; the distance moved approximates flaw length for reflectors larger than beam.

IIW/V1 block

Calibration block used to determine index point, refracted angle, and probe resolution; contains a 100 mm radius and a 50 mm hole.

V2 block

DIN 54-122 block used for time base and sensitivity calibration; has multiple reflectors at known distances and a 25 mm radius.

Side-drilled hole

Reference reflector used in DAC calibration; a cylindrical hole drilled parallel to the surface at a known depth, providing a repeatable indication.

Flat-bottom hole

Reference reflector with a flat bottom of known area; used for area linearity and sensitivity calibration, often in ASME blocks.

Piezoelectric effect

Property of certain crystals (quartz, PZT) to generate voltage when deformed and to deform when voltage applied; basis of ultrasonic transducers.

Transducer damping

Backing material that absorbs rearward waves, shortening pulse duration and improving axial resolution; reduces sensitivity but increases bandwidth.

Axial resolution

Ability to separate two reflectors along the beam path; approximately half the spatial pulse length. Shorter pulses (higher damping, higher frequency) improve it.

Lateral resolution

Ability to separate two reflectors perpendicular to beam; best at focal point, approximately beam width there. Improved by focusing.

Couplant

Material (oil, gel, water) used to transmit ultrasound between transducer and test surface by eliminating air gap; must have acoustic impedance between those of transducer and test material.

Angle beam probe

Transducer mounted on a wedge to introduce refracted shear waves into the test piece at a selected angle (e.g., 45°, 60°, 70°).

Index point

Point on the wedge where the beam exits; used as reference for surface distance measurements; determined using IIW block.

Refracted angle

Angle of the beam in the test material after refraction at interface; measured from normal. Determined by Snell's law and verified on calibration block.

Attenuation

Loss of sound energy due to scattering and absorption; increases with frequency and grain size. Compensated by DAC/TCG.

Acoustic velocity

Speed of sound in a material; longitudinal velocity in steel ~5900 m/s, shear ~3200 m/s. Depends on elastic modulus and density.

Wavelength

λ = V/f. Determines sensitivity and resolution; smaller wavelength (higher frequency) detects smaller flaws but attenuates more.

Pulse-echo technique

Method where a single transducer sends and receives pulses; flaw detected by echo between initial pulse and back-wall echo.

Through-transmission technique

Two transducers on opposite sides; flaw detected by reduction in transmitted signal. Not sensitive to flaw depth but good for attenuative materials.

Immersion testing

Technique where part and transducer are submerged in water; allows precise focusing and scanning; water path must exceed near field in water.

Reference reflector

Known artificial flaw (SDH, FBH, notch) used to establish sensitivity and DAC curve; must be in material similar to test piece.

Transfer correction

Adjustment made when calibration block material differs from test material; compensates for attenuation and velocity differences.

Scanning sensitivity

Gain setting that brings reference reflector echo to a specified screen height (e.g., 80% FSH); ensures consistent detection.

Indication classification

Categorizing indications as relevant, non-relevant, or false; based on origin, shape, and response to probe movement.