Ultrasonic Testing Level 2
Ultrasonic Testing Level 2
The PCN/ISO 9712 Level 2 UT domain tests whether you can select a technique, set up and calibrate equipment, perform and supervise scanning, distinguish relevant from non-relevant indications, and report results against a specified acceptance standard. It assumes Level 1 competence and adds technique responsibility: probe selection, sensitivity setting, transfer correction, and interpretation within a written procedure.
Core rules and concepts
- Probe choice follows geometry and discontinuity orientation: frequency sets wavelength and resolution; crystal size and frequency set near-field length and beam spread; angle is chosen so the beam intersects the expected fusion line or defect at a useful angle.
- For a circular crystal, near-field length N = D²f/(4c) and the half-angle to the –6 dB edge is approximately sin θ = 0.51λ/D. Keep the reflector beyond N or correct for near-field effects.
- Set reference sensitivity on a calibrated block (e.g. ISO 2400 or ISO 7963 block, or a written reference) using side-drilled holes or notches as specified; construct DAC or TCG from the same reflector type and depth range.
- Transfer correction compensates for couplant, surface roughness and material differences between reference block and test piece; apply it before evaluation. Verify velocity and zero offset on the test material or a similar block, and check probe index and refracted angle.
- Scanning must cover the required volume with overlap; record probe angle, index, scan increment and speed in the technique sheet.
- Indications are evaluated against the acceptance standard only after maximizing signal, measuring length/position, and classifying geometry (e.g. ISO 23279 for welds). Reporting must identify equipment, probe, reference block, sensitivity, corrections and standard used.
Worked example
A 5 MHz, 10 mm diameter longitudinal probe in steel (c = 5900 m/s). N = 10² × 5×10⁶ / (4 × 5.9×10⁶) = 21.2 mm. Wavelength λ = c/f = 1.18 mm; –6 dB half-angle sin θ = 0.51 × 1.18/10 = 0.060, θ ≈ 3.4°. A 10 mm deep reflector lies inside the near field, so amplitude–distance behaviour is non-linear and a DAC made from far-field side-drilled holes cannot be extrapolated to it without care.
Traps that cost marks
- Using shear-wave velocity (≈3240 m/s) in a longitudinal calculation, or vice versa.
- Treating DAC amplitude as an acceptance limit; DAC is a sensitivity reference, acceptance is in the standard.
- Forgetting transfer correction or applying it with the wrong sign.
- Confusing indication length with through-wall height; use diffraction/TOFD or sizing techniques where required.
- Quoting a probe angle without stating the reference block or refracted angle in the material.