Ultrasonic Testing (UT) – Cheat Sheet
1. Basics of Sound
- Sound = vibration. UT uses ultrasound (0.5–50 MHz).
- Wavelength (λ) = Velocity / Frequency. Shorter λ → detect smaller flaws.
- Amplitude shown in dB (signal strength).
2. Wave Types
- Longitudinal (compression, works in solids, liquids, gases).
- Shear (transverse, only in solids).
- Surface (Rayleigh), Lamb (thin plates).
3. UT Generation
- Piezo-electric crystal → voltage → vibration → ultrasound.
4. Test Methods
- Pulse-Echo (most common, 1 probe).
- Through-Transmission (2 probes).
- Angle Beam / Tandem (weld inspection).
- Immersion (water couplant).
5. Equipment
- Flaw detector shows echoes (A-scan). X-axis = depth, Y-axis = signal.
6. Calibration
- Use reference blocks to check probe angle, range, sensitivity.
7. Weld Flaws
- Root flaws: excess penetration, root crack, lack of fusion, misalignment.
- Face/body flaws: crack, porosity, slag, lack of fusion.
8. Flaw Sizing
- 6 dB drop (½ signal), 20 dB drop (1/10 signal).
- DAC / DGS curves for depth correction.
9. Advantages
- Detects surface + internal flaws, depth sizing, safe, portable.
10. Limitations
- Skilled operator needed, hard on coarse-grain/rough shapes, orientation dependent.
Summary for quick revision – UT Welds
