🔊 Ultrasonic Testing (UT)
Detection and sizing of internal and surface defects in metallic materials using ultrasonic waves. Allows testing of full material volume — including welds, forgings and plates.
Overview
Ultrasonic testing (UT — Ultrasonic Testing) is one of the most important and frequently used non-destructive testing methods, allowing detection of internal discontinuities (cracks, lack of fusion, inclusions, porosity) and external defects in metallic and non-metallic materials. Standard PN-EN ISO 16810 specifies general principles of UT testing, and standard PN-EN ISO 17640 — specific requirements for weld testing.
The method is based on propagation of ultrasonic waves (typically 1–10 MHz) in material. Wave emitted by piezoelectric probe propagates in material and reflects from discontinuity or opposite wall. Based on propagation time and echo amplitude, depth, position and size of defect are determined. UT testing is particularly effective in detecting planar defects (cracks, lack of fusion) — difficult to detect by other methods.
Currently, besides conventional UT, advanced techniques are used: Phased Array UT (PAUT) — multi-element probes with electronic beam steering, TOFD (Time of Flight Diffraction) — diffraction technique for precise sizing, and Full Matrix Capture (FMC/TFM) — latest volumetric imaging technique.
UT testing requires personnel qualification according to PN-EN ISO 9712 (level 2 or 3 for evaluation). The method is used in steel construction (EN 1090), power industry, oil industry (API), shipbuilding and aerospace.
Method principle
Ultrasonic probe (piezoelectric transducer) emits ultrasonic wave pulse into tested material. Wave propagates with velocity characteristic for given material (e.g. ~5 900 m/s in steel — longitudinal wave). At boundary of media with different acoustic impedance (discontinuity, opposite wall) wave is reflected. Reflected echo is recorded by probe and displayed on screen as A-scan signal (amplitude vs time). Reflector depth is calculated: d = v × t / 2, and its size is assessed based on echo amplitude compared to reference reflector (e.g. flat-bottom hole — DAC).
Applications
- Testing of welded joints in steel structures (EN ISO 17640)
- Control of plates and steel products (EN 10160 — plates, EN 10228 — forgings)
- Testing of oil and gas pipelines (API 5L, ASME B31.3)
- Wall thickness measurement (corrosion, erosion) — without installation disassembly
- Testing of castings (search for shrinkage cavities, porosity)
- Control of railway rails and wagon wheels
- Testing of aircraft components (CFRP composites — immersion technique)
Key parameters
| Parameter | Value |
|---|---|
| Frequency range | 1–10 MHz (typically 2–5 MHz for steel) |
| Thickness range | 1 mm – several meters (depending on material and frequency) |
| Wave velocity in steel | 5 900 m/s (longitudinal), 3 250 m/s (transverse) |
| Wave introduction angles | 0° (straight probe), 45°/60°/70° (angle probe) |
| Sensitivity | Detection of reflectors ≥ 1.5 mm (FBH) in steel |
| Location accuracy | ±1 mm (depth), ±2 mm (position along weld) |
Standard
- Standard number
- PN-EN ISO 16810:2014-02
- Title (PL)
- Badania nieniszczące — Badania ultradźwiękowe — Zasady ogólne
- Title (EN)
- Non-destructive testing — Ultrasonic testing — General principles
Step-by-step procedure
1. Surface preparation
Clean and smooth scanning surface. Remove irregularities, paint, rust, weld spatter. Roughness ≤ 6.3 µm Ra.
2. Range calibration
On V1 block set display range (e.g. 100 mm, 250 mm). Check wave velocity in material.
3. Angle and index point calibration
On V1/V2 block check wave introduction angle and angle probe index point. Correction if deviation > 2°.
4. Sensitivity setting
Set DAC (Distance Amplitude Correction) or TCG (Time Corrected Gain) curve on block reflectors. Evaluation level according to ISO 11666.
5. Couplant application
Apply coupling gel to tested surface. Ensure continuous probe contact with material.
6. Scanning
Move probe over surface at speed ≤ 150 mm/s. Scan in two perpendicular directions. Strip overlap min. 10%.
7. Indication identification
Record indications above recording level. Determine: depth, position, amplitude, length.
8. Defect sizing
Size indications by 6 dB drop technique (length) and amplitude (height). For TOFD — direct measurement of diffraction time.
9. Results assessment
Compare indications with acceptance criteria (e.g. EN ISO 11666 — acceptance levels 1/2/3). Classify defects.
10. Report
Prepare test report: element identification, UT technique, parameters, indication map, assessment according to standard.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Ultrasonic flaw detector | Olympus EPOCH 650, Krautkrämer USM 100, GE USM Go+ | 25 000–80 000 PLN |
| PAUT / TOFD flaw detector | Olympus OmniScan X3, Zetec TOPAZ 64, Sonatest Veo+ | 80 000–250 000 PLN |
| Straight probe (0°) | Olympus V106 (2.25 MHz), V109 (5 MHz), diameter 24 mm | 500–2 000 PLN |
| Angle probe | Olympus A545S-SB (45°), A560S-SB (60°), A570S-SB (70°) | 800–3 000 PLN |
| Calibration blocks | Block V1 (EN ISO 2400), V2 (EN ISO 7963), step block | 1 000–5 000 PLN |
| Couplant | Ultrasonic gel Olympus Couplant D, glycerin, cellulose paste | 30–100 PLN / liter |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Coupling gel | — | Ensures wave transmission from probe to material — eliminates air layer, glycerin or water gel |
| Block V1 (EN ISO 2400) | — | Steel block with slots — for range, angle and sensitivity calibration, with certificate |
| Block V2 (EN ISO 7963) | — | Small pocket block — for quick check of angle probe angle and index point |
| Blocks with DAC reflectors | — | Specimens with flat-bottom holes (FBH) or notches — DAC / TCG curve |
Health and safety (OHS)
- Work at heights (steel structures) — harness, helmet, safety measures
- Coupling gel — slippery, risk of slipping on floor
- Work in noise (e.g. production halls) — hearing protection
- Hot elements (in-situ) — heat-resistant gloves, high-temperature probes (up to 500°C)