TechnicalPublished on 2026-10-12
Eddy Current vs Ultrasonic Testing: Which Should You Use?
Both find cracks, but their scenarios differ. This compares principle, effective depth, material requirements and field efficiency.
Eddy currentUltrasonicMethod selection
Both are NDT, but they solve different problems
Eddy current (ET)
- Principle: electromagnetic induction creates eddy currents in conductive material; defects disturb the field
- Effective depth: surface to roughly 2–3 mm
- Material: conductive metals only
- Strengths: fast, automatable, ideal for batch inline inspection
Ultrasonic (UT)
- Principle: sound waves propagate in the material and reflect at interfaces
- Effective depth: through the full material thickness
- Material: nearly all solids
- Strengths: measures wall thickness, covers internal defects
Selection table
| Scenario | Recommended |
|---|---|
| Batch sorting of machined part surface cracks | Eddy current |
| Internal weld lack of fusion / porosity | Ultrasonic |
| Pipe wall thickness and corrosion | Ultrasonic thickness |
| Aluminium aerospace part surface cracks | Eddy current |
| Pressure vessel periodic inspection | Ultrasonic + magnetic particle |
