ET · Advanced NDT
Eddy Current Testing
The Method
How ET works.
An alternating current in a probe coil creates a changing magnetic field that induces eddy currents in the conductive part. Cracks, changes in conductivity or permeability, and changes in geometry disturb those currents and change the coil's impedance.
The instrument shows that change, usually on an impedance-plane display, where an experienced technician separates crack signals from lift-off, edge effects, and material variation. Surface probes, specialized weld probes, eddy current arrays, and bobbin probes for tubing suit different applications.
Applications
Where ET is used
- Surface crack detection on welds, often through paint or coatings
- In-service inspection for fatigue cracking
- Fastener holes and machined components
- Heat exchanger and condenser tubing (bobbin and array techniques)
- Conductivity measurement and alloy or heat-treatment sorting
- Nonconductive coating thickness measurement
Detection capability
What ET can detect
- Surface-breaking cracks
- Near-surface discontinuities, within the method's limited penetration depth
- Wall loss and pitting in thin-wall tubing
- Conductivity variations from alloy or heat-treatment differences
- Coating thickness on conductive substrates
Methods & Equipment
Typical equipment
- Impedance-plane eddy current instruments
- Pencil, surface, and weld-inspection probes
- Eddy current array (ECA) probes
- Bobbin probes for tubing
- Reference standards with machined notches
Technical Considerations
Limits and requirements to plan for.
Conductive materials only
ET requires an electrically conductive part. It does not work on plastics, composites without conductive fibers, or ceramics.
Depth of penetration
Eddy currents concentrate near the surface (the skin effect). Lower frequencies reach deeper but lose sensitivity to small surface flaws.
Ferromagnetic steels
Permeability variations in carbon steel and weld zones create noise. Purpose-designed weld probes and arrays are used to manage it.
Reference standards
Setup uses reference standards of similar material and geometry, with notches representing the flaws of interest.
In Practice
ET in industry.
Coated structures
Crack screening of welds without stripping protective coatings, followed by confirmation as specified.
Aerospace
Surface and fastener-hole inspection on conductive components.
Power & process
Tubing inspection and in-service crack detection.
Industries that benefit
How TCI Supports You
What you get from TCI.
- ET technicians qualified for the techniques the job requires
- Technique development and reference standards specified by Level III personnel
- ET used alongside MT, PT, and PAUT where it saves time or coating removal
Let's discuss your inspection requirements.
Tell us about your project, schedule, and the specifications you work to. A member of our leadership team will respond directly.