# Eddy current testing (ET / ECT)

> Eddy current testing (ET or ECT) drives an alternating current through a coil to induce circulating currents in a conductive material; cracks, thickness changes or conductivity variations alter the coil impedance and are displayed as signals.

- Source: https://amps.global/glossary/eddy-current-testing/
- Type: Glossary
- Published: 2026-09-05
- Tags: NDT, eddy current testing, surface methods

## Key facts

- Conductive materials only; no couplant, works through paint, very fast for surface cracks
- Bobbin probes inspect heat-exchanger and condenser tubes; array probes map surfaces
- Also measures coating thickness, conductivity (alloy sorting) and heat-treatment condition
- Codes: ASME BPVC Section V Article 8, ISO 15549, ISO 17643 (welds)

Also known as: ET, ECT, eddy current inspection, electromagnetic testing.

## How it works

The coil's alternating magnetic field induces eddy currents in the test surface. A crack interrupts the current paths and changes the coil impedance; the change is plotted on an impedance plane and compared against calibration notches. Penetration depth depends on frequency and material, so ET is a surface and near-surface method.

## Where it is used

Aircraft structures and fasteners, heat-exchanger tube bundles during shutdowns, weld caps on stainless and aluminium, bolt holes, and quick sorting of alloys or heat treatments.

## ET in AMPS

Tube-bundle and shutdown inspections generate large numbers of reports in a short window. In AMPS every asset and job carries a QR code. Scanning it opens the asset page and the history of jobs performed on it, assets can hold sub-assets, and jobs can be grouped, for example per shutdown. In AMPS, reports are produced from your own Microsoft Word templates through the template engine: job data such as the client, purchase order number, equipment serial numbers, location and dates is filled in automatically, an AI assistant can tidy the wording, the report can be signed in AMPS, and the finished Word file is saved in the job's report folder in your OneDrive, SharePoint or Google Drive.

## Related pages

- [How to manage a shutdown with AMPS](https://amps.global/case-studies/03-shutdown-management/)
- [Shutdown and turnaround](https://amps.global/glossary/shutdown-and-turnaround/)
- [Ultrasonic testing (UT)](https://amps.global/glossary/ultrasonic-testing/)

## Sources

- [Eddy-current testing on Wikipedia](https://en.wikipedia.org/wiki/Eddy-current_testing)
- [ASME Boiler and Pressure Vessel Code](https://www.asme.org/codes-standards/bpvc-standards)
- [ISO - International Organization for Standardization](https://www.iso.org/)