What is the method?
Eddy Current Testing (ECT) is an electromagnetic inspection technique used to detect surface and near-surface discontinuities in electrically conductive materials. The method works by inducing eddy currents into the component using an alternating electromagnetic field. Any change in material condition, such as cracking, corrosion pitting, geometry variation, or material change, disturbs the eddy current flow and produces a measurable signal response. For specialised applications, different probe configurations are used: pencil probes for highly localised weld and crack inspection, array probes for improved weld coverage and faster scanning, and gear probes for the inspection of girth gear teeth and similar rotating equipment profiles.
Application
Eddy Current Testing (ECT) is an electromagnetic inspection technique used to detect surface and near-surface discontinuities in electrically conductive materials. The method works by inducing eddy currents into the component using an alternating electromagnetic field. Any change in material condition, such as cracking, corrosion pitting, geometry variation, or material change, disturbs the eddy current flow and produces a measurable signal response. For specialised applications, different probe configurations are used: pencil probes for highly localised weld and crack inspection, array probes for improved weld coverage and faster scanning, and gear probes for the inspection of girth gear teeth and similar rotating equipment profiles.
Key Benefits
- Highly sensitive to surface and near-surface cracking in conductive materials.
- No couplant is required, allowing clean and efficient inspection.
- Suitable for complex shapes, weld profiles, and localised inspection areas.
- Fast and effective for both targeted crack detection and broader surface screening.
- Can often be used on painted or thin-coated surfaces, depending on coating thickness and probe selection.
- Provides a practical alternative where DPI or MPI may be less suitable.
- Array probes improve productivity and inspection coverage on welds.
- Gear probes provide a focused solution for critical girth gear tooth inspection.
Inspection Capabilities
- Pencil probes provide precise, localised inspection of weld caps, toes, accessible root regions, fillets, and complex geometries, making them ideal for detecting fatigue cracks, toe cracking, and small surface-breaking flaws.
- Array probes extend ECT capability by enabling wider weld coverage, faster data collection, improved repeatability, and enhanced visualisation, especially for surface crack screening on weld seams and large conductive surfaces.
- Gear probes are specifically suited to the inspection of girth gear teeth, allowing targeted detection of surface-breaking cracks, root cracking, flank damage, wear-related discontinuities, and localised tooth deterioration.
- Unlike DPI and MPI, ECT can often be applied with minimal surface preparation and without penetrants or magnetic particles.
- Particularly effective on non-ferromagnetic materials, stainless steel welds, and conductive components where electromagnetic surface inspection offers an operational advantage.
- Well suited to repeat inspections and trending, especially in crack growth monitoring and rotating equipment maintenance programmes.
Limitations
- Limited primarily to electrically conductive materials.
- Typically effective for surface and near-surface defects only.
- Signal response can be influenced by geometry changes, lift-off, surface condition, and material conductivity.
- Probe selection and calibration are critical to reliable results.
- Skilled interpretation is required, particularly for complex weld geometries and gear tooth profiles.
- Coatings, heavy scale, rough surfaces, and irregular contact can affect sensitivity.
- For deep internal flaws or full volumetric assessment, ECT may need to be complemented by UT, PAUT, or RT.