Eddy Current Testing

Continuous wave eddy current testing is one of several non-destructive testing methods that use the electromagnetism principle. Conventional eddy current testing utilises electromagnetic induction to detect discontinuities in conductive materials.

A specially designed coil energised with alternating current is placed in proximity to the test surface generating changing magnetic-field which interacts with the test-part producing eddy current in the vicinity.

The electrical conductivity variations or magnetic permeability of the test-part, or the presence of any discontinuities, will cause a change in eddy current and a corresponding change in phases and amplitude of the measured current. The changes are shown on a screen for easy interpretation.

Inspection of surfaces at high temperature are possible with the eddy current technique as it is a non-contact method.

Characteristics of the ECT technique :

• Suitable for non-ferrous tubing such as SS304/316, Brass, Titanium, Inconel, Cu, Cu-Ni, etc.
• Can detect pits, corrosion, erosion and axial cracking
• Uses multiple frequencies for better analysis and flaw sizing.
• The probe needs a good fill factor to remain sensitive (about 0.85 to 0.9).
• Probe centering is important for uniform sensitivity and reduce lift-off signal.
• Very fast technique, up to 2m/s pulling speed.

Applications

• Checking for surface breaking cracks on metal
• Metal tube inspection for discontinuities
• Heat treat verification of metals
• Checking conductivity of metals, thickness of coatings and of thin metals
• Testing gas turbine blades
• Inspection of a cast iron bridge
• Inspection of Hurricane propeller hubs
• Testing nozzle welds in nuclear reactor