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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