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
