Eddy Current testing is a method of nondestructive testing that is based on the principals of electromagnetism. When an eddy current probe in the close proximity of a test material is energized at a given oscillating frequency, eddy currents are induced in the conductive test material by means of electromagnetic induction. This technique requires no couplant or constant contact with the material being examined. The presence or absence of flaws can be evaluated by monitoring changes reflected back in the electrical characteristic of an eddy current coil, referred to as coil impedance. Any changes in the coil impedance are displayed as voltage changes in terms of signal amplitude and signal phase. These variations in phase angle and/or signal amplitude are correlated to flaw conditions,such as percent wall loss and volumetric wall loss. Therefore, ET is a comparative method instead of an absolute method.Eddy current testing is a widely used and well understood inspection technique for flaw detection, as well as thickness and conductivity measurements.
A main application for eddy current testing is tubing inspection in heat exchangers and condensers.
Several types of defects can be detected in tubing:
- Inner-diameter (ID) pitting
- Outer-diameter (OD) pitting
- Wear (from support structures, other tubes, and loose parts)
- OD and ID Erosion