ELECTROMAGNETIC METHODS

Eddy-current testing is based on the electromagnetic induction principle. Testing probe coils, or permanent magnets, generate magnetic field that induces voltage and current inside the tested material. In the event of a barrier (defect), there is a detectable voltage change.

Eddy current is used in more testing techniques:

• Eddy current testing – classics: Basic technique, suitable for testing of surfaces using pick up probes, and of pipes using inner through probes. The suitable materials are non-magnetic metals (austenitic steel and non-ferrous metals), and duplex steel.
• ECA technique: Eddy current array – controlled eddy current field. In this case the probe includes more coils (usually dozens). The technique is able to check belts of different widths, displayed as 3D and 2D maps. It allows identification and evaluation of surface and sub-surface defects. Major advantage is the possibility to test through coating – excellent alternative to PT and MT methods.
• RFT technique: Remote field testing using eddy current method. Suitable for the testing of pipes made from magnetic materials, such as carbon steel.
• MFL technique: Magnetic flux leakage is a method applied to check tubes and pipelines made from magnetic materials like carbon steel in cases where RFT cannot be used. This applies to pipes with numerous partitions, support plates etc. (air coolers).