Eddy Current Inspection Instruments

Eddy current testing is now a widely used and well understood inspection technique for flaw detection, as well as thickness and conductivity measurements.

Applications

The two major applications of eddy current testing are surface inspection and tubing inspections. Surface inspection is used extensively in the aerospace industry, but also in the petrochemical industry. The technique is very sensitive and can detect tight cracks. Surface inspection can be performed both on ferromagnetic and non-ferromagnetic materials.

Tubing inspection is generally limited to non-ferromagnetic tubing and is known as conventional eddy current testing. Conventional ECT is used for inspecting steam generator tubing in nuclear plants and heat exchangers tubing in power and petrochemical industries. The technique is very sensitive to detect and size pits. Wall loss or corrosion can be detected but sizing is not accurate.

A variation of conventional ECT for partially magnetic materials is full saturation ECT. In this technique, permeability variations are suppressed by applying a magnetic field. The saturation probes contain conventional eddy current coils and magnets. This inspection is used on partially ferromagnetic materials such as nickel alloys, duplex alloys, and thin-ferromagnetic materials such as ferritic chromium molybdenum stainless steel. The application of a saturation eddy current technique depends on the permeability of the material, tube thickness, and diameter.

A method used for carbon steel tubing is remote field eddy current testing. This method is sensitive to general wall loss and not sensitive to small pits and cracks.

Reference: Wikipedia