Non-Destructive Testing Spotlight: Eddy Current

Manufacturers looking for the best inspection material testing to improve speed and efficiency might want to take a look at the Eddy Current Non-Destructive Inspection (NDI) method. This fast, reliable test offers advantages many may have not considered since they last reviewed whether non-destructive testing would work for an application.

An Eddy Current NDI Testing Primer

Eddy Current Non-Destructive Inspection uses an A/C voltage applied across an eddy current probe or inspection coil. The coil creates an electromagnetic field which causes a current flow in the surface of the material being inspected. The currents resemble the eddies in a stream, hence the name.

The coil or probe is scanned across the inspected material’s surface. Changes in the material, such as defects or flaws, affect the currents. Measurements of changes in voltage amplitude and phase angle shift indicate if a defect is present. An operator sees the results of the Eddy Current test on an impedance plane display.

Applications for Eddy Current NDI

There are a number of applications for Eddy Current inspection. Here are some of the most common:

Flaw/Crack Detection

Flaw detection typically makes use of pencil probes or ‘pancake’ problems to find defects in both ferrous and non-ferrous metals. Cracks 0.1mm or less can be found with frequencies that range from 100 kHz to several MHz. Tubing inspection is a common application.

Material Sorting

Manufacturers often need to confirm material characteristics, not just defects. Eddy current testing can determine the purity of raw and processed metals. Heat treatments can affect metallurgical structures and eddy current testing can report any undesired conditioning.

Weld Testing

Eddy currents can be used to find toe cracks in ferrous welds. This method can even detect cracks in welds that have already been painted. Eddy Current testing offers advantages in that no consumables are used, areas with poor access can be tested, and no surface prep is needed.

Offshore Structures

Eddy Current testing is used frequently in the offshore industry. Tides and severe weather put extra stress on welds on offshore rigs. Cracks often begin to form underwater making conventional inspection difficult. Divers and remote-operated vehicles can administer the tests.

Find out how you can view live demonstrations of Automated Eddy Current Non-Destructive Inspection.

Posted in Non-Destructive Inspection
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