Continuous wave eddy current testing is one of a number of non-destructive testing methods that use the electromagnetism principle. Conventional eddy current testing uses electromagnetic induction to detect discontinuities in conductive materials.
The technique, which can be used in any industry sector where metals – including aluminium – are used, uses a specially designed coil that is energised with alternating current and placed close to the test surface. A magnetic field is generated, which interacts with the test part to produce an eddy current. These eddy currents are then measured for variations in the changing phases and magnitude, either through the use of receiver-coil(s) or by measuring changes to the alternate current flowing in the primary excitation-coil.
Discontinuities in the test part will cause a change in the eddy current which are measured and shown on a screen for easy interpretation. Because eddy current testing is a non-contact technique it can be used to inspect surfaces at high temperatures. Providing immediate feedback, eddy current systems can investigate physically complex geometries, measure electrical conductivity, ascertain the thickness of a coating, and detect very small cracks in or near the surface of the test part, without the need for a couplant.
Eddy Current Array Testing (ECAT) is an enhancement of conventional Eddy Current Testing (ECT), utilising an array of eddy current coils working simultaneously in specified firing patterns to provide larger surface area coverage in a single pass. ECAT has also the potential to offer a quicker cleaner alternative to dye penetrant (PT) or magnetic particle testing (MT), reducing inspection and manufacturing lead times in comparison. ECAT does not require the application of a chemical and can therefore be deployed in an environment where chemical residue is an issue. This also reduces the need for laborious cleaning regimes for inspection, leading to increased productivity.
Placing the eddy current technologies in arrays allows for larger parts to be measured quickly as TWI works to further develop the process through automation and continuous testing that will reduce downtimes and increase efficiency. This includes validating new probes as well as comparing the process to other inspection methods. TWI are also working on R&D and qualification and procedure development of eddy current array inspection for nuclear power plants and hydroelectric power stations as well as inspections for applications in industries including manufacture, marine, nuclear, transportation and aerospace.
You can find out more about eddy current array testing, here: https://www.twi-global.com/what-we-do/services-and-support/asset-management/non-destructive-testing/ndt-techniques/eddy-current-testing
