EDDY CURRENT INSPECTION (ECT)

What Is Eddy Current Testing?

Eddy current testing (ECT) is an electromagnetic NDT method for checking conductive metals. An alternating current is driven through a probe coil, and that changing field induces small circulating currents — eddy currents — in the material below the probe. Any crack, change in thickness, or shift in the metal's electrical or magnetic properties disturbs those eddy currents, and the probe picks up the change as a shift in coil impedance. The inspector reads that signal to find and size the flaw. There is no couplant and nothing is cut or marked, so the part goes straight back into service once the scan is done.

How Eddy Current Testing Works

The probe sits against or just above the surface and the instrument plots the coil response on an impedance plane. A sound area gives a steady baseline; a defect or a change in the material kicks the trace in a direction and to a depth the technician learns to read against calibration standards with known notches and holes. Drive frequency is the main lever — higher frequencies concentrate the currents near the surface for fine crack detection, while lower frequencies push them deeper to pick up wall loss. For tube work, multi-frequency and bobbin or array probes are run through the bore so a long length of tube can be assessed quickly. Because the coil reacts to lift-off as well, the same physics that lets ECT read through paint also means the probe and frequency have to be matched to the job.

Eddy Current Testing Applications

ECT earns its keep wherever a conductive part needs checking without stripping it back. Common work includes surface and near-surface crack detection — often through thin paint or coatings, with no need to remove them first. Heat-exchanger, condenser and boiler tube inspection is a major use, where the method maps pitting, wall thinning and cracking along each tube. Conductivity measurement supports material sorting and heat-treatment verification, picking up mixed alloys or a missed temper before they reach the field. Weld inspection rounds it out, and ECT often runs alongside ultrasonic inspection when volumetric coverage of the weld body is also needed.

ECT vs Magnetic Particle and Penetrant Testing

The big difference is what each method can see and where. Magnetic particle inspection only works on ferromagnetic steels, and dye penetrant only finds flaws that break the surface on a clean part. Eddy current testing handles non-ferromagnetic conductive metals too — aluminium, copper, brass, titanium and austenitic stainless — needs no couplant, and reads through coatings that the other two methods would need stripped off first. It also reaches a little below the surface. The trade-off is that ECT signals take training to interpret and the setup has to be calibrated to the material, so the right choice still comes down to the part in front of you.

Australian & International Standards and Compliance

APEC carries out eddy current testing to the recognised standards for each application: ISO 15549 for the general principles of eddy current testing, ISO 15548 and ASTM E243 for eddy current examination of tubular products such as copper and copper-alloy tubes, and ISO 17643 for eddy current testing of welds by complex-plane analysis. Personnel are certified to ISO 9712 / AS 3998, and APEC is NATA-accredited with AINDT-certified technicians, so the report holds up with clients, regulators and insurers.

Why Choose APEC Inspection for Eddy Current Testing

APEC Inspection is a NATA-accredited inspection body, and our eddy current work is done by AINDT-certified technicians who calibrate to the job and report in plain terms you can act on. We mobilise across Newcastle, the Hunter and nationally, and fit ECT into the wider NDT and pressure vessel inspection programme your plant relies on. To talk through a tube bundle, a coated structure or a sorting job, request a quote or call the team direct.