10 Things to Know to Choose the Right Eddy Current Array ...

1. What is the test material? 

From zirconium alloys to graphite composites, ECA is usable on almost any conductive material. Knowing the exact composition, or grade, of the material is helpful. For example, different grades of stainless steel have their own specific electromagnetic properties: 400-series stainless steel is ferromagnetic while 300-series is not, and both contain exceptions. This can influence the configuration of the selected ECA probe and affect inspection results.

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2. What is the geometry of the test surface?

Is the inspected surface perfectly flat or does it have strong curvature? What is the bend radius? Does it have uneven geometry? If there is a weld cap, how far is it protruding from the surface? Having access to a 3D model or to clear pictures of the surface can be of tremendous help when determining how flexible or how rugged a surface probe needs to be.

3. What types of defects are expected?

Cracks, corrosion, porosities, scabbing, hardening, lack of fusion, delamination&#; the list of potential integrity threats can be endless. But they all interact with eddy currents in their own unique way, and it may be beneficial to optimize some probe parameters, like the frequency and topology, based on the type of defect of interest.

4. What is the target flaw size?

ECA is a very sensitive technique when it comes to the detection of surface-breaking flaws. But in some applications, flaws below a certain target size don&#;t represent an integrity threat and may not need to be reported. To detect only the indications that are relevant, the coil sensors should be chosen based on an approximate target flaw size. From there, the coil size will dictate the resolution and surface coverage of the probe. This often makes the target flaw size the starting point of an entire probe design.

Speaking of size: is quantitative defect sizing required, or is detection enough? While ECA is mostly known for its detection performance, some probes like the Sharck&#; and Sharck HR are built specifically for measuring the depth of surface cracks.

5. Where are the defects expected?

In non-ferromagnetic materials, ECA can detect flaws located on the near-side surface, far-side surface, or mid-wall. Knowing the expected location of the target defects relative to the component&#;s surface will help fine-tune the operational frequency and topology of the ECA probe to obtain the right amount of eddy current penetration. When penetration is necessary, knowing the wall thickness also becomes crucial.

6. What is the expected orientation of the defects?

Nowadays, most ECA probes can detect defects in all orientations, including axial, transverse, circumferential, and diagonal. But in applications where linear flaws are always expected with the same specific orientation, it may be beneficial to use a probe with channels in this preferential orientation only.

7. What&#;s the test surface condition?

Is the surface drenched in lubricant, covered with paint, epoxy, or rust, or does it have a high surface roughness? Knowing these details is essential and will dictate the type of contact interface to choose for the ECA probe. Surface condition also has an impact on the smallest defects that can be detected. Looking for very small defects on rough surfaces may require some compromises.

If the surface is coated, the characteristics of the coating will be just as important as those of the material itself since they will have a strong effect on the probe&#;s magnetic field. The nominal coating thickness, thickness variation, and coating material are three things that will need to be considered.

8. Is the test surface difficult to reach?

Is the surface in a restricted location, high up, or interspaced with gaps and supports? This can influence the shape and size of the ECA probe, making accessories such as poles or harnesses necessary, or require deploying the probe on an inspection crawler like the VersaTrax&#; NDT.

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9. In what type of environment must the probe be used?

Is the probe operating in a humid, dusty, or even radioactive environment? Is the probe used near welding equipment, near strong magnetic fields, or underwater? Is it used indoors or outdoors? Is the inspected surface kept at a very high &#; or very low &#; temperature? Is there easy access to a power source, a wi-fi network, or a cellular network? The environment will not only affect the choice of the probe, but also the instrument and its software.

10. What testing equipment is available?

Is the probe handled by a human operator, a robotic arm, or is it part of an automated inspection line? Is the data analyzed manually, or does a logical computer verify the presence of defects based on a go/no-go signal threshold? All these details, combined with the required number of eddy current channels, will determine the best probe and instrument model that should be used.

On top of these 10 questions, we suggest two favorite topics of any good project manager: budget and timeframe. Eddyfi Technologies&#; ECA offering covers the full spectrum price range, from the single-frequency MIZ®-21C and advanced portable Reddy® to the almighty 256-channel Ectane® 3.

Similarly for lead times, our most common probes may be available off-the-shelf while very niche and custom equipment will first require some engineering work. Having a clear vision of a project&#;s budget and timeframe helps when selecting the right ECA equipment.

In conclusion, like with any modern technology, there is no such thing as a perfect ECA probe that can do everything. There will always be a choice to make when selecting or designing a probe, and the above list of questions can help pave the way towards the probe that is best tailored to your inspection needs. Eddy current array probes are now more versatile than ever, capable of inspecting a wide variety of applications and surface geometries, ensuring you find the perfect equipment for your needs.

View our entire product catalog with pricing on the Eddyfi eStore and get in touch with our experts to discuss your next inspection campaign!

With QuellTech laser scanner-based surface inspection, there are a large number of application examples, including these:

Quality classification in sheet metal production

In stainless steel and aluminium sheet production, quality grading of each sheet is achieved by 3 D laser scanner surface inspection. Thus, 100% monitoring is achieved in the sheet metal production.

Surface inspection of metal rolls in paper production

Metal rolls for paper production with a diameter of approx. 3 m and a length of 6 m are inspected for surface defects using QuellTech laser scanners: This enables the customer to verify that the surface is free of defects during final inspection. If defects are nevertheless detected, these defects can be reworked and eliminated before the roll is delivered. Before the use of a QuellTech surface inspection system, it happened that surface defects were only discovered at the customer&#;s premises and a time-consuming and expensive return shipment had to be made so that the defects could be repaired.

Checking sealing surfaces of flange connections

Sealing surfaces of flange connections must be free of flaws and surface defects in order to achieve optimum sealing. Thus, the QuellTech laser scanners can check not only the surface quality but also the flatness.

Surface inspection with multiple laser scanners for complex geometries

In the production of rubber seal profiles, which often have complex geometries, several laser scanners are used at different angles to subject the complete envelope of the rubber seal to a surface inspection. This procedure can be used for continuous profiles as well as for very special profile segments.

Testing of plastic parts in the automotive industry

When inspecting plastic parts, laser scanners are used to inspect the surface of both continuous material and complex bodies. The main incentive for surface inspection of plastics is aesthetic reasons.

Weld seam inspection

An increasingly important area of application is weld inspection, which is basically a surface inspection. In this process, a whole range of welding defects become visible, such as pores, penetration notches, asymmetries, weld protrusions, cracks, component misalignment, end craters and weld spatter. Automated weld inspection with laser scanners is increasingly replacing manual visual inspection, achieving greater efficiency with a high and consistent defect detection rate.

Surface inspection in battery production

During battery production, very thin copper carrier foils are coated with various materials. It is important not only to measure the coating thicknesses but also to identify surface defects at an early stage, since these surface defects can strongly influence the subsequent electrical behavior of the battery.

Continuous product testing in throughput in Cable production

In cable production, typically 4 laser scanners are used to scan the entire surface on the 360° of the circumferences. These are mostly continuous products. If a surface defect is measured, the length coordinate of the defect location is recorded so that the defective segment can be cut out later. In the production of continuous products, very high throughput speeds are sometimes used, which means that QuellTech laser scanners with a very high scan rate (max. 200 kHz) are also used here.

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