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BKN eddy current testing machines provide non-destructive inspection for tubes, bars, and wires, detecting surface defects, cracks, and material inconsistencies while supporting high-speed production, automation, customization, and reliable industrial quality control.
An eddy current probe uses an alternating current in a coil to generate a changing magnetic field. When the probe approaches an electrically conductive material, this field induces circulating electrical currents within the material. Cracks, changes in conductivity or permeability, part geometry and the distance between the probe and surface can alter the probe coil’s impedance. The testing instrument processes these signal changes to identify material or defect-related indications.
The operating process begins when an eddy current instrument supplies alternating current to the probe coil. The coil creates an alternating magnetic field around the probe.
When the probe is positioned near a conductive test piece, the magnetic field induces eddy currents in the material. These currents generate a secondary magnetic field that interacts with the original field produced by the coil.
A surface or near-surface discontinuity interrupts the normal eddy current path. Changes in material conductivity, magnetic permeability, geometry or probe lift-off can also affect the signal. The instrument measures the resulting changes in coil impedance and displays them for analysis.
Test frequency, probe configuration, part geometry and inspection speed all influence the response. For this reason, probe selection and calibration should be based on the actual material, expected defect direction and inspection conditions.
Different inspection tasks require different probe or coil configurations.
| Inspection task | Part geometry | Typical configuration | Selection consideration |
|---|---|---|---|
| Local surface inspection | Flat or accessible surfaces | Surface or pencil probe | Suitable for scanning selected areas and localized indications |
| Tube, bar or wire inspection | Continuous round products | Encircling coil | Provides rapid inspection as the product passes through the coil |
| Internal tube inspection | Tube inner surface | Internal or bobbin probe | Probe size should match the tube’s internal geometry |
| Weld seam inspection | Welded pipe | Saddle-shaped or weld seam probe | Probe position should follow the weld seam and expected defect direction |
| Rotating inspection | Bars, tubes or cylindrical parts | Rotating probe configuration | Useful when circumferential coverage is required |
The configurations above describe common industry applications. The final probe design should be confirmed according to the tested material, product dimensions, inspection speed and target defect.
Eddy current probes are mainly used to inspect electrically conductive materials. Typical applications include detecting surface and near-surface cracks, inspecting tubes, bars and wires, monitoring weld seams and evaluating variations in material properties.
For continuous production lines, probes can be integrated with eddy current testing equipment to support automated inspection and signal processing. Tube, bar and wire manufacturers can also select dedicated tube, bar and wire inspection systems according to product diameter, line speed and inspection coverage.
For welded pipe production, localized probes or coils may be positioned around the weld area. BKN’s ERW weld seam inspection equipment provides a relevant example of how probe configuration can be matched to a specific production task.
Probe selection should begin with the inspection task rather than only the probe dimensions. The following information should be confirmed before choosing a probe:
Test material and its electrical and magnetic properties
Part shape, diameter and accessible surface
Expected defect type, location and orientation
Required surface or near-surface inspection depth
Online or offline inspection method
Production speed and automation requirements
Probe lift-off and available installation space
Operating environment and cable protection requirements
A probe that works well for local surface scanning may not be suitable for high-speed inspection of tubes or bars. Likewise, a weld seam probe must be positioned and oriented according to the seam geometry and expected defect direction.
To request a probe or testing recommendation, provide BKN with the material, part dimensions, expected defect, inspection speed and installation conditions through the contact page. This information helps determine an appropriate probe configuration and testing system for the application.
