English 
日本語 
한국어 
Deutsch 
Español 
italiano 
русский 
português 
العربية 
ไทย 
tiếng việt 
中文
NEWS
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.
Eddy current testing and ultrasonic testing are both non-destructive testing methods, but they are suited to different inspection tasks. Eddy current testing is primarily used to detect surface and near-surface discontinuities in electrically conductive materials. Ultrasonic testing uses high-frequency sound waves to evaluate internal conditions and material thickness. The appropriate method depends on the material, expected defect depth and orientation, component geometry, surface condition, coupling requirements and inspection objective.
| Comparison factor | Eddy Current Testing (ECT) | Ultrasonic Testing (UT) | Selection note |
|---|---|---|---|
| Testing principle | Uses electromagnetic induction and measures changes in the probe coil response. | Sends ultrasonic waves into the material and analyzes returning echoes. | Choose according to the required signal response and inspection target. |
| Applicable materials | Requires electrically conductive materials. | Can inspect many materials that transmit ultrasonic energy effectively. | Material type is the first selection condition. |
| Typical defect focus | Surface and near-surface discontinuities. | Internal discontinuities, thickness variations and other volumetric conditions. | Expected defect depth strongly affects the choice. |
| Coupling requirements | Does not normally require liquid couplant, but probe lift-off must be controlled. | Contact testing generally requires couplant; immersion systems use a liquid transmission medium. | Consider surface condition and production-line requirements. |
| Defect orientation | Most sensitive when a discontinuity interrupts the eddy current flow. | Strongest response occurs when the sound beam reflects sufficient energy back to the probe. | Probe direction and scanning method must match the expected defect orientation. |
| Geometry | Suitable probes and coils can inspect tubes, bars, wires and repetitive industrial components. | Complex shapes may require different probe angles, scanning paths or customized fixtures. | Component shape and available access affect setup design. |
| Automation | Well suited to high-speed and automated inspection of conductive components. | Can also be automated, but coupling and scanning conditions must remain consistent. | Both methods can support production-line inspection when properly configured. |
| Main limitations | Limited to conductive materials and generally has less penetration depth. | Results may be affected by attenuation, coarse grain, rough surfaces, coupling and complex geometry. | Neither method is universally better for every application. |
Eddy current testing uses an alternating electrical current in a probe coil to generate a changing magnetic field. When the probe approaches a conductive test material, the magnetic field induces circulating electrical currents within the material.
Surface cracks, changes in conductivity, magnetic permeability, dimensions or probe lift-off can alter the eddy current flow. These changes affect the amplitude and phase of the coil response, allowing the inspection system to identify signal variations associated with material or surface conditions.
Eddy current testing is commonly considered for conductive tubes, bars, wires and industrial components where rapid surface or near-surface inspection is required. Probe type, coil configuration, frequency and scanning direction must be selected according to the component and expected discontinuity.
Explore BKN eddy current testing equipment for tube, bar, wire and industrial component inspection.
Ultrasonic testing sends high-frequency mechanical sound waves into the test material through a transducer. In contact testing, couplant helps transfer the ultrasonic energy from the probe into the component.
When the sound reaches a material boundary, back wall or discontinuity, part of the energy is reflected. The transducer receives the returning echoes, and the instrument displays information such as travel time, echo position and signal amplitude.
With suitable calibration, probe selection and an established inspection procedure, these signals can be used to evaluate possible internal discontinuities or thickness variations. Material structure, surface condition, component geometry, sound path and discontinuity orientation can all influence the result.
View BKN ultrasonic testing equipment for industrial bars, pipes and other applicable components.
Eddy current testing may be the more suitable option when:
The test material is electrically conductive.
The main inspection target is at or near the surface.
Liquid couplant is undesirable.
Tubes, bars, wires or repetitive components require rapid inspection.
The application involves crack detection, conductivity comparison or material sorting.
The inspection needs to be integrated into an automated production line.
ECT results can be affected by lift-off, geometry, conductivity, permeability and probe position. The inspection setup should therefore use suitable reference samples and controlled operating conditions.
Ultrasonic testing may be more suitable when:
Internal or volumetric discontinuities are the main inspection target.
Material thickness must be measured or monitored.
The component provides a suitable sound path.
Couplant or an immersion setup can be used.
Welds, bars, pipes, forgings, castings or other suitable components require internal inspection.
The inspection procedure can define the correct probe frequency, angle, calibration and acceptance criteria.
UT performance can be affected by coarse-grained materials, rough surfaces, complex geometry and discontinuities that do not reflect sufficient sound energy toward the transducer.
ECT and UT are not always competing methods. They may be used as complementary inspection techniques when a component requires both surface and internal evaluation.
For example, ECT may be used for rapid surface or near-surface inspection of a conductive component, while UT is used to examine internal conditions or thickness. The combined inspection plan should be based on the material, component geometry, expected discontinuities, production process and applicable testing standard.
Before choosing an inspection method or equipment configuration, prepare the following information:
Material and electrical conductivity
Component shape and dimensions
Expected defect type, depth and orientation
Required inspection area
Surface condition and available access
Production speed and automation requirements
Applicable testing and acceptance standards
Manual, offline or inline inspection requirements
Need help choosing between eddy current and ultrasonic testing? Share your material, component dimensions, expected defect type and inspection requirements through the BKN contact page. BKN can review the application and discuss an appropriate NDT testing approach.
