tests

Eddy current testing (ECT)

September 22, 2025
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Eddy current testing (EDT) is an electromagnetic non-destructive  testing (NDT) method         for detecting surface and subsurface defects in conductive materials. This fast, precise, and non-contact technique is used in various industries. In this comprehensive article, we explain the basics, equipment, applications, and benefits of this method.

Table of contents

  1. Introduction and physical principles of ET testing

  2. Equipment required for eddy current testing

  3. Types of eddy current testing methods

  4. Industrial application of ET

  5. Advantages and disadvantages of the eddy current method

  6. International standards for  hazardous  waste

  7. Conclusion and future prospects

1. Introduction to ET tests and their physical principles

Eddy current testing is based on the principle of     electromagnetic induction     . When a coil carrying alternating current approaches a conductive material, eddy currents are generated within the material. These eddy currents generate secondary magnetic fields, which in turn influence the primary magnetic field.

Important parameters in ET:

  • Test frequency     : 50 Hz to 6 MHz (higher frequencies are better suited for detecting surface defects)

  • Magnetic permeability of the skin     : δ=503√(ρ/μf) (where ρ is the resistivity, μ is  the magnetic  permeability and f is the frequency)

  • Signal phase and amplitude     : Determine the type and extent of the error.

2. Equipment required for eddy current testing

  • Test files     :  absolute  , differential and matrix

  • ET device     : generates alternating current and analyzes the reaction.

  • Standard calibration     : samples with known   defects

  • Data analysis programs     : interpreting results

  • Mechanical scanners     : for systematic inspection of large areas.

3. Types of eddy current testing methods

Test method How does it work? General use
Absolute file method Measuring the change in coil impedance Thickness measurement, material analysis
Differential file method Comparing responses from two adjacent files Detection of local defects
File matrix Use multiple files to expand your reach. Explore a large area
Transition path Use separate send and receive files. Tubes and rods

4. Industrial applications of electronic tracking technologies

  • Aerospace     : Inspection of turbine blades and aircraft structures

  • Power plant    :     Inspection of   heat exchanger tubes

  • Automotive industry     : quality control during casting

  • Oil and  gas industry     :  drill pipe inspection

  • Railway industry     : Inspection of rails and railway wheels

  • Medicine     : Examination of metal implants

5. Advantages and disadvantages of the eddy current method

Special feature:

  • High recognition rate

  • No     pairing  required (direct connection)

  • Very sensitive to surface cracks.

  • Automation and digital data recording functions

  • Several parameters ( thickness   , hardness) can   be measured simultaneously.

End:

  • Use only with conductive materials.

  • Penetration is limited to the surface (usually no more than a few millimeters).

  • Sensitivity to     physical changes

  • An experienced operator is required to interpret the results.

6. International ET Standards

  • ASTM E309     : Standard for Eddy Current Testing of Pipes

  • ISO 15549     : International Standard for Eddy Current Testing

  • ASME Section V     :      ET  Welding Testing Standard

  • EN 1711     : European welding test standard

7. Conclusion and outlook

Eddy current testing combines speed     , precision, and digital capabilities,     making it an indispensable method in modern non-destructive testing. The development of array coils, multi-frequency systems, and artificial intelligence algorithms for data analysis promises a promising future for this technology.

Frequently asked questions:

  • Is ET applicable to non-metallic materials?
    No, this method is only applicable to conductive materials such as metals.

  • What is the penetration depth of the ET?
    It typically ranges between 1 and 5 mm, depending on the frequency and material properties, and can be calculated using the skin penetration formula.

  • Can ETs detect subsurface defects?
    Yes, but lower frequencies can increase penetration, although the technology’s sensitivity to surface defects decreases.