Eddy Current Testing (ET) is an electromagnetic testing (EMT) method, where a high frequency alternating magnetic field is used to induce currents in the material under examination. ET is a non-contact method, which makes it able to inspect conductive materials covered by thin coatings and paints. This makes it a very good alternative to dye penetrant inspection (PT) and magnetic particle inspection (MPI), also said magnetic testing (MT) since it requires less surface preparation.
Despite these advantages, conventional ET has limitations—particularly when it comes to accurately sizing the depth of surface cracks, especially in carbon steel materials. This is where Tangential Eddy Current Array (TECA) technology provides a significant improvement.
Carbon steel components are especially susceptible to cracking due to fatigue, stress, or environmental factors. While not all cracks are immediately critical, their depth and length are essential parameters for assessing structural integrity. TECA enables accurate evaluation of these characteristics.
TECA (Tangential Eddy Current Array) is an advanced electromagnetic inspection technology that uses Eddy Current Array (ECA) to introduce alternating currents into the surface of a component, enabling the detection and sizing of surface-breaking cracks.
As with other eddy current techniques, any crack present in the material disturbs the induced current field. These disturbances are immediately detected, and the system provides real-time feedback on the presence and severity of defects. This allows operators to evaluate indications instantly. In addition, TECA support data recording and automated report generation, offering clear advantages over more traditional NDT methods.
A key feature of TECA is its probe design, which combines multiplexed tangential coils with pancake coils. This configuration allows wide surface areas to be scanned in a single pass, eliminating the need for multiple or raster scans and significantly reducing inspection time. The tangential coils are positioned with their axes parallel to the surface, causing eddy currents to flow along the surface and “dive” beneath cracks. This behavior enables more accurate measurement of crack depth.
Another important advantage of TECA is its ability to handle lift-off variations. The system continuously monitors and compensates for coating thickness, ensuring accurate crack depth measurements even when inspecting components with thicker coatings.
Figure 1: Data representation of our Butt weld TECA probe with: a) Top Left C-scan, is representing
the processed crack depth channels; b) Bottom C-scan are the crack length reprentation.
Where on the bottom right the automatic depth and length readings are showed.
Typical applications of TECA within TÜV AUSTRIA Belgium cover a wide range of carbon steel inspections where surface cracking is a concern. One key example is the inspection of Pressure Swing or Surge Adsorbers (PSA), which are used in gas treatment and purification processes. These vessels operate under repeated cycles of pressurization and depressurization, making them susceptible to fatigue cracking. In such cases, TECA is often used in combination with Time of Flight Diffraction (TOFD). While TOFD is effective for detecting and assessing subsurface defects, TECA is specifically applied to detect and size surface-breaking cracks, providing a complementary and comprehensive evaluation.
Another important application is the inspection of gas storage spheres. These structures can develop cracks at welding joints and at the connections between the sphere and its supporting legs due to thermal and mechanical fatigue. In these areas, traditional techniques such as magnetic testing are not always practical, especially when coatings are present, as they often require paint removal. TECA offers a more efficient solution by allowing inspections to be carried out directly through coatings.
Figure 8. SCC data and results collected with the Sharck HR array probe on a CS pipe.
More generally, TECA can be used to monitor all types of cracking in carbon steel materials. This includes very fine defects such as stress corrosion cracking (SCC), which can be detected using dedicated high-resolution (HR) probe sets. This capability makes TECA a versatile and powerful tool for early detection and ongoing monitoring of structural integrity.
General Sharck (TECA) probe range Characteristics:
- Versions: Pencil probes, Butt – and Fillet Array weld Probes
- Temperature range: up to 100°C
- Depth Sizing capabilities: up to 7.0mm ±20%
- Minimum detectable crack length: from 3.0 to 4.0mm
- Minimum detectable crack depth: 0.5mm
- Lift-off Tolerance (paint thickness): up to 3.0mm
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HR Sharck (TECA) probe Characteristics:
- Versions: Pencil HR Probes, Pipeline Surface – and Butt weld probes
- Temperature range: up to 70°C
- Depth Sizing capabilities: up to 3.0mm ±10%
- Minimum detectable crack length: From 1.5 to 2.0mm
- Minimum detectable crack depth: 0.25mm
- Lift-off Tolerance (paint thickness): up to 1.5mm
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