Qualiti - Project Developments

Eddy Current Inspection System

With ultrasonic inspection, the strong interface echo from the front face of the billet makes it impossible to reliably detect defects near the surface. The interface echo creates a blind zone of approximately 5 mm at the edge of the billet. In order to have complete inspection coverage, a complementary eddy current (EC) inspection system was developed. The eddy current system is able to inspect the titanium within 5 mm of the surface, ensuring complete inspection coverage.

The EC system, a hybrid eddy current probe consisting of 5 coils, was developed at West Pomeranian University of Technology, Poland. Figure 1 shows (a) the arrangement of the coils and (b) the electrical connections of the probe. The 4 coils situated at even spacing around outside of the probe induce eddy currents into the billet material. The central coil is a receiver, detecting the resulting eddy currents. Each pair of transmitting coils, on opposing sides of the centre, operate in differential mode. This favours detection of defects oriented perpendicular to a line drawn between them. Using both pairs of transmitting coils, defects in any orientation can be detected.

Two test samples have been manufactured to replicate the near edge of a 10" diameter titanium billet. At the thickest part of the sample (7 mm) flat bottom holes of diameter 0.8 mm and EDM slots have been introduced. These flat bottom holes and slots have depths of 100%, 80%, 60%, 40%, 20% and 10% of the through wall thickness. All the slots have been successfully detected. The flat bottom holes at depths of 100%, 80%, 60% and 40% of the through wall thickness have been successfully detected.

Figure 1. a) schematic diagram of the hybrid eddy current probe of 5 coils, b) simplified electrical scheme of the transducer

Figure 1.



European Commission Seventh Framework Programme

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