Eddy current (EC) method is one of the more perspective for detection and estimation of surface and subsurface flaws of different types, especially for detection of dangerous fatigue and corrosion flaws in structural components in aircraft, nuclear power plants in service. The differential type EC probes are applied in situations where the good suppression of undesirable influences in the EC probe signal response it is needed. But the selective possibilities of multidifferential eddy current probes and new practical possibilities of this kind of probes are not investigated and developed enough yet. In this paper we represent the new LEOTEST 2DD family multidifferential EC probes and some new practical results obtained with this type probe application.

The dual differential (in different directions) connection of four pick-up coils it is used in this probes to reach the better selective ability and sensitivity. In this case for good noise and undesirable signal suppression in multidifferential EC probes it is very important to supply the parameter identity of multiwinding coils installed on ferrite cores. Good parameter identity of coils depends, among other things, upon the identity and stability of material magnetic parameters and geometrical parameters of used ferrite core. On the basis of new Fair-Rite Corp. (USA) ferrite materials and new precise producing technology a new series of small size high and low-frequency EC probes with a sharp response on high and low operational frequencies were designed in “Leotest-Medium” Center. The Fair-Rite ferrite materials have also small own noise level and temperature stability. The special calculations also were done for the ferrite core coils sensitivity optimisation on needed operational frequencies.

The main features of designed LEOTEST type EC probes are:

• Excellent sensitivity to shallow long and short cracks;

• Excellent sensitivity to local flaws, such as pore or pitting;

• Good lift-off compression due multi-differential construction;

• Excellent spatial resolution;

• The sensitivity to conductivity anisotropy;

• Excellent depth of testing for low frequency probes;

• Small size (best ratio of probe size to penetration depth);

• Flaw parameters estimation ability.

The probes were investigated in Otto-von-Guerike Magdeburg University in connection with scanning system for two-dimensional pseudo-colour visualization.

The detection and flaw sizing ability of the probes were evaluated in Uppsala University using sandwich specimens to simulate flaws in copper canisters of different volumes and located at different depths.

Some new testing technologies with the Leotest type probes applications in aircraft and space engineering are developed. Due small size and flaw sizing ability Leotest probes may be recommended also for heat exchanger tube testing with rotational probe tool.

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